bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth/Differentiation Factor-15/Macrophage Inhibitory Cytokine-1 Is a Novel Trophic Factor for Midbrain Dopaminergic NeuronsIn Vivo
Authors: Strelau Jens , Sullivan Aideen , Böttner Martina , Lingor Paul , Falkenstein Elisabeth , Suter-Crazzolara Clemens , Galter Dagmar , Jaszai Jozsef , Krieglstein Kerstin , Unsicker Klaus
Published: April 2018

Transforming growth factor-βs (TGF-βs) constitute an expanding family of multifunctional cytokines with prominent roles in development, cell proliferation, differentiation, and repair. We have cloned, expressed, and raised antibodies against a distant member of the TGF-βs, growth/differentiation factor-15 (GDF-15). GDF-15 is identical to macrophage inhibitory cytokine-1 (MIC-1). GDF-15/MIC-1 mRNA and protein are widely distributed in the developing and adult CNS and peripheral nervous systems, including choroid plexus and CSF. GDF-15/MIC-1 is a potent survival promoting and protective factor for cultured and iron-intoxicated dopaminergic (DAergic) neurons cultured from the embryonic rat midbrain floor. The trophic effect of GDF-15/MIC-1 was not accompanied by an increase in cell proliferation and astroglial maturation, suggesting that GDF-15/MIC-1 probably acts directly on neurons. GDF-15/MIC-1 also protects 6-hydroxydopamine (6-OHDA)-lesioned nigrostriatal DAergic neuronsin vivo. Unilateral injections of GDF-15/MIC-1 into the medial forebrain bundle just above the substantia nigra (SN) and into the left ventricle (20 μg each) immediately before a 6-OHDA injection (8 μg) prevented 6-OHDA-induced rotational behavior and significantly reduced losses of DAergic neurons in the SN. This protection was evident for at least 1 month. Administration of 5 μg of GDF-15/MIC-1 in the same paradigm also provided significant neuroprotection. GDF-15/MIC-1 also promoted the serotonergic phenotype of cultured raphe neurons but did not support survival of rat motoneurons. Thus, GDF-15/MIC-1 is a novel neurotrophic factor with prominent effects on DAergic and serotonergic neurons. GDF-15/MIC-1 may therefore have a potential for the treatment of Parkinson's disease and disorders of the serotonergic system.
Estrogen Is Essential for Maintaining Nigrostriatal Dopamine Neurons in Primates: Implications for Parkinson's Disease and Memory
Authors: Leranth Csaba , Roth Robert H. , Elsworth John D. , Naftolin Frederick , Horvath Tamas L. , Redmond D. Eugene
Published: April 2018

There are sexual differences in several parameters of the nigrostriatal dopamine neurons, as well as in the progression of diseases associated with this system, e.g., Parkinson's disease and dementia. These differences, as well as direct experimental data in rodents, suggest that gonadal hormones play a role in modulating this system. To determine whether circulating estrogen might have long-term effects by altering the number of dopamine neurons, the density of dopamine neurons was calculated in the compact zone of the substantia nigra of male and intact female short- (10 d) and longer-term (30 d) ovariectomized and short- and longer-term ovariectomized but estrogen-replaced nonhuman primates (African green monkeys). Furthermore, the number of tyrosine hydroxylase-expressing neurons, the total number of all types of neurons, and the volume of the compact zone of the substantia nigra were calculated in 30 d ovariectomized and in 30 d ovariectomized and estrogen-replaced monkeys. Unbiased stereological analyses demonstrated that a 30 d estrogen deprivation results in an apparently permanent loss of >30% of the total number of substantia nigra dopamine cells. Furthermore, the density calculations showed that brief estrogen replacement restores the density of tyrosine hydroxylase-immunoreactive cells after a 10 d, but not after a 30 d, ovariectomy. Moreover, the density of dopamine cells is higher in females than in males. These observations show the essential role of estrogen in maintaining the integrity of the nigral dopamine system, suggest a new treatment strategy for patients with Parkinson's disease and with certain forms of memory-impairing disorders, and provide another rationale for estrogen replacement therapy for postmenopausal women.
The Human Skeletal Muscle Na Channel Mutation R669H Associated with Hypokalemic Periodic Paralysis Enhances Slow Inactivation
Authors: Struyk Arie F. , Scoggan Kylie A. , Bulman Dennis E. , Cannon Stephen C.
Published: April 2018

Missense mutations of the human skeletal muscle voltage-gated Na channel (hSkM1) underlie a variety of diseases, including hyperkalemic periodic paralysis (HyperPP), paramyotonia congenita, and potassium-aggravated myotonia. Another disorder of sarcolemmal excitability, hypokalemic periodic paralysis (HypoPP), which is usually caused by missense mutations of the S4 voltage sensors of the L-type Ca channel, was associated recently in one family with a mutation in the outermost arginine of the IIS4 voltage sensor (R669H) of hSkM1 (Bulman et al., 1999). Intriguingly, an arginine-to-histidine mutation at the homologous position in the L-type Ca2+channel (R528H) is a common cause of HypoPP. We have studied the gating properties of the hSkM1-R669H mutant Na channel experimentally in human embryonic kidney cells and found that it has no significant effects on activation or fast inactivation but does cause an enhancement of slow inactivation. R669H channels exhibit an ∼10 mV hyperpolarized shift in the voltage dependence of slow inactivation and a twofold to fivefold prolongation of recovery after prolonged depolarization. In contrast, slow inactivation is often disrupted in HyperPP-associated Na channel mutants. These results demonstrate that, in R669H-associated HypoPP, enhanced slow inactivation does not preclude, and may contribute to, prolonged attacks of weakness and add support to previous evidence implicating the IIS4 voltage sensor in slow-inactivation gating.
Zinc Inhibits Miniature GABAergic Currents by Allosteric Modulation of GABAAReceptor Gating
Authors: Barberis Andrea , Cherubini Enrico , Mozrzymas Jerzy W.
Published: April 2018

Zinc is abundantly present in the CNS, and after nerve stimulation is thought to be released in sufficient quantity to modulate the synaptic transmission. Although it is known that this divalent cation inhibits the GABAergic synaptic currents, the underlying mechanisms were not fully elucidated. Here we report that zinc reduced the amplitude, slowed the rise time, and accelerated the decay of mIPSCs in cultured hippocampal neurons. The analysis of current responses to rapid GABA applications and model simulations indicated that these effects on mIPSCs are caused by zinc modulation of GABAAreceptor gating. In particular, zinc slowed the onset of GABA-evoked currents by decreasing both the binding (kon) and the transition rate from closed to open state (β2). Moreover, slower onset and recovery from desensitization as well as an increased unbinding rate (koff) were shown to underlie the accelerated deactivation kinetics in the presence of zinc. The nonequilibrium conditions of GABAAreceptor activation were found to strongly affect zinc modulation of this receptor. In particular, an extremely fast clearance of synaptic GABA is implicated to be responsible for a stronger zinc effect on mIPSCs than on current responses to exogenous GABA. Finally, the analysis of currents evoked by GABA coapplied with zinc indicated that the interaction between zinc and GABAAreceptors was too slow to explain zinc effects in terms of competitive antagonism. In conclusion, our results provide evidence that inhibition of mIPSCs by zinc is attributable to the allosteric modulation of GABAAreceptor gating.
Dopamine D3Receptors Expressed by All Mesencephalic Dopamine Neurons
Authors: Diaz Jorge , Pilon Catherine , Le Foll Bernard , Gros Claude , Triller Antoine , Schwartz Jean-Charles , Sokoloff Pierre
Published: April 2018

A polyclonal antibody was generated using synthetic peptides designed in a specific sequence of the rat D3receptor (D3R). Using transfected cells expressing recombinant D3R, but not D2receptor, this antibody labeled 45–80 kDa species in Western blot analysis, immunoprecipitated a soluble fraction of [125I]iodosulpride binding, and generated immunofluorescence, mainly in the cytoplasmic perinuclear region of the cells. In rat brain, the distribution of immunoreactivity matched that of D3R binding, revealed using [125I]R(+)trans-7-hydroxy-2-[N-propyl-N-(3′-iodo-2′-propenyl)amino] tetralin ([125I]7-trans-OH-PIPAT), with dense signals in the islands of Calleja and mammillary bodies, and moderate to low signals in the shell of nucleus accumbens (AccSh), frontoparietal cortex, substantia nigra (SN), ventral tegmental area (VTA) and lobules 9 and 10 of the cerebellum. Very low or no signals could be detected in other rat brain regions, including dorsal striatum, or in D3R-deficient mouse brain. Labeling of perikarya of AccSh and SN/VTA appeared with a characteristic punctuate distribution, mostly at the plasma membrane where it was not associated with synaptic boutons, as revealed by synaptophysin immunoreactivity. In SN/VTA, D3R immunoreactivity was found on afferent terminals, arising from AccSh, in which destruction of intrinsic neurons by kainate infusions produced a loss of D3R binding in both AccSh and SN/VTA. D3R-immunoreactivity was also found in all tyrosine hydroxylase (TH)-positive neurons observed in SN, VTA and A8 retrorubral fields, where it could represent D3autoreceptors controlling dopamine neuron activities, in agreement with the elevated dopamine extracellular levels in projection areas of these neurons found in D3R-deficient mice.
Increased Production of Tumor Necrosis Factor-α by Glial Cells Exposed to Simulated Ischemia or Elevated Hydrostatic Pressure Induces Apoptosis in Cocultured Retinal Ganglion Cells
Authors: Tezel Gülgün , Wax Martin B.
Published: April 2018

Although glial cells in the optic nerve head undergo a reactivation process in glaucoma, the role of glial cells during glaucomatous neurodegeneration of retinal ganglion cells is unknown. Using a coculture system in which retinal ganglion cells and glial cells are grown on different layers but share the same culture medium, we studied the influences of glial cells on survival of retinal ganglion cells after exposure to different stress conditions typified by simulated ischemia and elevated hydrostatic pressure. After the exposure to these stressors, we observed that glial cells secreted tumor necrosis factor-α (TNF-α) as well as other noxious agents such as nitric oxide into the coculture media and facilitated the apoptotic death of retinal ganglion cells as assessed by morphology, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, and caspase activity. The glial origin of these noxious effects was confirmed by passive transfer experiments. Furthermore, retinal ganglion cell apoptosis was attenuated ∼66% by a neutralizing antibody against TNF-α and 50% by a selective inhibitor of inducible nitric oxide synthase (1400W). Because elevated intraocular pressure and ischemia are two prominent stress factors identified in the eyes of patients with glaucoma, these findings reveal a novel glia-initiated pathogenic mechanism for retinal ganglion cell death in glaucoma. In addition, these findings suggest that the inhibition of TNF-α that is released by reactivated glial cells may provide a novel therapeutic target for neuroprotection in the treatment of glaucomatous optic neuropathy.
Presenilin-1 P264L Knock-In Mutation: Differential Effects on Aβ Production, Amyloid Deposition, and Neuronal Vulnerability
Authors: Siman Robert , Reaume Andrew G. , Savage Mary J. , Trusko Stephen , Lin Yin-Guo , Scott Richard W. , Flood Dorothy G.
Published: April 2018

The pathogenic mechanism linking presenilin-1 (PS-1) gene mutations to familial Alzheimer's disease (FAD) is uncertain, but has been proposed to include increased neuronal sensitivity to degeneration and enhanced amyloidogenic processing of the β-amyloid precursor protein (APP). We investigated this issue by using gene targeting with the Cre-lox system to introduce an FAD-linked P264L mutation into the endogenous mousePS-1gene, an approach that maintains normal regulatory controls over expression. Primary cortical neurons derived from PS-1 homozygous mutant knock-in mice exhibit basal neurodegeneration similar to their PS-1 wild-type counterparts. Staurosporine and Aβ1–42 induce apoptosis, and neither the dose dependence nor maximal extent of cell death is altered by the PS-1 knock-in mutation. Similarly, glutamate-induced neuronal necrosis is unaffected by the PS-1P264L mutation. The lack of effect of the PS-1P264L mutation is confirmed by measures of basal- and toxin-induced caspase and calpain activation, biochemical indices of apoptotic and necrotic signaling, respectively. To analyze the influence of the PS-1P264L knock-in mutation on APP processing and the development of AD-type neuropathology, we created mouse lines carrying mutations in both PS-1 and APP. In contrast to the lack of effect on neuronal vulnerability, cortical neurons cultured from PS-1P264L homozygous mutant mice secrete Aβ42 at an increased rate, whereas secretion of Aβ40 is reduced. Moreover, the PS-1 knock-in mutation selectively increases Aβ42 levels in the mouse brain and accelerates the onset of amyloid deposition and its attendant reactive gliosis, even as a single mutant allele. We conclude that expression of an FAD-linked mutant PS-1 at normal levels does not generally increase cortical neuronal sensitivity to degeneration. Instead, enhanced amyloidogenic processing of APP likely is critical to the pathogenesis of PS-1-linked FAD.
Glial-Derived Neurotrophic Factor Upregulates Expression of Functional SNS and NaN Sodium Channels and Their Currents in Axotomized Dorsal Root Ganglion Neurons
Authors: Cummins Theodore R. , Black Joel A. , Dib-Hajj Sulayman D. , Waxman Stephen G.
Published: April 2018

Dorsal root ganglion (DRG) neurons produce multiple sodium currents, including several different TTX-sensitive (TTX-S) currents and TTX-resistant (TTX-R) currents, which are produced by distinct sodium channels. We previously demonstrated that, after sciatic nerve transection, the levels of SNS and NaN sodium channel α-subunit transcripts and protein in small (18–30 μm diameter) DRG neurons are reduced, as are the amplitudes and densities of the slowly inactivating and persistent TTX-R currents produced by these two channels. In this study, we asked whether glial-derived neurotrophic factor (GDNF), which has been shown to prevent some axotomy-induced changes such as the loss of somatostatin expression in DRG neurons, can ameliorate the axotomy-induced downregulation of SNS and NaN TTX-R sodium channels. We show here that exposure to GDNF can significantly increase both slowly inactivating and persistent TTX-R sodium currents, which are paralleled by increases in SNS and NaN mRNA and protein levels, in axotomized DRG neuronsin vitro. We also show that intrathecally administered GDNF increases the amplitudes of the slowly inactivating and persistent TTX-R currents, and SNS and NaN protein levels, in peripherally axotomized DRG neuronsin vivo. Finally, we demonstrate that GDNF upregulates the persistent TTX-R current in SNS-null mice, thus demonstrating that the upregulated persistent sodium current is not produced by SNS. Because TTX-R sodium channels have been shown to be important in nociception, the effects of GDNF on axotomized DRG neurons may have important implications for the regulation of nociceptive signaling by these cells.
Fetal Hippocampal Grafts Containing CA3 Cells Restore Host Hippocampal Glutamate Decarboxylase-Positive Interneuron Numbers in a Rat Model of Temporal Lobe Epilepsy
Authors: Shetty Ashok K. , Turner Dennis A.
Published: April 2018

Degeneration of CA3-pyramidal neurons in hippocampus after intracerebroventricular kainic acid (KA) administration, a model of temporal lobe epilepsy, results in hyperexcitability within both dentate gyrus and the CA1 subfield. It also leads to persistent reductions in hippocampal glutamate decarboxylase (GAD) interneuron numbers without diminution in Nissl-stained interneuron numbers, indicating loss of GAD expression in a majority of interneurons. We hypothesize that enduring loss of GAD expression in hippocampal interneurons after intracerebroventricular KA is attributable to degeneration of their CA3 afferent input; therefore, fetal CA3 grafts can restore GAD interneuron numbers through graft axon reinnervation of the host. We analyzed GAD interneuron density in the adult rat hippocampus at 6 months after KA administration after grafting of fetal mixed hippocampal, CA3 or CA1 cells into the CA3 region at 45 d after lesion, in comparison with “lesion-only” and intact hippocampus. In dentate and CA1 regions of the lesioned hippocampus receiving grafts of either mixed hippocampal or CA3 cells, GAD interneuron density was both significantly greater than lesion-only hippocampus and comparable with the intact hippocampus. In the CA3 region, GAD interneuron density was significantly greater than lesion-only hippocampus but less than the intact hippocampus. Collectively, the overall GAD interneuron density in the lesioned hippocampus receiving either mixed hippocampal or CA3 grafts was restored to that in the intact hippocampus. In contrast, GADinterneuron density in the lesioned hippocampus receiving CA1 grafts remained comparable with lesion-only hippocampus. Thus, grafts containing CA3 cells restore CA3 lesion-induced depletions in hippocampal GAD interneurons, likely by reinnervation of GAD-deficient interneurons. This specific graft-mediated effect is beneficial because reactivation of interneurons could ameliorate both loss of functional inhibition and hyperexcitability in CA3-lesioned hippocampus.
GABAergic Inhibition Suppresses Paroxysmal Network Activity in the Neonatal Rodent Hippocampus and Neocortex
Authors: Wells Jason E. , Porter James T. , Agmon Ariel
Published: April 2018

In the adult cerebral cortex, the neurotransmitter GABA is strongly inhibitory, as it profoundly decreases neuronal excitability and suppresses the network propensity for synchronous activity. When fast, GABAAreceptor (GABAAR)-mediated neurotransmission is blocked in the mature cortex, neuronal firing is synchronized via recurrent excitatory (glutamatergic) synaptic connections, generating population discharges manifested extracellularly as spontaneous paroxysmal field potentials (sPFPs). This epileptogenic effect of GABAAR antagonists has rarely been observed in the neonatal cortex, and indeed, GABA in the neonate has been proposed to have an excitatory, rather than inhibitory, action. In contrast, we show here that when fast GABAergic neurotransmission was blocked in slices of neonatal mouse and rat hippocampus and neocortex, sPFPs occurred in nearly half the slices from postnatal day 4 (P4) to P7 neocortex and in most slices from P2 to P7 hippocampus. In Mg2+-free solution, GABAAR antagonists elicited sPFPs in nearly all slices of P2 and older neocortex and P0 and older hippocampus. Mg2+-free solution alone induced spontaneous events in the majority of P2 and older slices from both regions; addition of GABAAR antagonists caused a dramatic increase in the mean amplitude, but not frequency, of these events in the hippocampus and in their mean frequency, but not amplitude, in the neocortex. In the hippocampus, GABAAR agonists suppressed amplitudes, but not frequency, of sPFPs, whereas glutamate antagonists suppressed frequency but not amplitudes. We conclude that neonatal rodent cerebral cortex possesses glutamatergic circuits capable of generating synchronous network activity and that, as in the adult, tonic GABAAR-mediated inhibition prevents this activity from becoming paroxysmal.
DOI-Induced Activation of the Cortex: Dependence on 5-HT2AHeteroceptors on Thalamocortical Glutamatergic Neurons
Authors: Scruggs Jennifer L. , Patel Sachin , Bubser Michael , Deutch Ariel Y.
Published: April 2018

Administration of the hallucinogenic 5-HT2A/2Cagonist 1-[2,5-dimethoxy-4-iodophenyl]-2-aminopropane (DOI) induces expression of Fos protein in the cerebral cortex. To understand the mechanisms subserving this action of DOI, we examined the consequences of pharmacological and surgical manipulations on DOI-elicited Fos expression in the somatosensory cortex of the rat. DOI dose-dependently increased cortical Fos expression. Pretreatment with the selective 5-HT2Aantagonist MDL 100,907 completely blocked DOI-elicited Fos expression, but pretreatment with the 5-HT2Cantagonist SB 206,553 did not modify DOI-elicited Fos expression. These data suggest that DOI acts through 5-HT2Areceptors to increase cortical Fos expression. However, we found that DOI did not induce Fos in cortical 5-HT2Aimmunoreactive neurons but did increase expression in a band of neurons spanning superficial layer V to deep III, within the apical dendritic fields of layer V 5-HT2A-immunoreactive cells. This band of Fos immunoreactive neurons was in register with anterogradely labeled axons from the ventrobasal thalamus, which have previously been shown to be glutamatergic and express the 5-HT2Atranscript. The effects of DOI were markedly reduced in animals pretreated with the AMPA/KA antagonist GYKI 52466, and lesions of the ventrobasal thalamus attenuated DOI-elicited Fos expression in the cortex. These data suggest that DOI activates 5-HT2Areceptors on thalamocortical neurons and thereby increases glutamate release, which in turn drives Fos expression in cortical neurons through an AMPA receptor-dependent mechanism. These data cast new light on the mechanisms of action of hallucinogens.
The Effect of Lesions of the Insular Cortex on Instrumental Conditioning: Evidence for a Role in Incentive Memory
Authors: Balleine Bernard W. , Dickinson Anthony
Published: April 2018

In three experiments, we assessed the effect of lesions aimed at the gustatory region of the insular cortex on instrumental conditioning in rats. In experiment 1, the lesion had no effect on the acquisition of either lever pressing or chain pulling in food-deprived rats whether these actions earned food pellets or a maltodextrin solution. The lesion did, however, attenuate the impact of outcome devaluation, induced by sensory-specific satiety, on instrumental performance but only when assessed in an extinction test. This effect was not secondary to an impairment in instrumental learning; in experiment 2, no evidence was found to suggest that the lesioned rats differed from shams in their ability to encode the specific action-outcome contingencies to which they were exposed during training. In experiment 3, however, lesioned rats were found to be insensitive to the impact of an incentive learning treatment conducted when they were undeprived; although, again, this deficit was confined to a test conducted in extinction. These results are consistent with the view that, in instrumental conditioning, the gustatory region of the insular cortex is involved in encoding the taste of food outcomes in memory and, hence, in encoding the incentive value assigned to these outcomes on the basis of prevailing motivational conditions.
Presynaptic Kainate Receptors Regulate Spinal Sensory Transmission
Authors: Kerchner Geoffrey A. , Wilding Timothy J. , Li Ping , Zhuo Min , Huettner James E.
Published: April 2018

Small diameter dorsal root ganglion (DRG) neurons, which include cells that transmit nociceptive information into the spinal cord, are known to express functional kainate receptors. It is well established that exposure to kainate will depolarize C-fiber afferents arising from these cells. Although the role of kainate receptors on sensory afferents is unknown, it has been hypothesized that presynaptic kainate receptors may regulate glutamate release in the spinal cord. Here we show that kainate, applied at low micromolar concentrations in the presence of the AMPA-selective antagonist (RS)-4-(4-aminophenyl)-1,2-dihydro-1-methyl-2-propyl-carbamoyl-6,7-methylenedioxyphthalazine, suppressed spontaneous NMDA receptor-mediated EPSCs in cultures of spinal dorsal horn neurons. In addition, kainate suppressed EPSCs in dorsal horn neurons evoked by stimulation of synaptically coupled DRG cells in DRG–dorsal horn neuron cocultures. Interestingly, although the glutamate receptor subunit 5-selective kainate receptor agonist (RS)-2-α-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) propanoic acid (ATPA) (2 μm) was able to suppress DRG–dorsal horn synaptic transmission to a similar extent as kainate (10 μm), it had no effect on excitatory transmission between dorsal horn neurons. Agonist applications revealed a striking difference between kainate receptors expressed by DRG and dorsal horn neurons. Whereas DRG cell kainate receptors were sensitive to both kainate and ATPA, most dorsal horn neurons responded only to kainate. Finally, in recordings from dorsal horn neurons in spinal slices, kainate and ATPA were able to suppress NMDA and AMPA receptor-mediated EPSCs evoked by dorsal root fiber stimulation. Together, these data suggest that kainate receptor agonists, acting at a presynaptic locus, can reduce glutamate release from primary afferent sensory synapses.
Fornix-Dependent Induction of Hippocampal CCAAT Enhancer-Binding Protein β and δ Co-Localizes with Phosphorylated cAMP Response Element-Binding Protein and Accompanies Long-Term Memory Consolidation
Authors: Taubenfeld Stephen M. , Wiig Kjesten A. , Monti Barbara , Dolan Bridget , Pollonini Gabriella , Alberini Cristina M.
Published: April 2018

The cAMP response element-binding protein (CREB) is an evolutionarily conserved transcription regulator essential for long-term memory formation. It is not known, however, whether the molecular events downstream of CREB activation are also conserved. An early, cAMP-dependent event necessary for learning-related long-term synaptic plasticity in the invertebrateAplysia californicais the induction of the transcription factor CCAAT enhancer-binding protein (C/EBP). Here we show that two homologs in the rat, C/EBPβ and C/EBPδ, are induced at discrete times after inhibitory avoidance learning and co-localize with phosphorylated CREB in the hippocampus. This induction is blocked by fornix lesions, which are known to disrupt activation of CREB in the hippocampus and to impair memory consolidation. These results indicate that C/EBPs are evolutionarily conserved components of the CREB-dependent gene cascade activated in long-term memory.
Localization and Mechanisms of Action of Cannabinoid Receptors at the Glutamatergic Synapses of the Mouse Nucleus Accumbens
Authors: Robbe David , Alonso Gérard , Duchamp Florence , Bockaert Joël , Manzoni Olivier J.
Published: April 2018

Despite the role of excitatory transmission to the nucleus accumbens (NAc) in the actions of most drugs of abuse, the presence and functions of cannabinoid receptors (CB1) on the glutamatergic cortical afferents to the NAc have never been explored. Here, immunohistochemistry has been used to show the localization of CB1 receptors on axonal terminals making contacts with the NAc GABAergic neurons. Electrophysiological techniques in the NAc slice preparation revealed that cannabimimetics [WIN 55,212,2 (WIN-2) and CP55940] strongly inhibit stimulus-evoked glutamate-mediated transmission. The inhibitory actions of WIN-2 were dose-dependent (EC50of 293 ± 13 nm) and reversed by the selective CB1 antagonist SR 141716A. In agreement with a presynaptic localization of CB1 receptors, WIN-2 increased paired-pulse facilitation, decreased miniature EPSC (mEPSC) frequency, and had no effect on the mEPSCs amplitude. Perfusion with the adenylate cyclase activator forskolin enhanced glutamatergic transmission but did not alter presynaptic CB1 actions, suggesting that cannabinoids inhibit glutamate release independently from the cAMP–PKA cascade. CB1 did not reduce evoked transmitter release by inhibiting presynaptic voltage-dependent Ca2+currents through N-, L-, or P/Q-type Ca2+channels, because CB1 inhibition persisted in the presence of ω-Conotoxin-GVIA, nimodipine, or ω-Agatoxin-IVA. The K+channel blockers 4-aminopyridine (100 μm) and BaCl2(300 μm) each reduced by 40–50% the inhibitory actions of WIN-2, and their effects were additive. These data suggest that CB1 receptors are located on the cortical afferents to the nucleus and can reduce glutamate synaptic transmission within the NAc by modulating K+channels activity.
The Contribution of Dendritic Kv3 K+Channels to Burst Threshold in a Sensory Neuron
Authors: Rashid Asim J. , Morales Ezequiel , Turner Ray W. , Dunn Robert J.
Published: April 2018

Voltage-gated ion channels localized to dendritic membranes can shape signal processing in central neurons. This study describes the distribution and functional role of a high voltage-activating K+channel in the electrosensory lobe (ELL) of an apteronotid weakly electric fish. We identify a homolog of the Kv3.3 K+channel, AptKv3.3, that exhibits a high density of mRNA expression and immunolabel that is distributed over the entire soma–dendritic axis of ELL pyramidal cells. The kinetics and pharmacology of native K+channels recorded in pyramidal cell somata and apical dendrites match those of AptKv3.3 channels expressed in a heterologous expression system. The functional role of AptKv3.3 channels was assessed using focal drug ejections in somatic and dendritic regions of anin vitroslice preparation. Local blockade of AptKv3.3 channels slows the repolarization of spikes in pyramidal cell somata as well as spikes backpropagating into apical dendrites. The resulting increase in dendritic spike duration lowers the threshold for a γ-frequency burst discharge that is driven by inward current associated with backpropagating dendritic spikes. Thus, dendritic AptKv3.3 K+channels influence the threshold for a form of burst discharge that has an established role in feature extraction of sensory input.
Vaccination for Neuroprotection in the Mouse Optic Nerve: Implications for Optic Neuropathies
Authors: Fisher Jasmin , Levkovitch-Verbin Hanna , Schori Hadas , Yoles Eti , Butovsky Oleg , Kaye Joel F. , Ben-Nun Avraham , Schwartz Michal
Published: April 2018

T-cell autoimmunity to myelin basic protein was recently shown to be neuroprotective in injured rat optic nerves. In the present study, using the mouse optic nerve, we examined whether active immunization rather than passive transfer of T-cells can be beneficial in protecting retinal ganglion cells (RGCs) from post-traumatic death. Before severe crush injury of the optic nerve, SJL/J and C3H.SW mice were actively immunized with encephalitogenic or nonencephalitogenic peptides of proteolipid protein (PLP) or myelin oligodendrocyte glycoprotein (MOG), respectively. At different times after the injury, the numbers of surviving RGCs in both strains immunized with the nonencephalitogenic peptides pPLP 190–209 or pMOG 1–22 were significantly higher than in injured controls treated with the non-self-antigen ovalbumin or with a peptide derived from β-amyloid, a non-myelin-associated protein. Immunization with the encephalitogenic myelin peptide pPLP 139–151 was beneficial only when the disease it induced, experimental autoimmune encephalomyelitis, was mild. The results of this study show that survival of RGCs after axonal injury can be enhanced by vaccination with an appropriate self-antigen. Furthermore, the use of nonencephalitogenic myelin peptides for immunization apparently allows neuroprotection without incurring the risk of an autoimmune disease. Application of these findings might lead to a promising new approach for treating optic neuropathies such as glaucoma.
An Evolutionarily Conserved Transmembrane Protein That Is a Novel Downstream Target of Neurotrophin and Ephrin Receptors
Authors: Kong Haeyoung , Boulter Jim , Weber Janet L. , Lai Cary , Chao Moses V.
Published: April 2018

Appropriate development of nervous system connectivity involves a variety of processes, including neuronal life-and-death decisions, differentiation, axon guidance and migration, and synaptogenesis. Although these activities likely require specialized signaling events, few substrates unique to these neurotrophic functions have been identified. Here we describe the cloning of ankyrin repeat-rich membrane spanning (ARMS), which encodes a novel downstream target of neurotrophin and ephrin receptor tyrosine kinases, Trk and Eph, respectively. The amino acid sequence of ARMS is highly conserved from nematode to human, suggesting an evolutionarily conserved role for this protein. The ARMS protein consists of 1715 amino acids containing four putative transmembrane domains, multiple ankyrin repeats, a sterile α motif domain, and a potential PDZ-binding motif. In the rat, ARMS is specifically expressed in the developing nervous system and in highly plastic areas of the adult brain, regions enriched in Trks and Eph receptors. ARMS can physically associate with TrkA and p75 neurotrophin receptors. Moreover, endogenous ARMS protein is tyrosine phosphorylated after neurotrophin treatment of pheochromocytoma 12 cells and primary hippocampal neurons or ephrin B treatment of NG108-15 cells, demonstrating that ARMS is a downstream target for both neurotrophin and ephrin receptors.
Functional Plasticity Triggers Formation and Pruning of Dendritic Spines in Cultured Hippocampal Networks
Authors: Goldin Miri , Segal Menahem , Avignone Elena
Published: April 2018

Despite widespread interest in dendritic spines, little is known about the mechanisms responsible for spine formation, retraction, or stabilization. We have now found that a brief exposure of cultured hippocampal neurons to a conditioning medium that favors activation of the NMDA receptor produces long-term modification of their spontaneous network activity. The conditioning protocol enhances correlated activity of neurons in the culture, in a process requiring an increase in [Ca2+]iand is associated with both formation of novel dendritic spines and pruning of others. The novel spines are likely to be touched by a presynaptic terminal, labeled with FM4-64 dye, whereas the absence of such terminals increases the likelihood of spine pruning. These results indicate that long-term functional changes are correlated with morphological modifications of dendritic spines of neurons in a network.
Age and Gender Predict Volume Decline in the Anterior and Posterior Hippocampus in Early Adulthood
Authors: Pruessner J. C. , Collins D. L. , Pruessner M. , Evans A. C.
Published: April 2018

Magnetic Resonance Imaging (MRI) provides a noninvasive method for investigating brain morphology. Within the medial temporal lobe, special attention has been paid to the hippocampus (HC) and amygdala (AG) because of their role in memory, depression, emotion, and learning. Volume changes in these areas have been observed in conjunction with certain disease states, e.g. Alzheimer's disease, post-traumatic stress disorder, and depression. Aging has also been shown to result in gray matter volume loss of the overall brain, including the HC. With regard to gender specificity, results suggest a larger shrinkage for men of brain gray matter, with controversial observations being made for the HC.

With recently refined MRI acquisition and segmentation protocols, the HC and AG of 80 subjects in early adulthood (39 men and 41 women, age 18–42 years) were investigated. Whereas the volume of the AG appeared to be independent of age and gender, a significant negative correlation with age for both left and right HC was found in men (r= −0.47 and −0.44, respectively) but not in women (r= 0.01 and 0.02, respectively). The volume decline in men appeared to be linear, starting at the beginning of the third life decade and approximating 1.5% per annum. Using voxel-based regressional analysis, it was shown that changes with age occurred mostly in the head and tail of the HC. This finding underscores the need to include sociodemographic variables in functional and anatomical MRI designs.
Nerve Injury Induces a Rapid Efflux of Nitric Oxide (NO) Detected with a Novel NO Microsensor
Authors: Kumar Shanta M. , Porterfield D. Marshall , Muller Kenneth J. , Smith Peter J. S. , Sahley Christie L.
Published: April 2018

An early step in repair of the leech CNS is the appearance of endothelial nitric oxide synthase (eNOS) immunoreactivity and NOS activity, but coincident generation of NO at the lesion after injury has not been shown. This is important because NO can regulate microglial cell motility and axon growth. Indirect measurement of NO with the standard citrulline assay demonstrated that NO was generated within 30 min after nerve cord injury. A polarographic NO-selective self-referencing microelectrode that measures NO flux noninvasively was developed to obtain higher spatial and temporal resolution. With this probe, it was possible to demonstrate that immediately after the leech CNS was injured, NO left the lesion with a mean peak efflux of 803 ± 99 fmol NO cm−2sec−1. NO efflux exponentially declined to a constant value, as described through the equationf(t) =yo+ae−t/τ, with τ = 117 ± 30 sec. The constantyo= 15.8 ± 4.5 fmol cm−2represents a sustained efflux of NO. Approximately 200 pmol NO cm−2is produced at the lesion (n= 8). Thus, injury activates eNOS already present in the CNS and precedes the accumulation of microglia at the lesion, consistent with the hypothesis that NO acts to stop the migrating microglia at the lesion site.
Expression of Neuronal Connexin36 in AII Amacrine Cells of the Mammalian Retina
Authors: Feigenspan Andreas , Teubner Barbara , Willecke Klaus , Weiler Reto
Published: April 2018

We have studied the expression pattern of neuronal connexin36 (Cx36) in the mouse and rat retina. In vertical sections of both retinas, a polyclonal antibody directed against Cx36 produced punctate labeling in the inner plexiform layer (IPL). Intense immunoreactivity was localized to the entire OFF sublamina of the IPL, and much weaker staining could be observed in the ON sublamina. Double-labeling experiments in the rat retina with antibodies directed against parvalbumin indicate that Cx36 is expressed on dendrites of AII amacrine cells. Cx36-like immunoreactivity in sublamina a of the IPL did not overlap with lobular appendages or cell bodies of AII amacrine cells. In a mouse retinal slice preparation, AII amacrine and ON cone bipolar cells were intracellularly injected with Neurobiotin and counterstained with antibody against Cx36. Punctate labeling appeared to be in register with dendritic arborization of AII amacrines and cone bipolar cells in the ON sublamina of the IPL. Whereas AII amacrine cells isolated from the rat retina clearly displayed Cx36-like immunoreactivity, isolated ON cone bipolar cells were negative for Cx36. Axon terminals of rod bipolar cells were decorated with Cx36-positive contacts but did not express Cx36 themselves.

These results indicate that Cx36 is expressed by AII amacrine cells in homologous and heterologous gap junctions made with AII amacrines and cone bipolar cells, respectively. The heterologous gap junctions appear to be heterotypic, because ON cone bipolar cells do not express Cx36.
Connectional and Architectonic Evidence for Dorsal and Ventral V3, and Dorsomedial Area in Marmoset Monkeys
Authors: Lyon David C. , Kaas Jon H.
Published: April 2018

The existence of a third visual area, V3, along the outer margin of V2 was originally proposed for primates on the basis of projections from V1. The evidence for V3 was never totally convincing because investigators failed to demonstrate V1 projections to ventral V3, and projections to dorsal V3 could be attributed to the dorsomedial visual area (DM). We have reexamined the issue by placing large injections into both dorsal and ventral portions of V1 and subsequently processing flattened cortex for myelin and cytochrome oxidase so that borders of V1 and V2 could be determined accurately. The injections were in small-brained marmosets, where ventral V1 was most accessible and cortex could be flattened easily. The results indicate that dorsal V1 (representing the lower visual quadrant) projects to a narrow “dorsal V3” located between DM and dorsal V2, whereas ventral V1 (representing the upper visual quadrant) projects to a narrow “ventral V3.” Architectonic borders for these dorsal and ventral strips were clearly apparent. In addition, all parts of V1 project to DM, whereas ventral V1 connections indicate that the dorsolateral area (DL) extends more ventral than has been established previously. We also placed injections within dorsal V2, dorsal and ventral DM, and dorsal, central, and ventral middle temporal (MT) area. Results from these injections were consistent with the proposed retinotopic organizations of V3, DM, and DL. We provide compelling evidence for the existence of areas V3, DM, and DL in marmosets and suggest that these areas are likely to be found in all primates.
Neural Correlates of Auditory–Visual Stimulus Onset Asynchrony Detection
Authors: Bushara Khalafalla O. , Grafman Jordan , Hallett Mark
Published: April 2018

Intersensory temporal synchrony is an ubiquitous sensory attribute that has proven to be critical for binding multisensory inputs, sometimes erroneously leading to dramatic perceptual illusions. However, little is known about how the brain detects temporal synchrony between multimodal sensory inputs. We used positron emission tomography to demonstrate that detecting auditory–visual stimulus onset asynchrony activates a large-scale neural network of insular, posterior parietal, prefrontal, and cerebellar areas with the highest and task-specific activity localized to the right insula. Interregional covariance analysis further showed significant task-related functional interactions between the insula, the posterior thalamus, and superior colliculus. Based on these results and the available electrophysiological and anatomical connectivity data in animals, we propose that the insula, via its known short-latency connections with the tectal system, mediates temporally defined auditory–visual interaction at an early stage of cortical processing permitting phenomena such as the ventriloquist and the McGurk illusions.
Prepulse Inhibition Deficits and Perseverative Motor Patterns in Dopamine Transporter Knock-Out Mice: Differential Effects of D1 and D2 Receptor Antagonists
Authors: Ralph Rebecca J. , Paulus Martin P. , Fumagalli Fabio , Caron Marc G. , Geyer Mark A.
Published: April 2018

Dopamine is known to regulate several behavioral phenomena, including sensorimotor gating and aspects of motor activity. The roles of dopamine D1 and D2 receptors in these behaviors have been documented in the rat literature, but few reports exist on their role in mice. We used dopamine transporter (DAT) (−/−) mice to examine the behavioral consequences of a chronically hyperdopaminergic state, challenging them with the preferential dopamine D2 receptor antagonist raclopride and D1 receptor antagonist SCH23390. At baseline, DAT (−/−) mice exhibited deficient sensorimotor gating as measured by prepulse inhibition (PPI) of the startle response, exhibited nonfocal perseverative patterns of locomotion, and were hyperactive in a novel environment. Pretreatment with raclopride significantly increased PPI in the DAT (−/−) mice, whereas SCH23390 had no significant effect. Blockade of D2 receptors did not affect the predominantly straight patterns of motor behavior produced by the DAT (−/−) mice, but antagonism of D1 receptors significantly attenuated the perseverative patterns, producing more of a meandering behavior seen in the DAT (+/+) control mice. Both D1 and D2 receptor antagonists decreased the hyperactivity seen in the DAT (−/−) mice. These findings support the role of the D2, but not the D1, receptor in the modulation of PPI in mice. Furthermore, D1 receptor activation appears to be the critical substrate for the expression of perseverative patterns of motor behavior, whereas both D1 and D2 receptors appear to regulate the amount of motor activity.
Motivational Effects of Ethanol in DARPP-32 Knock-Out Mice
Authors: Risinger Fred O. , Freeman Pierre A. , Greengard Paul , Fienberg Allen A.
Published: April 2018

DARPP-32 (dopamine and adenosine 3′,5′-monophosphate-regulated phosphoprotein, 32 kDa) is an important component of dopaminergic function in brain areas thought to be important for drug and alcohol addiction. The present experiments characterized the acquisition of ethanol-induced conditioned taste aversion, ethanol-induced conditioned place preference, and ethanol self-administration in DARPP-32 knock-out (KO) mice compared to wild-type (WT) controls. For taste conditioning, KO and WT mice received access to 0.2mNaCl solution followed immediately by intraperitoneal injection of 0–4 gm/kg ethanol. Ethanol produced dose-dependent conditioned taste aversion that was the same in both genotypes. For place conditioning, KO and WT mice received eight pairings of a tactile stimulus with ethanol (2 gm/kg, i.p.), and a different stimulus with saline. Ethanol produced increases in locomotor activity during conditioning, with KO mice showing higher activity levels after ethanol compared to WT mice. WT mice, but not KO mice, acquired conditioned preference for the ethanol-paired stimulus. In the self-administration procedure, KO and WT mice were trained to lever press for access to 10% v/v ethanol. Subsequently, the mice had 23 hr/d access to food, ethanol, and water. Response patterns were determined using 0–30% v/v ethanol concentrations. WT mice displayed concentration-dependent responding for ethanol. Responding on the ethanol lever by KO mice did not change as a function of ethanol concentration. Saccharin (0.2% w/v) was subsequently added to the ethanol mixture, and responding was examined at 0, 5, 10, and 20% ethanol concentrations. Ethanol responding increased in both genotypes, although WT mice showed higher rates at all concentrations.
Nerve Growth Factor Antiserum Induces Axotomy-Like Changes in Neuropeptide Expression in Intact Sympathetic and Sensory Neurons
Authors: Shadiack Annette M. , Sun Yi , Zigmond Richard E.
Published: April 2018

Axonal transection of adult sympathetic and sensory neurons leads to a decrease in their content of target-derived nerve growth factor (NGF) and to dramatic changes in the expression of several neuropeptides and enzymes involved in transmitter biosynthesis. For example, axotomy of sympathetic neurons in the superior cervical ganglion (SCG) dramatically increases levels of galanin, vasoactive intestinal peptide (VIP), and substance P and their respective mRNAs and decreases mRNA levels for neuropeptide Y (NPY) and tyrosine hydroxylase (TH). Axotomy of sensory neurons in lumbar dorsal root ganglia (DRG) increases protein and mRNA levels for galanin and VIP and decreases levels for substance P and calcitonin gene-related peptide (CGRP). To assess whether reduction in the availability of endogenous NGF might play an important role in triggering these changes, we injected nonoperated animals with an antiserum against NGF (αNGF). αNGF increased levels of peptide and mRNA for galanin and VIP in neurons in both the SCG and DRG. NPY protein and mRNA were decreased in the SCG, but levels of TH protein and mRNA remained unchanged. In sensory neurons the levels of SP and CGRP protein decreased after αNGF treatment. These data suggest that the reduction in levels of NGF in sympathetic and sensory neurons after axotomy is partly responsible for the subsequent changes in neuropeptide expression. Thus, the peptide phenotype of these axotomized neurons is regulated both by the induction of an “injury factor,” leukemia inhibitory factor, as shown previously, and by the reduction in a target-derived growth factor.