ASCENDING PROJECTIONS OF THE POSTERIOR NUCLEUS OF THE HYPOTHALAMUS - PHA-L ANALYSIS IN THE RAT

With the exception of a report by R.B. Veazey, D.G. Amaral, and W.M. C owan (1982, J. Comp. Neurol. 207:135-156) that examined the projection s of the posterior hypothalamic area in the monkey by using the autora diographic technique, the ascending projections of the posterior nucle us (PH) of the hypothalamus have not been systematically examined in a ny species. The present report describes the ascending projections of PH in the rat by using the anterograde anatomical tracer, Phaseolus vu lgaris-leucoagglutinin (PHA-L). The major ascending route for PH fiber s is the medial forebrain bundle. PH fibers project densely to several subcortical and cortical sites. The subcortical sites are the subthal amus/hypothalamus (zona incerta, the supramammillary nucleus, lateral, perifornical, dorsal, and anterior nuclei/areas), the thalamus (later oposterior, laterodorsal, parafascicular, reuniens, paraventricular, c entral medial, paracentral, central lateral and intermediodorsal nucle i), the amygdala (central, lateral, and medial nuclei), the septal are a (bed nucleus of stria terminalis, medial and lateral septum), and th e basal forebrain (horizontal/vertical limbs of diagonal band nuclei a nd lateral preoptic area). The cortical sites are the perirhinal, insu lar, frontal (lateral agranular), prelimbic, and infralimbic cortices. The diversity of PH projections to subcortical and cortical ''limbic- related'' sites and to several structures with direct input to the hip pocampus (supramammillary nucleus, reuniens, paraventricular and later odorsal nuclei of the thalamus, medial and lateral septum, and perirhi nal cortex) suggest that the PH may serve a critical role in various c omponents of emotional behavior, including mnemonic processes associat ed with significant emotional events. (C) 1995 Wiley-Liss, Inc.