The organum vasculosum of the lamina terminalis regulates noradrenaline release in the anterior hypothalamic nucleus

Changes in either plasma sodium concentration or arterial pressure can diff erentially affect hypothalamic neurons. For instance, increases in plasma N aCl concentration decrease noradrenaline release from nerve terminals in th e anterior hypothalamic nucleus, while increases in arterial pressure unrel ated to an elevation in plasma NaCl enhance noradrenaline release in anteri or hypothalamic nucleus. The present study tests the hypothesis that in the rat the organum vasculosum of the lamina terminalis (an osmosensitive area of the brain) detects rises in plasma NaCl concentration and conveys this information to anterior hypothalamic nucleus. The axons projecting from the organum vasculosum of the lamina terminalis to the hypothalamus were unila terally cut immediately caudal to organum vasculosum of the lamina terminal is, and five days later, 3-methoxy-4-hydroxy phenylglycol (the major metabo lite of noradrenaline in brain) was continuously monitored in the ipsilater al or contralateral anterior hypothalamic nucleus in response to an intrave nous infusion of hypertonic saline. In spontaneously hypertensive rats, the infusion decreased the 3-methoxy-4-hydroxy phenylglycol concentration by 2 4 +/- 2% in the anterior hypothalamic nucleus contralateral to the lesion, and in control spontaneously hypertensive rats. In contrast, in the anterio r hypothalamic nucleus ipsilateral to the lesion, hypertonic saline infusio n caused a 58 +/-:3% increase in 3-methoxy-4-hydroxy phenylglycol. These data support the hypothesis that the organum vasculosum of the lamina terminalis is part of the circuit that transmits information concerning pl asma NaCl concentration to anterior hypothalamic nucleus. (C) 2000 IBRO. Pu blished by Elsevier Science Ltd. All rights reserved.