bluuebunny/crossref_metadata_2025 huggingface dataset:
Ciliary Neurotrophic Factor and Stress Stimuli Activate the Jak-STAT Pathway in Retinal Neurons and Glia
Authors: Peterson Ward M. , Wang Quan , Tzekova Roumiana , Wiegand Stanley J.
Published: April 2018

Ciliary neurotrophic factor (CNTF) is pleiotrophic for central, peripheral, and sensory neurons. In the mature retina, CNTF treatment enhances survival of retinal ganglion and photoreceptor cells exposed to otherwise lethal perturbation. To understand its mechanism of actionin vivo,the adult rat retina was used as a model to investigate CNTF-mediated activation of Janus kinase/signal transducer and activator of transcription (Jak-STAT) and ras-mitogen activated protein kinase (ras-MAPK). Intravitreal injection of Axokine, an analog of CNTF, phosphorylates STAT3 and MAPK and produces delayed upregulation of total STAT3 and STAT1 protein in rat retina. Activated STAT3 is predominantly localized in nuclei of retinal Müller (glial) cells, ganglion cells, and astrocytes, but not in photoreceptors. Although CNTF α-receptor (CNTFRα) mRNA and protein are localized predominantly if not exclusively in retinal neurons, coincident CNTF-mediated STAT3 signaling was observed in both glia and neurons. CNTF-induced activation of Jak-STAT signaling prompted us to investigate STAT3 phosphorylation after a variety of stress-mediated, conditioning stimuli. We show that STAT3 is activated in the retina after exposure to subtoxic bright light, mechanical trauma, and systemic administration of the α2-adrenergic agonist xylazine, all of which have been shown previously to condition photoreceptors to resist light-induced degeneration. These results demonstrate that CNTF directly stimulates Jak-STAT and ras-MAPK cascadesin vivoand strongly suggest that STAT3 signaling is an underlying component of neural responsiveness to stress stimuli. The observation that CNTF activates STAT3 in ganglion cells, but not in photoreceptors, suggests that Jak-STAT signaling influences neuronal survival via both direct and indirect modes of action.
Role of Founder Cell Deficit and Delayed Neuronogenesis in Microencephaly of the Trisomy 16 Mouse
Authors: Haydar Tarik F. , Nowakowski Richard S. , Yarowsky Paul J. , Krueger Bruce K.
Published: April 2018

Development of the neocortex of the trisomy 16 (Ts16) mouse, an animal model of Down syndrome (DS), is characterized by a transient delay in the radial expansion of the cortical wall and a persistent reduction in cortical volume. Here we show that at each cell cycle during neuronogenesis, a smaller proportion of Ts16 progenitors exit the cell cycle than do control, euploid progenitors. In addition, the cell cycle duration was found to be longer in Ts16 than in euploid progenitors, the Ts16 growth fraction was reduced, and an increase in apoptosis was observed in both proliferative and postmitotic zones of the developing Ts16 neocortical wall. Incorporation of these changes into a model of neuronogenesis indicates that they are sufficient to account for the observed delay in radial expansion. In addition, the number of neocortical founder cells, i.e., precursors present just before neuronogenesis begins, is reduced by 26% in Ts16 mice, leading to a reduction in overall cortical size at the end of Ts16 neuronogenesis. Thus, altered proliferative characteristics during Ts16 neuronogenesis result in a delay in the generation of neocortical neurons, whereas the founder cell deficit leads to a proportional reduction in the overall number of neurons. Such prenatal perturbations in either the timing of neuron generation or the final number of neurons produced may lead to significant neocortical abnormalities such as those found in DS.
Vertical Shifts in Self-Administration Dose–Response Functions Predict a Drug-Vulnerable Phenotype Predisposed to Addiction
Authors: Piazza Pier Vincenzo , Deroche-Gamonent Véronique , Rouge-Pont Françoise , Le Moal Michel
Published: April 2018

The role of individual differences in the etiology of addiction is a very controversial issue. Neuroendocrine phenotypes that are able to predispose an individual to the development of drug intake have been identified previously. However, such information has been gathered by comparing individuals who differ in their sensitivity to low doses of the drug. Consequently, it remains unclear whether a phenotype predicting a higher sensitivity to low drug doses would be relevant in environmental conditions, such as the ones encountered by humans in which high drug doses are available. In this report, we studied dose–response, dose–intake, and ratio–intake functions for intravenous cocaine self-administration in the laboratory rat. We show that individual differences in drug self-administration originate from vertical shift in the dose–response function. Thus, no matter the dose, drug intake is very high in some “vulnerable” subjects and very low in other “resistant” ones. Vulnerable subjects, the upward shifted ones, would then have a higher chance to develop drug abuse also when high drug doses are available. In conclusion, these results provide a solid foundation for the existence of a drug-vulnerable phenotype relevant for the etiology of addiction.
Reflex Excitability Regulates Prepulse Inhibition
Authors: Schicatano Edward J. , Peshori Kavita R. , Gopalaswamy Ramesh , Sahay Eva , Evinger Craig
Published: April 2018

Presentation of a weak stimulus, a prepulse, before a reflex-evoking stimulus decreases the amplitude of the reflex response relative to reflex amplitude evoked without a preceding prepulse. For example, presenting a brief tone before a trigeminal blink-eliciting stimulus significantly reduces reflex blink amplitude. A common explanation of such data are that sensory processing of the prepulse modifies reflex circuit behavior. The current study investigates the converse hypothesis that the intrinsic characteristics of the reflex circuit rather than prepulse processing determine prepulse modification of trigeminal and acoustic reflex blinks.

Unilateral lesions of substantia nigra pars compacta neurons created rats with hyperexcitable trigeminal reflex blinks but normally excitable acoustic reflex blinks. In control rats, presentation of a prepulse reduced the amplitude of both trigeminal and acoustic reflex blinks. In 6-OHDA-lesioned rats, however, the same acoustic prepulse facilitated trigeminal reflex blinks but inhibited acoustic reflex blinks. The magnitude of prepulse modification correlated with reflex excitability.

Humans exhibited the same pattern of prepulse modification. An acoustic prepulse facilitated the trigeminal reflex blinks of subjects with hyperexcitable trigeminal reflex blinks caused by Parkinson's disease. The same prepulse inhibited trigeminal reflex blinks of age-matched control subjects. Prepulse modification also correlated with trigeminal reflex blink excitability. These data show that reflex modification by a prepulse reflects the intrinsic characteristics of the reflex circuit rather than an external adjustment of the reflex circuit by the prepulse.
Dopamine Activates Masculine Sexual Behavior Independent of the Estrogen Receptor α
Authors: Wersinger Scott R. , Rissman Emilie F.
Published: April 2018

Estrogen receptor α (ERα) is believed to be a critical part of the regulatory processes involved in normal reproduction and sexual behavior. However, in this study we show the ERα is not required for display of masculine sexual behavior. Male and female, ERα knock-out (ERαKO) and wild-type mice were gonadectomized and implanted with testosterone. Sexual behavior and social preferences were tested after injection of the dopamine agonist, apomorphine (APO), or vehicle. All wild-type mice showed normal masculine behavior, including mounts and pelvic thrusts in females, and ejaculation in males. In agreement with past reports, ERαKO mice, given vehicle, failed to show mating behavior. Yet, ERαKO males given APO showed masculine copulatory behavior and chemoinvestigatory behavior directed at females. ERαKO females, treated with APO, mounted and thrusted when tested with receptive females. HPLC revealed that wild-type and ERαKO mice had equivalent catecholamine content in brain regions associated with masculine sexual behavior. These data show that the ERα is not essential during development or adulthood for the expression of masculine sexual behavior in mice. Moreover, dopamine can activate sexual behavior via a mechanism that either acts on an ER other than ERα or via an estrogen-independent pathway.
Control of Response Selection by Reinforcer Value Requires Interaction of Amygdala and Orbital Prefrontal Cortex
Authors: Baxter Mark G. , Parker Amanda , Lindner Caroline C. C. , Izquierdo Alicia D. , Murray Elisabeth A.
Published: April 2018

Goal-directed actions are guided by expected outcomes of those actions. Humans with bilateral damage to ventromedial prefrontal cortex, or the amygdala, are deficient in their ability to use information about positive and negative outcomes to guide their choice behavior. Similarly, rats and monkeys with orbital prefrontal or amygdala damage have been found to be impaired in their responses to changing values of outcomes. In the present study, we tested whether direct, functional interaction between the amygdala and the orbital prefrontal cortex is necessary for guiding behavior based on expected outcomes. Unlike control monkeys, rhesus monkeys with surgical disconnection of these two structures, achieved by crossed unilateral lesions of the amygdala in one hemisphere and orbital prefrontal cortex in the other, combined with forebrain commissurotomy, were unable to adjust their choice behavior after a change in the outcome (here, a reduction in the value of a particular reinforcer). The lesions did not affect motivation to work for a food reinforcer, or food preferences, per se. Hence, the amygdala and orbital prefrontal cortex act as part of an integrated neural system guiding decision-making and adaptive response selection.
Mutations of theCaenorhabditis elegansBrain-Specific Inorganic Phosphate Transportereat-4Affect Habituation of the Tap–Withdrawal Response without Affecting the Response Itself
Authors: Rankin Catharine H. , Wicks Stephen R.
Published: April 2018

The studies reported here were designed to investigate the role of the mutationeat-4in the response to tap and in habituation in the nematodeCaenorhabditis elegans. InC. elegans eat-4has been found to affect a number of glutamatergic pathways. It has been hypothesized to positively regulate glutaminase activity and therefore glutamatergic neurotransmission. In theeat-4(ky5)loss-of-function worms, there is presumably insufficient glutamate available for sustained transmission. In the experiments reported hereeat-4worms showed no differences from wild-type in the magnitude of response to a single tap, indicating that the neural circuit underlying the response was intact and functional in the mutant worms. However, wheneat-4worms were given repeated taps the resulting habituation was different from that seen in wild-type worms:eat-4worms habituate more rapidly and recover more slowly than wild-type worms at all interstimulus intervals tested. In addition,eat-4worms do not show dishabituation. The same transgene rescues pharyngeal activity defects and both the habituation and dishabituation deficits seen in theeat-4worms. Our results suggest that neurotransmitter regulation plays a role in habituation and may play a role in dishabituation.
Opioid Modulation of Recurrent Excitation in the Hippocampal Dentate Gyrus
Authors: Terman Gregory W. , Drake Carrie T. , Simmons Michele L. , Milner Teresa A. , Chavkin Charles
Published: April 2018

κ opioid receptor activation inhibits granule cell-mediated excitatory neurotransmission in the hippocampal formation via a decrease in glutamate release from both perforant path and mossy fiber terminals. We now report a third, anatomically and pharmacologically distinct site of such κ opioid inhibition within the hippocampus. Granule cell population responses to selective stimulation of an excitatory hilar pathway were decreased by the κ1opioid receptor agonist U69,593, an effect blocked by the κ1antagonist norbinaltorphimine. U69,593 also inhibited hilar path induced long-term potentiation (LTP) of granule cell responses. LTP in this pathway was also blocked by the NMDA receptor antagonistd-2-amino-5-phosphonovalerate, unlike granule cell mossy fiber LTP in CA3.

The κ opioid peptide dynorphin is present in hilar mossy fiber collaterals. Ultrastructural analysis of these collaterals demonstrated dynorphin-containing vesicles in asymmetric synapses formed between axon terminals and granule cell dendrites, suggesting direct granule cell–granule cell connections. Evoked release of endogenous dynorphin within the hilus was effective in reducing hilar excitation of granule cells, although this release, in contrast to the release of dynorphin in the dentate molecular layer, was not dependent on L-type calcium channels.

No hilar path excitation was observed in the absence of bicuculline, suggesting a strong GABAA-mediated inhibition of this pathway. However, hilar path activity could be seen after LTP, with or without bicuculline. Thus, κ opioids can inhibit granule cell recurrent excitation, likely via effects on excitatory mossy fiber collaterals. Such collaterals are thought to be important in mediating temporal lobe epilepsy.
Neuroprotective Effects of Creatine in a Transgenic Mouse Model of Huntington's Disease
Authors: Ferrante Robert J. , Andreassen Ole A. , Jenkins Bruce G. , Dedeoglu Alpaslan , Kuemmerle Stefan , Kubilus James K. , Kaddurah-Daouk Rima , Hersch Steven M. , Beal M. Flint
Published: April 2018

Huntington's disease (HD) is a progressive neurodegenerative illness for which there is no effective therapy. We examined whether creatine, which may exert neuroprotective effects by increasing phosphocreatine levels or by stabilizing the mitochondrial permeability transition, has beneficial effects in a transgenic mouse model of HD (line 6/2). Dietary creatine supplementation significantly improved survival, slowed the development of brain atrophy, and delayed atrophy of striatal neurons and the formation of huntingtin-positive aggregates in R6/2 mice. Body weight and motor performance on the rotarod test were significantly improved in creatine-supplemented R6/2 mice, whereas the onset of diabetes was markedly delayed. Nuclear magnetic resonance spectroscopy showed that creatine supplementation significantly increased brain creatine concentrations and delayed decreases inN-acetylaspartate concentrations. These results support a role of metabolic dysfunction in a transgenic mouse model of HD and suggest a novel therapeutic strategy to slow the pathological process.
Probing Fundamental Aspects of Synaptic Transmission with Strontium
Authors: Xu-Friedman Matthew A. , Regehr Wade G.
Published: April 2018

Strontium is capable of supporting synaptic transmission, but release is dramatically different from that evoked in calcium. By measuring presynaptic strontium levels, we gain insight into the actions of strontium, which has implications for the identification of molecules involved in different aspects of synaptic transmission. We examined presynaptic divalent levels and synaptic release at the granule cell to stellate cell synapse in mouse cerebellar slices. We find that the prolonged duration of release and paired-pulse facilitation in the presence of strontium can be accounted for by the slower removal of strontium from the presynaptic terminal. Phasic and delayed release are both driven by strontium less effectively than by calcium, indicating that a heightened sensitivity to strontium is not a feature of the binding sites involved in facilitation and delayed release. We also find that the cooperativity for phasic release is 1.7 for strontium compared with 3.2 for calcium, suggesting that differential binding may help to identify the calcium sensor involved in phasic release.
In CA1 Pyramidal Neurons of the Hippocampus Protein Kinase C Regulates Calcium-Dependent Inactivation of NMDA Receptors
Authors: Lu Wei-Yang , Jackson Michael F. , Bai Donglin , Orser Beverley A. , MacDonald John F.
Published: April 2018

The NMDA subtype of the glutamate-gated channel exhibits a high permeability to Ca2+. The influx of Ca2+through NMDA channels is limited by a rapid and Ca2+/calmodulin (CaM)-dependent inactivation that results from a competitive displacement of cytoskeleton-binding proteins from the NR1 subunit of the receptor by Ca2+/CaM (Zhang et al., 1998; Krupp et al., 1999). The C terminal of this subunit can be phosphorylated by protein kinase C (PKC) (Tingley et al., 1993). The present study sought to investigate whether PKC regulates Ca2+-dependent inactivation of the NMDA channel in hippocampal neurons. Activation of endogenous PKC by 4β-phorbol 12-myristate 13-acetate enhanced peak (Ip) and depressed steady-state (Iss) NMDA-evoked currents, resulting in a reduction in the ratio of these currents (Iss/Ip). We demonstrated previously that PKC activity enhancesIPvia a sequential activation of the focal adhesion kinase cell adhesion kinase β/proline-rich tyrosine kinase 2 (CAKβ/Pyk2) and the nonreceptor tyrosine kinase Src (Huang et al., 1999; Lu et al., 1999). Here, we report that the PKC-induced depression ofIssis unrelated to the PKC/CAKβ/Src-signaling pathway but depends on the concentration of extracellular Ca2+. Intracellular applications of CaM reducedIss/Ipand occluded the Ca2+-dependent effect of phorbol esters onIss.Moreover, increasing the concentration of intracellular Ca2+buffer or intracellular application of the inhibitory CaM-binding peptide (KY9) greatly reduced the phorbol ester-induced depression ofIss. Taken together, these results suggest that PKC enhances Ca2+/CaM-dependent inactivation of the NMDA channel, most likely because of a phosphorylation-dependent regulation of interactions between receptor subunits, CaM, and other postsynaptic density proteins.
Presynaptic Protein Kinase Activity Supports Long-Term Potentiation at Synapses Between Individual Hippocampal Neurons
Authors: Pavlidis Paul , Montgomery Johanna , Madison Daniel V.
Published: April 2018

Simultaneous microelectrode recording from two individual synaptically connected neurons enables the direct analysis of synaptic transmission and plasticity at a minimal synaptic connection. We have recorded from pairs of CA3 pyramidal neurons in organotypic hippocampal slices to examine the properties of long-term potentiation (LTP) at such minimal connections. LTP in minimal connections was found to be identical to the NMDA-dependent LTP expressed by CA3–CA1 synapses, demonstrating this system provides a good model for the study of the mechanisms of LTP expression. The LTP at minimal synaptic connections does not behave as a simple increase in transmitter release probability, because the amplitude of unitary EPSCs can increase several-fold, unlike what is observed when release probability is increased by raising extracellular calcium. Taking advantage of the relatively short axon connecting neighboring CA3 neurons, we found it feasible to introduce pharmacological agents to the interior of presynaptic terminals by injection into the presynaptic soma and have used this technique to investigate presynaptic effects on basal transmission and LTP. Presynaptic injection of nicotinamide reduced basal transmission, but LTP in these pairs was essentially normal. In contrast, presynaptic injection of H-7 significantly depressed LTP but not basal transmission, indicating a specific role of presynaptic protein kinases in LTP. These results demonstrate that pharmacological agents can be directly introduced into the presynaptic cell and that a purely presynaptic perturbation can alter this plasticity.
C-Terminal Truncation of NR2A Subunits Impairs Synaptic But Not Extrasynaptic Localization of NMDA Receptors
Authors: Steigerwald Frank , Schulz Torsten W. , Schenker Leslie T. , Kennedy Mary B. , Seeburg Peter H. , Köhr Georg
Published: April 2018

NMDA receptors interact via the extended intracellular C-terminal domain of the NR2 subunits with constituents of the postsynaptic density for purposes of retention, clustering, and functional regulation at central excitatory synapses. To examine the role of the C-terminal domain of NR2A in the synaptic localization and function of NR2A-containing NMDA receptors in hippocampal Schaffer collateral–CA1 pyramidal cell synapses, we analyzed mice which express NR2A only in its C-terminally truncated form. In CA1 cell somata, the levels, activation, and deactivation kinetics of extrasynaptic NMDA receptor channels were comparable in wild-type and mutant NR2AΔC/ΔCmice. At CA1 cell synapses, however, the truncated receptors were less concentrated than their full-length counterparts, as indicated by immunodetection in cultured neurons, synaptosomes, and postsynaptic densities. In the mutant, the NMDA component of evoked EPSCs was reduced in a developmentally progressing manner and was even more reduced in miniature EPSCs (mEPSCs) elicited by spontaneous glutamate release. Moreover, pharmacologically isolated NMDA currents evoked by synaptic stimulation had longer latencies and displayed slower rise and decay times, even in the presence of an NR2B-specific antagonist. These data strongly suggest that the C-terminal domain of NR2A subunits is important for the precise synaptic arrangement of NMDA receptors.
Potentiation of NMDA Receptor Function by the Serine Protease Thrombin
Authors: Gingrich Melissa B. , Junge Candice E. , Lyuboslavsky Polina , Traynelis Stephen F.
Published: April 2018

Although serine proteases and their receptors are best known for their role in blood coagulation and fibrinolysis, the CNS expresses many components of an extracellular protease signaling system including the protease-activated receptor-1 (PAR1), for which thrombin is the most effective activator. In this report we show that activation of PAR1 potentiates hippocampal NMDA receptor responses in CA1 pyramidal cells by 2.07 ± 0.27-fold (mean ± SEM). Potentiation of neuronal NMDA receptor responses by thrombin can be blocked by thrombin and a protein kinase inhibitor, and the effects of thrombin can be mimicked by a peptide agonist (SFLLRN) that activates PAR1. Potentiation of the NMDA receptor by thrombin in hippocampal neurons is significantly attenuated in mice lacking PAR1. Although high concentrations of thrombin can directly cleave both native and recombinant NR1 subunits, the thrombin-induced potentiation we observe is independent of NMDA receptor cleavage. Activation of recombinant PAR1 also potentiates recombinant NR1/NR2A (1.7 ± 0.06-fold) and NR1/NR2B (1.41 ± 0.11-fold) receptor function but not NR1/NR2C or NR1/NR2D receptor responses. PAR1-mediated potentiation of recombinant NR1/NR2A receptors occurred after activation with as little as 300 pmthrombin. These data raise the intriguing possibility that potentiation of neuronal NMDA receptor function after entry of thrombin or other serine proteases into brain parenchyma during intracerebral hemorrhage or extravasation of plasma proteins during blood–brain barrier breakdown may exacerbate glutamate-mediated cell death and possibly participate in post-traumatic seizure. Furthermore, the ability of neuronal protease signaling to control NMDA receptor function may also have roles in normal brain development.
Axonal Regulation of Schwann Cell Proliferation and Survival and the Initial Events of Myelination Requires PI 3-Kinase Activity
Authors: Maurel Patrice , Salzer James L.
Published: April 2018

In this report, we have investigated the signaling pathways that are activated by, and mediate the effects of, the neuregulins and axonal contact in Schwann cells. Phosphatidylinositol 3-kinase (PI 3-kinase) and mitogen-activated protein kinase kinase (MAPK kinase) are strongly activated in Schwann cells by glial growth factor (GGF), a soluble neuregulin, and by contact with neurite membranes; both kinase activities are also detected in Schwann cell-DRG neuron cocultures. Inhibition of the PI 3-kinase, but not the MAP kinase, pathway reversibly inhibited Schwann cell proliferation induced by GGF and neurites. Cultured Schwann cells undergo apoptosis after serum deprivation and can be rescued by GGF or contact with neurites; these survival effects were also blocked by inhibition of PI 3-kinase. Finally, we have examined the role of these signaling pathways in Schwann cell differentiation in cocultures. At early stages of coculture, inhibition of PI 3-kinase, but not MAPK kinase, blocked Schwann cell elongation and subsequent myelination but did not affect laminin deposition. Later, after Schwann cells established a one-to-one relationship with axons, inhibition of PI 3-kinase did not block myelin formation, but the myelin sheaths that formed were shorter, and the rate of myelin protein accumulation was markedly decreased. PI 3-kinase inhibition had no observable effect on the maintenance of myelin sheaths in mature myelinated cocultures. These results indicate that activation of PI 3-kinase by axonal factors, including the neuregulins, promotes Schwann cell proliferation and survival and implicate PI 3-kinase in the early events of myelination.
Adult Learning Deficits after Neonatal Exposure tod-Methamphetamine: Selective Effects on Spatial Navigation and Memory
Authors: Vorhees Charles V. , Inman-Wood Sandra L. , Morford LaRonda L. , Broening Harry W. , Fukumura Masao , Moran Mary S.
Published: April 2018

The effects of neonatald-methamphetamine (MA) treatment on cued and spatial learning and memory were investigated. MA was administered to neonatal rats on postnatal days 11–20. All groups received four subcutaneous injections per day. Group MA40–4 received 40 mg · kg−1 · d−1of MA in four divided doses (10 mg/kg per injection). Group MA40–2 received 40 mg · kg−1 · d−1of MA in two divided (20 mg/kg/injection) and saline for the other two injections per day. Controls received saline for four injections per day. As adults, both MA groups showed no differences in swimming ability in a straight swimming channel. The MA40–4 group showed no differences in cued learning, but was impaired in hidden platform learning in the Morris water maze on acquisition. They also showed reduced memory performance on probe trials. Similar trends were seen on reversal learning and reversal probe trials. Reduced platform-size learning trials caused spatial learning impairments to re-emerge in the MA40–4 group. The MA40–2 group showed no differences in straight channel swimming, but was slower at finding the visible platform during cued learning. They were also impaired during acquisition and memory trials in the Morris hidden platform maze. They showed a similar trend on reversal learning and memory trials, but were not different during reduced platform-size learning trials. When the MA40–2 group's performance on hidden platform learning and memory trials was adjusted for cued trial performance, the spatial learning deficits remained. Deficits of spatial learning and memory are a selective effect of neonatal methamphetamine treatment irrespective of other learning and performance variables.
Local Disparity Not Perceived Depth Is Signaled by Binocular Neurons in Cortical Area V1 of the Macaque
Authors: Cumming Bruce G. , Parker Andrew J.
Published: April 2018

Binocular neurons that are closely related to depth perception should respond selectively for stimuli eliciting an appropriate depth sensation. To separate perceived depth from local disparity within the receptive field, sinusoidal luminance gratings were presented within a circular aperture. The disparity of the aperture was coupled to that of the grating, thereby rendering unambiguous the psychophysical matching between repeating cycles of the grating. In cases in which the stimulus disparity differs by one horizontal period of the grating, the portion of the grating that locally covers a receptive field is binocularly identical, but the depth sensation is very different because of the aperture. For 117 disparity-selective V1 neurons tested in two monkeys, the overwhelming majority responded equally well to configurations that were locally identical but led to different perceptions of depth. Because the psychophysical sensation is not reflected in the firing rate of V1 neurons, the signals that make stereo matches explicit are most likely elaborated in extrastriate cortex.
Alternative Splicing in the Cytoplasmic II–III Loop of the N-Type Ca Channel α1BSubunit: Functional Differences Are β Subunit-Specific
Authors: Pan Jennifer Qian , Lipscombe Diane
Published: April 2018

Structural diversity of voltage-gated Ca channels underlies much of the functional diversity in Ca signaling in neurons. Alternative splicing is an important mechanism for generating structural variants within a single gene family. In this paper, we show the expression pattern of an alternatively spliced 21 amino acid encoding exon in the II–III cytoplasmic loop region of the N-type Ca channel α1Bsubunit and assess its functional impact. Exon-containing α1BmRNA dominated in sympathetic ganglia and was present in ∼50% of α1BmRNA in spinal cord and caudal regions of the brain and in the minority of α1BmRNA in neocortex, hippocampus, and cerebellum (<20%). The II–III loop exon affected voltage-dependent inactivation of the N-type Ca channel. Steady-state inactivation curves were shifted to more depolarized potentials without affects on either the rate or voltage dependence of channel opening. Differences in voltage-dependent inactivation between α1Bsplice variants were most clearly manifested in the presence of Ca channel β1bor β4, rather than β2aor β3, subunits. Our results suggest that exon-lacking α1Bsplice variants that associate with β1band β4subunits will be susceptible to voltage-dependent inactivation at voltages in the range of neuronal resting membrane potentials (−60 to −80 mV). In contrast, α1Bsplice variants that associate with either β2aor β3subunits will be relatively resistant to inactivation at these voltages. The potential to mix and match multiple α1Bsplice variants and β subunits probably represents a mechanism for controlling the plasticity of excitation–secretion coupling at different synapses.
Bidirectional Modulation of Exocytosis by Angiotensin II Involves Multiple G-Protein-Regulated Transduction Pathways in Chromaffin Cells
Authors: Teschemacher Anja G. , Seward Elizabeth P.
Published: April 2018

Angiotensin II (AngII) receptors couple to a multitude of different types of G-proteins resulting in activation of numerous signaling pathways. In this study we examined the consequences of this promiscuous G-protein coupling on secretion. Chromaffin cells were voltage-clamped at −80 mV in perforated-patch configuration, and Ca2+-dependent exocytosis was evoked with brief voltage steps to +20 mV. Vesicle fusion was monitored by changes in membrane capacitance (ΔCm), and released catecholamine was detected with single-cell amperometry. Ca2+signaling was studied by recording voltage-dependent Ca2+currents (ICa) and by measuring intracellular Ca2+([Ca2+]i) with fura-2 AM.

AngII inhibitedICa(IC50= 0.3 nm) in a voltage-dependent, pertussis toxin (PTX)-sensitive manner consistent with Gi/o-protein coupling to Ca2+channels. ΔCmwas modulated bi-directionally; subnanomolar AngII inhibited depolarization-evoked exocytosis, whereas higher concentrations, in spite ofICainhibition, potentiated ΔCmfivefold (EC50= 3.4 nm). Potentiation of exocytosis by AngII involved activation of phospholipase C (PLC) and Ca2+mobilization from internal stores. PTX treatment did not affect AngII-dependent Ca2+mobilization or facilitation of exocytosis. However, protein kinase C (PKC) inhibitors decreased the facilitatory effects but not the inhibitory effects of AngII on stimulus-secretion coupling. The AngII type 1 receptor (AT1R) antagonist losartan blocked both inhibition and facilitation of secretion by AngII. The results of this study show that activation of multiple types of G-proteins and transduction pathways by a single neuromodulator acting through one receptor type can produce concentration-dependent, bi-directional regulation of exocytosis.
Ultrastructural Localization of Nitrotyrosine within the Caudate-Putamen Nucleus and the Globus Pallidus of Normal Rat Brain
Authors: Bolan Elizabeth A. , Gracy K. Noelle , Chan June , Trifiletti Rosario R. , Pickel Virginia M.
Published: April 2018

Nitration of protein tyrosine residues by nitric oxide (NO)-derived reactive species results in the production of stable nitrotyrosine (NT) moieties that are immunochemically detectable in many regions of normal brain and enriched in those areas containing constitutive nitric oxide synthase (cNOS). These include the caudate-putamen nucleus (CPN) and the globus pallidus, which receives major inhibitory input from the CPN. To determine the functional sites for NT production in these critical motor nuclei, we examined the electron microscopic immunocytochemical localization of NT and cNOS in rat brain. In the CPN, NT was localized to the somata and dendrites of cNOS-containing interneurons and spiny neurons, some of which received input from cNOS-labeled terminals. The NT immunoreactivity was most prevalent on outer mitochondrial membranes and nearby segments of the plasma membranes in dendrites and within asymmetric synapses on dendritic spines. In the CPN and globus pallidus, there was also a prominent labeling of NT in astrocytic processes, small axons, and tubulovesicles and/or synaptic vesicles in axon terminals. These terminals formed mainly asymmetric synapses in the CPN and inhibitory-type synapses in the globus pallidus where they often apposed cNOS-containing terminals that also formed asymmetric, excitatory-type synapses. Our results suggest that NT is generated by mechanisms requiring the dual actions of excitatory transmitters and NO derived either from interneurons in the CPN or from excitatory afferents in the globus pallidus. The findings also implicate NT in the physiological actions of NO within the striatal circuitry and, particularly, in striatopallidal neurons severely affected in Huntington's disease.
Calcium-Dependent Persistent Facilitation of Spike Backpropagation in the CA1 Pyramidal Neurons
Authors: Tsubokawa Hiroshi , Offermanns Stefan , Simon Melvin , Kano Masanobu
Published: April 2018

Sodium-dependent action potentials initiated near the soma are known to backpropagate over the dendrites of CA1 pyramidal neurons in an activity-dependent manner. Consequently, later spikes in a train have smaller amplitude when recorded in the apical dendrites. We found that depolarization and resultant Ca2+influx into dendrites caused a persistent facilitation of spike backpropagation. Dendritic patch recordings were made from CA1 pyramidal neurons in mouse hippocampal slices under blockade of fast excitatory and inhibitory synaptic inputs. Trains of 10 backpropagating action potentials induced by antidromic stimulation showed a clear decrement in the amplitude of later spikes when recorded in the middle apical dendrites. After several depolarizing current pulses, the amplitude of later spikes increased persistently, and all spikes in a train became almost equal in size. BAPTA (10 mm) contained in the pipette or low-Ca2+perfusing solution abolished this depolarization-induced facilitation, indicating that Ca2+influx is required. This facilitation was present in Gαqknock-out mice that lack the previously reported muscarinic receptor-mediated enhancement of spike backpropagation. Therefore, these two forms of facilitation are clearly distinct in their intracellular mechanisms. Intracellular injection of either calmodulin binding domain (100 μm) or Ca2+/calmodulin-kinase II (CaMKII) inhibitor 281–301 (10 μm) blocked the depolarization-induced facilitation. Bath application of a membrane-permeable CaMKII inhibitor KN-93 (10 μm) also blocked the facilitation, but KN-92 (10 μm), an inactive isomer of KN-93, had no effect. These results suggest that increases in [Ca2+]icause persistent facilitation of spike backpropagation in the apical dendrite of CA1 pyramidal neuron by CaMKII-dependent mechanisms.
Active Zones on Motor Nerve Terminals Contain α3β1 Integrin
Authors: Cohen Monroe W. , Hoffstrom Benjamin G. , DeSimone Douglas W.
Published: April 2018

Active zones are the sites along nerve terminals where synaptic vesicles dock and undergo calcium-dependent exocytosis during synaptic transmission. Here we show, by immunofluorescent staining with antibodies generated againstXenopus laevisintegrins, that α3β1 integrin is concentrated at the active zones ofXenopusmotor nerve terminals. Because integrins can link extracellular matrix molecules to cytoskeletal elements and participate in the formation of signaling complexes, the localization of integrin at active zones suggests that it may play a role in the adhesion of the nerve terminals to the synaptic basal lamina, in the formation and maintenance of active zones, and in some of the events associated with calcium-dependent exocytosis of neurotransmitter. Our findings also indicate that the integrin composition of the terminal Schwann cells differs from that of the motor nerve terminals, and this may account at least in part for differences in their adhesiveness to the synaptic basal lamina.
Intracellular Ca2+Dynamics During Spontaneous and Evoked Activity of Leech Heart Interneurons: Low-Threshold Ca Currents and Graded Synaptic Transmission
Authors: Ivanov Andrei I. , Calabrese Ronald L.
Published: April 2018

In oscillatory neuronal networks that pace rhythmic behavior, Ca2+entry through voltage-gated Ca channels often supports bursting activity and mediates graded transmitter release. We monitored simultaneously membrane potential and/or ionic currents and changes of Ca fluorescence (using the fluorescence indicator Ca Orange) in spontaneously active and experimentally manipulated oscillator heart interneurons in the leech. We show that changes in Ca fluorescence in these interneurons during spontaneous bursting and evoked activity reflect the slow wave of that activity and that these changes in Ca fluorescence are mediated by Ca2+entry primarily through low-threshold Ca channels. Spatial and temporal maps of changes in Ca fluorescence indicate that these channels are widely distributed over the neuritic tree of these neurons. We establish a correlation between the amount of transmitter released, as estimated by the integral of the postsynaptic current, and the change in Ca fluorescence. In experiments in which we were able to record presynaptic low-threshold Ca currents, associated IPSCs, and presynaptic changes in Ca fluorescence from fine neuritic branches of heart interneurons near their region of synaptic contact with their contralateral partner, there was a close association between the rise in Ca fluorescence and the rise of the postsynaptic conductance. The changes in Ca fluorescence that we record at the end of fine neuritic branches appear to reflect changes in [Ca2+]ithat mediate graded synaptic release in leech heart interneurons. These results indicate that widely distributed low-threshold Ca currents play an important role in generating rhythmic activity and in mediating graded transmitter release.
Critical Period for Activity-Dependent Synapse Elimination in Developing Cerebellum
Authors: Kakizawa Sho , Yamasaki Miwako , Watanabe Masahiko , Kano Masanobu
Published: April 2018

Synapse elimination is considered to be the final step in neural circuit formation, by causing refinement of redundant connections formed at earlier developmental stages. The developmental loss of climbing fiber innervation from cerebellar Purkinje cells is an example of such synapse elimination. It has been suggested that NMDA receptors are involved in the elimination of climbing fiber synapses. In the present study, we probed the NMDA receptor-dependent period of climbing fiber synapse elimination by using daily intraperitoneal injections of the NMDA receptor antagonist MK-801. We found that blockade of NMDA receptors during postnatal day 15 (P15) and P16, but not before or after this period, resulted in a higher incidence of multiple climbing fiber innervation and caused a mild but persistent loss of motor coordination. Neither basic synaptic functions nor cerebellar morphology were affected by this manipulation. Chronic local application of MK-801 to the cerebellum during P15 and P16 also yielded a higher incidence of multiple climbing fiber innervation. During P15–P16, large NMDA receptor-mediated EPSCs were detected at the mossy fiber–granule cell synapse, but not at the parallel fiber–Purkinje cell or climbing fiber–Purkinje cell synapse. It is therefore likely that the NMDA receptors located at the mossy fiber–granule cell synapse mediate signals leading to the elimination of surplus climbing fibers. These results suggest that an NMDA receptor-dependent phase of climbing fiber synapse elimination lasts 2 d at most. During this phase, the final refinement of climbing fiber synapses occurs, and disruption of this process leads to permanent impairment of cerebellar function.
Slit Inhibition of Retinal Axon Growth and Its Role in Retinal Axon Pathfinding and Innervation Patterns in the Diencephalon
Authors: Ringstedt Thomas , Braisted Janet E. , Brose Katja , Kidd Thomas , Goodman Corey , Tessier-Lavigne Marc , O'Leary Dennis D. M.
Published: April 2018

We have analyzed the role of the Slit family of repellent axon guidance molecules in the patterning of the axonal projections of retinal ganglion cells (RGCs) within the embryonic rat diencephalon and whether the slits can account for a repellent activity for retinal axons released by hypothalamus and epithalamus. At the time RGC axons extend over the diencephalon,slit1andslit2are expressed in hypothalamus and epithalamus but not in the lateral part of dorsal thalamus, a retinal target.slit3expression is low or undetectable. The Slit receptorsrobo2, and to a limited extentrobo1, are expressed in the RGC layer, as areslit1andslit2. In collagen gels, axon outgrowth from rat retinal explants is biased away fromslit2-transfected 293T cells, and the number and length of axons are decreased on the explant side facing the cells. In addition, in the presence of Slit2, overall axon outgrowth is decreased, and bundles of retinal axons are more tightly fasciculated. This action of Slit2 as a growth inhibitor of retinal axons and the expression patterns ofslit1andslit2correlate with the fasciculation and innervation patterns of RGC axons within the diencephalon and implicate the Slits as components of the axon repellent activity associated with the hypothalamus and epithalamus. Our findings suggest thatin vivothe Slits control RGC axon pathfinding and targeting within the diencephalon by regulating their fasciculation, preventing them or their branches from invading nontarget tissues, and steering them toward their most distal target, the superior colliculus.
Differential Downregulation of GABAAReceptor Subunits in Widespread Brain Regions in the Freeze-Lesion Model of Focal Cortical Malformations
Authors: Redecker Christoph , Luhmann Heiko J. , Hagemann Georg , Fritschy Jean-Marc , Witte Otto W.
Published: April 2018

Focal cortical malformations comprise a heterogeneous group of disturbances of brain development, commonly associated with drug-resistant epilepsy and/or neuropsychological deficits. Electrophysiological studies on rodent models of cortical malformations demonstrated intrinsic hyperexcitability in the lesion and the structurally intact surround, indicating widespread imbalances of excitation and inhibition. Here, alterations in regional expression of GABAAreceptor subunits were investigated immunohistochemically in adult rats with focal cortical malformations attributable to neonatal freeze-lesions. These lesions are morphologically characterized by a three- to four-layered cortex with microsulcus formation. Widespread regionally differential reduction of GABAAreceptor subunits α1, α2, α3, α5, and γ2 was observed. Within the cortical malformation, this downregulation was most prominent for subunits α5 and γ2, whereas medial to the lesion, a significant and even stronger decrease of all subunits was detected. Lateral to the dysplastic cortex, the decrease was most prominent for subunit γ2 and moderate for subunits α1, α2, and α5, whereas subunit α3 was not consistently altered. Interestingly, the downregulation of GABAAreceptor subunits also involved the ipsilateral hippocampal formation, as well as restricted contralateral neocortical areas, indicating widespread disturbances in the neocortical and hippocampal network. The described pattern of downregulation of GABAAreceptor subunits allows the conclusion that there is a considerable modulation of subunit composition. Because alterations in subunit composition critically influence the electrophysiological and pharmacological properties of GABAAreceptors, these alterations might contribute to the widespread hyperexcitability and help to explain pharmacotherapeutic characteristics in epileptic patients.
Connections between Anterior Inferotemporal Cortex and Superior Temporal Sulcus Regions in the Macaque Monkey
Authors: Saleem K. S. , Suzuki W. , Tanaka K. , Hashikawa T.
Published: April 2018

We examined the connections between the anterior inferotemporal cortex and the superior temporal sulcus (STS) in the macaque monkey by injectingPhaseolus vulgarisleucoagglutinin (PHA-L) or wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the dorsoanterior and ventroanterior subdivisions of TE (TEad and TEav, respectively) and observing the labeled terminals and cell bodies in STS. We found a clear dichotomy in the connections of the rostral part of STS: the injections into TEad resulted in a dense distribution of labeled terminals and cell bodies in the upper bank of rostral STS, whereas labeling was confined to the lower bank and fundus of rostral STS after injections into TEav. The distribution of labeling in the rostral STS was discontinuous from the distribution of labeling surrounding the injection sites: the lower bank of the rostral STS was spared from labeling in the TEad injection cases, and TEad had only sparse distribution in the TEav injection cases. These results revise the classical view that the lower bank of rostral STS is connected with TE, whereas the upper bank of rostral STS is connected with the parietal, prefrontal, and superior temporal regions (Seltzer and Pandya, 1978, 1991, 1994). The upper bank of the rostral STS is called the superior temporal polysensory area (STP), because it was previously found that neurons there respond to auditory, somatosensory, and visual stimuli. The present results thus suggest that the polymodal representation in STP interacts more with information processing in TEad than TEav. It is also suggested that the information processing in the ventral bank of the rostral STS is distinct from that in TEad, and the former more directly interacts with TEav than TEad.