Glutamate release in the nucleus accumbens during competitive presentation of aversive and appetitive stimuli.

In vivo intracerebral microdialysis/HPLC studies on Sprague-Dawley rats showed that simultaneous presentation of food and a tone previously combined with a pain stimulus was accompanied by transient elevation of the glutamate level in the extracellular space of the nucleus accumbens, the extent of this increase being proportional to the latent period of initiation of the act of eating. Conversely, sequential presentation of the conditioned aversive signal followed by food and isolated presentation of the conditioned aversive signal alone were not accompanied by changes in the level of extracellular glutamate. It is suggested that glutamate release in the nucleus accumbens in conditions of competition between presentation of food and a tone previously combined with pain stimulation is not related to the process of selecting between the aversive and appetitive strategies of behavior, but may be associated with inhibition of preparation to perform or performance of the food-related behavior.