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

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Abstract
The responses of 55 single units to changes in skin temperature were recorded in 23 guinea-pig anesthetized 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. Units (33) were stereotaxically and histologically verified as being within a circumscribed area of the pontine dorsomedial reticular formation (subcoeruleus region). Units (21) were located in the surrounding areas, and 1 U in the nucleus raphe magnus region. Of 33 recorded subcoeruleus units, 27 were specifically excited by cooling of the abdominal or leg skin, while 5 units were non-thermoresponsive and 1 unit was warm-responsive. The cold-responsive units had peak activity at skin temperatures between 22-29.degree. C, in accordance with the maximum activity in cutaneous cold-receptors. A markedly different distribution of units was found in the surrounding areas. Only 4 units were cold-responsive. Units (13) were non-thermoresponsive, and 4 units were warm-responsive. The cold-responsive subcoeruleus units were situated in regions known to contain accumulations of noradrenergic cell bodies, and to project to hypothalamic neurons. Electrical stimulation of these regions causes excitatory metabolic responses in unanesthetized guinea-pigs. Part of the cutaneous cold-afferents projects to hypothalamic thermointegrative neurons via noradrenergic pathways that ascend from these subcoeruleus regions.