Two Ascending Thermosensory Pathways from the Lateral Parabrachial Nucleus That Mediate Behavioral and Autonomous Thermoregulation.

Thermoregulatory behavior in homeothermic animals is an innate behavior to defend body core temperature from environmental thermal challenges in coordination with autonomous thermoregulatory responses. In contrast to the progress in understanding the central mechanisms of autonomous thermoregulation, those of behavioral thermoregulation remain poorly understood. We have previously shown that the lateral parabrachial nucleus (LPB) mediates cutaneous thermosensory afferent signaling for thermoregulation. To understand the thermosensory neural network for behavioral thermoregulation, in the present study, we investigated the roles of ascending thermosensory pathways from the LPB in avoidance behavior from innocuous heat and cold in male rats. Neuronal tracing revealed two segregated groups of LPB neurons projecting to the median preoptic nucleus (MnPO), a thermoregulatory center (LPBfiMnPO neurons), and those projecting to the central amygdaloid nucleus (CeA), a limbic emotion center (LPBfiCeA neurons). While LPBfiMnPO neurons include separate subgroups activated by heat or cold exposure of rats, LPBfiCeA neurons were only activated by cold exposure. By selectively inhibiting LPBfiMnPO or LPBfiCeA neurons using tetanus toxin light chain or chemogenetic or optogenetic techniques, we found that LPBfiMnPO transmission mediates heat avoidance, whereas LPBfiCeA transmission contributes to cold avoidance. In vivo electrophysiological experiments showed that skin cooling-evoked thermogenesis in brown adipose tissue requires not only LPBfiMnPO neurons but also LPBfiCeA neurons, providing a novel insight into the central mechanism of autonomous thermoregulation. Our findings reveal an important framework of central thermosensory afferent pathways to coordinate behavioral and autonomous thermoregulation and to generate the emotions of thermal comfort and discomfort that drive thermoregulatory behavior. [ABSTRACT FROM AUTHOR]