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BEHAVIORAL PHARMACOLOGY
Department of Psychology (E.W.F., S.F., K.A.M.) and Department of Psychiatry, Pharmacology, and Neuroscience (K.A.M.), Tufts University, Medford and Boston, Massachusetts; and Department of Pharmacology and Toxicology (S.G.), Forest Research Institute, Jersey City, New Jersey
The S-enantiomer of citalopram, escitalopram, is a selective serotonin reuptake inhibitor (SSRI) that appears to be responsible for citalopram's antidepressant and anxiolytic effects. Clinically, escitalopram is reported to have fewer adverse side effects than do other SSRIs. This study compared escitalopram to other antidepressants in a preclinical procedure predicting anxiolytic-like effects of drugs. Carworth Farms Webster (CFW) mouse pups (7 days old) were separated from the dam and maintained at a temperature of 34°C. Forty-five minutes after administering citalopram (0.5610 mg/kg), escitalopram (0.00563 mg/kg), R-citalopram (110 mg/kg), paroxetine (0.33 mg/kg), fluoxetine (130 mg/kg), or venlafaxine (356 mg/kg) subcutaneously, the pups were placed individually on a 19.5°C surface for 4 min. Ultrasonic vocalizations (USVs) (3080 kHz), grid crossing, rolling (i.e., the pup turned on one side or its back), and colonic temperature were recorded. All the drugs reduced USV emission; escitalopram was the most potent (ED50 0.05 mg/kg), followed by paroxetine (0.17 mg/kg), citalopram (1.2 mg/kg), fluoxetine (4.3 mg/kg), R-citalopram (6 mg/kg), and venlafaxine (7 mg/kg). The doses that decreased USVs differed from those that increased motor activity. Increased grid crossing occurred after low doses of paroxetine (0.03 or 0.1 mg/kg) and fluoxetine (1 mg/kg), but only after the highest doses of the citalopram enantiomers and venlafaxine (0.3, 10, and 56 mg/kg, respectively). Except for escitalopram and venlafaxine, high doses of the treatments increased rolling. R-Citalopram caused a 10-fold rightward shift in escitalopram's dose-effect curve, suggesting that R-citalopram inhibits escitalopram's anxiolytic-like effects. These data support clinical findings that escitalopram is a potent, well tolerated SSRI with anxiolytic-like effects.
Address correspondence to: Klaus A. Miczek, Tufts University, 530 Boston Ave. (Bacon Hall), Medford, MA 02155. E-mail klaus.miczek{at}tufts.edu
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