Kir2.1 Channel Regulation of Glycinergic Transmission Selectively Contributes to Dynamic Mechanical Allodynia in a Mouse Model of Spared Nerve Injury

Neuropathic pain is a chronic debilitating symptom characterized by spontaneous pain and mechanical allodynia. It occurs in distinct forms, including brushevoked dynamic and filament-evoked punctate mechanical allodynia. Potassium channel 2.1(Kir2.1), which exhibits strong inward rectification, is and regulates the activity of lamina I projection neurons. However, the relationship between Kir2.1 channels and mechanical allodynia is still unclear. In this study, we first found that pretreatment with ML133, a selective Kir2.1 inhibitor, by intrathecal administration, preferentially inhibited dynamic, but not punctate, allodynia in mice with spared nerve injury(SNI).Intrathecal injection of low doses of strychnine, a glycine receptor inhibitor, selectively induced dynamic, but not punctate allodynia, not only in na¨?ve but also in ML133-pretreated mice. In contrast, bicuculline, a GABAAreceptor antagonist, induced only punctate, but not dynamic,allodynia. These results indicated the involvement of glycinergic transmission in the development of dynamic allodynia. We further found that SNI significantly suppressed the frequency, but not the amplitude, of the glycinergic spontaneous inhibitory postsynaptic currents(gly-sIPSCs) in neurons on the lamina II-III border of the spinal dorsal horn, and pretreatment with ML133 prevented the SNI-induced gly-sIPSC reduction. Furthermore, 5 days after SNI, ML133, either by intrathecal administration oracute bath perfusion, and strychnine sensitively reversed the SNI-induced dynamic, but not punctate, allodynia and the gly-sIPSC reduction in lamina IIi neurons, respectively.In conclusion, our results suggest that blockade of Kir2.1 channels in the spinal dorsal horn selectively inhibits dynamic, but not punctate, mechanical allodynia by enhancing glycinergic inhibitory transmission.

Investigation of Some Possible Mechanisms Involved in the Anticonvulsant Activity of Tulbaghia violacea Harv

Even though Tulbaghia violacea has been used to treat and manage epilepsy in South Africa by traditional medicine practitioners, no evidence in any literature has shown any scientific scrutiny of the effectiveness of the plant species in therapy. This study was intended, therefore, to investigate the anticonvulsant effect of the leaf methanol extract of Tulbaghia violacea by studying its effect against tonic convulsion induced by either PTZ （pentylenetetrazole）, bicuculline, picrotoxin, strychnine or NMDLA （N-methyl-DL-aspartic acid） in mice. Qualitative phytochemical analysis, acute toxicity and HPLC studies were also carried out on the plant species. Leaf methanol extract of Tulbaghia violacea, phenobarbitone, diazepam or muscimol significantly antagonised PTZ, bicuculline or picrotoxin-induced convulsion. Combined treatment of sub-effective doses of T. violacea and muscimol significantly antagonised tonic convulsion induced by PTZ. T. violacea or phenobarbitone significantly antagonised strychnine-induced tonic convulsion. T. violacea or LY233053 significantly antagonised NMDLA-elicited tonic convulsion. Phenytoin or DMSO （dimethylsulfoxide） did not significantly affect the tonic convulsion produced by PTZ, bicuculline, picrotoxin, strychnine or NMDLA. The phytochemical qualitative analysis of the plant species showed the presence of alkaloids, saponins, reducing sugars, flavonoids, cardiac glycosides, triterpene steroids, quinones and tannins. The LD50 value obtained following oral administration of the plant extract was over 4000 mg/kg. The data in the present study indicate that the leaf methanol extract of T. violacea has anticonvulsant activity which is probably underpinned by GABAergic, glutaminergic and glycinergic mechanisms.

Evaluation of the Anticonvulsant Activity of the Leaf Methanol Extract of Crassula arborescens （Mill.） Willd. （Crassulaceae） in Mice

Crassula arborescens （Mill.） Willd. subsp. Arborescens is widely used for the treatment of various ailments including diarrhoea, corns, epilepsy and as a purgative. However, no information exists in any literature to verify the acclaimed effectiveness of C. arborescens in the treatment of the various ailments. The study, therefore, intended to investigate the anticonvulsant activity of the leaf methanol extract of C. arborescens in mice. Acute toxicity study and phytochemical qualitative analysis of the plant extracts were also carried out. Chemically-induced convulsion methods were used to assess the anticonvulsant activity of C. arborescens. Standard methods were used for the acute toxicity study and phytochemical analysis of the chemical components of the plant extract. PTZ （pentylenetetrazole）, bicuculline, picrotoxin, NMDLA （N-methyl-DL-aspartic acid） or strychnine produced tonic convulsions in all the mice used. Leaf methanol extract of Crassula arborescens, muscimol, phenobarbitone or diazepam significantly antagonised PTZ, bicuculline or picrotoxin-induced convulsion. C. arborescens or LY233053 significantly antagonised NMDLA-induced tonic convulsion. C. arborescens or phenobarbitone significantly antagonised strychnine-elicited tonic convulsion. Phenytoin or DMSO （dimethylsulfoxide） did not significantly affect the tonic convulsion produced by PTZ, bicuculline, picrotoxin, NMDLA or strychnine. The LDso value obtained from intraperitoneal administration of C. arborescens was 781.6 mg/kg while that following oral administration of the plant extract was over 4,000 mg/kg. The phytochemical qualitative analysis done showed the presence of flavonoids, tannins, reducing sugar, saponins and triterpene steroids. The data obtained in the study show that the leaf methanol extract of Crassula arborescens has anticonvulsant activity which may be underpinned by GABAergic, glutaminergic and glycinergic mechanisms. The high LDso value obtained following the oral administration of the plant extract shows that the leaf methanol extract is non-toxic to animals.