Luteinizing hormone-releasing hormone in the vomeronasal system and terminal nerve of the hamster.

The vomeronasal system of mammals is a specialized chemosensory pathway that parallels the main olfactory system but is anatomically distinct from its peripheral aspect through its projections into the central nervous system.'.' Recent evidence suggests a predominant role for the vomeronasal system in conveying the influence of odor stimuli upon neuroendocrine and on a variety of motivated behaviors, including sex,6 aggression,' and maternal behavior.' This functional role probably reflects the relatively direct projections of this chemosensory system to areas of the ventral forebrain important in the control of neuroendocrine and behavioral events. The sole central target of the vomeronasal organ is the accessory olfactory bulb (AOB), neurons which in turn project to several nuclei of the medial amygdala.'.' In particular, the medial nucleus of the amygdala (M), has projections to the preoptic area and hypothalamus, and has been strongly implicated in mediating the influence of odor cues upon the neuroendocrine system and behavior.'".'' Axons containing immunoreactive luteinizing hormone-releasing hormone (LHRH) are found throughout the vomeronasal system in the rat and Sparse LHRH fibers are seen within the neuroepithelium of the vomeronasal organ itself.'*." LHRH fibers and cells, defined as a subset of the terminal are present in close proximity to the vomeronasal nerve in the nasal cavity. Centrally, a dense plexus of LHRH fibers innervates the glomerular layer of the AOB, the site of the first synapse in this sensory system. Occasionally, isolated LHRH perikarya are found within the AOB as well. Further caudally, LHRH fibers are seen adjacent to the optic tract within the superficial plexiform layer of M, that layer which receives