Stimulation of the locus coeruleus suppresses trigeminal sensorimotor function in the rat

The nucleus locus coeruleus (LC) has been implicated in the modulation of t he spinal sensorimotor function. The aim of the present study was to examin e the effect of electrical stimulation of the LC on sensorimotor function i n the trigeminal system, The following two cases of sensorimotor behaviors mediated by the trigeminal brainstem sensory nu clear complex were examined : (1) the activity of the masseter muscle evoked by pressure on the region of the temporomandibular joint (TMJ); and (2) the activity of the digastric muscle evoked by electrical stimulation of the tooth pulp, resulting in th e jaw-opening reflex, In the first case, LC stimulation at 10, 30 and 50 mu A resulted in a 70%, 68% and 55% reduction in the magnitude of electromyogr am (EMG) activity of the masseter muscle compared with the control (without LC stimulation), respectively. The threshold intensity for the onset of ma sseter EMG activity increased to 106%, 111% and 121% of the control with 10 , 30 and 50 muA LC stimulation, respectively, In the second case, EMG magni tude in response to the digastric muscle decreased to 42% of the control wh en 30 muA Of Le stimulation was delivered. These results suggest that desce nding influences from the LC can act in suppression of the trigeminal senso rimotor function. (C) 2001 Elsevier Science Inc.