Direct Projections From The Periaqueductal Gray To The Nucleus Tractus Solitarius In The Rat

The nucleus of the solitary tract (NTS) has been thought to be a very important site for receiving primary visceral information from thoraic and abdominal organs. Recently, physiological and morphological studies have demonstrated that NTS receives both visceral nociceptive information by afferent vagal nerve and afferent projections from the medullary oblongata and spinal cord as well in which noxions somatic or visceral afferents were included. In addition, the NTS may also be one of the important part concerning with the role of vagual afferent in antinociception. The periaqueductal gray (PAG) has been considered to be an important structure for antinociptive effect in the desending pain inhibitory system and has close realationship with many autonomic functions. It has been reported that PAG sends its axons to the NTS, howeveer, few systematic studies have focused on this projection pathway. Thus, in the present study, an atempt was made to examine the projections from the PAG to the NTS using fluorogold (FG) retrograde and PHA-L and WGA-HRP anterograde tract tracing techneques. To explore possible significances of this pathway, we used FOS immunochemisty method combined with FG retrograde tracing techniques to examine the expression of FOS protein in reciprocal projection...