A food-associated CS activates c-Fos in VTA DA neurons and elicits conditioned approach.

Neutral stimuli associated with unconditioned stimuli (USs) acquire the ability to act as conditioned stimuli (CSs), which can elicit behaviors similar to the US with which they are associated. The neural mechanisms by which this occurs are not fully known. We have previously proposed a model stipulating CSs function as such because they acquire the capacity to activate dopamine (DA) neurons at the level of the ventral tegmental area (VTA).

Environmental enrichment, administered after establishment of cocaine self-administration, reduces lever pressing in extinction and during a cocaine context renewal test.

The objective of this study was to test the hypothesis that environmental enrichment (EE) administered to rats previously trained to self-administer cocaine would reduce responding in extinction and in a cocaine-context renewal test. Long-Evans male rats were trained to press an active lever reinforced by cocaine (1.0 mg/kg/injection) under a fixed-ratio 1 schedule of reinforcement (inactive lever presses produced no consequences).

The effects of VTA NMDA receptor antagonism on reward-related learning and associated c-fos expression in forebrain.

The mechanisms whereby reward-associated stimuli come to function as conditioned stimuli and acquire the capacity to activate the same neural regions activated by primary rewards (i.e., dopamine terminal regions) is not fully understood.

NMDA receptor antagonism in the ventral tegmental area impairs acquisition of reward-related learning.

Mechanisms underlying reward-related learning presumably involve neural plasticity integrating signals representing unconditioned and conditioned stimuli in regions mediating reward. The ventral tegmental area (VTA) receives such signals and shows synaptic plasticity which is NMDA receptor-dependent. To test the hypothesis that NMDA receptor stimulation in the VTA is necessary for the acquisition of food-reinforced appetitive learning, Long-Evans male rats were prepared with bilateral VTA cannulae and tested in operant chambers with the opportunity to lever press for food for 10 sessions.

Repeated heroin in rats produces locomotor sensitization and enhances appetitive Pavlovian and instrumental learning involving food reward.

We tested the hypothesis that sensitization to heroin enhances appetitive motivational processes involving food reward. In Experiment 1, sixteen rats were exposed to positive pairings of a light stimulus and food for 4 consecutive daily sessions. Then, the rats received either saline or heroin (2 mg/kg) injections before placement in activity monitors for 9 consecutive daily sessions.