Effect of Special Research Conditions on Psychological Well-Being
Research on nonhuman primates includes a wide array of activities. Much of it involves study of human diseases or conditions that can be studied only in living organisms and cannot be investigated experimentally in humans. Because of their many similarities to humans, nonhuman primates are often the subjects of choice for such research. Basic and applied knowledge gained from this research can improve the well-being of both humans and nonhuman primates.
Animals used in research sometimes experience unavoidable pain or discomfort and conditions that threaten their psychological well-being. Whereas every effort must be made to minimize those effects, it is the conditions that impair psychological well-being that sometimes are the subject of research themselves. Under all circumstances, however, negative effects on psychological well-being should be reduced to the greatest extent consistent with the research objectives. To help investigators to anticipate, mitigate, or avoid procedures that are likely to cause distress in research animals, many scientific organizations have drawn up codes of practice and ethical standards as guidelines for the care and use of animals. In addition, the Guide for the Care and Use of Laboratory Animals (the Guide) (NRC 1996) and the U.S. Government Principles for the Utilization and Care of Vertebrate Animals Used in Testing, Research, and Training (IRAC 1985) contain numerous specific recommendations that are observed by those whose research is supported by federal funds (see also NRC 1992) and by many in commercial and private institutions as well.
Among those recommendations, the Guide, the Public Health Service (PHS) Policy on Humane Care and Use of Laboratory Animals (OPRR 1996), and the
Animal Welfare Regulations state that institutions should appoint a committee (an institutional animal care and use committee, or IACUC) that is responsible for evaluating their animal care and use programs. Investigators have the obligation to assure review committees that animals will be treated humanely. Research on infectious diseases, effects of atypical rearing conditions, and pathological behavior pose special problems both for those establishing and maintaining enrichment programs and for those inspecting and reviewing such programs. Other circumstances in which experimental manipulations lead to changes in an animal's behavior—such as those related to surgery, drug or chemical treatment, or restriction of movement—also require special consideration to evaluate the animals appropriately and provide as well as possible for their psychological well-being. Investigators and IACUCs should periodically re-evaluate protocols in which animals experience special research conditions. They should be aware that knowledge about aspects of research procedures that cause distress and about methods to mitigate unwanted and unnecessary negative effects is changing continuously.
Conditions Involving Infectious Diseases
Studies that use nonhuman primates for infectious-disease research of necessity invoke several precautionary measures, for example, specialized animal holding units for animal and personnel safety (CDC/NIH 1993; NRC 1997a), use of protective clothing, and restricted access to animal areas. A frequent result of such safety measures is an environment that lacks sensory input or challenge to the animal. This is a particular concern when animals are housed in biocontainment units.
It is the responsibility of the investigator, veterinarian, and IACUC to determine the type of biocontainment necessary for a particular research study. Topics that should form the basis of the assessment include the goals of biocontainment, the mode of transmission and biosafety level of the agent, and the object of protection (the personnel, subject animals, and other animals in the facility). For example, research animals might be maintained in biocontainment units to protect personnel from a hazardous agent, to protect the subject animals from adventitious agents in the environment that could interfere with the research, or to protect other animals in the facility from the agent by isolating the infected subject animals. The means of achieving biocontainment should also be carefully evaluated, especially considering the psychological well-being of the primates. For some hazardous agents, protective clothing can be a sufficient biosafety barrier; in other cases, both cage and room barriers with specialized ventilation equipment are necessary.
Regardless of the degree of biocontainment, it is the consensus of this committee that biosafety concerns alone do not justify sensory or behavioral isolation
of subject animals. For example, the use of protective clothing does not have to keep personnel from interacting with the animals through appropriate postural and auditory cues, such as lip-smacking with many Old World species. Personnel should learn which human gestures and vocalizations are inappropriate and avoid the ones that stress the animals. Among the latter are threat faces, stares, threat vocalizations, imitations of alarm calls, and territorial calls. In some cases, physical contact between personnel and animal can be permitted, depending on the animal species and the hazardous agent. Likewise, social housing of animals used for infectious-disease research can be permitted in some studies. The use of biocontainment cage units with transparent walls, rather than solid or opaque walls, is preferred because they provide animals with visual contact with conspecifics. Recommendations provided in the Guide (NRC 1996) regarding acceptable ranges of illumination, cage size, temperature, humidity, ventilation, and noise level for conventional housing should be followed for biocontainment housing.
The enrichment program for animals in studies of infectious disease need not deviate substantially from that applied to conventionally housed animals. Typically, infected animals can receive the food treats used in the enrichment program for noninfected animals. Similarly, toys or other enrichment devices can be used with animals housed in biocontainment conditions if the devices are disposable or appropriately sanitized.
Conditions Involving Atypical Rearing Environments
The source of nonhuman primates for research is steadily shifting from wild-born animals to subjects that are born and raised in captivity. Whereas the psychological well-being of an animal is best promoted in a social context that approximates the species-typical norm, sometimes this is not possible. Some mothers might reject or be unable to care for an infant, the infant might be ill and require special care, or an approved research protocol might preclude maintenance of normal social compositions. Under such conditions, every effort should be made to provide infants and other immature animals with appropriate social stimulation so as to minimize the adverse effects of rearing in socially restricted environments. In the case of macaques, daily, but not continuous, nontraumatic contact with age peers seems to prevent the worst symptoms of isolation rearing (Mason 1991). As outlined in Chapter 3, however, hand rearing will seldom succeed in producing a completely psychologically normal animal.
Conditions Involving Physical Restraint of Animals
Some research protocols require that primates be physically restrained for various periods. In general, the least restraint that accomplishes the research objective should be used (NRC 1996). Restraint can be achieved by either
pharmacological agents or special equipment. For purposes of this discussion, only nonpharmacological means of restraint are addressed.
The method of restraint chosen should reflect the purpose of restraint, the period and degree of restraint, maintenance requirements, and the degree of discomfort imposed on an animal. For example, if the research protocol requires that an animal be chronically restrained but does not require strict immobility of the animal, this might be achieved in the animal's home cage by using a jacket and tether system, rather than a more confining primate chair. Animal restraint for periodic weighing, examinations, or testing can be achieved by training the animal to enter a transfer cage, rather than be hand-captured, netted, or chemically immobilized. Pole and collar systems also avoid hand capture and close restraint (Reinhardt 1995).
To achieve the restraint objective best, a balance between maximizing the safety of the procedure and maximizing the comfort of the animals should be struck. If animals are to be chaired for long periods, careful attention should be paid to chair design. A chair that allows the animal to assume a natural sitting or perching posture is preferable to a chair that constrains an animal in an unnatural position. Appropriate use of padding and soft surfaces with restraint devices can also reduce the incidence of injuries, such as decubital ulcers.
The use of restraint equipment does not necessarily preclude an animal from participating in an enrichment program. Manipulable objects and foraging devices that will not become entangled with a tether can be provided to animals that are maintained on a tether. In fact, a tethered animal can be housed with visual, auditory, chemical, and even tactile contact with another without compromising its safety. Similarly, a subject restrained in a chair in a procedure room might profit by having its usual cagemate placed in a cage in its view. Chair-restrained animals can also be provided with enrichment devices attached to the chair. Group housing of animals that are caught daily is still possible if the animals are trained to enter a transfer box (Clarke and others 1988; Reinhardt 1992a) or present themselves for pole and collar capture (Reinhardt 1995).
When deciding on a mode of restraint, the investigator, veterinarian, and IACUC should consider multiple criteria. Does the device provide the minimal restraint required to achieve the research objective? Is it safe for animals and personnel? Are its design and construction appropriate to the age, size, behavior, and normal posture of the animal that will be restrained? Has due consideration been given in the design of the equipment to the animal's comfort, such as use of padding and wide straps and the elimination of sharp or abrasive surfaces? How long will the animal be required to remain in restraint on a single occasion? Will the period of restraint be supervised by trained personnel? Is the animal adapted to the method of restraint and thoroughly trained to the apparatus? Finally, what specific procedures will be used to accomplish these goals, and who will carry them out?
Conditions Involving Minimally Invasive Procedures
Precise application of physiological stimuli and accurate measurement of physiological effects might require invasive procedures. If several functionally equivalent procedures are available, a decision should be made as to which is least likely to have a negative effect on psychological well-being. For example, blood can be taken from indwelling catheters or by venipuncture. When samples need to be obtained with high frequency and minimal disturbance, a catheter or vascular access port might be preferred. Taking blood via catheter or vascular access port causes no pain, but the animal should be anesthetized while the equipment is being installed and should be prevented later from pulling it out. A primate chair can prevent the animal from removing the catheter, but it severely restricts the animal's mobility. Another method that might protect the catheter but cause less restriction of movement is a tether system that includes a protective cover on the catheter.
The stress involved in venipuncture lies primarily in the physical restraint necessary to obtain the sample. A variety of nonhuman primates have been successfully trained to extend a limb voluntarily to permit a sample to be collected if repeated brief sampling is required (Bernstein and others 1991; Laule and others 1996; Rose and others 1975). For some purposes, hormonal data can be obtained from samples of urine and feces, rather than blood samples (Crockett and others 1993b; Kelley and Bramblett 1981; Lopez-Anaya and others 1990; Lunn 1989). Baboons have also been trained to submit routinely for taking blood pressure (Turkkan and others 1989). In addition, a variety of devices are available, including commercial products, for telemetric recording of some physiological characteristics and for the delivery of stimuli or active substances. Personnel safety is paramount when people are working with and training nonhuman primates, and no single technique for gaining access to an animal's arm or leg safely is universally accepted. What is considered the best safe practice is to train the animal to extend its limb (and sometimes to hold a firmly attached bar with the fist), or place a limb or shoulder against the cage, but persons should NEVER reach into the cage of any but the smallest species. Macaques, chimpanzees, and other large species can do great damage to those who fail to heed this tenet. Readers should become very familiar with the training literature before initiating these programs (see ''Restraint and Training" in Chapter 3 and Laule and others 1992).
Investigators should always be mindful of the effects of procedures on the well-being of the animals involved. If a choice is possible, instrumentation that appears least likely to cause a subject discomfort or distress should be chosen.
Conditions Involving Surgery
Some research protocols require surgical procedures. Experimental surgery is often referred to as major or minor, depending on the nature of the procedure. Both major and minor surgical procedures are potentially painful and can have negative effects on the well-being of the subject animal. Surgical procedures should be carefully considered to determine the least-invasive and least-stressful method of accomplishing the research goal. Most minor procedures and all major procedures are carried out under general anesthesia. Therefore, the well-being of a subject animal is most likely to be compromised during the postoperative or healing period. Although humans can indicate when they do or do not wish to use analgesics to contend with temporary postsurgical pain, nonhuman primates cannot so indicate and so should be given analgesics to prevent distress and reduce pain. Appropriate use of analgesics should result in improved appetite and more interaction of an animal with its environment (NRC 1992), but care should be taken that sutures are not removed by the animal.
It should also be recognized that surgery performed with the goal of altering the normal function of a physiological system can affect the psychological well-being of animals in the postsurgical period. Such procedures include those which reduce a subject's ability to interact socially or with the environment. Examples are procedures that result in impaired sensory perception, limit an animal's movement capacities, and impair cognitive abilities. After those procedures, appropriate accommodations should be made in an animal's housing environment or access to enrichment devices to maximize the extent to which it can interact socially and with the environment. Such accommodations can include housing the animal in a social group where it will not be subject to aggressive attacks, giving it manipulable objects that can be used with a particular sensory or motor deficit, and giving increased personnel attention to an animal that can no longer be put in social housing.
Multiple Research Use
Nonhuman primates are long-lived, expensive, and often threatened with extinction in nature. Animals maintained in a state of good health and well-being can contribute to research for many years. Facilities should assume that many nonhuman primates will participate in multiple studies and plan accordingly. This committee believes that appropriate multiple use of primates is in the best interest of conservation goals. Appropriate rest and recovery periods should be provided after each protocol that an animal participates in.
A subject of some controversy is the use of primates for multiple survival surgical projects. With most species, multiple survival surgery is not recommended; however, multiple survival surgery using nonhuman primates should be considered. To conserve as many animals as possible and maximize the long-
range research contribution of each animal, it might be necessary to use animals in multiple protocols that involve surgery. IACUC participation in making these decisions is very important. The well-being of the animals is not necessarily compromised by this approach if careful attention is given to the use of analgesics and enough time is allowed for recovery between operations.1
Conditions Involving Pain
Pain involves stimulation of physiological systems that process information about tissue damage (this process is called nociception) and systems that contribute to the perception of such events as painful. The two kinds of systems are not necessarily both active in all situations (Wall 1979). Nevertheless, the most conservative stance with respect to pain in nonhuman primates is to consider that both systems are operative. As stated in Principle IV of the U.S. Government Principles for the Utilization and Care of Vertebrate Animals Used in Testing, Research, and Training, "Unless the contrary is established, investigators should consider that procedures that cause pain or distress in human beings may cause pain and distress in other animals." (IRAC 1985; NRC 1992, 1996). Accordingly, we should assume that pain is potentially stressful for these animals and that severe or prolonged pain can threaten their psychological well-being.
Pain can occur in research animals for several reasons. It can be an unintended and unwanted byproduct of research. It can be an integral and explicit part of a research protocol, although not an objective (such as the use of electric shock in avoidance conditioning). It can occur as the principal focus of the research, as in experimental studies of pain itself and analgesia. Whatever its source, pain should be carefully monitored and controlled. Pain can occur as an unintended byproduct of research because of deficiencies in the design of equipment or as a postoperative response to surgery. In the first instance, equipment redesign is mandated; in the second, appropriate use of drugs is required (NRC 1992). When pain is used to motivate behavior or in experimental investigations of the nature and treatment of pain, the recommended procedure is to allow the animal to control the amount of pain it receives. For example, it might choose not to perform when the level of aversive stimulation is unacceptable or choose to avoid or escape from a painful stimulus. In any protocol involving the use of pain, the investigator should assess the pain by actually experiencing the maximal stimulus that would be delivered to the animal (NRC 1992).
Animal Models of Substance Abuse
Nonhuman primates (principally macaques, squirrel monkeys, and baboons) are used as subjects in behavioral and neuropharmacology experiments to study the effects of psychoactive drugs on specific types of behavior and to investigate the potential for abuse and drug dependence that such drugs present (e.g., Barrett 1985; Brady and Lukas 1984; Brady and others 1987; Meisch and Carroll 1987; Yanagita 1987). Some of the research conditions already considered—such as those involving restraint, invasive procedures, and aversive stimulation—are also used in research on psychoactive drugs, and the same concerns apply with respect to psychological well-being. In addition, the creation of physical or psychological drug dependence raises the possibility of intense withdrawal responses that might continue—or even become more severe—when an animal is no longer in the experimental setting. If such effects can be anticipated and are not part of the aims of the research, the IACUC and the investigator are obliged to consider them and if possible mitigate or eliminate them. Subjects in these studies present a special problem in providing for psychological well-being. They are often not compatible with social partners and might be unresponsive to other enrichment techniques, depending on the pharmacological agent being used and the degree of dependence. Their comfort and well-being require special attention and consideration.
Conditions Involving Aggression
Aggression is a part of the lives of nonhuman primates. In its most extreme form, aggression can cause extensive injury or death, and even the milder forms of aggression—which are generally expressed as species-typical postures or facial expressions—can be a marked source of stress. Different types of aggression can be directed toward conspecifics or caregivers, or toward the physical environment. Self-injurious behavior is a special type of behavior of concern.
Although investigators can find many opportunities to study the mechanisms involved in the expression and control of aggression by observing spontaneous outbreaks of aggression, some forms of research into aggression might involve the use of methods that instigate aggression under controlled conditions. That aggression is the subject of an approved study does not relieve the investigator, veterinarian, and IACUC of the responsibility for ensuring that consequent injuries and stress are minimized. Aggressive episodes, whether fortuitously detected or instigated according to an applied protocol, should be carefully monitored and controlled. In both instances, investigators have an obligation to intervene to protect their subjects from harm. When aggression is studied as part of an approved protocol, there should be a clear statement of the criteria to be used in deciding when intervention is necessary and a protocol to follow to keep the risk of injury and the degree of stress to the minimum consistent with the aims of the research. For many research purposes, injury is an unnecessary and undesirable consequence of research on aggression.