Fluoxetine increases plasticity and modulates the proteomic profile in the adult mouse visual cortex

The multifaceted effects of fluoxetine treatment on cognitive functions

Fluoxetine, the prototypical selective serotonin reuptake inhibitor (SSRI), is widely used to treat major depressive disorder (MDD) and a variety of other central nervous system conditions, primarily due to its established clinical safety profile. Although its efficacy in treating depression is well-recognized, the impact of fluoxetine on cognitive functions remains inconsistent and elusive. In this review, we first examine the well-substantiated biological mechanisms underlying fluoxetine's antidepressant effects, which include serotonin reuptake inhibition and activation of TrkB receptors-key to brain-derived neurotrophic factor (BDNF) signaling. Subsequently, we delve into the cognitive side effects observed in both preclinical and clinical studies, affecting domains such as memory, attention, and executive functions. While certain studies indicate cognitive improvements in patients with underlying disorders, there is also evidence of negative effects, influenced by variables like gender, duration of treatment, age, disease pathology, and the specifics of cognitive testing. Significantly, the negative cognitive outcomes reported in preclinical research often involve healthy, non-diseased animals. This review underscores the necessity for heightened caution in fluoxetine prescription and further investigation into its potentially detrimental cognitive effects, even when used prophylactically.

Shared and Unique Changes in Brain Connectivity Among Depressed Patients After Remission With Pharmacotherapy Versus Psychotherapy

OBJECTIVE

The authors sought to determine the shared and unique changes in brain resting-state functional connectivity (rsFC) between patients with major depressive disorder who achieved remission with cognitive-behavioral therapy (CBT) or with antidepressant medication.

METHODS

The Predictors of Remission in Depression to Individual and Combined Treatments (PReDICT) trial randomized adults with treatment-naive major depressive disorder to 12 weeks of treatment with CBT (16 1-hour sessions) or medication (duloxetine 30-60 mg/day or escitalopram 10-20 mg/day). Resting-state functional MRI scans were performed at baseline and at week 12. The primary outcome was change in the whole-brain rsFC of four seeded brain networks among participants who achieved remission.

RESULTS

Of the 131 completers with usable MRI data (74 female; mean age, 39.8 years), remission was achieved by 19 of 40 CBT-treated and 45 of 91 medication-treated patients. Three patterns of connectivity changes were observed. First, those who remitted with either treatment shared a pattern of reduction in rsFC between the subcallosal cingulate cortex and the motor cortex. Second, reciprocal rsFC changes were observed across multiple networks, primarily increases in CBT remitters and decreases in medication remitters. And third, in CBT remitters only, rsFC increased within the executive control network and between the executive control network and parietal attention regions.

CONCLUSIONS

Remission from major depression via treatment with CBT or medication is associated with changes in rsFC that are mostly specific to the treatment modality, providing biological support for the clinical practice of switching between or combining these treatment approaches. Medication is associated with broadly inhibitory effects. In CBT remitters, the increase in rsFC strength between networks involved in cognitive control and attention provides biological support for the theorized mechanism of CBT. Reducing affective network connectivity with motor systems is a shared process important for remission with both CBT and medication.

Combined therapy of bilateral transcranial direct current stimulation and ocular occlusion improves visual function in adults with amblyopia, a randomized pilot study

Background

Amblyopia is the interocular visual acuity difference of two lines or more with the best correction in both eyes. It is treated with ocular occlusion therapy, but its success depends on neuroplasticity, and thus is effective in children but not adults. Transcranial Direct Current Stimulation (tDCS) is suggested to increase neuroplasticity.

Objective

To determine if combined intervention of bilateral tDCS and ocular occlusion improves visual function in adults with amblyopia.

Methods

A double-blind randomized, controlled pilot trial was conducted in 10 volunteers with amblyopia. While applying ocular occlusion and performing a reading task, participants received bilateral tDCS (n = 5) or sham stimulation (n = 5), with the anodal tDCS electrode in the contralateral visual cortex and the cathodal in the ipsilateral visual cortex in relation to the amblyopic eye. Visual function (through visual acuity, stereopsis, and contrast sensitivity tests) and visual evoked potential (with checkerboard pattern stimuli presentation) were evaluated immediately after.

Results

A total of 30 min after treatment with bilateral tDCS, visual acuity improved by 0.16 (± 0.025) LogMAR in the treatment group compared with no improvement (-0.02 ± 0.02) in five controls (p = 0.0079), along with a significant increase in the amplitude of visual evoked potentials of the amblyopic eye response (p = 0.0286). No significant changes were observed in stereopsis and contrast sensitivity. No volunteer reported any harm derived from the intervention.

Conclusion

Our study is the first to combine anodal and cathodal tDCS for the treatment of amblyopia, showing transient improved visual acuity in amblyopic adults.

Leptin, the brain and energy homeostasis: From an apparently simple to a highly complex neuronal system

Leptin, produced and secreted by white adipose tissue in tight relationship with adipose mass, informs the brain about the status of the energy stores serving as the main peripheral signal for energy balance regulation through interaction with a multitude of highly interconnected neuronal populations. Most obese patients display resistance to the anorectic effect of the hormone. The present review unravels the multiple levels of complexity that trigger hypothalamic response to leptin with the objective of highlighting those critical hubs that, mainly in the hypothalamic arcuate nucleus, may undergo obesity-induced alterations and create an obstacle to leptin action. Several mechanisms underlying leptin resistance have been proposed, possibly representing useful targets to empower leptin effects. Among these, a special focus is herein dedicated to detail how leptin gains access into the brain and how neuronal plasticity may interfere with leptin function.

Role of fluoxetine in pharmacological enhancement of motor functions in stroke patients: A randomized, placebo-controlled, single-blind trial

BACKGROUND

Stroke is the primary cause of disability worldwide, the second most common cause of dementia and the third leading cause of death. Only few studies were conducted to study the role of fluoxetine in motor recovery in either ischemic or hemorrhagic stroke patients with probably less severe paresis. However, the current study evaluates both the effectiveness and safety of fluoxetine in the stroke population with a more severe motor deficit.

METHODS

Patients who had acute or subacute stroke with hemiparesis and aged between 18 and 80 years with medical research council (MRC) scale score <4 were included in this randomized, Single-blind, placebo-controlled trial in 1:1 ratio to placebo or fluoxetine 20 mg/day orally for 90 days. The primary outcome measures were changes in barthel index, time taken to complete nine hole peg test and number of hand tapping movements in 30 s by the affected limb between baseline, 45th day and 90th day. The secondary outcome measure was evaluation of the drug tolerability.

RESULTS

A total of 168 patients were assigned to fluoxetine (n = 84) or placebo (n = 84) group. Mean BI score significantly improved at 90th day in fluoxetine group (70.42 ± 10.56) than in placebo group (44.23 ± 8.52). Mean dexterity value decreased significantly at 90th day (2.61 ± 0.81) compared to baseline (3.98 ± 0.53) in fluoxetine group. However higher rate of decrease of mean dexterity value was seen in fluoxetine group when compared to placebo group. Mean number of hands tapping movements in 30 s increased significantly at 90th day (16.33 ± 3.58) compared to baseline (9.83 ± 2.92) in fluoxetine group. Few ADR reported during this study were dizziness, drowsiness and insomnia.

CONCLUSION

The present study indicates that early prescription of fluoxetine is safe and may enhance motor function in patients presenting with severe motor impairments after stroke. However, the findings of the study should be confirmed in future controlled studies with large sample size.

Identification of cofilin 1 as a candidate protein associated to mouse visual cortex plasticity

In order to characterize the mechanisms controlling plasticity in the mouse visual cortex, we used, for the first time on brain samples, an unconventional proteomic approach to separate acid-extracted proteins by bi-dimensional electrophoresis (AUT/SDS or AUT/AU gels). The analysis was performed on high plasticity critical period young vs. low plasticity adult, and on fluoxetine-induced high plasticity vs. low plasticity untreated adult mice. Mass spectrometry allowed for the identification of 11 proteins that are differentially expressed between critical period and adult mice, and 5 between fluoxetine-treated and control adult mice. We then focused on cofilin 1, as the intensity level of the corresponding spot on 2D gels was higher in both high plasticity conditions. Western blot showed that cofilin 1 expression is dynamically regulated during postnatal life, reaching a peak at the critical period, and decreasing at adult stage, and that it increases in fluoxetine-treated vs. untreated adult mice. In summary, by using a 2D gel electrophoresis differential approach on basic proteins followed by mass spectrometry and immunoblot analysis, we identified cofilin 1 as a potential candidate controlling plasticity levels of the mouse visual cortex.

The effects of fluoxetine on oligodendrocytes in the hippocampus of chronic unpredictable stress-induced depressed model rats

Depression is a mental illness which is harmful seriously to the society. This study investigated the effects of fluoxetine on the CNPase⁺ oligodendrocytes in hippocampus of the depressed rats to explore the new target structure of antidepressants. Male Sprague-Dawley rats were used to build chronic unpredictable stress (CUS) depressed model of rats. Then, the depressed rats were divided into the CUS standard group and the CUS + fluoxetine (CUS/FLX) group. The CUS/FLX group was treated with fluoxetine at dose of 5 mg/(kg·d) from the fifth week to seventh week. After 7 weeks CUS intervention, the sucrose preference of the CUS standard group was significantly lower than that of the control group and the CUS/FLX group. The stereological results showed that the total number of the CNPase⁺ cells in the CA1, CA3, and DG subfield of the hippocampus in the CUS standard group were significantly decreased, when compared with the CNPase⁺ cells in the control group. However, the total number of the CNPase⁺ cells in the CA1 and CA3 subfield of the hippocampus in the CUS standard group was significantly decreased when it compared with CNPase⁺ cells in the CUS/FLX group. Therefore, fluoxetine might prevent the loss of CNPase⁺ oligodendrocytes in CA1 and CA3 subfields of hippocampus of the depressed rats. The oligodendrocytes in hippocampus may play an important role in the pathogenesis of depression. The current result might provide structural basis for the future studies that search for new antidepressant strategies.

Modification of the head proteome of nurse honeybees (Apis mellifera) exposed to field-relevant doses of pesticides

Understanding the effect of pesticides on the survival of honeybee colonies is important because these pollinators are reportedly declining globally. In the present study, we examined the changes in the head proteome of nurse honeybees exposed to individual and combined pesticides (the fungicide pyraclostrobin and the insecticide fipronil) at field-relevant doses (850 and 2.5 ppb, respectively). The head proteomes of bees exposed to pesticides were compared with those of bees that were not exposed, and proteins with differences in expression were identified by mass spectrometry. The exposure of nurse bees to pesticides reduced the expression of four of the major royal jelly proteins (MRJP1, MRJP2, MRJP4, and MRJP5) and also several proteins associated with carbohydrate metabolism and energy synthesis, the antioxidant system, detoxification, biosynthesis, amino acid metabolism, transcription and translation, protein folding and binding, olfaction, and learning and memory. Overall, when pyraclostrobin and fipronil were combined, the changes in protein expression were exacerbated. Our results demonstrate that vital proteins and metabolic processes are impaired in nurse honeybees exposed to pesticides in doses close to those experienced by these insects in the field, increasing their susceptibility to stressors and affecting the nutrition and maintenance of both managed and natural colonies.

Pharmacologically diverse antidepressants facilitate TRKB receptor activation by disrupting its interaction with the endocytic adaptor complex AP-2

Several antidepressant drugs activate tropomyosin-related kinase B (TRKB) receptor, but it remains unclear whether these compounds employ a common mechanism for TRKB activation. Here, using MS, we found that a single intraperitoneal injection of fluoxetine disrupts the interaction of several proteins with TRKB in the hippocampus of mice. These proteins included members of adaptor protein complex-2 (AP-2) involved in vesicular endocytosis. The interaction of TRKB with the cargo-docking μ subunit of the AP-2 complex (AP2M) was confirmed to be disrupted by both acute and repeated fluoxetine treatments. Of note, fluoxetine disrupted the coupling between full-length TRKB and AP2M, but not the interaction between AP2M and the TRKB C-terminal region, indicating that the fluoxetine-binding site in TRKB lies outside the TRKB:AP2M interface. ELISA experiments revealed that in addition to fluoxetine, other chemically diverse antidepressants, such as imipramine, rolipram, phenelzine, ketamine, and its metabolite 2R,6R-hydroxynorketamine, also decreased the interaction between TRKB and AP2M in vitro Silencing the expression of AP2M in a TRKB-expressing mouse fibroblast cell line (MG87.TRKB) increased cell-surface expression of TRKB and facilitated its activation by brain-derived neurotrophic factor (BDNF), observed as levels of phosphorylated TRKB. Moreover, animals haploinsufficient for the Ap2m1 gene displayed increased levels of active TRKB, along with enhanced cell-surface expression of the receptor in cultured hippocampal neurons. Taken together, our results suggest that disruption of the TRKB:AP2M interaction is a common mechanism underlying TRKB activation by several chemically diverse antidepressants.

Chronic Fluoxetine Treatment Induces Maturation-Compatible Changes in the Dendritic Arbor and in Synaptic Responses in the Auditory Cortex

Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) used to treat mood and anxiety disorders. Chronic treatment with this antidepressant drug is thought to favor functional recovery by promoting structural and molecular changes in several forebrain areas. At the synaptic level, chronic fluoxetine induces an increased size and density of dendritic spines and an increased ratio of GluN2A over GluN2B N-methyl-D-aspartate (NMDA) receptor subunits. The "maturation"-promoting molecular changes observed after chronic fluoxetine should also induce structural remodeling of the neuronal dendritic arbor and changes in the synaptic responses. We treated adult rats with fluoxetine (0.7 mg/kg i.p. for 28 days) and performed a morphometric analysis using Golgi stain in limbic and nonlimbic cortical areas. Then, we focused especially on the auditory cortex, where we evaluated the dendritic morphology of pyramidal neurons using a 3-dimensional reconstruction of neurons expressing mRFP after in utero electroporation. With both methodologies, a shortening and decreased complexity of the dendritic arbors was observed, which is compatible with an increased GluN2A over GluN2B ratio. Recordings of extracellular excitatory postsynaptic potentials in the auditory cortex revealed an increased synaptic response after fluoxetine and were consistent with an enrichment of GluN2A-containing NMDA receptors. Our results confirm that fluoxetine favors maturation and refinement of extensive cortical networks, including the auditory cortex. The fluoxetine-induced receptor switch may decrease GluN2B-dependent toxicity and thus could be applied in the future to treat neurodegenerative brain disorders characterized by glutamate toxicity and/or by an aberrant network connectivity.

5-HTR2A and 5-HTR3A but not 5-HTR1A antagonism impairs the cross-modal reactivation of deprived visual cortex in adulthood

Visual cortical areas show enhanced tactile responses in blind individuals, resulting in improved behavioral performance. Induction of unilateral vision loss in adult mice, by monocular enucleation (ME), is a validated model for such cross-modal brain plasticity. A delayed whisker-driven take-over of the medial monocular zone of the visual cortex is preceded by so-called unimodal plasticity, involving the potentiation of the spared-eye inputs in the binocular cortical territory. Full reactivation of the sensory-deprived contralateral visual cortex is accomplished by 7 weeks post-injury. Serotonin (5-HT) is known to modulate sensory information processing and integration, but its impact on cortical reorganization after sensory loss, remains largely unexplored. To address this issue, we assessed the involvement of 5-HT in ME-induced cross-modal plasticity and the 5-HT receptor (5-HTR) subtype used. We first focused on establishing the impact of ME on the total 5-HT concentration measured in the visual cortex and in the somatosensory barrel field. Next, the changes in expression as a function of post-ME recovery time of the monoamine transporter 2 (vMAT2), which loads 5-HT into presynaptic vesicles, and of the 5-HTR_1A and 5-HTR_3A were assessed, in order to link these temporal expression profiles to the different types of cortical plasticity induced by ME. In order to accurately pinpoint which 5-HTR exactly mediates ME-induced cross-modal plasticity, we pharmacologically antagonized the 5-HTR_1A, 5-HTR_2A and 5-HTR_3A subtypes. This study reveals brain region-specific alterations in total 5-HT concentration, time-dependent modulations in vMAT2, 5-HTR_1A and 5-HTR_3A protein expression and 5-HTR antagonist-specific effects on the post-ME plasticity phenomena. Together, our results confirm a role for 5-HTR_1A in the early phase of binocular visual cortex plasticity and suggest an involvement of 5-HTR_2A and 5-HTR_3A but not 5-HTR_1A during the late cross-modal recruitment of the medial monocular visual cortex. These insights contribute to the general understanding of 5-HT function in cortical plasticity and may encourage the search for improved rehabilitation strategies to compensate for sensory loss.

Gating of long-term potentiation (LTP) in the thalamocortical auditory system of rats by serotonergic (5-HT) receptors

The neuromodulator serotonin (5-hydroxytryptamine, 5-HT) plays an important role in controlling the induction threshold and maintenance of long-term potentiation (LTP) in the visual cortex and hippocampus of rodents. Serotonergic fibers also innervate the rodent primary auditory cortex (A1), but the regulation of A1 plasticity by 5-HT receptors (5-HTRs) is largely uncharted. Thus, we examined the role of several, predominant 5-HT receptor classes (5-HT_1ARs, 5-HT₂Rs, and 5-HT₃Rs) in gating in vivo LTP induction at A1 synapses of adult, urethane-anesthetized rats. Theta-burst stimulation (TBS) applied to the medial geniculate nucleus resulted in successful LTP induction of field postsynaptic potentials (fPSPs) generated by excitation of thalamocortical and intracortical A1 synapses. Local application (by reverse microdialysis in A1) of the broad-acting 5-HTR antagonist methiothepin suppressed LTP at both thalamocortical and intracortical synapses. In fact, rather than LTP, TBS elicited long-term depression during methiothepin application, an effect that was mimicked by the selective 5-HT₂R antagonist ketanserin, but not the 5-HT_1AR blocker WAY 100635. Interestingly, antagonism of 5-HT₃Rs by granisetron selectively blocked LTP at thalamocortical, but not intracortical A1 synapses. Further, in the absence of TBS, granisetron application resulted in a pronounced increase in fPSP amplitude, suggesting that 5-HT₃Rs play an important role in regulating baseline (non-potentiated) transmission at A1 synapses. Together, these results indicate that activation of 5-HT₂Rs and 5-HT₃Rs, but not 5-HT_1ARs, exerts a clear, facilitating effect on LTP induction at A1 synapses, allowing 5-HT to act as a powerful regulator of long-term plasticity induction in the fully matured A1 of mammalian species.

Evaluation of the effectiveness of chronic antidepressant drug treatments in the hippocampal mitochondria - A proteomic study in an animal model of depression

Several lines of evidence indicate that adverse experience in early life may be a triggering factor for disturbances in the brain mitochondrial proteins and lead to the development of depression in adulthood. On the other hand, little is known about the impact of chronic administration of various antidepressant drugs on the brain mitochondria, as a target for the pharmacotherapy of depression. The purpose of our study was to compare the impact of chronic treatment with two antidepressant drugs with different mechanisms of action, a tricyclic antidepressant (TCA), imipramine, and an antidepressant of the selective serotonin reuptake inhibitor (SSRI) class, fluoxetine, on the mitochondria-enriched subproteome profile in the hippocampus of 3-month-old male rats following a prenatal stress procedure (an animal model of depression). We clearly confirmed that chronic imipramine and fluoxetine administration not only normalized depression-like disturbances evoked by the prenatal stress procedure but also modulated the mitochondria-enriched subproteome profile in the hippocampus of adult offspring rats. In line with this, two-dimensional electrophoresis coupled with mass spectrometry showed a statistically significant down-regulation of 14-3-3 and cytochrome bc1 proteins and an up-regulation of COP9 signalosome expression after chronic imipramine treatment in the hippocampus of prenatally stressed offspring. Fluoxetine administration strongly up-regulated the expression of cathepsin D, one of the key proteins involved in the prevention of the development of neurodegenerative processes. Furthermore, this antidepressant treatment enhanced expression of proteins engaged in the improvement of learning and memory processes (STMN1, Dnm-1) as well as in mitochondrial biogenesis and defense against oxidative stress (DJ-1). These findings provide new evidence that chronic administration of antidepressants exerts a varied impact on the mitochondria-enriched subproteome in the hippocampus of adult rats following a prenatal stress procedure. In particular, the effect of fluoxetine requires additional experiments to elucidate the possible beneficial biological consequences underlying the effects mediated by this antidepressant.

Fluoxetine treatment affects the inflammatory response and microglial function according to the quality of the living environment

It has been hypothesized that selective serotonin reuptake inhibitors (SSRIs), the most common treatment for major depression, affect mood through changes in immune function. However, the effects of SSRIs on inflammatory response are contradictory since these act either as anti- or pro-inflammatory drugs. Previous experimental and clinical studies showed that the quality of the living environment moderates the outcome of antidepressant treatment. Therefore, we hypothesized that the interplay between SSRIs and the environment may, at least partially, explain the apparent incongruence regarding the effects of SSRI treatment on the inflammatory response. In order to investigate such interplay, we exposed C57BL/6 mice to chronic stress to induce a depression-like phenotype and, subsequently, to fluoxetine treatment or vehicle (21days) while being exposed to either an enriched or a stressful condition. At the end of treatment, we measured the expression levels of several anti- and pro-inflammatory cytokines and inflammatory mediators in the whole hippocampus and in isolated microglia. We also determined microglial density, distribution, and morphology to investigate their surveillance state. Results show that the effects of fluoxetine treatment on inflammation and microglial function, as compared to vehicle, were dependent on the quality of the living environment. In particular, fluoxetine administered in the enriched condition increased the expression of pro-inflammatory markers compared to vehicle, while treatment in a stressful condition produced anti-inflammatory effects. These findings provide new insights regarding the effects of SSRIs on inflammation, which may be crucial to devise pharmacological strategies aimed at enhancing antidepressant efficacy by means of controlling environmental conditions.

Treatment of Amblyopia and Amblyopia Risk Factors Based on Current Evidence

PURPOSE

Amblyopia is a leading cause of low vision and warrants timely management during childhood. We performed a literature review of the management of amblyopia and potential risk factors for amblyopia.

METHODS

Literature review of the management of amblyopia and risk factors for amblyopia.

RESULTS

Common amblyopia risk factors include anisometropic or high refractive error, strabismus, cataract, and ptosis. Often a conservative approach with spectacles is enough to prevent amblyopia. However, surgery may be necessary to clear the visual axis or align the eyes.

CONCLUSION

Amblyopia risk factors should be managed early. Though amblyopia treatment is more likely to be successful at a younger age, those who are older but treatment-naïve may still respond to treatment. Promoting binocular or dichoptic experiences may be the future direction of amblyopia management.

H3 and H4 Lysine Acetylation Correlates with Developmental and Experimentally Induced Adult Experience-Dependent Plasticity in the Mouse Visual Cortex

Histone posttranslational modifications play a fundamental role in orchestrating gene expression. In this work, we analyzed the acetylation of H3 and H4 histones (AcH3-AcH4) and its modulation by visual experience in the mouse visual cortex (VC) during normal development and in two experimental conditions that restore juvenile-like plasticity levels in adults (fluoxetine treatment and enriched environment). We found that AcH3-AcH4 declines with age and is upregulated by treatments restoring plasticity in the adult. We also found that visual experience modulates AcH3-AcH4 in young and adult plasticity-restored mice but not in untreated ones. Finally, we showed that the transporter vGAT is downregulated in adult plasticity-restored models. In summary, we identified a dynamic regulation of AcH3-AcH4, which is associated with high plasticity levels and enhanced by visual experience. These data, along with recent ones, indicate H3-H4 acetylation as a central hub in the control of experience-dependent plasticity in the VC.

Functional synchrony and stimulus selectivity of visual cortical units: Comparison between cats and mice

In spite of the fact that the functional organization of primary visual cortices (V1) differs across species, the dynamic of orientation selectivity is highly structured within neuronal populations. In fact, neurons functionally connect each other in an organized Hebbian process, wherein their wiring and firing are intimately related. Moreover, neuronal ensembles have been suggested to be strongly implicated in sensory processing. Within these ensembles, neurons may be sharply or broadly tuned in relation to the stimulus. Therefore, it is important to determine the relationship between the response selectivity of neurons and their functional connectivity pattern across species. In the present investigation, we sought to compare the stimulus-evoked functional connectivity between the broadly tuned and the sharply tuned neurons in two species exhibiting different cortical organization for orientation selectivity: cats (columnar-organized) and mice (salt-and-pepper organization). In addition, we examined the distribution of connectivity weights within cell-assemblies in the visual cortex during visual adaptation. First, we report that the sharply tuned neurons exhibited higher synchrony index than the broadly tuned cells in the cat visual cortex. On the contrary, in mice, the broadly tuned cells displayed higher connectivity index. Second, a significant correlation was found between the connectivity strength and the difference of preferred orientations of neurons for both species. Finally, we observed a systematic adjustment of the connectivity weights within neuronal ensembles in mouse primary visual cortex similarly to the cat V1.

Effects of Fluoxetine and Visual Experience on Glutamatergic and GABAergic Synaptic Proteins in Adult Rat Visual Cortex

Fluoxetine has emerged as a novel treatment for persistent amblyopia because in adult animals it reinstates critical period-like ocular dominance plasticity and promotes recovery of visual acuity. Translation of these results from animal models to the clinic, however, has been challenging because of the lack of understanding of how this selective serotonin reuptake inhibitor affects glutamatergic and GABAergic synaptic mechanisms that are essential for experience-dependent plasticity. An appealing hypothesis is that fluoxetine recreates a critical period (CP)-like state by shifting synaptic mechanisms to be more juvenile. To test this we studied the effect of fluoxetine treatment in adult rats, alone or in combination with visual deprivation [monocular deprivation (MD)], on a set of highly conserved presynaptic and postsynaptic proteins (synapsin, synaptophysin, VGLUT1, VGAT, PSD-95, gephyrin, GluN1, GluA2, GluN2B, GluN2A, GABAAα1, GABAAα3). We did not find evidence that fluoxetine shifted the protein amounts or balances to a CP-like state. Instead, it drove the balances in favor of the more mature subunits (GluN2A, GABAAα1). In addition, when fluoxetine was paired with MD it created a neuroprotective-like environment by normalizing the glutamatergic gain found in adult MDs. Together, our results suggest that fluoxetine treatment creates a novel synaptic environment dominated by GluN2A- and GABAAα1-dependent plasticity.