Pontine gustatory activity is altered by electrical stimulation in the central nucleus of the amygdala

Visceral signals and experience modulate the responses of brain stem neuron s to gustatory stimuli. Both behavioral and anatomical evidence suggests th at this modulation may involve descending input from the forebrain. The pre sent study investigates the centrifugal control of gustatory neural activit y in the parabrachial nucleus (PBN). Extracellular responses were recorded from 51 single PBN neurons during application of sucrose, NaCl, NaCl mixed with amiloride, citric acid, and QHCl with or without concurrent electrical stimulation in the ipsilateral central nucleus of the amygdala (CeA). Base d on the sapid stimulus that evoked the greatest discharge, 3 neurons were classified as sucrose-best, 32 as NaCl-best, and 16 as citric acid-best. In most of the neurons sampled, response rates to an effective stimulus were either inhibited or unchanged during electrical stimulation of the CeA. Sti mulation in the CeA was without effect in two sucrose-best neurons, nine Na Cl-best neurons, and one citric acid-best neuron. Suppression was evident i n 1 sucrose-best neuron, 18 NaCl-best neurons, and 15 citric acid-best neur ons. In NaCl-best neurons inhibited by CeA stimulation, the magnitude of th e effect was similar for spontaneous activity and responses to the five tas te stimuli. Nonetheless, the inhibitory modulation of gustatory sensitivity increased the relative effectiveness of NaCl resulting in narrower chemica l selectivity. For citric acid-best neurons, the magnitude of inhibition pr oduced by CeA activation increased with an increase in stimulus effectivene ss. The responses to citric acid were inhibited significantly more than the responses to all other stimuli with the exception of NaCl mixed with amilo ride. The overall effect was to change these CA-best neurons to CA/NaCl-bes t neurons. In a smaller subset of NaCl-best neurons (n = 5), CeA stimulatio n augmented the responsiveness to NaCl but was without effect on the other stimuli or on baseline activity. It appears that electrical stimulation in the CeA modulates response intensity, as well as the type of gustatory info rmation that is transmitted in a subset of NaCl-best neurons. These finding s provide an additional link between the amygdala and the PBN in the contro l of NaCl intake, modulating the response and the chemical selectivity of a n amiloride-sensitive Na+-detecting input pathway.