Modulation of synaptic transmission and excitation-contraction coupling in the opener muscle of the crayfish, Astacus leptodactylus, by 5-hydroxytryptamine and octopamine.
The modulatory actions of 5-hydroxytryptamine (5-HT) and octopamine (OA) were investigated in the opener nerve-muscle preparation of the crayfish, Astacus leptodactylus. Membrane resistance and resting potential were unaltered by 5-HT and OA at concentrations up to 2.5 X 10(-5) M; but EPSP-amplitudes were increased, up to 3-fold by OA and up to 18-fold by 5-HT. The lowest effective concentration was 2.5 X 10(-9) M; a maximal effect was produced at 2.5 X 10(-6) M. The effect was reversible only after prolonged washing. The enhancement of EPSPs by 5-HT or OA is due to an increased amplitude of the synaptic current; the current duration is not altered. The facilitation ratio (ratio of amplitudes of a pair of EPSPs) is not significantly affected by 5-HT or OA despite the often enormous increase of the absolute EPSP-amplitudes. The modulatory action also affects the excitation-contraction (e-c) coupling process: the effectiveness of e-c coupling was increased 7.4-fold by 5-HT (2.5 X 10(-6) M) and 18.7-fold by OA (5 X 10(-6) M). The threshold potential of e-c coupling was not affected.
D000818:Animals; D003400:Astacoidea; D001369:Axons / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009132:Muscles / Q000294:innervation; D009655:Octopamine / Q000494:pharmacology*; D012701:Serotonin / Q000494:pharmacology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects*
D009655:Octopamine; D012701:Serotonin