Avoidance learning at two levels of shock in rats receiving MSH1,2

Rats receiving MSH or diluent were trained in a two-way shuttle box to avoid shock presented at two levels of intensity. At the low level MSH improved acquisition; at the high level rats given MSH tended to perform more poorly, but were not statistically different from controls. No differences were found in measures of activity or excitability, but higher defecation rates, which may indicate more emotionality, were found in groups receiving high levels of current and in groups receiving MSH. The study suggests that MSH may facilitate learning at low, but not at high, levels of shock.