Effects of ACTH and ACTH 4-10 on aversive memory retrieval in rats

Semax, an ACTH(4-10) analogue with nootropic properties, activates dopaminergic and serotoninergic brain systems in rodents

Corticotrophin (ACTH) and its analogues, particularly Semax (Met-Glu-His-Phe-Pro-Gly-Pro), demonstrate nootropic activity. Close functional and anatomical links have been established between melanocortinergic and monoaminergic brain systems. The aim of present work was to investigate the effects of Semax on neurochemical parameters of dopaminergic- and serotonergic systems in rodents. The tissue content of 5-hydroxyindoleacetic acid (5-HIAA) in the striatum was significantly increased (+25%) 2 h after Semax administration. The extracellular striatal level of 5-HIAA gradually increased up to 180% within 1-4 h after Semax (0.15 mg/kg, ip) administration. This peptide alone failed to alter the tissue and extracellular concentrations of dopamine and its metabolites. Semax injected 20 min prior D: -amphetamine dramatically enhanced the effects of the latter on the extracellular level of dopamine and on the locomotor activity of animals. Our results reveal the positive modulatory effect of Semax on the striatal serotonergic system and the ability of Semax to enhance both the striatal release of dopamine and locomotor behavior elicited by D-amphetamine.

Melanocortins and opiate addiction

Adrenocorticotropic hormone (ACTH) and alpha-melanocyte stimulating hormone (alpha-MSH) are centrally acting melanocortin peptides with numerous reported functions, including induction of excessive grooming and antipyresis, among others. Also reported is a role for melanocortins in aspects of opiate action. Although early work examined the effects of ACTH and MSH on opiate-induced behaviors, further progress has been limited. Recently, however, advances in the identification and characterization of melanocortin receptor (MC-R) subtypes have provided novel tools with which to study interactions between melanocortins and addiction. The present review discusses the effects of ACTH and MSH on opiate-induced behaviors and relates these findings to more recent reports on the regulation of melanocortin systems by exogenous opiates. Emerging from these data is the possibility that melanocortin receptor activation, specifically at the MC4-R subtype, may act to antagonize certain properties of exogenous opiates, including perhaps addiction.

Alpha-helical CRF blocks differential influence of corticotropin releasing factor (CRF) on appetitive and aversive memory retrieval in rats

This study examined whether corticotropin releasing factor (CRF), given prior to test, would produce an improved retrieval of aversive memory in the same way as pre-exposure to inescapable footshocks and the CRF antagonist, alpha-helical CRF 9-41 (a-h CRF), blocks this effect in rats. For this purpose animals conditioned in a T-maze with appetitive (10% sucrose) and aversive (2.0mA footshock) events were given intracerebroventricularly (i.c.v.) 20 min before testing, a single dose of 0.05, 0.1, 0.2 or 0.4 microgram/rat of CRF, or 5 micrograms/rat of a-h CRF, or both at 10 min interval. In the retention test conducted with the same training apparatus 72-hr after conditioning, CRF (0.05, 0.1 and 0.2 microgram) treated rats showed a dose-dependent increase in latencies to enter the previously shocked goalarm, with the absence of such a difference in responding to the nonshocked goalarm. The highest dose of CRF (0.4 microgram), however, increased the latencies to enter both the goalboxes. Alpha-helical CRF, administered 10 min before, antagonized the memory-enhancing effect of CRF. Further, CRF (0.1, 0.2 and 0.4 microgram) significantly decreased the total number of center entries in the open field, consistent with the view that i.c.v. administered CRF produces "anxiogenic-like" effect. Alpha-helical CRF reversed this effect. The effect of CRF on memory retrieval was similar to that seen following inescapable footshock in rats. The results thus suggest the possible involvement of central CRF mechanisms in the differential enhancement of memory of helplessness condition.