Presence of alpha-1 adrenoreceptors on thermosensitive neurons in the medial preoptico-anterior hypothalamic area in rats.

Earlier microinjection studies showed that norepinephrine in the medial preoptico-anterior hypothalamic area (mPOAH) regulates body temperature and the action is mediated through alpha-1 adrenoceptors. This study was conducted to confirm if the thermosensitive neurons in the mPOAH of rats possess alpha-1 adrenoceptors. First, the thermosensitivity of mPOAH neurons was tested and then the effects of microiontophoretic application of prazosin, alpha 1 adrenoceptor antagonist, on the firing rate of both the thermosensitive as well as the insensitive neurons were recorded. Prazosin significantly inhibited the firing rate of the thermosensitive neurons suggesting that most of the cold and warm sensitive neurons in the mPOAH possess alpha-1 adrenoceptors. These results at the single neuronal level confirm our earlier hypothesis that in the mPOAH, norepinephrine regulates body temperature by acting on alpha-1 adrenoceptors. The data also suggest that sensitivity of the mPOAH neurons to norepinephrine alter with changes in body temperature. The detailed physiological significance of the results with special reference to thermoregulation at the single neuronal level has been discussed.