Central mechanisms of conditioned place preference in rats

Abstract

The purpose of the investigation was to clear the significance of dopamine, GABA, opioids and sodium influx ionic currents of the nucleus accumbens neurons for the reinforcing effects of a number of psychotropic drugs (opiates, opioids, psychostimulants) on conditioned place preference (CPP) in rats. The microcannules were implanted into the nucleus accumbens (the extended amygdala system) of the Wistar male rats to inject the drugs studied (1 μg in 1 μl in volume for each injection). The rats were learned CPP of a one of narcogenics during 8 days. Some drugs, lidocain, a blocker of sodium influx ionic currents, antagonists of GABAA receptors bicuculline, D1 dopamine receptors SCH23390, D2 dopamine receptors sulpiride and opioid receptors naloxone, administered intrastructurally into the nucleus accumbens, were used for pharmacological analysis. The majority of the blockers studied decreased or abolished the reinforcing effects of amphetamine. Activation of reinforcement by means of fentanyl was reversed with bicuculline, lidocain and naloxone but did not change with dopamine antagonists (SCH23390 and sulpiride). None of the blockers studied effect on CPP of sodium ethaminal excluding bicuculline which reduced it. At last, the leu-enkephaline effects were reversed with naloxone and SCH23390, but strengthened with bicuculline. Sulpiride and lidocain did not effect on CPP of leu-enkephaline. Therefore, the different mechanisms (GABA-, dopamine- and opioidergic) controlling the positive conditioned reinforcement are collected in the nucleus accumbens.