The neurotropic activity of a structural analog of ACTH(5-7).

The tripeptide glutamyl-arginyl-proline (ERP) mimicking some structural features of the N-terminal fragment of adrenocorticotropic hormone, ACTH(5-7), has been synthesized. In contrast with ACTH fragments, ERP (0.015-0.15 mg/kg; intraperitoneal injection) hindered the formation of food-reinforced task in adult albino male rats. Besides, ERP caused a rapid inhibition of the previously formed conditioned task. Similar doses of ERP changed orientative-trying reaction and emotional behavior in rats in the 'open field' test. ERP at a dose of 0.15 mg/kg administered prior to the injection of 0.5 mg/kg ACTH(1-39) prevented increases in locomotor activity normally induced by this hormone. Thus, ERP disrupts learning, impairs performance of acquired task and blocks behavioral effects of ACTH and its fragments.