Neural regulation of the circadian vasopressin rhythm in cerebrospinal fluid: a pre-eminent role for the suprachiasmatic nuclei.

The neuroanatomical system responsible for the generation and expression of the circadian vasopressin rhythm in cerebrospinal fluid (CSF) is investigated. CSF was serially withdrawn in individual, unanesthetized, unrestrained rats after neuroendocrine extirpations or stereotaxic brain lesions were made; the peptide was assayed using a sensitive and specific radioimmunoassay. Hypophysectomy or pinealectomy did not eliminate vasopressin from CSF; both day and night-time peptide levels in hypophysectomized rats were elevated above control levels. Complete lesions of the suprachiasmatic nuclei (SCN) abolished both the rhythm and in most cases the measurable level of peptide in CSF. Neither lesions of the paraventricular nuclei nor hypothalamic knife cuts interrupting most neural efferents from the SCN had this effect; in these cases, vasopressin rhythms persisted with diminished amplitude. Our results suggest that the circadian CSF vasopressin rhythm is produced by a neural system topographically separate from the classical magnocellular hypothalamo-neurohypophyseal system for the secretion of peptide into blood. The SCN are an important component of this new system and are necessary for the generation of the CSF rhythm.