Long-term effects of lesions of the tissue surrounding the preoptic recess on paraventricular nuclei in rats.

In this investigation we have observed the effects of withholding water for 5 days, the effects of long-term (5 weeks) lesions of the tissue surrounding the preoptic recess in the anteroventral third ventricle (AV3V region), and the interaction of the effects of long-term AV3V lesions and water deprivation on paraventricular nuclei. The purpose of these observations was to see if recovery of the antidiuretic response after AV3V lesions is associated with recovery of fine structural responses in these neurosecretory cells. Paraventricular neurosecretory cells of rats deprived of water for 5 days were hypertrophied in controls and in rats with AV3V lesions. Areas of cell bodies and their nuclei were increased, as were the number of Golgi stacks and electron dense (immature) neurosecretory granules. A greater percentage of nucleoli were adjacent to the nuclear envelope. Paraventricular neurons of rats with AV3V lesions also had fine structural changes characteristic of increased secretory activity, even in animals with free access to drinking water. The areas of cells and their nucleoli in coronal sections, and the number of Golgi stacks and electron-dense neurosecretory granules per cell were significantly increased in both treatment groups with AV3V lesions. There was a greater increase in the numbers of Golgi stacks and immature neurosecretory granules tended to be more numerous in water-deprived lesioned rats than in water-deprived controls. We suggest that recovery of body fluid balance in rats with chronic AV3V lesions involves enhanced secretory activity of neurosecretory cells in paraventricular nuclei, possibly stimulated via undamaged descending connections from the subfornical organ and by ascending pathways activated by cardiovascular volume receptors.