Selective blockade of serotonin(2C/2B) receptors enhances dopamine release in the rat nucleus accumbens

The effects of mesulergine (100 and 200 μg/kg s.c.), SB 206553 (1 and 2.5 mg/kg i.p.), RP 62203 (2.5 and 4 mg/kg i.p.) and ritanserin (630 μg/kg i.p.) were studied on the extracellular concentration of dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens of chloral hydrate-anesthetized rats, using intracerebral microdialysis. Mesulergine, a non selective serotonin(2C/2B/2A) (5-HT(2C/2B/2A)) receptor antagonist, significantly increased DA release, which reached a peak level (+ 20%) 60 min after drug injection and slowly returned back to baseline values. Mesulergine also caused a dose-dependent increase in DOPAC outflow. Pretreatment with mesulergine (200 μg/kg) did not change the inhibition of DA release induced by apomorphine (100 μg/kg), whereas it prevented the reduction of DOPAC outflow induced by apomorphine (100 μg/kg). Administration of SB 206553, a selective blocker of 5-HT(2C/2B) receptors, dose-dependently increased DA outflow. The dose of 2.5 mg/kg SB 206553 caused a linear increase of DA output which reached a peak (+ 75%) 40 min after injection, while 1 mg/kg induced a more gradual increase of DA release which peaked (+ 54%) 60 min after administration of the drug. Treatment with RP 62203, a selective 5- HT(2A) receptor antagonist, did not produce any significant effect on DA outflow. Administration of ritanserin, a mixed 5-HT(2A/2C) receptor antagonist, did not cause any significant change of DA and DOPAC outflow. Taken together, these data indicate that selective blockade of 5-HT(2C/2B) receptor subtypes increases DA release in the rat nucleus accumbens.