Early intervention with fluoxetine reverses abnormalities in the serotonergic system and behavior of rats exposed prenatally to dexamethasone.

Many psychiatric disorders emerge after adolescence. Among a variety of predisposing factors, prenatal stress has been thought to cause the symptoms of anxiety disorders. We recently reported that prenatal dexamethasone (DEX) exposure, which mimics some aspects of prenatal stress, induced anxiety-related behaviors in male offspring when they reached adulthood. Before the emergence of behavioral changes, abnormalities occurred in the hypothalamic-pituitary-adrenal axis during postnatal development. In the present study, we found abnormalities in serotonin (5-HT) signaling, including decreased expression of 5-HT(1A) receptor (5-HT(1A)-R) mRNA in the medial prefrontal cortex (mPFC) and 5-HT content in the hippocampus at postnatal week (PW) 4. These results support using early therapeutic interventions with serotonergic drugs to prevent late-emerging anxiety symptoms. To test this hypothesis, we treated rat pups born to DEX-administered mothers with fluoxetine (FLX), a selective serotonin reuptake inhibitor commonly used as an anti-anxiety medication, via breast milk from postnatal day (PD) 2-21. Anxiety-related behaviors examined at PW11-13 were not observed in the prenatally DEX-exposed offspring that were treated with FLX. Likewise, FLX increased 5-HT concentrations in the mPFC and ventral hippocampus at PW3 and normalized 5-HT(1A)-R mRNA concentrations in the mPFC at PW4. The decrease in brain-derived neurotrophic factor (BDNF) protein in the mPFC and dorsal hippocampus was also restored at PW4. Furthermore, administration of the 5-HT(1A)-R full agonist (R)-(+)-8-hydroxy-2-(di-n-propylamino)tetralin from PD2 to 21 also prevented the emergence of behavioral abnormalities in the prenatally DEX-exposed offspring, implicating the involvement of 5-HT(1A)-Rs in the neonatal FLX effect. Collectively, an early pharmacological intervention to normalize serotonergic transmission effectively suppressed the emergence of symptoms induced by prenatal DEX exposure in rats.