The nervus terminalis (NT) is a ganglionated cranial nerve which connects the brain and the peripheral olfactory structures. The NT has been found in most vertebrates, including adult humans and, although studied repeatedly with a variety of techniques, the NT remains the only cranial nerve for which the function is completely unknown in humans or in any species. Based on the connections of the nerve and the morphology of cells in the NT ganglion, anatomists have suggested that the nerve may serve a combined sensory and autonomic function. Perhaps one of the most significant recent findings concerning the NT is that some neurons in the nerve contain high levels of luteinizing hormone- releasing hormone (LHRH) immunoreactivity. Some of these LHRH-immunoreactive cells project to brain areas involved with reproduction and some appear to have direct connections with blood vessels. The presence of LHRH-immunoreactivity in the NT neurons and the central and peripheral connections of the nerve has led some researchers to suggest that the NT may be chemosensitive to pheromones and involved in reproductive functions in fish and mammals, possibly by releasing LHRH directly into the blood. However, there has been no electrophysiological evidence for either a chemosensory or a neuroendocrine function for the NT and it is not known if the circuitry of the NT ganglion is compatible with these suggested functions. Investigation of the physiological and morphological organization of the NT ganglion will provide a ground-plan for a more informed investigation of NT function. Elasmobranchs will be used in these studies, because it is only in these animals that the NT is separate from the brain and directly accessible for electrophysiological experiments. Experiments proposed here include: 1) electrophysiological, pharmacological and morphological investigations of NT ganglion cells, which will provide data on the afferent and/or efferent projections of physiologically characterized cells; 2) combined electrophysiology, dye-fills and immunocytochemistry will investigate the function(s) of peptide containing cells, including the possibility that such cells constitute the afferent or efferent component of the nerve; 3) integration of data from all experiments will provide the first coherent picture of the neuronal circuitry of the NT ganglion, including the synaptic interactions between elements within the ganglion.
