The role of neuropeptides in learning and memory: possible mechanisms.

Endogenous neuropeptides such as vasopressin, adrenocorticotropin and opioids have significant effects on learning and memory. However, because of the complexity of behaviour, that is defined as 'learning' and 'memory' and, because of the limitation of current knowledge, it has been difficult to interpret these behavioural data, especially via neural mechanisms. The application of modern experimental techniques including molecular biology such as cloning and electrophysiology, such as patch-clamp, has had a significant impact upon the concepts about drugs, including neuropeptides action sites. This allows us to try to interpret some behavioural consequences influenced by neuropeptides. The data on effects of some neuropeptides on behaviours and their possible mechanisms are reviewed. Whatever the mechanisms, vasopressin, adrenocorticotropic hormone and endogenous opioids seem to have important effects upon learning and memory and these open up the possibility that drugs enhance cognitive functions or treat dementia via alteration of functions of neuropeptides. Some criteria are proposed for evaluating the validity of behavioural tests for neuropeptides.