Dopaminergic neurons, originating in the midbrain, and projecting to forebrain areas including the prefontral cortex, amygdala, and nucleus accumbens are critical for the manifestation of goal directed behavior for both natural rewards and drugs of abuse. While the exact role DAergic transmission plays in goal-directed behavior is still under investigation, one particularly attractive hypothesis is that DAergic neurons act as a learning signal to code relationships between reinforcers and environmental cues that predict them. Although both in vivo electrophysiological and electrochemical studies have demonstrated that DAergic signaling is plastic, and can be modified by manipulating the learned association between cues and reinforcers, little is known about the cellular changes that occur in DAergic neurons following stimulus-reward learning. The proposed experiments plan to examine whether the properties and plasticity of excitatory synapses on DAergic neurons are altered following reward-related learning and extinction. These studies will further the understanding of how dopaminergic signaling is involved in reinforcement and conditioning.