Parameters of Oxidative Stress and Behavior in Animals Treated with Dexametasone and Submitted to Pentylenetetrazol Kindling

Background and Purpose: Oxidative stress (OS) is defined as an excessive production of reactive oxygen species that cannot be neutralized by the action of antioxidants, but also as an alteration of the cellular redox balance. The relationship between OS and epilepsy is not yet fully understood. The objective of this study was to evaluate the effect of dexamethasone on OS levels and memory in the kindling model induced by pentylenetetrazole.Methods: The animals were divided in six groups: control group that received no treatment, vehicle group treated with vehicle, diazepam group, and groups treated with dexamethasone (1, 2 and 4 mg/kg). Treated animals received pentylenetetrazole in alternated days for 15 days. Inhibitory avoidance test was conducted in 2 hours and OS was evaluated after animal sacrifice.Results: Regarding the treatment with dexamethasone, there was no significant difference when compared to the control groups in relation to the inhibitory avoidance test. On OS levels, there was a decrease in catalase activity levels in the hippocampus and an increase in thiobarbituric acid reactive substances and glutathione peroxidase levels in the hippocampus.Conclusions: The anticonvulsant effect of dexametasone remains uncertain. Immunological mechanisms, with the release of cytokines and inflammatory mediators, seem to be the key to this process. The mechanisms that generate OS are probably related to the anticonvulsant effects found.

The Discordance between Network Excitability and Cognitive Performance Following Vigabatrin Treatment during Epileptogenesis

Vigabatrin (VGB), a potent selective γ-aminobutyric acid transaminase (GABA-T) inhibitor, is an approved non-traditional anti-seizure drug for patients with intractable epilepsy. Nevertheless, its effect on epileptogenesis, and whether this effect is correlated with post-epileptogenic cognitive function remain unclear. Based on lithium-pilocarpine-induced seizure modeling, we evaluated the effect of VGB on epileptogenesis and neuronal damage following status epilepticus in Sprague–Dawley rats. Cognitive evaluations were performed with the aid of inhibitory avoidance testing. We found that VGB could interrupt epileptogenesis by reducing spontaneous recurrent seizures, hippocampal neuronal damage, and chronic mossy fiber sprouting. Nevertheless, VGB did not help with the retention of cognitive performance. Our findings suggest that further research into the role of VGB in epileptogenesis and the treatment of epilepsy in clinical practice is warranted.

Experience-induced remodeling of the hippocampal post-synaptic proteome and phosphoproteome

The post synaptic density (PSD) of excitatory synapses contains a highly organized protein network with thousands of proteins and is key node in the regulation of synaptic plasticity. To gain new mechanistic insight into experience-induced changes in the PSD, we examined the global dynamics of the PSD proteome and phosphoproteome in mice following various treatments. Mice were trained using an inhibitory avoidance (IA) task and hippocampal PSD fractions were isolated for quantitative proteomic and phosphoproteomics analysis. We used a sequential enrichment strategy to explore the concurrent events of protein expression and phosphorylation in the hippocampal PSD following IA training (IA) or immediate shock (Shock). We identified more than 6,200 proteins and 3,000 phosphoproteins in the sequential strategy covering a total of 7,429 proteins. On the phosphoproteins we identified a total of 9,589 phosphosites. Strikingly, of the significantly IA-regulated proteins and phosphoproteins, a large fraction of the proteins displayed an overall decrease in phosphorylation level. Bioinformatic analysis of proteins and phosphoproteins that were regulated by IA were annotated for an involvement in regulation of glutamate receptor functionality, calcium signaling, and synaptic plasticity. We also identified synaptic kinases, phosphatases and their respective phosphosites regulated by IA training or iimmediate shock. Furthermore, we found that AMPA receptor surface expression was regulatedby protein phosphatase, Mg2+/Mn2+ dependent 1H (Ppm1h). Together, these results unravel the dynamic remodeling of the PSD upon IA learning or immediate shock and serve as a resource for elucidating the synaptic proteome dynamics induced by experience-dependent plasticity.

The Effect of Spironolactone on β-amyloid-Induced Memory Impairment in Male Rats: The Role of Microglial Inhibition

Purpose: Neuroinflammation was indicated in the pathophysiology of Alzheimer’s disease. Previous reports have also signified that spironolactone has anti-inflammatory effects. Therefore, the aim of this study was to assess the modulatory effects of spironolactone on neuroinflammation and memory loss in a rat model of Alzheimer’s disease. Methods: The β-amyloid protein fragment 25-35 (Aβ) was injected in the dorsal hippocampus (5μg/2.5μl each side) of male Sprague-Dawley rats for four consecutive days to induce memory impairment. Animals have intraperitoneally received spironolactone (10, 25, or 50 mg/kg, N=6/group) or vehicle for 14 days. The passive inhibitory avoidance and the novel recognition tests were used for memory evaluation. Neuroinflammation was assessed by measuring the level of Iba1 protein, a marker of microglial activation, using western immunoblotting. Results: Different doses of spironolactone showed no significant changes in latency times and discriminations ratios in passive inhibitory avoidance and novel recognition tests, respectively, as compared to vehicle. However, spironolactone-treated groups showed significantly lower Iba1 protein levels in comparison to the vehicle-treated group (p<0.01). Conclusion: Spironolactone had a modulatory effect on neuroinflammation through a repressive effect on microglial activation with no valuable effect on memory improvement in a rat model of Alzheimer’s disease. The findings of this study suggest that Ab-induced memory loss may not be directly linked to microglial activation. Spironolactone may be a potential candidate to be examined in other neuroinflammatory disorders.

mGluR5 Negative Modulators for Fragile X: Treatment Resistance and Persistence

Fragile X syndrome (FXS) is caused by silencing of the human FMR1 gene and is the leading monogenic cause of intellectual disability and autism. Abundant preclinical data indicated that negative allosteric modulators (NAMs) of metabotropic glutamate receptor 5 (mGluR5) might be efficacious in treating FXS in humans. Initial attempts to translate these findings in clinical trials have failed, but these failures provide the opportunity for new discoveries that will improve future trials. The emergence of acquired treatment resistance (“tolerance”) after chronic administration of mGluR5 NAMs is a potential factor in the lack of success. Here we confirm that FXS model mice display acquired treatment resistance after chronic treatment with the mGluR5 NAM CTEP in three assays commonly examined in the mouse model of FXS: (1) audiogenic seizure susceptibility, (2) sensory cortex hyperexcitability, and (3) hippocampal protein synthesis. Cross-tolerance experiments suggest that the mechanism of treatment resistance likely occurs at signaling nodes downstream of glycogen synthase kinase 3α (GSK3α), but upstream of protein synthesis. The rapid emergence of tolerance to CTEP begs the question of how previous studies showed an improvement in inhibitory avoidance (IA) cognitive performance after chronic treatment. We show here that this observation was likely explained by timely inhibition of mGluR5 during a critical period, as brief CTEP treatment in juvenile mice is sufficient to provide a persistent improvement of IA behavior measured many weeks later. These data will be important to consider when designing future fragile X clinical trials using compounds that target the mGluR5-to-protein synthesis signaling cascade.

Effects of New Galantamine Derivatives in a Scopolamine Model of Dementia in Mice

Alzheimer’s disease (AD), a progressive neurodegenerative disorder characterized by memory loss and cognitive functions decline, is a leading cause for dementia and currently ranked as the sixth foremost cause of death. As of present, treatment of AD is symptomatic without convincing therapeutic benefits and new, effective, therapeutic agents are pursued. Due to massive loss of cholinergic neurons and decreased acetylcholine levels, cholinesterase inhibitors like galantamine, remain the backbone of pharmacological treatment of the disease. In the present study, using behavioral and biochemical methods, four newly synthesized galantamine derivatives, Gal 34, Gal 43, Gal 44, and Gal 46, were evaluated for a beneficial effect in a scopolamine model of dementia in mice. They were designed to have all the advantages of galantamine and additionally to inhibit β-secretase and exert favorable effects on plasma lipids. Behavioral tests included step-through inhibitory avoidance, T-maze, and the hole-board test, whereas biochemical evaluations involved assessment of acetylcholinesterase activity, brain monoamines levels, lipid peroxidation, catalase, glutathione peroxidase, and superoxide dismutase activities along with measurement of total glutathione. Results show that Gal 43, Gal 44, and, in particular, Gal 46 are especially effective in improving both short- and long-term memory and in the case of Gal 46 having a significant effect on exploratory activity as well. Although Gal 34 did not show behavioral effects as convincing as those of the other three galantamine derivatives, it demonstrated persuasive antioxidant and restorative capacities, making all four galantamine derivatives promising AD treatment agents and prompting further research, especially that in many of our studies they performed better than galantamine.

Perinatal Inflammation Disturbs Secondary Germinal Zone Neurogenesis and Gliogenesis Producing Deficits in Sociability

Epidemiologic studies have demonstrated that infections during pregnancy increase the risk of offspring developing Schizophrenia, Autism, Depression and Bipolar Disorder and have implicated interleukin-6 (IL-6) as a causal agent. However, other cytokines have been associated with psychiatric disorders; therefore, it remains to be established whether elevating IL-6 is sufficient to alter the trajectory of neural development. Furthermore, most rodent studies have manipulated the maternal immune system at mid-gestation, which affects the stem cells and progenitors in both the primary and secondary germinal matrices. Therefore, a question that remains to be addressed is whether elevating IL-6 when the secondary germinal matrices are most active will affect brain development. Here, we have increased IL-6 from postnatal days 3-6, when the secondary germinal matrices are rapidly expanding. Using Nestin-CreERT2 fate mapping we show that this transient increase in IL-6 decreased neurogenesis in the dentate gyrus of the dorsal hippocampus, reduced astrogliogenesis in the prefrontal cortex and amygdala and decreased oligodendrogenesis in the body and splenium of the corpus callosum all by ~50%. Moreover, the IL-6 treatment elicited behavioral changes classically associated with neurodevelopmental disorders. As adults, IL-6 injected male mice lost social preference in the social approach test, spent ~30% less time socially engaging with sexually receptive females and produced ~50% fewer ultrasonic vocalizations during mating. They also engaged ~50% more time in self-grooming behavior and had an increase in inhibitory avoidance. Altogether, these data provide new insights into the biological mechanisms linking perinatal immune activation to complex neurodevelopmental brain disorders.

Recovery of memory from infantile amnesia is developmentally constrained

Episodic memories formed during infancy are rapidly forgotten, a phenomenon associated with infantile amnesia, the inability of adults to recall early-life memories. In both rats and mice, infantile memories, although not expressed, are actually stored long term in a latent form. These latent memories can be reinstated later in life by certain behavioral reminders or by artificial reactivations of neuronal ensembles activated at training. Whether the recovery of infantile memories is limited by developmental age, maternal presence, or contingency of stimuli presentation remains to be determined. Here, we show that the return of inhibitory avoidance memory in rats following a behavioral reactivation consisting of an exposure to the context (conditioned stimuli [CS]) and footshock (unconditioned stimuli [US]) given in a temporally unpaired fashion, is evident immediately after US and is limited by the developmental age at which the reactivations are presented; however, it is not influenced by maternal presence or the time interval between training and reactivation. We conclude that one limiting factor for infantile memory reinstatement is developmental age, suggesting that a brain maturation process is necessary to allow the recovery of a “lost” infantile memory.