1 . The aim of this study was to investigate the
neurophysiological basis for thermal analgesia. The
speculation that part of this analgesia may be mediated
via depression of nociceptor driven spinal cord tract
neurones was tested.
Spinal segments L6 to S1 were explored with extracellular mi'cropipette electrodes filled with a mixture
of 5M sodium chloride and pontamine sky blue (2% in
0.5 M sodium acetate) in rats anaesthetised with
chloralose (100 mg kg⁻¹) and urethane (700 mg kg⁻¹).
3. 258 neurones were recorded from within the dorsal
horn and were tested for the inhibitory effect of
thermal stimulation applied to the perineal, inguinal
and scrotal skin. Ten of the 258 units received only
a warm inhibitory input from the skin. 57 units had
an excitatory input from nociceptors, of these 24 were
inhibited by warming and 2 by cooling the skin.
4. Data has also teen obtained on the light
microscopic anatomy of the scrotal skin and also on 73
units that had an input from thermoreceptors.
5. It is suggested that thermal inhibition of units
that have an input from nociceptors may provide some
neurophysiological basis for thermal analgesia.