Effects of metenkephalin on the formation and fixation of defensive temporal associations and on the incorporation of C14-leucine in brain proteins of the rat.

When 25 microgram of metenkephalin is injected subcutaneously into rats, the development of temporal associations is somewhat impaired, but the fixation of them is enhanced. The latter effect is observed more clearly when metenkephalin is injected not before, but immediately after the development of conditioned reflexes. Under the influence of metenkephalin, there is an increase in the incorporation of C14-leucine into the insoluble proteins of the hippocampus and basal ganglia. It is hypothesized that metenkephalin mainly affects the process of consolidation.