Descending projections from the nucleus accumbens shell suppress activity of taste-responsive neurons in the hamster parabrachial nuclei.

The parabrachial nuclei (PbN), the second central relay for the gustatory pathway, transfers taste information to various forebrain gustatory nuclei and to the gustatory cortex. The nucleus accumbens is one of the critical neural substrates of the reward system, and the nucleus accumbens shell region (NAcSh) is associated with feeding behavior. Taste-evoked neuronal responses of PbN neurons are modulated by descending projections from the gustatory nuclei in the forebrain. In the present study, we investigated whether taste-responsive neurons in the PbN project to the NAcSh and whether pontine gustatory neurons are subject to modulatory influence from the NAcSh in urethane-anesthetized hamsters. Extracellular single-unit activity was recorded in the PbN, and taste responses were confirmed by the delivery of 32 mM sucrose, NaCl, quinine hydrochloride, and 3.2 mM citric acid to the anterior tongue. The NAcSh was then stimulated (0.5 ms, ≤100 μA) bilaterally using concentric bipolar stimulating electrodes. A total of 98 taste neurons were recorded from the PbN. Eighteen neurons were antidromically invaded from the NAcSh, mostly the ipsilateral NAcSh (n = 16). Stimulation of the ipsilateral and contralateral NAcSh suppressed the neuronal activity of 88 and 55 neurons, respectively; 52 cells were affected bilaterally. In a subset of pontine neurons tested, electrical stimulation of the NAcSh during taste stimulation also suppressed taste-evoked neuronal firing. These results demonstrated that taste-responsive neurons in the PbN not only project to the NAcSh but also are under substantial descending inhibitory influence from the bilateral NAcSh.