Increased hypothalamic norepinephrine metabolism after water deprivation in the rat

Rat brain catecholamine metabolism was changed over a period of several days by limited access to water (10 min/day). One or two weeks limited access to water caused an increase in hypothalamic norepinephrine metabolism as measured with alpha-methyl-para-tyrosine. Brain stem and telencephalon norepinephrine was not affected by the limited access to water regimen. Dopamine metabolism in the corpus striatum and the hypothalamus was not altered by limited access to water. If the limited access to water was continued for 3 or more weeks, hypothalamic norepinephrine metabolism then returned to normal. The increase in hypothalamic norepinephrine metabolism was confirmed by a second method measuring in vivo tyrosine hydroxylase activity. Additional experiments demonstrate that this affect is specific for water deficits. Limited access to food had no effect on the metabolism of norepinephrine in the hypothalamus. Water deficits produced by replacing water with a 2% NaCl solution caused a similar increase in hypothalamic norepinephrine metabolism to that observed after one week limited access to water. Furthermore, 10 min access to water stopped the increased hypothalamic metabolism of norepinephrine seen after one week of limited access to water. The regional specificity (effect seen in hypothalamus but not the telencephalon and brain stem), and the stimulus specificity (water and not food deficits) suggest hypothalamic norepinephrine involvement in thirst or hormonal control of water regulation.