Striatal modulation of the jaw opening reflex

The effect of striatal electrical and chemical conditioning stimulation (L- glutamate 80-160 nmoles/0.5 mul) on the jaw opening reflex (JOR) was studie d in Sprague-Dawley male rats anesthetized with urethane. The JOR was evoke d by stimulation of the tooth pulp of lower incisors. This response was sup pressed by transection of the dental root, which indicates according with t he bibliography, a specific activation of the pulp nerves. Three type of re sponses were obtained on the evoked JOR by conditioning stimulation of the striatum; being the main one the suppression of the reflex elicited by toot h pulp activation. A second type of response was an increase of the tooth-J OR amplitude. This effect was observed more Frequently with glutamate stimu lation rather than with electrical activation of the striatum. A third resp onse was observed with chemical stimulation but not by electrical stimulati on of the striatum. This was a triphasic response which consisted in an inc rease followed by an inhibition and a late increase of the tooth-JOR amplit ude. A biphasic effect, an increase prior to a decrease of the JOR amplitud e, was also recorded with a minor frequency. The distribution of effective sites for electrical and chemical stimulation within the striatum are mainl y similar located in the rostral aspect of the nucleus, with the inhibitory sites in the middle of the nucleus and intermingled with the excitatory on es. The complex responses (tri/biphasic) were observed ventrally and caudal ly in the nucleus. On the basis of the results mentioned above, one could a ssume that the striatum is related to the modulation of the JOR evoked prob ably by nociceptive stimulation. However, activation of other type of fiber s could not be ruled out. (C) 2001 Elsevier Science B.V. All rights reserve d.