Modulation of Parabrachial Taste Neurons by Electrical and Chemical Stimulation of the Lateral Hypothalamus and Amygdala

Abstract

The lateral hypothalamus (LH) and the central nucleus of the amygdala (CeA) exert an influence on ingestive behavior and are reciprocally connected to gustatory and viscerosensory areas, including the nucleus of the solitary tract (NST) and the parabrachial nuclei (PbN). We investigated the effects of LH and CeA stimulation on the activity of 101 taste-responsive neurons in the hamster PbN. Eighty three of these neurons were antidromically activated by stimulation of these sites; 57 were antidromically driven by both. Of these 83 neurons, 21 were also orthodromically activated-8 by the CeA and 3 by the LH. Additional neurons were excited (n ϭ 5) or inhibited (n ϭ 8) by these forebrain nuclei but not antidromically activated. Taste stimuli were: 0.032 M sucrose, 0.032 M sodium chloride (NaCl), 0.032 M quinine hydrochloride (QHCl), and 0.0032 M citric acid. Among the 34 orthodromically activated neurons, more sucrose-best neurons were excited than inhibited, whereas the opposite occurred for citric-acidand QHCl-best cells. Neurons inhibited by the forebrain responded significantly more strongly to citric acid and QHCl than cells excited by these sites. The effects of electrical stimulation were mimicked by microinjection of DL-homocysteic acid, indicating that cells at these forebrain sites were responsible for these effects. These data demonstrate that many individual PbN gustatory neurons project to both the LH and CeA and that these areas modulate the gustatory activity of a subset of PbN neurons. This neural substrate is likely involved in the modulation of taste activity by physiological and experiential factors.

Modulation of activity of gustatory neurons in the hamster parabrachial nuclei by electrical stimulation of the ventroposteromedial nucleus of the thalamus

“…The anterior-posterior distribution of the recording marks extended rostrally from the level at which LC is first apparent and caudally to the appearance of the accessory trigeminal nucleus. The locations of the recording sites in the PbN were similar to those of our laboratory's previous recordings (34,35).…”

“…These forebrain nuclei likely have a role in gustatory modulation of the cells in the PbN. Indeed, electrophysiological investigations have reported that gustatory responses of pontine neurons are modulated by electrical stimulation of the LH, CeA, and GC in the hamster and the rat (11,35,39,40).The VPMpc, the third-order gustatory relay in the rodent, is less understood in several aspects (56,68,85,86). For example, whereas the afferent projections from the PbN to the VPMpc were well documented, the efferent projections from the VPMpc to the PbN were not demonstrated (4,21,64).…”

“…These forebrain nuclei likely have a role in gustatory modulation of the cells in the PbN. Indeed, electrophysiological investigations have reported that gustatory responses of pontine neurons are modulated by electrical stimulation of the LH, CeA, and GC in the hamster and the rat (11,35,39,40).…”

“…The involvement of the forebrain gustatory nuclei in the ventral forebrain pathway, e.g., LH, CeA, BNST, and GC, on modulation of activity of PbN taste neurons has been well documented (10,11,34,35,39,40). However, the possibility of the involvement of the VPMpc in the thalamocortical pathway on modulation of activity of taste neurons in the PbN has never been investigated.…”

Identification of central projections from amylin-activated neurons to the lateral hypothalamus

“…Our results showed that the amylin-activated area of the NTS and BSTL project sparsely, while the LPB projects densely to the dLHA subregion where amylin reduces the fasting induced activation. Our findings extend previous studies (Ricardo and Koh, 1978;Kobashi and Adachi, 1988;Li et al, 2005;Hui et al, 2006;Yoshida et al, 2006) and demonstrate that the inputs to the dLHA partly arise from amylin responsive neurons. Many LPB efferents were found in proximity to dLHA c-Fos-positive nuclei, i.e., neurons that respond to changes in food availability (fasted vs. fed).…”