Peripheral nerve activity in response to heating the cat's skin.

1. The sensitivity of the cat hind-limb skin to non-noxious heating was studied. Neural activity was recorded with micro-electrodes from intact multifibre fascicles of the saphenous nerve while the skin was actively heated or passively cooled.2. Moderate warming from indifferent temperatures of 30-34 degrees C to temperatures of 38-39 degrees C produced a reduction in the total rate of firing of the integrated discharge. Firing picked up sharply again at skin temperatures above 39 degrees C. A considerable fraction of the impulse activity elicited above 39 degrees C was carried by C-fibre afferents.3. Prolonged heating to temperatures in excess of 45 degrees C rendered the skin insensitive to further non-noxious heating or to touch.4. The neural response to a step increase in skin temperature consisted of a delayed overshoot and then a steady-state level of firing. Steady-state firing was proportional to the level of skin temperature.5. Nerves whose C-fibre input to the spinal cord had been selectively blocked showed a potentiation of the neural response to skin heating.6. The sensitivity of hind-limb skin to heating, as judged by the character of the multifibre discharge, appears similar to that reported for a highly warm-sensitive region of the nose.