N-methyl-D-aspartate receptors in the ventral tegmental area mediate the excitatory influence of Pavlovian stimuli on instrumental performance.

Abstract

Pavlovian stimuli predictive of food can markedly amplify instrumental responding for food. This effect is termed Pavlovian-instrumental transfer (PIT). The ventral tegmental area (VTA) plays a key role in mediating PIT, however, it is yet unknown whether N-methyl-D-aspartate (NMDA)-type glutamate receptors in the VTA are involved in PIT. Here, we examined the effects of an NMDA-receptor blockade in the VTA on PIT. Immediately prior to PIT testing, rats were subjected to intra-VTA infusions of vehicle or of the NMDA-receptor antagonist 2-amino-5-phosphonopentanoic acid (AP-5) (1, 5µg/side). In rats that received AP-5 at the lower dose, the PIT effect was intact, i.e. presentation of the Pavlovian stimulus enhanced instrumental responding. By contrast, in rats that received AP-5 at the higher dose, the PIT effect was blocked. The data suggest that NMDA receptors in the VTA mediate the activating effects of Pavlovian stimuli on instrumental responding.