The achievements in neuroscience research over recent years have greatly advanced the authors' understanding of nervous system structure and function. Yet, with each increment in knowledge, the realization of the overwhelming complexity of this organ system is evident. Gone are the days when the brain can be viewed as a complexly wired collection of a few neuronal cell types surrounded by an apparently inert contingent of supporting glia. It is now known that neurons exist in a seemingly endless array of subtypes, each of which has been revealed by the presence of an identifying constituent. Classically, these cell type 'markers' took the form of specific neurotransmitter/neuromodulator candidates. More recently, these neuron-specific tags have grown to encompass an enormous number of well characterized peptides and macromolecules. That glia also exist as a large collection of specific subtypes, each with a potentially unique function, has only recently been appreciated. These recent advances in neuroscience have now enabled scientists to utilize nerve cells and neuroglia and their associated proteins, to develop meaningful neurotoxicological assays and methods of studying important neuroregulators.

"EPA/600/D-91/126." Microfiche.