Neurochemistry

Dopamine receptor activation mitigates mitochondrial dysfunction and oxidative stress to enhance dopaminergic neurogenesis in 6-OHDA lesioned rats: A role of Wnt signalling Publication date: October 2019 Source: Neurochemistry International, Volume 129 Author(s): Akanksha Mishra, Sonu Singh, Virendra Tiwari, Swati Chaturvedi, M. Wahajuddin, Shubha Shukla Abstract Nigral dopaminergic (DAergic) cell degeneration and depletion of dopamine neurotransmitter in the midbrain are cardinal features of Parkinson's disease (PD). Dopamine system regulates different aspects of behavioural phenotypes such as motor control, reward, anxiety and depression via acting on dopamine receptors (D1-D5). Recent studies have shown the potential effects of dopamine on modulation of neurogenesis, a process of newborn neuron formation from neural stem cells (NSCs). Reduced proliferative capacity of NSCs and net neurogenesis has been reported in subventricular zone, olfactory bulb and hippocampus of patients with PD. However, the molecular and cellular mechanism of dopamine mediated modulation of DAergic neurogenesis is not defined. In this study, we attempted to investigate the molecular mechanism of dopamine receptors mediated control of DAergic neurogenesis and whether it affects mitochondrial biogenesis in 6-hydroxydopamine (6-OHDA) induced rat model of PD-like phenotypes. Unilateral administration of 6-OHDA into medial forebrain bundle potentially reduced tyrosine hydroxylase immunoreactivity, dopamine content in substantia nigra pars compacta (SNpc) and striatum region and impaired motor functions in adult rats. We found decreased D1 receptor expression, mitochondrial biogenesis, mitochondrial functions and DAergic differentiation associated with down-regulation of Wnt/β-catenin signalling in SNpc of 6-OHDA lesioned rats. Pharmacological stimulation of D1 receptor enhanced mitochondrial biogenesis, mitochondrial functions and DAergic neurogenesis that lead to improved motor functions in 6-OHDA lesioned rats. D1 agonist induced effects were attenuated following administration of D1 antagonist, whereas shRNA mediated knockdown of Axin-2, a negative regulator of Wnt signalling significantly abolished D1 antagonist induced impairment in mitochondrial biogenesis and DAergic neurogenesis in 6-OHDA lesioned rats. Our results suggest that dopamine receptor regulates DAergic neurogenesis and mitochondrial functions by activation of Wnt/β-catenin signaling in rat model of PD-like phenotypes.

Chrysin ameliorates cerebral ischemia/reperfusion (I/R) injury in rats by regulating the PI3K/Akt/mTOR pathway Publication date: October 2019 Source: Neurochemistry International, Volume 129 Author(s): Teng-Fei Li, Ji Ma, Xin-Wei Han, Yong-Xu Jia, Hui-Fei Yuan, Shao-Feng Shui, Dong Guo, Lei Yan Abstract In this study, the effects of chrysin on cerebral ischemia by establishing middle cerebral artery occlusion (MCAO) in rat were investigated. In vivo experiments, the rats were orally administrated with clopidogrel or chrysin once daily for 7 days before the experimental of ischemia and the rats were divided into 5 groups: the sham group, the I/R group, I/R + clopidogrel group, I/R + chrysin (10 mg/kg), I/R + chrysin (20 mg/kg) group. Chrysin significantly ameliorated the I/R rats, evaluated by TTC staining, determination of brain wet to dry weight ratio and neurological deficits. Moreover, in serum and brain tissues of the I/R rats, chrysin also could effectively suppress the release of inflammatory cytokines, including levels of interleukin-6 (IL-6), interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). In addition, chrysin could improve the SOD activity in the I/R rats. Mechanically, chrysin could activate the PI3K/Akt/mTOR pathway, inhibited inflammation and apoptosis. In oxygen-glucose deprivation and recovery (OGD/R)-induced SH-SY5Y cells in vitro. Chrysin markedly decreased the levels of TNF-α, IL-6 and IL-1β in supernatant of OGD/R-induced SH-SY5Y cells via activating PI3K/Akt/mTOR pathway. In conclusion, our study demonstrated that chrysin might be a potential therapeutic agent for cerebral ischemia.

Dexmedetomidine protects neurons from kainic acid-induced excitotoxicity by activating BDNF signaling Publication date: October 2019 Source: Neurochemistry International, Volume 129 Author(s): Kuan-Ming Chiu, Tzu-Yu Lin, Ming-Yi Lee, Cheng-Wei Lu, Ming-Jiuh Wang, Su-Jane Wang Abstract Glutamatergic excitotoxicity is crucial in the pathogenesis of epileptic seizures. Dexmedetomidine, a potent and highly selective α2 adrenoceptor agonist, inhibits glutamate release from nerve terminals in rat cerebrocortical nerve terminals. However, the ability of dexmedetomidine to affect glutamate-induced brain injury is still unknown. Therefore, the present study evaluated the protective effect of dexmedetomidine against brain damage by using a kainic acid (KA) rat model, a frequently used model for temporal lobe epilepsy. Rats were treated with dexmedetomidine (1 or 5 μg/kg, intraperitoneally) 30 min before the KA (15 mg/kg) intraperitoneal injection. KA-induced seizure score and elevations of glutamate release in rat hippocampi were inhibited by pretreatment with dexmedetomidine. Histopathological and TUNEL staining analyzes showed that dexmedetomidine attenuated KA-induced neuronal death in the hippocampus. Dexmedetomidine ameliorated KA-induced apoptosis, and this neuroprotective effect was accompanied by inhibited the KA-induced caspase-3 expression as well as MAPKs phosphorylation, and reversed Bcl-2 down-expression, coupled with increased Nrf2, BDNF and TrkB expression in KA-treated rats. The results suggest that dexmedetomidine protected rat brains from KA-induced excitotoxic damage by reducing glutamate levels, suppressing caspase-3 activation and MAPKs phosphorylation, and enhancing Bcl-2, Nrf2, BDNF and TrkB expression in the hippocampus. Therefore, dexmedetomidine may be beneficial for preventing or treating brain disorders associated with excitotoxic neuronal damage. In conclusion, these data suggest that dexmedetomidine has the therapeutic potential for treating epilepsy.

Involvement of anxiety-like behaviors and brain oxidative stress in the chronic effects of alarm reaction in zebrafish populations Publication date: October 2019 Source: Neurochemistry International, Volume 129 Author(s): Vanessa A. Quadros, Luiz V. Rosa, Fabiano V. Costa, Talise E. Müller, Flavia V. Stefanello, Vania L. Loro, Denis B. Rosemberg Abstract Aversive conditions elicit anxiety responses that prepare the organism to an eventual threat. Nonetheless, prolonged anxiety is a pathological condition associated with various neuropsychiatric disorders. Here, we evaluated whether the conspecific alarm substance (CAS), a chemical cue that elicits aversion, influences anxiety-like behaviors and modulates brain oxidative stress-related parameters in wild-type (WT) and leopard (leo) zebrafish following a repeated exposure protocol. CAS exposure was performed for 5 min, once daily for 7 consecutive days. In the 8th day, animals were tested in the light/dark and novel tank tests and their brains were further dissected for biochemical analyses. CAS chronically induced anxiogenic-like states in WT and leo populations when their behaviors were analyzed in the light/dark and novel tank tests. CAS also increased catalase (CAT) and glutathione S-transferase (GST) activities, as well as non-protein thiol (NPSH) content in WT and leo, but only leo had increased thiobarbituric reactive substance (TBARS) levels in the brain. At baseline conditions, leo was more 'anxious' when compared to WT, displaying lower CAT activity and carbonylated protein (CP) levels. Overall, CAS chronically triggers anxiety-like behavior in zebrafish populations, which may be associated with changes in oxidative stress-related parameters. Furthermore, the use of different zebrafish populations may serve as an interesting tool in future research aiming to investigate the neurobehavioral bases of neuropsychiatric disorders in vertebrates. Graphical abstract

Phospho-mTOR expression in human glioblastoma microglia-macrophage cells Publication date: October 2019 Source: Neurochemistry International, Volume 129 Author(s): Lucia Lisi, Gabriella Maria Pia Ciotti, Marta Chiavari, Michela Pizzoferrato, Annunziato Mangiola, Sergey Kalinin, Douglas L. Feinstein, Pierluigi Navarra Abstract The glioblastoma (GBM) immune microenvironment is highly heterogeneous, and microglia may represent 30–70% of the entire tumor. However, the role of microglia and other specific immune populations is poorly characterized. Activation of mTOR signaling occurs in numerous human cancers and has roles in microglia-glioma cell interactions. We now show in human tumor specimens (42 patients), that 39% of tumor-associated microglial (TAM) cells express mTOR phosphorylated at Ser-2448; and similar mTOR activation is observed using a human microglia-glioma interaction paradigm. In addition, we confirm previous studies that microglia express urea and ARG1 (taken as M2 marker) in the presence of glioma cells, and this phenotype is down-regulated in the presence of a mTOR inhibitor. These results suggest that mTOR suppression in GBM patients might induce a reduction of the M2 phenotype expression in up to 40% of all TAMs. Since the M2 profile of microglial activation is believed to be associated with tumor progression, reductions in that phenotype may represent an additional anti-tumor mechanism of action of mTOR inhibitors, along with direct anti-proliferative activities.

Repeated exposure to methiopropamine increases dendritic spine density in the rat nucleus accumbens core Publication date: October 2019 Source: Neurochemistry International, Volume 129 Author(s): Wen Ting Cai, Hyung Shin Yoon, Sooyeun Lee, Jeong-Hoon Kim Abstract Repeated exposure to classical psychomotor stimulants, like amphetamine (AMPH), produces locomotor sensitization and accompanied structural plasticity of dendritic spines in the nucleus accumbens (NAcc). Following our previous report that repeated administration of methiopropamine (MPA), a structural analog to meth-AMPH, produces locomotor sensitization, it was examined in the present study whether this behavioral change also accompanies with structural plasticity in the NAcc in a similar way to AMPH. A week after adeno-associated viral vectors containing enhanced green fluorescent protein (eGFP) were microinjected into the NAcc core, rats were repeatedly injected with saline, AMPH (1 mg/kg, IP), or MPA (5 mg/kg, IP) once every 2–3 days for a total of 4 times. Two weeks after last injection, all rats were perfused and their brains were processed for immunohistochemical staining. The image stacks for dendrite segments of medium spiny neuronal cells in the NAcc core were obtained and dendritic spines were quantitatively analyzed. Interestingly, it was found that the number of total spine density, with thin spine as a major contributor, was significantly increased in MPA compared to saline pre-exposed group, in a similar way to AMPH. These results indicate that MPA, a novel psychoactive substance, has similar characteristics with AMPH in that they both produce structural as well as behavioral changes, further supporting MPA's dependence and abuse potential.

Effect of phosphodiesterase (1B, 2A, 9A and 10A) inhibitors on central nervous system cyclic nucleotide levels in rats and mice Publication date: October 2019 Source: Neurochemistry International, Volume 129 Author(s): Jie Chen, Douglas Zook, Lindsay Crickard, Ali Tabatabaei Abstract Phosphodiesterase (PDE) inhibition has been broadly investigated as a target for a wide variety of indications including central nervous system (CNS) disorders. Cyclic nucleotide (cNT) changes within associated tissues may serve as a biomarker of PDE inhibition. We recently developed robust sample harvesting and bioanalytical methods to quantify cNT levels in rodent brain and cerebrospinal fluid (CSF). Herein, we report on the application of those methods to study rodent species-specific and rodent brain region-specific cNT changes following individual or concomitant PDE inhibitor administration. Male Sprague Dawley (Crl:CD® [SD]) rats were dosed subcutaneously (sc) with a PDE1B inhibitor (DNS-0056), a PDE2A inhibitor (PF-05180999), a PDE9A inhibitor (PF-4447943), and a PDE10A inhibitor (MP10), each at a single dose of 10 or 30 mg/kg, or concomitantly with all 4 inhibitors at 10 mg/kg each. Male Carworth Farms (Crl:CF1 ®[CF-1]) mice were dosed intraperitoneally (ip) with the four individual inhibitors at a single dose of 10 mg/kg or concomitantly with all 4 inhibitors at 10 mg/kg each. The doses studied are generally adequate for affecting measurable cNT levels in the tissues of interest and were thereby chosen for this investigation. Measured 3′,5′-cyclic adenosine monophosphate (cAMP) changes were generally statistically insignificant in the brain, striatum and CSF after administration of the aforementioned PDE inhibitors. However, the levels of 3′,5′-cyclic guanosine monophosphate (cGMP) increased in both rat and mouse striatum (2.2-, 2.1- and 1.7-fold and 6.4-, 2.8- and 1.7-fold, respectively) after PDE2A, 9A, and 10A inhibitor dosing. In all cases, the cNT changes followed the same trend in the brain, striatum and CSF after PDE inhibitor dosing and dose response was observed in rats. Concomitant treatment with PDE1B, PDE2A, PDE9A and PDE10A inhibitors resulted in a 4.4- and 36.7-fold increase of cGMP in rat and mouse striatum. The drug exposures after concomitant treatment were also higher than in the individual inhibitor-treated animals. cGMP enhancement observed could be due to synergistic effects, though an additive effect of the combined inhibitor concentrations may also contribute.

Effects of exercise-induced fatigue on the morphology of asymmetric synapse and synaptic protein levels in rat striatum Publication date: October 2019 Source: Neurochemistry International, Volume 129 Author(s): Zhifeng Wang, Lijuan Hou, Dongmei Wang Abstract Corticostriatal synaptic plasticity is considered to be a cellular basis for somatic motor regulation and motor skill learning. Changes in synaptic transmission efficiency underlie functional plasticity, while structural plasticity involves changes in the ultrastructure of the synapse and the levels of synaptic proteins. Exercise-induced fatigue may impair corticostriatal synaptic plasticity, and this impairment may be an important mechanism for exercise-induced fatigue. However, prior research focused mainly on functional plasticity such that the structural plasticity was not well understood. Because corticostriatal synapses are typical asymmetric synapses, here we have used transmission electron microscopy to examine the changes of asymmetry synaptic ultrastructure in rat striatum before and after repetitive exercise-induced fatigue; we have also used western blotting to detect the levels of synaptic active region protein Munc 13, RIM1 and synaptic vesicle protein Rab3A and postsynaptic density PSD-95 protein in rat striatum before and after exercise-induced fatigue. The results showed that the ultrastructure of asymmetry corticostriatal synapses and synaptic protein levels in the striatum of rats were abnormally changed after repetitive exercise-induced fatigue. These abnormal changes in synaptic ultrastructure and related protein levels may be the structural basis for the corticostriatal plasticity impairment after exercise-induced fatigue.

Glutamate receptor metabotropic 7 (GRM7) gene polymorphisms in mood disorders and attention deficit hyperactive disorder Publication date: October 2019 Source: Neurochemistry International, Volume 129 Author(s): Rezvan Noroozi, Mohammad Taheri, Mir Davood Omrani, Soudeh Ghafouri-Fard Abstract L-glutamate is the chief excitatory neurotransmitter in the central nervous system (CNS) which activates metabotropic receptors including the metabotropic glutamate receptor GRM7. Single nucleotide polymorphisms (SNPs) within GRM7 gene have been associated with several psychiatric conditions. In the present study, we assessed association between two GRM7 SNPs (rs6782011 and rs779867) and two neuropsychiatric disorders including attention deficit hyperactive disorder (ADHD) and mood disorders. There were no significant differences in genotype, allele and haplotypes frequencies of the rs6782011 and rs779867 between bipolar disorder 1 (BPD1) patients and controls. The CC genotype of the rs6782011 was significantly associated with BPD2 in recessive model (OR (95% CI) = 1.78 (1.09–2.91), adjusted P value = 0.04) and with ADHD in dominant and co-dominant models (OR (95% CI) = 1.98 (1.11–3.53), adjusted P value = 0.04; OR (95% CI) = 2.27 (1.23–4.17), adjusted P value = 0.04 respectively). The C G haplotype (rs6782011 and rs779867 respectively) was more prevalent among both BPD2 patients (OR (95%CI) = 2.03 (1.36–3.01), adjusted P value = 0.002) and MDD patients (OR (95%CI) = 2.08 (1.37–3.16), adjusted P value = 0.002) compared with controls. The current study provides further evidences for participation of GRM7 variants in conferring risk of neuropsychiatric disorders.

Ammonium induced dysfunction of 5-HT2B receptor in astrocytes Publication date: October 2019 Source: Neurochemistry International, Volume 129 Author(s): Tingting Yue, Baoman Li, Li Gu, Jingyang Huang, Alexei Verkhratsky, Liang Peng Abstract Previously we reported that gene expression of astrocytic 5-HT2B receptors was decreased in brains of depressed animals exposed to chronic mild stress (CMS) (Li et al., 2012) and of Parkinson's disease (Song et al., 2018). Depression is also one of the psychiatric symptoms in hyperammonemia, and astrocyte is a primary target of ammonium in brain in vivo. In the present study, we have used preparations of the brains of urease-treated mice and ammonium-treated astrocytes in culture to study gene expression and function of 5-HT2B receptors. The urease-treated mice showed depressive behaviour. Both mRNA and protein of 5-HT2B receptors were increased in the brains of urease-treated mice and in ammonium-treated cultured astrocytes. Further study revealed that mRNA and protein expression of adenosine deaminase acting on RNA 2 (ADAR2), an enzyme catalyze RNA deamination of adenosine to inosine was increased in the brains of urease-treated mice and in ammonium-treated cultured astrocytes. This increase in ADAR2 induced RNA editing of 5-HT2B receptors. Cultured astrocytes treated with ammonium lost 5-HT induced Ca2+ signalling and ERK1/2 phosphorylation, indicating dysfunction of 5-HT2B receptors. This is in agreement with our previous observation that edited 5-HT2Breceptors no longer respond to 5-HT (Hertz et al., 2014). Ammonium effects are inhibited by ADAR2 siRNA in cultured astrocytes, suggesting that increased gene expression and editing and loss of function of 5-HT2Breceptors are results of increased activity of ADAR2. In summary, we have demonstrated that functional malfunction of astrocytic 5-HT2B receptors occurs in animal models of major depression, Parkinson depression and hepatic encephalopathy albeit via different mechanisms. Understanding the role of astrocytic 5-HT2B receptors in different pathological contexts may instigate development of novel therapeutic strategies for treating disease-specific depressive behaviour.

Alexandros Sfakianakis
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alsfakia@gmail.com