Neurohypophysial Peptides in Cerebrospinal Fluid

Abstract

The neurohypophysial peptides in cerebrospinal fluid (CSF) are believed to function as neurotransmitters or neuromodulators within the central nervous system (CNS). This chapter describes the neurohypophysial peptides and their actions on the CNS,often following administration of exogenous peptides or their antisera into CSF. Oxytocin (OXT), vasopressin (AVP), and neurophysin (NP) are found in many areas of the brain and spinal cord. Because, there is a blood–CSF barrier to these peptides, CSF levels probably reflect release from central terminals rather than the hypothalamo–neurohypophysial system. The physiological stimuli, which release these peptides into CSF, are poorly understood. Endocrine stimuli (suckling, dehydration) causing release into plasma do not change CSF levels of OXT, AVP, or NP, but central release of AVP occurs during hemorrhage. Electrical stimulation of the hypothalamus releases all three peptides into CSF and perfusates of different parts of the ventricular system. There is a marked diurnal rhythm of AVP in CSF and a large molar excess of NP over the nonapeptides. Although OXT and AVP are cleared somewhat faster than NP, this cannot explain the NP excess, which is mostly due to the OXT-related protein. Much of the AVP cleared from CSF reaches the bloodstream in a biologically active form, and it now seems likely that central OXT and AVP neurons are both morphologically and functionally separate from the neurohypophysial system. CSF measurements, thus, provide a useful, though indirect, means of studying these peptides within the central nervous system.