Figure 2.

Possible circuit arrangements for the detection and integration of warm thermal information into sleep-promoting circuitry.

Warmth is detected by TRPM2 channels on neuronal afferents in the skin and this information is transmitted to the lateral parabrachial nucleus (LPb) and on to nitrergic-glutamate neurons in the MPO/MnPO hypothalamus. Both nitrergic and glutamatergic populations have a degree of heterogeneity and express a mixture of transient receptor potential melastatin 2 (TRPM2) channels and leptin receptors. These nitrergic-glutamate neurons in MPO/MnPO can initiate warm defence, probably through innervation of dorsal medial hypothalamus (DMH) neurons, but they also promote sleep. This circuit could involve short range innervation of local GABAergic populations or longer projections to LPO GABA/galanin neurons or directly to arousal or sleep promoting regions. Adapted from [6,15^••,47,48,50,57^••,58^••].