Variations of the jaw opening reflex observed in awake, freely moving rats
Pajot, J.; Vassel, A.; Aigouy, L.; Rajaona, J.; Woda, A.
Archives Internationales de Pharmacodynamie et de Therapie 270(2): 309-317
1984
ISSN/ISBN: 0003-9780 PMID: 6486976 Document Number: 223574
Long term variations of the jaw opening reflex (JOR) induced by tooth pulp stimulation (TPS) were investigated in the awake, freely moving rat. This study was specially centered on variations which could occur during the utilization of the JOR as a test for analgesic drugs. Bipolar electrodes were implanted in the inferior incisor tooth pulp for stimulation and in digastric muscle for recording. JOR recordings were subsequently integrated. Long term variations of JOR were then observed during uninterrupted TPS (1 Hz) alone or during s.c. injection, gavage or foot shock in addition to TPS. Of a total of 24 rats, observed during long uninterrupted TPS, 8 showed a decrease of the JOR. The mean of reflex values, 15 min later, was 74 .+-. 6% (n = 8) of the prestimulation level; s.c. injection of saline, light handling, experimentor's brisk irruption or sudden noise evoked a total disappearance of the reflex which completely returned within 30 s; gavage of arabic gum syrup gave either of the following; the same transient disappearance as for the s.c. injection of 6 rats; a progressive, 28 min .+-. 11 (n = 6), return to the initial value; a progressive return to a subcontrol value of 52 .+-. 4% (n = 7); a 30 min foot shock delivered for 10 s twice a minute at the infravocalization threshold evoked a marked decrease of the reflex reaching to 68 .+-. 6% (n = 10) of the control (prestimulation level). Marked fluctuations in the JOR were seen, which therefore does not make the JOR a good test for analgesic drugs in awake rats.