Fluoxetine exposure throughout neurodevelopment differentially influences basilar dendritic morphology in the motor and prefrontal cortices

The significance of serotonin (5HT) in mental health is underscored by the serotonergic action of many classes of psychiatric medication. 5HT is known to have a significant role in neurodevelopment, thus 5HT disruption during development may have a long term impact on brain structure and circuits. We previously generated a model of 5HT alteration throughout neurodevelopment by maternal administration of the selective serotonin reuptake inhibitor fluoxetine. We found resulting social behavior alterations in the offspring during both postnatal and adult ages. Previous work by others has indicated that early 5HT disruption influences neuronal morphology. Therefore, in the current study we sought to determine if dendritic morphological changes occur in areas involved in the social behavior deficits we previously observed, specifically the primary motor (M1) and medial prefrontal (mPFC) cortices. We quantified dendritic morphology of projection neurons in M1 and mPFC at postnatal day (P)10 and P79 in mice exposed to fluoxetine. Basilar dendritic complexity and spine density were persistently decreased in M1 fluoxetine-exposed neurons while in the mPFC, similar reductions were observed at P79 but were not present at P10. Our findings underscore that the developing brain, specifically the projection cortex, is vulnerable to 5HT system perturbation, which may be related to later behavioral disruptions.