The effect of tryptamine on excitatory postsynaptic potentials at a crayfish neuromuscular junction

R. B. Rodgers, J. S. Staser, K. Si, R. N. Friedman

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Abstract

Purpose: Several substances have been shown to potentiate the short-term-facilitated excitatory junctional potentials (EJPs) at neuromuscular junctions (NMJs) of walking limb dactyl opener muscles of the crayfish, Procambarus clarkii and simulans. Tryptamine (Trp) has been shown to have such an effect on NMJs of the stretcher muscle in the carpopodite of walking limbs of the lobster Homarus americanus. The current study was undertaken to determine whether Trp, a structural analog of serotonin and several psychotomimetic substances (e.g., LSD, DMT, bufotenin), affects EJPs in the crayfish model and to characterize the nature of its effect. Materials and Methods: The excitatory axon in the meropodite of the first and second walking limbs and the dactyl opener muscle of the crayfish were exposed. The limb was bathed sequentially in Van Harreveld's (Van H) solution, and in 10μM, 50μM, 100μM, 500μM, 1000μM, and 2000μM solutions of Trp in Van H. The pH of the solution was adjusted to 7.2 ± 0.1. A 30 Hz stimulus was applied to the excitatory axon for 10 sec prior to data collection, and EJPs were recorded intracellularly for 10 sec from a superficial opener muscle fiber via a 3.0 M KCl glass micro-electrode. Results: In all of the experiments the EJP amplitude was enhanced, and this effect continued to increase through the range of studied concentrations without a plateau or an inhibitory effect at the higher concentrations. These results were qualitatively reproducible in experiments with twelve different limbs. The effect was reversible following washing of the preparation with Van H for 1 to 4 repetitions of three complete exchanges of the bath. Post-wash potentiation (pwp), an additional increase in EJP amplitude, was seen upon washing preparations exposed to higher concentrations of Trp (100μM to 2000μM). Conclusions: Trp enhances the EJP in the crayfish model by a mechanism that was not saturable to a concentration of 2000μM. The EJP-enhancing effect of Trp at the crayfish NMJ differs from that in the lobster model, in which EJPs are enhanced at lower and depressed at higher concentrations. Also, while pwp was observed following Trp-induced enhancement in the crayfish NMJ, it was observed only following EJP depression by Trp in the lobster preparation. These observations are important for selecting preparations for and interpreting results of future studies using invertebrate models to examine excitatory neurotransmission mechanisms.

Original languageEnglish (US)
Pages (from-to)79A
JournalJournal of Investigative Medicine
Volume47
Issue number2
StatePublished - Feb 1999

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ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)

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