RESUMO
BACKGROUND: Transient receptor potential ankyrin-1 (TRPA1) channels expressed in the central terminal of dorsal root ganglion neurons in the spinal substantia gelatinosa (SG) play a role in modulating nociceptive transmission. Although plant-derived compounds exhibiting antinociception (such as eugenol, carvacrol and thymol) activate TRPA1 channels to enhance spontaneous excitatory transmission while hyperpolarizing membranes in SG neurons without TRPA1 activation, specific chemical moieties involved in synaptic modulation are unknown. METHODS: We examined the effects of other plant-derived compounds (guaiacol, vanillin, vanillic acid and p-cymene) on holding current and spontaneous excitatory transmission at -70 mV by applying the whole-cell patch-clamp technique to SG neurons in adult rat spinal cord slices. RESULTS: None of the compounds affected the frequency or amplitude of spontaneous excitatory postsynaptic current. Guaiacol and vanillic acid had no effect on holding currents, while vanillin and p-cymene produced an inward and outward current, respectively, in some neurons tested. Synaptic modulation was also observed within the same neuron as the activities of eugenol, carvacrol, thymol, and the chemically-related plant-derived compound zingerone occurred. CONCLUSION: A substituted group in eugenol and zingerone, but not in guaiacol, vanillin or vanillic acid, as well as an OH bound to the benzene ring of carvacrol and thymol, but not p-cymene, play a role in producing outward current and TRPA1 activation. Thus, the binding of such chemical moeties to the benzene ring of plant-derived compounds appears necessary to modulate nociceptive transmission in the SG. This information provides insight for the development of new analgesics based on plant-derived compounds.
Assuntos
Analgésicos/farmacologia , Extratos Vegetais/farmacologia , Substância Gelatinosa/efeitos dos fármacos , Canal de Cátion TRPA1/agonistas , Analgésicos/química , Animais , Benzaldeídos/química , Benzaldeídos/farmacologia , Cimenos , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Guaiacol/química , Guaiacol/farmacologia , Técnicas In Vitro , Masculino , Estrutura Molecular , Monoterpenos/química , Monoterpenos/farmacologia , Extratos Vegetais/química , Ratos Sprague-Dawley , Relação Estrutura-Atividade , Substância Gelatinosa/metabolismo , Canal de Cátion TRPA1/metabolismo , Ácido Vanílico/química , Ácido Vanílico/farmacologiaRESUMO
ETHNOPHARMACOLOGICAL RELEVANCE: Traditional Japanese (Kampo) medicines have a variety of clinical effects including pain alleviation, but evidence for a mechanism for their pain relief has not yet been elucidated fully. Considering that Kampo medicine contains many plant-derived chemicals having an ability to inhibit nerve action potential conduction, it is possible that this medicine inhibits nerve conduction. The purpose of the present study was to know how various Kampo medicines affect nerve conduction. MATERIALS AND METHODS: We examined the effects of Kampo and crude medicines on compound action potentials (CAPs) recorded from the frog sciatic nerve by using the air-gap method. RESULTS: Daikenchuto, rikkosan, kikyoto, rikkunshito, shakuyakukanzoto and kakkonto concentration-dependently reduced the peak amplitude of the CAP. Among the Kampo medicines, daikenchuto was the most effective in inhibiting CAPs. Daikenchuto is composed of three kinds of crude medicine, Japanese pepper, processed ginger and ginseng radix. When the crude medicines were tested, Japanese pepper and processed ginger reduced CAP peak amplitudes, while ginseng radix hardly affected CAPs. Moreover, there was an interaction between the Japanese pepper and processed ginger activities in such that one medicine at low but not high concentrations increased the extent of the inhibition by the other one that was co-applied. CONCLUSIONS: Kampo medicines have an ability to inhibit nerve conduction. This action of daikenchuto is due to Japanese pepper and processed ginger but not ginseng radix, probably through an interaction between Japanese pepper and processed ginger in a manner dependent on their concentrations. Nerve conduction inhibition could contribute to at least a part of Kampo medicine's clinical effects such as pain alleviation.
Assuntos
Potenciais de Ação/efeitos dos fármacos , Medicamentos de Ervas Chinesas/farmacologia , Condução Nervosa/efeitos dos fármacos , Nervo Isquiático/efeitos dos fármacos , Animais , Combinação de Medicamentos , Zingiber officinale/química , Glycyrrhiza , Japão , Medicina Kampo/métodos , Medicina Tradicional/métodos , Paeonia , Panax/química , Extratos Vegetais/farmacologia , Ranidae , Zanthoxylum/química , ZingiberaceaeRESUMO
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.
Assuntos
Capsaicina/farmacologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Substância Gelatinosa/efeitos dos fármacos , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Vias Aferentes/efeitos dos fármacos , Vias Aferentes/fisiologia , Animais , Animais Recém-Nascidos , Potenciais Pós-Sinápticos Excitadores/fisiologia , Técnicas In Vitro , Ratos , Medula Espinal/efeitos dos fármacos , Medula Espinal/crescimento & desenvolvimento , Substância Gelatinosa/crescimento & desenvolvimentoRESUMO
Although hyperalgesia elicited by inflammation has been shown to be partly due to central sensitization, the cellular mechanisms are not clear at the moment. The present study was designed to address this issue using the blind whole-cell patch-clamp technique; glutamatergic primary-afferent inputs to substantia gelatinosa (SG) neurons were compared between spinal cord slices of naive rats and rats inflamed by an intraplantar injection of complete Freund's adjuvant. In naive rats, a large number of SG neurons examined received monosynaptic A delta- (69% of 41 neurons innervated by A fibers) and/or polysynaptic C- (94% of 36 neurons innervated by C fibers) afferent inputs, and only a few neurons received monosynaptic A beta inputs (7%). In addition, when examined in neurons which have both of the A- and C-afferent inputs, A afferent-evoked excitatory postsynaptic currents (EPSCs) were larger in amplitude than C afferent-induced ones; a ratio (A/C ratio) of the former to latter amplitude was 1.8 +/- 0.1 (n = 36). In inflamed rats, a change in the synaptic responses was observed: (1) SG neurons receiving monosynaptic A delta-afferent inputs decreased in number (to 20% of 30 neurons tested, innervated by A fibers), whereas those having monosynaptic A beta-afferent inputs increased to 33%, and (2) the A/C ratio decreased to 0.7 +/- 0.1 (n = 33). These results suggest that after inflammation, a substantial number of A beta-afferents sprout into the SG from their original location (laminae III-V) and that sensory information that used to be conveyed directly to the SG through A delta afferents is transmitted there indirectly through interneurons. These reorganizations of sensory pathway may contribute, at least in part, to underlying mechanisms for the development of hyperalgesia due to inflammation.