CHEMICAL TOPOGRAPHY OF EFFERENT PROJECTIONS FROM THE MEDIAN PREOPTIC NUCLEUS TO PONTINE MONOAMINERGIC CELL GROUPS IN THE RAT

This study examined efferent output from the median preoptic nucleus ( MnPO) to pontine noradrenergic and serotonergic cell groups using an a nterograde tracing technique (Phaseolus vulgaris leucoagglutinin, PHA- L) combined with glucose oxidase immuno-cytochemistry ro serotonin (5- HT) or to dopamine-beta-hydroxylase (DBH). Injections of PHA-L into th e ventral MnPO resulted in moderate axonal labeling within the region of the B7 and B8 serotonergic groups in the dorsal raphe. PHA-L labele d fibers and punctate processes were observed in close apposition to m any of the 5-HT immunoreactive neurons in these regions. In contrast, sparse terminal labeling was found within the B5 group in the raphe po ntis nucleus, and only trace fiber labeling observed in the B3 and B6 groups. Efferents from the MnPO also provided moderate innervation to the A6 and A7 noradrenergic groups. PHA-L labeled punctate processes w ere found most frequently in close apposition to DBH-immunoreactive ne urons at mid- to caudal levels of the locus coeruleus. Some labeled ax ons were also present within the A7 and A5 groups. Additionally, a clo se apposition between labeled MnPO efferents and 5-HT fibers within th e lateral parabrachial nucleus was observed. The results indicate the MnPO provides a topographic innervation of monoaminergic groups in the upper brainstem.