Ghai, U. | Search bioRxiv

bioRxiv2023

Fluoxetine treatment during postnatal and juvenile temporal epochs evokes diametrically opposing changes in anxio-depressive behaviors, gene expression, mitochondrial function, and neuronal architecture in the medial prefrontal cortex

BackgroundThe selective serotonin reuptake inhibitor, fluoxetine is reported to evoke distinct effects on anxio-depressive behaviors based on the temporal window of administration. Here, we systematically addressed the influence of postnatal or juvenile fluoxetine treatment on anxio-depressive behavior, gene expression, mitochondrial biogenesis, and neuronal cytoarchitecture in adulthood. MethodsRat pups received postnatal fluoxetine (PNFlx) or juvenile fluoxetine (JFlx) treatment from postnatal day 2 (P2)-P21 or P28-48 respectively, and were assessed for changes in anxio-depressive behaviors, global gene expression, mitochondrial biogenesis/function, and dendritic cytoarchitecture in the medial prefrontal cortex (mPFC) in adulthood. ResultsPNFlx evoked long-lasting increases in anxio-depressive behaviors, whereas JFlx elicited persistent decreases in anxio-depressive behavior, accompanied by differential and minimally overlapping transcriptional changes in the mPFC in adulthood. We noted opposing changes in mitochondrial function and dendritic cytoarchitecture in the mPFC of PNFlx and JFlx animals, with a decline observed following PNFlx and an increase in response to JFlx treatment. Furthermore, the enhanced despair-like behavior in the PNFlx cohort was reversed by adult-onset treatment with nicotinamide, a precursor for NAD+ which enhances mitochondrial bioenergetics. ConclusionsFluoxetine treatment in early postnatal versus juvenile windows evokes opposing and persistent effects on anxio-depressive behavior in adult male rats, along with differential effects on gene expression, mitochondrial function, and dendritic morphology in the mPFC. Collectively, our findings highlight two distinct temporal windows in which fluoxetine exposure programs starkly differing outcomes in mood-related behavior, and posits a role for altered bioenergetics within the mPFC in contributing to these distinctive changes in emotionality.

neuroscience↗

bioRxiv2020

Postnatal fluoxetine treatment alters perineuronal net formation and maintenance in the hippocampus

Elevation of serotonin via postnatal fluoxetine (PNFlx) treatment during critical temporal windows is hypothesized to perturb the development of limbic circuits thus establishing a substratum for persistent disruption of mood-related behavior. We examined the impact of PNFlx treatment on the formation and maintenance of perineuronal nets (PNNs), extracellular matrix (ECM) structures that deposit primarily around inhibitory interneurons, and mark the closure of critical period plasticity. PNFlx treatment evoked a significant decline in PNN number, with a robust reduction in PNNs deposited around parvalbumin (PV) interneurons, within the CA1 and CA3 hippocampal subfields at postnatal day 21 in Sprague-Dawley rat pups. While the reduction in CA1 subfield PNN number was still observed in adulthood, we observed no change in colocalization of PV-positive interneurons with PNNs in the hippocampi of adult PNFlx animals. PNFlx treatment did not alter hippocampal parvalbumin, calretinin, or reelin-positive neuron numbers in PNFlx animals at P21 or in adulthood. We did observe a small, but significant increase in somatostatin (SST)-positive interneurons in the DG subfield of PNFlx-treated animals in adulthood. This was accompanied by altered GABA-A receptor subunit composition, increased dendritic complexity of apical dendrites of CA1 pyramidal neurons, and enhanced neuronal activation revealed by increased c-Fos-positive cell numbers within hippocampi of PNFlx-treated animals in adulthood. These results indicate that PNFlx treatment alters the developmental trajectory of PNNs within the hippocampus, raising the possibility of a disruption of critical period plasticity and the establishment of an altered excitation-inhibition balance within this key limbic brain region. Significance StatementClinical and preclinical studies indicate that developmental exposure to fluoxetine programs persistent dysregulation of mood-related behaviors. This is hypothesized to involve the disruption of the normal development of key brain regions, such as the hippocampus that regulate mood behaviors. We show that postnatal exposure to fluoxetine alters hippocampal perineuronal nets (PNNs), extracellular matrix structures that regulate plasticity and mark the closure of critical periods. The decline in PNNs is noted in early postnatal life, and persists into adulthood in specific hippocampal subfields. Adult animals with a history of postnatal fluoxetine exposure exhibit altered numbers of somatostatin interneurons, GABA receptor subunit expression and neuronal activation within the hippocampus. This indicates that postnatal fluoxetine disrupts the normal developmental trajectory of the hippocampus.

neuroscience↗