Evidence for a nucleus accumbens CCK 2 receptor regulation of rat ventral pallidal GABA levels : A dual probe microdialysis study

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We employed dual probe microdialysis in the nucleus accumbens and ipsilateral ventral pallidum of the halothane anaesthetized rat to investigate the effect of intra-accumbens perfusion with the sulphated octapeptide cholecystokinin (CCK-8S, 10–1000 nM, 60 min) alone and in the presence of the selective CCK 1 and CCK 2 receptor antagonists L-364,718 (10 and 100 nM) and PD134308 (10 nM), tetrodotoxin (TTX, 1000 nM) and the GABA A receptor antagonist bicuculline (1000 nM), on dialysate GABA levels in the ventral pallidum. Intra-accumbens perfusion with the 100 and 1000 nM concentration of CCK-8S was associated with a significant decrease (−16 ± 3% and −23 ± 3% vs basal, respectively) in ventral pallidum GABA levels. The CCK-8S (1000 nM) induced decrease in ventral pallidal dialysate GABA levels was abolished when PD134308, TTX and bicuculline, but not L-364,718, were included into the perfusion medium of the accumbens probe. The data indicate that nucleus accumbens CCK-8S exerts a CCK 2 receptor mediated inhibition of ventral pallidal GABA levels. Furthermore, the TTX and bicuculline sensitivity of this effect suggests that this is possibly mediated via CCK 2 receptors probably located on local GABA interneurons.