Neuropeptides and cerebrospinal fluid.

Neuropeptides are present in brain tissue as well as in cerebrospinal fluid. Studies from a variety of disciplines have demonstrated that neuropeptides have neuromodulatory activities. Such activities are apparent in the involvement of neuropeptides in the regulation of adaptive, autonomic, and endocrine functions of the brain. Neuropeptides exert their neuromodulating influences by acting as neurotransmitters or as neurohormones. The neurotransmitter function of neuropeptides is associated with their synthesis in situ in brain and anatomical distribution via neuropeptidergic fibre systems. The presence of such neuropeptides in cerebrospinal fluid may be due primarily to drainage into the cerebrospinal fluid compartments, their levels being a reflection of cellular processes such as biosynthesis, release, and metabolism. On the other hand, neuropeptides functioning as neurohormones may be actively delivered into the cerebrospinal fluid from central or peripheral sources. They employ the pathways of cerebrospinal fluid circulation as avenues of transport, and their cerebrospinal fluid levels may be functionally related to neurohormonal activity. In either case the cerebrospinal fluid levels are informative on the neuropeptide climate in brain; thus their determination is meaningful. The methodology for the sensitive and specific determination of neuropeptides is becoming available. Determination of neuropeptides may well be of diagnostic value in clinical practice.