Diffuse noxious inhibitory controls (DNIC). Effects on trigeminal nucleus caudalis neurones in the rat

We have extended our previous description at the dorsal horn level of Diffuse Noxious Inhibitory Controls (DNIC) to the trigeminal nucleus caudalis of the intact anaesthetized rat. These controls produce powerful long-lasting inhibitions of all activities of convergent neurones and can be elicited by noxious stimuli applied to widespread areas of the body unrelated to the receptive fields of the neurones under study. In nucleus caudalis, 39/40 convergent neurones were found to be under DNIC produced from the tail, paws, viscerae, nose and ears. DNIC was only elicited by noxious stimuli which included pinch, noxious heat and intraperitoneal bradykinin. DNIC strongly inhibited both the A fibre and C fibre related activities of trigeminal convergent neurones whether evoked electrically or naturally with the degree of inhibition ranging between 55 and 100% in the most cases. Of 43 non-convergent neurones, noxious only, innocuous, proprioceptive and cold responsive, 42 were unaffected by DNIC. The results demonstrate that both the neuronal responses and DNIC at the trigeminal nucleus caudalis level in the rat are similar to those reported for the dorsal horn.