Increased glutamate release into the intercellular space of the nucleus accumbens (N. accumbens) during substitution of food reinforcement with aversive or neutral stimuli.

Experiments on Sprague-Dawley rats using vital intracerebral dialysis and HPLC with electrochemical detection demonstrated that presentation of the animals with inedible imitation food or food containing a bitter flavor instead of the expected food reinforcement led to rapid increases in glutamate levels in the intercellular space of the nucleus accumbens. There was no change in the glutamate level during presentation of the same stimuli to rats not expecting to receive food reinforcement. These data suggest that non-correspondence between the expected and actual values of reinforcement may be an important factor determining the extracellular glutamate level in the nucleus accumbens during food-related behavior.