Self-administration of morphine by rats causes monoamine release in the anterior cingulate cortex.

Monoamine content in the microdialysate from the anterior cingulate cortex was measured in rats after injections and self-administration of morphine. Forced intraperitoneal injection of morphine did not lead to appreciable changes in the monoamine levels in the dialysate. Self-administration significantly increased monoamine levels in the extracellular space of the anterior cingulate cortex. Changes in catecholamine levels in the extracellular space of the anterior cingulate cortex correlated with the intensity of self-administration. The more morphine the animals injected to themselves, the greater was the increment in dopamine and norepinephrine levels. It seems that the increase of serotonin content in the anterior cingulate cortex did not depend on blood morphine concentration, but just reflected the fact of narcotic self-administration. The release of serotonin from nerve endings in the anterior cingulate cortex gradually increased at the beginning of the session, after which serotonin concentration started to decrease. The results indicate that monoamines are released from nerve endings in the anterior cingulate cortex only in response to self-administration of morphine. Catecholamines were released after each self-administration of the narcotic, while serotonin release seemed to be associated with the general status of the animal realizing this behavior.