The dose-dependent effect of the D2R agonist quinpirole microinjected into the ventral pallidum on information flow in the limbic system

Abstract

Abstract The ventral pallidum (VP) receives its primary inputs from the nucleus accumbens (NAC) and the basolateral amygdala (BLA). We demonstrated recently that in the VP, the D2 DA receptor (D2R) agonist quinpirole dose-dependently facilitates memory consolidation in inhibitory avoidance and spatial learning. In the VP, D2R can be found both on NAC and BLA terminals. According to our hypothesis, quinpirole microinjected into the VP can facilitate memory consolidation via modulation of synaptic plasticity on NAC and/or BLA terminals. The effect of intra-VP quinpirole on BLA-VP and NAC shell-VP synapses was investigated via a high frequency stimulation (HFS) protocol. Quinpirole was administered in three doses into the VP of male rats after HFS; controls received vehicle. To examine whether an interaction between the NAC shell and the BLA at the level of the VP was involved, tetrodotoxin (TTX) was microinjected into one of the nuclei while stimulating the other nucleus. Our results showed that quinpirole dose-dependently modulates BLA-VP and NAC shell-VP synapses, similar to those observed in inhibitory avoidance and spatial learning, respectively. The lower dose inhibits BLA inputs, while the larger doses facilitates NAC shell inputs. Independent from the synaptic facilitation, intra-VP quinpirole increases the amplitude of gamma frequency band (GFB) of the power spectral density after NAC HFS. The experiments with TTX demonstrates that the two nuclei do not influence each others’ evoked responses in the VP, but intra-BLA TTX increases the GFB. These findings demonstrate the important role of VP D2Rs in the regulation of limbic information flow.