Alterations in primary afferent input to substantia gelatinosa of adult rat spinal cord after neonatal capsaicin treatment
✍ Scribed by Kun Yang; Hidemasa Furue; Tsugumi Fujita; Eiichi Kumamoto; Megumu Yoshimura
- Publisher
- John Wiley and Sons
- Year
- 2003
- Tongue
- English
- Weight
- 195 KB
- Volume
- 74
- Category
- Article
- ISSN
- 0360-4012
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✦ Synopsis
Abstract
Primary afferent fibers are divided into three main subgroups: Aβ‐, Aδ‐, 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 Aβ‐fiber responses. In NCT rats, however, SG neurons exhibiting C‐fiber‐mediated EPSCs decreased to 7% (3 of 41 neurons tested), whereas Aβ‐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 Aδ‐fiber innervation after NCT. Our electrophysiological data suggest that NCT diminishes primary afferent C‐fiber inputs while enhancing Aβ‐fiber direct innervation in the SG in adulthood. © 2003 Wiley‐Liss, Inc.