Influence of ACTH/MSH peptides and corticosterone of habituation of prey catching behavior in the toad, Bufo cognatus
Carpenter, Anne Marie
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The effect of adrenocorticotropin and melanotropin peptides, corticosterone, and the a-MSH antagonist, U-76188E, was studied on the acquisition and extinction of the prey-catching behavior in the toad, Bufo cognatus. Male toads were injected with corticosterone, porcine ACTH[l-39], a-MSH, (Nle4-D-Phe7)a-MSH, desacetyl- a-MSH, ACTH[4-10], a-MSH antagonist (U-76188E), or control vehicle 30 min prior to acquisition. ACTH[l-39], ACTH[4-10] and a-MSH significantly decreased the number of turning reactions during acquisition in relation to controls. The effect of these peptides was rapid, occurring within the first 20 min of acquisition. Corticosterone caused a significant decrease in the number of turning reactions, although this effect was not observed until 40 min after the onset of testing. (Nle^4-DPhe^ 7) a-MSH and des-acetyl-a-MSH did not influence acquisition. The a-MSH antagonist (U-76188E) abolished the behavioral response to a-MSH during acquisition, but did not significantly influence extinction. ACTH[ 1-391 was the only peptide to delay extinction. These data suggest that the ability of ACTH to facilitate acquisition is independent of interrenal corticosterone secretion. Furthermore, it appears that minor structural differences can dramatically influence the ability of ACTH/MSH peptides to modulate learning and memory processes in toads.