Abstract
The preoptic area (POA) is known as the center for body temperature regulation. Based on previous experimental results, we hypothesize that GABAergic projection neurons in the POA provide descending tonic inhibition to sympathoexcitatory neurons in the dorsomedial hypothalamus and in the medullary raphe and thereby, regulate the tone of sympathetic outflows to thermoregulatory effectors, such as brown adipose tissue (BAT) and cutaneous vasoconstrictors. If this is the case, stimulation of POA neurons should inhibit thermoregulatory sympathetic outflows. In this study, we examined the effect of optogenetic stimulation of POA neurons on metabolic thermogenesis in BAT in anesthetized rats. Expression of the light‐activated cation channel channelrhodopsin‐2 (ChR2) was introduced into many neurons in the POA by injection of adeno‐associated virus and an optical fiber was inserted into the brain to illuminate the POA. Skin cooling‐evoked sympathetic nerve activity in BAT and increase in heart rate were consistently inhibited only during illumination of the POA. This result supports the hypothesis that tonic descending inhibition from the POA determines the tone of sympathoexcitatory outflows to thermoregulatory effectors.
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