6-cyano-7-nitroquinoxaline-2-3-dione and anatoxin-a

In this work, the involvement of ionotropic glutamatergic receptors and nitric oxide on striatal dopamine release induced by anatoxin-a was investigated in conscious and freely-moving rats. To study the participation of glutamatergic receptors, the effects of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptors antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and N-methyl-D-aspartate (NMDA) receptor antagonists, dizocilpine (MK-801) and d(-)-2-amino-5-phosphonopentanoic acid (APV), were examined. The perfusion of 3.5 mM anatoxin-a increased the extracellular dopamine levels to 701% relative to the basal. When CNQX was administered with 3.5 mM anatoxin-a, the increase of dopamine levels was 29% smaller than that observed with anatoxin-a alone. When MK-801 and APV were administered, the effect of anatoxin-a was attenuated 26% and 25% respectively in terms of that observed with anatoxin-a alone. And with CNQX plus MK-801, the effect of anatoxin-a was 53% inhibited in terms of the effect of anatoxin-a alone. These results suggest that the striatal dopamine release induced by anatoxin-a is partly mediated by activation of both ionotropic glutamatergic receptors. Since the neuronal form of nitric oxide synthase (nNOS) produces nitric oxide (NO) primarily in response to activation of NMDA receptors, it was tested if NO could play any role in the effect of anatoxin-a. Treatment with NOS inhibitors, L-nitro-arginine methyl ester (L-NAME) and d(-)-2-amino-5-phosphonopentanoic acid (7-NI), induced decreased anatoxin-a effects of 22% and 26% respectively. In conclusion, the present in vivo results demonstrate that anatoxin-a induced an indirect activation of ionotropic glutamatergic receptors (NMDA and AMPA/kainite receptors), which stimulate striatal dopamine release. On the other hand, activation of NMDA receptors may elicit NO increased levels enhancing dopamine release.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Corpus Striatum; Cyanobacteria Toxins; Dizocilpine Maleate; Dopamine; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Female; Indazoles; Microcystins; Microdialysis; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Tropanes

1. Nicotinic effects on glycine release were investigated in slices of lumbar spinal cord using conventional whole-cell recordings. In most of the substantia gelatinosa (SG) neurons tested, nicotine increased the frequency of the glycinergic spontaneous miniature inhibitory postsynaptic currents (mIPSCs). In a smaller proportion, nicotine evoked not only this same presynaptic response but also a postsynaptic response. 2. Nicotinic facilitation of glycinergic mIPSCs was investigated in mechanically dissociated SG neurons using nystatin-perforated patch recordings. Nicotine (3 x 10(-6) to 10(-5) M) reversibly enhanced the frequency of glycinergic mIPSCs without altering their amplitudes, thus indicating that nicotine facilitates glycine release through a presynaptic mechanism. 3. Choline, a selective alpha7 subunit of nicotinic acetylcholine receptor (nAChR) agonist, had no effect on the mIPSC frequency while anatoxin A, a broad-spectrum agonist of nAChR, facilitated the mIPSC frequency. 4. alpha-Bungarotoxin, a selective alpha7 subunit antagonist, failed to block the nicotinic facilitatory action. Mecamylamine, a broad-spectrum nicotinic antagonist, reversibly inhibited nicotinic action. Dihydro-beta-erythroidine, a selective antagonist of nAChRs containing alpha4-beta2 subunits, completely blocked nicotinic action. 5. Ca(2+)-free but not Cd(2+)-containing bath solutions blocked nicotinic actions. 6. We therefore conclude that nicotine facilitates glycine release in the substantia gelatinosa of the spinal dorsal horn via specific nAChRs containing alpha4-beta2 subunits. This action on a subset of presynaptic nAChRs may underlie nicotine's modulation of noxious signal transmission and provide a cellular mechanism for the analgesic function of nicotine.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; alpha7 Nicotinic Acetylcholine Receptor; Anesthetics, Local; Animals; Bacterial Toxins; Bicuculline; Bungarotoxins; Calcium; Calcium Channels; Choline; Cyanobacteria Toxins; Dihydro-beta-Erythroidine; Excitatory Amino Acid Antagonists; GABA Antagonists; gamma-Aminobutyric Acid; Glycine; Marine Toxins; Mecamylamine; Microcystins; Nerve Endings; Neural Inhibition; Nicotine; Nicotinic Agonists; Nicotinic Antagonists; Nootropic Agents; Organ Culture Techniques; Patch-Clamp Techniques; Rats; Rats, Wistar; Receptors, Nicotinic; Substantia Gelatinosa; Tetrodotoxin; Tropanes; Valine