A Practical Approach, Second Edition=Ronald D. Ho.pdf

310 DEVELOPMENTAL REPRODUCTIVE TOXICOLOGY: A PRACTICAL APPROACH, SECOND EDITIONthan two days would likely be test article–related. Similarly, Merck performed calculations usinghistorical data to determine the power of a standard two-tailed test to detect changes in the age atacquisition of both balanopreputial separation and vaginal patency. 137 As an example, their calculationsdemonstrated that with a sample size of 20 Sprague-Dawley rats/group, a 2.5-day changein the mean age at acquisition of balanopreputial separation would have a probability of 0.87 ofbeing a true change from control. Likewise, the data indicated that a difference in the mean age atacquisition of vaginal patency of 2.0 days would have a probability of 0.87 of being a true changefrom control. 137c. Behavioral AssessmentsThe decision to conduct behavioral testing as part of the juvenile study can be a difficult onebecause assessment of behavior may be required for other agents in addition to neuroactivecompounds. Factors influencing the decision include the age at initiation of clinical dose administration,the duration of the dose administration period, whether the central or peripheral nervoussystems are still developing in the species, and whether the test article has been shown to causeadverse changes in organ systems that are key to internal homeostasis in adult animals. As mentionedearlier, there are critical windows during which organ systems may be susceptible to test articleadministration. For example, the development of the human nervous system extends well beyondbirth. 148 If the pediatric indication includes the period of nervous system development, regulatoryagencies may recommend an evaluation of behavioral endpoints. In addition, functional deficits inkey organ systems can produce detrimental effects on behavior that are separate from directneurotoxicity. However, these potential secondary changes in behavior should not be ignoredbecause they can provide important clues to the clinician regarding the types of side effects thatpediatric patients may experience. The next several sections describe basic behavioral testingparadigms that may be employed to evaluate changes in motor function and coordination, sensoryperception, and cognition. The list of endpoints discussed is not meant to cover every possibleparameter, and the reader is invited to review the extensive literature on these topics for more detail.1) Locomotor Activity — Locomotor activity can be generally quantified as total, fine, andambulatory activities. There are several styles of test chambers for rats, and the authors’ facilityemploys an open-field environment surrounded by four-sided black plastic enclosures to decreasethe potential for distraction by extraneous environmental stimuli. Activity is measured electronicallywith a series of infrared photobeams surrounding the clear plastic rectangular open field environment.The animal’s activity can be expressed as total and ambulatory activity (for rodents), althoughthis is not a universally applied approach. Total activity is generally the sum of both gross and finemotor movements (any photobeam break during the testing paradigm). Ambulatory activity is ameasure of only gross movements (two or more consecutive photobeam breaks, i.e., the animal ismoving from one location to another). Testing is usually conducted over a 60- to 90-min session,although some laboratories conduct locomotor activity test sessions over a 23-h period. The lengthof the test session is determined by the desire to demonstrate habituation during a particular test.Many laboratories have based the session length on EPA guideline recommendations that “the testsession should be long enough for motor activity to approach asymptotic levels by the last 20percent of the session for nontreated control animals.” 56 Appropriate validation and positive controlstudies must be conducted prior to the conduct of any animal study to determine the session lengthnecessary to evaluate habituation, using the equipment available for testing.For the rat, total activity will normally be relatively low at PND 13, will increase to a maximumpreweaning level by PND 17, and will decrease by PND 21. This ontogenic profile of activity hasbeen well characterized. 149 For rats and mice, locomotor activity is generally assessed longitudinallyduring early postnatal life (PND 13, 17, and 21 for rats) and again at young adulthood (PND 60to 61) in standard developmental neurotoxicity studies. 56 More limited assessments are generally© 2006 by Taylor & Francis Group, LLC