title: Enhancement of cortical extracellular 5-HT by 5-HT1A and 5-HT2C receptor blockade restores the antidepressant-like effect of citalopram in non-responder mice.
abstract: We recently found that the response of DBA/2 mice to SSRIs in the forced swim test (FST) was impaired and they also had a smaller basal and citalopram-stimulated increase in brain extracellular serotonin (5-HT) than 'responder' strains. We employed intracerebral microdialysis, FST and selective antagonists of 5-HT1A and 5-HT2C receptors to investigate whether enhancing the increase in extracellular 5-HT reinstated the anti-immobility effect of citalopram in the FST. WAY 100635 (0.3 mg/kg s.c.) or SB 242084 (1 mg/kg s.c.), respectively a selective 5-HT1A and 5-HT2C receptor antagonist, raised the effect of citalopram (5 mg/kg) on extracellular 5-HT in the medial prefrontal cortex of DBA/2N mice (citalopram alone 5.2+/-0.3 fmol/20 microl, WAY 100635+citalopram 9.9+/-2.1 fmol/20 microl, SB 242084+ citalopram 7.6+/-1.0 fmol/20 microl) to the level reached in 'responder' mice given citalopram alone. The 5-HT receptor antagonists had no effect on the citalopram-induced increase in extracellular 5-HT in the dorsal hippocampus. The combination of citalopram with WAY 100635 or SB 242084 significantly reduced immobility time in DBA/2N mice that otherwise did not respond to either drug singly. Brain levels of citalopram in mice given citalopram alone or with 5-HT antagonists did not significantly differ. The results confirm that impaired 5-HT transmission accounts for the lack of effect of citalopram in the FST and suggest that enhancing the effect of SSRIs on extracellular 5-HT, through selective blockade of 5-HT1A and 5-HT2C receptors, could be a useful strategy to restore the response in treatment-resistant depression.
authors.affiliation: Laboratory of Neurochemistry and Behaviour, Istituto di Ricerche Farmacologiche 'Mario Negri', Via La Masa 19, 20156 Milan, Italy.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Calcagno
authors.forename: Sara
authors.initials: S
authors.lastname: Guzzetti
authors.forename: Alessandro
authors.initials: A
authors.lastname: Canetta
authors.forename: Claudia
authors.initials: C
authors.lastname: Fracasso
authors.forename: Silvio
authors.initials: S
authors.lastname: Caccia
authors.forename: Luigi
authors.initials: L
authors.lastname: Cervo
authors.forename: Roberto W
authors.initials: RW
authors.lastname: Invernizzi
mesh_terms: D000631:Aminopyridines / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D000928:Antidepressive Agents / Q000493:pharmacokinetics; D002540:Cerebral Cortex / Q000166:cytology* / Q000187:drug effects; D015283:Citalopram / Q000493:pharmacokinetics; D004347:Drug Interactions; D005106:Exploratory Behavior / Q000187:drug effects; D045604:Extracellular Fluid / Q000187:drug effects / Q000378:metabolism*; D007211:Indoles / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D017551:Microdialysis / Q000379:methods; D010879:Piperazines / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D012701:Serotonin / Q000378:metabolism*; D058829:Serotonin 5-HT1 Receptor Antagonists; D058830:Serotonin 5-HT2 Receptor Antagonists; D012702:Serotonin Antagonists / Q000494:pharmacology
chemical_list: C107820:6-chloro-5-methyl-1-((2-(2-methylpyrid-3-yloxy)pyrid-5-yl)carbamoyl)indoline; D000631:Aminopyridines; D000928:Antidepressive Agents; D007211:Indoles; D010879:Piperazines; D011725:Pyridines; D058829:Serotonin 5-HT1 Receptor Antagonists; D058830:Serotonin 5-HT2 Receptor Antagonists; D012702:Serotonin Antagonists; D015283:Citalopram; D012701:Serotonin; C090413:N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide