Responses of pontine units to skin-temperature changes in the guinea-pig.

1. The responses of fifty-five single units to changes in skin temperature were recorded in twenty-three guinea-pigs anaesthetized with urethane. Skin-temperature changes were induced by changing the temperature of the water-perfused support plate of the stereotaxic apparatus and that of the double-walled Perspex jacket that was put on the support plate.2. Thirty-three units were stereotaxically and histologically verified as being within a circumscribed area of the pontine dorsomedial reticular formation (subcoeruleus region). Twenty-one units were located in the surrounding areas, and one unit in the nucleus raphé magnus region.3. Twenty-seven of thirty-three recorded subcoeruleus units were specifically excited by cooling of the abdominal or leg skin, whereas only five units were non-thermoresponsive and one unit was warm-responsive. The cold-responsive units had peak activity at skin temperatures between 22 and 29 degrees C, in accordance with the maximum activity in cutaneous cold-receptors.4. A markedly different distribution of units was found in the surrounding areas. Only four units were cold-responsive. Thirteen units were non-thermoresponsive, and four units were warm-responsive.5. The cold-responsive subcoeruleus units were situated in regions which are known to contain accumulations of noradrenergic cell bodies, and to project to hypothalamic neurones. Electrical stimulation of these regions is known to cause excitatory metabolic responses in unanaesthetized guinea-pigs. It is concluded that part of the cutaneous cold-afferents projects to hypothalamic thermointegrative neurones via noradrenergic pathways that ascend from these subcoeruleus regions.