Properties of A delta high threshold mechanoreceptors in the rat hairy and glabrous skin and their response to heat.

Forty-three high threshold mechanoreceptors (HTMs) with myelinated fibres were characterized in hairy and glabrous skin of the hind limb of the rat. Mechanical thresholds and conduction velocities were similar in both skin areas. The behaviour of 15 hairy and 14 glabrous skin HTMs were studied in response to repeated heating to 55-60 degrees C. Responses to heating were either very weak or absent, except for two units, one from each group, that fired on second and subsequent heat trials. A delta-HTMs in rat skin, either hairy or glabrous, are thus much less easily excited by heat than are similar units in rabbit, cat or monkey skin. C-fibres in rat skin are known to respond well to heating, and therefore provide the only significant input about noxious heat in this species.