Neuropharmacology Poster Session
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Introduction
Many phenolic polyamines naturally found in plants, especially the Solanceae such as tomatoes, show similarities to spider and wasp toxins and may be partially responsible for pest resistance. The aim of the present study was to determine whether or not plant-derived phenolic polyamines act like spider and wasp toxins such as Nephila maculata (NSTX-3), which is known to block glutamate receptors in arthropod muscle1. We studied the effects of N1- coumaroyl spermidine (N1CS), on the synapses of the deep extensor muscles of Procambarus clarkii . Crayfish were used because their glutamate receptors are sensitive to spider toxins 2.
Fig.1:N1CS and NSTX-3 are structurally similar.
Materials and Methods
EPSPs were elicited in the lateral abdominal extensor muscle of Procambarus clarkii and were recorded intracellularly as in3. Chemicals were applied to a static bath in small volumes of various concentrations. Inert dye (fast green) was used to assess the actual local concentration of N1CS, by removing a small amount of bathing solution prior to washout and analyzing the sample in a spectrophotometer. Temperature was maintained between 10 and 11.5 degrees Celsius. EPSPs were acquired and analyzed for changes in amplitude on a computer.
Fig.2:Diagram of experimental preparation as previously done 3.
In other experiments, glutamate-induced potentials were elicited in the lateral abdominal extensor muscle by iontophoretic application of glutamate and chemicals were applied to the static bath.
Results
Fig.3:EPSPs are attenuated in a dose dependent manner. EC50 is approximately 0.08mM.
Fig.4:Both N1CS (0.03mM) and NSTX-3 (0.03mM) suppressed L-glu induced potentials. However, N1CS washed out and NSTX-3 did not.
Fig 5: Spermidine (0.03mM) had no effect on L-glu induced potentials.
Discussion and Conclusion
N1CS blocks EPSPs in a dose-dependant manner.
N1CS like NSTX-3 acts postsynaptically on glutamate receptors. Unlike NSTX-3, the effect of N1CS is reversible.
The phenyl group is required for block of glutamate receptors. EC50 for suppression of EPSPs by N1CS is 100 times higher than the published EC50 for suppression of lobster EPSPs by Nephila spider toxins 4.
References
- Jackson, H. and Usherwood, PNR (1988) Spider toxins as tools for dissecting elements of excitory amino acid transmission. TINS, 11:278-283.
- Araque, A, Ferreira, SL, and Buno, W (1992) Glutamatergic postsynaptic block by Pamphobeteus spider venoms in crayfish. Brain Research, 571 :109-114.
- Mercier, AJ, Scheibe, M, and Atwood, HL (1990) Pericardial peptides enhance synaptic transmission in phasic extensor muscles of crayfish. Neurosci.Lett. 111:92-98
- Abe, T, Kawai, N, and Miwa, A (1983) Effects of Spider Toxin on the Glutaminergic Synapse of Lobster Muscle. J.Physiol.,229:243-252
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