Reduced Brd1 expression leads to reversible depression-like behaviors and gene-expression changes in female mice.

The schizophrenia-associated gene, BRD1, encodes an epigenetic regulator in which chromatin interactome is enriched with genes implicated in mental health. Alterations in histone modifications and epigenetic regulation contribute to brain transcriptomic changes in affective disorders and preclinical data supports a role for BRD1 in psychopathology. However, the implication of BRD1 on affective pathology remains poorly understood. In this study, we assess affective behaviors and associated neurobiology in Brd1+/- mice along with their responses to Fluoxetine and Imipramine. This involves behavioral, neurostructural, and neurochemical characterizations along with regional cerebral gene expression profiling combined with integrative functional genomic analyses. We report behavioral changes in female Brd1+/- mice with translational value to depressive symptomatology that can be alleviated by the administration of antidepressant medications. Behavioral changes are accompanied by altered brain morphometry and imbalances in monoaminergic systems. In accordance, gene expression changes across brain tissues reveal altered neurotransmitter signaling and cluster in functional pathways associated with depression including 'Adrenergic-, GPCR-, cAMP-, and CREB/CREM-signaling'. Integrative gene expression analysis specifically links changes in amygdaloid intracellular signaling activity to the behavioral treatment response in Brd1+/- mice. Collectively, our study highlights the importance of BRD1 as a modulator of affective pathology and adds to our understanding of the molecular mechanisms underlying affective disorders and their treatment response.

Structural Plasticity and Molecular Markers in Hippocampus of Male Rats after Acute Stress.

Stress plays a crucial role in the pathogenesis of psychiatric disorders and affects neuronal plasticity in different brain regions. We have previously found that acute foot-shock (FS) stress elicits fast and long-lasting functional and morphological remodeling of excitatory neurons in the prefrontal cortex (PFC), which were partly prevented by the pretreatment with antidepressants. Here we investigated, whether acute stress and pretreatment with desipramine (DMI) interfere in hippocampal dendritic remodeling. Male Sprague-Dawley rats were subjected to acute FS-stress, followed by measurement of time-dependent (1, 7 and 14 days) structural plasticity (dendritic arborization, spine number and morphology) in hippocampal CA1 pyramidal neurons and expression patterns of molecular markers implicated in neuronal plasticity. We found that acute stress significantly decreased spine number, dendritic length, and altered spine morphometric parameters at all time points evaluated after stress. This was paralleled by changes in the gene expression of Spinophilin and Cdc42, and protein expression of homer1. Pretreatment with DMI prevented the stress-induced dendritic atrophy and spine loss 14 days after acute FS. However, DMI treatment without stress differentially affected the expression patterns of spine-related genes and proteins. In conclusion, acute FS-stress and pretreatment with DMI significantly changed dendritic morphology, including number and morphology of spines, and the length of dendrites in hippocampal CA1 pyramidal cells as early as 1 day, and sustained up to 14 days after acute FS. The findings were paralleled by changes in gene and protein expression of actin binding and cytoskeletal proteins, Rho GTPases, and postsynaptic scaffolding proteins.

Temporal Dynamics of Acute Stress-Induced Dendritic Remodeling in Medial Prefrontal Cortex and the Protective Effect of Desipramine.

Stressful events are associated with increased risk of mood disorders. Volumetric reductions have been reported in brain areas critical for the stress response, such as medial prefrontal cortex (mPFC), and dendritic remodeling has been proposed as an underlying factor. Here, we investigated the time-dependent effects of acute stress on dendritic remodeling within the prelimbic (PL) region of the PFC, and whether treatment with the antidepressant desipramine (DMI) may interfere. Rodents were subjected to foot-shock stress: dendritic length and spine density were analyzed 1 day, 7 days, and 14 days after stress. Acute stress produced increased spine density and decreased cofilin phosphorylation at 1 day, paralleled with dendritic retraction. An overall shift in spine population was observed at 1 day, resulting in a stress-induced increase in small spines. Significant atrophy of apical dendrites was observed at 1 day, which was prevented by chronic DMI, and at 14 days after stress exposure. Chronic DMI resulted in dendritic elaboration at 7 days but did not prevent the effects of FS-stress. Collectively, these data demonstrate that 1) acute stressors may induce rapid and sustained changes of PL neurons; and 2) chronic DMI may protect neurons from rapid stress-induced synaptic changes.

The expression of plasticity-related genes in an acute model of stress is modulated by chronic desipramine in a time-dependent manner within medial prefrontal cortex.

It is well established that stress plays a major role in the pathogenesis of neuropsychiatric diseases. Stress-induced alteration of synaptic plasticity has been hypothesized to underlie the morphological changes observed by neuroimaging in psychiatric patients in key regions such as hippocampus and prefrontal cortex (PFC). We have recently shown that a single acute stress exposure produces significant short-term alterations of structural plasticity within medial PFC. These alterations were partially prevented by previous treatment with chronic desipramine (DMI). In the present study we evaluated the effects of acute Foot-shock (FS)-stress and pre-treatment with the traditional antidepressant DMI on the gene expression of key regulators of synaptic plasticity and structure. Expression of Homer, Shank, Spinophilin, Densin-180, and the small RhoGTPase related gene Rac1 and downstream target genes, Limk1, Cofilin1 and Rock1 were investigated 1 day (1d), 7 d and 14d after FS-stress exposure. We found that DMI specifically increases the short-term expression of Spinophilin, as well as Homer and Shank family genes, and that both acute stress and DMI exert significant long-term effects on mRNA levels of genes involved in spine plasticity. These findings support the knowledge that acute FS stress and antidepressant treatment induce both rapid and sustained time-dependent alterations in structural components of synaptic plasticity in rodent medial PFC.

Chronic desipramine prevents acute stress-induced reorganization of medial prefrontal cortex architecture by blocking glutamate vesicle accumulation and excitatory synapse increase.

BACKGROUND: Although a clear negative influence of chronic exposure to stressful experiences has been repeatedly demonstrated, the outcome of acute stress on key brain regions has only just started to be elucidated. Although it has been proposed that acute stress may produce enhancement of brain plasticity and that antidepressants may prevent such changes, we still lack ultrastructural evidence that acute stress-induced changes in neurotransmitter physiology are coupled with structural synaptic modifications. METHODS: Rats were pretreated chronically (14 days) with desipramine (10mg/kg) and then subjected to acute foot-shock stress. By means of serial section electron microscopy, the structural remodeling of medial prefrontal cortex glutamate synapses was assessed soon after acute stressor cessation and stress hormone levels were measured. RESULTS: Foot-shock stress induced a remarkable increase in the number of docked vesicles and small excitatory synapses, partially and strongly prevented by desipramine pretreatment, respectively. Acute stress-induced corticosterone elevation was not affected by drug treatment. CONCLUSIONS: Since desipramine pretreatment prevented the stress-induced structural plasticity but not the hormone level increase, we hypothesize that the preventing action of desipramine is located on pathways downstream of this process and/or other pathways. Moreover, because enhancement of glutamate system remodeling may contribute to overexcitation dysfunctions, this aspect could represent a crucial component in the pathophysiology of stress-related disorders.

A new efficient method for synaptic vesicle quantification reveals differences between medial prefrontal cortex perforated and nonperforated synapses.

Communication between neurons is mediated by the release of neurotransmitter-containing vesicles from presynaptic terminals. Quantitative characterization of synaptic vesicles can be highly valuable for understanding mechanisms underlying synaptic function and plasticity. We performed a quantitative ultrastructural analysis of cortical excitatory synapses by mean of a new, efficient method, as an alternative to three-dimensional (3D) reconstruction. Based on a hierarchical sampling strategy and unequivocal identification of the region of interest, serial sections from excitatory synapses of medial prefrontal cortex (mPFC) of six Sprague-Dawley rats were acquired with a transmission electron microscope. Unbiased estimates of total 3D volume of synaptic terminals were obtained through the Cavalieri estimator, and adequate correction factors for vesicle profile number estimation were applied for final vesicle quantification. Our analysis was based on 79 excitatory synapses, nonperforated (NPSs) and perforated (PSs) subtypes. We found that total number of docked and reserve-pool vesicles in PSs significantly exceeded that in NPSs (by, respectively, 77% and 78%). These differences were found to be related to changes in size between the two subtypes (active zone area by 86%; bouton volume by 105%) rather than to postsynaptic density shape. Positive significant correlations were found between number of docked and reserve-pool vesicles, active zone area and docked vesicles, and bouton volume and reserve pool vesicles. Our method confirmed the large size of mPFC PSs and a linear correlation between presynaptic features of typical hippocampal synapses. Moreover, a greater number of docked vesicles in PSs may promote a high synaptic strength of these synapses.