title: Urethane inhibits the GABAergic neurotransmission in the nucleus of the solitary tract of rat brain stem slices.
abstract: Because urethane is a widely used anesthetic in animal experimentation, in the present study, we evaluated its effects on neurons of the nucleus of the solitary tract (NTS) in brain stem slices from young rats (25-30 days old). Using the whole cell configuration of the patch-clamp technique, spontaneous postsynaptic currents (sPSCs) and evoked excitatory postsynaptic currents (eEPSCs) were recorded. Urethane (20 mM) decreased by approximately 60% the frequency of GABAergic sPSCs (1.0 +/- 0.2 vs. 0.4 +/- 0.1 Hz) but did not change the frequency, amplitude, or half-width of glutamatergic events or TTX-resistant inhibitory sPSCs [miniature inhibitory postsynaptic currents (IPSCs)]. Miniature IPSCs were measured in the presence of urethane plus 1 mM diazepam (1 mM), and no changes were seen in their amplitude. This suggests that the GABA concentration in the NTS synapses is set at saturating level. We also evaluated the effect of urethane on eEPSCs, and no significant change was observed in the amplitude of N-methyl-d-aspartate [NMDA; 44.2 +/- 11.5 vs. 37.6 +/- 10.6 pA (holding potential = 40 mV)] and non-NMDA currents [204.4 +/- 35.5 vs. 196.6 +/- 31.2 pA (holding potential = -70 mV)]. Current-clamp experiments showed that urethane did not alter the action potential characteristics and passive membrane properties. These data suggest that urethane has an inhibitory effect on GABAergic neurons in the NTS but does not change the spontaneous or evoked excitatory responses.
authors.affiliation: Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Av. Bandeirantes 3900, 14049-900 Ribeirão Preto, SP, Brazil.
authors.forename: Daniela
authors.initials: D
authors.lastname: Accorsi-Mendonça
authors.forename: Ricardo M
authors.initials: RM
authors.lastname: Leão
authors.forename: José F
authors.initials: JF
authors.lastname: Aguiar
authors.forename: Wamberto A
authors.initials: WA
authors.lastname: Varanda
authors.forename: Benedito H
authors.initials: BH
authors.lastname: Machado
mesh_terms: D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D001933:Brain Stem / Q000187:drug effects*; D003975:Diazepam / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D006993:Hypnotics and Sedatives / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors; D017552:Solitary Nucleus / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects*; D013779:Tetrodotoxin / Q000494:pharmacology; D014520:Urethane / Q000494:pharmacology*; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
chemical_list: D018686:Anesthetics, Intravenous; D000779:Anesthetics, Local; D006993:Hypnotics and Sedatives; D011810:Quinoxalines; D016194:Receptors, N-Methyl-D-Aspartate; D014520:Urethane; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; C056723:FG 9041; D003975:Diazepam