AI Article Synopsis
- Primary afferent fibers are classified into three types: Abeta-, Adelta-, and C-fibers, with neonatal capsaicin treatment (NCT) reducing C-fiber inputs in the spinal dorsal horn.
- Electrophysiological studies showed that in control rats, nearly half of the spinal neurons had C-fiber EPSCs, but in NCT rats, this dropped significantly while Abeta-fiber responses increased.
- The findings indicate that NCT leads to a reduction of C-fiber inputs and an enhancement of Abeta-fiber innervation in the substantia gelatinosa as the organism matures.
Article Abstract
Primary afferent fibers are divided into three main subgroups: Abeta-, Adelta-, and C-fibers. Morphological studies have demonstrated that neonatal capsaicin treatment (NCT) depletes C-fiber inputs in the spinal dorsal horn; the electrophysiological features of the NCT-induced changes, however, remain unclear. This issue was addressed by performing whole-cell voltage-clamp recordings from substantia gelatinosa (SG) neurons in dorsal root-attached spinal cord slices. When estimated from excitatory postsynaptic currents (EPSCs) evoked by stimulating primary afferent fibers, 24 (49%) of 49 neurons examined exhibited C-fiber EPSCs that were either monosynaptic (n = 15) or polysynaptic (n = 9) in origin; only two of the neurons had Abeta-fiber responses. In NCT rats, however, SG neurons exhibiting C-fiber-mediated EPSCs decreased to 7% (3 of 41 neurons tested), whereas Abeta-fiber EPSCs were observed in 21 (51%) of the neurons, and 14 (67%) of them exhibited monosynaptic ones. There was no change in the cell proportion having Adelta-fiber innervation after NCT. Our electrophysiological data suggest that NCT diminishes primary afferent C-fiber inputs while enhancing Abeta-fiber direct innervation in the SG in adulthood.
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