Alterations in primary afferent input to substantia gelatinosa of adult rat spinal cord after neonatal capsaicin treatment.
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.
Yang
Kun
K
Department of Integrative Physiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan. yankun@post.saga-med.ac.jp
Furue
Hidemasa
H
Fujita
Tsugumi
T
Kumamoto
Eiichi
E
Yoshimura
Megumu
M
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000344:Afferent Pathways / Q000187:drug effects / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn; D002211:Capsaicin / Q000494:pharmacology*; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D051381:Rats; D013116:Spinal Cord / Q000187:drug effects / Q000254:growth & development; D013376:Substantia Gelatinosa / Q000187:drug effects* / Q000254:growth & development
D002211:Capsaicin