Extraction of Rat Mandibular Incisor Induces Face Sensorimotor Cortex Neuroplasticity

Neuroplasticity of the sensorimotor cortex is thought to be an adaptive process that may occur following peripheral tissue injury, amputation or rehabilitation. It is unclear whether loss of teeth and accompanying changes in sensorimotor functions (e.g. chewing, pain) are associated with neuroplastic changes in the primary face sensorimotor cortex (face-M1, face-S1).

OBJECTIVE:  To determine if sensorimotor cortical neuroplasticity, as reflected by alteration in the representation of the jaw-opening muscles (right and left anterior digastric - RAD,LAD) in face-M1 and adjacent face-S1, occurs following extraction of the rat mandibular incisor.

METHODS: Three groups of adult male Sprague-Dawley rats were used. Under local and general anaesthesia, extraction group (N=8) received muco-alveolar bone surgery and extraction of the mandibular right incisor; sham group (N=6) received surgery with no extraction; naive group (N=6) had neither anaesthesia nor surgery. One week later, under general anaesthesia (ketamine-HCl), intracortical microstimulation (ICMS)(5x35ms train, 12x0.2ms pulses, 333Hz; 60µA) was applied every 200µm of depth within the left sensorimotor cortex in systematic series of microelectrode penetrations at 4 coronal planes. ICMS-evoked electromyographic (EMG) activity was recorded from RAD and LAD. Cortical sites from which EMG activity could be evoked by ICMS were considered “positive-sites” and statistically analyzed (ANOVAs, Bonferroni, p<0.05).

RESULTS:

CONCLUSION: Dental extraction may be associated 1 week later with face-M1 and face-S1 neuroplastic changes reflected in an enhanced RAD representation. These changes may be related to the animal's ability to adapt to the altered oral environment and may have clinical implications.

Supported by CIHR grant-MT-4918