Blockade of muscarinic acetylcholine receptors in the ventral tegmental area blocks the acquisition of reward-related learning
In the present study we investigated whether stimulation of muscarinic acetylcholine (mACh) receptors in the ventral tegmental area (VTA) plays a role in the acquisition of food-based conditioned approach learning. Rats were exposed to 3 (in Experiment 1) or 7 (in Experiment 2) conditioning sessions in which 30, randomly presented light (CS) presentations were paired with delivery of food pellets (US), followed by one session with no light or food and finally one CS-only test session with only light stimulus presentations. Bilateral microinjections of scopolamine (a mACh receptor antagonist) were made either prior to each conditioning session (Experiment 1; to test effects on acquisition) or prior to the CS-only test (Experiment 2; to test effects on performance of the learned response). Scopolamine produced a dose-related significant reduction in the acquisition of conditioned approach but had no effect on its performance. These results suggest that mACh receptor stimulation in the VTA plays a necessary role in the acquisition of reward-related learning.