Comparison of potencies of 5-HT3 receptor antagonists at inhibiting aversive behavior to illumination and the von Bezold-Jarisch reflex in the mouse.
The inhibitory effects of ondansetron and R and S zacopride on aversive behavior to light and the von Bezold-Jarisch reflex have been compared in mouse. The potencies (ID50, microgram/kg i.v.) of compounds at inhibiting the von Bezold-Jarisch reflex, elicited by 2-methyl-5-HT (mouse 100 micrograms/kg, i.v.; rat 10-80 micrograms/kg i.v.) were: S zacopride (0.02), granisetron (0.17), R zacopride (0.30) ondansetron (3.16). A similar rank order of ID50 values was observed in rat, i.e. S zacopride (0.02), granisetron (0.36), R zacopride (0.25) and ondansetron (2.65). These data suggest that the activity of compounds at 5-HT3 receptors mediating this effect was similar in both mouse and rat. In mouse behavioral studies, ondansetron and R and S zacopride potently inhibited aversive behavior to light (0.0003-30 micrograms/kg, p.o.), when the amount of time spent in the dark and locomotor activity were measured. Thus, at 0.3 ng/kg, the mean percentage time spent in the dark significantly decreased from 84 to 72, for both R and S zacopride, respectively. The maximal effects of these compounds were modest in comparison to the 'anxiolytic' effects of diazepam (0.3-1.4 mg/kg, i.p.; at 0.3 mg/kg the mean percentage time spent in the dark significantly decreased from 84 to 36) or chlordiazepoxide (3-40 mg/kg, i.p.; at 3 mg/kg, the mean percentage time spent in the dark significantly decreased from 85 to 40). The doses of the 5-HT3 antagonists were approx 1000-fold lower than those effective inhibitory doses determined in the von Bezold-Jarisch reflex studies, in either mouse or rat.(ABSTRACT TRUNCATED AT 250 WORDS)
Eglen
R M
RM
Institute of Pharmacology, Syntex Discovery Research, Palo Alto, CA 94304.
Lee
C H
CH
Khabbaz
M
M
Fontana
D J
DJ
Daniels
S
S
Kilfoil
T
T
Wong
E H
EH
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D001549:Benzamides / Q000494:pharmacology; D001643:Bridged Bicyclo Compounds / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic; D004305:Dose-Response Relationship, Drug; D017829:Granisetron / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects*; D008029:Lighting; D051379:Mice; D009043:Motor Activity / Q000187:drug effects; D017294:Ondansetron / Q000494:pharmacology; D012018:Reflex / Q000187:drug effects*; D012702:Serotonin Antagonists / Q000494:pharmacology*; D013237:Stereoisomerism
D001549:Benzamides; D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D017829:Granisetron; D017294:Ondansetron; D012702:Serotonin Antagonists; C055971:zacopride