bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhancement of Associative Long-Term Potentiation by Activation of β-Adrenergic Receptors at CA1 Synapses in Rat Hippocampal Slices
Authors: Lin Yi-Wen , Min Ming-Yuan , Chiu Tsai-Hsien , Yang Hsiu-Wen
Published: April 2018

The objective of this study was to evaluate the role of β-adrenergic receptors in modulating associative long-term potentiation (LTP) induced at CA1 synapses. Two independent Schaffer collateral pathways were stimulated in hippocampal slices. The field EPSP (fEPSP) response evoked in one pathway (the weak pathway) was small, whereas a large response, usually 80–90% of the maximum, was evoked in the strong pathway. After recording of the baseline fEPSP evoked at 0.033 Hz, LTP of the weak pathway could be associatively induced by paired stimulation of the weak and strong pathways 100 times at 6 sec intervals, with stimulation of the weak pathway preceded 3–10 msec. However, pairing protocols with an interval between stimulation of the two pathways >10 msec resulted in no LTP. The induced LTP was NMDA receptor dependent, because 50μm d,l-APV blocked its induction. Bath application of 1μmisoproterenol enhanced LTP by increasing the window of the stimulation interval up to 15 msec but did not affect the magnitude of the LTP induced by pairing protocols with intervals <10 msec. Similar results were obtained when the experiments were repeated using whole-cell recording. These results suggest that activation of β-adrenergic receptors can enhance associative LTP by increasing the width of the time window rather than the magnitude of the LTP. Enhancement of LTP by β-adrenergic receptors was blocked in slices by pretreatment with inhibitors of protein kinase A or mitogen-activated protein kinase, suggesting that these signaling cascades are involved in this process.
Delayed Systemic Nogo-66 Receptor Antagonist Promotes Recovery from Spinal Cord Injury
Authors: Li Shuxin , Strittmatter Stephen M.
Published: April 2018

Traumatized axons possess an extremely limited ability to regenerate within the adult mammalian CNS. The myelin-derived axon outgrowth inhibitors Nogo, oligodendrocyte-myelin glycoprotein, and myelin-associated glycoprotein, all bind to an axonal Nogo-66 receptor (NgR) and at least partially account for this lack of CNS repair. Although the intrathecal application of an NgR competitive antagonist at the time of spinal cord hemisection induces significant regeneration of corticospinal axons, such immediate local therapy may not be as clinically feasible for cases of spinal cord injury. Here, we consider whether this approach can be adapted to systemic therapy in a postinjury therapeutic time window. Subcutaneous treatment with the NgR antagonist peptide NEP1–40 (Nogo extracellular peptide, residues 1–40) results in extensive growth of corticospinal axons, sprouting of serotonergic fibers, upregulation of axonal growth protein SPRR1A (small proline-rich repeat protein 1A), and synapse re-formation. Locomotor recovery after thoracic spinal cord injury is enhanced. Furthermore, delaying the initiation of systemic NEP1–40 administration for up to 1 week after cord lesions does not limit the degree of axon sprouting and functional recovery. This indicates that the regenerative capacity of transected corticospinal tract axons persists for weeks after injury. Systemic Nogo-66 receptor antagonists have therapeutic potential for subacute CNS axonal injuries such as spinal cord trauma.
Vasopressin Differentially Modulates Non-NMDA Receptors in Vasopressin and Oxytocin Neurons in the Supraoptic Nucleus
Authors: Hirasawa Michiru , Mouginot Didier , Kozoriz Michael G. , Kombian Samuel B. , Pittman Quentin J.
Published: April 2018

Magnocellular neurons of the supraoptic nucleus release the neuropeptides oxytocin and vasopressin from their dendrites to regulate their synaptic inputs. This study aims to determine the cellular mechanism by which vasopressin modulates excitatory synaptic transmission. Presumably by electroporation through perforated patch, we were able to successfully introduce biocytin into cells in which we performed an electrophysiological study. This method enabled us to determine that roughly half of the recorded neurons were immunoreactive to oxytocin-associated neurophysin and showed two characteristic features: an inward rectification and a sustained outward rectification. The remaining half showed a linear voltage-current relationship and was immunoreactive to vasopressin-associated neurophysin. Using these electrophysiological characteristics andpost hocimmunohistochemistry to identify vasopressin or oxytocin neurons, we found that vasopressin decreased evoked EPSCs in vasopressin neurons while increasing EPSCs in oxytocin neurons. In both types of neurons, EPSC decay constants were not affected, indicating that desensitization of non-NMDA receptors did not underlie the EPSC amplitude change. In vasopressin neurons, both vasopressin and a V1a receptor agonist, F-180, decreased AMPA-induced currents, an effect blocked by a V1a receptor antagonist SR49059. In oxytocin neurons, AMPA-induced currents were facilitated by vasopressin, whereas F-180 had no effect. An oxytocin receptor antagonist blocked the facilitatory effect of vasopressin. Thus, we conclude that vasopressin inhibits EPSCs in vasopressin neurons via postsynaptic V1a receptors, whereas it facilitates EPSCs in oxytocin neurons through oxytocin receptors.
Differential Frequency Dependence of P2Y1- and P2Y2- Mediated Ca2+Signaling in Astrocytes
Authors: Fam Sami R. , Gallagher Conor J. , Kalia Lorraine V. , Salter Michael W.
Published: April 2018

ATP is a key extracellular messenger that mediates the propagation of Ca2+waves in astrocyte networks in various regions of the CNS. ATP-mediated Ca2+signals play critical roles in astrocyte proliferation and differentiation and in modulating neuronal activity. The actions of ATP on astrocytes are via two distinct subtypes of P2Y purinoceptors, P2Y1and P2Y2receptors (P2Y1Rs and P2Y2Rs), G-protein coupled receptors that stimulate mobilization of intracellular Ca2+([Ca2+]i) via the phospholipase Cβ-IP3pathway. We report here that P2Y1R-mediated and P2Y2R-mediated Ca2+responses differentially show two forms of activity-dependent negative feedback. First, Ca2+responses mediated by either receptor exhibit slow depression that is independent of stimulation frequency. Second, responses mediated by P2Y1Rs, but not those mediated by P2Y2Rs, show rapid oscillations after high-frequency stimulation. We demonstrate that the oscillations are mediated by recruiting negative feedback by protein kinase C, and we map the site responsible for the effect of protein kinase C to Thr339in the C terminus of P2Y1R. We propose that frequency-dependent changes in ATP-mediated Ca2+signaling pathways may modulate astrocyte function and astrocyte–neuron signaling in the CNS.
Cell-Autonomous Mechanisms and Myelin-Associated Factors Contribute to the Development of Purkinje Axon Intracortical Plexus in the Rat Cerebellum
Authors: Gianola Sara , Savio Tiziana , Schwab Martin E. , Rossi Ferdinando
Published: April 2018

The highly specific connection patterns of the mature CNS are shaped through finely regulated processes of axon growth and retraction. To investigate the relative contribution of cell-autonomous mechanisms and extrinsic cues in these events, we examined the development of Purkinje axon intracortical plexus in the rat cerebellum. During the first postnatal week, several new processes sprout from focal swellings along the initial portion of the Purkinje neurite and spread in the granular layer. Intense structural plasticity occurs during the following week, with pruning of collateral branches and remodeling of terminal arbors. The mature distribution of the Purkinje infraganglionic plexus, confined within the most superficial portion of the granular layer, is attained at approximately postnatal day 15. A similar neuritic branching pattern is also developed by Purkinje cells grown in cultures of dissociated cerebellar cells or transplanted to extracerebellar CNS regions, suggesting that cell-autonomous mechanisms contribute to determining the Purkinje axon phenotype.

The structural remodeling of Purkinje intracortical plexus is concomitant with the development of cerebellar myelin. To ask whether myelin-associated factors contribute to the morphological maturation of Purkinje neurites, we prevented normal myelinogenesis by killing oligodendrocyte precursors with 5′-azacytidine or by applying neutralizing antibodies against the myelin-associated neurite growth inhibitor Nogo-A. In both conditions, Purkinje axons retained exuberant branches, and the terminal plexus spanned the entire extent of the granular layer. Thus, the formation of Purkinje axon collaterals is, in part, controlled by intrinsic determinants, but their growth and distribution are regulated by environmental signals, among which are myelin-derived cues.
Calcium Signaling in Single Peripheral Sensory Nerve Terminals
Authors: Gover Tony D. , Kao Joseph P. Y. , Weinreich Daniel
Published: April 2018

Peripheral sensory nerve terminals (PSNTs) have a dual function: reporting normal and abnormal sensations and releasing trophic factors to maintain the structure and function of epithelial cells. Although it is widely considered that intracellular Ca2+plays a critical signaling role for both functions, the role of Ca2+signaling has never been studied in PSNTs, primarily because of their small size and anatomical inaccessibility. Here, using epifluoresence microscopy and a fluorescent Ca2+indicator, we report that action potentials or chemical irritation can elicit transient rises in [Ca2+]i(Ca2+transients) in PSNTs within the corneal epithelium of the rat.In vitroelectrical stimulation of the ciliary nerves in the eye, or electrical field stimulation of the cornea, evoked Ca2+transients with a magnitude that was proportional to the number of stimuli applied over the range of 1–10 stimuli. Ca2+transients were significantly blocked by 1 mmlidocaine, 4.1 μmsaxitoxin (STX), or L-type Ca2+channel antagonists (1 mmdiltiazem or 20 μmnifedipine). The nociceptive agonist capsaicin (1 μm) elicited Ca2+transients in all nerve terminals studied. Capsaicin-evoked Ca2+transients were completely blocked by the vanilloid receptor 1 antagonist capsazepine (100 μm). In contrast, capsaicin-evoked Ca2+transients were not attenuated by preincubation with 4.1 μmSTX or 20 μmnifedipine. These findings demonstrate, for the first time, that nerve impulses or chemical stimulation promote Ca2+entry into PSNTs, including nociceptors.
Distinguishing between Presynaptic and Postsynaptic Mechanisms of Short-Term Depression during Action Potential Trains
Authors: Wong Adrian Y. C. , Graham Bruce P. , Billups Brian , Forsythe Ian D.
Published: April 2018

Short-term facilitation and depression have a profound influence on transmission at many glutamatergic synapses, particularly during trains of stimuli. A major component of these processes is postsynaptic receptor desensitization. Both presynaptic and postsynaptic mechanisms can contribute to synaptic efficacy, but it is often difficult to define their respective contributions. Blockers of desensitization such as cyclothiazide (CTZ) can be used, but many of these drugs have nonspecific effects on transmitter release, complicating attempts to define synaptic effectiveness under physiological conditions. We describe and validate a new method to minimize desensitization during trains of synaptic stimuli that is based on the low-affinity competitive glutamate receptor antagonists γ-d-glutamylglycine or kynurenic acid. A computational model of AMPA receptor kinetics shows that the mechanism can be accounted for by simple competitive antagonism of AMPA receptors, where the rapid off-rate of the antagonist permits re-equilibration between blocked and unblocked pools during the interstimulus interval. Our results at the calyx of Held show that desensitization makes little contribution to synaptic depression at frequencies below 10 Hz, but at higher frequencies it makes an important contribution, with accumulating desensitization masking short-term facilitation and causing an underestimation of quantal content. This novel method of protection from desensitization is compatible with physiological studies but cannot be used in conjunction with CTZ. Although presynaptic vesicle depletion makes the dominant contribution to short-term depression, our results show that AMPA receptor desensitization contributes to the depression at auditory synapses after hearing onset and in a frequency-dependent manner.
A Novel Antigen Sensitive to Calcium Chelation That is Associated with the Tip Links and Kinocilial Links of Sensory Hair Bundles
Authors: Goodyear Richard J. , Richardson Guy P.
Published: April 2018

Tip links are extracellular, cell-surface-associated filaments of unknown molecular composition that are thought to gate the mechanotransducer channel of the sensory hair cell. They disappear from the hair bundle in response to calcium chelation and lanthanum treatment and resist degradation by the protease subtilisin. A monoclonal antibody derived from a hybridoma screen identified a novel antigen associated with tip links, the tip-link antigen. The tip-link antigen is also associated with kinocilial links, subtilisin-resistant filaments that are sensitive to calcium chelation and connect the kinocilium to the tallest stereocilia of the hair bundle. Furthermore, the tip-link antigen is expressed in the retina, where it is associated with the ciliary calyx, a ring of microvilli that surrounds the outer segment of the photoreceptor. The tip-link antigen rapidly disappears from the surface of the hair bundle in response to calcium chelation. It is also subtilisin resistant, relative to the ankle-link antigen, an antigen associated with another type of hair bundle link. The tip-link antigen is lanthanum sensitive and, like tip links, reappears on the surface of the hair bundle after calcium chelation. The monoclonal antibody to the tip-link antigen immunoprecipitates two concanavalin A-reactive polypeptides with apparent molecular masses of 200 and 250 kDa from detergent extracts of the retina. These results provide the first identification of a cell surface antigen associated with tip links, indicate that tip links share properties in common with kinocilial links, and reveal a second epitope that, along with the ankle-link antigen, is common to both sensory hair bundles and the ciliary calyx of photoreceptors.
Regulation of δ-Opioid Receptor Trafficking via μ-Opioid Receptor Stimulation: Evidence from μ-Opioid Receptor Knock-Out Mice
Authors: Morinville Anne , Cahill Catherine M. , Esdaile M. James , Aibak Haneen , Collier Brian , Kieffer Brigitte L. , Beaudet Alain
Published: April 2018

We recently demonstrated that prolonged treatment with morphine increases the antinociceptive potency of the δ-opioid receptor (δOR) agonist deltorphin and promotes cell surface targeting of δORs in neurons of the dorsal horn of the rat spinal cord (Cahill et al., 2001b). In the present study we examined whether these effects were mediated selectively via μOR. Using the same intermittent treatment regimen as for morphine, we found that methadone and etorphine, but not fentanyl, enhanced [d-Ala2]-deltorphin-mediated antinociception. However, continuous delivery of fentanyl for 48 hr resulted in augmented δOR-mediated antinociception when compared with saline-infused animals. Time course studies confirmed that a 48 hr treatment with morphine was necessary for the establishment of enhanced δOR-mediated antinociception. The observed increases in δOR agonist potency and δOR plasma membrane density were reversed fully 48 hr after discontinuation of morphine injections. Wild-type C57BL/6 mice pretreated with morphine for 48 hr similarly displayed enhanced δOR-mediated antinociception in a tonic pain paradigm. Accordingly, the percentage of plasma membrane-associated δOR in the dorsal horn of the spinal cord, as assessed by immunogold electron microscopy, increased from 6.6% in naive to 12.4% in morphine-treated mice. In contrast, morphine treatment of μOR gene knock-out (KO) mice did not produce any change in δOR plasma membrane density. These results demonstrate that selective activation of μOR is critical for morphine-induced targeting of δOR to neuronal membranes, but not for basal targeting of this receptor to the cell surface.
The Contribution of Resurgent Sodium Current to High-Frequency Firing in Purkinje Neurons: An Experimental and Modeling Study
Authors: Khaliq Zayd M. , Gouwens Nathan W. , Raman Indira M.
Published: April 2018

Purkinje neurons generate high-frequency action potentials and express voltage-gated, tetrodotoxin-sensitive sodium channels with distinctive kinetics. Their sodium currents activate and inactivate during depolarization, as well as reactivate during repolarization from positive potentials, producing a “resurgent” current. This reopening of channels not only generates inward current after each action potential, but also permits rapid recovery from inactivation, leading to the hypothesis that resurgent current may facilitate high-frequency firing.

Mutantmedmice are ataxic and lack expression of theScn8agene, which encodes the NaV1.6 protein. InmedPurkinje cells, transient sodium current inactivates more rapidly than in wild-type cells, and resurgent current is nearly abolished. To investigate how NaV1.6-specific kinetics influence firing patterns, we recorded action potentials of Purkinje neurons isolated from wild-type andmedmice. We also recorded non-sodium currents from Purkinje cells of both genotypes to test whether theScn8amutation induced changes in other ion channels. Last, we modeled action potential firing by simulating eight currents directly recorded from Purkinje cells in both wild-type andmedmice.

Regular, high-frequency firing was slowed inmedPurkinje neurons. In addition to disrupted sodium currents,medneurons had small but significant changes in potassium and leak currents. Simulations indicated that these modified non-sodium currents could not account for the reduced excitability ofmedcells but instead slightly facilitated spiking. The loss of NaV1.6-specific kinetics, however, slowed simulated spontaneous activity. Together, the data suggest that across a range of conditions, sodium currents with a resurgent component promote and accelerate firing.
Na-K-Cl Cotransporter Contributes to Glutamate-Mediated Excitotoxicity
Authors: Beck Joe , Lenart Brett , Kintner Douglas B. , Sun Dandan
Published: April 2018

We hypothesized that cation-dependent Cl-transport protein Na-K-Cl cotransporter isoform 1 (NKCC1) plays a role in the disruption of ion homeostasis in cerebral ischemia. In the current study, a role for NKCC1 in neuronal death was elucidated in neurotoxicity induced by glutamate and oxygen and glucose deprivation (OGD). Incubation of cortical neurons cultured for 14–15 din vitro(DIV) with 100 μmglutamate for 24 hr resulted in 50% cell death. Three hours of OGD followed by 21 hr of reoxygenation led to 70% cell death. Inhibition of NMDA receptors with dizocilpine hydrogen maleate (1 μm) prevented both OGD- and glutamate-mediated cell death. Moreover, blocking of NKCC1 activity with bumetanide (5–10 μm) abolished glutamate- or OGD-induced neurotoxicity. Bumetanide was ineffective if added after 10–120 min of glutamate incubation or 3–6 hr of OGD treatment. Accumulation of intracellular Na+and36Cl content after NMDA receptor activation was inhibited by bumetanide. Blockage of NKCC1 significantly attenuated cell swelling after OGD or NMDA receptor activation. This neuroprotection was age dependent. Inhibition of NKCC1 did not protect DIV 7–8 neurons against OGD-mediated cell death. In contrast, cell death in DIV 7–8 neurons was prevented by the protein-synthesis inhibitor, cycloheximide. Taken together, the results suggest that NKCC1 activity is involved in the acute excitotoxicity as a result of excessive Na+and Cl-entry and disruption of ion homeostasis.
State-Dependent Processing of Sensory Stimuli by Thalamic Reticular Neurons
Authors: Hartings Jed A. , Temereanca Simona , Simons Daniel J.
Published: April 2018

Inhibitory neurons of the thalamic reticular (RT) nucleus fire in two activity modes, burst and tonic, depending on an animal's behavioral state. In tonic mode, depolarized RT cells fire single action potentials continuously, whereas burst firing consists of grouped discharges separated by periods of quiescence. To determine how these firing modes affect sensory-evoked RT responses, single-unit responses to controlled whisker deflections were analyzed according to the burst versus tonic mode of spontaneous activity (SA) preceding the response. After burst mode activity (i.e., either quiescence or spontaneous bursts), responses exhibited a slow ∼15 msec rise to peak firing rates followed by a ∼35 msec decay. Interspike intervals within the response exhibited accelerando–decelerando patterns similar to those of spontaneous bursts. After tonic mode activity (i.e., single spikes), responses had a nearly instantaneous ∼1.5 msec rise-to-peak followed by a ∼40 msec decay, with large spike counts (5.2 spikes per stimulus) similar to those evoked in burst mode (6.2 spikes per stimulus). Interspike intervals were longer in tonic mode and exhibited a decelerando pattern. Initial evoked spikes, however, had shorter latencies and greater synchrony, contributing to the rapid onset of tonic population response. Shifts from quiescent (presumed burst mode) to tonic SA could be induced by either previous whisker deflections or iontophoretic application of NMDA; both manipulations effected appropriate shifts from burst to tonic response spike patterns. In awake animals, burst and tonic firing in RT, as in thalamocortical relay nuclei, may reflect sensory processing strategies appropriate for different behavioral and attentional states.
Concerted GABAergic Actions ofAplysiaFeeding Interneurons in Motor Program Specification
Authors: Jing Jian , Vilim Ferdinand S. , Wu Jin-Sheng , Park Ji-Ho , Weiss Klaudiusz R.
Published: April 2018

GABAergic inhibitory interneurons regulate the activity of diverse types of neural networks, but the specific roles of these interneurons in motor control are poorly understood. In theAplysiafeeding motor network, three interneurons, cerebral–buccal interneuron-3 (CBI-3) and buccal interneurons B40 and B34, are GABA-immunoreactive and evoke fast IPSPs in their postsynaptic followers. Using a combination of pharmacological experiments with GABA antagonists, agonists, and uptake inhibitors, we found that these fast IPSPs are likely mediated by GABA. Functionally, these fast IPSPs specify two parameters for ingestive motor programs elicited by the command-like interneuron CBI-2: (1) the appropriate phasing of activity of the radula closer motor neuron B8 relative to protraction–retraction, and (2) protraction duration. First, in ingestive programs, B8 activity is phased such that it fires minimally during protraction. CBI-3 and B40 exert fast inhibition to minimize B8 activity during protraction, by either acting directly on B8 (B40) or indirectly on B8 (CBI-3). Second, these ingestive programs are characterized by long protraction duration, which is promoted by B40 and B34 because hyperpolarization of either cell shortens protraction. Such effects of B40 and B34 are attributable, at least partly, to their inhibitory effects on the retraction-phase interneuron B64 whose activation terminates protraction. Consistent with a GABAergic contribution to both B8 phasing and protraction duration, blockade of GABAergic inhibition by picrotoxin increases B8 activity during protraction and shortens protraction, without disrupting the integrity of motor programs. Thus, the concerted actions of GABAergic inhibition from threeAplysiafeeding interneurons contribute to the specification of multiple features that define the motor program as an ingestive one.
Increased Depression-Like Behaviors in Corticotropin-Releasing Factor Receptor-2-Deficient Mice: Sexually Dichotomous Responses
Authors: Bale Tracy L. , Vale Wylie W.
Published: April 2018

Depressive disorders affect nearly 19 million American adults, making depression and the susceptibility for developing depression a critical focus of mental health research today. Females are twice as likely to develop depression as males. Stress is a known risk factor for developing depression, and recent hypotheses suggest an involvement of an overactive stress axis. As mediators of the stress response, corticotropin-releasing factor (CRF) and its receptors (CRFR1 and CRFR2) have been implicated in the propensity for developing stress-related mood disorders. Mice deficient in CRFR2 display increased anxiety-like behaviors and a hypersensitive stress response. As a possible animal model of depression, these mice were tested for depression-like behaviors in the forced swim test. Comparisons were made between wild-type and mutant animals, as well as between sexes. Male and female CRFR2-mutant mice showed increased immobility as an indicator of depression compared with wild-type mice of the same sex. In addition, mutant and wild-type female mice demonstrated increased immobile time compared with males of the same genotype. Treatment of CRFR2-deficient mice with the CRFR1 antagonist antalarmin decreased immobile time and increased swim time in both sexes. We found a significant effect of sex for both time spent immobile and swimming after antalarmin treatment. Because differences in behaviors in the forced swim test are good indicators of serotonergic and catecholaminergic involvement, our results may reveal an interaction of CRF pathways with other known antidepressant systems and may also support an involvement of CRF receptors in the development of depression such that elevated CRFR1 activity, in the absence of CRFR2, increases depression-like behaviors.
Synchronization of Kainate-Induced Epileptic Activity via GABAergic Inhibition in the Superfused Rat HippocampusIn Vivo
Authors: Khazipov Roustem , Holmes Gregory L.
Published: April 2018

We studied cellular mechanisms of synchronization of epileptiform activity induced by kainic acid in a novel preparation of superfused rat hippocampusin vivo. Under urethane anesthesia, kainate induced epileptic population spikes occurring at 30–40 Hz. Pyramidal cells fired exclusively during population spikes with an average probability of 0.34 on rebound of rhythmic GABAA-mediated inhibitory postsynaptic events. Excitatory synaptic events contributed little to seizure activity. Rhythmic epileptiform activity was suppressed by blocking GABAAreceptors and was slowed by barbiturates. Thus, GABAergic inhibition is instrumental in synchronizing kainate-induced epileptiform rhythmic activity in the gamma frequency band in the intact hippocampusin vivo.
Proteolytic Processing of the p75 Neurotrophin Receptor and Two Homologs Generates C-Terminal Fragments with Signaling Capability
Authors: Kanning Kevin C. , Hudson Mark , Amieux Paul S. , Wiley Jesse C. , Bothwell Mark , Schecterson Leslayann C.
Published: April 2018

The 75 kDa neurotrophin receptor (p75NTR) and two neurotrophin receptor homologs (NRH1, NRH2) constitute a subfamily of the nerve growth factor/tumor necrosis factor receptor superfamily. NRH1 coexists with p75NTRin fish, amphibians, and birds but is absent in mammals, whereas NRH2 exists only in mammals. Unlike p75NTRand NRH1, NRH2 lacks a canonical extracellular ligand binding domain. The similarity of NRH2 to the product of metalloproteinase cleavage of p75NTRprompted us to examine the cleavage of p75NTRin greater detail. p75NTR, NRH1, and NRH2 undergo multiple proteolytic cleavages that ultimately release cytoplasmic fragments. For p75NTR, cleavage in the extracellular domain by a PMA-inducible membrane metalloproteinase is followed by cleavage within or near the transmembrane domain, releasing the intracellular domain into the cytoplasm. This processing resembles the α- and γ-secretase-mediated processing of β-amyloid precursor protein and the similar processing of Notch. Although neurotrophins did not regulate p75NTRprocessing, theα- andγ-secretase-mediated cleavage of p75 is modulated by receptor tyrosine kinases (Trks) TrkA and TrkB but not TrkC. Surprisingly, although NRH1 and NRH2 also undergo proteolytic cytoplasmic release of intracellular domains, a different protease mediates the cleavage. Furthermore, whereas the p75NTRsoluble intracellular domain accumulates only in the presence of proteasome inhibitors, the equivalent fragment of NRH2 is stable and localizes in the nucleus. Because soluble intracellular domains of p75NTRand NRH2 were found to activate NF-κB in concert with TNF receptor associated factor 6 (TRAF6), we propose that cleavage of these proteins may serve conserved cytoplasmic and nuclear signaling functions through distinct proteases.
Antibody Cross-Linking of Myelin Oligodendrocyte Glycoprotein Leads to Its Rapid Repartitioning into Detergent-Insoluble Fractions, and Altered Protein Phosphorylation and Cell Morphology
Authors: Marta C. B. , Taylor C. M. , Coetzee T. , Kim T. , Winkler S. , Bansal R. , Pfeiffer S. E.
Published: April 2018

Myelin oligodendrocyte glycoprotein (MOG) is, quantitatively, a relatively minor component of the myelin membrane. Nevertheless, peritoneal administration of MOG evokes potent cellular and humoral immunoreactivity, resulting in an experimental allergic encephalitis with immunopathology similar to multiple sclerosis. Moreover, antibodies against MOG cause myelin destructionin situ. Therefore, it appears that MOG-related demyelination is dependent on anti-MOG antibody, but the mechanism(s) by which it occurs is unclear. Of potential significance are observations that some proteins are selectively partitioned into specialized plasma membrane microdomains rich in glycosphingolipids and cholesterol (“lipid rafts”). In particular, during ligand or antibody cross-linking, various plasma membrane receptors undergo enhanced partitioning into rafts as an obligatory first step toward participation in early signal transduction events. In contrast to mature myelin, in oligodendrocytes (OLs) in culture MOG is not raft associated [Triton X-100 (TX-100) soluble, 4°C]. However, in this study we show that antibody cross-linking (anti-MOG plus secondary antibody) of MOG on the surface of OLs results in the repartitioning of ∼95% of MOG into the TX-100-insoluble fraction. This repartitioning of MOG is rapid (≤1 min), antibody dose dependent, requires an intact cytoskeleton, leads to phosphorylation or dephosphorylation of tyrosine, serine, and threonine residues in specific proteins (e.g., β-tubulin, Gβ1–2), and invokes a rapid retraction of OL processes. After removal of the cross-linking antibodies, these events are reversed. We hypothesize that antibody-mediated repartitioning of MOG into TX-100-insoluble glycosphingolipid–cholesterol-rich microdomains initiates specific cellular signaling that could be related to initial steps of MOG-mediated demyelination.
The Production of Amyloid β Peptide Is a Critical Requirement for the Viability of Central Neurons
Authors: Plant Leigh D. , Boyle John P. , Smith Ian F. , Peers Chris , Pearson Hugh A.
Published: April 2018

The amyloid β peptide (Aβ) is a product of the sequential γ- and β-secretase cleavage of amyloid precursor protein. Inhibitors of secretase enzymes have been proposed as a potential therapeutic strategy in the treatment of Alzheimer's disease. Here, we investigate the effect of inhibiting these key enzymes on the viability of a range of cell types.

Treatment of rat cortical neurons for 24 hr with secretase inhibitors or an antibody that binds Aβ resulted in a marked reduction in cell viability, as measured by MTT reduction. Incubation with secretase inhibitors caused similar effects on other neuronal cell types (rat cerebellar granule neurons and the human SH-SY5Y cell line). Interestingly, rat astrocytes and a number of non-neuronal cell lines investigated (HEK293, DDT1-FM2, and human teratorhabdoid tumor cells) were unaffected by incubation with secretase inhibitors.

The coincubation of Aβ1–40prevented the toxicity of secretase inhibitors in neuronal cells. Aβ1–40was protective in a concentration-dependent manner, and its effects were significant at concentrations as low at 10 pm. Importantly, the protective effects of Aβ were Aβ size-form specific, with the Aβ1–42size form affording limited protection and the Aβ25–35size form having very little protective effect.

The present study demonstrates that inhibition of β-or γ-secretase activity induces death in neuronal cells. Importantly, this toxicity, which our data suggest is a consequence of a decline in neuronal Aβ levels, was absent in non-neuronal cells. This study further supports a key physiological role for the enigmatic Aβ peptide.
Central Cellular Mechanisms Underlying Temperature-Dependent Changes in the Goldfish Startle-Escape Behavior
Authors: Preuss Thomas , Faber Donald S.
Published: April 2018

Activation of auditory afferents on the lateral dendrite of the Mauthner (M)-cell triggers an escape response (C-start) in goldfish. To study distinct behavioral changes and their physiological correlates on a cellular level we examined the effect of acute changes of temperature on M-cell membrane properties and intracellular responses to sound clicks and on C-start kinematics and behavior, focusing on threshold and initial escape direction, two properties determined on the M-cell level. Cooling slowed C-start motor performance, increasing response latency and decreasing peak velocity and peak acceleration, but increased the probability of triggering the escape. In addition, the likelihood of escapes in an inappropriate direction (e.g., responses toward the stimulus instead of away from it) increased at low temperatures. On a cellular level, cooling caused a distinct increase in input resistance of the M-cell and in the dendritic space constant for the auditory-evoked synaptic potentials. Moreover, cooling decreased the magnitude and delayed the onset of feedforward inhibition of the M-cell. These temperature-induced changes in the network and in the intrinsic M-cell properties combine to support behavioral hyperexcitability, but apparently also alter the directional decision-making process during an escape. More generally, our results illustrate that the balance between excitatory and inhibitory influences can determine the expression of a behavior and its modification and at the same time underline the significance of temperature for nervous system function and behavior.
Brain-Derived Neurotrophic Factor Mediates Activity-Dependent Dendritic Growth in Nonpyramidal Neocortical Interneurons in Developing Organotypic Cultures
Authors: Jin Xiaoming , Hu Hang , Mathers Peter H. , Agmon Ariel
Published: April 2018

Brain-derived neurotrophic factor (BDNF) promotes postnatal maturation of GABAergic inhibition in the cerebral and cerebellar cortices, and its expression and release are enhanced by neuronal activity, suggesting that it acts in a feedback manner to maintain a balance between excitation and inhibition during development. BDNF promotes differentiation of cerebellar, hippocampal, and neostriatal inhibitory neurons, but its effects on the dendritic development of neocortical inhibitory interneurons remain unknown. Here, we show that BDNF mediates depolarization-induced dendritic growth and branching in neocortical interneurons. To visualize inhibitory interneurons, we biolistically transfected organotypic cortical slice cultures from neonatal mice with green fluorescent protein (GFP) driven by the glutamic acid decarboxylase (GAD)67 promoter. Nearly all GAD67–GFP-expressing neurons were nonpyramidal, many contained GABA, and some expressed markers of neurochemically defined GABAergic subtypes, indicating that GAD67–GFP-expressing neurons were GABAergic. We traced dendritic trees from confocal images of the same GAD67–GFP-expressing neurons before and after a 5 d growth period, and quantified the change in total dendritic length (TDL) and total dendritic branch points (TDBPs) for each neuron. GAD67–GFP-expressing neurons growing in control medium exhibited a 20% increase in TDL, but in 200 ng/ml BDNF or 10 mmKCl, this increase nearly doubled and was accompanied by a significant increase in TDBPs. Blocking action potentials with TTX did not prevent the BDNF-induced growth, but antibodies against BDNF blocked the growth-promoting effect of KCl. We conclude that BDNF, released by neocortical pyramidal neurons in response to depolarization, enhances dendritic growth and branching in nearby inhibitory interneurons.
κ Opioid Receptor Antagonism and Prodynorphin Gene Disruption Block Stress-Induced Behavioral Responses
Authors: McLaughlin Jay P. , Marton-Popovici Monica , Chavkin Charles
Published: April 2018

Previous studies have demonstrated that stress may increase prodynorphin gene expression, and κ opioid agonists suppress drug reward. Therefore, we tested the hypothesis that stress-induced release of endogenous dynorphin may mediate behavioral responses to stress and oppose the rewarding effects of cocaine. C57Bl/6 mice subjected to repeated forced swim testing (FST) using a modified Porsolt procedure at 30°C showed a characteristic stress-induced immobility response and a stress-induced analgesia observed with a tail withdrawal latency assay. Pretreatment with the κ opioid receptor antagonist nor-binaltorphimine (nor-BNI; 10 mg/kg, i.p.) blocked the stress-induced analgesia and significantly reduced the stress-induced immobility. The nor-BNI sensitivity of the behavioral responses suggests an activation of the κ opioid receptor by a stress-induced release of dynorphin peptides. Supporting this hypothesis, transgenic mice possessing a disrupted prodynorphin gene showed no increase in immobility or stress-induced analgesia after exposure to repeated FST. Because both stress and the κ opioid system can modulate the response to drugs of abuse, we tested the effects of forced swim stress on cocaine-conditioned place preference (CPP). FST-exposed mice conditioned with cocaine (15 mg/kg, s.c.) showed significant potentiation of place preference for the drug-paired chamber over the responses of unstressed mice. Surprisingly, nor-BNI pretreatment blocked stress-induced potentiation of cocaine CPP. Consistent with this result, mice lacking the prodynorphin gene did not show a stress-induced potentiation of cocaine CPP, whereas wild-type littermates did. The findings suggest that chronic swim stress may activate the κ opioid system to produce analgesia, immobility, and potentiation of the acute rewarding properties of cocaine in C57Bl/6 mice.
Brain-Derived Neurotrophic Factor Inhibits Human Immunodeficiency Virus-1/gp120-Mediated Cerebellar Granule Cell Death by Preventing gp120 Internalization
Authors: Bachis Alessia , Major Eugene O. , Mocchetti Italo
Published: April 2018

The human immunodeficiency virus type 1 (HIV-1) envelope protein gp120 has been implicated in the pathogenesis of HIV-1 dementia. Thus, inhibition of gp120 activity could reduce HIV toxicity in the brain. We have used primary cultures of rat cerebellar granule cells to examine mechanisms whereby gp120 causes cell death and to characterize neuroprotective agents. gp120 induced a time- and concentration-dependent apoptotic cell death, which was caspase-3-mediated but caspase-1 independent, and was totally blocked by the irreversible caspase-3-like protease inhibitorN-acetyl-Asp-Glu-Val-Asp-chloromethylketone. Caspase-3 activation was observed only in neurons that internalize gp120, indicating that internalization is key to gp120 toxicity. Because brain-derived neurotrophic factor (BDNF) prevents caspase-3-mediated neuronal cell death, we examined whether BDNF could prevent gp120-mediated apoptosis. Preincubation of neurons with BDNF before the addition of gp120 reduced caspase-3 activation, and consequently rescued 80% of neurons from apoptosis. Most importantly, BDNF reduced the levels of CXC chemokine receptor-4 (CXCR4), a receptor that mediates HIV-1 gp120-induced apoptosis. This effect correlated with the ability of BDNF to reduce gp120 internalization and apoptosis. Moreover, BDNF blocked the neurotoxic effect of stromal-derived factor-1α, a natural ligand for CXCR4, further establishing a correlation between neuroprotection and downregulation of CXCR4. We propose that BDNF may be a valid therapy to slow down the progression of HIV/gp120-mediated neurotoxicity.
The Trophic Role of Oligodendrocytes in the Basal Forebrain
Authors: Dai Xudong , Lercher Lauren D. , Clinton Patricia M. , Du Yangzhou , Livingston Denise L. , Vieira Cristina , Yang Lu , Shen Michael M. , Dreyfus Cheryl F.
Published: April 2018

Traditionally, the primary function of oligodendrocytes (OLGs) in the CNS has been considered to be myelination. Here, we investigated whether OLGs may play a trophic role, particularly during development. Neurotrophin expression was assessed in postnatal day 7 basal forebrain (BF) OLGs, usingin situhybridization and detection of myelin basic protein. Nerve growth factor, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) mRNAs were revealed in OLGsin vivoand in culture. To determine whether OLGs support nearby neurons, we examined the influence of OLGs on BF cholinergic neurons. Neuronal function was enhanced by cocultured OLGs and OLG conditioned medium. Moreover, trophic effects of OLG conditioned medium were partially blocked by K252a, a trk tyrosine kinase inhibitor, and by neutralizing anti-BDNF or anti-NT-3 antisera, indicating that neurotrophins may mediate these effects, perhaps in concert with other signals. Our studies support a novel role for OLGs in providing local trophic support for neurons in the CNS.
Excitatory Effects of Orexin-A on Nucleus Tractus Solitarius Neurons Are Mediated by Phospholipase C and Protein Kinase C
Authors: Yang Bo , Samson Willis K. , Ferguson Alastair V.
Published: April 2018

Orexin (ORX)-A is a 33-amino acid peptide with demonstrated roles in the regulation of energy metabolism, autonomic control, and sleep. Orexin receptors (OXRs), OX1R and OX2R, and immunoreactive axons are present in the nucleus tractus solitarius (NTS). We demonstrated previously that bath application of ORX-A depolarizes NTS neurons through activation of a nonselective cationic conductance (NSCC) and inhibition of a sustained potassium current (IK). The present study examined the signaling pathways underlying the excitatory effects of ORX-A on NTS neurons using whole-cell patch-clamp recording techniques. Inclusion of guanosine 5′-O-(2-thiodiphosphate) in the internal pipette solution abolished the effects of ORX-A, confirming that the actions of ORX-A are mediated by G-protein-coupled receptors. The responses of ORX-A were also blocked by a phospholipase C (PLC) inhibitor, D609, and by a nonselective protein kinase (PK) inhibitor, H7, demonstrating the involvement of PLC and protein kinases. However, PKA appears not to play a role, because the depolarizing effects of ORX-A were still observed when the PKA inhibitor peptide (6–22) was included in the pipette solution, and bath application of 8-bromo-cAMP (a PKA agonist) was without effect on NTS neurons. In contrast, 12-O-tetradecanoylphorbol-13-acetate (a PKC agonist) depolarized NTS neurons, and bisindolylmaleimide (BIS), a PKC inhibitor, abolished the depolarizing effects of ORX-A. Finally, voltage-clamp experiments demonstrated that BIS also blocked the activation of NSCC and inhibition ofIKby ORX-A in NTS neurons. These results therefore show that the excitatory effects of ORX-A on NTS neurons are mediated through activation of the PLC–PKC–NSCC and -IKsignaling pathways, which probably result from OXR-coupled activation of Gq.
Acute Induction of Conserved Synaptic Signaling Pathways inDrosophilaMelanogaster
Authors: Hoeffer C. A. , Sanyal S. , Ramaswami M.
Published: April 2018

Analyses of early molecular and cellular events associated with long-term plasticity remain hampered inDrosophilaby the lack of an acute procedure to activate signal transduction pathways, gene expression patterns, and other early cellular events associated with long-term synaptic change. Here we describe the development and first use of such a technique. Bursts of neural activity induced inDrosophila comatosetsandCaP60AKumtsmutants, with conditional defects inN-ethylmaleimide-sensitive fusion factor 1 and sarco-endoplasmic reticulum Ca2+ATPase, respectively, result in persistent (>4 hr) activation of neuronal extracellular signal-regulated kinase (ERK). ERK activation at the larval neuromuscular junction coincides with rapid reduction of synaptic Fasciclin II; in soma, nuclear translocation of activated ERK occurs together with increased transcription of the immediate-early genes Fos and c/EBP (CCAAT element binding protein). The effect of “seizure-stimulation” on ERK activation requires neural activity and is mediated through activation of MEK (MAPK/erk kinase), the MAPKK (mitogen-activated protein kinase kinase) that functions upstream of ERK. Our results (1) provide direct proof for the conservation of synaptic signaling pathways in arthropods, (2) demonstrate the utility of a new genetic tool for analysis of synaptic plasticity inDrosophila, and (3) potentially enable new proteomic and genomic analyses of activity-regulated molecules in an important model organism.
Identification of aPax6-Dependent Epidermal Growth Factor Family Signaling Source at the Lateral Edge of the Embryonic Cerebral Cortex
Authors: Assimacopoulos Stavroula , Grove Elizabeth A. , Ragsdale Clifton W.
Published: April 2018

In an emerging model, area patterning of the mammalian cerebral cortex is regulated in part by embryonic signaling centers. Two have been identified: an anterior telencephalic source of fibroblast growth factors and the cortical hem, a medial structure expressing winglessint (WNT) and bone morphogenetic proteins. We describe a third signaling source, positioned as a mirror image of the cortical hem, along the lateral margin of the cortical primordium. The cortical antihem is identified by gene expression for three epidermal growth factor (EGF) family members, Tgfα, Neuregulin 1, and Neuregulin 3, as well as two other signaling molecules, Fgf7 and the secreted WNT antagonist Sfrp2. We find that the antihem is lost in mice homozygous for theSmall eye(Pax6) mutation and suggest the loss of EGF signaling at least partially explains defects in cortical patterning and cell migration inSmall eyemice.
Long-Term Effects of Permanent Vestibular Lesions on Hippocampal Spatial Firing
Authors: Russell Noah A. , Horii Arata , Smith Paul F. , Darlington Cynthia L. , Bilkey David K.
Published: April 2018

The hippocampus is thought to be important for spatial representation processes that depend on the integration of both self-movement and allocentric cues. The vestibular system is a particularly important source of self-movement information that may contribute to this spatial representation. To test the hypothesis that the vestibular system provides self-movement information to the hippocampus, rats were given either a bilateral labyrinthectomy (n= 6) or a sham surgery (n= 6), and at least 60 d after surgery hippocampal CA1 neurons were recorded extracellularly while the animals foraged freely in an open arena. Recorded cells were classified as complex spiking (n= 80) or noncomplex spiking (n= 33) neurons, and their spatial firing fields (place fields) were examined. The most striking effect of the lesion was that it appeared to completely abolish location-related firing. The results of this and previous studies provide converging evidence demonstrating that vestibular information is processed by the hippocampus. The disruption of the vestibular input to the hippocampus may interfere with the reconciliation of internal self-movement signals with the changes to the external sensory inputs that occur as a result of that movement. This would disrupt the ability of the animal to integrate allocentric and egocentric information into a coherent representation of space.