Mechanisms of thermoreception on isolated hypothalamic neurons.

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The ionic current responses to temperature of dissociated cells from the preoptic and anterior hypothalamus (PO/AH) of rat were investigated, using the 'whole-cell' configuration. The majority of the recorded neurons showed a linear increase in a non-inactivating inward current during warming (32 to 40ﾟC), and the Q_<10> was about 2. This current is mainly caused by Na^+-influx because the inward current was reduced by half when external solution was substituted choline for half of Na^+. On the other hand, about 24% of PO/AH neurons were markedly sensitive to warming and the increase in non-inactivating inward current to a rise in temperature in hyperthermic range (35-40ﾟC) had a high Q_<10> (4.3-7.0). This increase in current in the hyperthermic range was reversibly blocked by tetrodotoxin (TTX). The inward current in neurons with a Q_<10> of 2 was not affected by TTX. The results show that some neurons in the PO/AH possess a non-inactivating sodium channel that is highly temperature-sensitive in the hyperthermic range. These neurons should be the 'primary' warm-sensitive neurons which are thermometer in the brain.