Effects of MSH/ACTH 4-10 on the classically-conditioned rabbit nictitating membrane

Subjects were conditioned/extinguished under four experimental conditions using either MSH/ACTH 4-10(A) or diluent (D): D/D, D/A, A/D, and A/A. The major question investigated was whether or not the peptide has an effect on this classically-conditioned behavior similar to that reported for instrumental conditioning paradigms. The results indicated that it does not. An effect was seen on performance, not on learning or attentional processes. Animals treated with the peptide performed more poorly (i.e., displayed fewer conditioned responses) during both acquisition and extinction. In addition, there was an apparent residual effect of the peptide that lasted 24 but not 48 hours.