Forebrain modulation of brainstem gustatory processing.

Taste information in rodents is carried to the rostral portion of the nucleus of the solitary tract (NST) by axons of the VIIth, IXth and Xth cranial nerves (Beckstead and Norgren, 1979). From the NST, ascending gustatory fibers project to third-order cells within the parabrachial nuclei (PbN) of the pons (Norgren, 1978), and in turn to multiple forebrain nuclei, including the thalamus, insular cortex (IC), lateral hypothalamus (LH), central nucleus of the amygdala (CeA) and bed nucleus of the stria terminalis (BST) (Norgren, 1976; Saper and Loewy, 1980; Halsell, 1992). These forebrain targets send centrifugal axons to both the PbN and NST (van der Kooy et al., 1984; Allen et al., 1991; Halsell, 1998). The present manuscript summarizes recent work on the descending modulation of NST neuronal activity by these various forebrain targets of the gustatory system.