Failure of α-MSH to delay extinction of conditioned avoidance behavior in rats with lesions in the parafascicular nuclei of the thalamus

Abstract

Bilateral lesions in the thalamic parafascicular area facilitate the rate of extinction of a conditioned avoidance response without affecting avoidance learning. Treatment with long-acting α-MSH during extinction failed to affect the rate of extinction of the avoidance response. Since this peptide delays extinction of the avoidance response in posterior lobectomized rats in which a similar rapid rate of extinction is found as in rats with lesions in the parafascicular nuclei (De Wied, 1965), the results stress the importance of the central nervous system for the effect of α-MSH on conditioned avoidance behavior.