Journal
EUROPEAN JOURNAL OF NEUROSCIENCE
Volume 24, Issue 7, Pages 1976-1986Publisher
WILEY
DOI: 10.1111/j.1460-9568.2006.05065.x
Keywords
current analysis; ganglion neurons; neuropathic pain; trigeminal nerve; whisker pad
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In order to clarify the mechanisms underlying the changes in primary afferent neurons in trigeminal neuropathic pain, a chronic constriction nerve injury model of the infraorbital nerve (ION-CCI) was developed in rats. Mechanical allodynia was observed at 3 days after ION-CCI and lasted more than 14 days. Single-unit activities were recorded from the ION of anesthetized rats. C-, A beta- and A delta-units were identified on the basis of their conduction velocity. A delta-units were frequently encountered at a later period after ION-CCI. The highest A delta-spontaneous activity was recorded at 3 days after ION-CCI and progressively decreased after that, but spontaneous activity was still higher at 14 days after ION-CCI than that of naive rats. Mechanical-evoked responses of A delta-units were also highest at 3 days after ION-CCI and then gradually decreased. In consideration of these data, patch-clamp recordings were performed on medium to large size neurons of the dissociated trigeminal ganglion (TRG). Patch-clamp recordings revealed that the I-K (sustained) and I-A (transient) in rats with ION-CCI were significantly smaller than those of naive rats, and correlated with an increase in duration of repolarization phase and a decrease in duration of depolarization phase, respectively. The hyperpolarization-activated current (I-h) was significantly larger in TRG neurons of rats with ION-CCI as compared with those of naive rats. The present results suggest that I-h, I-K and I-A in A delta-afferent neurons in TRG are significantly involved in the changes in afferent spontaneous activity and mechanically evoked activity that accompany mechanical allodynia produced by trigeminal nerve injury.
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