Abstract
1 The effects of Gymnodinium breve neurotoxin (GT) on smooth muscles were studied using the guinea-pig isolated ileum.
2 The toxin caused strong spasmogenic effects at 1-4 μg/ml, characterized by prolonged tonic contraction with superimposed pronounced pendular movements. Tachyphylaxis was observed upon administration of successive doses.
3 Atropine blocked the contractile response elicited by GT, whereas mepyramine and hexamethonium failed to do so. These findings tentatively suggested a cholinergic involvement at a post-ganglionic site of action.
4 In the presence of tetrodotoxin the effects of GT were abolished, excluding direct action of the toxin on the smooth muscle.
5 It is concluded that GT exerts its spasmogenic effects through stimulation of the post-ganglionic cholinergic nerve fibres.
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Selected References
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