Adrenocorticotropic hormone fragment ACTH/MSH(4-10 can act as a discriminative stimulus in rats

Five of eight male albino rats learned to discriminate the effects of ACTH/MSH(4-10) (100 micrograms/kg, SC) from those of saline vehicle in a food-reinforced T-maze task. Generalization tests showed that the ACTH/MSH(4-10) cue was dose related with an ED50 of approximately 68.0 micrograms/kg. These findings indicate that ACTH/MSH(4-10) has interoceptive stimulus properties discriminable to some animals, which might provide a useful model for studying the pharmacology of this neuroactive peptide. Moreover, since ACTH/MSH(4-10) induces effects similar to those of ACTH/MSH in the central nervous system but not hormonally, these data suggest that endogenous ACTH or MSH may also have interoceptive stimulus effects unrelated to peripheral endocrine activity.