Regional-specific effects of cerebral ischemia/reperfusion and dehydroepiandrosterone on synaptic NMDAR/PSD-95 complex in male Wistar rats

Effects of transcranial direct current stimulation on the glutamatergic pathway in the male rat hippocampus after experimental focal cerebral ischemia

This study aimed to assess the focal cerebral ischemia-induced changes in learning and memory together with glutamatergic pathway in rats and the effects of treatment of the animals with transcranial Direct Current Stimulation (tDCS). One hundred male rats were divided into five groups as sham, tDCS, Ischemia/Reperfusion (IR), IR + tDCS, and IR + E-tDCS groups. Learning, memory, and locomotor activity functions were evaluated by behavioral experiments in rats. Glutamate and glutamine levels, alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate receptor (AMPAR1), N-Methyl-D-Aspartate receptors (NMDAR1 and NMDAR2A), vesicular glutamate transporter-1 (VGLUT-1), and excitatory amino acid transporters (EAAT1-3) mRNA expressions in hippocampus tissues were measured. Ischemic areas were analyzed by TTC staining. The increase was observed in IR + tDCS, and IR + E-tDCS groups compared to the IR group while a significant decrease was observed in IR group compared to the sham in the locomotor activity, learning, and memory tests. While glutamate and glutamine levels, AMPAR1, NMDAR1, NMDAR2A, VGLUT1, and EAAT1 mRNA expressions were significantly higher in IR group compared to the sham group, it was found to be significantly lower in IR + tDCS and IR + E-tDCS groups compared to the IR group. EAAT2 and EAAT3 mRNA expressions were significantly higher in IR + tDCS and IR + E-tDCS groups compared to the IR group. Ischemic areas were significantly decreased in IR + tDCS and IR + E-tDCS groups compared to the IR group. Current results suggest that tDCS application after ischemia improves learning and memory disorders and these effects of tDCS may be provided through transporters that regulate glutamate levels.

Prolonged Zaleplon Treatment Increases the Expression of Proteins Involved in GABAergic and Glutamatergic Signaling in the Rat Hippocampus

Zaleplon is a positive allosteric modulator of the γ-aminobutyric acid (GABA)A receptor approved for the short-term treatment of insomnia. Previous publications on zaleplon have not addressed the proteins involved in its mechanism of action but have mostly referred to behavioral or pharmacological studies. Since both GABAergic and glutamatergic signaling have been shown to regulate wakefulness and sleep, we examined the effects of prolonged zaleplon treatment (0.625 mg/kg for 5 days) on these systems in the hippocampus of male Wistar rats. Western blot and immunohistochemical analyses showed that the upregulated components of GABAergic signaling (glutamate decarboxylase, vesicular GABA transporter, GABA, and α1 subunit of the GABAA receptor) were accompanied by increased protein levels in the glutamatergic system (vesicular glutamate transporter 1 and NR1, NR2A, and NR2B subunits of N-methyl-d-aspartate receptor). Our results, showing that zaleplon enhances GABA neurotransmission in the hippocampus, were not surprising. However, we found that treatment also increased glutamatergic signaling. This could be the result of the downregulation of adenosine A1 receptors, important modulators of the glutamatergic system. Further studies are needed to investigate the effects of the zaleplon-induced increase in hippocampal glutamatergic neurotransmission and the possible involvement of the adenosine system in zaleplon's mechanism of action.

Delayed administration of Trichilia catigua A. Juss. Ethyl-acetate fraction after cerebral ischemia prevents spatial memory deficits, decreases oxidative stress, and impacts neural plasticity in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Trichilia catigua A. Juss (Meliaceae) is used in Brazilian folk medicine to alleviate fatigue and emotional stress and improve memory. Previous studies from our laboratory reported that an ethyl-acetate fraction (EAF) of T. catigua that was given before cerebral ischemia in vivo prevented memory loss and reduced oxidative stress and neuroinflammation. Despite the value of these findings of a neuroprotective effect of T. catigua, treatment that was given immediately before or immediately after ischemia limits its clinical relevance. Thus, unknown is whether T. catigua possesses a specific time window of efficacy (TWE) when administered postischemia.

AIM OF THE STUDY

Given continuity to previous studies, we investigated whether an EAF of T. catigua maintains its neuroprotective properties if treatment begins at different time windows of efficacy after ischemia. We also evaluated, for the first time, whether T. catigua possesses neuroplasticity/neurotrophic properties.

MATERIAL AND METHODS

Rats were subjected to transient global brain ischemia (TGCI) and then given a single dose of the EAF (400 mg/kg) or vehicle (1 ml/kg) orally 1, 4, or 6 h postischemia. The levels of protein PCG, GSH, and GSSG, and activity of SOD and CAT were assayed as markers of oxidative stress on the day after ischemia. In another experiment, naive rats underwent spatial learning training in a radial maze task and then subjected to TGCI. Delayed treatment with the EAF began 4 or 6 h later and continued for 7 days. Retrograde memory performance was assessed 10, 17, and 24 days postischemia. Afterward, brains were examined for neurodegeneration and neuronal dendritic morphology in the hippocampus and cerebral cortex. Another group received the EAF at 4 h of reperfusion, and 4 days later their brains were examined for GFAP and Iba-1 immunoreactivity. Lastly, ischemic rats received the EAF 4 h after ischemia and neural plasticity-related proteins, BDNF, SYN, PSD 95, and NeuN were measured in the hippocampus 7 and 14 days after ischemia.

RESULTS

A single EAF administration 1, 4, or 6 h postischemia alleviated oxidative stress that was caused by ischemia, expressed as a reduction of the amount of the PCG and GSSG, normalization of the GSH/GSSG ratio, and the restoration of SOD activity. Ischemia caused the persistent loss of memory (i.e., amnesia), an outcome that was consistently ameliorated by treatment with the EAF that was initiated 4 or 6 h postischemia. The 4 h delay in EAF treatment positively impacted dendritic morphology in neurons that survived ischemia. TGCI reduced BDNF, SYN, PSD-95, and NeuN protein levels in the hippocampus and cerebral cortex. The EAF normalized SYN and PSD-95 protein levels. Ischemia-induced neurodegeneration and glial cell activation were not prevented by EAF treatment.

CONCLUSION

The present study corroborates prior data that demonstrated the neuroprotective potential of T. catigua and extends these data by showing that the delayed administration of EAF postischemia effectively prevented memory impairment and decreased oxidative stress, dendritic deterioration, and synaptic protein loss within a TWE that ranged from 1 to 6 h. This specific TWE in preclinical research may have clinical relevance by suggesting the possible utility of this plant for the development of neuroprotective strategies in the setting of ischemic brain diseases. Another innovative finding of the present study was the possible neurotrophic/neuroplastic properties of T. catigua.

DNA hypomethylation promotes learning and memory recovery in a rat model of cerebral ischemia/reperfusion injury

Cerebral ischemia/reperfusion injury impairs learning and memory in patients. Studies have shown that synaptic function is involved in the formation and development of memory, and that DNA methylation plays a key role in the regulation of learning and memory. To investigate the role of DNA hypomethylation in cerebral ischemia/reperfusion injury, in this study, we established a rat model of cerebral ischemia/reperfusion injury by occlusion of the middle cerebral artery and then treated the rats with intraperitoneal 5-aza-2′-deoxycytidine, an inhibitor of DNA methylation. Our results showed that 5-aza-2′-deoxycytidine markedly improved the neurological function, and cognitive, social and spatial memory abilities, and dose-dependently increased the synaptic density and the expression of SYP and SHANK2 proteins in the hippocampus in a dose-dependent manner in rats with cerebral ischemia/reperfusion injury. The effects of 5-aza-2′-deoxycytidine were closely related to its reduction of genomic DNA methylation and DNA methylation at specific sites of the Syp and Shank2 genes in rats with cerebral ischemia/reperfusion injury. These findings suggest that inhibition of DNA methylation by 5-aza-2′-deoxycytidine promotes the recovery of learning and memory impairment in a rat model of cerebral ischemia/reperfusion injury. These results provide theoretical evidence for stroke treatment using epigenetic methods.

Brain Microvascular Endothelial Cell-Derived Exosomes Protect Neurons from Ischemia–Reperfusion Injury in Mice

Stroke often results in neurological and neuropsychiatric sequela. Exosomes derived from brain endothelial cells (EC-Exo) protect neurons from hypoxic injury. However, the biological role of exosomes in apoptosis and synaptic plasticity remains unclear. This research aimed to assess whether cerebral microvascular endothelial cells inhibit apoptosis and promote synaptic remodeling through exosome-mediated cell–cell interaction after the ischemic attack. The effects of EC-Exo on primary neuronal apoptosis and synapses in oxyglucose deprivation reoxygenation (OGD/R) injury were first assessed in vitro. Animal experiments were performed using C57BL/6J mice, divided into three groups: a sham group, a model (middle cerebral artery occlusion/reperfusion, MCAO/R) group, and an EC-Exo group (tail vein injection of EC-Exo, once/2 days for 14 days) to evaluate the neuromotor and exploratory abilities of mice after MCAO/R. Apoptosis and synaptic protein expression levels were detected. The results demonstrated that EC-Exo inhibited neuronal apoptosis and increased synaptic length after OGD/R. In vivo, EC-Exo not only improved neural motor behavior and increased regional cerebral blood flow (rCBF) in MCAO/R-injured mice but also promoted the expression of synaptic regulatory proteins and inhibited apoptosis in the brain. These results suggest that EC-Exo may provide neuroprotection against stroke by promoting synaptic remodeling and inhibiting apoptosis from protecting neurons.

Inhibition of JNK Alleviates Chronic Hypoperfusion-Related Ischemia Induces Oxidative Stress and Brain Degeneration via Nrf2/HO-1 and NF-κB Signaling

Cerebral ischemia is one of the leading causes of neurological disorders. The exact molecular mechanism related to chronic unilateral cerebral ischemia-induced neurodegeneration and memory deficit has not been precisely elucidated. In this study, we examined the effect of chronic ischemia on the induction of oxidative stress and c-Jun N-terminal kinase-associated detrimental effects and unveiled the inhibitory effect of specific JNK inhibitor (SP600125) on JNK-mediated brain degeneration in adult mice. Our behavioral, biochemical, and immunofluorescence studies revealed that chronic ischemic injuries sustained increased levels of oxidative stress-induced active JNK for a long time, whereas SP600125 significantly reduced the elevated level of active JNK and further regulated Nrf2/HO-1 and NF-κB signaling, which have been confirmed in vivo. Neuroinflammatory mediators and loss of neuronal cells was significantly reduced with the administration of SP600125. Ischemic brain injury caused synaptic dysfunction and memory impairment in mice. However, these were significantly improved with SP600125. On the whole, these findings suggest that elevated ROS-mediated JNK is a key mediator in chronic ischemic conditions and has a crucial role in neuroinflammation, neurodegeneration, and memory dysfunction. Our findings suggest that chronic oxidative stress associated JNK would be a potential target in time-dependent studies of chronic ischemic conditions induced brain degeneration.

Steroid hormone secretion after stimulation of mineralocorticoid and NMDA receptors and cardiovascular risk in patients with depression

Major depressive disorder (MDD) is associated with altered mineralocorticoid receptor (MR) and glucocorticoid receptor function, and disturbed glutamatergic signaling. Both systems are closely intertwined and likely contribute not only to the pathophysiology of MDD, but also to the increased cardiovascular risk in MDD patients. Less is known about other steroid hormones, such as aldosterone and DHEA-S, and how they affect the glutamatergic system and cardiovascular disease risk in MDD. We examined salivary cortisol, aldosterone, and DHEA-S secretion after stimulation of MR and glutamatergic NMDA receptors in 116 unmedicated depressed patients, and 116 age- and sex-matched healthy controls. Patients (mean age = 34.7 years, SD = ±13.3; 78% women) and controls were randomized to four conditions: (a) control condition (placebo), (b) MR stimulation (0.4 mg fludrocortisone), (c) NMDA stimulation (250 mg D-cycloserine (DCS)), and (d) combined MR/NMDA stimulation (fludrocortisone + DCS). We additionally determined the cardiovascular risk profile in both groups. DCS had no effect on steroid hormone secretion, while cortisol secretion decreased in both fludrocortisone conditions across groups. Independent of condition, MDD patients showed (1) increased cortisol, increased aldosterone, and decreased DHEA-S concentrations, and (2) increased glucose levels and decreased high-density lipoprotein cholesterol levels compared with controls. Depressed patients show profound alterations in several steroid hormone systems that are associated both with MDD pathophysiology and increased cardiovascular risk. Prospective studies should examine whether modulating steroid hormone levels might reduce psychopathology and cardiovascular risk in depressed patients.

Progesterone Protects Prefrontal Cortex in Rat Model of Permanent Bilateral Common Carotid Occlusion via Progesterone Receptors and Akt/Erk/eNOS

Sustained activation of pro-apoptotic signaling due to a sudden and prolonged disturbance of cerebral blood circulation governs the neurodegenerative processes in prefrontal cortex (PFC) of rats whose common carotid arteries are permanently occluded. The adequate neuroprotective therapy should minimize the activation of toxicity pathways and increase the activity of endogenous protective mechanisms. Several neuroprotectants have been proposed, including progesterone (P₄). However, the underlying mechanism of its action in PFC following permanent bilateral occlusion of common carotid arteries is not completely investigated. We, thus herein, tested the impact of post-ischemic P₄ treatment (1.7 mg/kg for seven consecutive days) on previously reported aberrant neuronal morphology and amount of DNA fragmentation, as well as the expression of progesterone receptors along with the key elements of Akt/Erk/eNOS signal transduction pathway (Bax, Bcl-2, cytochrome C, caspase 3, PARP, and the level of nitric oxide). The obtained results indicate that potential amelioration of histological changes in PFC might be associated with the absence of activation of Bax/caspase 3 signaling cascade and the decline of DNA fragmentation. The study also provides the evidence that P₄ treatment in repeated regiment of administration might be effective in neuronal protection against ischemic insult due to re-establishment of the compromised action of Akt/Erk/eNOS-mediated signaling pathway and the upregulation of progesterone receptors.

Molecular Alterations and Effects of Acute Dehydroepiandrosterone Treatment Following Brief Bilateral Common Carotid Artery Occlusion: Relevance to Transient Ischemic Attack

Transient ischemic attack (TIA) represents brief neurological dysfunction of vascular origin without detectable infarction. Despite major clinical relevance characterization of post-TIA molecular changes using appropriate experimental model is lacking and no therapeutic agent has been established yet. Neurosteroid dehydroepiandrosterone (DHEA) arose as one of the candidates for cerebral ischemia treatment but its effects on TIA-like condition remain unknown. Seeking an animal model applicable for investigation of molecular alterations in mild ischemic conditions such as TIA, 15-min bilateral common carotid artery occlusion with 24-h reperfusion was performed to induce ischemia/ reperfusion (I/R) injury in adult male Wistar rats. Additionally, effects of 4-h post-operative DHEA treatment (20 mg/kg) were investigated in physiological and I/R conditions in hippocampus (HIP) and prefrontal cortex (PFC). The study revealed absence of sensorimotor deficits, cerebral infarcts and neurodegeneration along with preserved HIP and PFC overall neuronal morphology and unaltered malondialdehyde and reduced glutathione level following I/R and/or DHEA treatment. I/R induced nitric oxide burst in HIP and PFC was accompanied with increased neuronal nitric oxide synthase protein level exclusively in HIP. DHEA had no effects in physiological conditions, while increase of Bax/Bcl2 ratio and dissipation of mitochondrial membrane potential in treated I/R group suggested DHEA-mediated exacerbation of post-ischemic changes that might lead to pro-apoptotic events in HIP. Interestingly, DHEA restored I/R-induced NO to the control level in PFC. Obtained results indicated that I/R may serve as an appropriate model for investigation of molecular changes and treatment outcome following mild ischemic conditions such as TIA.