Elucidation of the important roles played by peptides as hypothalamic-adenohypo physeal releasing factors, or regulatory hormones, has in recent years led to the recognition that peptides may also be of significance as intercellular messengers in other regions of the nervous system. In this regard, it is interesting that Sub stance P, which has been proposed as a putative neurotransmitter in the spinal cord, was rediscovered by Leeman and her co-workers during their search for the corticotropin-releasing factor in the hypothalamus. Indeed, with the wide spread availability and use of...