Response properties of the parabrachio-thalamic taste and mechanoreceptive neurons in rats

Abstract

A total of 66 taste and 33 mechanoreceptive neurons were isolated from the parabrachial nucleus (PB) of rats. Among them, 39 taste and 8 mechanoreceptive neurons were identified as parabrachio-thalamic relay (P-T) neurons on the basis of antidromic activation from either or both sides of the thalamic taste areas (TTAs). On average, the P-T taste neurons produced larger response magnitudes than the non-P-T taste neurons, and whereas about half the P-T taste neurons were NaCl-best, only a small number of the non-P-T taste neurons were NaCl-best. Both the P-T and non-P-T taste neurons showed a similar breadth of responsiveness to four basic taste stimuli. The response magnitudes of the P-T taste neurons to all taste stimuli were ca. 3 times larger than those of the solitario-parabrachial relay (SP) neurons (afferents to the PB); in particular, the response magnitudes of the NaCl-best P-T neurons were 4-5 times larger than those of the NaCl-best SP neurons. The response magnitudes and breadth of taste responsiveness of the P-T taste neurons were reciprocally correlated with the antidromic latencies from either side of the TTAs. A histological examination revealed that the P-T taste neurons in the ventral part of the PB had a shorter antidromic latency from the ipsilateral TTA than those in the dorsal part of the nucleus. Mechanoreceptive neurons were excited by stroking the tissue in the oral cavity or perioral tissue, or by pinching them with non-serrated forceps. The mechanoreceptive P-T neurons were also activated from either or both sides of the TTAs. No particular relation was noticed between the antidromic latency of the mechanoreceptive P-T neurons and their response properties or locations in the nucleus.

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

“…tralateral VPMpc, respectively. These results confirmed earlier tract tracing studies and the reports of Ogawa and colleagues (51,52) that taste neurons in the PbN project to the VPMpc bilaterally. We found that a much higher proportion of tasteresponsive PbN neurons project to either or both of the ipsilateral or contralateral VPMpc (95.6%) than were reported by Ogawa and colleagues (55-59%).…”

“…Norgren (47) demonstrated that a subset of NaCl and/or thermal-responsive PbN neurons in the rat were antidromically driven by stimulation of the ipsilateral amygdala and/or VPMpc. Ogawa and colleagues (51,52) reported in two separate studies that 55-59% of taste neurons in the PbN project to either or both of the ipsilateral or contralateral VPMpc in the rat.…”

“…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. Earlier electrophysiological studies concerning parabrachio-thalamic relay were focused mainly on the projection status of PbN taste neurons to the VPMpc but not on neuronal modulation of gustatory PbN neurons (25,45,47,51,52). The purpose of the present study was to examine the effect of electrical stimulation of the VPMpc on the responses of the gustatory PbN neurons and whether VPMpc stimulation modulates gustatory responses of the neurons in the hamster PbN.…”

Differential projections to the intralaminar and gustatory thalamus from the parabrachial area: A PHA-L study in the rat

“…The core of the PB''G'' corresponds precisely to the region in which most of the gustatory neurons were recorded (Norgren, 1974;Norgren and Pfaffman, 1975;Ogawa et al, 1987;Halsell and Travers, 1997), confirming that the PB''G''-VPpc pathway described in the present study conveys primarily gustatory messages. In addition, our study points out that the more medial portion of the pPBm, the properties of which were not clearly determined, also project to the VPpc.…”

“…Ventral to the bc, the pPB area centered in the waist area (pPBwa) and the medial subnucleus (pPBm) deal mainly with gustatory functions Leonard, 1971, 1973;Norgren and Pfaffmann, 1975;Norgren, 1978Norgren, , 1995Ogawa et al, 1987;Halsell and Travers, 1997).…”