Polysialylation and lipopolysaccharide‐induced shedding of E‐selectin ligand‐1 and neuropilin‐2 by microglia and THP‐1 macrophages

Microglia are tissue macrophages and mediators of innate immune responses in the brain. The protein‐modifying glycan polysialic acid (polySia) is implicated in modulating microglia activity. Cultured murine microglia maintain a pool of Golgi‐confined polySia, which is depleted in response to lipopolysaccharide (LPS)‐induced activation. Polysialylated neuropilin‐2 (polySia‐NRP2) contributes to this pool but further polySia protein carriers have remained elusive. Here, we use organotypic brain slice cultures to demonstrate that injury‐induced activation of microglia initiates Golgi‐confined polySia expression in situ. An unbiased glycoproteomic approach with stem cell‐derived microglia identifies E‐selectin ligand‐1 (ESL‐1) as a novel polySia acceptor. Together with polySia‐NRP2, polySia‐ESL‐1 is also detected in primary cultured microglia, in brain slice cultures and in phorbol ester‐induced THP‐1 macrophages. Induction of stem cell‐derived microglia, activated microglia in brain slice cultures and THP‐1 macrophages by LPS, but not interleukin‐4, causes polySia depletion and, as shown for stem cell‐derived microglia, a metalloproteinase‐dependent release of polySia‐ESL‐1 and polySia‐NRP2. Moreover, soluble polySia attenuates LPS‐induced production of nitric oxide and proinflammatory cytokines. Thus, shedding of polySia‐ESL‐1 and polySia‐NRP2 after LPS‐induced activation of microglia and THP‐1 macrophages may constitute a mechanism for negative feedback regulation. GLIA 2016 GLIA 2016;64:1314–1330     

Use of catechol‐O‐methyltransferase inhibition to minimize L‐3,4‐dihydroxyphenylalanine‐induced dyskinesia in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐lesioned macaque

L‐3,4‐dihydroxyphenylalanine (L‐DOPA)‐induced dyskinesia is a complication of dopaminergic treatment in Parkinson's disease. Lowering the L‐DOPA dose reduces dyskinesia but also reduces the antiparkinsonian benefit. A therapy that could enhance the antiparkinsonian action of low‐dose L‐DOPA (LDl) without exacerbating dyskinesia would thus be of considerable therapeutic benefit. This study assessed whether catechol‐O‐methyltransferase (COMT) inhibition, as an add‐on to LDl, might be a means to achieve this goal. Cynomolgus macaques were administered 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine. Dyskinesia was established by chronic treatment with L‐DOPA. Two doses of L‐DOPA were identified – high‐dose L‐DOPA (LDh), which provided good antiparkinsonian benefit but was compromised by disabling dyskinesia, and LDl, which was sub‐threshold for providing significant antiparkinsonian benefit, without dyskinesia. LDh and LDl were administered in acute challenges in combination with vehicle and, for LDl, with the COMT inhibitor entacapone (5, 15 and 45 mg/kg). The duration of antiparkinsonian benefit (ON‐time), parkinsonism and dyskinesia were determined. The ON‐time after LDh was ～170 min and the ON‐time after LDl alone (～98 min) was not significantly different to vehicle (～37 min). In combination with LDl, entacapone significantly increased the ON‐time (5, 15 and 45 mg/kg being ～123, ～148 and ～180 min, respectively). The ON‐time after LDl/entacapone 45 mg/kg was not different to that after LDh. However, whereas the percentage ON‐time that was compromised by disabling dyskinesia was ～56% with LDh, it was only ～31% with LDl/entacapone 45 mg/kg. In addition to the well‐recognized action of COMT inhibition to reduce wearing‐OFF, the data presented suggest that COMT inhibition in combination with low doses of L‐DOPA has potential as a strategy to alleviate dyskinesia.     

Exercise modifies α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptor expression in striatopallidal neurons in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐lesioned mouse

The α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic‐acid‐type glutamate receptor (AMPAR) plays a critical role in modulating experience‐dependent neuroplasticity, and alterations in AMPAR expression may underlie synaptic dysfunction and disease pathophysiology. Using the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) mouse model of dopamine (DA) depletion, our previous work showed exercise increases total GluA2 subunit expression and the contribution of GluA2‐containing channels in MPTP mice. The purpose of this study was to determine whether exercise‐dependent changes in AMPAR expression after MPTP are specific to the striatopallidal (D₂R) or striatonigral (D₁R) medium spiny neuron (MSN) striatal projection pathways. Drd₂‐eGFP‐BAC transgenic mice were used to delineate differences in AMPAR expression between striatal D₂R‐MSNs and D₁R‐MSNs. Striatal AMPAR expression was assessed by immunohistochemical (IHC) staining, Western immunoblotting (WB) of preparations enriched for postsynaptic density (PSD), and alterations in the current–voltage relationship of MSNs. We found DA depletion results in the emergence of GluA2‐lacking AMPARs selectively in striatopallidal D₂R‐MSNs and that exercise reverses this effect in MPTP mice. Exercise‐induced changes in AMPAR channels observed after DA depletion were associated with alterations in GluA1 and GluA2 subunit expression in postsynaptic protein, D₂R‐MSN cell surface expression, and restoration of corticostriatal plasticity. Mechanisms regulating experience‐dependent changes in AMPAR expression may provide innovative therapeutic targets to increase the efficacy of treatments for basal ganglia disorders, including Parkinson's disease. © 2013 Wiley Periodicals, Inc.     

Training‐, muscle‐ and task‐specific up‐ and downregulation of cortical inhibitory processes

Motor cortical contribution was shown to be important for balance control and for ballistic types of movements. However, little is known about the role of cortical inhibitory mechanisms and even less about long(er)‐term adaptations of these inhibitory processes. Therefore, the aim of the present study was to investigate the role of intracortical inhibition before and after four weeks of explosive or balance training. Two groups of subjects participated for four weeks either in an explosive training programme of the plantar flexor muscles or in a balance training programme on unstable devices. Adaptations in short‐interval intracortical inhibition (SICI) were assessed by applying paired‐pulse TMS to the soleus muscle during dynamic plantar flexions, balance perturbations and at rest. Furthermore, SICI was assessed for the untrained tibialis anterior muscle. The results show task‐, muscle‐ and group‐specific adaptations in SICI after the training (p = .021) with significantly increased SICI after balance training in the balance task and decreased SICI after explosive training in the ballistic task. The training also caused task‐ and group‐specific behavioural adaptations indicated by improved balance performance after balance training and increased ballistic performance after explosive training. There were no changes in SICI when measured at rest or in the untrained tibialis anterior muscle. This study shows that long(er)‐term training improves the ability to modulate cortical inhibitory processes in a task‐ and muscle‐specific manner.     

Sparing of orexin‐A and orexin‐B neurons in the hypothalamus and of orexin fibers in the substantia nigra of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐treated macaques

Several studies conducted in patients with Parkinson's disease have reported that the degeneration of substantia nigra dopaminergic neurons, which are essential for motor control, is associated with the loss of hypothalamic orexin neurons, which are involved in sleep regulation. In order to better explore the mutual interactions between these two systems, we wished to determine in macaques: (i) if the two orexin peptides, orexin‐A and orexin‐B, are distributed in the same hypothalamic cells and if they are localized in nerve terminals that project onto nigral dopaminergic neurons, and (ii) if there is a loss of orexin neurons in the hypothalamus and of orexin fibers innervating nigral dopaminergic neurons in macaques rendered parkinsonian by 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) intoxication. We showed that virtually all cells stained for orexin‐A in the hypothalamus co‐expressed orexin‐B. Numerous terminals stained for both orexin‐A and orexin‐B immunoreactivity that innervated the whole extent of the ventral tegmental area and substantia nigra pars compacta were found in close proximity to tyrosine hydroxylase‐immunoreactive dendrites. These data indicate that orexin‐A and orexin‐B peptides are in a position to play a role in controlling the activity of nigral dopaminergic neurons. However, no loss of orexin‐A or orexin‐B neurons in the hypothalamus and no loss of orexin fibers in the substantia nigra pars compacta was found in MPTP‐treated macaques when compared with control macaques. We conclude that a relatively selective dopaminergic lesion, such as that performed in MPTP‐treated macaques, is not sufficient to induce a loss of hypothalamic orexin neurons.     

Top‐down and bottom‐up control of stress‐coping

In this 30th anniversary issue review, we focus on the glucocorticoid modulation of limbic‐prefrontocortical circuitry during stress‐coping. This action of the stress hormone is mediated by mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs) that are co‐expressed abundantly in these higher brain regions. Via both receptor types, the glucocorticoids demonstrate, in various contexts, rapid nongenomic and slower genomic actions that coordinate consecutive stages of information processing. MR‐mediated action optimises stress‐coping, whereas, in a complementary fashion, the memory storage of the selected coping strategy is promoted via GR. We highlight the involvement of adipose tissue in the allocation of energy resources to central regulation of stress reactions, point to still poorly understood neuronal ensembles in the prefrontal cortex that underlie cognitive flexibility critical for effective coping, and evaluate the role of cortisol as a pleiotropic regulator in vulnerability to, and treatment of, trauma‐related psychiatric disorders.     

Anticonvulsant and proconvulsant actions of 2‐deoxy‐d‐glucose

Purpose: 2‐Deoxy‐d ‐glucose (2‐DG), a glucose analog that accumulates in cells and interferes with carbohydrate metabolism by inhibiting glycolytic enzymes, has anticonvulsant actions. Recognizing that severe glucose deprivation can induce seizures, we sought to determine whether acute treatment with 2‐DG can promote seizure susceptibility by assessing its effects on seizure threshold. For comparison, we studied 3‐methyl‐glucose (3‐MG), which like 2‐DG accumulates in cells and reduces glucose uptake, but does not inhibit glycolysis. Methods: Mice were treated with 2‐DG or 3‐MG and the seizure threshold determined in the 6‐Hz test, the mouse electroshock seizure threshold (MEST) test, and the intravenous pentylenetetrazol (i.v. PTZ) or kainic acid (i.v. KA) seizure threshold tests. 2‐DG was also tested in fully amygdala‐kindled rats. Results: 2‐DG (125–500 mg/kg, i.p., 30 min before testing) significantly elevated the seizure threshold in the 6‐Hz seizure test. 2‐DG (250–500 mg/kg) decreased the threshold in the MEST and i.v. PTZ and i.v. KA tests. 3‐MG had no effect on seizure threshold in the 6‐Hz test but, like 2‐DG, decreased seizure threshold in the i.v. PTZ test. 2‐DG (250 and 500 mg/kg, i.p., 30 min before testing) had no effect on amygdala‐kindled seizures. Conclusions: Although 2‐DG protects against seizures in the 6‐Hz seizure test, it promotes seizures in some other models. The proconvulsant action may relate to reduced glucose uptake, whereas the anticonvulsant action may require inhibition of glycolysis and shunting of glucose metabolism through the pentose phosphate pathway.     

Chronic periodic lateralised epileptic discharges and anti‐N‐methyl‐D‐aspartate receptor antibodies

Periodic lateralised epileptiform discharges (PLEDs) are uncommon transient electroencephalographic findings accompanied by acute brain lesions. A small proportion of PLEDs persist for more than three months and are called “chronic” PLEDs, the pathophysiology of which is still debated. Herein, we report a man with right hemispheric PLEDs which lasted for more than 14 months and mild left hemispatial neglect after he experienced status epilepticus. Although MRI was normal, positron emission tomography revealed right temporo‐parieto‐occipital hypometabolism, which coincided with the source area of PLEDs estimated by magnetoencephalography. In addition, levels of anti‐N‐methyl‐d ‐aspartate (NMDA) receptor antibodies and granzyme B were found to be high in the cerebrospinal fluid. Following two courses of steroid pulse therapy, the patient's left spatial neglect improved and the PLEDs were partially resolved. These findings suggest that the chronic PLEDs present in this case were an interictal phenomenon and that their pathophysiology involved autoimmune processes.     

Evaluation of N‐benzyl‐N‐[11C]methyl‐2‐ (7‐methyl‐8‐oxo‐2‐phenyl‐7,8‐dihydro‐9H‐purin‐9‐yl)acetamide ([11C]DAC) as a novel translocator protein (18 kDa) radioligand in kainic acid‐lesioned rat

The aim of this study was to evaluate N‐benzyl‐N‐[¹¹C]methyl‐2‐(7‐methyl‐8‐oxo‐2‐phenyl‐7,8‐dihydro‐9H‐purin‐9‐yl)acetamide ([¹¹C]DAC) as a new translocator protein (18 kDa) [TSPO, formerly known as the peripheral‐type benzodiazepine receptor (PBR)] positron emission tomography (PET) ligand in normal mice and unilateral kainic acid (KA)‐lesioned rats. DAC is a derivative of AC‐5216, which is a potent and selective PET ligand for the clinical investigation of TSPO. The binding affinity and selectivity of DAC for TSPO were similar to those of AC‐5216, and DAC was less lipophilic than AC‐5216. The distribution pattern of [¹¹C]DAC was in agreement with TSPO distribution in rodents. No radioactive metabolite of [¹¹C]DAC was found in the mouse brain, although it was metabolized rapidly in mouse plasma. Using small‐animal PET, we examined the in vivo binding of [¹¹C]DAC for TSPO in KA‐lesioned rats. [¹¹C]DAC and [¹¹C]AC‐5216 exhibited similar brain uptake in the lesioned and nonlesioned striatum, respectively. The binding of [¹¹C]DAC to TSPO was increased significantly in the lesioned striatum, and [¹¹C]DAC showed good contrast between the lesioned and nonlesioned striatum (the maximum ratio was about threefold). In displacement experiments, the uptake of [¹¹C]DAC in the lesioned striatum was eventually blocked using an excess of either unlabeled DAC or PK11195 injected. [¹¹C]DAC had high in vivo specific binding to TSPO in the injured rat brain. Therefore, [¹¹C]DAC is a useful PET ligand for TSPO imaging, and its specific binding to TSPO is suitable as a new biomarker for brain injury. Synapse 63:961–971, 2009. © 2009 Wiley‐Liss, Inc.     

Co‐expression of C‐terminal truncated alpha‐synuclein enhances full‐length alpha‐synuclein‐induced pathology

Lewy bodies, which are a pathological hallmark of Parkinson’s disease, contain insoluble polymers of alpha‐synuclein (αsyn). Among the different modifications that can promote the formation of toxic αsyn species, C‐terminal truncation is among the most abundant alterations in patients with Parkinson’s disease. In vitro, C‐terminal truncated αsyn aggregates faster and sub‐stoichiometric amounts of C‐terminal truncated αsyn promote aggregation of the full‐length αsyn (αsynFL) and induce neuronal toxicity. To address in vivo the putative stimulation of αsyn‐induced pathology by the presence of truncated αsyn, we used recombinant adeno‐associated virus to express either αsynFL or a C‐terminal truncated αsyn (1‐110) in rats. We adjusted the recombinant adeno‐associated virus vector concentrations so that either protein alone led to only mild to moderate axonal pathology in the terminals of nigrostriatal dopamine neurons without frank cell loss. When these two forms of αsyn were co‐expressed at these pre‐determined levels, it resulted in a more aggressive pathology in fiber terminals as well as dopaminergic cell loss in the substantia nigra. Using an antibody that did not detect the C‐terminal truncated αsyn (1‐110) but only αsynFL, we demonstrated that the co‐expressed truncated protein promoted the progressive accumulation of αsynFL and formation of larger pathological accumulations. Moreover, in the co‐expression group, three of the eight animals showed apomorphine‐induced turning, suggesting prominent post‐synaptic alterations due to impairments in the dopamine release, whereas the mild pathology induced by either form alone did not cause motor abnormalities. Taken together these data suggest that C‐terminal truncated αsyn can interact with and exacerbate the formation of pathological accumulations containing αsynFL in vivo.     

Role of N‐methyl‐D‐aspartate and non‐N‐methyl‐D‐aspartate receptors in the cardiovascular effects of L‐glutamate microinjection into the hypothalamic paraventricular nucleus of unanesthetized rats

We report on the cardiovascular effects of L‐glutamate (L‐glu) microinjection into the hypothalamic paraventricular nucleus (PVN) as well as the mechanisms involved in their mediation. L‐glu microinjection into the PVN caused dose‐related pressor and tachycardiac responses in unanesthetized rats. These responses were blocked by intravenous (i.v.) pretreatment with the ganglion blocker pentolinium (PE; 5 mg/kg), suggesting sympathetic mediation. Responses to L‐glu were not affected by local microinjection of the selective non‐NMDA receptor antagonist NBQX (2 nmol) or by local microinjection of the selective NMDA receptor antagonist LY235959 (LY; 2 nmol). However, the tachycardiac response was changed to a bradycardiac response after treatment with LY235959, suggesting that NMDA receptors are involved in the L‐glu heart rate response. Local pretreatment with LY235959 associated with systemic PE or dTyr(CH₂)₅(Me)AVP (50 μg/kg) respectively potentiated or blocked the response to L‐glu, suggesting that L‐glu responses observed after LY235959 are vasopressin mediated. The increased pressor and bradycardiac responses observed after LY + PE was blocked by subsequent i.v. treatment with the V₁‐vasopressin receptor antagonist dTyr(CH₂)₅(Me)AVP, suggesting vasopressin mediation. The pressor and bradycardiac response to L‐glu microinjection into the PVN observed in animals pretreated with LY + PE was progressively inhibited and even blocked by additional pretreatment with increasing doses of NBQX (2, 10, and 20 nmol) microinjected into the PVN, suggesting its mediation by local non‐NMDA receptors. In conclusion, results suggest the existence of two glutamatergic pressor pathways in the PVN: one sympathetic pathway that is mediated by NMDA receptors and a vasopressinergic pathway that is mediated by non‐NMDA receptors. © 2009 Wiley‐Liss, Inc.     

Quantitative tract‐based white matter heritability in 1‐ and 2‐year‐old twins

White matter (WM) microstructure, as determined by diffusion tensor imaging (DTI), is increasingly recognized as an important determinant of cognitive function and is also altered in neuropsychiatric disorders. Little is known about genetic and environmental influences on WM microstructure, especially in early childhood, an important period for cognitive development and risk for psychiatric disorders. We studied the heritability of DTI parameters, fractional anisotropy (FA), radial diffusivity (RD) and axial diffusivity (AD) along 34 tracts, including 10 bilateral fiber pathways and the respective subdivision, using quantitative tractography in a longitudinal sample of healthy children at 1 year (N = 215) and 2 years (N = 165) of age. We found that heritabilities for whole brain AD, RD, and FA were 0.48, 0.69, and 0.72 at age 1, and 0.59, 0.77, and 0.76 at age 2 and that mean heritabilities of tract‐averaged AD, RD, and FA for individual bundles were moderate (over 0.4). However, the heritability of DTI change between 1 and 2 years of age was not significant for most tracts. We also demonstrated that point‐wise heritability tended to be significant in the central portions of the tracts and was generally spatially consistent at ages 1 and 2 years. These results, especially when compared to heritability patterns in neonates, indicate that the heritability of WM microstructure is dynamic in early childhood and likely reflect heterogeneous maturation of WM tracts and differential genetic and environmental influences on maturation patterns.