PREOPTIC NEURONAL CIRCUIT - ATRIAL NATRIURETIC PEPTIDE-CONTAINING NEURONS ARE SENSITIVE TO ACUTE AND CHRONIC ALTERATIONS IN BODY-FLUID VOLUME

Atrial antriuretic peptide (ANP) concentrations were determined in ros tral preoptic midline structures (organum vasculosum laminae terminali s, periventricular and medial preoptic nuclei) and in the subfornical organ by radioimmunoassay in rats with acute volume load and volume de pletion, as well as during water deprivation. ANP-containing neuronal elements in all four areas (to a lesser extent in the medial preoptic nucleus) reacted very sensitively to acute and chronic changes in body fluid volume: volume load resulted in an elevation, volume depletion in a depletion in ANP concentrations. These alterations were significa nt and completely matched changes in plasma ANP concentrations. Water deprivation increased ANP levels on the first experimental day, follow ed by a marked depletion in the organum vasculosum laminae terminalis, subfornical organ and the periventricular preoptic nucleus. It is hyp othesized that three major neuropeptides (angiotensin Il, vasopressin, ANP) regulate body fluid volume through a close neuronal network alon g a subfornical organ-preoptic-hypothalamic axis. The subfornical orga n, which is very rich in angiotensin II and ANP receptors, serves as a n open gate for circulating hormones and is neuronally interconnected with volume-sensitive ANP neurons in the preoptic area (organum vascul osum laminae terminalis and preoptic periventricular nucleus). Neurons in the subfornical organ and the preoptic area project to the supraop tic and paraventricular nuclei and control the activity of vasopressin -synthesizing neurosecretory cells.