ALPHA-MSH AND MCH ARE FUNCTIONAL ANTAGONISTS IN A CNS AUDITORY GATING PARADIGM

The peptides alpha-melanocyte stimulating hormone (alpha-MSH) and melanin concentrating hormone (MCH; rat and salmon sequence) were administered to anesthetized rats by intracerebroventiicular infusion. Depth recordings were carried out in the dorsal hippocampus, and auditory gating was assessed. Auditory gating in this paradigm refers to the decrease in amplitude of the second of two tone-evoked CNS potentials that can be measured when pairs of identical tones are presented 500 ms apart. Alpha-MSH increases auditory gating, whereas MCH has the opposite effect. When MCH was administered prior to alpha-MSH, the ability of alpha-MSH to increase auditory gating was blocked. Thus, the two peptides appear to be functional antagonists.