A series of immunocytochemical, Golgi and connectional experiments are proposed to study the intrinsic organization of the gustatory zone of the nucleus of the solitary tract (NST) in the adult hamster. Special emphasis is placed on the association among primary gustatory and other somatosensory afferent inputs and the various classes of neurons within the gustatory NST. These studies are carried out at the light and electron microscopic levels. Primary gustatory afferent fibers and their central terminals are destroyed after their exposure to the toxic lectin ricin. The same material is then processed with the use of other methods that primarily visualize neuronal somata and processes, in this way, degenerating peripheral inputs are related to identifiable classes of neurons. Immunocytochemistry associates particular classes with specific chemical markers such as monoamines (e-g., the catechols and GABA) and neuropeptides (e.g., substance P and enkephalins) that are implicated in neurotransmission; separate classes of output neurons that project rostrally or caudally are retrogradely labelled (and differentiated) after wheat-germ agglutinin- horseradish peroxidase injections into the appropriate target sites; and Golgi and correlated Golgi-EM studies fully characterize the morphological features and orientations of gustatory NST neurons. These studies evolve from ongoing work in the gustatory NST that deals with the general morphologies of the classes of NST neurons and are designed to assign potential functional attributes (e.g., output neurons vs. local circuit neurons) to morphologically and chemically distinct classes of neurons. This proposal continues our efforts to clarify the basic anatomical principles governing the processing of gustatory information,
