Presynaptic neuromuscular action of a methanolic extract from the venom of Rhinella schneideri toad

BackgroundRhinella schneideri, previously known as Bufo paracnemis, is a common toad in many regions of Brazil. Its venom exerts important cardiovascular effects on humans and other animals. Although this toad venom has been the subject of intense investigations, little is known about its neuromuscular activity.MethodsThe neurotoxicity of a methanolic extract of R. schneideri venom was tested on mouse phrenic nerve-diaphragm (PND) preparations mounted for conventional twitch tension recording – in response to indirect stimulation – and for electrophysiological measurements.ResultsVenom extract (50 μg/mL) increased the muscle twitch tension in PND preparations but did not significantly alter the resting membrane potential values. Electrophysiological evaluations showed that the extract (50 μg/mL) significantly augmented the frequency of miniature end-plate potential (from 38 ± 3.5 to 88 ± 15 after 60 minutes; n = 5; p< 0.05) and quantal content (from 128 ± 13 to 272 ± 34 after five minutes; n = 5; p< 0.05). Pretreatment with ouabain (1 μg/mL) for five minutes prevented the increase in quantal content (117 ± 18 and 154 ± 33 after five and 60 minutes, respectively).ConclusionThese results indicate that the methanolic extract of R. schneiderivenom acts primarily presynaptically to enhance neurotransmitter release in mouse phrenic-diaphragm preparations.

背景 施氏蟾蜍（Rhinella schneideri）曾被称为副蹼蟾蜍（Bufo paracnemis），是巴西诸多区域常见的蟾蜍物种。其毒液对人类及其他动物具有显著的心血管效应。尽管该蟾蜍毒液已得到广泛深入的研究，但学界对其神经肌肉活性的认知仍较为匮乏。方法 本研究采用制备完成的小鼠膈神经-膈肌（phrenic nerve-diaphragm, PND）标本，通过间接刺激引发常规抽搐张力记录，并结合电生理检测，评估施氏蟾蜍毒液甲醇提取物的神经毒性。结果 毒液提取物（50 μg/mL）可升高小鼠膈神经-膈肌标本的肌肉抽搐张力，但未显著改变静息膜电位值。电生理评估显示，该提取物（50 μg/mL）可显著提升微小终板电位（miniature end-plate potential）频率（60分钟后从38±3.5升至88±15；n=5；p<0.05）及量子释放量（quantal content）（5分钟后从128±13升至272±34；n=5；p<0.05）。使用哇巴因（ouabain，1 μg/mL）预处理5分钟，可阻断该量子释放量的升高（5分钟及60分钟后分别为117±18和154±33）。结论 上述结果表明，施氏蟾蜍毒液的甲醇提取物主要通过突触前机制，增强小鼠膈神经-膈肌标本的神经递质释放。