title: The selective serotonin reuptake inhibitor citalopram induces the storage of serotonin in catecholaminergic terminals.
abstract: We investigated whether selective inhibition of serotonin (5-hydroxytryptamine; 5-HT) transporter with citalopram leads to accumulation of 5-HT in catecholaminergic neurons. In the rabbit olfactory tubercle, citalopram (1-10 microM) inhibited [(3)H]5-HT uptake; however, the maximal degree of inhibition achieved was 70%. Addition of nomifensine (1-10 microM) was required for complete inhibition of [(3)H]5-HT uptake. In slices labeled with 0.1 microM [(3)H]5-HT, cold 5-HT (0.03-1 microM) induced a large increase in the efflux (release) of stored [(3)H]5-HT, an effect blocked by coperfusion with 1 microM citalopram. Similar concentrations (0.03-1 microM) of norepinephrine (NE) or dopamine (DA) failed to release [(3)H]5-HT. When labeling with 0.1 microM [(3)H]5-HT was carried out in the presence of citalopram, 1) low concentrations of 5-HT failed to release [(3)H]5-HT; 2) DA and NE were more potent and effective in releasing [(3)H]5-HT than in control slices; 3) coperfusion of NE, DA, or 5-HT with citalopram enhanced the release of [(3)H]5-HT induced by the catecholamines but not by 5-HT; and 4) coperfusion of NE or DA with nomifensine antagonized NE- and DA-evoked [(3)H]5-HT release, with a greater effect on NE than on DA. These results suggest that in the rabbit olfactory tubercle, where there is coexistence of 5-HT, NE, and DA neurons, inhibition of the 5-HT transporter led to accumulation of 5-HT in catecholaminergic terminals. Thus, during treatment with selective serotonin uptake inhibitors (SSRIs), 5-HT may be stored in catecholaminergic neurons acting as a false neurotransmitter and/or affecting the disposition of DA and/or NE. Transmitter relocation may be involved in the antidepressant action of SSRIs.
authors.affiliation: Pharmacology Section, Instituto de Investigaciones Clinicas, School of Medicine, University of Zulia, Maracaibo, Venezuela.
authors.forename: Heberto
authors.initials: H
authors.lastname: Suarez-Roca
authors.forename: Luigi X
authors.initials: LX
authors.lastname: Cubeddu
mesh_terms: D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D002395:Catecholamines / Q000502:physiology*; D015283:Citalopram / Q000494:pharmacology*; D004298:Dopamine / Q000378:metabolism; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism*; D009627:Nomifensine / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism; D009830:Olfactory Bulb / Q000187:drug effects / Q000378:metabolism; D011817:Rabbits; D012701:Serotonin / Q000378:metabolism* / Q000494:pharmacology; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*
chemical_list: D002395:Catecholamines; D015283:Citalopram; D004298:Dopamine; D018765:Dopamine Uptake Inhibitors; D009627:Nomifensine; D009638:Norepinephrine; D012701:Serotonin; D017367:Selective Serotonin Reuptake Inhibitors