5-nitro-6-7-8-9-tetrahydrobenzo(g)indole-2-3-dione-3-oxime and 2-3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline

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

In an in vitro spinal cord slice preparation whole cell electrophysiological recordings of rat superficial dorsal horn neurons responding differentially to glutamate (Glu) and N-methyl-D-aspartate (NMDA) were investigated systematically for the role of kainate (KA) receptors in modulating their activity. In these neurons, coapplication of Glu and NMDA, as well as application of Glu immediately before NMDA, induced long- and short-lasting depressions of NMDA-induced currents as well as depression of NMDA-receptor-mediated excitatory postsynaptic currents. KA applied before NMDA mimicked Glu-induced attenuating effects. Furthermore, the low-affinity KA receptor antagonist 5-nitro-6,7,8,9- tetrahydrobenzo[G]indole-2,3-dione-3-oxime potentiated Glu-induced NMDA-receptor-mediated currents in neurons responding differentially to Glu and NMDA. These results provide evidence for a novel mechanism, which may relate to classical long-term depression, involving low-affinity KA receptors in long-lasting modulation of NMDA-receptor-mediated currents. This implies a physiological role of KA receptors in long-term modulation of sensory transmission in the superficial dorsal horn of rat spinal cord.

Topics: Action Potentials; Animals; Calcium; Cycloleucine; Electrophysiology; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Ganglia, Spinal; Glutamic Acid; Indoles; Ion Channel Gating; Kainic Acid; Male; N-Methylaspartate; Neurons, Afferent; Neuroprotective Agents; Oximes; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Spinal Cord; Spinal Nerve Roots; Synaptic Transmission

5-Nitro-6,7,8,9-tetrahydrobenzo[G]indole-2,3-dione-3-oxime (NS-102), a new competitive glutamate receptor antagonist displaced binding to non-N-methyl-D-aspartate (non-NMDA) binding sites with no activity at the NMDA and strychnine-insensitive glycine binding sites. Under experimental conditions in which both high- and low-affinity sites were labelled, NS-102 only partially inhibited the binding of [3H]kainate. Studies of NS-102 displacement of high-affinity versus low-affinity [3H]kainate binding showed a high selectivity of NS-102 for the low-affinity [3H]kainate binding site (Ki = 0.6 microM) compared to the high-affinity [3H]kainate binding site (Ki > 10 microM). NS-102 was a relatively weak inhibitor of 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) binding (IC50 = 7.2 microM). NS-102 and related compounds with similar pharmacological profiles may become valuable tools in the characterization of the functional importance of the low-affinity [3H]kainate binding site.

Topics: Animals; Binding, Competitive; Calcium; Calcium Chloride; Cerebral Cortex; Excitatory Amino Acid Antagonists; Indoles; Kainic Acid; Male; Membranes; Molecular Structure; Neuromuscular Depolarizing Agents; Oximes; Quinoxalines; Radioligand Assay; Rats; Rats, Wistar; Tritium