Chronic treatment with fluoxetine decreases cerebral metabolic responses to the 5-HT1A agonist 8-hydroxy-2(di-N-propylamino)tetralin and increases those to the 5-HT2A/2C agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane and to the dopaminergic agonist apomorphine.
Fluoxetine is a selective serotonin (5-HT) reuptake inhibitor that, when given chronically, alters different neurotransmitter systems. To assess functional changes occurring in the 5-HT and dopaminergic systems, we investigated the effects of 5-HT(1A) agonist 8-hydroxy-2(di-N-propylamino)tetralin (8-OH-DPAT), of the 5-HT(2A/2C) agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and of the dopamine D(1/2) agonist apomorphine (APO) on behavior and on regional cerebral metabolic rates for glucose (rCMRglc) in rats pretreated for 3weeks with saline or fluoxetine (8mg/kg/day). Behavioral effects were assessed for 8-OH-DPAT by scoring the 5-HT syndrome, for DOI by counting head shakes and for APO with an activity monitor. rCMRglc were measured with quantitative autoradiographic [(14)C]2-deoxyglucose technique in 60 brain regions at 10min after acute administration of 8-OH-DPAT 1mg/kg, at 30min after DOI 5mg/kg or at 10min after APO 1mg/kg. Chronic fluoxetine did not alter the 5-HT syndrome by 8-OH-DPAT, decreased head shakes by DOI and enhanced hyperlocomotion by APO. 8-OH-DPAT produced rCMRglc increases in sensorimotor regions that were unaffected by fluoxetine pretreatment and diffuse metabolic decrements that were attenuated by fluoxetine in limbic and raphe areas (17% and 4% mean decreases, respectively, in saline control and fluoxetine-pretreated rats). DOI produced widespread rCMRglc declines that were intensified by fluoxetine (14% and 20% decreases, in control and fluoxetine rats). APO caused rCMRglc increases in 22 brain regions that were potentiated by fluoxetine in dopaminergic motor areas (10% and 25% increases, in control and fluoxetine rats). In conclusion, fluoxetine enhances 5-HT neurotransmission by blunting responsivity of 5-HT(1A) autoreceptors and increasing that of 5-HT(2A/2C) postsynaptic receptors and enhances dopaminergic D(1/2) receptor neurotransmission.
Freo
Ulderico
U
Dipartimento di Farmacologia e Anestesiologia, Università di Padova, I-35121 Padova, Italy. ulderico.freo@unipd.it
Merico
Antonio
A
Ermani
Mario
M
Ori
Carlo
C
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000494:pharmacology; D000662:Amphetamines / Q000819:agonists / Q000494:pharmacology; D000818:Animals; D001058:Apomorphine / Q000494:pharmacology*; D001921:Brain / Q000187:drug effects* / Q000378:metabolism*; D018491:Dopamine Agonists / Q000494:pharmacology*; D015536:Down-Regulation / Q000187:drug effects*; D004334:Drug Administration Schedule; D005473:Fluoxetine / Q000494:pharmacology*; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344; D044282:Receptor, Serotonin, 5-HT1A / Q000378:metabolism; D044402:Receptor, Serotonin, 5-HT2A / Q000378:metabolism; D011985:Receptors, Serotonin / Q000378:metabolism; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects*
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D000662:Amphetamines; D001058:Apomorphine; D018491:Dopamine Agonists; D005473:Fluoxetine; D044282:Receptor, Serotonin, 5-HT1A; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin; D017366:Serotonin Receptor Agonists; D017367:Selective Serotonin Reuptake Inhibitors; C015952:4-iodo-2,5-dimethoxyphenylisopropylamine