Presynaptic facilitation by the new nootropic drug nebracetam, of ganglionic muscarinic transmission in the dog cardiac sympathetic ganglion.
Effects of nebracetam (4-aminomethyl-1-benzylpyrrolidine-2-one hemifumarate, WEB 1881 FU, CAS 118607-07-1), a new nootropic drug, on impulse transmission in the cardiac sympathetic ganglia were studied in spinal dogs by monitoring heart rate as an indicator of the ganglionic function. The ganglionic stimulants were given directly into the cardiac sympathetic ganglia through the right subclavian artery (i.a.). Nebracetam, 5 mg/kg, i.v. caused a slight and temporal increase in heart rate. After nebracetam, the frequency-response curves of heart rate for preganglionic stellate stimulation (0.25-4 Hz) were not altered in the untreated and atropine-pretreated animals, but the curves (2.5-40 Hz) were shifted to the left in the hexamethonium-pretreated animals. The enhancement of ganglionic muscarinic transmission was dose-dependent on nebracetam i.v. at doses ranging from 0.5 to 15 mg/kg, with a maximal effect at 5 mg/kg. This enhanced muscarinic transmission by nebracetam was almost abolished after subsequent administration of pirenzepine 0.5 mg/kg i.v. The enhancement in the muscarinic transmission by nebracetam was also eliminated after depletion of acetylcholine at preganglionic sites caused by treatment with hemicholinium-3 in combination with preganglionic stimulation. Furthermore, nebracetam failed to affect dose-dependent post-ganglionic stimulation by McN-A-343 (1-32 micrograms), 1,1-dimethyl-4-phenylpiperazinium (1-32 micrograms) and angiotensin II (0.1 and 0.2 micrograms) administered i.a. directly to the ganglia. These results suggest that nebracetam facilitates the ganglionic muscarinic transmission through acting on presynaptic sites.
Kushiku
K
K
Department of Pharmacology, School of Medicine, Fukuoka University, Japan.
Ohjimi
H
H
Yamada
H
H
Furukawa
T
T
D008455:(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D004246:Dimethylphenylpiperazinium Iodide / Q000494:pharmacology; D004285:Dogs; D004558:Electric Stimulation; D005260:Female; D005728:Ganglia, Sympathetic / Q000187:drug effects*; D006321:Heart / Q000294:innervation; D006339:Heart Rate / Q000187:drug effects; D006426:Hemicholinium 3 / Q000494:pharmacology; D008297:Male; D010275:Parasympathetic Nervous System / Q000187:drug effects*; D010277:Parasympathomimetics / Q000494:pharmacology*; D011619:Psychotropic Drugs / Q000494:pharmacology*; D011760:Pyrrolidinones / Q000494:pharmacology*; D009435:Synaptic Transmission / Q000187:drug effects*
D010277:Parasympathomimetics; D011619:Psychotropic Drugs; D011760:Pyrrolidinones; D000804:Angiotensin II; D006426:Hemicholinium 3; D004246:Dimethylphenylpiperazinium Iodide; D008455:(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride; C056640:nebracetam