Alteration of Medullary Dorsal Horn Neuronal Activity Following Inferior Alveolar Nerve Transection in Rats

Abstract

The effects of inferior alveolar nerve (IAN) transection on escape behavior and MDH neuronal activity to noxious and nonnoxious stimulation of the face were precisely analyzed. Relative thresholds for escape from mechanical stimulation applied to the whisker pad area ipsilateral to the transection were significantly lower than that for the contralateral and sham-operated whisker pad until 28 days after the transection, then returned to the preoperative level at 40 days after transection. A total of 540 neurons were recorded from the medullary dorsal horn (MDH) of the nontreated naive rats [low-threshold mechanoreceptive (LTM), 27; wide dynamic range (WDR), 31; nociceptive specific (NS), 11] and sham-operated rats with skin incision (LTM, 34; WDR, 30; NS, 23) and from the ipsilateral (LTM, 82; WDR, 82; NS, 31) and contralateral MDH relative to the IAN transection (LTM, 77; WDR, 82; NS, 33). The electrophysiological properties of these neurons were precisely analyzed. Background activity of WDR neurons on the ipsilateral side relative to the transection was significantly increased at 2-14 days after the operation as compared with that of naive rats. Innocuous and noxious mechanical-evoked responses of LTM and WDR neurons were significantly enhanced at 2-14 days after IAN transection. The mean area of the receptive fields of WDR neurons was significantly larger on the ipsilateral MDH at 2-7 days after transection than that of naive rats. We could not observe any modulation of thermal responses of WDR and NS neurons following IAN transection. Also, no MDH neurons were significantly affected in the rats with sham operations. The present findings suggest that the increment of neuronal activity of WDR neurons in the MDH following IAN transection may play an important role in the development of the mechano-allodynia induced in the area adjacent to the area innervated by the injured nerve.

Dietary constituent, decanoic acid suppresses the excitability of nociceptive trigeminal neuronal activity associated with hypoalgesiaviamuscarinic M2receptor signaling

“…Graded nociceptive stimulation was applied to the most sensitive area of the receptive field, which exhibited increased firing frequency of SpVc WDR neurons in proportion to stimulus intensity, and many of them also responded to noxious heat stimulation, suggesting that WDR neurons send encoding stimulus intensity to higher centers. 28,29 …”

Fractalkine Signaling in Microglia Contributes to Ectopic Orofacial Pain following Trapezius Muscle Inflammation

“…Single neuronal activity was recorded using tungsten microelectrodes (impedance, 13 M⍀; 1000 Hz; FHC) from histologically determined sites in Vc and C1-C2. Each neuron was functionally identified as a wide dynamic range (WDR) neuron or a nociceptive-specific neuron on the basis of their responses to innocuous or noxious mechanical stimulation to the lateral facial skin ipsilateral to the CFA injection into trapezius muscle, as described previously (Iwata et al, 2001). WDR neurons responding to innocuous stimulation and, to a greater degree, noxious stimulation of the lateral facial skin were analyzed in this study.…”

Aberrant TRPV1 Expression in Heat Hyperalgesia Associated with Trigeminal Neuropathic Pain

“…However, only a few animal models in the trigeminal system have been reported. Trigeminal neuropathic pain models have been developed in which the infraorbital nerve (ION) 5, 9 or inferior alveolar nerve (IAN) 10 is injured. These models demonstrate mechanical allodynia and heat hyperalgesia.…”