The Central Organization of the Thermoregulatory System

Summary

The body temperature of homeothermic animals is regulated by systems that utilize multiple behavioral and autonomic effector responses. The thermoreceptors that provide inputs to the regulatory systems are distributed throughout the body. Although the regulatory aspects of this multiple input-output system are largely nervous, knowledge about the “neuronal circuit” for thermoregulation remained rather stagnant for several decades. However, the last few years have brought new approaches that have led to new information and new ideas about neuronal interconnections in the thermoregulatory network. This advance is especially true for efferent pathways from the preoptic area (PO). Recent studies utilizing chemical stimulation of the PO have revealed that not only heat loss but also heat production responses are controlled by PO warm-sensitive neurons. These neurons send excitatory efferent signals for heat loss and inhibitory efferent signals for heat production. The warm-sensitive neurons that control these two opposing responses are different and work independently. Recent electrophysiological analysis identified some neurons sending axons directly to the spinal cord for the control of thermoregulatory effectors. Included are midbrain reticulospinal neurons for shivering and premotor neurons in the medullary raphé nuclei for skin vasomotor control. Even though many neurons in the efferent pathways remain unidentified, recent advances in experimental techniques promise a much more detailed understanding of the neuronal circuit underlying thermoregulation in the near future.