GABAergic transmission in the rat ventral pallidum mediates a saccharin palatability shift in conditioned taste aversion.

We previously found that the blockade of gamma-aminobutyric acid (GABA)(A) receptors in the ventral pallidum (VP) alters the taste palatability of a conditioned stimulus (CS) from aversive to ingestive after the establishment of conditioned taste aversion (CTA). Because these results suggest that GABAergic transmission in the VP mediates decreased palatability of the taste in CTA, the present study aimed to examine the effects of taste stimulation on the extracellular release of GABA in the VP using in vivo microdialysis. Initially, rats received a paired presentation of 5 mm saccharin or 0.3 mm quinine solution with an intraperitoneal injection of 0.15 m lithium chloride (S-CTA and Q-CTA groups) or saline (S-control and Q-control groups). After conditioning, microdialysis was carried out before, during and after the presentation of the CS via an intra-oral cannula. We measured the latency of the first aversive orofacial responses to the CS as behavioral indices. In the S-CTA group, which rapidly rejected the CS (within 100 s), the GABA efflux was significantly increased (147%) and was maintained for 2 h. On the other hand, the S-control group expressed no aversive responses and showed no significant alterations in GABA efflux. Although the Q-CTA group immediately expressed aversive responses to the CS (within 30 s), GABA release was not changed by presentation of the CS, which was similar in the Q-control group. These findings suggest that the palatability shift from ingestive to aversive in conditioned aversion to saccharin, but not quinine, is mediated by the change in GABAergic transmission in the VP.