Somatosensory evoked response and jaw opening reflex elicited by tooth pulp stimulation in awake freely moving rats.
OBJECTIVE
Investigation of pain and nociception refers to different models. Depending upon the intensity of stimulation, unmyelinated pulpal fibers or periodontal A-fibers can be stimulated producing a short or a long latency jaw opening reflex of the digastric muscle. This paper investigates the different components of the jaw opening reflex in addition to the correlation between afferent fibers involved in the cortical evoked response.


METHODS
Fifteen awake male rats were implanted with tooth pulp stimulation electrodes, digastric and cortical recording electrodes. Ten rats were submitted to recordings after a single tooth pulp stimulation, while five rats were using conditioning and test stimulation. Tooth pulp evoked potentials and digastric EMG were simultaneously recorded. A multiresolution denoising method was used for signal processing.


RESULTS
Following tooth pulp stimulation, a cortical response was produced including the following peaks: P6.5 +/- 1.1, N11 +/- 1.2, P17 +/- 1.2, P27 +/- 2.9, N53 +/- 7.5, P69 +/- 5.8, P88 +/- 13, N160 +/- 9.7, P204 +/- 14.2. The distribution and amplitude of these peaks are correlated to the stimulation intensity (r=0.96, p<0.01). An interaction between the different components of the jaw opening reflex was identified on EMG, following a conditioning shock, where a cortical evoked response showed a P30 +/- 2.7 peak which was observed concurrently with the jaw opening long latency reflex.


CONCLUSIONS
Our results identify the interaction between the different components of the jaw opening reflex and the correlation to the cortical evoked response.
Barek
Stephane
S
Laboratoire de physiologie de la manducation, University Paris VII - Denis Diderot, Paris, France. dr.barek@wanadoo.fr
Rusina
Robert
R
Pollin
Bernard
B
Azerad
Jean
J
D000818:Animals; D003213:Conditioning, Psychological; D003782:Dental Pulp / Q000294:innervation; D004597:Electroshock; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D007568:Jaw; D008297:Male; D009068:Movement; D010147:Pain Measurement; D051381:Rats; D017207:Rats, Sprague-Dawley; D012018:Reflex; D014070:Tooth; D014851:Wakefulness