In vitro osmosensitive hypothalamic neurons from hypertensive and normotensive rats.

Single-unit activity was recorded in hypothalamic tissue slices from spontaneously hypertensive (SH) and normotensive Wistar-Kyoto (WKY) rats to identify differences in neuronal osmosensitivity between these two strains. Neurons were characterized according to location, firing rate, temperature sensitivity, and response to hyposmotic (280 mosmol/kgH2O) and hyperosmotic (320 mosmol/kgH2O) media. More than half of the thermosensitive neurons were also osmosensitive. Three groups of osmosensitive neurons were identified: 1) low-firing neurons excited by hyposmolality and inhibited by hyperosmolality, 2) high-firing neurons excited by hyposmolality, and 3) high-firing neurons excited by hyperosmolality. There were no differences between strains in terms of the proportions of osmosensitive neurons. Compared with WKY neurons, however, SH osmosensitive neurons displayed reduced sensitivity to hyperosmotic media. Also, SH osmotically insensitive neurons displayed lower spontaneous firing rates. These differences in osmosensitivity and spontaneous activity may provide a neuronal basis to explain some of the differences in water and sodium regulation observed in hypertensive rats.