THE EFFERENT PROJECTIONS OF THE PERIAQUEDUCTAL GRAY IN THE RAT - A PHASEOLUS-VULGARIS-LEUKOAGGLUTININ STUDY .1. ASCENDING PROJECTIONS

This study has examined the ascending projections of the periaqueducta l gray in the rat. Injections of Phaseolus vulgaris-leucoagglutinin we re placed in the dorsolateral or ventrolateral subregions, at rostral or caudal sites. From either region, fibers ascended via two bundles. The periventricular bundle ascended in the periaqueductal and perivent ricular gray matter. At the posterior commissure level, this bundle di vided into a dorsal component that terminated in the intralaminar and midline thalamic nuclei, and a ventral component that supplied the hyp othalamus. The ventral bundle formed in the deep mesencephalic reticul ar formation and supplied the ventral tegmental area, substantia nigra pars compacta, and the retrorubral field. The remaining fibers were i ncorporated into the medial forebrain bundle. These supplied the later al hypothalamus and forebrain structures, including the preoptic area, the nuclei of the diagonal band, and the lateral division of the bed nucleus of the stria terminalis. The dorsolateral subregion preferenti ally innervated the centrolateral and paraventricular thalamic nuclei and the anterior hypothalamic area. The ventrolateral subregion prefer entially innervated the parafascicular and central medial thalamic nuc lei, the lateral hypothalamic area, and the lateral division of the be d nucleus of the stria terminalis. Although the dorsolateral and ventr olateral subregions gave rise to differential projections, the project ions from both the rostral and caudal parts of either subregion were s imilar. This suggests that the dorsolateral and ventrolateral subregio ns are organized into longitudinal columns that extend throughout the length of the periaqueductal gray. These columns may correspond to tho se demonstrated in recent physiological studies. (C) 1995 Wiley-Liss, Inc.