Functional heterogeneity within neurotransmitter systems.

This paper reviews experiments that have revealed distinct differences between the dorsal and median raphe nuclei in the rat midbrain. The raphe nuclei appear to be hetrogeneous with respect to their anatomical projections to the forebrain, their relevance to specific behaviors, and their pharmacological responses. Startle response measures are useful indicators of the functional state of serotonergic system originating in the median raphe. As a way to study individual cells within the various raphe nuclei, microspectroflurimetric techniques are promising.