抄録
Heat loss responses are suppressed during dehydration, and hyperosmolality in the extracellular fluid is thought to be involved in this mechanism. In an in-vitro brain slice, warm-sensitive neurons in the medial preoptic area (MPA) are deactivated in a hyperosmotic medium. In contrast, neural activities in the median preoptic nucleus (MnPO) increase during both heat and osmotic stimuli. In the present study, we hypothesized that tail vasodilatation induced by local warming of the MPA in urethane-anesthetized rats would be suppressed by a selective infusion of hypertonic saline to the brain. In addition, rats with the MnPO lesion would lack this suppression. The MPA warming at ∼40 °C increased skin temperature at the tail. Hypertonic saline (1500 mM) infusion into the left internal carotid artery suppressed this response when the MPA was warmed in its dorsolateral area. In MnPO-lesioned rats, there was no effect of hypertonic-saline infusion on the tail skin temperature during the MPA warming. These results indicate that the tail vasodilatation elicited by MPA warming is suppressed during osmotic stimulus. Moreover, the dorsolateral area in the MPA is a crucial site for such a response. The MnPO is also involved in this mechanism. [J Physiol Sci. 2006;56 Suppl:S231]
