[The behavior of rats under chronic activation and blockade of the neostriatal opiate system]

Effects of three-week daily intrastriatal microinjections of morphine, naloxone, Leu-enkephalin and its tetrapeptide analogues in doses of 5 and 15 mcg were investigated in rats. Inhibition of the avoidance conditioning in a shuttle-box was observed in the first days of tetrapeptides microinjection; dopamine-like stimulatory effects, i.e. the stereotyped behaviour were seen during the development of chronic enkephalin effects. The most effective were the influences of ornitin-containing enkephalin analogues. There were no changes in avoidance conditioning during all three weeks of naloxone treatment. The findings suggest an involvement of the enkephalin neostriatal system in complex behavioural acts and its functional relationship with the dopaminergic system.