Effects of repeated doses of azapirones on rat brain 5-HT 1A receptors and plasma corticosterone levels

Abstract

Chronic buspirone or ipsapirone (3 mg/kg, twice daily) administration to rats for 10 days decreased the sensitivity of inhibition of single-unit activity of serotonergic dorsal raphe neurons to a challenge by each drug. The ED 50 for buspirone was increased from 0.1 mg/kg to 1.8 mg/kg, and the ED 50 for ipsapirone was increased from 0.7 mg/kg to 1.2 mg/kg. The binding properties ( K d and B max) of [ 3H]8-OHDPAT to membranes of cerebral cortex and hippocampus were unaffected by chronic administration of either buspirone or ipsapirone. Chronic buspirone or ipsapirone administration increased the tolerance of the hypothalamic-pituitary-adrenal axis (HPAA) following a challenge by each drug. The ED 50 for elevation of plasma corticosterone levels was increased from 4.0 mg/kg to 7.6 mg/ kg for buspirone and 6.2 mg/kg to 8.0 mg/kg for ipsapirone. Chronic buspirone administration decreased the basal activity of the HPAA by 63%. Chronic buspirone administration did not alter the plasma corticosterone response of the HPAA to a 1-min episode of rotational stress. (Mg 2+)-ATPase, (Na + + K +)-ATPase, (Ca 2++Mg 2+)-ATPase and calmodulin-stimulated (Ca 2++Mg 2+)-ATPase activities of erythrocyte plasma membrane were unaffected by either chronic or acute buspirone treatment, or by the addition of the drug to the in vitro assay systems.