EFFECTS OF LESIONS IN THE TRIGEMINAL ORALIS AND CAUDALIS SUBNUCLEI ONDIFFERENT OROFACIAL NOCICEPTIVE RESPONSES IN THE RAT

Behavioural responses to two different orofacial noxious stimulations were analysed following lesion of spinal trigeminal subnucleus oralis (Sp5O) in the rat. Lesions were obtained by intranuclear microinjectio ns of quinolinic acid (0.4 mu l of 60 nmol/mu l solution). The control groups received microinjection of saline. Noxious stimulation was a s ubcutaneous injection of formalin into the upper Lip or electrical sti mulation of the tooth pulp. The measured behavioural responses were du ration of rubbing induced by the formalin injection and thresholds of the jaw-opening reflex (JOR), head rotation (HR) and face rubbing (FR) evoked by the pulp stimulation. In addition, formalin injection was a lso performed in two groups of rats that had received intranuclear inj ection of quinolinic acid or saline into rostral subnucleus caudalis ( Sp5C). Rubbing duration was not significantly modified by the lesion o f Sp5O, whereas a significant decrease occurred after the lesion of ro stral Sp5C. After the lesion Of Sp5O, an increase in the threshold of JOR was observed whereas the thresholds of HR and FR were not signific antly modified. These results suggest that Sp5O is not necessary for t he processing and relay of nociceptive inputs triggered by intense sti mulations of oral and perioral areas. However further experiments are needed to reconcile these results with the re:levant data obtained fro m cell recording experiments which indicate the existence, in Sp5O, of neuronal activities related to the sensory discriminative aspect of i ntense nociception. (C) 1998 Elsevier Science B.V. All rights reserved .