Abstract
The dose-effect relationships of two tryptamine antagonists, methysergide and cyproheptadine, on lever-pressing behavior of rats were determined. A concurrent fixedinterval 1 minute water, fixed-ratio 5 electric shock punishment schedule was used. Since cyproheptadine shows antihistaminic as well as antimuscarinic actions, dose-response curves for atropine and the three antihistaminic drugs, diphenhydramine, pyrilamine and HS-592, on punished responding were determined. The effects of selected doses of the minor tranquilizers, chlordiazepoxide and pentobarbital on punished performance were also measured. Appropriate doses of methysergide, cyproheptadine, chlordiazepoxide, pentobarbital and atropine increased response rates suppressed by punishment. The mean response rate was maximally increased to 218% of control by 5.6 mg/kg of cyproheptadine, as compared to 163% for methysergide (3 mg/kg) and the 248% rate increase caused by 5.6 mg/kg of clordiazepoxide in the same animal group. The dose of 10 mg/kg of pentobarbital increased the mean response rate to 192% of control in this group of rats and 212% in another. Small, but measurable, increases in mean response rate (maximum 136% of control) followed the administration of 1 to 10 mg/kg of atropine. In contrast, the three antihistaminics caused only rate-decreasing effects on punished responding. These results suggest that tryptamine antagonists increase response rates suppressed by punishment by interfering with a tryptaminergic mechanism in brain involved in behavioral inhibition.
Footnotes
- Received September 11, 1973.
- Accepted January 7, 1974.
- © 1974 by The Williams & Wilkins Co.
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|