The efferent projections of the periaqueductal gray in the rat: A Phaseolus vulgaris‐leucoagglutinin study. II. Descending projections

Abstract

The descending projections of the periaqueductal gray (PAG) have been studied in the rat using the anterograde tracer Phaseolus vulgaris-leucoagglutinin. The tracer was injected into the dorsolateral or ventrolateral subdivisions of the PAG at rostral or caudal sites. It was found that the patterns of the descending projections of the rostral and caudal parts of the dorsolateral PAG were the same and that the patterns of the descending projections of the rostral and caudal parts of the ventrolateral PAG were the same. However, the patterns of projections of the dorsolateral and ventrolateral PAG subregions were substantially different. These results suggest that the dorsolateral and ventrolateral parts of the PAG are organized into longitudinal columns that extend throughout the length of the PAG. The axons of PAG neurons descended through the pons and medulla via two routes. A small fiber bundle was present in the periaqueductal gray and in the periventricular area. This bundle distributed fibers and terminals locally within the periaqueductal gray and in the locus coeruleus and Barrington's nucleus. A larger bundle had a diffuse arrangement in the pontine reticular formation, however, and it had a more restricted distribution in the medulla, where it occupied a position dorsolateral to the pyramid. This bundle supplied structures in the pontine and medullary tegmentum. The dorsolateral column preferentially supplied the locus coeruleus, subcoeruleus, the gigantocellular nucleus pars alpha, the rostral part of the paragigantocellular nucleus, and the region of the A5 noradrenergic cell group. The ventrolateral column preferentially supplied the nucleus raphe magnus, the caudal part of the lateral paragigantocellular nucleus, and the rostroventrolateral reticular nucleus.

Connections of the lateral hypothalamic area juxtadorsomedial region in the male rat

“…NIH-PA Author Manuscript NIH-PA Author Manuscript direct (possibly inhibitory) projection from the PAGd to the ventral PAGvl is suggested, as was previously described in the rat (Cameron et al, 1995;Jansen et al, 1998).…”

Genotype-dependent responsivity to inflammatory pain: A role for TRPV1 in the periaqueductal grey

“…Although, the DLPAG has no direct medullary projections to the RVM, it indirectly influences the RVM via projections to the cuneiform nucleus which in turn projects to the RVM (Holstege and Kuypers, 1982;Holstege, 1991;Keay and Bandler, 2001;Mitchell et al, 1988;Mitchell et al, 1988;Redgrave et al, 1988)., and can thus modulate descending pain transmission. The DLPAG has dense projections to hypothalamic nuclei mediating defensive responses (Cameron et al, 1995). In turn, neurons from the ventromedial hypothalamus and dorsal premamillary nucleus also project to the DLPAG (Canteras, 2002;Canteras and Swanson, 1992).…”

Effects of Substance P in the Amygdala, Ventromedial Hypothalamus, and Periaqueductal Gray on Fear-Potentiated Startle

“…Lesions of the VMH have been shown to disrupt other affective behaviors (Colpaert and Wiepkema, 1976;de Oliveira et al, 1997;Dielenberg et al, 2001;Han et al, 1996;Sudakov, 1987). Moreover, SP-containing afferents from the VMH project to the periaqueductal gray (PAGFDornan et al, 1990), which in turn projects to the pontine startle reflex circuit (Cameron et al, 1995;Canteras et al, 1994;Fendt et al, 1994;Meloni and Davis, 1999;Siegel et al, 1997). Thus, it is conceivable that the SP-containing MeA-VMH-PAG-pontine circuit may participate in or be required for the full expression of fear-potentiated startle.…”