Objective
Adolescence is a developmental stage in which the incidence of psychiatric disorders, such as anxiety disorders, peaks. Selective serotonin reuptake inhibitors (SSRIs) are the main class of agents used to treat anxiety disorders. However, the impact of SSRIs on the developing brain during adolescence remains unknown. The present study sought to determine the impact of developmentally-timed SSRI administration in a genetic mouse model displaying elevated anxiety-like behaviors.
Method
Knock-in mice containing a common human SNP (Val66Met; rs6265) in BDNF, a growth factor implicated in the mechanism of action of SSRIs, were studied based on their established phenotype of increased anxiety-like behavior. Timed administration of fluoxetine was delivered during one of three developmental periods (postnatal days (P)21–42, P40–61, or P60–81), spanning the transition from childhood to adulthood. Neurochemical and anxiety-like behavioral analyses were performed.
Results
We identified a “sensitive period” in peri-adolescence (P21–P42), in which developmentally-timed fluoxetine administration rescued anxiety-like phenotypes in BDNF Val66Met mice in adulthood. Compared to littermate controls, BDNFMet/Met mice exhibited diminished maturation of serotonergic fibers projecting particularly to the prefrontal cortex, as well as decreased expression of the serotonergic trophic factor S100B in the dorsal raphe. Interestingly, deficient serotonergic innervation, as well as S100B levels, were rescued with timed peri-adolescent fluoxetine administration.
Conclusions
Our findings suggest that SSRI administration during a peri-adolescent “sensitive period” leads to long-lasting anxiolytic effects in a genetic mouse model of elevated anxiety-like behaviors. These persistent effects highlight the role of BDNF in the maturation of the serotonin system, and the capacity to enhance its development through a pharmacological intervention.