Differential Local Connectivity and Neuroinflammation Profiles in the Medial Prefrontal Cortex and Hippocampus in the Valproic Acid Rat Model of Autism.

Autism spectrum disorders (ASD) are a group of developmental disabilities characterized by impaired social interaction, communication deficit and repetitive and stereotyped behaviors. Neuroinflammation and synaptic alterations in several brain areas have been suggested to contribute to the physiopathology of ASD. Although the limbic system plays an important role in the functions found impaired in ASD, reports on these areas are scarce and results controversial. In the present study we searched in the medial prefrontal cortex (mPFC) and hippocampus of rats exposed to the valproic acid (VPA) model of ASD for early structural and molecular changes, coincident in time with the behavioral alterations. After confirming delayed growth and maturation in VPA rats, we were able to detect decreased exploratory activity and social interaction at an early time point (postnatal day 35). In mPFC, although typical cortical column organization was preserved in VPA animals, we found that interneuronal space was wider than in controls. Hippocampal CA3 (cornu ammonis 3) pyramidal layer and the granular layer of the dentate gyrus both showed a disorganized spatial arrangement in VPA animals. Neuronal alterations were accompanied with increased tomato lectin and glial fibrillary acidic protein (GFAP) immunostainings both in the mPFC and hippocampus. In the latter region, the increased GFAP immunoreactivity was CA3 specific. At the synaptic level, while mPFC from VPA animals showed increased synaptophysin (SYN) immunostaining, a SYN deficit was found in all hippocampal subfields. Additionally, both the mPFC and the hippocampus of VPA rats showed increased neuronal cell adhesion molecule (NCAM) immunostaining together with decreased levels of its polysialylated form (PSA-NCAM). Interestingly, these changes were more robust in the CA3 hippocampal subfield. Our results indicate that exploratory and social deficits correlate with region-dependent neuronal disorganization and reactive gliosis in the mPFC and hippocampus of VPA rats. While microgliosis is spread in these two limbic areas, astrogliosis, although extended in the mPFC, is circumscribed to the CA3 hippocampal subfield. Our work indicates that neuroinflammation and synaptic alterations do coexist in VPA rats, making this model suitable for studying novel aspects of neuron-glia interactions. Moreover, it suggests that the mPFC and hippocampus might behave differently in the context of the local hyperconnectivity and synaptic hypotheses of autism. © 2015 S. Karger AG, Basel.

Distinctive PSA-NCAM and NCAM hallmarks in glutamate-induced dendritic atrophy and synaptic disassembly.

Dendritic and synapse remodeling are forms of structural plasticity that play a critical role in normal hippocampal function. Neural cell adhesion molecule (NCAM) and its polysialylated form (PSA-NCAM) participate in neurite outgrowth and synapse formation and plasticity. However, it remains unclear whether they contribute to dendritic retraction and synaptic disassembly. Cultured hippocampal neurons exposed to glutamate (5 µM) showed a reduced MAP-2 (+) area in the absence of neuronal death 24 h after the insult. Concomitantly, synapse loss, revealed by decreased synaptophysin and post-synaptic density-95 cluster number and area, together with changes in NCAM and PSA-NCAM levels were found. Dendritic atrophy and PSA-NCAM reduction proved NMDA-receptor dependent. Live-imaging experiments evidenced dendritic atrophy 4 h after the insult; this effect was preceded by smaller NCAM clusters (1 h) and decreased surface and total PSA-NCAM levels (3 h). Simultaneously, total NCAM cluster number and area remained unchanged. The subsequent synapse disassembly (6 h) was accompanied by reductions in total NCAM cluster number and area. A PSA mimetic peptide prevented both the dendritic atrophy and the subsequent synaptic changes (6 h) but had no effect on the earliest synaptic remodeling (3 h). Thus, NCAM-synaptic reorganization and PSA-NCAM level decrease precede glutamate-induced dendritic atrophy, whereas the NCAM level reduction is a delayed event related to synapse loss. Consequently, distinctive stages in PSA-NCAM/NCAM balance seem to accompany glutamate-induced dendritic atrophy and synapse loss.

Fluoxetine potentiation of omega-3 fatty acid antidepressant effect: evaluating pharmacokinetic and brain fatty acid-related aspects in rodents.

We previously reported that combined fluoxetine administration at antidepressant doses renders additive antidepressant effects, whereas non-antidepressant doses potentiate the omega-3 fatty acid antidepressant effect. In the present study, we aimed to evaluate putative pharmacokinetic and brain omega-3 fatty acid-related aspects for fluoxetine potentiation of omega-3 fatty acid antidepressant effect in rats. Coadministration of omega-3 fatty acids with a non-antidepressant dose of fluoxetine (1 mg/kg day) failed to affect both brain fluoxetine concentration and norfluoxetine plasma concentration profile. Fluoxetine plasma concentrations remained below the sensitivity limit of the detection method. Either antidepressant (10 mg/kg day) or non-antidepressant (1 mg/kg day) doses of fluoxetine in combination with omega-3 fatty acids increased hippocampal docosapentaenoic acid (DPA, 22:5 omega-3) levels. Although individual treatments had no effects on DPA concentration, DPA increase was higher when omega-3 were combined with the non-antidepressant dose of fluoxetine. Chronic DPA administration exerted antidepressant-like effects in the forced swimming test while increasing hippocampal docosahexaenoic (22:6 omega-3) and DPA levels. Our results suggest no pharmacokinetic interaction and reveal specific hippocampal DPA changes after fluoxetine and omega-3 combined treatments in our experimental conditions. The DPA role in the synergistic effect of fluoxetine and omega-3 combined treatments will be for sure the focus of future studies. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:3316-3325, 2014.

Maintenance treatment with fluoxetine is necessary to sustain normal levels of synaptic markers in an experimental model of depression: correlation with behavioral response.

Dysfunction of hippocampal plasticity has been proposed to play a critical role in the pathophysiology of depression. However, antidepressant drug effects on synaptic plasticity and cytoskeletal remodeling remain controversial. The aim of the present study was to evaluate in animals exposed to the learned helplessness (LH) paradigm, an accepted experimental model of depression, the effect of chronic treatment with fluoxetine (FLX) on synaptic and cytoskeletal proteins known to undergo plastic changes. Synaptophysin (SYN), postsynaptic density 95 (PSD-95), axon growth-associated protein 43 (GAP-43), and cytoskeletal proteins (intermediate neurofilaments and MAP-2) were studied in the hippocampus by immunohistochemistry. Whereas LH animals treated 21 days with saline (LH-S group) displayed diminished SYN and PSD-95 immunostainings in the CA3 but not in the DG, chronic treatment with FLX not only reversed the despaired behavior induced by exposure to LH paradigm, but also fully recovered SYN and PSD-95 labeling to control values. Similar results were obtained for the axonal remodeling marker GAP-43. FLX treatment did not modify either the decreased light neurofilament subunit (NFL) observed in the hippocampus of LH animals or any other cytoskeletal protein studied. When FLX treatment was withdrawn for 90 days in those LH-FLX animals in which reversion of despair had been observed at day 25, recurrence of despaired behavior was found accompanied by decreased SYN, PSD-95, and NFL labelings. Results indicate that the synapse remodeling induced by FLX in the CA3 region could underlie its behavioral efficacy despite the absence of cytoskeletal remodeling and that the stability of synaptic changes would depend on the continuous administration of the drug.