FIGURE 9.

An extension of the proposed⁷ schematic model of the thermoregulatory reflex circuit for the regulation of BAT and shivering thermogenesis by cutaneous thermoreceptors: proposed role for neurons in the vLPO. Cool and warm cutaneous thermoreceptors transmit signals to respective primary sensory neurons in the dorsal root ganglia (DRG) which relay this information to the second-order thermal sensory neurons in the dorsal horn (DH). Cool-activated and warm-activated DH neurons excite the third-order sensory neurons in the external lateral subnucleus of the lateral parabrachial nucleus (LPB) and in the dorsal subnucleus of the LPB respectively. Neurons in the median preoptic (MnPO) subnucleus of the preoptic area (POA) receive these thermosensory signals from the LPB. Distinct populations (BAT: red circles; shivering: red ovals) of GABAergic, potentially warm-sensitive (W-S), neurons in the medial preoptic area (MPA) are postulated (dashed lines) to inhibit (red lines) separate populations of BAT and shivering thermogenesis-promoting neurons in the dorsomedial hypothalamus (DMH). Cooling-activated, GABAergic MnPO interneurons are postulated (dashed lines) to inhibit MPA GABAergic neurons during cold exposure, thereby disinhibiting thermogenesis-promoting neurons in the DMH. DMH neurons also receive a tonic excitation from an unknown (?) source. Distinct populations (BAT: red circles; shivering: red ovals) of GABAergic neurons in the ventral part of the lateral preoptic area (vLPO) inhibit respectively, sympathetic and shivering premotor neurons in the rostral raphe pallidus (rRPa). vLPO neurons may (dashed lines) inhibit thermogenesis-promoting neurons in the DMH. Warm-activated MnPO neurons are postulated (dashed lines) to excite (green lines) MPA GABAergic neurons, leading to warm-activated inhibition of thermogenesis-promoting neurons in the DMH. MnPO glutamatergic neurons may (dashed lines) provide a warm-activated excitatory drive to vLPO GABAergic neurons. Thermogenesis-inhibiting neurons in the vLPO may receive an excitatory input (green dashed lines) from an unknown (?) source. Sympathetic preganglionic neurons (SPNs) in the intermediolateral nucleus (IML) and alpha (α) and gamma (γ) motoneurons in the ventral horn (VH) of the spinal cord are excited by their antecedent premotor neuron populations in the rRPa to drive BAT and shivering thermogenesis respectively