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Preparing Chimpanzees for Laboratory Research

Mollie A. Bloomsmith, Steven J. Schapiro, and Elizabeth A. Strobert

Mollie A. Bloomsmith, Ph.D., is the Head of Enrichment at the Yerkes National Primate Research Center (YNPRC), Emory University, Atlanta, GA. Steven J. Schapiro, Ph.D., is Associate Professor of Comparative Medicine at The Michale E. Keeling Center for Comparative Medicine and Research, Department of Veterinary Sciences, The University of Texas M.D. Anderson Cancer Center, Bastrop, TX. Elizabeth A. Strobert, D.V.M., is the Chief of Veterinary Medicine at YNPRC, Emory University, Atlanta, GA.

Address inquiries and reprint requests to Dr. Bloomsmith, Yerkes National Primate Research Center, Emory University, 954 Gatewood Road NE, Atlanta, GA 30329, or email mabloom@emory.edu.

Abstract

The chimpanzee is the only representative of the Great Apes that is extensively involved in biomedical research in primate laboratories. These apes are used as animal models in a variety of studies, including research on infectious disease, parasitic disease, pharmacokinetic studies, neuroscience, cognition, and behavior. Chimpanzees used in biomedical research in the United States reside largely in six specialized research and holding facilities, and most of the research with them is conducted at these sites. Given the relatively small population of chimpanzees and its importance to biomedical research, it is imperative that we carefully manage the care, production, and use of these animals in biomedical research studies. Selection criteria and preparation techniques are reviewed in this article in an effort to begin a discussion on best practices for choosing and handling chimpanzees participating in biomedical research. The use of routine health assessment information is described for subject selection, as are behavioral issues to be considered. Due to the relatively small number of chimpanzees available, issues related to experimental design and multiple uses of chimpanzees are discussed. Practices related to the transportation and acclimation of chimpanzees are described. Finally, behavioral conditioning procedures are discussed, including habituation, desensitization, and positive reinforcement training that have been applied to reduce animal distress and improve the quality of the science being conducted with chimpanzee subjects.

Key Words: chimpanzees; desensitization; habituation; health; Pan troglodytes; subject selection; training; welfare

Chimpanzees as an Animal Model in Biomedical Research

Research involving nonhuman primates accounts for only about 0.3% of biomedical research that uses animals. Within this small percentage, chimpanzees, or biological materials from chimpanzees, are used in approximately 5% of primate-related research publications (Carlsson et al. 2004). Although the other Great Ape species have been used in biomedical research occasionally, chimpanzees are the only Great Ape that is involved frequently. As the closest living relative of humans, chimpanzees have played a unique role in biomedical research. Chimpanzees are, for example, the only animal model that can be infected successfully with the hepatitis B or C viruses, so chimpanzees are important in research developing vaccines and drug therapies for these diseases (VandeBerg et al. 2005). In recent years, chimpanzees have proven to be uniquely suited for testing monoclonal antibodies (ultimately intended for the treatment of cancer, autoimmune diseases, and more), and as a model for the human pharmacokinetic response to new drugs (see VandeBerg et al. 2005 for more information). Biomedical studies with chimpanzees typically focus on infectious disease (e.g., human immunodeficiency virus [HIV1]), hepatitis, respiratory syncytial virus [RSV1]), parasitic disease (e.g., malaria), pharmacokinetic evaluations of newly developed drugs, neuroscience, genetics, reproduction, cognition, and behavior (Bukh 2004; Feuk et al. 2005; Nehete et al. 1998; Parr et al. 2005; Roof et al. 2005; Silk et al. 2005; Skiadopoulos et al. 2002; Wieland et al. 2004; Wong et al. 2004). With the recent publication of the chimpanzee genome, there is a strong expectation that the use of chimpanzees will increase in a variety of research fields.

Chimpanzees used in biomedical research reside largely in six specialized research and holding facilities, and the number of chimpanzees in this community is currently about 1200 (see Bloomsmith and Else 2005 for more information). These institutions have specialized facilities and staff members knowledgeable in the care and handling of chimpanzees. The vast majority of contract- and grant-funded biomedical research with chimpanzees is conducted at these sites. Most of this research is conducted where the chimpanzees live, rather than moving the animals between laboratory facilities, although there are some exceptions.

Currently, chimpanzee reproduction is restricted in federally owned animals, and in those supported by the National Institutes of Health National Center for Research Resources, by a breeding moratorium that is in place from 1995 to 2007 (Report of the Chimpanzee Management Plan Working Group to the National Advisory Research Resources Council 2005). Because wild chimpanzees are considered vulnerable and possibly endangered on the IUCN Red List (IUCN 2004), and because chimpanzees have not been legally imported from the wild into the United States since the mid-1970s, increasing the population through importation is neither possible nor desirable. Given the relatively small population of chimpanzees and its importance to biomedical research, it is imperative that we carefully manage the care, production, and use of these animals in biomedical research studies.

Biomedical research with chimpanzees involves manipulation of the subjects, including moving them into temporary testing areas, changing their housing, removing them from social groups, collecting biological samples (e.g., blood, urine, liver biopsies) from them, injecting them with drugs, anesthetizing them for various procedures (e.g., brain imaging), or teaching them particular responses within research tasks (e.g., responding to certain stimuli for a learning task) (Barron et al. 2005; Freeman et al. 2004; Payette et al. 2006; Peng et al. 2005). Many of these manipulations may be disturbing to chimpanzees. As has been previously described (Bloomsmith and Else 2005), it is important to distinguish “direct distress” from “contingent distress” when examining the use of chimpanzees in biomedical research protocols. As Russell and Burch (1959) first described, direct distress is an unavoidable consequence of a research intervention or other procedure conducted on an animal. If, for example, a chimpanzee has a fever after being experimentally infected with malaria, the chimpanzee is experiencing direct distress. Contingent distress, however, is an incidental or inadvertent by-product of a procedure. For example, if the same chimpanzee on the malaria study is physically restrained for the withdrawal of a blood sample needed for the study, the animal is experiencing contingent distress due to the restraint. If contingent distress can be eliminated or reduced, the result improves both animal welfare and the quality of the biomedical research (by reducing possible confounding influences of the distress).

Most biomedical research using chimpanzees involves minimal disease and direct distress, but the degree of contingent distress can be significant. Procedures to better prepare chimpanzees for such research procedures, and to improve their housing and social lives during the conduct of biomedical research projects, can significantly reduce this contingent distress. Much effort in the last two decades has focused on developing and testing such techniques for chimpanzees, including environmental enrichment practices, conducting biomedical research with socially housed chimpanzees rather than with individually housed subjects, improving the design of caging, and applying animal training procedures (see Bloomsmith and Else 2005). The widespread and effective use of these behavioral management techniques can simultaneously improve chimpanzee welfare and improve the accuracy of biomedical research findings.

This article provides a review of selection criteria and preparation techniques in an effort to begin a discussion on best practices for selecting and handling chimpanzees that serve as subjects in biomedical research. Some of these procedures have been objectively evaluated and findings have been published (Bloomsmith et al., 1998; Lambeth et al. 2005, 2006; Schapiro et al. 2003, 2005); however, many have not. Further evaluation of some of these practices is needed. This process will require determining what outcome measures would be the most important for evaluating the effectiveness of selection and preparation techniques. In addition to dependent measures relevant to animal welfare, Capitanio and colleagues (2006) propose that “outcome measures of biomedical interest” should be considered when assessing the preparedness of subjects for research. Taking this approach, variables that will be used in the biomedical studies are assessed to evaluate any preparatory techniques applied. Such investigations should be conducted with chimpanzee subjects.

Chimpanzee Natural History and Managing Chimpanzees for Research

Understanding the social organization and social behavior of wild chimpanzees should be informative in devising ways to best care for chimpanzees who are subjects in biomedical research. Chimpanzees are intensely social animals. For that reason, substantial changes in behavior are associated with removing these animals from compatible groupings or housing them alone, as is sometimes done for biomedical research.

Like most primate species, chimpanzees require a social environment during early development to facilitate the expression of normal behavior throughout their long lives. If chimpanzees experience inadequate early rearing conditions, there may be deficiencies in later sexual behavior, maternal behavior, and agonistic interactions compared with mother-reared, captive chimpanzees (Bloomsmith et al. 2003; Brent et al. 1996; King and Mellen 1994; Rogers and Davenport 1970). A variety of abnormal and stereotyped behaviors may also be expressed by these animals, sometimes over their entire lifetimes (Davenport and Menzel 1963; Fritz et al. 1992; Nash et al. 1999; Pazol and Bloomsmith 1993, 1997). To avoid these behavioral problems it is important, whenever possible, to allow more than 1 yr of social rearing for infant chimpanzees (Bloomsmith and Baker 2001).

It is certainly preferable to house chimpanzees in compatible social groupings at all times. However, if periods of individual housing must be imposed, doing so later in the life of a chimpanzee, rather than earlier, is believed to have fewer long-term negative impacts on the animal. This belief is based on research conducted with other nonhuman primates because these studies have not been carried out with chimpanzees (Baker et al. 2004; Bellanca and Crockett 2002; Lutz et al. 2003; Novak 2003; Harlow and Novak 1973). For this reason, more mature chimpanzees should be considered for studies that require social restriction, rather than infant or juvenile animals, whenever possible. However, this is not to say that individual housing of older chimpanzees is without consequence to the animals—both short-term and long-term behavioral effects have been reported (Baker 1996; Brent et al. 1989). Periods of social restriction to accommodate research protocols should be minimized, both for the animal's welfare and for the integrity of the research. Indeed, in a recent survey, only 7.6% of the chimpanzees at the six major facilities were individually housed on the single day chosen to sample for the survey (Bloomsmith and Else 2005). This number included all chimpanzees singly housed for any reason on that particular day, whether due to research protocol, health problems, behavioral problems, or other reasons. It is clear that at the point sampled, the vast majority of chimpanzees in biomedical laboratories were living socially.

In some cases, young chimpanzees are removed from their mothers and raised in a nursery by humans to facilitate the use of these young subjects in biomedical research. For example, research in RSV vaccine development requires chimpanzees that have not been exposed to RSV. Because RSV is naturally occurring and is prevalent in chimpanzee colonies, young chimpanzees that are raised in groups are unsuitable as subjects for such studies. The nursery rearing practices for such young chimpanzees are critical for their long-term welfare. If nursery rearing must be conducted, practices that include social stimulation from compatible peers and humans, physical activity in complex enclosures, visual exposure to adult chimpanzees, and experience with varied stimuli are considered important (Fulk and Garland 1992). Although there continue to be behavioral consequences associated with even this enriched type of nursery rearing, chimpanzees raised under such circumstances are not showing the devastating behavioral deficits that were present among chimpanzees reared in more restrictive settings in the past (Bloomsmith et al. 2006).

In contrast to the social organization of many other common laboratory primates, adult male-male interactions are the core of wild chimpanzee social networks (Nishida 1979). Many facilities strive to maintain chimpanzees in multimale-multifemale social groups to facilitate species-typical social interactions (Alford et al. 1995; Riddle et al. 1982). Although this simulation of natural social groupings is important, it can complicate the process of removing and reintroducing chimpanzees to their groups as they are assigned to studies or when there is a need to collect biological samples from them. Difficulties are sometimes found with severe aggression when attempting to reintroduce chimpanzees to their previous social groups, even after separations of just a few hours. To avoid this problem, all of the adult males in a social group are often given their annual physical examinations on the same day so that all males can be removed from and reintroduced to the group in a single, well-controlled episode (S. Buchl, The Michale E. Keeling Center for Comparative Medicine and Research, Department of Veterinary Sciences, The University of Texas (U.T.1) M.D. Anderson Cancer Center, Bastrop TX, personal communication, 2006). Perhaps this aggression at reunion is not surprising. Even though wild chimpanzees live in a “fission-fusion” type of social organization, with frequent separations from and reunions with many members of their large communities, these reunions of familiar animals comprise one of the most frequent contexts for aggression in the wild (Goodall 1986). Different captive facilities have different procedures for such reintroductions, but all chimpanzees that have been removed should be carefully reintroduced back into their groups and observed for adjustment problems. To accomplish this objective, we recommend having available someone skilled in assessing chimpanzee behavior to monitor these reintroductions. Investigators should also consider minimizing the number of social separations in their research protocols, and/or chimpanzee subjects should be well-acclimated to repeated social separations.

Selecting Chimpanzees as Subjects for Laboratory Research

The proper selection of subjects for specific research protocols is a critical aspect of all research and is particularly challenging for studies with chimpanzees. In general, subjects for studies can be selected (1) for certain criteria, to enhance the specificity of the model/protocol; or (2) at random, to maximize the generality of the findings (Capitanio et al. 2006). The small number of captive chimpanzees available for research overall, and at any one facility in particular, precludes random assignment of animals to projects. It is often difficult to attain an adequate sample of chimpanzees chosen for similarity on a set of experimental criteria. Instead, the general approach is to maintain and consult thorough historical records on health, pedigree, behavior, and previous experimental history, and to use that information to select the best subjects from those potentially available. Due to the complexity of health and behavioral issues that come into play when selecting chimpanzee subjects for study, effective communication among those with expertise in veterinary science, behavioral science, and chimpanzee husbandry is essential for the best outcomes.

Routine Health Assessments

As others (Capitanio et al. 2006; Tardif et al. 2006) have mentioned in this issue, standard factors such as age, sex, weight, experimental history, genetic factors, and health condition must be considered when choosing chimpanzees as animal models. Routine health assessments are important for evaluating the suitability of individual chimpanzees before research assignment, and these assessments should generally be the first information reviewed for screening. In most biomedical facilities housing chimpanzees, routine health examinations of chimpanzees are performed at 6- or 12-mo intervals. These examinations typically include blood collection for complete blood counts, serum chemistries, serology panels as appropriate based on the characteristics of the colony (e.g., for hepatitis B, hepatitis C, human T-cell lymphotropic virus), and routine screening for viruses, depending on the inoculation history of the colony. Assessments using flow cytometry techniques may be needed for animals that have previously served in infectious disease studies or for purposes specific to certain research investigations. Routine tuberculosis testing is also a component of routine health assessments. Given that most chimpanzee colonies are aging, with concomitant increases in the risk of cardiac fibrosis and cardiomyopathies, cardiac imaging and additional cardiac monitoring should be routine. Electrocardiograms may be performed as a subject selection tool. Depending on the findings of the physical examination and these routine tests, diagnostic imaging and additional minimally invasive procedures such as a percutaneous biopsy may be conducted. An example of how these evaluations might be useful for project assignment would be the exclusion of a chimpanzee with hepatamegaly and amyloidosis from use in hepatitis research, a use common in some laboratory facilities. Finally, selection of female chimpanzees as subjects may be affected by the contraceptive status of the animal. For example, hormonally based methods such as the use of synthetic progestins may be inappropriate for subjects for some cognitive or neuroscience studies because the hormonal manipulation may affect performance on cognitive tasks (Lacreuse et al. 2001).

An animal's baseline values related to pertinent physiological parameters provide relevant criteria for selection of subjects for some studies. “Normal ranges” for a variety of physiological measures for captive chimpanzees should be consulted (Herndon and Tigges 2001; Howell et al. 2003; Ihrig et al. 2001; Lamperez and Rowell 2005). As an example, a chimpanzee whose immunological baseline values are well outside the published normal range of baselines for captive chimpanzees would not be an ideal subject for a study with immunologically dependent measures, even if that animal appeared healthy. In situations in which baseline measures will be assessed, the sampling should be done when potential subjects are living in their “normal” environment. If blood values are found to deviate significantly from normal, the potential subject should be rechecked because an unusual husbandry procedure or similar activity may have affected measures on a single day. Some studies involve moving a chimpanzee from a group to individual housing or moving a chimpanzee from outdoors to indoors. Although it might be preferable to make these changes before the collection of the baseline sample for subject selection, this decision should be balanced with the desire to minimize periods of individual or indoor housing. Typically at the Yerkes National Primate Research Center, baseline measures are taken while the chimpanzee is living in its normal housing, within its normal social group. Then, if the chimpanzee is selected and if the study requires a move, the housing change is made after this time but before any experimental procedures are conducted. A brief period of acclimation may then occur, depending on study design.

The issue of using normal ranges may be complicated by the effect of sampling procedures on the measured physiological values. The anesthetic agents used (typically ketamine hydrochloride or zolazepam hydrochloride, Telazol®), routes of delivery and doses may have an impact on physiological values such as blood pressure and heart rate (Thurmon et al. 1996). In addition, the method of managing the chimpanzee may affect the resulting blood values (Lambeth et al. 2005, 2006). White blood cell counts and blood glucose levels have been reported to differ under two conditions: (1) when chimpanzees voluntarily presented for an injection of anesthetic compared with when they were anesthetized nonvoluntarily (Lambeth et al. 2006), and (2) when blood samples were collected via a voluntary conscious presentation for venipuncture compared with when the animals were anesthetized for the blood sample collection (Lambeth et al. 2005). Some of the mean values for these physiological parameters collected using refined collection techniques (i.e., when animals have been trained to cooperate) are outside the published normal ranges. We suggest that normal ranges for such values should be published while controlling for the method used to obtain the blood samples. We also advise investigators to consider controlling these possible confounds as they plan research protocols. Due to the complexities involved, it is essential for a qualified veterinarian capable of interpreting such results to be a part of the subject selection process.

Behavioral Issues to Consider

Chimpanzees are sometimes chosen for studies due to individual characteristics such as superior performance on a cognitive task or a predicted reaction to a particular condition or procedure required for a study. It is generally believed that chimpanzees show a high level of interindividual variation in behavior and cognitive performance. Even though formal behavioral data are not typically used as selection tools, at least two types of assessment could be of use and should be evaluated. First, when studies require group-living chimpanzees to be moved from their normal social group to experimental housing, there can be resulting disruption in the remaining social group, including increased aggression. If behavioral data indicate that Chimpanzee A is an integral member of the social group and Chimpanzee B is relatively peripheral (Wasserman and Faust 1995), then with all other factors being equal, it seems sensible to leave Chimpanzee A in the social group and remove Chimpanzee B for use in the experiment. Second, some animals may respond better to the restrictions that come with being assigned to certain research protocols.

It is common to use anecdotal impressions about temperament or personality when assigning chimpanzees to research studies. A more formal and objective measurement of personality or temperament in chimpanzees could perhaps be further exploited to assist in the selection of the most appropriate subjects. Most of the work in chimpanzee personality assessment is being conducted with zoo-housed chimpanzees (Dutton et al. 1999; King and Figueredo 1997; Pederson et al. 2005; Vazire et al. 2006; although see Lillienfeld et al. 1999), and the potential to apply this approach to subject selection has not been explored. Because personality assessments predict observable behavior in chimpanzees (Pederson et al. 2005), such assessments could perhaps predict which chimpanzees may respond with less behavioral disruption to “stressors” that are commonly a part of biomedical research (e.g., being housed individually, being moved to a different enclosure). For example, temperament assessments have been shown to predict ease of training in adult rhesus monkeys (Coleman et al. 2005), and this type of approach could be helpful in determining which chimpanzees could be trained more readily to cooperate with necessary research procedures.

Experimental Design Issues

Because the adequacy of experimental design is an issue for those reviewing chimpanzee research studies, such as institutional animal care and use committee (IACUC1) members, we will comment on this issue. The experimental design of studies with chimpanzees is often influenced by the relatively small pool of chimpanzee subjects from which to draw. Within-subjects designs with repeated measures on the same animal are often the most appropriate in this situation, in which each chimpanzee essentially serves as its own control. Using within-subjects designs and counterbalancing techniques are considered important when a high level of interindividual variability is expected, as might be the case with chimpanzees.

To conduct high-quality science, the statistical power of an experiment must be considered. The statistical power of an experiment is a function of several factors: its sensitivity, the size of the effect in the population, and the criteria used to test statistical hypotheses (Murphy and Myors 1998). One method of increasing the sensitivity of a study is to increase the sample size. According to Murphy and Myors (1998), statistical power of approximately 0.80 is desirable. They note that it is difficult to justify a study design that yields power of less than 0.50 (because such a study is more likely to lead to an incorrect conclusion of not rejecting the null hypothesis when it is virtually certain that this hypothesis is wrong), and that power exceeding 0.80 is prohibitively difficult to obtain. Murphy and Myors (1998) suggest setting the desirable level of power at 0.80, then using the estimated effect size (expressed as percentage of variance scores or standardized mean difference), along with information about the study design and the type of hypothesis being tested, to determine an appropriate sample size. When reviewing the value of scientific studies performed with chimpanzees, such power calculations should be taken into consideration.

Using Chimpanzee Subjects in Multiple Protocols

The case for having chimpanzee subjects serve on multiple research protocols is of particular consequence given their limited availability, their long lives, their unique value as an animal model for human conditions, and their high cost of maintenance. For these reasons, many managers of captive chimpanzees believe that chimpanzees should be used in multiple studies as long as the studies are compatible with one another and all IACUC and other regulations are met. This multiple use can be accomplished sequentially or simultaneously. In general, a sequential approach has been taken with chimpanzees, in which subjects serve as their own controls and experimental effects are measured relative to individual baselines. This approach helps to account for potential carryover effects of previous manipulations. For example, some chimpanzees have been used in a progression of sequential experiments such as early participation as a young subject in an RSV study, followed sometime later by participation in a hepatitis B virus study, and ultimately culminating with participation in an HIV study. However, this sequential use is predicated on the assumption that participation in one experiment does not compromise an animal's value as a subject in the next, and few data that address this issue exist. In some situations, sequential use is certainly not possible. For example, if a chimpanzee has previously been exposed to a particular monoclonal antibody, even of human or rodent origin, then that chimpanzee will not be suitable for a study of that antibody. Because it is difficult to predict which exposures might be relevant in the future, it is important to maintain complete records concerning study participation for chimpanzees during their entire lifetimes. If chimpanzees are to be used repeatedly in research protocols, then it is justifiable to invest substantial resources in their preparation for research compared with some other species because numerous opportunities for reaping benefits from these efforts are likely. This matter should be considered early in the life of a chimpanzee, so that, for example, early training can be initiated for appropriate animals.

Transportation and Initial Acclimation

Chimpanzees are only very occasionally transported between research facilities to facilitate particular research projects. In such a case, new chimpanzee arrivals undergo a quarantine period. At some facilities this period may be 6 wk long to allow three negative tuberculosis tests, but other facilities (e.g., Yerkes National Primate Research Center and U.T. M.D. Anderson Cancer Center) have much longer quarantine periods (≥ 6 mo) to protect against possible latent forms of tuberculosis that have occurred in a captive chimpanzee colony. Transporting chimpanzees often involves alterations in type of housing, weather, personnel, conspecific partners, diet, living indoors or outdoors, and other husbandry and management procedures, all of which can disrupt behavioral and physiological measures. For this reason, maintaining a chimpanzee that is being moved between facilities in a stable social grouping is preferable, if at all possible, to reduce the impact on factors important to their health or biomedical research studies. An intact group of chimpanzees can be quarantined together or separated temporarily into pairs for the quarantine period. Some facilities have allowed social housing by bringing an animal out of a “clean” colony and placing it in quarantine along with a new arrival (U.T. M.D. Anderson Cancer Center). Another option that appears to be effective is to ensure that a person familiar to the chimpanzee accompanies the animal during transfer, even for 1 or 2 days. In such a situation, the chimpanzee seeks reassurance from the familiar person, which appears to be beneficial for the animal's adjustment (L. Brent, Chimp Haven, Inc., Keithville, LA, personal communication, 2006).

When chimpanzees are transferred between facilities, it is helpful to send in advance some type of behavioral profile of each chimpanzee to the receiving institution. This profile can include subjective assessments of personality, food preferences, typical reactions to people, trained behaviors the chimpanzee knows, and the cues associated with that behavior. It is also advisable to include behavioral history information such as early rearing (mother or nursery reared), size and composition of groups in which the chimpanzee has lived, general response when introduced to unfamiliar chimpanzees, breeding history, and parental behavior. To reduce the negative effects of a rapid change in diet, the sending and receiving facilities should exchange detailed diet information. Chimpanzees are fed a wide variety of fresh produce, browse, and other feeding enrichment items at most facilities (Howell and Fritz 1999), and this information should be documented. Some chimpanzees have food sensitivities or allergies that must be taken into account before the animals are fed at the receiving facility. If the primate “chow” being fed must change significantly, the ideal approach is to make the change gradually by mixing portions of the old and new types of chow so that a change is made incrementally, over time.

No data on acclimation are currently available for chimpanzees. To accommodate this void, it is important for investigators and animal care personnel to begin collecting data, perhaps following the example described by Capitanio and colleagues (2006) for Old World monkeys. Studies should be conducted on chimpanzees moved to new facilities or after a chimpanzee has been transferred to a new housing area in the same facility. Data should include behavioral, health, and research-relevant dependent measures, to identify timeframes needed for acclimation.

Behavioral Conditioning of Subjects for Research Procedures

The size, strength, and intellect of chimpanzees create special problems for their management and use. For example, restraint techniques that work quite well with rodents, ferrets, pigs, dogs, marmosets, or Old World monkeys (e.g., restraint tubes, slings, chairs) are not effective or are too dangerous to employ with chimpanzees. For this reason, it is incumbent upon those interested in using chimpanzees in research to develop progressive methods to refine the manner in which chimpanzees are prepared for, restrained, and handled during research. Because chimpanzees can be dangerous, the safe accomplishment of this objective requires the involvement of individuals who are careful and experienced in working with chimpanzees. Since the early 1990s, considerable progress has been made in this area as animal training procedures have been applied to gaining the voluntary cooperation of chimpanzees with research procedures. In a recent survey, it was reported that five of the six main facilities that house chimpanzees had formal chimpanzee training programs and employed, on average, one chimpanzee trainer for every 156 animals (Bloomsmith and Else 2005). Since the time of that survey, the sixth facility has initiated a formal program. All of these programs have reported relying primarily on positive reinforcement techniques to gain chimpanzee cooperation with procedures. Clearly, positive reinforcement training is regarded as a valuable tool in chimpanzee management.

At least three processes are often employed in conditioning chimpanzees for use in research: habituation, desensitization, and positive reinforcement training (Laule et al. 2003; Whittaker et al. 2001). These techniques are implemented to facilitate acclimation to research procedures, both to improve animal welfare and to enhance the quality of the research data. The rationale is that research projects conducted with animals that have been properly habituated, desensitized, and trained are likely to yield data that are of high utility to the scientific community because there will be fewer stress-related confounds embedded in the data. This important hypothesis should be tested in a variety of situations with a variety of chimpanzee subjects.

Habituation is a process that leads to a decrease in the strength of a response after repeated presentation of a stimulus that elicits that response (Mazur 2002). At the beginning of a research protocol, subjects are typically confronted with a variety of new equipment, materials, procedures, and personnel, and they sometimes have fearful reactions to these stimuli. Habituation can reduce these fearful reactions because subjects are allowed access to or contact with research equipment, materials, or personnel in the absence of any imposed consequences for this access/contact. For example, a transport cage (in which the chimpanzees may be required to ride) may be connected to or placed in the animals' primary enclosure for the animals to explore. Similarly, syringes, cotton swabs, or other materials may be left in clear view of, but not accessible to, the subjects. Research personnel may visit the animals during periods when no manipulations are being performed. Chimpanzees are free to interact with safe materials and people as they wish, but there are no consequences imposed on these interactions.

In some instances, habituation alone may not eliminate the fearful reactions. In such cases, systematic desensitization can be applied. Systematic desensitization is a behavioral treatment for phobias that involves slowly presenting the subject with increasingly strong fear-provoking stimuli while keeping the subject in a relaxed state (Mazur 2002). The treatment differs from habituation in that when the subjects perform a desired response in the presence of or toward the target apparatus, material, or personnel, the animal is reinforced for this response. The goal is to change the animal's reaction to the object or person from negative to neutral or positive. A simple example would be providing the animal with a small treat each time it enters the transport box attached to its enclosure. Another application would be to change the animal's response to the technician responsible for anesthetic inductions. For some chimpanzees, the only time they may see a particular technician is when they are going to receive an injection or before some other negative interaction. Because these procedures provoke fear, and the presence of the technician has been repeatedly associated with these procedures, the technician can elicit a strong, negative reaction in the chimpanzee. However, by repeatedly pairing the presence of the technician with a more positive experience such as receiving a treat, it is possible to moderate the negative response to the technician. It is possible to desensitize the chimpanzee to the technician, and this desensitization can be maintained, even when the technician is still sometimes associated with negative experiences. Such desensitization can greatly facilitate later treatment of the chimpanzee in addition to reducing subsequent stress for the animal.

The final step in the behavioral conditioning process is to train the animals to perform behaviors that are desirable for research (Bloomsmith et al. 1998; Lambeth et al. 2005, 2006; Perlman et al. 2001, 2003, 2004; Schapiro et al. 2003, 2005). These behaviors may include presentation of a body part for an intramuscular injection (e.g., of an anesthetic or a tracer before positron emission tomography imaging) or a subcutaneous injection, allowing conscious venipuncture, supplying a semen or urine sample, or moving from one room to another for testing purposes. These behaviors have been trained in chimpanzees using positive reinforcement training techniques. The process provides the animals with positive consequences when they perform the requested behavior, thus increasing the likelihood that the behavior will occur again (Laule et al. 2003). Behaviors are typically trained using the process of shaping, wherein subjects are reinforced as they make successive approximations of the target behavior (Mazur 2002). This technique is very powerful, and considerable progress has been made in training chimpanzees to voluntarily participate in a variety of research procedures (Bloomsmith 1992; Bloomsmith et al. 1998; Lambeth et al. 2005; 2006; Laule et al. 1996; Perlman et al. 2001, 2003, 2004; Schapiro et al. 2003, 2005).

Several publications have included data on the duration of training effort required for chimpanzees to reliably perform certain behaviors. In these cases, most of the chimpanzees were already familiar with training and were being trained by experienced people; both of these factors (and others) undoubtedly influenced the speed of acquisition. For example, training chimpanzees to offer a body part for an intramuscular injection required a mean of 86.9 min of training over 30.8 sessions in 82 chimpanzees who learned this behavior, although others never reliably cooperated (Schapiro et al. 2005). Cooperating with a subcutaneous injection took a mean of 98 minutes of training and was reliable after 17 training sessions in three of four chimpanzees trained (Perlman et al. 2004). Training for conscious venipuncture took a mean of 219 minutes in 31 training sessions for four adult chimpanzees (Pranger et al. 2006). This procedure also involves using a custom-designed “blood sleeve” device to attach to the animal's cage to safely acquire the blood sample. Another study found that six male chimpanzees trained to use an artificial vagina for semen collection required 172.6 min over 16 sessions to be reliably trained (Perlman et al. 2003). Training eight chimpanzee groups with a total of 66 members to move from one area of their enclosure to another took a mean of 16.1 training sessions of a few minutes each (Bloomsmith et al. 1998).

Training animals requires personnel with specific skill sets, which in turn requires investment in the training of the people. Most chimpanzee trainers have learned these skills by working directly with others who are experienced, some by taking courses in animal learning and some by using the services of an animal training consultant. Greater availability of this information to increase training skills among all of those working with chimpanzees is needed. Although having trained subjects initially requires a costly investment in personnel and an investment of time in the initial training of chimpanzees, the investment can return great value to the research enterprise (Laule et al. 2003; Prescott and Buchanan-Smith 2003).

Some chimpanzee research facilities are taking the approach of creating pools of subjects trained for frequently requested behaviors needed for research protocols. This approach will allow investigators to choose subjects from the trained pool, rather than waiting for the subjects to be trained after they have been selected. This method is also beneficial because it allows people experienced in working with chimpanzees to perform the “hands on” aspects of the research, rather than requiring the time that would be needed for members of each investigators' laboratory to become familiar with and safe in performing these activities. At U.T. M. D. Anderson Cancer Center, a pool of seven animals has been trained for conscious venipuncture (Lambeth et al. 2005) and these chimpanzees are available for research use. (For more information about specific services and rates, email wsatterf@mdanderson.org.) At the Yerkes National Primate Research Center, 20 chimpanzees have been trained on a variety of computerized and behavioral tasks used in cognitive and neuroscience research. This “Cognitive Testing Facility and Chimpanzee Research Core” is dedicated to providing expertise to scientists wishing to use chimpanzees in their research but who do not have access to chimpanzees in their own research institution. (For more information about specific services and rates, email the director at chimp-cognition@rmy.emory.edu.)

Conclusions

The ultimate goal of attempting to prepare chimpanzees for biomedical research is to improve their fidelity as an animal model for studies requiring a human-like system, and to minimize any negative impacts of research procedures on the chimpanzees. This combined objective is accomplished through mechanisms that promote their health and welfare because healthy animals yield good scientific data.

In the preceding text, in describing criteria for selection of subjects, their transportation and acclimation, as well as training them to better tolerate research-related procedures, we have made a number of recommendations for best practices. These recommendations are reiterated below.

  1. Whenever possible, provide more than 1 yr of social rearing for infant chimpanzees who are likely to serve as biomedical research subjects.
  2. House chimpanzees in compatible social groupings at all times possible, including while they are participating in biomedical research protocols.
  3. If individual housing or other social restriction must be imposed due to a research protocol, whenever possible consider more mature chimpanzees as subjects rather than infants or juveniles.
  4. Arrange for a person skilled in assessing chimpanzee behavior to monitor reintroductions of chimpanzees when they are returned to their social groups following participation in research protocols.
  5. Conduct routine health assessments (e.g., analyses of blood, organ health, contraceptive status) every 6 to 12 mo to screen chimpanzee subjects.
  6. Perform baseline assessments of physiological values with potential subjects living in their normal environment.
  7. When studies require removing a group-living chimpanzee from a social group, perform a behavioral assessment of the importance of that individual to the group.
  8. Consider the individual temperament and personality of chimpanzees before assigning the animals to certain protocols.
  9. Consider the statistical power of experiments with chimpanzee subjects in the evaluation of such studies.
  10. Maintain complete records concerning study participation, health, and behavior for chimpanzees during their entire lifetimes.
  11. When chimpanzees are moved between facilities or within a facility, maintain them in a stable social group if possible. Such a case might include quarantining chimpanzees in pairs.
  12. When chimpanzees are transferred between facilities, send in advance some type of behavioral profile of each chimpanzee to the receiving institution.
  13. Apply behavioral conditioning techniques such as habituation, desensitization, and positive reinforcement training to enhance chimpanzee welfare and improve the quality of research.
  14. Use chimpanzees already trained to cooperate with specific research procedures.
  15. Maintain effective communication among those with expertise in veterinary science, behavioral science, and chimpanzee husbandry. Communication is essential for the best outcomes due to the complexity of health and behavioral issues that come into play when selecting chimpanzee subjects for study.

We have also identified a number of areas that require further research and documentation. We urge the scientific community to conduct the following necessary work:

We believe that the efforts described above are necessary to begin addressing the paucity of science-based data related to research with chimpanzees. Importantly, advancing this knowledge will also simultaneously promote the health and welfare of these important animals.

Acknowledgments

This project was supported by the National Institutes of Health/National Center for Research Resources Grant RR-00165 to the Yerkes National Primate Research Center and U42-RR15090 to The University of Texas (U.T.) M.D. Anderson Cancer Center. The Yerkes Center and U.T. M. D. Anderson facilities are both fully accredited by the Association for Assessment and Accreditation of Laboratory Animal Care-International.

Abbreviations used in this article: HIV, human immunodeficiency virus; IACUC, institutional animal care and use committee; RSV, respiratory syncytial virus; U.T., The University of Texas.

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