A growing body of evidence suggests the existence of a functional interaction between gabapentin (GBP)-morphine system. However, the neuro-anatomical sites and molecular mechanism of action of gabapentin-morphine interaction to prevent and reverse morphine side effects as well as enhancement of the analgesic effect of morphine is not clear. Therefore, we examined the combined effects of GBP-morphine on acute morphine-induced c-Fos expression in rat nucleus accumbens. The combined effect of GBP-morphine was examined by means of c-Fos immunohistochemistry. A single intraperitoneal injection (i.p.) of morphine (10 mg/kg), saline (control), and co-injection of GBP (150 mg/kg) with morphine (5 mg/kg) was administered under anesthesia. The deeply anesthetized rats were perfused transcardially with 4% paraformaldehyde 2 h after drugs administration. Serial 40 μm thick sections of brain were cut and processed by immunohistochemistry to locate and quantify the sites and number of neurons with c-Fos immunoreactivity. Detection of c-Fos protein was performed using the peroxidase-antiperoxidase detection protocol. The present study demonstrated that, administration of GBP (150 mg/kg, i.p.) in combination with morphine (5 mg/kg, i.p.) significantly (p < 0.01) attenuated the acute morphine (5 mg/kg, i.p.)-induced c-Fos expression in the rat nucleus accumbens shell. Present results showed that GBP-morphine combination action prevented the acute morphine-induced c-Fos expression in rat nucleus accumbens. Moreover, this study provides first evidence of neuro-anatomical site and that GBP neutralized the morphine-induced activation of rat nucleus accumbens shell.
Neurodevelopmental disorders are defined as a set of abnormal brain developmental conditions marked by the early childhood onset of cognitive, behavioral, and functional deficits leading to memory and learning problems, emotional instability, and impulsivity. Autism spectrum disorder, attention-deficit/hyperactivity disorder, Tourette syndrome, fragile X syndrome, and Down's syndrome are a few known examples of neurodevelopmental disorders. Although they are relatively common in both developed and developing countries, very little is currently known about their underlying molecular mechanisms. Both genetic and environmental factors are known to increase the risk of neurodevelopmental disorders. Current diagnostic and screening tests for neurodevelopmental disorders are not reliable; hence, individuals with neurodevelopmental disorders are often diagnosed in the later stages. This negatively affects their prognosis and quality of life, prompting the need for a better diagnostic biomarker. Recent studies on microRNAs and their altered regulation in diseases have shed some light on the possible role they could play in the development of the central nervous system. This review attempts to elucidate our current understanding of the role that microRNAs play in neurodevelopmental disorders with the hope of utilizing them as potential biomarkers in the future.
The γ-aminobutyric acid type A receptor (GABA (A) receptor) is a membrane protein activated by the neurotransmitter GABA. Structurally, this major inhibitory neurotransmitter receptor in the human central nervous system is a pentamer that can be built from a selection of 19 subunits consisting of α(1,2,3,4,5 or 6), β (1,2 or 3), γ (1,2 or 3), ρ (1,2 or 3), and δ, π, θ, and ε. This creates several possible pentameric arrangements, which also influence the pharmacological and physiological properties of the receptor. The complexity and heterogeneity of the receptors are further increased by the addition of short and long splice variants in several subunits and the existence of multiple allosteric binding sites and expansive ligands that can bind to the receptors. Therefore, a comprehensive understanding of the structure and function of the receptors is required to gain novel insights into the consequences of receptor dysfunction and subsequent drug development studies. Notably, advancements in computational-aided studies have facilitated the elucidation of residual interactions and exploring energy binding, which may otherwise be challenging to investigate. In this review, we aim to summarize the current understanding of the structure and function of GABA (A) receptors obtained from advancements in computational-aided applications.
The coronavirus disease 2019 (COVID-19) pandemic is an issue of global significance that has taken the lives of many across the world. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus responsible for its pathogenesis. The pulmonary manifestations of COVID-19 have been well described in the literature. Initially, it was thought to be limited to the respiratory system; however, we now recognize that COVID-19 also affects several other organs, including the nervous system. Two similar human coronaviruses (CoV) that cause severe acute respiratory syndrome (SARS-CoV-1) and Middle East respiratory syndrome (MERS-CoV) are also known to cause disease in the nervous system. The neurological manifestations of SARS-CoV-2 infection are growing rapidly, as evidenced by several reports. There are several mechanisms responsible for such manifestations in the nervous system. For instance, post-infectious immune-mediated processes, direct virus infection of the central nervous system (CNS), and virus-induced hyperinflammatory and hypercoagulable states are commonly involved. Guillain-Barré syndrome (GBS) and its variants, dysfunction of taste and smell, and muscle injury are numerous examples of COVID-19 PNS (peripheral nervous system) disease. Likewise, hemorrhagic and ischemic stroke, encephalitis, meningitis, encephalopathy acute disseminated encephalomyelitis, endothelialitis, and venous sinus thrombosis are some instances of COVID-19 CNS disease. Due to multifactorial and complicated pathogenic mechanisms, COVID-19 poses a large-scale threat to the whole nervous system. A complete understanding of SARS-CoV-2 neurological impairments is still lacking, but our knowledge base is rapidly expanding. Therefore, we anticipate that this comprehensive review will provide valuable insights and facilitate the work of neuroscientists in unfolding different neurological dimensions of COVID-19 and other CoV associated abnormalities.
Quercetin glycosides, rutin and isoquercitrin, are potent antioxidants that have been found to possess neuroprotective effect in diseases like Parkinson's and Alzheimer's disease. In the present study, we have examined the gene expression changes with rutin and isoquercitrin pretreatment on 6-hydroxydopamine (6-OHDA)-treated toxicity in rat pheochromocytoma (PC12) cells. PC12 cells were pretreated with rutin or isoquercitrin and subsequently exposed to 6-OHDA. Rutin-pretreated PC12 attenuated the Park2, Park5, Park7, Casp3, and Casp7 genes which were expressed significantly in the 6-OHDA-treated PC12 cells. Rutin upregulated the TH gene which is important in dopamine biosynthesis, but isoquercitrin pretreatment did not affect the expression of this gene. Both rutin and isoquercitrin pretreatments upregulated the ion transport and antiapoptotic genes (NSF and Opa1). The qPCR array data were further validated by qRT-PCR using four primers, Park5, Park7, Casp3, and TH. This finding suggests that changes in the expression levels of transcripts encoded by genes that participate in ubiquitin pathway and dopamine biosynthesis may be involved in Parkinson's disease.
GABAA receptors are the major inhibitory neurotransmitter receptor in the human brain. The receptors are assembled from combination of protein subunits in pentameric complex which may consist of α1-6, β1-3, γ1-3, ρ1-3, δ, ε, θ, or π subunits. There are a theoretical > 150,000 possible assemblies and arrangements of GABAA subunits, although only a few combinations have been found in human with the most dominant consists of 2α1, 2β2, and 1γ2 in a counterclockwise arrangement as seen from the synaptic cleft. The receptors also possess binding sites for various unrelated substances including benzodiazepines, barbiturates, and anesthetics. The α5-containing GABAARs only make up ≤ 5% of the entire receptor population, but up to 25% of the receptor subtype is located in the crucial learning and memory-associated area of the brain-the hippocampus, which has ignited myriads of hypotheses and theories in regard to its role. As well as exhibiting synaptic phasic inhibition, the α5-containing receptors are also extrasynaptic and mediate tonic inhibition with continuously occurring smaller amplitude. Studies on negative-allosteric modulators for reducing this tonic inhibition have been shown to enhance learning and memory in neurological disorders such as schizophrenia, Down syndrome, and autism with a possible alternative benzodiazepine binding site. Therefore, a few α5 subunit-specific compounds have been developed to address these pharmacological needs. With its small population, the α5-containing receptors could be the key and also the answer for many untreated cognitive dysfunctions and disorders.
The rs9958947 single nucleotide polymorphism (SNP) resides in the promoter region of the lipase G (LIPG) gene. This newly discovered SNP increases the risk of stroke in some Asian populations, including Chinese and Korean populations. Stroke is one of the top 5 leading causes of death in Malaysia, so it is of interest to investigate whether this SNP is associated with stroke risk in the Malaysian population. Therefore, this study investigates this association through a case-control study on a Malaysian population along with a comprehensive meta-analysis. Genotyping of LIPG rs9958947 SNP was performed for 241 Malaysians using real-time polymerase chain reaction, and the odds ratios (OR) with 95% confidence intervals were calculated. The meta-analysis was conducted using the software Comprehensive Meta-Analysis ver. 2.2.064. A p value less than 0.05 was considered statistically significant. We observed that the mean age of Malaysian stroke patients was less than that of stroke patients from Korea and China. The meta-analysis showed that the LIPG rs9958947 SNP was significantly associated with an increased risk of ischemic stroke in Asian populations (dominant (CC vs. CT + TT): OR = 1.45, p 0.05) and blood lipid levels.
Mesenchymal stem cell (MSC) therapy is a promising prospect for the treatment of Alzheimer's disease (AD); however, the underlying mechanisms by which MSCs mediate positive effects are still unclear. We speculated that MSCs mediate microglial autophagy and enhance the clearance of Aβ. To test this hypothesis, we cultured BV2 microglial cells with umbilical cord mesenchymal stem cells conditioned medium (ucMSCs-CM) in the presence or absence of Aβ25-35 oligomers. We investigated BV2 cell proliferation, cell death, and Aβ25-35 phagocytosis as well as protein expression levels of LC3, Beclin-1, p62, insulin-degrading enzyme (IDE), and neprilysin (Nep) with western blotting. The results showed that ucMSCs-CM inhibited the proliferation and decreased cell death of BV2 cells induced by Aβ25-35. ucMSCs-CM also promoted the phagocytosis of Aβ25-35 by BV2 cells and changed the expression of autophagy-related proteins LC3, Beclin-1, and p62. Treatment also upregulated the expression of Aβ-degrading enzymes IDE and Nep. Furthermore, the culture medium in BV2 cells with Aβ25-35 and ucMSCs-CM prevented neuronal cell SH-SY5Y from cell death compared to control medium without ucMSCs-CM. Altogether, these data suggested that ucMSCs-CM protect microglial and neuronal cells from Aβ25-35-induced cell death and promote Aβ phagocytosis by modulating autophagy and enhancing the expression of Aβ-degrading enzymes in microglia.
During nervous system development, neurons project axons over long distances to reach the appropriate targets for correct neural circuit formation. Sonic hedgehog (Shh) is a secreted protein and plays a key role in regulating vertebrate embryogenesis, especially in central nervous system (CNS) patterning, including neuronal migration and axonal projection in the brain and spinal cord. In the developing ventral midbrain, Shh is sufficient to specify a striped pattern of cell fates. Little is known about the molecular mechanisms underlying the Shh regulation of the neural precursor cell fate during the optic tectum development. Here, we aimed at studying how Shh might regulate chicken optic tectum patterning. In the present study, in ovo electroporation methods were employed to achieve the overexpression of Shh in the optic tectum during chicken embryo development. Besides, the study combined in ovo electroporation and neuron isolation culturing to study the function of Shh in vivo and in vitro. The fluorescent immunohistochemistry methods were used to check the related indicators. The results showed that Shh overexpression caused 87.8% of cells to be distributed to the stratum griseum central (SGC) layer, while only 39.3% of the GFP-transfected cells resided in the SGC layer in the control group. Shh overexpression also reduced the axon length in vivo and in vitro. In conclusion, we provide evidence that Shh regulates the neural precursor cell fate during chicken optic tectum development. Shh overexpression impairs neuronal migration and may affect the fate determination of transfected neurons.
Notch signalling pathway is involved in the proliferation of neural progenitor cells (NPCs), to inhibit neuronal cell commitment and to promote glial cell fate. Notch protein is cleaved by gamma-secretase, a multisubunit transmembrane protein complex that releases the Notch intracellular domain (NICD) and subsequently activates the downstream targets. Down syndrome (DS) individuals exhibit an increased number of glial cells (particularly astrocytes), and reduced number of neurons suggesting the involvement of Notch signalling pathway in the neurogenic-to-gliogenic shift in DS brain. Ts1Cje is a DS mouse model that exhibit similar neuropathology to human DS individuals. To date, the spatiotemporal gene expression of the Notch and gamma-secretase genes have not been characterised in Ts1Cje mouse brain. Understanding the expression pattern of Notch and gamma-secretase genes may provide a better understanding of the underlying mechanism that leads to the shift. Gene expression analysis using RT-qPCR was performed on early embryonic and postnatal development of DS brain. In the developing mouse brain, mRNA expression analysis showed that gamma-secretase members (Psen1, Pen-2, Aph-1b, and Ncstn) were not differentially expressed. Notch2 was found to be downregulated in the developing Ts1Cje brain samples. Postnatal gene expression study showed complex expression patterns and Notch1 and Notch2 genes were found to be significantly downregulated in the hippocampus at postnatal day 30. Results from RT-qPCR analysis from E15.5 neurosphere culture showed an increase of expression of Psen1, and Aph-1b but downregulation of Pen-2 and Ncstn genes. Gamma-secretase activity in Ts1Cje E15.5 neurospheres was significantly increased by fivefold. In summary, the association and the role of Notch and gamma-secretase gene expression throughout development with neurogenic-to-gliogenic shift in Ts1Cje remain undefined and warrant further validation.
Heritability of major depressive disorder (MDD) is between 36 and 44%, suggesting that up to nearly half of the phenotypic variability is attributable to genes. A number of genetic polymorphisms have been shown to predispose certain individuals to depression. Of particular interest are the polymorphisms of the vitamin D receptor (VDR) gene. Although the VDR gene has been well characterized and a vast number of polymorphisms have been identified, the association between BsmI (rs1544410), ApaI (rs7975232) and TaqI (rs731236) single-nucleotide polymorphisms (SNPs), together with their haplotypes, and MDD risk have yet to be established. We conducted a matched case-control study with a total of 600 participants comprising 300 major depressive disorder (MDD) cases and 300 controls matched by age, gender and ethnicity in a 1:1 ratio, in four public hospitals in Kuala Lumpur and Selangor. Three adjacent SNPs of the VDR gene-BsmI (rs1544410), ApaI (rs7975232) and TaqI (rs731236)-were genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Odds ratios and 95% confidence intervals (CIs) were obtained from conditional logistic regression using Stata 16. Linkage disequilibrium and haplotype association with MDD were analyzed using the online SNPStats program. None of the genotypes of the three SNPs was significantly associated with risk of developing MDD after adjusting for confounding factors. However, the TAC (BAt) haplotype was associated with increased odds of MDD (adjusted OR = 2.17, 95% CI = 1.30-3.61, p = 0.003) using CCT (baT) as reference haplotype. The findings suggest that the BsmI-ApaI-TaqI TAC (BAt) haplotype of the VDR gene increases susceptibility to MDD.
The pharmacological inhibition of glial activation is one of the new approaches for combating neuropathic pain in which the role of glia in the modulation of neuropathic pain has attracted significant interest and attention. Neuron-glial crosstalk is achieved with N-methyl-D-aspartate-2B receptor (NMDAR-2B) activation. This study aims to determine the effect of ifenprodil, a potent noncompetitive NMDAR-2B antagonist, on activated microglia, brain-derived neurotrophic factors (BDNF) and downstream regulatory element antagonist modulator (DREAM) protein expression in the spinal cord of streptozotocin-induced painful diabetic neuropathy (PDN) rats following formalin injection. In this experimentation, 48 Sprague-Dawley male rats were randomly selected and divided into four groups: (n = 12): control, PDN, and ifenprodil-treated PDN rats at 0.5 μg or 1.0 μg for 7 days. Type I diabetes mellitus was then induced by injecting streptozotocin (60 mg/kg, i.p.) into the rats which were then over a 2-week period allowed to progress into the early phase of PDN. Ifenprodil was administered in PDN rats while saline was administered intrathecally in the control group. A formalin test was conducted during the fourth week to induce inflammatory nerve injury, in which the rats were sacrificed at 72 h post-formalin injection. The lumbar enlargement region (L4-L5) of the spinal cord was dissected for immunohistochemistry and western blot analyses. The results demonstrated a significant increase in formalin-induced flinching and licking behavior with an increased spinal expression of activated microglia, BDNF and DREAM proteins. It was also shown that the ifenprodil-treated rats following both doses reduced the extent of their flinching and duration of licking in PDN in a dose-dependent manner. As such, ifenprodil successfully demonstrated inhibition against microglia activation and suppressed the expression of BDNF and DREAM proteins in the spinal cord of PDN rats. In conclusion, ifenprodil may alleviate PDN by suppressing spinal microglia activation, BDNF and DREAM proteins.
Diabetic neuropathy (DN) is a late complication of diabetic mellitus and may rise into painful and painless variants. Limited studies have looked at nociceptive mechanisms of painless DN variant. The study aimed to determine phosphorylation and total NR2B subunit of N-methyl-D-aspartate receptor in the spinal cord of painless DN rat during early phase following formalin injection. Thirty-six Sprague-Dawley male rats were randomly assigned into three groups: control, painful, and painless DN (n = 12). The rats were developed into the early phase of DN for 2 weeks following diabetic induction. Two weeks later, the rats were injected with 5% formalin solution and flinching and licking responses were recorded for 60 min. The rats were sacrificed 3 days later, and the spinal cord enlargement region was collected. Immunohistochemistry and Western blot procedures were conducted to determine the phosphorylated and total NR2B subunit expressions. The results showed reduced flinching and licking responses in painless DN rats compared to control and painful DN groups, followed by a significant reduction in phosphorylated and total NR2B expression at both ipsilateral and contralateral regions of the spinal cord. In conclusion, reduced pain behavior responses in painless DN rats following formalin injection is possibly contributed by the reduced expression of phosphorylated and total NR2B subunit in the spinal cord.
Alzheimer's disease (AD) is a neurodegenerative disease characterized by impaired memory function and oxidative damage. NO is a major signaling molecule produced in the central nervous system to modulate neurological activity through modulating nitric oxide synthase. Recently, PPAR-γ agonists have shown neuroprotective effects in neurodegenerative disorders. However, there have been only a few studies identifying mechanisms through which cognitive benefits may be exerted. The present study was designed to investigate the possible nitric oxide mechanism in the protective effect of pioglitazone against streptozotocin (STZ)-induced memory dysfunction. Wistar rats were intracerebroventricularly (ICV) injected with STZ. Then rats were treated with pioglitazone, NO modulators [L-arginine and nitro-L-arginine methyl ester (L-NAME)] for 21 days. Behavioral alterations were assessed in between the study period. Animals were sacrificed immediately after behavioral session, and mito-oxidative parameters, TNF-α, IL-6, and caspase-3 activity were measured. STZ-treated rats showed a memory deficit and significantly increased in mito-oxidative damage and inflammatory mediators and apoptosis in the hippocampus. Chronic treatment of pioglitazone significantly improved memory retention and attenuated mito-oxidative damage parameters, inflammatory markers, and apoptosis in STZ-treated rats. However, L-arginine pretreatment with lower dose of pioglitazone has not produced any protective effect as compared to per se. Furthermore, pretreatment of L-NAME significantly potentiated its protective effect, which indicates the involvement of nitric oxide for activation of PPAR-γ action. These results demonstrate that pioglitazone offers protection against STZ-induced memory dysfunction possibly due to its antioxidant, anti-inflammatory, and anti-apoptotic action mediating nitric oxide pathways and, therefore, could have a therapeutic potential in AD.
Alzheimer's disease (AD) is a neurodegenerative disease that is imposing an increasing burden on society. Currently, AD is the leading cause of senile dementia worldwide. Despite the long existence of AD, there is lack of therapies for AD, suggesting that new and effective treatment strategy must be explored. At present, sirtuin pathway has attracted attention from the researchers due to its promising results in laboratory models of aging. In addition, our understanding in the roles of sirtuin 6 in AD has expanded. It has been identified to be involved in telomere maintenance, DNA repair, genome integrity, energy metabolism, and inflammation, which ultimately regulate life span. Recent findings also demonstrate that sirtuin 6 is lacking in AD patients, proposing that it can be a new potential therapeutic target in AD. Therefore, exploring on how sirtuin 6 is related in AD manifestation may accelerate the research of AD further and benefits future AD patients. Keeping that in mind, this review aims to highlight the possible roles of sirtuin 6 in AD manifestation.
Hypothalamus is central to food intake and satiety. Recent data unveiled the expression of N-methyl-D-aspartate receptors (NMDAR) on hypothalamic neurons and their interaction with GABAA and serotoninergic neuronal circuits. However, the precise mechanisms governing energy homeostasis remain elusive. Notably, in females, the consumption of progesterone-containing preparations, such as hormonal replacement therapy and birth control pills, has been associated with hyperphagia and obesity-effects mediated through the hypothalamus. To elucidate this phenomenon, we employed the progesterone-induced obesity model in female Swiss albino mice. Four NMDAR modulators were selected viz. dextromethorphan (Dxt), minocycline, d-aspartate, and cycloserine. Obesity was induced in female mice by progesterone administration for 4 weeks. Mice were allocated into 7 groups, group-1 as vehicle control (arachis oil), group-2 (progesterone + arachis oil), and group-3 as positive-control (progesterone + sibutramine); other groups were treated with test drugs + progesterone. Various parameters were recorded like food intake, thermogenesis, serum lipids, insulin, AST and ALT levels, organ-to-body weight ratio, total body fat, adiposity index, brain serotonin levels, histology of liver, kidney, and sizing of fat cells. Dxt-treated group has shown a significant downturn in body weight (p
The use of methamphetamine (METH) is a growing worldwide epidemic that bears grave societal implications. METH is known to exert its neurotoxic effects on the dopaminergic and serotonergic systems of the brain. In addition to this classical studied mechanism of damage, findings from our laboratory and others have shown that acute METH treatment and mechanical injury, i.e. traumatic brain injury (TBI), share common cell injury mechanism(s). Since neuro-inflammation is a signature event in TBI, we hypothesize that certain cytokine levels might also be altered in rat brain exposed to an acute METH insult. In this study, using a cytokine antibody array chip, we evaluated the serum levels of 19 cytokines in rats 24 h after exposure to a 40 mg/kg acute regimen of METH. Data were compared to rats subjected to experimental TBI using the controlled cortical impact (CCI) injury model and saline controls. Sandwich ELISA method was used to further validate some of the findings obtained from the antibody cytokine array. We confirmed that three major inflammatory-linked cytokines (IL-1β, IL-6, and IL-10) were elevated in the METH and TBI groups compared to the saline group. Such finding suggests the involvement of an inflammatory process in these brain insults, indicating that METH use is, in fact, a stressor to the immune system where systemic involvement of an altered cytokine profile may play a major role in mediating chemical brain injury after METH use.