Gustatory Projections from the Nucleus of the Solitary Tract to the Parabrachial Nuclei in the Hamster

Abstract

Taste-responsive cells in the nucleus of the solitary tract (NST) either project to the parabrachial nuclei (PbN) of the pons, through which taste information is transmitted to forebrain gustatory nuclei, or give rise to axons terminating locally within the medulla. Numerous anatomical studies clearly demonstrate a substantial projection from the rostral NST, where most taste-responsive cells are found, to the PbN. In contrast, previous electrophysiological studies in the rat have shown that only a small proportion (21-45%) of taste-responsive NST cells are antidromically activated from the PbN, suggesting that less than half the cells recorded from the NST are actually involved in forebrain processing of gustatory information. In the present experiment we investigated the projections from the NST to the PbN electrophysiologically in urethane anesthetized hamsters. Responses of 101 single neurons in the rostral NST were recorded extracellularly following lingual stimulation with 32 mM NaCl, sucrose and quinine hydrochloride (QHCl) and 3.2 mM citric acid. The taste-responsive region of the PbN was identified electrophysiologically and stimulated with a concentric bipolar electrode to antidromically activate each NST cell. Of the 101 taste-responsive NST cells, 81 (80.2%) were antidromically activated from the ipsilateral PbN. The mean firing rates to taste stimulation and the spontaneous activity of these projection neurons were significantly greater than those of non-projecting cells. Every sucrose-best neuron in the sample projected to the PbN. The mean conduction velocity of the 23 QHCl-best neurons was significantly lower than that of the other 58 PbN projection neurons, suggesting that the most QHCl-responsive cells are a subset of smaller neurons. These data show that a large majority of NST cells responsive to taste stimulation of the anterior tongue project to the gustatory subdivisions of the PbN and that these cells have the most robust responses to gustatory stimulation.

Endogenous central amygdala mu-opioid receptor signaling promotes sodium appetite in mice

“…From a technical perspective, although our local infusion studies targeted the mCeA, it is likely that the entire CeA was within the boundaries of drug/vehicle injections. Finally, we report here that the rNTS and LPB were also activated in response to sodium gratification; however, such a finding was expected given the known role of these structures in receiving and processing sodium taste information (42,43).…”

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

“…An interspecies difference between rat and hamster has also been reported in the proportion of afferent projection of second-order gustatory relay neurons to the PbN. For instance, it was reported that 34.1% (53) or 45% (42) of the taste neurons in the NST project to the PbN in the rat, whereas a larger percentage (80.2%) was reported in an investigation with hamsters (7).…”

“…Gustatory information elicited from the tongue and oropharyngeal cavity is initially carried to the rostral portion of the nucleus of the solitary tract (NST) by the VIIth, IXth, and Xth cranial nerves, and these terminals are distributed in a topographic fashion with rostral-caudal sequence in the rostral NST (2,9,23,24,89). From the NST, ascending gustatory fibers project to third-order taste cells within the PbN of the pons (7,22,42,46,(53)(54)(55)87). Two separate routes carry taste information from the PbN further to the forebrain taste areas and cortex: the ventral forebrain pathway that involves the central nucleus of the amygdala (CeA), the lateral hypothalamus (LH), the bed nucleus of the stria terminalis (BNST), the substantia innominata (3,12,16,21,31,33,34,41,47,63,64,71); and the thalamocortical pathway that is characterized by the involvement of the bilateral VPMpc, which, in turn, carries taste information to the gustatory cortex (GC) (5,25,45,48,51).…”

Activity in the Hypothalamus, Amygdala, and Cortex Generates Bilateral and Convergent Modulation of Pontine Gustatory Neurons

“…Electrophysiological experiments find that from about 35 to 80% of NST taste neurons are antridromically invaded by stimulation in the PBN (Cho et al 2002b;Monroe and DiLorenzo 1995;Ogawa and Kaisaku 1982;Ogawa et al 1984). Moreover, stimulating the CeA, LH, and GC influences taste responses in both the NST and PBN cells.…”