Medullary inputs to nucleus accumbens neurons.

Extracellular single-unit recording experiments were done in alpha-chloralose-anesthetized, paralyzed, and artificially ventilated rats to investigate the effect of stimulation of the nucleus of the solitary tract (NTS) and the ventrolateral medulla (VLM) in the region of the A1 noradrenergic cell group on the activity of neurons in the nucleus accumbens (NA). In addition, the response of NA neurons to activation of the arterial baroreceptors was investigated. Electrical or glutamate (Glu) stimulation of the ipsilateral NTS excited 47 of 99 (48%) and inhibited 10 of 99 (10%) of the units tested in the NA. Similarly, electrical or Glu stimulation of the ipsilateral VLM excited 24 of 97 (24.7%) or inhibited 7 of 97 (7.2%) of the units tested. Approximately 22% (17 of 77) of these units responded to stimulation of both the NTS and VLM. Simultaneous stimulation of both the NTS and VLM potentiated the response of the NA neuron tested. CoCl2 injection into the ipsilateral NTS did not alter the response of NA neurons to stimulation of the VLM. Similarly, CoCl2 injections into the ipsilateral VLM did not alter the response of NA neurons to NTS stimulation. The discharge rate of some of the units (6 of 49) that were activated by both NTS and VLM was also increased during the activation of arterial baroreceptors by the acute rise in systemic arterial pressure to phenylephrine injection. Units that responded to stimulation of the NTS and VLM and to baroreceptor activation were located in the shell region of the NA. These data indicate that afferent inputs from the NTS and VLM converge onto NA neurons and suggest that visceral and cardiovascular afferent inputs may influence the output of neurons in the shell region of the NA.