Abstract
Systematic observations of rat behavior are required for both standard subchronic safety studies and for neurotoxicity studies. The requirements specify subjective out-of-cage observations (eg, posture, gait, and reactivity to various stimuli such as, auditory, tactile, and noxious) using defined scales. Measurement of forelimb/hind limb grip strength, landing foot splay, and locomotor activity are also required. The observational endpoints are organized into a battery, eg, the Environmental Protection Agency functional observational battery (FOB) or expanded clinical observations (ECO). Functional and neuropathologic data are most easily integrated when the functional endpoints are organized as a neurologic exam (ie, each endpoint has a known anatomical basis and there are sufficient endpoints to cover the nervous system). Current batteries do not constitute a neurologic exam. Although ECOs and FOBs contain some components of a neurologic exam (ie, observations of gait, response to pinch), the anatomic basis for other components (eg, hind limb splay) is poorly defined. And although some functions (eg, somatomotor) are well characterized by current batteries, others (eg, vision, somatosensation) are evaluated less effectively. The measurement of locomotor activity in a novel environment is one of the most problematic parts of current functional testing batteries, although contemporary technology may provide opportunities for improving this test. The influence of inherent limitations of functional test methods is magnified by factors associated with testing for neurotoxicant-related effects during safety studies. First, most personnel at contract laboratories have little or no formal training in conducting and interpreting a neurologic examination. Second, most neurotoxicant-related lesions are bilateral, which paradoxically may produce more subtle effects than unilateral lesions. Third, most chemicals will be tested only once, and sponsors are reluctant to evaluate results in "real time" and amend protocols to add endpoints (eg, neurophysiological tests) to clarify functional effects. Pathologists should have realistic expectations about the opportunities for integrating functional and neuropathologic findings.