Microinjection of bicuculline into the central nucleus of the amygdala alters gustatory responses of the rat parabrachial nucleus.

The central amygdaloid nucleus (CeA) receives projection from the parabrachial nucleus (PBN) gustatory neurons and descendingly projects to the PBN, and taste responses in the PBN are significantly affected by stimulation or lesion of the CeA. To examine whether the GABA receptors within the CeA are involved in this modulation, the effects of microinjection of bicuculline, a GABA(A)-selective antagonist, into the CeA on the activities of PBN taste neurons were observed by using extracellular recording technique. In general, after bicuculline was administered to ipsilateral CeA, the responses of PBN neurons to four tastants all increased, with the magnitudes significantly higher than those obtained before drug administration (P<0.01), respectively. However, after bicuculline was delivered into the contralateral CeA, only the responses to NaCl, HCl and QHCl increased. According to the best-stimulus category, 47% NaCl-best (8/17), 64% HCl-best (7/11), 80% QHCl-best (4/5), and 33% sucrose-best (1/3) increased their responses to at least one basic taste stimulus after GABA(A) receptors within the ipsilateral CeA were blocked. After contralteral CeA injection, more NaCl-best neurons (6/8) increased responses than that after ipsilateral CeA injection, but other best-stimulus units showed no differences before and after drug injection into the contralateral CeA. Analyses of across-unit patterns indicated that the correlation coefficient of responses between NaCl and sucrose was apparently higher after drug administration to the CeA. However, after drug injection into the contralateral CeA, the correlations between NaCl and the other three tastants were higher than those before. These results indicate that the GABA(A) receptors within the CeA play an important role in modulating the gustatory activities of PBN neurons.