Effects of noxious stimulation of orofacial tissues on rat licking behaviour.
OBJECTIVE
Since there is limited information of the effects of orofacial pain on oromotor behaviour, the aim of this study was to test the effects of injection of the algesic chemical glutamate into orofacial tissues on licking behaviour in rats.


METHODS
Male Sprague-Dawley rats were trained to carry out stereotyped licking from a water spout connected to a force transducer, and once they met preset licking motor requirements (peak force of licking of 2-20 g, interlick interval of 0.11-0.19s), their masseter muscle or tongue was injected with either isotonic saline (0.9%, 5 microL) or glutamate (1.0M, 5 microL) and several parameters of their licking performance were re-assessed.


RESULTS
There were significant effects (P<0.05; 1-way repeated measures ANOVA) of glutamate injection into the tongue on the number of clusters of licks, the number of licks per cluster, the intercluster period, the peak force of licking and the interlick interval, but there were no significant (P>0.05) effects on licking of isotonic saline injection into the tongue or isotonic saline or glutamate injection into the masseter muscle.


CONCLUSIONS
These findings provide the first documentation that noxious stimulation of the tongue, but not of the masseter muscle, has a modulatory effect on licking behaviour in the rat and suggest that the neural substrate for licking may be sensitive to selective nociceptive inputs from the orofacial region.
Bejat
G
G
Faculty of Dentistry, University of Toronto, 124 Edward Street, M5G 1G6, Toronto, Ontario, Canada.
Yao
D
D
Hu
J W
JW
Murray
G M
GM
Sessle
B J
BJ
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D004327:Drinking Behavior / Q000187:drug effects; D005157:Facial Pain / Q000139:chemically induced / Q000503:physiopathology*; D018698:Glutamic Acid; D008297:Male; D008406:Masseter Muscle / Q000294:innervation / Q000503:physiopathology*; D009043:Motor Activity / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time; D013268:Stimulation, Chemical; D014059:Tongue / Q000294:innervation / Q000503:physiopathology*; D014160:Transducers, Pressure
D018698:Glutamic Acid