dihydropyridines and Tremor

Activation of muscarinic m1 receptors which are coupled to the phosphoinositide (PI) second messenger transduction system is the initial objective of cholinergic replacement therapy in Alzheimer's disease. Thus, we evaluated the ability of the selective muscarinic receptor agonist (SMRA) xanomeline to stimulate in vivo phosphoinositide (PI) hydrolysis and compared it to a number of direct acting muscarinic agonists, two cholinesterase inhibitors and a putative m1 agonist/muscarinic m2 antagonist. Using a radiometric technique, it was determined that administration of xanomeline robustly stimulated in vivo PI hydrolysis and the effect was blocked by muscarinic antagonists, demonstrating mediation by muscarinic receptors. The non-selective muscarinic agonists pilocarpine, oxotremorine, RS-86, S-aceclidine, but not the less active isomer R-aceclidine, also effectively stimulated PI hydrolysis in mice. Amongst the putative m1 agonists, thiopilocarpine, hexylthio-TZTP as well as xanomeline effectively stimulated PI hydrolysis, but milameline, WAL 2014, SKB 202026 and PD 142505 did not significantly alter PI hydrolysis. Furthermore, WAL 2014 and SKB 202026 inhibited agonist-induced PI stimulation, suggesting that they act as antagonists at PI-coupled receptors in vivo. The cholinesterase inhibitors, tacrine and physostigmine, and the mixed muscarinic m1 agonist/m2 antagonist LU25-109 did not activate in vivo PI hydrolysis. Xanomeline, hexylthio-TZTP and thiopilocarpine were relatively free of cholinergic side effects, whereas milameline, WAL 2014 and SKB 202026 produced non-selective effects. Therefore, these data demonstrate that xanomeline selectively activates in vivo PI hydrolysis, consistent with activation of biochemical processes involved in memory and cognition and xanomeline's beneficial clinical effects on cognition in Alzheimers patients.

Topics: Animals; Binding, Competitive; Brain Chemistry; Bridged Bicyclo Compounds, Heterocyclic; Cholinergic Agents; Cholinesterase Inhibitors; Dihydropyridines; Dose-Response Relationship, Drug; Hydrolysis; Hypothermia; Imines; Lithium; Male; Mice; Mice, Inbred Strains; Muscarinic Agonists; Oximes; Parasympathomimetics; Phosphatidylinositols; Physostigmine; Pilocarpine; Pyridines; Quinuclidines; Radioligand Assay; Salivation; Tacrine; Tetrazoles; Thiadiazoles; Tremor

It has previously been shown that dihydropyridine calcium channel antagonists prevent the ethanol withdrawal syndrome and potentiate the acute effects of ethanol and other central depressant drugs. We now report that, in contrast, the benzothiazepine calcium channel antagonist, diltiazem, gave no protection against the behavioural hyperexcitability seen during ethanol withdrawal, when given either acutely, on withdrawal, or chronically, during the ethanol treatment. A significant increase in convulsive behaviour on handling was seen during the withdrawal period when diltiazem was given on cessation of a mild chronic ethanol treatment schedule. Diltiazem decreased the acute general anaesthetic effects of ethanol, and did not appear to potentiate the ataxic action of ethanol. Centrally administered diltiazem did not enhance the hypothermic action of ethanol, but this effect was significantly increased by diltiazem when the calcium channel antagonist was given peripherally. When given alone by the intraperitoneal route, diltiazem decreased spontaneous locomotor activity and lowered body temperature. When the intracerebral route was used for administration of diltiazem, a significantly decrease in body temperature was seen when this compound was given alone, accompanied by a brief hyperexcitability. The interactions between ethanol and diltiazem therefore appear to differ from those seen with other calcium channel antagonists.

Topics: Anesthesia, General; Animals; Ataxia; Behavior, Animal; Body Temperature; Calcium Channel Blockers; Dihydropyridines; Diltiazem; Drug Interactions; Ethanol; Injections, Intravenous; Injections, Intraventricular; Male; Mice; Mice, Inbred Strains; Motor Activity; Postural Balance; Spasm; Substance Withdrawal Syndrome; Tremor

Experiments on male Wistar rats and Icr:Icl mice studied the influence of the novel compound--amino acid-containing 1,4-dihydropyridine derivative glutapyrone (G) on acute generalized seizures, arecoline and nicotine tremor, and 45Ca2+ uptake in brain synaptosomes. It was shown that G produced significant antiepileptic effects on models of acute pentylenetetrazole seizures on rats and mice. Efficiency of antiepileptic effect depended on a dose and method of modeling seizures: it was more effective in case of intravenously pentylenetetrazole-induced seizure tested by clonic and tonic seizure components and death. The results suggest the participation of GABAergic system in realization of antiepileptic effect of G. Glutapyrone did not influence the 45Ca2+ uptake by rat cortical synaptosomes (evoked by a 1-min depdariration with 55 mM K+), this suggests that G lacked calcium antagonist properties characteristic of 1,4-dihydropyridine compounds such as nifedipine, nimodipine. In addition, G does not affect N- and M-cholinergic processes.

Topics: Animals; Anticonvulsants; Arecoline; Calcium; Cerebral Cortex; Dihydropyridines; Drug Evaluation, Preclinical; Epilepsy, Generalized; Glutamates; Male; Mice; Mice, Inbred ICR; Nicotine; Pentylenetetrazole; Rats; Rats, Wistar; Synaptosomes; Tremor