Abstract
The inferior alveolar nerve (IAN) is a mandibular branch of the trigeminal nerve and innervates to orofacial region. IAN transection (IANX) induces allodynia in the maxillary nerve-projecting region. However, it is not fully understood whether and how the nociceptive information processing in the cerebral cortex is changed by nerve injury. To address this question, we assessed neural activity during nociception in IANX rats using optical imaging and two-photon calcium imaging techniques. Since the dental pulps principally consist of Aδ and C fibers that transmit nociceptive information, we used dental pulp stimulation to investigate the cortical response to nociception. Optical imaging at macroscopic level revealed that cortical excitation induced by the upper molar pulp stimulation was enhanced in 1 week after IANX. Two-photon calcium imaging revealed that hyperexitability of both excitatory and inhibitory neurons. Whole-cell patch-clamp recording in slice preparation revealed inhibitory postsynaptic inputs to pyramidal neurons were decreased in IANX rats. These results suggest that IANX induces enhancement of neural activity during nociceptive information processing, and plastic changes of the local circuits in the cerebral cortex might contribute to the enhancement.
