bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of Dopaminergic Neurons in the Adult Brain from Mesencephalic Precursor Cells Labeled with anestin-GFPTransgene
Authors: Sawamoto Kazunobu , Nakao Naoyuki , Kakishita Koji , Ogawa Yuto , Toyama Yoshiaki , Yamamoto Atsuyo , Yamaguchi Masahiro , Mori Kensaku , Goldman Steven A. , Itakura Toru , Okano Hideyuki
Published: April 2018

Mesencephalic precursor cells may one day provide dopaminergic neurons for the treatment of Parkinson's disease. However, the generation of dopaminergic neurons from mesencephalic precursors has been difficult to follow, partly because an appropriate means for recognizing mesencephalic ventricular zone precursors has not been available. To visualize and isolate mesencephalic precursor cells from a mixed population, we used transgenic mice and rats carryinggreen fluorescent protein(GFP) cDNA under the control of thenestinenhancer.nestin-driven GFP was detected in the mesencephalic ventricular zone, and it colocalized with specific markers for neural precursor cells. In addition, data from flow-cytometry indicated that Prominin/CD133, a cell-surface marker for ventricular zone cells, was expressed specifically in these GFP-positive (GFP+) cells. After sorting by fluorescence-activated cell sorting, the GFP+cells proliferatedin vitroand expressed precursor cell markers but not neuronal markers. Using clonogenic sphere formation assays, we showed that this sorted population was enriched in multipotent precursor cells that could differentiate into both neurons and glia. Importantly, many neurons generated fromnestin-GFP-sorted mesencephalic precursors developed a dopaminergic phenotypein vitro. Finally,nestin-GFP+cells were transplanted into the striatum of a rat model of Parkinson's disease. Bromodeoxyuridine–tyrosine hydroxylase double-labeling revealed that the transplanted cells generated new dopaminergic neurons within the host striatum. The implanted cells were able to restore dopaminergic function in the host striatum, as assessed by a behavioral measure: recovery from amphetamine-induced rotation. Together, these findings indicate that precursor cells harvested from the embryonic ventral mesencephalon can generate dopaminergic neurons able to restore function to the chemically denervated adult striatum.
Target-Derived Neurotrophic Factors Regulate the Death of Developing Forebrain Neurons after a Change in their Trophic Requirements
Authors: Lotto R. Beau , Asavaritikrai Pundit , Vali Leila , Price David J.
Published: April 2018

Many neurons die as the normal brain develops. How this is regulated and whether the mechanism involves neurotrophic molecules from target cells are unknown. We found that cultured neurons from a key forebrain structure, the dorsal thalamus, develop a need for survival factors including brain-derived neurotrophic factor (BDNF) from their major target, the cerebral cortex, at the age at which they innervate it. Experimentsin vivohave shown that rates of dorsal thalamic cell death are reduced by increasing cortical levels of BDNF and are increased in mutant mice lacking functional BDNF receptors or thalamocortical projections; these experiments have also shown that an increase in the rates of dorsal thalamic cell death can be achieved by blocking BDNF in the cortex. We suggest that the onset of a requirement for cortex-derived neurotrophic factors initiates a competitive mechanism regulating programmed cell death among dorsal thalamic neurons.
Effects of Early Visual Experience and Diurnal Rhythms on BDNF mRNA and Protein Levels in the Visual System, Hippocampus, and Cerebellum
Authors: Pollock Graeme S. , Vernon Elizabeth , Forbes M. Elizabeth , Yan Qiao , Ma Yun-Tao , Hsieh Ted , Robichon Regine , Frost Douglas O. , Johnson James E.
Published: April 2018

The expression of brain-derived neurotrophic factor (BDNF) mRNA and the secretion of BDNF protein are tightly regulated by neuronal activity. Thus, BDNF has been proposed as a mediator of activity-dependent neural plasticity. Previous studies showed that dark rearing (DR) reduces BDNF mRNA levels in the primary visual cortex (V1), but the effects of visual experience on BDNF protein levels are unknown. We report that rearing in constant light or DR alters BDNF mRNA and protein levels in the retina, superior colliculus (SC), V1, hippocampus (HIPP), and cerebellum (CBL), although the changes in mRNA and protein are not always correlated. Most notably, DR increases BDNF protein levels in V1 although BDNF mRNA is decreased. BDNF protein levels also undergo diurnal changes. In the retina, V1, and SC, BDNF protein levels are higher during the light phase of the circadian cycle than during the dark phase. By contrast, in HIPP and CBL, the tissue concentration of BDNF protein is higher during the dark phase. The discrepancies between the experience-dependent changes in BDNF mRNA and protein suggest that via its effects on neuronal activity, early sensory experience alters the trafficking, as well as the synthesis, of BDNF protein. The circadian changes in BDNF protein suggest that BDNF could cause the diurnal modulation of synaptic efficacy in some neural circuits. The fluctuations in BDNF levels in nonvisual structures suggest a potential role of BDNF in mediating plasticity induced by hormones or motor activity.
Selective Adaptation to Color Contrast in Human Primary Visual Cortex
Authors: Engel Stephen A. , Furmanski Christopher S.
Published: April 2018

How neural activity produces our experience of color is controversial, because key behavioral results remain at odds with existing physiological data. One important, unexplained property of perception is selective adaptation to color contrast. Prolonged viewing of colored patterns reduces the perceived intensity of similarly colored patterns but leaves other patterns relatively unaffected. We measured the neural basis of this effect using functional magnetic resonance imaging. Subjects viewed low-contrast test gratings that were either red–green (equal and opposite long- and middle-wavelength cone contrast, L-M) or light–dark (equal, same-sign, long- and middle-wavelength cone contrast, L+M). The two types of test gratings generated approximately equal amounts of neural activity in primary visual cortex (V1) before adaptation. After exposure to high-contrast L-M stimuli, the L-M test grating generated less activity in V1 than the L+M grating. Similarly, after adaptation to a high-contrast L+M grating, the L+M test grating generated less activity than the L-M test grating. Behavioral measures of adaptation using the same stimuli showed a similar pattern of results. Our data suggest that primary visual cortex contains large populations of color-selective neurons that can independently adjust their responsiveness after adaptation. The activity of these neural populations showed effects of adaptation that closely matched perceptual experience.
Recognition Memory Correlates of Hippocampal Theta Cells
Authors: Wiebe Sherman P. , Stäubli Ursula V.
Published: April 2018

Investigations of hippocampal theta cell activity have typically involved behavioral tasks with modest cognitive demands. Recordings in rats locomoting through space or engaged in simple stimulus discrimination or conditioning have revealed some place specificity and S+/S−selectivity in addition to the hippocampal EEG theta-related behavioral/motor correlates. However, little data exist regarding theta cell activity during performance of more cognitively demanding, hippocampal-dependent recognition memory tasks. Here, we examined the cognitive firing correlates of theta cells in rats that were performing an olfactory recognition memory task with distinct sample and test phases. Discriminant analysis revealed odor and match/nonmatch memory correlates in theta cell activity comparable in relative magnitude to that of the principal cells. Odor-specific theta cell responses in the sample phase were restricted primarily to CA1 and linked to task performance. In the test recognition phase, match/nonmatch theta cells were found primarily in the CA3 and CA1 fields, most of which exhibited greater activity on correct nonmatch trials in which recognition occurred than on error match trials in which recognition failed. Odor selectivity of the match/nonmatch signaling was greatest in the dentate gyrus (DG) and CA3 and least in CA1. This inverted pattern of stimulus specificity in the sample versus test phase was similar to that observed in principal cells but with a greater contrast between the CA1 and DG/CA3 fields. Together, these findings suggest that theta cells actively participate in hippocampal recognition memory processing and play a specific role in shaping the cognitive firing properties of the hippocampal principal cells.
Neurons of a Limited Subthalamic Area Mediate Elevations in Cortical Cerebral Blood Flow Evoked by Hypoxia and Excitation of Neurons of the Rostral Ventrolateral Medulla
Authors: Golanov Eugene V. , Christensen John R. C. , Reis Donald J.
Published: April 2018

Sympathoexcitatory reticulospinal neurons of the rostral ventrolateral medulla (RVLM) are oxygen detectors excited by hypoxia to globally elevate regional cerebral blood flow (rCBF). The projection, which accounts for >50% of hypoxic cerebral vasodilation, relays through the medullary vasodilator area (MCVA). However, there are no direct cortical projections from the RVLM/MCVA, suggesting a relay that diffusely innervates cortex and possibly originates in thalamic nuclei. Systematic mapping by electrical microstimulation of the thalamus and subthalamus revealed that elevations in rCBF were elicited only from a limited area, which encompassed medial pole of zona incerta, Forel's field, and prerubral zone. Stimulation (10 sec train) at an active site increased rCBF by 25 ± 6%. Excitation of local neurons with kainic acid mimicked effects of electrical stimulation by increasing rCBF. Stimulation of the subthalamic cerebrovasodilator area (SVA) with single pulses (0.5 msec; 80 μA) triggered cortical EEG burst–CBF wave complexes with latency 24 ± 5 msec, which were similar in shape to complexes evoked from the MCVA. Selective bilateral lesioning of the SVA neurons (ibotenic acid, 2 μg, 200 nl) blocked the vasodilation elicited from the MCVA and attenuated hypoxic cerebrovasodilation by 52 ± 12% (p< 0.05), whereas hypercarbic vasodilation remained preserved. Lesioning of the vasodilator site in the basal forebrain failed to modify SVA-evoked rCBF increase. We conclude that (1) excitation of intrinsic neurons of functionally restricted region of subthalamus elevates rCBF, (2) these neurons relay signals from the MCVA, which elevate rCBF in response to hypoxia, and (3) the SVA is a functionally important site conveying vasodilator signal from the medulla to the telencephalon.
Modulators with Convergent Cellular Actions Elicit Distinct Circuit Outputs
Authors: Swensen Andrew M. , Marder Eve
Published: April 2018

Six neuromodulators [proctolin,Cancer borealistachykinin-related peptide Ia, crustacean cardioactive peptide (CCAP), red pigment-concentrating hormone, TNRNFLRFamide, and pilocarpine] converge onto the same voltage-dependent inward current in stomatogastric ganglion (STG) neurons of the crabC. borealis. We show here that each of these modulators acts on a distinct subset of pyloric network neurons in the STG. To ask whether the differences in cell targets could account for their differential effects on the pyloric rhythm, we systematically compared the motor patterns produced by proctolin and CCAP. The motor patterns produced in proctolin and CCAP differed quantitatively in a number of ways. Proctolin and CCAP both act on the lateral pyloric neuron and the inferior cardiac neuron. Proctolin additionally acts on the pyloric dilator (PD) neurons, the pyloric (PY) neurons, and the ventricular dilator neuron. Using the dynamic clamp, we introduced an artificial peptide-elicited current into the PD and PY neurons, in the presence of CCAP, and converted the CCAP rhythm into a rhythm that was statistically similar to that seen in proctolin. This suggests that the differences in the network effects of these two modulators can primarily be attributed to the known differential distributions of their receptors onto distinct subsets of neurons, despite the fact that they activate the same current.
Large Involuntary Forces Consistent with Plateau-Like Behavior of Human Motoneurons
Authors: Collins D. F. , Burke D. , Gandevia S. C.
Published: April 2018

When electrical stimulation is applied over human muscle, the evoked force is generally considered to be of peripheral origin. However, in relaxed humans, stimulation (1 msec pulses, 100 Hz) over the muscles that plantarflex the ankle produced more than five times more force than could be accounted for by peripheral properties. This additional force was superimposed on the direct response to motor axon stimulation, produced up to 40% of the force generated during a maximal voluntary contraction, and was abolished during anesthesia of the tibial nerve proximal to the stimulation site. It therefore must have resulted from the activation of motoneurons within the spinal cord. The additional force could be initiated by stimulation of low-threshold afferents, distorted the classical relationship between force and stimulus frequency, and often outlasted the stimulation. The mean firing rate of 27 soleus motor units recorded during the sustained involuntary activity after the stimulation was 5.8 ± 0.2 Hz. The additional force increments were not attributable to voluntary intervention because they were present in three sleeping subjects and in two subjects with lesions of the thoracic spinal cord. The phenomenon is consistent with activation of plateau potentials within motoneurons and, if so, the present findings imply that plateau potentials can make a large contribution to forces produced by the human nervous system.
A Mechanism for Savings in the Cerebellum
Authors: Medina Javier F. , Garcia Keith S. , Mauk Michael D.
Published: April 2018

The phenomenon of savings (the ability to relearn faster than the first time) is a familiar property of many learning systems. The utility of savings makes its underlying mechanisms of special interest. We used a combination of computer simulations and reversible lesions to investigate mechanisms of savings that operate in the cerebellum during eyelid conditioning, a well characterized form of motor learning. The results suggest that a site of plasticity outside the cerebellar cortex (possibly in the cerebellar nucleus) can be protected from the full consequences of extinction and that the residual plasticity that remains can later contribute to the savings seen during relearning.
Injections of the NMDA Receptor Antagonist Aminophosphonopentanoic Acid into the Lateral Nucleus of the Amygdala Block the Expression of Fear-Potentiated Startle and Freezing
Authors: Fendt Markus
Published: April 2018

NMDA receptors within the amygdala play an important role in the acquisition and expression of conditioned fear. Because amygdaloid injections of NMDA receptor antagonists did not block the expression of every behavioral sign of fear, a discussion arose as to whether amygdaloid NMDA receptors play different roles in different kinds of fear-conditioning tasks. To clarify the exact role of amygdaloid NMDA receptors, the present study measured the effects of amygdaloid NMDA receptor blockade on the two major animal models of conditioned fear. An experimental design was used that allowed simultaneous measurement of fear-potentiated startle and freezing during the same test session after animals had undergone identical training procedures. The present study clearly demonstrates that injections of the NMDA receptor antagonist AP-5 into the lateral nucleus of the amygdala significantly attenuated both behavioral fear responses (i.e., the amygdaloid NMDA receptors are necessary for the expression of fear-potentiated startle and freezing). The present results together with others from the literature indicate that NMDA receptors within the lateral amygdala are critically involved in normal synaptic transmission. It appears then that NMDA receptor antagonists may block the acquisition of fear conditioning by directly interfering with normal synaptic transmissions in the amygdala. Possible reasons for some discrepant results in earlier studies are also discussed.
Extracellular Calcium Modulates Persistent Sodium Current-Dependent Burst-Firing in Hippocampal Pyramidal Neurons
Authors: Su Hailing , Alroy Gil , Kirson Eilon D. , Yaari Yoel
Published: April 2018

The generation of high-frequency spike bursts (“complex spikes”), either spontaneously or in response to depolarizing stimuli applied to the soma, is a notable feature in intracellular recordings from hippocampal CA1 pyramidal cells (PCs)in vivo. There is compelling evidence that the bursts are intrinsically generated by summation of large spike afterdepolarizations (ADPs). Using intracellular recordings in adult rat hippocampal slices, we show that intrinsic burst-firing in CA1 PCs is strongly dependent on the extracellular concentration of Ca2+([Ca2+]o). Thus, lowering [Ca2+]o(by equimolar substitution with Mn2+or Mg2+) induced intrinsic bursting in nonbursters, whereas raising [Ca2+]osuppressed intrinsic bursting in native bursters. The induction of intrinsic bursting by low [Ca2+]owas associated with enlargement of the spike ADP. Low [Ca2+]o-induced intrinsic bursts and their underlying ADPs were suppressed by drugs that reduce the persistent Na+current (INaP), indicating that this current mediates the slow burst depolarization. Blocking Ca2+-activated K+currents with extracellular Ni2+or intracellular chelation of Ca2+did not induce intrinsic bursting. This and other evidence suggest that lowering [Ca2+]omay induce intrinsic bursting by augmentingINaP. Because repetitive neuronal activity in the hippocampus is associated with marked decreases in [Ca2+]o, the regulation of intrinsic bursting by extracellular Ca2+may provide a mechanism for preferential recruitment of this firing mode during certain forms of hippocampal activation.
A Labile Component of AMPA Receptor-Mediated Synaptic Transmission Is Dependent on Microtubule Motors, Actin, andN-Ethylmaleimide-Sensitive Factor
Authors: Kim Chong-Hyun , Lisman John E.
Published: April 2018

Glutamate receptor channels are synthesized in the cell body, are inserted into intracellular vesicles, and move to dendrites where they become incorporated into synapses. Dendrites contain abundant microtubules that have been implicated in the vesicle-mediated transport of ion channels. We have examined how the inhibition of microtubule motors affects synaptic transmission. Monoclonal antibodies that inactivate the function of dynein or kinesin were introduced into hippocampal CA1 pyramidal cells through a patch pipette. Both antibodies substantially reduced the AMPA receptor-mediated responses within 1 hr but had no effect on the NMDA receptor-mediated response. Heat-inactivated antibody or control antibodies had a much smaller effect. A component of transmission appeared to be resistant even to the combination of these inhibitors, and we therefore explored whether other agents also produce only a partial inhibition of transmission. A similar resistant component was found by using an actin inhibitor (phalloidin) or an inhibitor of NSF (N-ethylmaleimide-sensitive fusion protein)/GluR2 interaction. We then examined whether these effects were independent or occluded each other. We found that a combination of phalloidin and NSF/GluR2 inhibitor reduced the response to ∼30% of baseline level, an effect only slightly larger than that produced by each agent alone. The addition of microtubule motor inhibitors to this combination produced no further inhibition. We conclude that there are two components of AMPA receptor-mediated transmission; one is a labile pool sensitive to NSF/GluR2 inhibitors, actin inhibitors, and microtubule motor inhibitors. A second, nonlabile pool resembles NMDA receptor channels in being nearly insensitive to any of these agents on the hour time scale of our experiments.
Strain-Dependent Differences in Calcium Signaling Predict Excitotoxicity in Murine Hippocampal Neurons
Authors: Shuttleworth C. William R. , Connor John A.
Published: April 2018

Commonly used inbred murine strains differ substantially in their vulnerability to excitotoxic insults. We investigated whether differences in dendritic Ca2+signaling could underlie the differential vulnerability of C57BL/6 (resistant to kainate excitotoxicity) and C57BL/10 strains (vulnerable). A striking difference was found in fine dendrite Ca2+responses after kainate exposure. Ca2+signals in distal dendrites were large in C57BL/10 neurons, and, if a threshold concentration of ∼1.5 μmwas reached, a region of sustained high Ca2+was established in the distal dendritic tree. This region then served as an initiation site for a degenerative cascade, producing high Ca2+levels that slowly spread to involve the entire neuron and led to cell death. Dendritic Ca2+signals in C57BL/6 neurons were much smaller and did not trigger these propagating secondary responses. Strain differences in dendritic Ca2+signaling were also evident after tetanic stimulation of Schaffer collaterals. Ca2+responses were much larger and peaked earlier in distal dendrites of C57BL/10 compared with those in C57BL/6. Neurons from both strains had similar membrane properties and responded to kainate with intense action potential firing. Degenerative Ca2+responses were seen in both strains if soma Ca2+could be sustained above 1.5 μm. The early phases of secondary Ca2+responses were attributable to Ca2+influx and were abolished rapidly by buffered zero Ca2+saline. Taken together, these data indicate that the substantial difference in Ca2+signals in fine distal dendrites and in the initiation of spreading secondary responses may underlie the selective vulnerability of these neurons to excitotoxic insults.
BDNF Enhances Quantal Neurotransmitter Release and Increases the Number of Docked Vesicles at the Active Zones of Hippocampal Excitatory Synapses
Authors: Tyler William J. , Pozzo-Miller Lucas D.
Published: April 2018

Brain-derived neurotrophic factor (BDNF) is emerging as a key mediator of activity-dependent modifications of synaptic strength in the CNS. We investigated the hypothesis that BDNF enhances quantal neurotransmitter release by modulating the distribution of synaptic vesicles within presynaptic terminals using organotypic slice cultures of postnatal rat hippocampus. BDNF specifically increased the number of docked vesicles at the active zone of excitatory synapses on CA1 dendritic spines, with only a small increase in active zone size. In agreement with the hypothesis that an increased docked vesicle density enhances quantal neurotransmitter release, BDNF increased the frequency, but not the amplitude, of AMPA receptor-mediated miniature EPSCs (mEPSCs) recorded from CA1 pyramidal neurons in hippocampal slices. Synapse number, independently estimated from dendritic spine density and electron microscopy measurements, was also increased after BDNF treatment, indicating that the actions of BNDF on mEPSC frequency can be partially attributed to an increased synaptic density. Our results further suggest that all these actions were mediated via tyrosine kinase B (TrkB) receptor activation, established by inhibition of plasma membrane tyrosine kinases with K-252a. These results provide additional evidence of a fundamental role of the BDNF–TrkB signaling cascade in synaptic transmission, as well as in cellular models of hippocampus-dependent learning and memory.
p27Kip1and p57Kip2Regulate Proliferation in Distinct Retinal Progenitor Cell Populations
Authors: Dyer Michael A. , Cepko Constance L.
Published: April 2018

In the developing vertebrate retina, progenitor cell proliferation must be precisely regulated to ensure appropriate formation of the mature tissue. Cyclin kinase inhibitors have been implicated as important regulators of proliferation during development by blocking the activity of cyclin–cyclin-dependent kinase complexes. We have found that the p27Kip1cyclin kinase inhibitor regulates progenitor cell proliferation throughout retinal histogenesis. p27Kip1is upregulated during the late G2/early G1phase of the cell cycle in retinal progenitor cells, where it interacts with the major retinal D-type cyclin–cyclin D1. Mice deficient for p27Kip1exhibited an increase in the proportion of mitotic cells throughout development as well as extensive apoptosis, particularly during the later stages of retinal histogenesis. Retroviral-mediated overexpression of p27Kip1in mitotic retinal progenitor cells led to premature cell cycle exit yet had no dramatic effects on Müller glial or bipolar cell fate specification as seen with theXenopuscyclin kinase inhibitor, p27Xic1. Consistent with the overexpression of p27Kip1, mice lacking one or both alleles of p27Kip1maintained the same relative ratios of each major retinal cell type as their wild-type littermates. During the embryonic stages of development, when both p27Kip1and p57Kip2are expressed in retinal progenitor cells, they were found in distinct populations, demonstrating directly that different retinal progenitor cells are heterogeneous with respect to their expression of cell cycle regulators.
Repellent Signaling by Slit Requires the Leucine-Rich Repeats
Authors: Battye Robin , Stevens Adrienne , Perry Robert L. , Jacobs J. Roger
Published: April 2018

Slit is a repellent axon guidance cue produced by the midline glia inDrosophilathat is required to regulate the formation of contralateral projections and the lateral position of longitudinal tracts. Four sequence motifs comprise the structure of Slit: a leucine-rich repeat (LRR), epidermal growth factor-like (EGF) repeats, a laminin-like globular (G)-domain, and a cysteine domain. Here we demonstrate that the LRR is required for repellent signaling andin vitrobinding to Robo. Repellent signaling byslitis reduced by point mutations that encode single amino acid changes in the LRR domain. By contrast to the EGF or G-domains, the LRR domain is required in transgenes to affect axon guidance. Finally, we show that the midline repellent receptor, Robo, binds Slit proteins with internal deletions that also retain repellent activity. However, Robo does not bind Slit protein missing the LRR. Taken together, our data demonstrate that Robo binding and repellent signaling by Slit require the LRR region.
Induction of the Plasminogen Activator System Accompanies Peripheral Nerve Regeneration after Sciatic Nerve Crush
Authors: Siconolfi Lisa B. , Seeds Nicholas W.
Published: April 2018

Peripheral nerve regeneration is dependent on the ability of regenerating neurites to migrate through cellular debris and altered extracellular matrix at the injury site, grow along the residual distal nerve sheath conduit, and reinnervate synaptic targets. In cell culture, growth cones of regenerating axons secrete proteases, specifically plasminogen activators (PAs), which are believed to facilitate growth cone movement by digesting extracellular matrices and cell adhesions. In this study, the PA system was shown to be specifically activated in sensory neurons after sciatic nerve crush in adult mice. The number of sensory neurons expressing urokinase PA receptor (uPAR) mRNA levels increased above sham levels by 8 hr after crush, whereas the number of sensory neurons expressing uPA and tissue PA (tPA) mRNAs was significantly increased by 3 d after crush. PA mRNA levels were also increased at the crush site, with uPA mRNA elevated by 8 hr after crush and tPA and uPAR mRNA levels markedly increased by 7 d. PA-dependent enzymatic activity was significantly increased from 1 to 7 d after crush in nerves that had been crushed compared with uncrushed nerves. Immunohistochemistry showed that tPA was localized within regenerating axons of the sciatic nerve. There were no significant changes in plasminogen activator inhibitor 1 activity between crush and sham after the injury. These results clearly demonstrated that after injury the PA system was rapidly induced in sensory neurons, where it may play an important role in nerve regenerationin vivo.
Chronic Prenatal Ethanol Exposure Increases GABAAReceptor Subunit Protein Expression in the Adult Guinea Pig Cerebral Cortex
Authors: Bailey Craig D. C. , Brien James F. , Reynolds James N.
Published: April 2018

Excessive consumption of ethanol during pregnancy can produce teratogenic effects in offspring and is the leading cause of mental deficiency in the Western world. The objective of this study was to examine the effects of chronic prenatal ethanol exposure on the number of GABAAreceptors and relative protein levels for GABAAreceptor α1 and β2/3 subunits in the adult guinea pig cerebral cortex. Timed pregnant Dunkin-Hartley strain guinea pigs were given one of the following oral treatments daily throughout gestation: 4 gm of ethanol per kilogram of maternal body weight, isocaloric-sucrose with pair feeding, or isovolumetric water withad libitumaccess to food. The ethanol treatment resulted in a peak maternal blood ethanol concentration of 328 ± 55 mg/dl (71.3 ± 12.0 mm) on gestational day 57 (term, ∼68 d). Chronic prenatal exposure to ethanol resulted in increased spontaneous locomotor activity throughout development and decreased cerebral cortical weight in adult offspring. The number of cerebral cortical [3H]muscimol binding sites was increased in adult offspring from the ethanol treatment group, and there was a corresponding increase in the amount of GABAAreceptor α1 and β2/3 subunit proteins in these same animals. For individual offspring, there were correlations between locomotor activity and cerebral cortical weight, as well as between cerebral cortical weight and GABAAreceptor neurochemistry. There was no effect of chronic prenatal ethanol exposure on [3H]MK-801 binding in this tissue. These data demonstrate that chronic prenatal ethanol exposure has long-term consequences on the regulation of GABAAreceptor expression in the cerebral cortex.
Oriented Axon Projections in Primary Visual Cortex of the Monkey
Authors: Sincich Lawrence C. , Blasdel Gary G.
Published: April 2018

One important aspect of the functional architecture of primary visual cortex is the circuitry that accounts for the receptive field properties of neurons. The anatomy that underlies retinotopy and ocular dominance is well known, but no anatomical structure related to orientation selectivity has been found in primates. We examined whether the arrangement of local axon systems projecting within the cortical layers might be correlated with orientation preference in New World monkeys. We found that axons in layer 3 spread out from the site of a tracer injection in an anisotropic manner and that this elongated distribution is aligned with the preferred orientation recorded at each site. Moreover, within a few degrees of the foveal representation, the majority of the axon terminals fall within or just outside of the limits of the cortical mapping of the classical receptive field. Thus local axons produce a field of monosynaptic excitation that aligns with orientation axes and reaches neurons that have receptive fields which are adjacent in visual space.
Capsaicin Responses in Heat-Sensitive and Heat-Insensitive A-Fiber Nociceptors
Authors: Ringkamp Matthias , Peng Yuan B. , Wu Gang , Hartke Timothy V. , Campbell James N. , Meyer Richard A.
Published: April 2018

The recently cloned vanilloid receptor (VR1) is postulated to account for heat and capsaicin sensitivity in unmyelinated afferents. We sought to determine whether heat and capsaicin sensitivity also coexist in myelinated nociceptive afferents. Action potential (AP) activity was recorded from single A-fiber nociceptors that innervated the hairy skin in monkey. Before intradermal injection of capsaicin (10 μg/10 μl) into the receptive field, nociceptors were classified as heat-sensitive (threshold, ≤53°C, 1 sec) or heat-insensitive afferents and as mechanically sensitive (von Frey threshold, <6 bar) or mechanically insensitive afferents. All heat-sensitive afferents (n= 16) were insensitive to mechanical stimuli but responded to the intradermal injection of capsaicin (69 ± 7 APs in 10 min). Responsiveness to mechanical stimuli, thermal stimuli, and capsaicin varied in their receptive fields; the majority of receptive field sites (24 of 36) were responsive to only one or two stimulus modalities, whereas only eight sites responded to all three modalities. For most heat-insensitive afferents, the activity induced by the capsaicin injection did not exceed the activity induced by needle insertion alone. However, the largest response to capsaicin (314 ± 98 APs in 10 min) was observed for five afferents that were insensitive to heat as well as mechanical stimuli and therefore may be classified as cutaneous chemoreceptors. These results suggest that A-fiber nociceptors play a role in the pain and hyperalgesia associated with capsaicin injection. Our finding that a subgroup of capsaicin-sensitive A-fiber nociceptors are insensitive to heat predicts the existence of heat-insensitive capsaicin receptors.
Dual and Opposing Modulatory Effects of Serotonin on Crayfish Lateral Giant Escape Command Neurons
Authors: Teshiba Terri , Shamsian Ashkan , Yashar Bahram , Yeh Shih-Rung , Edwards Donald H. , Krasne Franklin B.
Published: April 2018

Serotonin modulates afferent synaptic transmission to the lateral giant neurons of crayfish, which are command neurons for escape behavior. Low concentrations, or high concentrations reached gradually, are facilitatory, whereas high concentrations reached rapidly are inhibitory. The modulatory effects rapidly reverse after brief periods of application, whereas longer periods of application are followed by facilitation that persists for hours. These effects of serotonin can be reproduced by models that involve multiple interacting intracellular signaling systems that are each stimulated by serotonin. The dependence of the neuromodulatory effect on dose, rate, and duration of modulator application may be relevant to understanding the effects of natural neuromodulation on behavior and cognition and to the design of drug therapies.
Voltage-Dependent Sodium Channels Are Expressed in Nonspiking Retinal Bipolar Neurons
Authors: Zenisek David , Henry Diane , Studholme Keith , Yazulla Stephen , Matthews Gary
Published: April 2018

Retinal bipolar neurons transmit visual information by means of graded synaptic potentials that spread to the synaptic terminal without sodium-dependent action potentials. Although action potentials are not involved, voltage-dependent sodium channels may enhance subthreshold depolarizing potentials in the dendrites and soma of bipolar cells, as they do in other CNS neurons. We report here that voltage-dependent sodium currents are observed in a subset of bipolar neurons from goldfish retina. Single-cell reverse transcriptase-PCR identified four different sodium channel α subunits in goldfish bipolar cells, putatively corresponding to the mammalian voltage-gated sodium channels Nav1.1, Nav1.2, Nav1.3, and Nav1.6. The amount of sodium current was largest in cells with smaller synaptic terminals, which probably represent cone bipolar cells. Localization of sodium channel immunoreactivity in goldfish retina confirmed the expression of voltage-gated sodium channels in cone bipolar cells of both ON and OFF types. Both immunocytochemical and physiological evidence suggests that the sodium channels are localized to the soma and dendrites where they may play a role in transmission of synaptic signals, particularly in the long, thin dendrites of cone bipolar cells.
Dissipation of Potassium and Proton Gradients Inhibits Mitochondrial Hyperpolarization and Cytochrome c Release during Neural Apoptosis
Authors: Poppe Monika , Reimertz Claus , Düßmann Heiko , Krohn Aaron J. , Luetjens C. Marc , Böckelmann Doris , Nieminen Anna-Liisa , Kögel Donat , Prehn Jochen H. M.
Published: April 2018

Exposure of rat hippocampal neurons or human D283 medulloblastoma cells to the apoptosis-inducing kinase inhibitor staurosporine induced rapid cytochrome c release from mitochondria and activation of the executioner caspase-3. Measurements of cellular tetramethylrhodamine ethyl ester fluorescence and subsequent simulation of fluorescence changes based on Nernst calculations of fluorescence in the extracellular, cytoplasmic, and mitochondrial compartments revealed that the release of cytochrome c was preceded by mitochondrial hyperpolarization. Overexpression of the anti-apoptotic protein Bcl-xL, but not pharmacological blockade of outward potassium currents, inhibited staurosporine-induced hyperpolarization and apoptosis. Dissipation of mitochondrial potassium and proton gradients by valinomycin or carbonyl cyanidep-trifluoromethoxy-phenylhydrazone also potently inhibited staurosporine-induced hyperpolarization, cytochrome c release, and caspase activation. This effect was not attributable to changes in cellular ATP levels. Prolonged exposure to valinomycin induced significant matrix swelling, and per se also caused release of cytochrome c from mitochondria. In contrast to staurosporine, however, valinomycin-induced cytochrome c release and cell death were not associated with caspase-3 activation and insensitive to Bcl-xL overexpression. Our data suggest two distinct mechanisms for mitochondrial cytochrome c release: (1) active cytochrome c release associated with early mitochondrial hyperpolarization, leading to neuronal apoptosis, and (2) passive cytochrome c release secondary to mitochondrial depolarization and matrix swelling.
The Presynaptic Function of Mouse Cochlear Inner Hair Cells during Development of Hearing
Authors: Beutner Dirk , Moser Tobias
Published: April 2018

Before mice start to hear at approximately postnatal day 10, their cochlear inner hair cells (IHCs) spontaneously generate Ca2+action potentials. Therefore, immature IHCs could stimulate the auditory pathway, provided that they were already competent for transmitter release. Here, we combined patch-clamp capacitance measurements and fluorimetric [Ca2+]irecordings to study the presynaptic function of IHCs during cochlear maturation. Ca2+-dependent exocytosis and subsequent endocytic membrane retrieval were already observed near the date of birth. Ca2+action potentials triggered exocytosis in immature IHCs, which probably activates the auditory pathway before it becomes responsive to sound. IHCs underwent profound changes in Ca2+-channel expression and secretion during their postnatal development. Ca2+-channel expression increased toward the end of the first week, providing for large secretory responses during this period and thereafter declined to reach mature levels. The efficacy whereby Ca2+influx triggers exocytosis increased toward maturation, such that vesicle fusion caused by a given Ca2+current occurred faster in mature IHCs. The observed changes in Ca2+-channel expression and synaptic efficacy probably reflected the ongoing synaptogenesis in IHCs that had been described previously in morphological studies.
Differential Expression of Genes Encoding Subthreshold-Operating Voltage-Gated K+Channels in Brain
Authors: Saganich M. J. , Machado E. , Rudy B.
Published: April 2018

The members of the three subfamilies (eag, erg, and elk) of the ether-a-go-go (EAG) family of potassium channel pore-forming subunits express currents that, like the M-current (IM), could have considerable influence on the subthreshold properties of neuronal membranes, and hence the control of excitability. A nonradioactivein situhybridization (NR-ISH) study of the distribution of the transcripts encoding the eight known EAG family subunits in rat brain was performed to identify neuronal populations in which the physiological roles of EAG channels could be studied. These distributions were compared with those of the mRNAs encoding the components of the classical M-current (Kcnq2 and Kcnq3). NR-ISH was combined with immunohistochemistry to specific neuronal markers to help identify expressing neurons. The results show that each EAG subunit has a specific pattern of expression in rat brain. EAG and Kcnq transcripts are prominent in several types of excitatory neurons in the cortex and hippocampus; however, only one of these channel components (erg1) was consistently expressed in inhibitory interneurons in these areas. Some neuronal populations express more than one product of the same subfamily, suggesting that the subunits may form heteromeric channels in these neurons. Many neurons expressed multiple EAG family and Kcnq transcripts, such as CA1 pyramidal neurons, which contained Kcnq2, Kcnq3, eag1, erg1, erg3, elk2, and elk3. This indicates that the subthreshold current in many neurons may be complex, containing different components mediated by a number of channels with distinct properties and neuromodulatory responses.
Pituitary Adenylyl Cyclase-Activating Peptides and α-Amidation in Olfactory Neurogenesis and Neuronal SurvivalIn Vitro
Authors: Hansel Donna E. , May Victor , Eipper Betty A. , Ronnett Gabriele V.
Published: April 2018

We investigated the role of amidated neuropeptides, and specifically pituitary adenylyl cyclase-activating polypeptide (PACAP), in olfactory neurogenesis and olfactory receptor neuronal survival. Using both immunohistochemistry andin situhybridization, we find that both peptidylglycine α-amidating monooxygenase (PAM), the enzyme responsible for amidation and therefore activation of all amidated neuropeptides, and amidated PACAP are expressed in developing and adult olfactory epithelium. Amidated PACAP is highly expressed in proliferative basal cells and in immature olfactory neurons. The PACAP-specific receptor PAC1receptor is also expressed in this population, establishing that these cells can be PACAP responsive. Experiments were conducted to determine whether amidated neuropeptides, such as PACAP38, might function in olfactory neurogenesis and neuronal survival. Addition of PACAP38 to olfactory cultures increased the number of neurons to >250% of control and stimulated neuronal proliferation and survival. In primary olfactory cultures, pharmacologically decreased PAM activity, as well as neutralization of PACAP38, caused neuron-specific loss that was reversed by PACAP38. Mottled (Brindled) mice, which lack a functional ATP7A copper transporter and serve as a model for Menkes disease, provided anin vivopartial loss-of-function PAM knock-out. These mice had decreased amidated PACAP production and concomitant decreased numbers of olfactory receptor neurons. These data establish amidated peptides and specifically PACAP as having important roles in proliferation in the olfactory system and suggest that a similar function existsin vivo.
Age-Related Impairment of Synaptic Transmission But Normal Long-Term Potentiation in Transgenic Mice that Overexpress the Human APP695SWE Mutant Form of Amyloid Precursor Protein
Authors: Fitzjohn Stephen M. , Morton Robin A. , Kuenzi Frederick , Rosahl Thomas W. , Shearman Mark , Lewis Huw , Smith David , Reynolds David S. , Davies Ceri H. , Collingridge Graham L. , Seabrook Guy R.
Published: April 2018

We have studied synaptic function in a transgenic mouse strain relevant to Alzheimer's disease (AD), overexpressing the 695 amino acid isoform of human amyloid precursor protein with K670N and M671L mutations (APP695SWE mice), which is associated with early-onset familial AD. Aged-transgenic mice had substantially elevated levels of Aβ (up to 22 μmol/gm) and displayed characteristic Aβ plaques. Hippocampal slices from 12-month-old APP695SWE transgenic animals displayed reduced levels of synaptic transmission in the CA1 region when compared with wild-type littermate controls. Inclusion of the ionotropic glutamate receptor antagonist kynurenate during preparation of brain slices abolished this deficit. At 18 months of age, a selective deficit in basal synaptic transmission was observed in the CA1 region despite treatment with kynurenate. Paired-pulse facilitation and long-term potentiation (LTP) were normal in APP695SWE transgenic mice at both 12 and 18 months of age. Thus, although aged APP695SWE transgenic mice have greatly elevated levels of Aβ protein, increased numbers of plaques, and reduced basal synaptic transmission, LTP can still be induced and expressed normally. We conclude that increased susceptibility to excitotoxicity rather than a specific effect on LTP is the primary cause of cognitive deficits in APP695SWE mice.
Boundary Formation and Compartition in the Avian Diencephalon
Authors: Larsen Camilla W. , Zeltser Lori M. , Lumsden Andrew
Published: April 2018

The diencephalon comprises three functionally distinct regions: synencephalon, dorsal thalamus, and ventral thalamus. Patterning of the diencephalon has been proposed to involve subdivision of its anteroposterior axis into segments, neuromeres or prosomeres (Bergquist and Kallen, 1954; Vaage, 1969; Figdor and Stern, 1993; Rubenstein et al., 1994; Redies et al., 2000; Yoon et al., 2000). However, the number and sequence of diencephalic neuromeres, or even their existence, are uncertain. We have examined the proposed subdivisions by morphology, gene expression, acquisition of boundary-specific phenotypes, and cell lineage restriction. We find that at stage 16 in chick the diencephalon is divided into synencephalon and parencephalon. The synencephalon exhibits neuromeric morphology, expressesProx, and acquires neuromere boundary properties at its interface with both the midbrain and the parencephalon. Although the mesencephalic/synencephalic boundary restricts cell mixing, the synencephalic/parencephalic boundary does not. Similarly, there is no lineage restriction between the parencephalon and the more rostral forebrain (secondary prosencephalon). Subdivision of the parencephalon into ventral and dorsal thalamus involves the formation of a narrow intraparencephalic territory, the zona limitans intrathalamica (zli). This is correlated with the acquisition of cell lineage restriction at both anterior and posterior borders of the zli, the appearance of boundary-specific properties, and Gbx2 and Dlx2 expression in dorsal thalamic and ventral thalamic territories, respectively. At stage 22, the synencephalon is divided into two domains, distinguished by differential gene expression and tissue morphology, but associated with neither a boundary phenotype nor cell lineage restriction. Our results suggest that the diencephalon does not have an overt segmental pattern.
Neuregulin Signaling Regulates Neural Precursor Growth and the Generation of OligodendrocytesIn Vitro
Authors: Calaora Viviane , Rogister Bernard , Bismuth Keren , Murray Kerren , Brandt Heidi , Leprince Pierre , Marchionni Mark , Dubois-Dalcq Monique
Published: April 2018

Neuregulin 1 (Nrg-1) isoforms have been shown to influence the emergence and growth of oligodendrocytes, the CNS myelin-forming cells. We have investigated how Nrg-1 signaling of ErbB receptors specifically controls the early stages of oligodendrocyte generation from multipotential neural precursors (NPs). We show here that embryonic striatal NPs express multiple Nrg-1 transcripts and proteins as well as their specific receptors, ErbB2 and ErbB4, but not ErbB3. The major isoform synthesized by striatal NPs is a transmembrane type III isoform called cysteine-rich domain Nrg-1. To examine the biological effect of Nrg-1, we added soluble ErbB3 (sErbB3) to growing neurospheres. This inhibitor of Nrg-1 bioactivity decreased mitosis of NPs and increased their apoptosis, resulting in a significant reduction in neurosphere size and number. When NPs were induced to migrate and differentiate by adhesion of neurospheres to the substratum, the level of type III isoforms detected by RT-PCR and Western blot decreased in parallel with a reduction in Nrg-1 fluorescence intensity in differentiating astrocytes, neurons, and oligodendrocytes. Pretreatment of growing neurospheres with sErbB3 induced a threefold increase in the proportion of oligodendrocytes generated from NPs migrating out of the neurosphere. This effect was not observed with an unrelated soluble receptor. Addition of sErbB3 during NP growth and differentiation enhanced oligodendrocyte maturation as shown by expression of galactocerebroside and myelin basic protein. We propose that both type III Nrg-1 signaling and soluble ErbB receptors modulate oligodendrocyte development from NPs.