Target organ toxicity: nervous system.

This conference was organized in response to the resurgence of interest in the behavioral and neurological effects resulting from low-level exposures to a wide variety of chemical and physical agents. One factor in this renewed interest was the passage of the Toxic Substance Control Act. This law specifically states, among other things, that chemicals should be evaluated for their behavioral effects. Unfortunately, real or potential risks to the nervous system are difficult to assess because of the complexity of the system. Some of the problems in assessment are associated with the wide variation in function which can occur and still lie within the classification of "normal." Some are associated with the plasticity of the nervous system. Other problems in assessment are related to our incomplete understanding of precisely what is being measured by certain tests. Clearly, no single test will suffice to examine the functional capacity of the nervous system. During the course of this conference , it became equally clear that the current state of our knowledge does not even warrant the selection of a battery of tests from the myriad procedures available. Dr. Dews stated, in his paper, that "no methods of predicting when prolonged exposure to a low level of an agent will lead to subtle and delayed behavioral effects in man have been validated ." Elsewhere in this volume, Drs. Tilson and Cabe present one approach toward the validation of such methods. Many behavioral toxicologists apparently either presume or hope that behavioral tests will prove to be more sensitive than other tests in detecting central nervous system toxicity. Dr. Norton reminded us, however, that "while the logical argument is easy to propose, critical experiments are rare in which careful behavioral studies have been paired with detailed morphological examination." To me, a more convincing argument for the use of be-havioral tests, rather than sensitivity, is that given by Dr. Mello (1). She stated, ""the behavior of the organism is the endpoint of the functional integration of the nervous system encompassing sensory, motor, and cognitive aspects. The functional capacity of the central nervous system cannot be determined by histological or even physiological studies independent of behavioral analysis." This theme was also espoused by Dr. Reiter in his introductory statements to this conference. Dr. Norton pointed out, however, that "it is the functioning of the central nervous system that is monitored by behavior , not damage for which compensation …