Abstract
This chapter focuses on the two-fold approach related to the actions of melanocyte-stimulating hormone (MSH) on the central nervous system (CNS): first, to determine whether MSH has any effect on the CNS of man; second, to attempt to identify the behavioral systems which are involved by also studying animals. A remarkable part of this second aspect involves special attention to the role of MSH during development of the organism. If it is possible that rats injected with MSH might be more active, then this might account at least in part for delayed extinction of the conditioned and voidance response, but it probably could not account for the inhibition of a passive avoidance response that is observed in a two-chambered shuttle box. MSH or its active component was administered to rats and human beings in a series of studies. The behavioral and electrographic changes that were observed reinforce the concept that MSH has extra-pigmentary actions in mammals.