A role for spinal lamina I neurokinin-1-positive neurons in cold thermoreception in the rat

Lamina I neurons of the spinal cord convey specific nociceptive activity to the brain. A subpopulation of lamina I cells bears substance P receptors ( neurokinin-1) and recent studies have shown that these neurons encode for t he intensity of noxious peripheral stimulation. Here, we report that cool t hermal stimuli, applied to the hindpaw of anaesthetized rats, induce Fos ex pression in lamina I neurokinin-1 neurons that is graded with respect to th e intensity of the thermal stimulus, Thus, as the temperature of the stimul us was reduced, both the total number of neurokinin-1-positive neurons expr essing Fos and the proportion of Fos nuclei present within neurokinin-1 cel ls showed a significant increase. These data show that lamina I neurokinin-1 cells encode the intensity of no xious cooling of the skin. In laminae III and IV, although there was no cor relation between neurokinin-1 cell activation and stimulus intensity, the t otal Fos count in these layers was inversely related to the depth of coolin g. Thus, neurons in laminae III and IV may also play a role in thermorecept ion. (C) 1999 IBRO. Published by Elsevier Science Ltd.