bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced Neurotensin Neurotransmission Is Involved in the Clinically Relevant Behavioral Effects of Antipsychotic Drugs: Evidence from Animal Models of Sensorimotor Gating
Authors: Binder Elisabeth B. , Kinkead Becky , Owens Michael J. , Kilts Clinton D. , Nemeroff Charles B.
Published: April 2018

To date, none of the available antipsychotic drugs are curative, all have significant side-effect potential, and a receptor-binding profile predictive of superior therapeutic ability has not been determined. It has become increasingly clear that schizophrenia does not result from the dysfunction of a single neurotransmitter system, but rather from an imbalance between several interacting systems. Targeting neuropeptide neuromodulator systems that concertedly regulate all affected neurotransmitter systems could be a promising novel therapeutic approach for schizophrenia. A considerable database is concordant with the hypothesis that antipsychotic drugs act, at least in part, by increasing the synthesis and release of the neuropeptide neurotensin (NT). In this report, we demonstrate that NT neurotransmission is critically involved in the behavioral effects of antipsychotic drugs in two models of antipsychotic drug activity: disrupted prepulse inhibition of the acoustic startle response (PPI) and the latent inhibition (LI) paradigm. Blockade of NT neurotransmission using the NT receptor antagonist 2-[[5-(2,6-dimethoxyphenyl)-1-(4-(N-(3-dimethylaminopropyl)-N-methylcarbamoyl)-2-isopropylphenyl)-1H- pyrazole-3-carbonyl]-amino]-adamantane-2-carboxylic acid, hydrochloride (SR 142948A) prevented the normal acquisition of LI and haloperidol-induced enhancement of LI. In addition, SR 142948A blocked the PPI-restoring effects of haloperidol and the atypical antipsychotic drug quetiapine in isolation-reared animals deficient in PPI. We also provide evidence of deficient NT neurotransmission as well as a left-shifted antipsychotic drug dose–response curve in isolation-reared rats. These novel findings, together with previous observations, suggest that neurotensin receptor agonists may represent a novel class of antipsychotic drugs.
Cerebellar Projections to the Prefrontal Cortex of the Primate
Authors: Middleton Frank A. , Strick Peter L.
Published: April 2018

The cerebellum is known to project via the thalamus to multiple motor areas of the cerebral cortex. In this study, we examined the extent and anatomical organization of cerebellar input to multiple regions of prefrontal cortex. We first used conventional retrograde tracers to map the origin of thalamic projections to five prefrontal regions: medial area 9 (9m), lateral area 9 (9l), dorsal area 46 (46d), ventral area 46, and lateral area 12. Only areas 46d, 9m, and 9l received substantial input from thalamic regions included within the zone of termination of cerebellar efferents. This suggested that these cortical areas were the target of cerebellar output. We tested this possibility using retrograde transneuronal transport of the McIntyre-B strain of herpes simplex virus type 1 from areas of prefrontal cortex. Neurons labeled by retrograde transneuronal transport of virus were found in the dentate nucleus only after injections into areas 46d, 9m, and 9l. The precise location of labeled neurons in the dentate varied with the prefrontal area injected. In addition, the dentate neurons labeled after virus injections into prefrontal areas were located in regions spatially separate from those labeled after virus injections into motor areas of the cerebral cortex. Our observations indicate that the cerebellum influences several areas of prefrontal cortex via the thalamus. Furthermore, separate output channels exist in the dentate to influence motor and cognitive operations. These results provide an anatomical substrate for the cerebellum to be involved in cognitive functions such as planning, working memory, and rule-based learning.
Reliability of Macaque Frontal Eye Field Neurons Signaling Saccade Targets during Visual Search
Authors: Bichot Narcisse P. , Thompson Kirk G. , Rao S. Chenchal , Schall Jeffrey D.
Published: April 2018

Although many studies have explored the neural correlates of visual attention and selection, few have examined the reliability with which neurons represent relevant information. We monitored activity in the frontal eye field (FEF) of monkeys trained to make a saccade to a target defined by the conjunction of color and shape or to a target defined by color differences. The difficulty of conjunction search was manipulated by varying the number of distractors, and the difficulty of feature search was manipulated by varying the similarity in color between target and distractors. The reliability of individual neurons in signaling the target location in correct trials was determined using a neuron—anti-neuron approach within a winner-take-all architecture. On average, approximately seven trials of the activity of single neurons were sufficient to match near-perfect behavioral performance in the easiest search, and ∼14 trials were sufficient in the most difficult search. We also determined how many neurons recorded separately need to be evaluated within a trial to match behavioral performance. Results were quantitatively similar to those of the single neuron analysis. We also found that signal reliability in the FEF did not change with task demands, and overall, behavioral accuracy across the search tasks was approximated when only six trials or neurons were combined. Furthermore, whether combining trials or neurons, the increase in time of target discrimination corresponded to the increase in mean saccade latency across visual search difficulty levels. Finally, the variance of spike counts in the FEF increased as a function of the mean spike count, and the parameters of this relationship did not change with attentional selection.
Hyperfunction of Dopaminergic and Serotonergic Neuronal Systems in Mice Lacking the NMDA Receptor ε1 Subunit
Authors: Miyamoto Yoshiaki , Yamada Kiyofumi , Noda Yukihiro , Mori Hisashi , Mishina Masayoshi , Nabeshima Toshitaka
Published: April 2018

NMDA receptors, an ionotropic subtype of glutamate receptors (GluRs) forming high Ca2+-permeable cation channels, are composed by assembly of the GluRζ subunit (NR1) with any one of four GluRε subunits (GluRε1–4; NR2A-D). In the present study, we investigated neuronal functions in mice lacking the GluRε1 subunit. GluRε1 mutant mice exhibited a malfunction of NMDA receptors, as evidenced by alterations of [3H]MK-801 binding as well as45Ca2+uptake through the NMDA receptors. A postmortem brain analysis revealed that both dopamine and serotonin metabolism were increased in the frontal cortex and striatum of GluRε1 mutant mice. The NMDA-stimulated [3H]dopamine release from the striatum was increased, whereas [3H]GABA release was markedly diminished in GluRε1 mutant mice. When (+)bicuculline, a GABAAreceptor antagonist, was added to the superfusion buffer, NMDA-stimulated [3H]dopamine release was significantly increased in wild-type, but not in the mutant mice. GluRε1 mutant mice exhibited an increased spontaneous locomotor activity in a novel environment and an impairment of latent learning in a water-finding task. Hyperlocomotion in GluRε1 mutant mice was attenuated by treatment with haloperidol and risperidone, both of which are clinically used antipsychotic drugs, at doses that had no effect in wild-type mice. These findings provide evidence that NMDA receptors are involved in the regulation of behavior through the modulation of dopaminergic and serotonergic neuronal systems. In addition, our findings suggest that GluRε1 mutant mice are useful as an animal model of psychosis that is associated with NMDA receptor malfunction and hyperfunction of dopaminergic and serotonergic neuronal systems.
Schwann Cell Proliferative Responses to cAMP andNf1Are Mediated by Cyclin D1
Authors: Kim Haesun A. , Ratner Nancy , Roberts Thomas M. , Stiles Charles D.
Published: April 2018

In most mammalian cells, the cAMP-dependent protein kinase A pathway promotes growth arrest and cell differentiation. However in Schwann cells, the reverse is true. Elevated levels of cAMP function as the cofactor to a broad range of mitogenic cues in culture and in animals. Previous studies have suggested that cAMP acts at an early point in the Schwann cell mitogenic response, perhaps by stimulating the expression of growth factor receptors. We show here that cAMP acts downstream rather than upstream of growth factor receptor expression. The essential function(s) of cAMP is exerted as Schwann cells progress through the G1phase of the cell cycle. Ectopic expression studies using an inducible retroviral vector show that the G1phase requirement for cAMP can be alleviated by a single protein, cyclin D1. We show, in addition, that at least one function of theNf1tumor suppressor is to antagonize the accumulation of cAMP and the expression of cyclin D1 in Schwann cells. Thus a G1phase-specific protein, cyclin D1, accounts for two salient features of Schwann cell growth control: the promitotic response to cAMP and the antimitotic response to theNf1tumor suppressor.
C-Terminal Interaction Is Essential for Surface Trafficking But Not for Heteromeric Assembly of GABABReceptors
Authors: Pagano Adriana , Rovelli Giorgio , Mosbacher Johannes , Lohmann Tania , Duthey Beatrice , Stauffer Daniela , Ristig Dorothee , Schuler Valerie , Meigel Ingeborg , Lampert Christina , Stein Thomas , Prézeau Laurent , Blahos Jaroslav , Pin Jean-Philippe , Froestl Wolfgang , Kuhn Rainer , Heid Jakob , Kaupmann Klemens , Bettler Bernhard
Published: April 2018

Assembly of fully functional GABABreceptors requires heteromerization of the GABAB(1)and GABAB(2)subunits. It is thought that GABAB(1)and GABAB(2)undergo coiled-coil dimerization in their cytoplasmic C termini and that assembly is necessary to overcome GABAB(1)retention in the endoplasmatic reticulum (ER). We investigated the mechanism underlying GABAB(1)trafficking to the cell surface. We identified a signal, RSRR, proximal to the coiled-coil domain of GABAB(1)that when deleted or mutagenized allows for surface delivery in the absence of GABAB(2). A similar motif, RXR, was recently shown to function as an ER retention/retrieval (ERR/R) signal in KATPchannels, demonstrating that G-protein-coupled receptors (GPCRs) and ion channels use common mechanisms to control surface trafficking. A C-terminal fragment of GABAB(2)is able to mask the RSRR signal and to direct the GABAB(1)monomer to the cell surface, where it is functionally inert. This indicates that in the heteromer, GABAB(2)participates in coupling to the G-protein. Mutagenesis of the C-terminal coiled-coil domains in GABAB(1)and GABAB(2)supports the possibility that their interaction is involved in shielding the ERR/R signal. However, assembly of heteromeric GABABreceptors is possible in the absence of the C-terminal domains, indicating that coiled-coil interaction is not necessary for function. Rather than guaranteeing heterodimerization, as previously assumed, the coiled-coil structure appears to be important for export of the receptor complex from the secretory apparatus.
Downregulation of Fasting-Induced cAMP Response Element-Mediated Gene Induction by Leptin in Neuropeptide Y Neurons of the Arcuate Nucleus
Authors: Shimizu-Albergine Masami , Ippolito Danielle L. , Beavo Joseph A.
Published: April 2018

States of increased metabolic demand such as fasting modulate hypothalamic neuropeptide gene expression and decrease circulating leptin levels. This study tested the hypotheses that fasting stimulates gene induction mediated by cAMP response element (CRE)-dependent increases in gene transcription and that fasting-induced decreases in leptin can regulate this CRE-mediated gene induction. Using C57BL/6J mice transgenic for a CRE-lacZconstruct, an immunocytochemical study showed that fasting activated reporter gene expression in the hypothalamic arcuate nucleus (Arc) in a small subset of neurons and increased phosphorylation of CRE binding protein. The increase of β-galactosidase expression caused by fasting was inhibited by a protein kinase A inhibitor, Rp-8-Br-cAMPS, when the compound was microinjected into the medial basal hypothalamus, and enhanced by intraperitoneal injection of selective phosphodiesterase inhibitors.In situhybridization studies showed that neuropeptide Y (NPY) mRNA levels increased in the Arc during fasting, whereas proopiomelanocortin (POMC) mRNA levels decreased. Double labeling of mRNA and β-galactosidase immunoreactivity in the fasted brain indicated that the subpopulation of the neurons expressing β-galactosidase all produced NPY but not POMC. To study the possible involvement of decreased circulating leptin during starvation on CRE-mediated gene induction, leptin was administered intraperitoneally to fasted mice. Leptin significantly attenuated both β-galactosidase expression and NPY gene expression stimulated by fasting, suggesting that leptin inhibits fasting-stimulated NPY gene expression at least in part through downregulation of CRE-mediated gene induction in the Arc. Leptin-induced modification of CRE-mediated gene induction in the Arc may play an essential role in the central regulation of feeding behavior and energy expenditure.
Inhibition of Cyclin E–Cyclin-Dependent Kinase 2 Complex Formation and Activity Is Associated with Cell Cycle Arrest and Withdrawal in Oligodendrocyte Progenitor Cells
Authors: Ghiani Cristina A. , Gallo Vittorio
Published: April 2018

Stimulatory and inhibitory signals regulate cell proliferation through the activity of specific enzymes that operate in distinct phases of the cell cycle. We have studied cell cycle progression, arrest, and withdrawal in the oligodendrocyte progenitor (OP) cell model system, focusing on the G1phase and G1–S transition. Not only were proliferating OPs found to display higher protein levels of cyclin E and D and cyclin-dependent kinases (cdk) 2, 4, and 6 than cells that had permanently withdrawn from the cycle, but the kinase activities of both cyclin D–cdk4/6 and cyclin E–cdk2 were also higher in dividing OPs. This was associated with a decrease in the formation of the cyclin E–cdk2 and cyclin D–cdk4/cyclin D–cdk6 complexes in differentiated oligodendrocytes that had permanently withdrawn from the cell cycle. Reversible cell cycle arrest in G1induced by glutamatergic and β-adrenergic receptor activation or cell depolarization, however, did not modify cyclin E and cdk2 protein expression compared with proliferating OPs. Instead, these agents caused a selective decrease in cdk2 activity and an impairment of cyclin E–cdk2 complex formation. Although cyclin D protein levels were higher than in proliferating cells, cyclin D-associated kinase activity was not modified in G1-arrested OPs. Analysis in corpus callosumin vivoshowed that cyclin E–cdk2 activity increased between postnatal days 3 and 15 and decreased between postnatal days 15 and 30. Our results indicate that the cyclin E–cdk2 complex is a major regulator of OP cell cycle progression and that the cdks involved in reversible cell cycle arrest are distinct from those implicated in permanent cell cycle withdrawal.
BMP4 Mediates Apoptotic Cell Death in the Developing Chick Eye
Authors: Trousse Françoise , Esteve Pilar , Bovolenta Paola
Published: April 2018

The bone morphogenetic protein (BMP) expression in vertebrates suggests a reiterative function of these molecules during eye development. However, genetic analysis in mice has provided only partial information. Using the chick embryo as a model system, we have analyzed possible additional functions of BMP4 during optic cup formation. Here we describe the expression pattern ofBmp4andBmp7and we show that, in contrast to the mouse, the prospective lens placode ectoderm expresses high levels ofBmp4but noBmp7. After optic vesicle invagination,Bmp4is expressed in the prospective dorsal neural retina, whereBmprIA,BmprII, andSmad1, components of the BMP4 signal transduction pathway, are also expressed.In tototerminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end-labeling analysis shows that the dorsal optic cup is the site of a spatiotemporally restricted apoptosis, which parallels the expression not only ofBmp4but also ofMsx1andMsx2, genes implicated in BMP4-mediated apoptosis. The use of optic vesicle cultures as well asin ovolocal addition of BMP4 and its antagonist Noggin proves that the local activity of BMP4 is responsible for programmed cell death in the dorsal optic cup. In addition, we show that Noggin is able to reduce the rate of cell proliferation in the dorsal part of the optic cup whereas BMP4 increases the number of BrdU-positive cells in retina cultures. These results provide evidence that BMP4 contributes to eye development by promoting cell proliferation and programmed cell death.
Late Oligodendrocyte Progenitors Coincide with the Developmental Window of Vulnerability for Human Perinatal White Matter Injury
Authors: Back Stephen A. , Luo Ning Ling , Borenstein Natalya S. , Levine Joel M. , Volpe Joseph J. , Kinney Hannah C.
Published: April 2018

Hypoxic-ischemic injury to the periventricular cerebral white matter [periventricular leukomalacia (PVL)] results in cerebral palsy and is the leading cause of brain injury in premature infants. The principal feature of PVL is a chronic disturbance of myelination and suggests that oligodendrocyte (OL) lineage progression is disrupted by ischemic injury. We determined the OL lineage stages at risk for injury during the developmental window of vulnerability for PVL (23–32 weeks, postconceptional age). In 26 normal control autopsy human brains, OL lineage progression was defined in parietal white matter, a region of predilection for PVL. Three successive OL stages, the late OL progenitor, the immature OL, and the mature OL, were characterized between 18 and 41 weeks with anti-NG2 proteoglycan, O4, O1, and anti-myelin basic protein (anti-MBP) antibodies. NG2+O4+ late OL progenitors were the predominant stage throughout the latter half of gestation. Between 18 and 27 weeks, O4+O1+ immature OLs were a minor population (9.9 ± 2.1% of total OLs;n= 9). Between 28 and 41 weeks, an increase in immature OLs to 30.9 ± 2.1% of total OLs (n= 9) was accompanied by a progressive increase in MBP+ myelin sheaths that were restricted to the periventricular white matter. The developmental window of high risk for PVL thus precedes the onset of myelination and identifies the late OL progenitor as the major potential target. Moreover, the decline in incidence of PVL at ∼32 weeks coincides with the onset of myelination in the periventricular white matter and suggests that the risk for PVL is related to the presence of late OL progenitors in the periventricular white matter.
Macrophages Are Eliminated from the Injured Peripheral Nerve via Local Apoptosis and Circulation to Regional Lymph Nodes and the Spleen
Authors: Kuhlmann Tanja , Bitsch Andreas , Stadelmann Christine , Siebert Heike , Brück Wolfgang
Published: April 2018

The present study investigated the fate of macrophages in peripheral nerves undergoing Wallerian degeneration, especially their disappearance from the injured nerves after phagocytosis of axonal and myelin debris. Wallerian degeneration was induced in adult male C57Bl/6 mice by transecting the right sciatic nerve. Five days after transection, the male sciatic nerves were transplanted into female recipient mice by placing them exactly parallel to the host sciatic nerves. Nerves of the female recipient mice were also transected to induce breakdown of the blood–nerve barrier in the host animal. Apoptosis was assessed by morphological, immunohistochemical (activated caspase-3), and molecular (DNA fragmentation) methods in transplanted, recipient, and in control nerves. A subpopulation of macrophages within the degenerating nerves died locally by apoptosis in each experiment. The fate of the male macrophages within the transplanted nerves and the host organism was investigated byin situhybridization with a Y-chromosome-specific DNA probe (145SC5).In situhybridization specifically stained cells within the transplanted male nerve. Y-chromosome-positive cells were detected not only inside the transplanted nerve, but also inside the female host nerve, the perineurial tissue, the local perineurial blood vessels, draining lymph nodes and the spleen of the female host, suggesting hematogenous as well as lymphatic elimination of macrophages from the injured nerve. These data indicate that local apoptosis and systemic elimination via circulation to the local lymph nodes and the spleen are involved in the disappearance of macrophages from the injured peripheral nervous system.
Pituitary Control of BK Potassium Channel Function and Intrinsic Firing Properties of Adrenal Chromaffin Cells
Authors: Lovell Peter V. , McCobb David P.
Published: April 2018

The discovery that the hypothalamic–pituitary–adrenocortical (HPA) endocrine stress axis controls an alternative splicing decision in chromaffinSlo-encoded BK (big potassium) channels raised the possibility that activation of the HPA could serve as a mechanism to tune the intrinsic electrical properties of epinephrine-secreting adrenal chromaffin cells. To test this, we compared BK functional properties and cell excitability in chromaffin cells from normal and hypophysectomized (pituitary-ablated) rats. Hypophysectomy was found to alter the voltage dependence and kinetics of BK gating, making channels less accessible for activation from rest. Perforated-patch recordings revealed changes in action potential waveform and repetitive firing properties. The maximum number of spikes that could be elicited with a 2 sec depolarizing current pulse was reduced by ∼50% by hypophysectomy. The results indicate that pituitary hormones can adapt the mechanics of adrenal catecholamine release by tailoring BK channel function.
Immature Neurons From CNS Stem Cells Proliferate in Response to Platelet-Derived Growth Factor
Authors: Erlandsson Anna , Enarsson Maria , Forsberg-Nilsson Karin
Published: April 2018

Identifying external signals involved in the regulation of neural stem cell proliferation and differentiation is fundamental to the understanding of CNS development. In this study we show that platelet-derived growth factor (PDGF) can act as a mitogen for neural precursor cells. Multipotent stem cells from developing CNS can be maintained in a proliferative state under serum-free conditions in the presence of fibroblast growth factor-2 (FGF2) and induced to differentiate into neurons, astrocytes, and oligodendrocytes on withdrawal of the mitogen. PDGF has been suggested to play a role during the differentiation into neurons. We have investigated the effect of PDGF on cultured stem cells from embryonic rat cortex. The PDGF α-receptor is constantly expressed during differentiation of neural stem cells but is phosphorylated only after PDGF-AA treatment. In contrast, the PDGF β-receptor is hardly detectable in uncommitted cells, but its expression increases during differentiation. We show that PDGF stimulation leads to c-fosinduction, 5′-bromo-2′deoxyuridine incorporation, and an increase in the number of immature cells stained with antibodies to neuronal markers. Our findings suggest that PDGF acts as a mitogen in the early phase of stem cell differentiation to expand the pool of immature neurons.
Prefrontal Microcircuits: Membrane Properties and Excitatory Input of Local, Medium, and Wide Arbor Interneurons
Authors: Krimer Leonid S. , Goldman-Rakic Patricia S.
Published: April 2018

To elucidate cortical mechanisms involved in higher cortical functions such as working memory, we have examined feedforward excitation transmitted by identified pyramidal cells to interneurons with predominantly horizontal axonal arbors, using dual somatic recordings in prefrontal cortical slices. Interneurons with local (narrow) axonal arbors, especially chandelier interneurons, exhibited extremely narrow action potentials and high evoked firing rates, whereas neurons identified with wide arbor axons generated wider spikes and lower evoked firing rates with considerable spike adaptation, resembling that of pyramidal cells. Full reconstruction of differentially labeled neuronal pairs revealed that local arbor cells generally received a single but functionally reliable putative synaptic input from the identified pyramidal neuron member of the pair. In contrast, more synapses (two to five) were necessary to depolarize medium and wide arbor neurons reliably. The number of putative synapses and the amplitude of the postsynaptic response were remarkably highly correlated within each class of local, medium, and wide arbor interneurons (r= 0.88, 0.95, and 0.99, respectively). Similarly strong correlations within these subgroups were also present between the number of putative synapses and variance in the EPSP amplitudes, supporting the validity of our morphological analysis. We conclude that interneurons varying in the span of their axonal arbors and hence in the potential regulation of different numbers of cortical modules differ also in their excitatory synaptic input and physiological properties. These findings provide insight into the circuit basis of lateral inhibition and functional interactions within and between cortical columns in the cerebral cortex.
NMDA Receptor Stimulation and Brain-Derived Neurotrophic Factor Upregulate Homer 1a mRNA via the Mitogen-Activated Protein Kinase Cascade in Cultured Cerebellar Granule Cells
Authors: Sato Masaaki , Suzuki Kazunori , Nakanishi Shigetada
Published: April 2018

In three alternative splice variants of Homer 1 transcripts, Homer 1a mRNA has been shown to be upregulated selectively and rapidly by neural stimulation and represents a member of the immediate early gene (IEG) family. We investigated the mechanism underlying Homer 1a mRNA induction in cerebellar granule cell culture. All Homer 1 variants were expressed in cultured granule cells as analyzed by RNA blotting and immunochemical characterization. Glutamate stimulation of granule cells selectively upregulated Homer 1a mRNA via NMDA receptor-mediated influx of extracellular calcium. The induction of Homer 1a mRNA was much slower (peaked at 4 hr) and sustained longer than that of the typical IEGc-fosmRNA. Actinomycin D and cycloheximide experiments have revealed that, despite the presence of the mRNA-destabilizing AU-rich motif, transcriptional activation is a main determinant for selective Homer 1a mRNA induction. Inhibitor analysis as well as immunochemical characterization has indicated that the MEK (MAPK/ERK kinase)–ERK (extracellular signal-regulated kinase) cascade plays an indispensable role in glutamate-stimulated induction of Homer 1a mRNA. Consistent with this observation, brain-derived neurotrophic factor, which is known to activate the ERK cascade, similarly upregulated Homer 1a mRNA. These results demonstrate that MAPK (mitogen-activated protein kinase) is a key mediator that links distinct extracellular stimuli to the transcriptional activation of Homer 1a mRNA.
Src-Class Kinases Act within the Agrin/MuSK Pathway to Regulate Acetylcholine Receptor Phosphorylation, Cytoskeletal Anchoring, and Clustering
Authors: Mohamed Ali S. , Rivas-Plata Kimberly A. , Kraas Jonathan R. , Saleh Suha M. , Swope Sheridan L.
Published: April 2018

Synaptogenesis at the neuromuscular junction requires agrin-induced stable localization of acetylcholine receptors (AChRs) at the endplate. The effects of agrin are transduced by the muscle-specific receptor tyrosine kinase (MuSK). This study provides evidence that Src-class protein tyrosine kinases mediate the effects of agrin-activated MuSK to regulate clustering and anchoring of AChRs in skeletal muscle. MuSK was complexed with both Src and Fyn in the C2 mouse muscle cell line. These associations were enhanced by agrin and by increasing protein tyrosine phosphorylation with pervanadate. Coupling between MuSK and the Src-class kinasesin vivoappeared to be caused by a phosphotyrosine–SH2 domain interaction because binding of MuSK to the SH2 domains of Fyn and Srcin vitrowas specific, enhanced by phosphorylation, and dependent on MuSK autophosphorylation. In addition, Src and Fyn phosphorylated MuSK. AChR phosphorylation, stimulated by agrin or pervanadate, was inhibited by blocking Src-class kinases with PP1. Furthermore, agrin-induced clustering and cytoskeletal anchoring of AChRs was dependent on Src-family kinases. These data support the conclusion that Fyn and Src act downstream of MuSK to regulate the stable localization of AChRs at the neuromuscular endplate during agrin-induced synaptogenesis.
Synapse–Glia Interactions at the Mammalian Neuromuscular Junction
Authors: Rochon Danielle , Rousse Isabelle , Robitaille Richard
Published: April 2018

Perisynaptic Schwann cells (PSCs) play critical roles in regulating and stabilizing nerve terminals at the mammalian neuromuscular junction (NMJ). However, although these functions are likely regulated by the synaptic properties, the interactions of PSCs with the synaptic elements are not known. Therefore, our goal was to study the interactions between mammalian PSCsin situand the presynaptic terminals using changes in intracellular Ca2+as an indicator of cell activity. Motor nerve stimulation induced an increase in intracellular Ca2+in PSCs, and this increase ÿas greatly reduced when transmitter release was blocked. Furthermore, local application of acetylcholine induced Ca2+responses that were blocked by the muscarinic antagonist atropine and mimicked by the muscarinic agonist muscarine. The nicotinic antagonist α-bungarotoxin had no effect on Ca2+responses induced by acetylcholine. Local application of the cotransmitter ATP induced Ca2+responses that were unaffected by the P2 antagonist suramin, whereas local application of adenosine induced Ca2+responses that were greatly reduced by the A1 receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (CPT). However, the presence of the A1 antagonist in the perfusate did not block responses induced by ATP. Ca2+responses evoked by stimulation of the motor nerve were reduced in the presence of CPT, whereas atropine almost completely abolished them. Ca2+responses were further reduced when both antagonists were present simultaneously. Hence, PSCs at the mammalian NMJ respond to the release of neurotransmitter induced by stimulation of the motor nerve through the activation of muscarinic and adenosine A1 receptors.
Pituitary Adenylyl Cyclase-Activating Polypeptide Stimulates DNA Synthesis But Delays Maturation of Oligodendrocyte Progenitors
Authors: Lee Matthew , Lelièvre Vincent , Zhao Paul , Torres Mike , Rodriguez Williams , Byun Ji-Yun , Doshi Sameer , Ioffe Yevgenyia , Gupta Gauree , de los Monteros Araceli Espinosa , de Vellis Jean , Waschek James
Published: April 2018

The neuropeptide pituitary adenylyl cyclase-activating peptide (PACAP) and one of its receptors (PAC1) are expressed in embryonic neural tube, where they appear to regulate neurogenesis and patterning. We now show that PAC1gene expression is also present in neonatal rats in the ventricular and subventricular zones and in the optic chiasm, areas that are rich in oligodendrocyte (OL) progenitors (OLP). Because actions of PACAP on OLP have not been reported, we examined the effects of PACAP on the proliferation of purified OLP in culture and on myelinogenesis in cerebellar slices. Northern analyses on total RNA from purified glial cell subtypes revealed an abundant 7 kb hybridizing transcript in OLP, which was confirmed to correspond to the PAC1receptor by reverse transcription-PCR. The presence of this receptor was also corroborated by radioligand binding and cAMP assay. In cultured OL, receptor density decreased during maturation but was partially counterbalanced by the appearance of sites that bound both PACAP and the related peptide vasoactive intestinal peptide. PACAP increased DNA synthesis in OLP cultures almost twofold and increased the bromodeoxyuridine-labeling index in O4-positive OLP. PACAP treatment also resulted in decreased sulfate incorporation into sulfatide in cultures of differentiating OL. The PACAP effect on sulfatide synthesis was fully reproduced in a cerebellar explant model. These findings indicate that PACAP may act at two stages during OL development to (1) stimulate proliferation and (2) delay maturation and/or myelinogenesis.
Fibroblast Growth Factor-2 Promotes Axon Branching of Cortical Neurons by Influencing Morphology and Behavior of the Primary Growth Cone
Authors: Szebenyi Györgyi , Dent Erik W. , Callaway John L. , Seys Chad , Lueth Helen , Kalil Katherine
Published: April 2018

Interstitial branching is an important mechanism for target innervation in the developing CNS. A previous study of cortical neuronsin vitroshowed that the terminal growth cone pauses and enlarges in regions from which interstitial axon branches later develop (Szebenyi et al., 1998). In the present study, we investigated how target-derived signals affect the morphology and behaviors of growth cones leading to development of axon branches. We used bath and local application of a target-derived growth factor, FGF-2, on embryonic pyramidal neurons from the sensorimotor cortex and used time-lapse digital imaging to monitor effects of FGF-2 on axon branching. Observations of developing neurons over periods of several days showed that bath-applied FGF-2 significantly increased growth cone size and slowed growth cone advance, leading to a threefold increase in axon branching. FGF-2 also had acute effects on growth cone morphology, promoting rapid growth of filopodia within minutes. Application of FGF-2-coated beads promoted local axon branching in close proximity to the beads. Branching was more likely to occur when the FGF-2 bead was on or near the growth cone, suggesting that distal regions of the axon are more responsive to FGF-2 than other regions of the axon shaft. Together, these results show that interstitial axon branches can be induced locally through the action of a target-derived growth factor that preferentially exerts effects on the growth cone. We suggest that, in target regions, growth factors such as FGF-2 and other branching factors may induce formation of collateral axon branches by enhancing the pausing and enlargement of primary growth cones that determine future branch points.
Transient Interhemispheric Neuronal Synchrony Correlates with Object Recognition
Authors: Mima Tatsuya , Oluwatimilehin Tomi , Hiraoka Taizo , Hallett Mark
Published: April 2018

Object recognition might be achieved by the recreation of a meaningful internal image from visual fragments. This recreation might be achieved by neuronal synchronization that has been proposed as a solution for the perceptual binding problem. In this study, we evaluated synchronization between the occipitotemporal regions bilaterally using electroencephalograms during several visual recognition tasks. Conscious recognition of familiar objects spanning the visual midline induced transient interhemispheric electroencephalographic coherence in the α band, which did not occur with meaningless objects or with passive viewing. Moreover, there was no interhemispheric coherence when midline objects were not recognized as meaningful or when familiar objects were presented in one visual hemifield. These data suggest a close link between site-specific interregional synchronization and object recognition.
Temporary Inactivation of the Retrosplenial Cortex Causes a Transient Reorganization of Spatial Coding in the Hippocampus
Authors: Cooper Brenton G. , Mizumori Sheri J. Y.
Published: April 2018

The ability to navigate accurately is dependent on the integration of visual and movement-related cues. Navigation based on metrics derived from movement is referred to as path integration. Recent theories of navigation have suggested that posterior cortical areas, the retrosplenial and posterior parietal cortex, are involved in path integration during navigation. In support of this hypothesis, we have found previously that temporary inactivation of retrosplenial cortex results in dark-selective impairments on the radial maze (Cooper and Mizumori, 1999). To understand further the role of the retrosplenial cortex in navigation, we combined temporary inactivation of retrosplenial cortex with recording of complex spike cells in the hippocampus. Thus, behavioral performance during spatial memory testing could be compared with place-field responses before, and during, inactivation of retrosplenial cortex. In the first experiment, behavioral results confirmed that inactivation of retrosplenial cortex only impairs radial maze performance in darkness when animals are at asymptote levels of performance. A second experiment revealed that retrosplenial cortex inactivation impaired spatial learning during initial light training. In both experiments, the normal location of hippocampal “place fields” was changed by temporary inactivation of retrosplenial cortex, whereas other electrophysiological properties of the cells were not affected. The changes in place coding occurred in the presence, and absence, of behavioral impairments. We suggest that the retrosplenial cortex provides mnemonic spatial information for updating location codes in the hippocampus, thereby facilitating accurate path integration. In this way, the retrosplenial cortex and hippocampus may be part of an interactive neural system that mediates navigation.
Substance P Plays a Critical Role in Photic Resetting of the Circadian Pacemaker in the Rat Hypothalamus
Authors: Kim Do Young , Kang Hee-Cheol , Shin Hyung Cheul , Lee Kyoung Jin , Yoon Young Wook , Han Hee Chul , Na Heung Sik , Hong Seung Kil , Kim Yang In
Published: April 2018

Glutamate is considered to be the primary neurotransmitter in the retinohypothalamic tract (RHT), which delivers photic information from the retina to the suprachiasmatic nucleus (SCN), the locus of the mammalian circadian pacemaker. However, substance P (SP) also has been suggested to play a role in retinohypothalamic transmission. In this study, we sought evidence that SP from the RHT contributes to photic resetting of the circadian pacemaker and further explored the possible interaction of SP with glutamate in this process. In rat hypothalamic slices cut parasagittally, electrical stimulation of the optic nerve in early and late subjective night produced a phase delay (2.4 ± 0.5 hr; mean ± SEM) and advance (2.6 ± 0.3 hr) of the circadian rhythm of SCN neuronal firing activity, respectively. The SP antagonist L-703,606 (10 μm) applied to the slices during the nerve stimulation completely blocked the phase shifts. Likewise, a cocktail of NMDA (2-amino-5-phosphonopentanoic acid, 50 μm) and non-NMDA (6,7-dinitroquinoxaline-2,3-dione, 10 μm) antagonists completely blocked the shifts. Exogenous application of SP (1 μm) or glutamate (100 μm) to the slices in early subjective night produced a phase delay (∼3 hr) of the circadian firing activity rhythm of SCN neurons. Coapplication of the NMDA and non-NMDA antagonist cocktail (as well as L-703,606) resulted in a complete blockade of the SP-induced phase delay, whereas L-703,606 (10 μm) had no effect on the glutamate-induced delay. These results suggest that SP, as well as glutamate, has a critical role in photic resetting. Furthermore, the results suggest that the two agonists act in series, SP working upstream of glutamate.
Calcineurin Links Ca2+Dysregulation with Brain Aging
Authors: Foster Thomas C. , Sharrow Keith M. , Masse James R. , Norris Christopher M. , Kumar Ashok
Published: April 2018

Brain aging is associated with altered Ca2+regulation. However, many Ca2+signal transduction mechanisms have not been explored in the aged brain. Here, we report that cytosolic expression and activity of the Ca2+-dependent protein phosphatase calcineurin (CaN) increases in the hippocampus during aging. CaN changes were paralleled by increased activation, but not expression, of CaN-regulated protein phosphatase 1 and a reduction in the phosphorylation state of CaN substrates involved in cell survival (i.e., Bcl-2-associated death protein and cAMP response element-binding protein). The age-related increase in CaN activity was not attributable to the inability of CaN to translocate to the membrane and was reduced by blocking L-type Ca2+channels. Finally, increased CaN activity correlated with memory function as measured with the Morris water escape task. The results suggest that altered regulation of CaN is one of the processes that could link Ca2+dyshomeostasis to age-related changes in neural function and cognition.
β-Amyloid Activates the Mitogen-Activated Protein Kinase Cascade via Hippocampal α7 Nicotinic Acetylcholine Receptors:In VitroandIn VivoMechanisms Related to Alzheimer's Disease
Authors: Dineley Kelly T. , Westerman Marcus , Bui Duy , Bell Karen , Ashe Karen Hsiao , Sweatt J. David
Published: April 2018

Alzheimer's Disease (AD) is the most common of the senile dementias, the prevalence of which is increasing rapidly, with a projected 14 million affected worldwide by 2025. The signal transduction mechanisms that underlie the learning and memory derangements in AD are poorly understood. β-Amyloid (Aβ) peptides are elevated in brain tissue of AD patients and are the principal component of amyloid plaques, a major criterion for postmortem diagnosis of the disease. Using acute and organotypic hippocampal slice preparations, we demonstrate that Aβ peptide 1-42 (Aβ42) couples to the mitogen-activated protein kinase (MAPK) cascade via α7 nicotinic acetylcholine receptors (nAChRs).In vivoelevation of Aβ, such as that exhibited in an animal model for AD, leads to the upregulation of α7 nAChR protein. α7 nAChR upregulation occurs concomitantly with the downregulation of the 42 kDa isoform of extracellular signal-regulated kinase (ERK2) MAPK in hippocampi of aged animals. The phosphorylation state of a transcriptional mediator of long-term potentiation and a downstream target of the ERK MAPK cascade, the cAMP-regulatory element binding (CREB) protein, were affected also. These findings support the model that derangement of hippocampus signal transduction cascades in AD arises as a consequence of increased Aβ burden and chronic activation of the ERK MAPK cascade in an α7 nAChR-dependent manner that eventually leads to the downregulation of ERK2 MAPK and decreased phosphorylation of CREB protein.
A Novel Extracellular Calcium Sensing Mechanism in Voltage-Gated Potassium Ion Channels
Authors: Johnson J. P. , Balser Jeffrey R. , Bennett Paul B.
Published: April 2018

Potassium (K+) channels influence neurotransmitter release, burst firing rate activity, pacing, and critical dampening of neuronal circuits. Internal and external factors that further modify K+channel function permit fine-tuning of neuronal circuits. Humanether-à-go-go-related gene (HERG) K+channels are unusually sensitive to external calcium concentration ([Ca2+]o). Small changes in [Ca2+]oshift the voltage dependence of channel activation to more positive membrane potentials, an effect that cannot be explained by nonspecific surface charge screening or channel pore block. The HERG–calcium concentration–response relationship spans the physiological range for [Ca2+]o. The modulatory actions of calcium are attributable to differences in the Ca2+affinity between rested and activated channels. Adjacent extracellular, negatively charged amino acids (E518 and E519) near the S4 voltage sensor influence both channel gating and Ca2+dependence. Neutralization of these charges had distinct effects on channel gating and calcium sensitivity. A change in the degree of energetic coupling between these amino acids on transition from closed to activated channel states reveals movement in this region during channel gating and defines a molecular mechanism for protein state-dependent ligand interactions. The results suggest a novel extracellular [Ca2+]osensing mechanism coupled to allosteric changes in channel gating and a mechanism for fine-tuning cell repolarization.
Synapsin Controls Both Reserve and Releasable Synaptic Vesicle Pools during Neuronal Activity and Short-Term Plasticity inAplysia
Authors: Humeau Yann , Doussau Frédéric , Vitiello Francesco , Greengard Paul , Benfenati Fabio , Poulain Bernard
Published: April 2018

Neurotransmitter release is a highly efficient secretory process exhibiting resistance to fatigue and plasticity attributable to the existence of distinct pools of synaptic vesicles (SVs), namely a readily releasable pool and a reserve pool from which vesicles can be recruited after activity. Synaptic vesicles in the reserve pool are thought to be reversibly tethered to the actin-based cytoskeleton by the synapsins, a family of synaptic vesicle-associated phosphoproteins that have been shown to play a role in the formation, maintenance, and regulation of the reserve pool of synaptic vesicles and to operate during the post-docking step of the release process. In this paper, we have investigated the physiological effects of manipulating synapsin levels in identified cholinergic synapses ofAplysia californica. When endogenous synapsin was neutralized by the injection of specific anti-synapsin antibodies, the amount of neurotransmitter released per impulse was unaffected, but marked changes in the secretory response to high-frequency stimulation were observed, including the disappearance of post-tetanic potentiation (PTP) that was substituted by post-tetanic depression (PTD), and increased rate and extent of synaptic depression. Opposite changes on post-tetanic potentiation were observed when synapsin levels were increased by injecting exogenous synapsin I. Our data demonstrate that the presence of synapsin-dependent reserve vesicles allows the nerve terminal to release neurotransmitter at rates exceeding the synaptic vesicle recycling capacity and to dynamically change the efficiency of release in response to conditioning stimuli (e.g., post-tetanic potentiation). Moreover, synapsin-dependent regulation of the fusion competence of synaptic vesicles appears to be crucial for sustaining neurotransmitter release during short periods at rates faster than the replenishment kinetics and maintaining synchronization of quanta in evoked release.
Diversity and Specificity of Actions of Slit2 Proteolytic Fragments in Axon Guidance
Authors: Ba-Charvet Kim T. Nguyen , Brose Katja , Ma Le , Wang Kuan H. , Marillat Valérie , Sotelo Constantino , Tessier-Lavigne Marc , Chédotal Alain
Published: April 2018

The Slits are secreted proteins that bind to Robo receptors and play a role in axon guidance and neuronal migration. In vertebrates, Slit2 is a major chemorepellent for developing axons and is involved in the control of midline crossing.In vivo, Slit2 is cleaved into 140 kDa N-terminal (Slit2-N) and 55–60 kDa C-terminal (Slit2-C) fragments, although the uncleaved/full-length form can also be isolated from brain extract. We explored the functional activities of Slit2 fragments by engineering mutant and truncated versions of Slit2 representing the N-, C-, and full/uncleavable (Slit2-U) fragments. Only Slit2-N and Slit2-U bind the Robo proteins. We found that in collagen gel, olfactory bulb (OB) but not dorsal root ganglia (DRG) axons are repelled by Slit2-N and Slit2-U. Moreover, only Slit2-N membranes or purified protein-induced OB growth cones collapse. Finally, we found that only recombinant Slit2-N could induce branching of DRG axons and that this effect was antagonized by Slit2-U. Therefore, different axons have distinct responses to Slit2 fragments, and these proteins have different growth-promoting capacities.