PREOPTIC PROJECTIONS TO BARRINGTONS NUCLEUS AND THE PERICOERULEAR REGION - ARCHITECTURE AND TERMINAL ORGANIZATION

The medial preoptic area (MPO), a sexually dimorphic region, plays a p ivotal role in neuroendocrine function and reproductive behavior. We r ecently reported that MPO projects heavily to the midbrain periaqueduc tal gray (PAG). We also noted that MPO projects to the dorsolateral po ntine tegmentum. Here we identified the cells of origin of the MPO-->t egmental projection and delineated the terminal organization of MPO pr ojections to Barrington's nucleus, locus coeruleus (LC), and the rostr omedial pericoerulear region (pLCrm). Correlative cyto- and chemoarchi tectonic studies were done to define better the nuclear groups of the dorsolateral pontine tegmentum. Retrograde tracing revealed that MPO n eurons projecting to the dorsolateral pontine tegmentum are preferenti ally distributed in distinct subregions of MPO, including the sexually dimorphic medial preoptic nucleus (MPN). Anterograde tracing with whe at germ agglutinin-horseradish peroxidase or Phaseolus vulgaris leucoa gglutinin demonstrated considerable target specificity in projections from MFO to the dorsolateral pontine tegmentum. Barrington's nucleus r eceives a dense focal input along its entire rostrocaudal axis. In add ition, pLCrm is heavily targeted by MPO inputs; pLCrm contains a conce ntrated plexus of extranuclear dendrites of LC neurons. The lateral do rsal tegmental (LDT) nucleus and LC proper receive only sparse input f rom MPO. MPO projections to Barrington's nucleus could regulate mictur ition reflexes during reproductive behavior. The MPO-->pLCrm projectio n could influence noradrenergic LC neurons in relation to reproductive and/or gonadal steroid function. Given the strong established connect ions from olfactory structures to MPO, it is possible that the MPO-->L C pathway provides an anatomical substrate for olfactory modulation of arousal. (C) 1994 Wiley-Liss, Inc.