Serotonergic mediation of the anxiolytic effect of intracerebrally injected propranolol measured in the elevated plus-made

ABSTRACT

the effect of intracerebrally injected propranolol was measured in the elevated plus-maze, an animal model of anxiety. Microinjection of 10 nmol of propranolol into the dorsal midbrain central gray of the perventage of open arm entries, without affecting the total number of arm entries.This selective anxiolytic effect of propranolol was antagonized by 10 nmol of ritanserin, also injected into the dorsal midbrain. The same dose of ritanserin, given alone, did not affect the percentage of open arn entries, thought it tended to decrease the total number of entries, an indication of unspecific behavioral depression. Since propranolol is a sterospecific antagonist of presynaptic serotpnin (5-HT) antoreceptors and ritanserin is a selective blocker of type 2 5-HT recptors, the present results suggest that the anxiolytic action of propranolol in the midbrain central gray is due to release of endogenous 5-HT acting upon 5-HT2 receptors