CNS effects of peripherally administered brain peptides.

Acceptance of enkephalins and endorphins into the family of brain peptides involves recognition that these endogenous opiates should share the general properties, including multiple and independent effects, previously described for neuropeptides. Several peptides first isolated by their pituitary-mediated endocrine effects, for example, are known to initiate CNS actions even in hypophysectomized animals. It was reasonable to expect, therefore, that the new opiate peptides would have effects not limited to the centrally induced analgesia by which they were originally identified, but, like the other brain peptides, would have additional CNS actions. Our concept that the multiple actions of peptides can be independent of each other is supported by evidence that even though peripheral administration of the brain opiates is essentially ineffective in producing analgesia, other actions of these peptides, such as changes in behavior, can be observed after administration by this route. Considerable evidence is accumulating in support of this concept of dissociation. The mechanisms by which the central effects of the peptides are exerted after systemic injection remain to be clarified, but analysis of their actions represents a new approach to understanding the performance of the brain. Studies already suggest a possible role of the brain peptides in the diagnosis and treatment of some mental and neurological disorders as well as in optimizing normal CNS functions.