Intrathecal vasoactive intestinal polypeptide modulates spinal reflex excitability primarily to cutaneous thermal stimuli in rats.

The effect of intrathecally (i.t.) injected vasoactive intestinal polypeptide (VIP) on spinal nocifensive flexor reflex excitability was examined in decerebrate, spinalized, unanesthetized rats. The hamstring reflex was evoked by intense cutaneous mechanical or thermal stimulation of the ipsilateral foot. I.t. VIP increased the excitability of the spinal cord to thermal much more than to mechanical stimuli. It is suggested that this neuropeptide is released by thermosensitive cutaneous afferents that respond poorly to mechanical stimuli.