title: Presynaptic neuromuscular action of a methanolic extract from the venom of Rhinella schneideri toad.
abstract: BACKGROUND
  Rhinella 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.
  
  
  METHODS
  The 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.
  
  
  RESULTS
  Venom 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).
  
  
  CONCLUSIONS
  These results indicate that the methanolic extract of R. schneideri venom acts primarily presynaptically to enhance neurotransmitter release in mouse phrenic-diaphragm preparations.
authors.affiliation: Departamento de Farmacologia, Faculdade de Ciências Médicas, Universidade Estadual de Campinas (UNICAMP), CP 6111, Campinas, SP 13083-970, Brasil.
authors.forename: Sandro
authors.initials: S
authors.lastname: Rostelato-Ferreira
authors.affiliation: Laboratório de Neurobiologia e Toxinologia, (LANETOX), Universidade Federal do Pampa, (UNIPAMPA), Av. Antônio Trilha, 1847, Centro, CEP 97300-000 São Gabriel, RS, Brazil.
authors.forename: Cháriston A
authors.initials: CA
authors.lastname: Dal Belo
authors.affiliation: Departamento de Farmacologia, Faculdade de Ciências Médicas, Universidade Estadual de Campinas (UNICAMP), CP 6111, Campinas, SP 13083-970, Brasil.
authors.forename: Gildo B
authors.initials: GB
authors.lastname: Leite
authors.affiliation: Departamento de Farmacologia, Faculdade de Ciências Médicas, Universidade Estadual de Campinas (UNICAMP), CP 6111, Campinas, SP 13083-970, Brasil.
authors.forename: Stephen
authors.initials: S
authors.lastname: Hyslop
authors.affiliation: Departamento de Farmacologia, Faculdade de Ciências Médicas, Universidade Estadual de Campinas (UNICAMP), CP 6111, Campinas, SP 13083-970, Brasil.
authors.forename: Léa
authors.initials: L
authors.lastname: Rodrigues-Simioni
keywords: Neurotransmitter release; Ouabain; Presynaptic; Rhinella schneideri; Toad venom