Fluoxetine and norfluoxetine stereospecifically and selectively increase brain neurosteroid content at doses that are inactive on 5-HT reuptake

Abstract

It has recently become more clearly understood that in human brain pathophysiology, neurosteroids play a role in anxiety disorders, premenstrual syndrome, postpartum depression, posttraumatic stress disorder, and depression. In the treatment of major depression, recent clinical studies indicate that the pharmacological profiles of fluoxetine and fluvoxamine are correlated with the ability of these drugs to increase the brain and cerebrospinal fluid content of allopregnanolone (Allo), a potent positive allosteric modulator of gamma-aminobutyric acid (GABA) action at GABAA receptors. Thus, the neurosteroid-induced positive allosteric modulation of GABA action at GABAA receptors is facilitated by fluoxetine or its congeners (i.e., paroxetine, fluvoxamine, sertraline), which may not block 5-HT reuptake at the doses currently prescribed in the clinic. However, these doses are effective in the treatment of premenstrual dysphoria, anxiety, and depression. In socially isolated mice, we tested the hypothesis that fluoxetine, norfluoxetine, and other specific serotonin reuptake inhibitor (SSRI) congeners stereoselectively upregulate neurosteroid content at doses insufficient to inhibit 5-HT reuptake; although they potentiate pentobarbital-induced sedation and exert antiaggressive action. Very importantly, the inhibition of 5-HT reuptake lacks stereospecificity and requires fluoxetine and norfluoxetine doses that are 50-fold greater than those required to increase brain Allo content, po…