Behavior of rats during chronic activation and blockade of the neostriatal opiate system

The effects of daily microinjections (MI), over of three weeks, bilaterally into the rostral striatum, of morphine, promedol, native leu-enkephalin and its synthetic tetrapeptide analogs were studied in experiments on rats. Naloxone was used as an antagonist. An active avoidance conditioned reflex was developed preliminary in a shuttle box. A decrease in the accuracy of the realization and an increase in the latent period of the reflex were observed after the first MI of morphine and enkephalins. The effect of the most stable aminated ornithine-containing tetrapeptides proved to be the strongest. A search stereotypy and increased motoric activity were recorded in the rats during the development of the chronic effects of the activators of the opiate system. A clear correlation was not found between the motor and conditioned reflex shifts. The blockade of the opiate receptors with naloxone did not lead to substantial changes in behavior. The data obtained confirm the current hypothesis regarding the important role of the enkephalinergic system of the neostriatum in the regulation of complex forms of behavior and its close functional association with the dopaminergic system.