The neuronal endocannabinoid system is known to depress synaptic inputs retrogradely in an activity‐dependent manner. This mechanism has been generally described for excitatory glutamatergic and inhibitory GABAergic synapses. Here, we report that neurones in the auditory brainstem of the Mongolian gerbil (Meriones unguiculatus) retrogradely regulate the strength of their inputs via the endocannabinoid system. By means of whole‐cell patch‐clamp recordings, we found that retrograde endocannabinoid signalling attenuates both glycinergic and glutamatergic post‐synaptic currents in the same types of neurones. Accordingly, we detected the cannabinoid receptor 1 in excitatory and inhibitory pre‐synapses as well as the endocannabinoid‐synthesising enzymes (diacylglycerol lipase α/β, DAGLα/β) post‐synaptically through immunohistochemical stainings. Our study was performed with animals aged 10–15 days, that is, in the time window around the onset of hearing. Therefore, we suggest that retrograde endocannabinoid signalling has a role in adapting inputs during the functionally important switch from spontaneously generated to sound‐related signals.
In this study, in vitro and in vivo experiments were carried out with the high‐affinity multifunctional D2/D3 agonist D‐512 to explore its potential neuroprotective effects in models of Parkinson's disease and the potential mechanism(s) underlying such properties. Pre‐treatment with D‐512 in vitro was found to rescue rat adrenal Pheochromocytoma PC12 cells from toxicity induced by 6‐hydroxydopamine administration in a dose‐dependent manner. Neuroprotection was found to coincide with reductions in intracellular reactive oxygen species, lipid peroxidation, and DNA damage. In vivo, pre‐treatment with 0.5 mg/kg D‐512 was protective against neurodegenerative phenotypes associated with systemic administration of MPTP, including losses in striatal dopamine, reductions in numbers of DAergic neurons in the substantia nigra (SN), and locomotor dysfunction. These observations strongly suggest that the multifunctional drug D‐512 may constitute a novel viable therapy for Parkinson's disease.
Cerebrospinal fluid (CSF) α‐synuclein (ASYN) levels are emerging as a possible biomarker in a number of neurodegenerative conditions; however, there has been little study of such levels in demyelinating conditions with neurodegeneration such as multiple sclerosis (MS). In this study, we aimed to assess CSF ASYN levels in MS spectrum [clinically isolated syndrome (CIS) and MS] patients and compare them to those obtained in control subjects with benign neurological conditions (BNC). We used a recently developed, ultra‐sensitive sandwich enzyme‐linked immunosorbent assay to measure and compare CSF ASYN levels in three categories of subjects: BNC (n = 38), CIS (n = 36) and MS [Relapsing Remitting (RRMS, n = 22) and Primary Progressive (PPMS, n = 15)]. We also performed secondary analyses, including relationship of CSF ASYN levels to aging, gender, presence of CSF oligoclonal bands (OB) and gadolinium (Gd)‐enhancing demyelinating lesions on T1‐weighted MRIs. CSF ASYN levels were found to be significantly lower in the CIS (78.2 ± 7.5 pg/mL), RRMS (76.8 ± 5.1 pg/mL), and PPMS (76.3 ± 6.7 pg/mL) groups compared to the BNC (125.7 ± 13.6 pg/mL) group. Secondary analyses did not reveal additional correlations. Our results suggest that in a cohort of CIS and MS patients, CSF ASYN levels are decreased, thus providing another possible link between MS and neurodegeneration. Future studies will need to be performed to confirm and extend these findings, to lead to a fuller understanding of the possible biological link between ASYN and MS.
Intra‐neuronal metabolism of dopamine (DA) begins with production of 3,4‐dihydroxyphenylacetaldehyde (DOPAL), which is toxic. According to the ‘catecholaldehyde hypothesis,’ DOPAL destroys nigrostriatal DA terminals and contributes to the profound putamen DA deficiency that characterizes Parkinson's disease (PD). We tested the feasibility of using post‐mortem patterns of putamen tissue catechols to examine contributions of altered activities of the type 2 vesicular monoamine transporter (VMAT2) and aldehyde dehydrogenase (ALDH) to the increased DOPAL levels found in PD. Theoretically, the DA : DOPA concentration ratio indicates vesicular uptake, and the 3,4‐dihydroxyphenylacetic acid : DOPAL ratio indicates ALDH activity. We validated these indices in transgenic mice with very low vesicular uptake (VMAT2‐Lo) or with knockouts of the genes encoding ALDH1A1 and ALDH2 (ALDH1A1,2 KO), applied these indices in PD putamen, and estimated the percent decreases in vesicular uptake and ALDH activity in PD. VMAT2‐Lo mice had markedly decreased DA:DOPA (50 vs. 1377, p < 0.0001), and ALDH1A1,2 KO mice had decreased 3,4‐dihydroxyphenylacetic acid:DOPAL (1.0 vs. 11.2, p < 0.0001). In PD putamen, vesicular uptake was estimated to be decreased by 89% and ALDH activity by 70%. Elevated DOPAL levels in PD putamen reflect a combination of decreased vesicular uptake of cytosolic DA and decreased DOPAL detoxification by ALDH.
Recent studies have emphasized the important role of microRNA (miRNA) clusters and common target genes in disease progression. Despite the known involvement of the miR‐192/215 family in many human diseases, its biological role in Hirschsprung disease (HSCR) remains undefined. In this study, we explored the role of the miR‐192/215 family in the pathogenesis of HSCR. Quantitative real‐time PCR and western blotting measured relative expression levels of miRNAs, mRNAs, and proteins in 80 HSCR patients and 77 normal colon tissues. Targets were evaluated by dual‐luciferase reporter assays, and the functional effects of miR‐192/215 on human 293T and SH‐SY5Y cells were detected by the Transwell assay, CCK8 assay and flow cytometry. MiR‐192/215 was significantly down‐regulated in HSCR tissue samples, and their knockdown inhibited cell migration and proliferation in the human 293T and SH‐SY5Y cell lines. Nidogen 1 (NID1) was confirmed as a common target gene of miR‐192/215 by dual‐luciferase reporter gene assay and its expression was inversely correlated with that of miR‐192/215 in tissue samples and cell lines. Silencing of NID1 could rescue the extent of the suppressing effects by miR‐192/215 inhibitor. The down‐regulation of miR‐192/215 may contribute to HSCR development by targeting NID1.
Nicotinic acetylcholine receptors (nAChRs) are major neurotransmitter receptors and targets of neonicotinoid insecticides in the insect nervous system. The full function of nAChRs is often dependent on associated proteins, such as chaperones, regulators and modulators. Here, three Lynx (Ly‐6/neurotoxin) proteins, Loc‐lynx1, Loc‐lynx2 and Loc‐lynx3, were identified in the locust, Locusta migratoria manilensis. Co‐expression with Lynx resulted in a dramatic increase in agonist‐evoked macroscopic currents on nAChRs Locα1/β2 and Locα2/β2 in Xenopus oocytes, but no changes in agonist sensitivity. Loc‐lynx1 and Loc‐lynx3 only modulated nAChRs Locα1/β2 while Loc‐lynx2 modulated Locα2/β2 specifically. Meanwhile, Loc‐lynx1 induced a more significant increase in currents evoked by imidacloprid and epibatidine than Loc‐lynx3, and the effects of Loc‐lynx1 on imidacloprid and epibatidine were significantly higher than those on acetylcholine. Among three lynx proteins, only Loc‐lynx1 significantly increased [3H]epibatidine binding on Locα1/β2. The results indicated that Loc‐lynx1 had different modulation patterns in nAChRs compared to Loc‐lynx2 and Loc‐lynx3. Taken together, these findings indicated that three Lynx proteins were nAChR modulators and had selective activities in different nAChRs. Lynx proteins might display their selectivities from three aspects: nAChR subtypes, various agonists and different modulation patterns.
The biogenic amine serotonin ( 5‐hydroxytryptamine, 5‐HT) is a neurotransmitter in vertebrates and invertebrates. It acts in regulation and modulation of many physiological and behavioral processes through G‐protein‐coupled receptors. Five 5‐HT receptor subtypes have been reported in Drosophila that share high similarity with mammalian 5‐HT1A, 5‐HT1B, 5‐HT2A, 5‐HT2B, and 5‐HT7 receptors. We isolated a cDNA (Pr5‐HT8) from larval Pieris rapae, which shares relatively low similarity to the known 5‐HT receptor classes. After heterologous expression in HEK293 cells, Pr5‐HT8 mediated increased [Ca2+]i in response to low concentrations (< 10 nM) of 5‐HT. The receptor did not affect [cAMP]i even at high concentrations (> 10 μM) of 5‐HT. Dopamine, octopamine, and tyramine did not influence receptor signaling. Pr5‐HT8 was also activated by various 5‐HT receptor agonists including 5‐methoxytryptamine, (±)‐8‐Hydroxy‐2‐(dipropylamino) tetralin, and 5‐carboxamidotryptamine. Methiothepin, a non‐selective 5‐HT receptor antagonist, activated Pr5‐HT8. WAY 10635, a 5‐HT1A antagonist, but not SB‐269970, SB‐216641, or RS‐127445, inhibited 5‐HT‐induced [Ca2+]i increases. We infer that Pr5‐HT8 represents the first recognized member of a novel 5‐HT receptor class with a unique pharmacological profile. We found orthologs of Pr5‐HT8 in some insect pests and vectors such as beetles and mosquitoes, but not in the genomes of honeybee or parasitoid wasps. This is likely to be an invertebrate‐specific receptor because there were no similar receptors in mammals.
The development of drugs to inhibit glioblastoma (GBM) growth requires reliable pre‐clinical models. To date, proteomic level validation of widely used patient‐derived glioblastoma xenografts (PDGX) has not been performed. In the present study, we characterized 20 PDGX models according to subtype classification based on The Cancer Genome Atlas criteria, TP53, PTEN, IDH 1/2, and TERT promoter genetic analysis, EGFR amplification status, and examined their proteomic profiles against those of their parent tumors. The 20 PDGXs belonged to three of four The Cancer Genome Atlas subtypes: eight classical, eight mesenchymal, and four proneural; none neural. Amplification of EGFR gene was observed in 9 of 20 xenografts, and of these, 3 harbored the EGFRvIII mutation. We then performed proteomic profiling of PDGX, analyzing expression/activity of several proteins including EGFR. Levels of EGFR phosphorylated at Y1068 vary considerably between PDGX samples, and this pattern was also seen in primary GBM. Partitioning of 20 PDGX into high (n = 5) and low (n = 15) groups identified a panel of proteins associated with high EGFR activity. Thus, PDGX with high EGFR activity represent an excellent pre‐clinical model to develop therapies for a subset of GBM patients whose tumors are characterized by high EGFR activity. Further, the proteins found to be associated with high EGFR activity can be monitored to assess the effectiveness of targeting EGFR.
Dopaminergic neurotransmission in the nucleus accumbens is important for various reward‐related cognitive processes including reinforcement learning. Repeated cocaine enhances hippocampal synaptic plasticity, and phasic elevations of accumbal dopamine evoked by unconditioned stimuli are dependent on impulse flow from the ventral hippocampus. Therefore, sensitized hippocampal activity may be one mechanism by which drugs of abuse enhance limbic dopaminergic activity. In this study, in vivo microdialysis in freely moving adult male Sprague–Dawley rats was used to investigate the effect of repeated cocaine on ventral hippocampus‐mediated dopaminergic transmission within the medial shell of the nucleus accumbens. Following seven daily injections of saline or cocaine (20 mg/kg, ip), unilateral infusion of N‐methyl‐d ‐aspartate (NMDA, 0.5 μg) into the ventral hippocampus transiently increased both motoric activity and ipsilateral dopamine efflux in the medial shell of the nucleus accumbens, and this effect was greater in rats that received repeated cocaine compared to controls that received repeated saline. In addition, repeated cocaine altered NMDA receptor subunit expression in the ventral hippocampus, reducing the NR2A : NR2B subunit ratio. Together, these results suggest that repeated exposure to cocaine produces maladaptive ventral hippocampal‐nucleus accumbens communication, in part through changes in glutamate receptor composition.
This study investigated the effects of 2‐(1‐chloro‐4‐hydroxyisoquinoline‐3‐carboxamido) acetic acid (IOX3), a selective small molecule inhibitor of hypoxia‐inducible factor (HIF) prolyl hydroxylases, on mouse brains subject to transient focal cerebral ischaemia. Male, 8‐ to 12‐week‐old C57/B6 mice were subjected to 45 min of middle cerebral artery occlusion (MCAO) either immediately or 24 h after receiving IOX3. Mice receiving IOX3 at 20 mg/kg 24 h prior to the MCAO had better neuroscores and smaller blood–brain barrier (BBB) disruption and infarct volumes than mice receiving the vehicle, whereas those having IOX3 at 60 mg/kg showed no significant changes. IOX3 treatment immediately before MCAO was not neuroprotective. IOX3 up‐regulated HIF‐1α, and increased EPO expression in mouse brains. In an in vitro BBB model (RBE4 cell line), IOX3 up‐regulated HIF‐1α and delocalized ZO‐1. Pre‐treating IOX3 on RBE4 cells 24 h before oxygen–glucose deprivation had a protective effect on endothelial barrier preservation with ZO‐1 being better localized, while immediate IOX3 treatment did not. Our study suggests that HIF stabilization with IOX3 before cerebral ischaemia is neuroprotective partially because of BBB protection, while immediate application could be detrimental. These results provide information for studies aimed at the therapeutic activation of HIF pathway for neurovascular protection from cerebral ischaemia.
Munc13‐1 is a pre‐synaptic active‐zone protein essential for neurotransmitter release and involved in pre‐synaptic plasticity in brain. Ethanol, butanol, and octanol quenched the intrinsic fluorescence of the C1 domain of Munc13‐1 with EC50s of 52 mM, 26 mM, and 0.7 mM, respectively. Photoactive azialcohols photolabeled Munc13‐1 C1 exclusively at Glu‐582, which was identified by mass spectrometry. Mutation of Glu‐582 to alanine, leucine, and histidine reduced the alcohol binding two‐ to five‐fold. Circular dichroism studies suggested that binding of alcohol increased the stability of the wild‐type Munc13‐1 compared with the mutants. If Munc13‐1 plays some role in the neural effects of alcohol in vivo, changes in the activity of this protein should produce differences in the behavioral responses to ethanol. We tested this prediction with a loss‐of‐function mutation in the conserved Dunc‐13 in Drosophila melanogaster. The Dunc‐13P84200/+ heterozygotes have 50% wild‐type levels of Dunc‐13 mRNA and display a very robust increase in ethanol self‐administration. This phenotype is reversed by the expression of the rat Munc13‐1 protein within the Drosophila nervous system. The present studies indicate that Munc13‐1 C1 has binding site(s) for alcohols and Munc13‐1 activity is sufficient to restore normal self‐administration to Drosophila mutants deficient in Dunc‐13 activity.
We developed the novel positron emission tomography (PET) ligand 2‐[5‐(4‐[11C]methoxyphenyl)‐2‐oxo‐1,3‐benzoxazol‐3(2H)‐yl]‐N‐methyl‐N‐phenylacetamide ([11C]MBMP) for translocator protein (18 kDa, TSPO) imaging and evaluated its efficacy in ischemic rat brains. [11C]MBMP was synthesized by reacting desmethyl precursor ( 1 ) with [11C]CH3I in radiochemical purity of ≥ 98% and specific activity of 85 ± 30 GBq/μmol (n = 18) at the end of synthesis. Biodistribution study on mice showed high accumulation of radioactivity in the TSPO‐rich organs, e.g., the lungs, heart, kidneys, and adrenal glands. The metabolite analysis in mice brain homogenate showed 80.1 ± 2.7% intact [11C]MBMP at 60 min after injection. To determine the specific binding of [11C]MBMP with TSPO in the brain, in vitro autoradiography and PET studies were performed in an ischemic rat model. In vitro autoradiography indicated significantly increased binding on the ipsilateral side compared with that on the contralateral side of ischemic rat brains. This result was supported firmly by the contrast of radioactivity between the ipsilateral and contralateral sides in PET images. Displacement experiments with unlabelled MBMP or PK11195 minimized the difference in uptake between the two sides. In summary, [11C]MBMP is a potential PET imaging agent for TSPO and, consequently, for the up‐regulation of microglia during neuroinflammation.
G protein‐coupled receptors are important regulators of cellular signaling processes. Within the large family of rhodopsin‐like receptors, those binding to biogenic amines form a discrete subgroup. Activation of biogenic amine receptors leads to transient changes of intracellular Ca2+‐([Ca2+]i) or 3′,5′‐cyclic adenosine monophosphate ([cAMP]i) concentrations. Both second messengers modulate cellular signaling processes and thereby contribute to long‐lasting behavioral effects in an organism. In vivo pharmacology has helped to reveal the functional effects of different biogenic amines in honeybees. The phenolamine octopamine is an important modulator of behavior. Binding of octopamine to its receptors causes elevation of [Ca2+]i or [cAMP]i. To date, only one honeybee octopamine receptor that induces Ca2+ signals has been molecularly and pharmacologically characterized. Here, we examined the pharmacological properties of four additional honeybee octopamine receptors. When heterologously expressed, all receptors induced cAMP production after binding to octopamine with EC50s in the nanomolar range. Receptor activity was most efficiently blocked by mianserin, a substance with antidepressant activity in vertebrates. The rank order of inhibitory potency for potential receptor antagonists was very similar on all four honeybee receptors with mianserin >> cyproheptadine > metoclopramide > chlorpromazine > phentolamine. The subroot of octopamine receptors activating adenylyl cyclases is the largest that has so far been characterized in arthropods, and it should now be possible to unravel the contribution of individual receptors to the physiology and behavior of honeybees.
Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an efficient neurosurgical treatment for advanced Parkinson's disease. Non‐invasive metabolic neuroimaging during the course of DBS in animal models may contribute to our understanding of its action mechanisms. Here, DBS was adapted to in vivo proton magnetic resonance spectroscopy at 11.7 T in the rat to follow metabolic changes in main basal ganglia structures, the striatum, and the substantia nigra pars reticulata (SNr). Measurements were repeated OFF and ON acute and subchronic (7 days) STN‐DBS in control and parkinsonian (6‐hydroxydopamine lesion) conditions. Acute DBS reversed the increases in glutamate, glutamine, and GABA levels induced by the dopamine lesion in the striatum but not in the SNr. Subchronic DBS normalized GABA in both the striatum and SNr, and glutamate in the striatum. Taurine levels were markedly decreased under subchronic DBS in the striatum and SNr in both lesioned and unlesioned rats. Microdialysis in the striatum further showed that extracellular taurine was increased. These data reveal that STN‐DBS has duration‐dependent metabolic effects in the basal ganglia, consistent with development of adaptive mechanisms. In addition to counteracting defects induced by the dopamine lesion, prolonged DBS has proper effects independent of the pathological condition.
The effect of psychoactive drugs on depression has usually been studied in cases of prolonged drug addiction and/or withdrawal, without much emphasis on the effects of subchronic or recreational drug use. To address this issue, we exposed laboratory rats to subchronic regimens of heroin or cocaine and tested long‐term effects on (i) depressive‐like behaviors, (ii) brain‐derived neurotrophic factor (BDNF) levels in reward‐related brain regions, and (iii) depressive‐like behavior following an additional chronic mild stress procedure. The long‐term effect of subchronic cocaine exposure was a general reduction in locomotor activity whereas heroin exposure induced a more specific increase in immobility during the forced swim test. Both cocaine and heroin exposure induced alterations in BDNF levels that are similar to those observed in several animal models of depression. Finally, both cocaine and heroin exposure significantly enhanced the anhedonic effect of chronic mild stress. These results suggest that subchronic drug exposure induces depressive‐like behavior which is accompanied by modifications in BDNF expression and increases the vulnerability to develop depressive‐like behavior following chronic stress. Implications for recreational and small‐scale drug users are discussed.
Both dopamine and glutamate are critically involved in cognitive processes such as working memory. Astrocytes, which express dopamine receptors, are essential elements in the termination of glutamatergic signaling: the astrocytic glutamate transporter GLT‐1 is responsible for > 90% of cortical glutamate uptake. The effect of dopamine depletion on glutamate transporters in the prefrontal cortex (PFC) remains unknown. In an effort to determine if astrocytes are a locus of cortical dopamine–glutamate interactions, we examined the effects of chronic dopamine denervation on PFC protein and mRNA levels of glutamate transporters. PFC dopamine denervation elicited a marked increase in GLT‐1 protein levels, but had no effect on levels of other glutamate transporters; high‐affinity glutamate transport was positively correlated with the extent of dopamine depletion. GLT‐1 gene expression was not altered. Our data suggest that dopamine depletion may lead to post‐translational modifications that result in increased expression and activity of GLT‐1 in PFC astrocytes.
The Ketogenic diet (KD) is an effective treatment with regards to treating pharmaco‐resistant epilepsy. However, there are difficulties around compliance and tolerability. Consequently, there is a need for refined/simpler formulations that could replicate the efficacy of the KD. One of the proposed hypotheses is that the KD increases cellular mitochondrial content which results in elevation of the seizure threshold. Here, we have focussed on the medium‐chain triglyceride form of the diet and the observation that plasma octanoic acid (C8) and decanoic acid (C10) levels are elevated in patients on the medium‐chain triglyceride KD. Using a neuronal cell line (SH‐SY5Y), we demonstrated that 250‐μM C10, but not C8, caused, over a 6‐day period, a marked increase in the mitochondrial enzyme, citrate synthase along with complex I activity and catalase activity. Increased mitochondrial number was also indicated by electron microscopy. C10 is a reported peroxisome proliferator activator receptor γ agonist, and the use of a peroxisome proliferator activator receptor γ antagonist was shown to prevent the C10‐mediated increase in mitochondrial content and catalase. C10 may mimic the mitochondrial proliferation associated with the KD and raises the possibility that formulations based on this fatty acid could replace a more complex diet.
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