dizocilpine-maleate and 4-methylglutamic-acid

1. Ingestion of a poisonous mushroom Clitocybe acromelalga is known to cause severe tactile pain (allodynia) in the extremities for a month and acromelic acid (ACRO), a kainate analogue isolated from the mushroom, produces selective damage of interneurons of the rat lower spinal cord when injected either systemically or intrathecally. Since ACRO has two isomers, ACRO-A and ACRO-B, here we examined their acute and late effects on induction of allodynia. 2. Intrathecal administration of ACRO-A and ACRO-B provoked marked allodynia by the first stimulus 5 min after injection, which lasted over the 50-min experimental period. Dose-dependency of the acute effect of ACRO-A on induction of allodynia showed a bell-shaped pattern from 50 ag x kg(-1) to 0.5 pg x kg(-1) and the maximum effect was observed at 50 fg x kg(-1). On the other hand, ACRO-B induced allodynia in a dose-dependent manner from 50 pg x kg(-1) to 50 ng x kg(-1). 3. N-methyl-d-aspartate (NMDA) receptor antagonists and Joro spider toxin, a Ca(2+)-permeable AMPA receptor antagonist, inhibited the allodynia induced by ACRO-A, but not by ACRO-B. However, other AMPA/kainate antagonists did not affect the allodynia induced by ACRO. 4. Whereas no neuronal damage was observed in the spinal cord in ACRO-A-treated mice, induction of allodynia by ACRO-A (50 fg x kg(-1)) and ACRO-B (50 ng x kg(-1)) was selectively lost 1 week after i.t. injection of a sublethal dose of ACRO-A (50 ng x kg(-1)) or ACRO-B (250 ng x kg(-1)). Higher doses of ACRO-A, however, could evoke allodynia dose-dependently from 50 pg x kg(-1) to 500 ng x kg(-1) in the ACRO-A-treated mice. The allodynia induced by ACRO-A (500 ng x kg(-1)) was not inhibited by Joro spider toxin or NMDA receptor antagonists. These properties of the late allodynia induced by ACRO-A were quite similar to those of the acute allodynia induced by ACRO-B. 5. ACRO-A could increase [Ca(2+)](i) in the deeper laminae, rather than in the superficial laminae, of the spinal cord. This increase was not blocked by the AMPA-preferring antagonist GYKI52466 and Joro spider toxin. 6. Taken together, these results demonstrate the stereospecificity of ACRO for the induction of allodynia and suggest the presence of a receptor specific to ACRO.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Basidiomycota; Benzodiazepines; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Glutamates; Heterocyclic Compounds; Indoles; Injections, Spinal; Japan; Kainic Acid; Lumbosacral Region; Male; Mice; Mice, Inbred Strains; Mushroom Poisoning; Oximes; Pain; Quinoxalines; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Spider Venoms; Spinal Cord; Stereoisomerism; Structure-Activity Relationship; Time Factors

We have used whole-cell recordings and rapid agonist applications to characterize the physiological properties of kainate receptors expressed by rat hippocampal neurons in dissociated cell culture. Activation of NMDA and AMPA receptors was prevented by inclusion of the noncompetitive antagonists MK-801 (2 microM) and GYKI 53655 (100 microM), respectively. In the presence of these inhibitors, both kainate (EC50 = 23 microM) and glutamate (EC50 = 310 microM) evoked desensitizing currents. Maximal peak currents for kainate with GYKI 53655 were 15 +/- 3% as large as in control solutions without GYKI. In contrast to currents mediated by AMPA receptors, kainate currents recorded in GYKI were blocked potently by lanthanum (IC50 = 2 microM) and were desensitized by 1 microM 2S,4R-4-methylglutamate (SYM 2081). Coapplication of either 5 microM AMPA or 500 microM aspartate had little effect on responses to kainate, although AMPA alone elicited current at 1 mM. In most cells, the currents evoked by kainate, glutamate, and SYM 2081 varied linearly with membrane potential and reversed near 0 mV. Kainate elicited substantial current at steady state (approximately 30% of peak), whereas responses to glutamate and SYM 2081 desensitized almost completely within 0.2-2 sec. Inhibition produced by a 10 sec desensitizing prepulse was half-maximal at 0.22 microM for SYM 2081 and 13 microM for glutamate. Recovery from desensitization to kainate and glutamate was >80% complete within 60 sec but was three- to fourfold slower after exposure to SYM 2081. Exposure to Concanavalin A blocked desensitization of the currents but also reduced the peak current amplitudes. Collectively, these results confirm that kainate-preferring receptors underlie the currents evoked by kainate, glutamate, or SYM-2081 in the presence of GYKI 53655; they are not mediated by electrogenic transport or by AMPA-preferring receptors that are insensitive to GYKI. In contrast to previous work on embryonic hippocampal neurons, our results show that the properties of kainate receptors expressed by cells from older animals are distinct from those displayed by homomeric assemblies of the GluR6 subunit.

Topics: Animals; Animals, Newborn; Benzodiazepines; Cells, Cultured; Dizocilpine Maleate; Evoked Potentials; Excitatory Amino Acid Antagonists; Glutamates; Glutamic Acid; Hippocampus; Kainic Acid; Lanthanum; Membrane Potentials; Neurons; Rats; Receptors, AMPA; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate