dizocilpine-maleate and Poisoning

The present study investigated the effect of MK-801, an N-methyl-D-aspartate antagonist, on the convulsant lethal action of cypermethrin administered centrally or peripherally. Cypermethrin produced severe convulsions and death in a dose-dependent manner. MK-801 (0.5, 1 and 2 mg kg-1, intraperitoneally) significantly increased the onset time of convulsions and decreased the mortality in the peripherally treated cypermethrin group. MK-801 (1.0 and 2.0 mg kg-1) attenuated the convulsant action of cypermethrin (50 micrograms, intracerebroventricularly) significantly. Survival rate was also increased significantly. However, MK-801 (0.5 mg kg-1) did not produce any significant protective effect against centrally administered cypermethrin. These results suggest excitatory amino acids to be a target for pyrethroid-induced neurotoxicity.

Topics: Animals; Dizocilpine Maleate; Injections, Intraperitoneal; Injections, Intraventricular; Insecticides; Male; Mice; Poisoning; Pyrethrins; Rats; Rats, Inbred Strains

Exposure to high doses of organophosphorus nerve agents such as soman, even with carbamate pretreatment, produces a variety of toxic cholinergic signs, including secretions, convulsions and death. Evidence suggests that soman-induced convulsions may be associated with postexposure brain neuropathology. The purpose of this study was to investigate the pharmacologic mechanism of action of soman-induced convulsions and of anticonvulsant drugs. Various classes of compounds were evaluated for their efficacy in preventing soman-induced convulsions in rats pretreated with the oxime HI-6 to increase survival time, along with various doses of the test compounds (IM) either in the absence or presence of atropine sulfate (16 mg/kg, IM) 30 minutes prior to a soman challenge dose (180 micrograms/kg, SC; equivalent to 1.6 x LD50) that produced 100% convulsions. Without atropine sulfate, only tertiary anticholinergics (scopolamine, trihexyphenidyl, biperiden, benactyzine, benztropine, azaprophen and aprophen), caramiphen, carbetapentane and MK-801 were effective anticonvulsants. In the presence of atropine sulfate, the benzodiazepines (diazepam, midazolam, clonazepam, loprazolam and alprazolam), mecamylamine, flunarizine, diphenylhydantoin, clonidine, CGS 19755 and Organon 6370 studied were effective. We have examined the possibility that diazepam may exert some of its anticonvulsant effects through cholinergic mechanisms and found that a reduced release of ACh into synapses after diazepam and atropine treatment may account for diazepam's anticonvulsant activity against soman. We also found that at anticonvulsant doses biperiden and trihexyphenidyl each significantly reversed the effects of soman on striatal levels of DOPAC and HVA, the metabolites of dopamine, and have concluded that in addition to actions on muscarinic receptors, the anticonvulsant effects of these anticholinergics in soman poisoning may be partially related to their actions on the striatal dopaminergic system. These findings allow us to postulate that central muscarinic cholinergic mechanisms are primarily involved in eliciting the convulsions following exposure to soman and that subsequent recruitment of other excitatory neurotransmitter systems and loss of inhibitory control may be responsible for sustaining the convulsions and for producing the subsequent brain damage. Future studies to confirm these neuropharmacological mechanisms are proposed.

Topics: Acetylcholine; Animals; Anti-Anxiety Agents; Anticonvulsants; Antidotes; Atropine; Brain Chemistry; Choline; Diazepam; Disease Models, Animal; Dizocilpine Maleate; Gas Chromatography-Mass Spectrometry; Male; Oximes; Parasympatholytics; Poisoning; Pyridinium Compounds; Rats; Rats, Inbred Strains; Receptors, Neurotransmitter; Seizures; Soman