bluuebunny/crossref_metadata_2025 huggingface dataset:
Natural Variation in Neuron Number in Mice Is Linked to a Major Quantitative Trait Locus on Chr 11
Authors: Williams Robert W. , Strom Richelle C. , Goldowitz Dan
Published: April 2018

Common genetic polymorphisms—as opposed to rare mutations—generate almost all heritable differences in the size and structure of the CNS. Surprisingly, these normal variants have not previously been mapped or cloned in any vertebrate species. In a recent paper (Williams et al., 1996a), we suggested that much of the variation in retinal ganglion cell number in mice, and the striking bimodality of strain averages, are caused by one or two quantitative trait loci (QTLs). To test this idea, and to map genes linked to this variable and highly heritable quantitative trait, we have counted ganglion cells in 38 recombinant inbred strains (BXD and BXH) derived from parental strains that have high and low cell numbers. A genome-wide search using simple and composite interval-mapping techniques revealed a major QTL on chromosome (Chr) 11 in a 3 cM interval betweenHoxbandKrt1(LOD = 6.8; genome-widep= 0.001) and possible subsidiary QTLs on Chr 2 and Chr 8. The Chr 11 locus,neuron number control1 (Nnc1), accounts for one third of the genetic variance among BXH strains and more than half of that among BXD strains, butNnc1has no known effects on brain weight, eye weight, or total retinal cell number. Three strong candidate genes have been mapped previously to the same region asNnc1. These genes—Rara,Thra, andErbb2— encode receptors for retinoic acid, thyroxine, and neuregulin, respectively. Each receptor is expressed in the retina during development, and their ligands affect the proliferation or survival of retinal cells.
Response of Postmitotic Neurons to X-Irradiation: Implications for the Role of DNA Damage in Neuronal Apoptosis
Authors: Gobbel Glenn T. , Bellinzona Mattia , Vogt Axel R. , Gupta Nalin , Fike John R. , Chan Pak H.
Published: April 2018

The molecular changes responsible for inducing neuronal apoptosis are unknown. Rat cortical neurons were treated with x-irradiation 7 d after isolation to test for the role of DNA damage in neuronal death. The response of neurons to x-irradiation was compared with that of astrocytes that had been isolated 3 weeks earlier from newborn rats. At the time of irradiation, the neurons appeared well differentiated morphologically and were predominantly (90–95%) noncycling, based on flow cytometric analysis. There was a similar, linear increase in DNA double-strand breaks with increasing radiation dose in neurons and astrocytes. However, whereas doses as low as 2 Gy induced typical apoptotic changes in neurons, including nuclear fragmentation and/or internucleosomal DNA fragmentation, doses as high as 32 Gy caused little or no apoptosis in astrocytes. Radiation-induced apoptosis of neurons started 4–8 hr after irradiation, was maximal at 12 hr, and was dependent on dose up to 16 Gy. It was prevented when cycloheximide, a protein synthesis inhibitor, was added up to 6 hr after irradiation. In addition to their distinct apoptotic response, neurons rejoined radiation-induced DNA double-strand breaks more slowly than astrocytes. Treatment with benzamide to inhibit ADP-ribosylation and strand break repair increased apoptosis; splitting the dose of radiation to allow increased time for DNA repair decreased apoptosis. These data suggest that DNA damage may induce neuronal apoptosis, that the extent of damage may determine the degree of apoptosis induced, and that slow repair of damage may play a role in the susceptibility of neurons to apoptosis.
Tissue and Zonal-Specific Expression of an Olfactory Receptor Transgene
Authors: Qasba Pankaj , Reed Randall R.
Published: April 2018

Discrimination of odorants is thought to arise from the selective expression of one of a small number of individual receptors in any single olfactory neuron. Receptor genes are expressed in a small subset of neurons throughout a zonally restricted region of the sensory epithelium. We demonstrate that a 6.7 kb region upstream of theM4olfactory receptor coding region was sufficient to direct expression in olfactory epithelium. Moreover, reporter expression recapitulated the zonal restriction and distributed neuronal expression observed for endogenous olfactory receptors. Transgenic lines were obtained that directed expression in two different receptor zones, one of which was identical to the endogenousM4receptor. When the reporter was expressed in the same zone as the endogenousM4receptor, the two expression patterns were, in large part, nonoverlapping. These results suggest a model in which important regulatory elements are located in close proximity to transcription initiation sites of the olfactory receptor genes and receive information defining zonal patterning via long-range processes.
Gamma Oscillations in the Entorhinal Cortex of the Freely Behaving Rat
Authors: Chrobak J. J. , Buzsáki G.
Published: April 2018

Gamma frequency field oscillations (40–100 Hz) are nested within theta oscillations in the dentate–hilar and CA1–CA3 regions of the hippocampus during exploratory behaviors. These oscillations reflect synchronized synaptic potentials that entrain the discharge of neuronal populations within the ∼10–25 msec range. Using multisite recordings in freely behaving rats, we examined gamma oscillations within the superficial layers (I–III) of the entorhinal cortex. These oscillations increased in amplitude and regularity in association with entorhinal theta waves. Gamma waves showed an amplitude minimum and reversed in phase near the perisomatic region of layer II, indicating that they represent synchronized synaptic potentials impinging on layer II–III neurons. Theta and gamma oscillations in the entorhinal cortex were coupled with theta and gamma oscillations in the dentate hilar region. The majority of layer II–III neurons discharged irregularly but were phase-related to the negative peak of the local (layer II–III) gamma field oscillation. These findings demonstrate that layer II–III neurons discharge in temporally defined gamma windows (∼10–25 msec) coupled to the theta cycle. This transient temporal framework, which emerges in both the entorhinal cortex and the hippocampus, may allow spatially distributed subpopulations to form temporally defined ensembles. We speculate that the theta–gamma pattern in the discharge of these neurons is essential for effective neuronal communication and synaptic plasticity in the perforant pathway.
Dissociation Of Working Memory from Decision Making within the Human Prefrontal Cortex
Authors: Bechara Antoine , Damasio Hanna , Tranel Daniel , Anderson Steven W.
Published: April 2018

We tested the hypothesis that cognitive functions related to working memory (assessed with delay tasks) are distinct from those related to decision making (assessed with a gambling task), and that working memory and decision making depend in part on separate anatomical substrates. Normal controls (n= 21), subjects with lesions in the ventromedial (VM) (n= 9) or dorsolateral/high mesial (DL/M) prefrontal cortices (n= 10), performed on (1) modified delay tasks that assess working memory and (2) a gambling task designed to measure decision making. VM subjects with more anterior lesions (n= 4) performed defectively on the gambling but not the delay task. VM subjects with more posterior lesions (n= 5) were impaired on both tasks.RightDL/M subjects were impaired on the delay task but not the gambling task.LeftDL/M subjects were not impaired on either task. The findings reveal a cognitive and anatomic double dissociation between deficits in decision making (anterior VM) and working memory (right DL/M). This presents the first direct evidence of such effects in humans using the lesion method and underscores the special importance of the VM prefrontal region in decision making, independent of a direct role in working memory.
Involvement of Presynaptic and Postsynaptic Mechanisms in a Cellular Analog of Classical Conditioning atAplysiaSensory-Motor Neuron Synapses in Isolated Cell Culture
Authors: Bao Jian-Xin , Kandel Eric R. , Hawkins Robert D.
Published: April 2018

Temporal pairing of presynaptic activity and serotonin produces enhanced facilitation atAplysiasensory-motor neuron synapses (pairing-specific facilitation), which may contribute to classical conditioning of the gill and siphon withdrawal reflex. This cellular analog of conditioning is thought to involve Ca2+priming of the cAMP pathway in the sensory neurons. Consistent with that idea, we have found that pairing-specific facilitation by serotonin is greatly reduced by presynaptic injection of a slow Ca2+chelator or a specific inhibitor of cAMP-dependent protein kinase and is accompanied by a transient increase in the frequency but by no change in the amplitude of spontaneous, miniature EPSPs. However, like post-tetanic potentiation (PTP) and long-term potentiation (LTP) at these synapses, pairing-specific facilitation is also greatly reduced by postsynaptic injection of a rapid Ca2+chelator or by postsynaptic hyperpolarization during training, although postsynaptic hyperpolarization has no effect on the increase in frequency or on the amplitude of spontaneous EPSPs. These results suggest that pairing-specific facilitation by serotonin involves Hebbian postsynaptic as well as non-Hebbian presynaptic components that interact in some way, perhaps via retrograde signaling, to specifically enhance evoked, synchronized release of transmitter.
Whole-Cell Plasticity in Cocaine Withdrawal: Reduced Sodium Currents in Nucleus Accumbens Neurons
Authors: Zhang Xu-Feng , Hu Xiu-Ti , White Francis J.
Published: April 2018

The nucleus accumbens is a forebrain region that mediates cocaine self-administration and withdrawal effects in animal models of cocaine dependence. Considerable evidence suggests an important role of dopamine D1 receptors in these effects. Using a combination of current-clamp recordings in brain slices and whole-cell patch-clamp recordings from freshly dissociated neurons, we found that nucleus accumbens neurons are less excitable in cocaine withdrawn rats because of a novel form of plasticity: reduced whole-cell sodium currents. Three days after discontinuation of repeated cocaine injections, nucleus accumbens neurons recorded in brain slices were less responsive to depolarizing current injections, had higher action potential thresholds, and had lower spike amplitudes. Freshly dissociated nucleus accumbens neurons from cocaine-pretreated rats exhibited diminished sodium current density and a depolarizing shift in the voltage-dependence of sodium channel activation. These effects appear to be related to enhanced basal phosphorylation of sodium channels because of increased transmission through the dopamine D1 receptor/cAMP-dependent protein kinase pathway. The effects of repeated cocaine administration were not mimicked by repeated injections of the local anesthetic lidocaine and were not observed in neurons within the motor cortex, indicating that they did not result from local anesthetic actions of cocaine. Because nucleus accumbens neurons are normally recruited to coordinate response patterns of movement and affect, the decreased excitability during cocaine withdrawal may be related to symptoms such as anergia, anhedonia, and depression.
Peripheral Neural Mechanisms Determining the Orientation of Cylinders Grasped by the Digits
Authors: Dodson M. J. , Goodwin A. W. , Browning A. S. , Gehring H. M.
Published: April 2018

When a human grasps a cylindrical object, feedback on the orientation of the cylinder with respect to the axes of the digits is crucial for successful manipulation of the object. We measured the ability of humans to discriminate the orientations of cylinders passively contacting the fingerpad. For a cylinder of curvature of 521 m−1(radius, 1.92 mm) subjects were able to discriminate, at the 75% level, orientation differences of 5.4°; for a less curved cylinder (curvature, 172 m−1; radius, 5.81 mm) the difference limen decreased to 4.2°. The neural mechanisms underlying the determination of tactile orientation were investigated by recording the responses of single slowly adapting type I afferents (SAIs) innervating the fingerpads of anesthetized monkeys. When cylinders were stepped across the receptive field of an SAI, the resulting response profiles were Gaussian in shape; the shape corresponded to the shape of the cylinder, increasing in height and decreasing in width for more curved cylinders. All SAIs had the same underlying profile shape except for a multiplicative constant determined by the sensitivity of the individual afferent. Thus it was possible to reconstruct the response of the population of active SAIs in the fingerpad. Changing the orientation of the cylinder resulted in a rotation of the population response, but the change in angle of the population response was greater than the change in orientation of the cylinder. This discrepancy increased as the orientation of the cylinder moved closer to the orientation of the axis of the finger and was more pronounced for the less curved cylinder. Measured contact areas between the cylinders and the skin were elliptical, with orientations exceeding those of the cylinder; again the differences were greater for the less curved cylinder and for orientations closer to that of the finger axis. The human discrimination performance could be explained in terms of the SAI population responses.
Chronic Stage Multiple Sclerosis Lesions Contain a Relatively Quiescent Population of Oligodendrocyte Precursor Cells
Authors: Wolswijk Guus
Published: April 2018

In the past decade, considerable progress has been made in the understanding of the biology of rodent oligodendrocyte precursor cells and their role in the generation of oligodendrocytes in the developing and adult rodent CNS. Much less is known about human oligodendrocyte lineage cells and about the reasons for the failure of the regeneration of the oligodendrocyte population during chronic stages of multiple sclerosis (MS). In particular, the fate of the oligodendrocyte precursor population in MS has remained elusive. The present study examined the possibility that oligodendrocyte regeneration ultimately fails because of the local destruction of both oligodendrocytes and their precursor cells. Analysis of chronic stage MS tissue suggested that this is not the case, because all chronic MS lesions studied contained significant numbers of oligodendrocyte precursor cells, identified as process-bearing cells that bound the O4 antibody but not antibodies to GalC and GFAP. The oligodendrocyte precursor cells appeared, however, to be relatively quiescent, because none expressed the nuclear proliferation antigen recognized by the Ki-67 antibody, and because most lesions lacked myelinating oligodendrocytes in their centers. Thus, it appears that the regeneration of the oligodendrocyte population fails during chronic stages of MS because of the inability of oligodendrocyte precursor cells to proliferate and differentiate rather than because of the local destruction of all oligodendrocyte lineage cells. The identification of ways of stimulating the endogenous oligodendrocyte precursor population to expand and generate remyelinating cells may represent an alternative to transplantation of oligodendrocyte lineage cells to promote myelin repair in MS.
Reorganization of the Dendritic Trees of Oxytocin and Vasopressin Neurons of the Rat Supraoptic Nucleus during Lactation
Authors: Stern Javier E. , Armstrong William E.
Published: April 2018

Oxytocin (OT) and vasopressin (VP) release from the neurohypophysis are correlated with the electrical activity of magnocellular cells (MNCs) in the supraoptic (SON) and paraventricular nuclei. Synaptic inputs to MNCs influence their electrical activity and, hence, hormone release. During lactation OT neurons display a synchronized high-frequency bursting activity preceding each milk ejection. In parallel to the adoption of this pattern of electrical activity, an ultrastructural reorganization of the SON has been observed during lactation. In the present study we performed a light microscopic, morphometric analysis of identified OT and VP neurons in the SON to determine whether the dendrites of these neurons participate in the plasticity observed during lactation. The dendritic trees of OT neurons shrunk during lactation (∼41% decrease in the total dendritic length) because of a decreased dendritic branching concentrated at a distance of 100–200 μm from the soma. No changes in the maximal distal extension were observed. The distribution pattern of dendritic length into branch orders also was affected. Strikingly, opposite effects were observed in VP neurons. The dendritic trees during lactation elongated (∼48% increase in the total dendritic length) because of an increased branching close to the soma. No changes in the maximal distal extension were observed. These results indicate that the length and geometry of the dendritic trees of OT and VP neurons are altered in opposite ways during lactation. These changes would influence the availability of postsynaptic space and alter the electrotonic properties of the neurons, affecting the efficacy of synaptic inputs.
An Open Rectifier Potassium Channel with Two Pore Domains in Tandem Cloned from Rat Cerebellum
Authors: Leonoudakis Dmitri , Gray Andrew T. , Winegar Bruce D. , Kindler Christoph H. , Harada Masato , Taylor Donald M. , Chavez Raymond A. , Forsayeth John R. , Yost C. Spencer
Published: April 2018

Tandem pore domain K+channels represent a new family of ion channels involved in the control of background membrane conductances. We report the structural and functional properties of a TWIK-related acid-sensitive K+channel (rTASK), a new member of this family cloned from rat cerebellum. The salient features of the primary amino acid sequence include four putative transmembrane domains and, unlike other cloned tandem pore domain channels, a PDZ (postsynaptic density protein, disk-large, zo-1) binding sequence at the C terminal. rTASK has distant overall homology to a putativeCaenorhabditis elegansK+channel and to the mammalian clones TREK-1 and TWIK-1. rTASK expression is most abundant in rat heart, lung, and brain. When exogenously expressed inXenopusoocytes, rTASK currents activate instantaneously, are noninactivating, and are not gated by voltage. Because rTASK currents satisfy the Goldman–Hodgkin–Katz current equation for an open channel, rTASK can be classified an open rectifier. Activation of protein kinase A produces inhibition of rTASK, whereas activation of protein kinase C has no effect. rTASK currents were inhibited by extracellular acidity. rTASK currents also were inhibited by Zn2+(IC50= 175 μm), the local anesthetic bupivacaine (IC50= 68 μm), and the anti-convulsant phenytoin (∼50% inhibition at 200 μm). By demonstrating open rectification and open probability independent of voltage, we have established that rTASK is a baseline potassium channel.
Mitochondrial Membrane Potential and Nuclear Changes in Apoptosis Caused by Serum and Nerve Growth Factor Withdrawal: Time Course and Modification by (−)-Deprenyl
Authors: Wadia J. S. , Chalmers-Redman R. M. E. , Ju W. J. H. , Carlile G. W. , Phillips J. L. , Fraser A. D. , Tatton W. G.
Published: April 2018

Studies in non-neural cells have suggested that a fall in mitochondrial membrane potential (ΔΨM) is one of the earliest events in apoptosis. It is not known whether neural apoptosis caused by nerve growth factor (NGF) and serum withdrawal involves a decrease in ΔΨM. We used epifluorescence and laser confocal microscopy with the mitochondrial potentiometric dyes chloromethyl-tetramethylrosamine methyl ester and 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethybenzimidazol carbocyanine iodide to estimate ΔΨM. PC12 cells were differentiated in media containing serum and NGF for 6 d before withdrawal of trophic support. After washing, the cells were incubated with media containing serum and NGF (M/S+N), media without serum and NGF, or media with the “trophic-like” monoamine oxidase B inhibitor, (−)-deprenyl. Mitochondria in cells without trophic support underwent a progressive shift to lower ΔΨMvalues that was significant by 3 hr after washing. The percentages of cells with nuclear chromatin condensation or nuclear DNA fragmentation were not significantly increased above those for cells in M/S+N until 6 hr after washing. Replacement of cells into M/S+N or treatment with (−)-deprenyl markedly reduced the proportion of mitochondria with decreased ΔΨM. Measurements of cytoplasmic peroxyl radical levels with 2′,7′-dihydrodichlorofluorescein fluorescence and intramitochondrial Ca2+with dihydro-rhodamine-2-acetylmethyl ester indicated that cytoplasmic peroxyl radical levels were not increased until after 6 hr, whereas increases in intramitochondrial Ca2+paralleled the decreases in ΔΨM. (−)-Deprenyl appeared to alter the relationship between intramitochondrial Ca2+levels and ΔΨM, possibly through its reported capacity to increase the synthesis of proteins such as BCL-2.
Patch-Clamp Recordings from Cerebellar Basket Cell Bodies and Their Presynaptic Terminals Reveal an Asymmetric Distribution of Voltage-Gated Potassium Channels
Authors: Southan Andrew P. , Robertson Brian
Published: April 2018

Cerebellar basket cells form highly specialized inhibitory synaptic contacts with Purkinje cells, namely the pericellular basket and pinceau nerve terminal structures, wrapping around the Purkinje cell somatic and axon hillock regions. These inhibitory synaptic contacts are ideally located to control the ultimate output of the cerebellar cortex. Previous immunohistochemical studies have shown that these synaptic structures possess a very high density of the dendrotoxin (DTX)-sensitive potassium channel subunit, Kv1.2. We have taken advantage of this unique anatomical arrangement offering a high concentration of identified Kv channel subunits by combining whole-cell patch-clamp recording and fluorescence microscopy to establish a novel preparation and perform the first recordings from unambiguously identified mammalian CNS inhibitory presynaptic terminals. We report that DTX-sensitive potassium channels are present in basket cell terminals but not in the basket cell soma. This selective cellular distribution suggests that these channels play an important role in modulating cerebellar inhibitory synaptic transmission.
Arginine Kinase Expression and Localization in Growth Cone Migration
Authors: Wang Yu-mei E. , Esbensen Pia , Bentley David
Published: April 2018

Migrating neuronal growth cones exert traction forces that are generated by ATP-driven F-actin/myosin interactions. Sustained generation of these forces may require an energy supply mediated by the guanidino kinases, creatine kinase and arginine kinase. We cloned and sequenced grasshopper arginine kinase and examined its expression during embryogenesis and its subcellular localizationin vivoandin vitro. During the first half of embryogenesis, arginine kinase is expressed selectively in a small percentage of ectodermal cells (dorsal closure cells), in a small percentage of mesodermal cells (muscle pioneers), and throughout the developing CNS. Most of these cell types are motile, including nascent neurons, muscle pioneers, dorsal closure cells, and many CNS glia. Neuroblasts also strongly express arginine kinase; they are nonmotile but are undergoing repeated rounds of (ATP-dependent) mitosis. Arginine kinase is colocalized with F-actin in a narrow band along the leading edges of lamellipodia of migrating glia. In neurons undergoing axonogenesis, arginine kinase is concentrated in growth cones and extends to the tips of filopodia. The amount of arginine kinase varies widely between growth cones, even between different growth cones of the same neuron. Energy for growth cone migration appears to be mobilized by (1) selective expression of arginine kinase by neurons, (2) localization of arginine kinase within growth cones, and (3) concentration of arginine kinase within specific growth cones, depending on the traction forces being generated. Mobilization of guanidino kinases may participate in the selective growth of specific growth cones.
Bcl-xLis an Antiapoptotic Regulator for Postnatal CNS Neurons
Authors: Parsadanian Alexander Sh. , Cheng Yu , Keller-Peck Cynthia R. , Holtzman David M. , Snider William D.
Published: April 2018

Bcl-xLis a death-inhibiting member of the Bcl-2/Ced9 family of proteins which either promote or inhibit apoptosis. Gene targeting has revealed that Bcl-xLis required for neuronal survival during brain development; however,Bcl-xLknock-out mice do not survive past embryonic day 13.5, precluding an analysis of Bcl-xLfunction at later stages of development. Bcl-xLexpression is maintained at a high level postnatally in the CNS, suggesting that it may also regulate neuron survival in the postnatal period. To explore functions of Bcl-xLrelated to neuron survival in postnatal life, we generated transgenic mice overexpressing humanBcl-xLunder the control of a pan-neuronal promoter. A line that showed strong overexpression in brainstem and a line that showed overexpression in hippocampus and cortex were chosen for analysis. We asked whether overexpression of Bcl-xLinfluences neuronal survival in the postnatal period by studying two injury paradigms that result in massive neuronal apoptosis. In the standard neonatal facial axotomy paradigm, Bcl-xLoverexpression had substantial effects, with survival of 65% of the motor neurons 7 d after axotomy, as opposed to only 15% in nontransgenic littermates. To investigate whether Bcl-xLregulates survival of CNS neurons in the forebrain, we used a hypoxia–ischemia paradigm in neonatal mice. We show here that hypoxia–ischemia leads to substantial apoptosis in the hippocampus and cortex of wild-type neonatal mice. Furthermore, we show that overexpression of Bcl-xLis neuroprotective in this paradigm. We conclude that levels of Bcl-xLin postnatal neurons may be a critical determinant of their susceptibility to apoptosis.
Multioscillatory Circadian Organization in a Vertebrate,Iguana iguana
Authors: Tosini Gianluca , Menaker Michael
Published: April 2018

The lizardIguana iguanawhen kept in constant ambient temperature displays endogenously generated circadian rhythms of body temperature and locomotor activity. Although surgical removal of the parietal eye has only slight effects on overt circadian rhythmicity, subsequent pinealectomy completely abolishes the rhythm of body temperature. However, the rhythm of locomotor activity is only slightly affected by parietalectomy plus pinealectomy. Our results demonstrate that the pineal complex is centrally involved in the generation and control of the circadian rhythm of body temperature but is only marginally involved in locomotor rhythmicity. Plasma melatonin levels are not significantly reduced by parietalectomy, whereas pinealectomy dramatically lowers the level and completely eliminates the circadian rhythm of melatonin in the circulation. Isolated parietal eye, pineal, and retina all synthesize melatonin with robust circadian rhythmicity when maintained for ≥4 d in culture, although in the intact animal all or almost all of the circulating melatonin comes from the pineal. The circadian system ofI. iguanais composed of multiple circadian oscillators that reside in different tissues and have specific and different roles.
Sex Difference in the Size of the Neural Song Control Regions in a Dueting Songbird with Similar Song Repertoire Size of Males and Females
Authors: Gahr Manfred , Sonnenschein Edith , Wickler Wolfgang
Published: April 2018

Previous studies have suggested a causal relation between sex differences in behavior such as singing and sex differences in the size of brain areas such as the forebrain song control areas of songbirds. In the present study we show that the size of the forebrain vocal control areas nucleus hyperstriatalis ventrale pars caudale (HVC) and nucleus robustus archistriatalis (RA) and its neuron numbers are about twice as large in males as in females of the African dueting bush shrikeLaniarius funebris. However, song types are of similar complexity (number of elements per song type, physical properties of elements) in both sexes, and repertoire size does not differ between males and females. Furthermore, in captivity male and female shrikes are able to learn the same song types. This demonstrates for the shrike that sex differences in the size of vocal control areas and in its neuron numbers do not predict the type of sex-typical vocal behavior. This result is supported by a statistical comparison of the sex differences in HVC size, RA size, and song repertoire size of all songbird species studied to date. Sex differences in species in which only the males sing are indeed larger than in species in which the females also sing; in songbird species with singing females, however, the sex differences in HVC and RA volume appear to be independent of the vocal repertoire size of females. The songbird model therefore does not support the notion that sex differences in area size and neuron number explain sex differences in a behavior that occurs in both sexes. Furthermore, in the shrike, neuron soma size is similar in males and females in the song motonucleus hypoglossus pars tracheosyringealis (nXIIts) and in the premotor nucleus RA, but is sexually dimorphic in the higher vocal center HVC. Thus, male and female shrikes produce songs of similar complexity with different neuron phenotypes.
Short-Term Afferent Axotomy Increases Both Strength and Depression at Ia–Motoneuron Synapses in Rat
Authors: Seburn Kevin L. , Cope Timothy C.
Published: April 2018

Synaptic efficacy at the rat Ia–motoneuron synapse has been reported to increasein vivo, within 3 d of sectioning a single muscle nerve (Miyata and Yasuda, 1988). We provide an indirect test of the hypothesis that this increase is caused by altered probability of transmitter release of axotomized afferents. Experiments consisted ofin vivorecording of maximal composite group I EPSPs evoked in intact rat medial gastrocnemius (MG) motoneurons by stimulation of the lateral gastrocnemius-soleus nerve (LG-S). We compared the maximal LG-S EPSP amplitude and the response to high-frequency stimulation (modulation) recorded in untreated rats, with the same measures recorded in rats that had the LG-S nerve axotomized 3 d before data collection. In confirmation of previous work, the mean amplitude of LG-S EPSPs evoked by stimulation of axotomized afferents was significantly larger than that measured in untreated rats (3.9 ± 0.34 and 2.3 ± 0.19 mV, respectively). The increase in EPSP amplitude was accompanied by significantly greater negative modulation (depression) of EPSP amplitude during high-frequency stimulation (−39 ± 4% and −53 ± 4%, untreated and treated, respectively). Modulation would not be expected to change if the increase in EPSP amplitude was attributable solely to a greater number of afferent connections (Koerber and Mendell, 1991). Therefore, the present results are consistent with the hypothesis that the initial axotomy-induced increase in synaptic efficacy occurs because of an increase in the probability of transmitter release. Furthermore, these results suggest that the probability of transmitter release at this synapse is regulated by either afferent activity and/or trophic communication with the target muscle.
Acetylcholine Activates an α-Bungarotoxin-Sensitive Nicotinic Current in Rat Hippocampal Interneurons, But Not Pyramidal Cells
Authors: Frazier Charles J. , Rollins Yvonne D. , Breese Charles R. , Leonard Sherry , Freedman Robert , Dunwiddie Thomas V.
Published: April 2018

The effects of acetylcholine on both pyramidal neurons and interneurons in the area CA1 of the rat hippocampus were examined, using intracellular recording techniques in anin vitroslice preparation. In current-clamp mode, fast local application of acetylcholine (ACh) to the soma of inhibitory interneurons in stratum radiatum resulted in depolarization and rapid firing of action potentials. Under voltage-clamp, ACh produced fast, rapidly desensitizing inward currents that were insensitive to atropine but that were blocked by nanomolar concentrations of the nicotinic α7 receptor-selective antagonists α-bungarotoxin (αBgTx) and methyllycaconitine. Nicotinic receptor antagonists that are not selective for α7-containing receptors had little (mecamylamine) or no effect (dihydro-β-erythroidine) on the ACh-induced currents. Glutamate receptor antagonists had no effect on the ACh-evoked response, indicating that the current was not mediated by presynaptic facilitation of glutamate release. However, the current could be desensitized almost completely by bath superfusion with 100 nmnicotine. In contrast to those actions on interneurons, application of ACh to the soma of CA1 pyramidal cells did not produce a detectable current. Radioligand-binding experiments with [125I]-αBgTx demonstrated that stratum radiatum interneurons express α7-containing nAChRs, andin situhybridization revealed significant amounts of α7 mRNA. CA1 pyramidal cells did not show specific binding of [125I]-αBgTx and only low levels of α7 mRNA. These results suggest that, in addition to their proposed presynaptic role in modulating transmitter release, α7-containing nAChRs also may play a postsynaptic role in the excitation of hippocampal interneurons. By desensitizing these receptors, nicotine may disrupt this action and indirectly excite pyramidal neurons by reducing GABAergic inhibition.
Activated Protein C Reduces the Severity of Compression-Induced Spinal Cord Injury in Rats by Inhibiting Activation of Leukocytes
Authors: Taoka Yuji , Okajima Kenji , Uchiba Mitsuhiro , Murakami Kazunori , Harada Naoaki , Johno Masayoshi , Naruo Masakuni
Published: April 2018

Activated protein C (APC), an important inhibitor of the coagulation system, has recently been shown to prevent tissue injury by blocking the activation of leukocytes. To determine whether APC can also prevent post-traumatic spinal cord injury (SCI), a condition in which leukocytes play an important role, we tested the effects of APC on SCI induced in rats by compression trauma. Administration of APC, either before or after the induction of SCI, markedly reduced the motor disturbances in these animals. In contrast, neither an inactive derivative of activated factor X (DEGR-Xa), a selective inhibitor of thrombin generation, nor active site-blocked APC (DIP-APC) reduced the motor disturbances. Histological examination revealed that intramedullary hemorrhages, observed 24 hr after trauma, were significantly reduced in the animals administered APC. The increase in the tissue level of tumor necrosis factor-α (TNF-α) and the accumulation of neutrophils in the damaged segment of the spinal cord were significantly inhibited in the animals that had received APC, but these were not inhibited in those administered DIP-APC or DEGR-Xa. The induction of leukocytopenia had the same effect as APC, in that it significantly reduced motor disturbances, tissue levels of TNF-α, and neutrophil accumulation in the animals subjected to compressive SCI. These findings suggest that in SCI, APC reduces motor disturbances primarily by reducing the amount of TNF-α at the site of injury, thus inhibiting neutrophil accumulation and the resultant damage to the endothelial cells.
Synergistic Effects of Schwann- and Muscle-Derived Factors on Motoneuron Survival Involve GDNF and Cardiotrophin-1 (CT-1)
Authors: Arce Vilma , Pollock Richard A. , Philippe Jean-Marc , Pennica Diane , Henderson Christopher E. , deLapeyrière Odile
Published: April 2018

The survival of central neurons depends on multiple neurotrophic factors produced by different cell types. We demonstrate that media conditioned by muscle and Schwann cell lines show strong synergistic effects on survival of purified embryonic day 14.5 rat motoneurons in culture. Different lines of evidence implicate glial cell line-derived neurotrophic factor (GDNF) and cardiotrophin-1 (CT-1) in this synergy. Their expression in the environment of the motoneuron is compartmentalized:gdnftranscripts are expressed principally in Schwann cell lines, whereasct-1mRNA is present in myotubes. Blocking antibodies to GDNF inhibit the trophic activity of Schwann cell line-conditioned media by 75%, whereas CT-1 antibodies diminish the myotube-derived activity by 46%. CT-1 and GDNF act synergistically to enhance motoneuron survivalin vitro.In vivo, individual motoneurons coexpress both GDNF and CT-1 receptor components. GDNF and CT-1, therefore, are major components of the trophic support provided by the Schwann and muscle cells, respectively. The possibility that they act together on individual motoneurons suggests that the motoneuron must integrate distinct signals from different cellular partners when deciding whether to die or to survive.
Prenatal Development of Layer-Specific Local Circuits in Primary Visual Cortex of the Macaque Monkey
Authors: Callaway Edward M.
Published: April 2018

Previous studies have demonstrated that axonal arbors specific for the four main cortical layers — 2/3, 4, 5, and 6 — develop precisely from the outset using activity-independent cues. In macaque primary visual cortex (V1), layer 2/3 is subdivided into layers named 2/3A, 3B, 4A, and 4B, and layer 4 is subdivided into 4Cα and 4Cβ. Individual neurons in V1 of mature macaques have axonal arbors that are highly specific for these sublayers. We have studied the prenatal development of laminar and sublaminar specificity of local circuits in macaque V1. Two-hundred thirty-eight neurons were labeled intracellularly in living brain slices prepared from V1 of five prenatal macaque monkeys aged 100 to 145 d postconception (E100–E145). Axonal and dendritic arbors of labeled neurons were reconstructed to assess their relationships to the cortical layers. We find that developing spiny neurons in layers 2–4B and layer 5 specifically target superficial and deep layers without forming “incorrect” branches in layer 4C. Similarly, layer 6 pyramidal neurons that target layer 4C do not form “incorrect” branches in layer 5. These results indicate that specific projections to the main cortical layers develop with a high degree of selectivity, as in other species. However, the development of sublayer-specific projections was not always precise from the outset. Unlike postnatal animals, axons of some prenatal layer 4Cβ spiny neurons branch in layer 4B. At similar ages, many pyramidal neurons in the upper half of layer 6 have axonal branches in layer 4Cα as well as 4Cβ; these projections are specific for 4Cβ in more mature animals. Also, there is similar “exuberance” in axonal arbors of other layer 6 cell types. Transient projections were also observed in the subplate and to the white matter for cells from all layers, except 4Cβ. These observations indicate that at least some sublayer-specific projections emerge by elimination of exuberant axonal branches and suggest that they may use activity-dependent mechanisms to identify “correct” target layers. Such cues could be provided by laminar differences in the patterns of spontaneous prenatal activity in the retino-geniculo-cortical network.
Extracellular Signal-Regulated Kinase and p38 Subgroups of Mitogen-Activated Protein Kinases Regulate Inducible Nitric Oxide Synthase and Tumor Necrosis Factor-α Gene Expression in Endotoxin-Stimulated Primary Glial Cultures
Authors: Bhat Narayan R. , Zhang Peisheng , Lee John C. , Hogan Edward L.
Published: April 2018

Tumor necrosis factor-α (TNFα) and nitric oxide (NO), the product of inducible NO synthase (iNOS), mediate inflammatory and immune responses in the CNS under a variety of neuropathological situations. They are produced mainly by “activated” astrocytes and microglia, the two immune regulatory cells of the CNS. In this study we have examined the regulation of TNFα and iNOS gene expression in endotoxin-stimulated primary glial cultures, focusing on the role of mitogen-activated protein (MAP) kinase cascades. The bacterial lipopolysaccharide (LPS) was able to activate extracellular signal-regulated kinase (ERK) and p38 kinase subgroups of MAP kinases in microglia and astrocytes. ERK activation was sensitive to PD98059, the kinase inhibitor that is specific for ERK kinase. The activity of p38 kinase was inhibited by SB203580, a member of the novel class of cytokine suppressive anti-inflammatory drugs (CSAIDs), as revealed by blocked activation of the downstream kinase, MAP kinase-activated protein kinase-2. The treatment of glial cells with either LPS alone (microglia) or a combination of LPS and interferon-γ (astrocytes) resulted in an induced production of NO and TNFα. The two kinase inhibitors, at micromolar concentrations, individually suppressed and, in combination, almost completely blocked glial production of NO and the expression of iNOS and TNFα, as determined by Western blot analysis. Reverse transcriptase-PCR analysis showed changes in iNOS mRNA levels that paralleled iNOS protein and NO while indicating a lack of effect of either of the kinase inhibitors on TNFα mRNA expression. The results demonstrate key roles for ERK and p38 MAP kinase cascades in the transcriptional and post-transcriptional regulation of iNOS and TNFα gene expression in endotoxin-activated glial cells.
Presynaptic Nicotinic Receptors Facilitate Monoaminergic Transmission
Authors: Li Xiangyang , Rainnie Donald G. , McCarley Robert W. , Greene Robert W.
Published: April 2018

Nicotine is reported to increase arousal and attention and to elevate mood, effects that are most often associated with changes in the function of monoaminergic neuromodulatory systems (Feldman et al., 1997). Recent studies have shown a nicotinic receptor-mediated presynaptic enhancement of fast glutamatergic (McGehee et al., 1995;Gray et al., 1996) and GABAergic (Léna and Changeux, 1997) transmission. However, the mechanism of nicotinic effects on metabotropic-mediated transmission in general, and on monoaminergic transmission in particular, is less well understood. We have examined nicotinic effects on dorsal raphe neurons of rats using whole-cell current and voltage-clamp recording techniquesin vitro. In the majority of these neurons, activation of presynaptic nicotinic receptors induced a depolarization mediated by norepinephrine acting on α1 receptors. Blockade of this response revealed a hyperpolarization mediated by serotonin acting on 5-HT1Areceptors. Because the norepinephrine effect was sensitive to methyllycaconitine (100 nm), it is concluded that nicotinic receptors with an α7 subunit can facilitate release of norepinephrine to activate metabotropic receptors. In contrast, methyllycaconitine-insensitive nicotinic receptors can induce 5-HT release in the dorsal raphe nucleus.
Developmental Changes in NMDA Receptor Glycine Affinity and Ifenprodil Sensitivity Reveal Three Distinct Populations of NMDA Receptors in Individual Rat Cortical Neurons
Authors: Kew James N. C. , Richards J. Grayson , Mutel Vincent , Kemp John A.
Published: April 2018

Previous work with recombinant receptors has shown that the identity of the NMDA NR2 subunit influences receptor affinity for both glutamate and glycine. We have investigated the developmental change in NMDA receptor affinity for both glutamate and glycine in acutely dissociated parietal cortex neurons of the rat, together with the expression during ontogeny of NR2A and NR2B mRNA and protein. Whereas there is little change in NMDA receptor glutamate affinity with age, a population of NMDA receptors emerges in 14- and 28-d-old animals with a markedly reduced affinity for glycine (mKD= ∼800 nm) and a reduced sensitivity to the NR2B subunit-selective NMDA antagonist ifenprodil. These changes are paralleled by a developmental increase in the expression of NR2A. Thus, in mature animals a population of NMDA receptors appears with a lower affinity for glycine that might not be saturated under normal physiological conditions. Ifenprodil (10 μm) inhibits virtually all of the NMDA receptor-evoked current in very young neurons that contain a single population of receptors exhibiting a high affinity for glycine (mKD= ∼20 nm). In older neurons, which contain NMDA receptors with both high and low affinities for glycine, ifenprodil (10 μm) inhibits both the high-affinity population and a significant proportion of the low-affinity component, thus revealing three pharmacologically distinct populations of NMDA receptors in single neurons. Moreover, these observations suggest that ifenprodil might bind with high affinity to NMDA receptors containing both NR2A and NR2B subunits as well as those containing only NR2B.
Delayed Expression of Osteopontin after Focal Stroke in the Rat
Authors: Wang Xinkang , Louden Calvert , Yue Tian-Li , Ellison Julie A. , Barone Frank C. , Solleveld Henk A. , Feuerstein Giora Z.
Published: April 2018

Focal brain ischemia induces inflammation, extracellular matrix remodeling, gliosis, and neovascularization. Osteopontin (OPN) is a secreted glycoprotein that has been implicated in vascular injury by promoting cell adhesion, migration, and chemotaxis. To investigate the possible involvement of OPN in brain matrix remodeling after focal stroke, we examined the expression of OPN in ischemic cortex after permanent or temporary occlusion of the middle cerebral artery (MCAO) of the rat. OPN mRNA and protein levels in nonischemic cortex were not detected consistently, although significant induction of OPN was observed in the ischemic cortex. OPN mRNA increased 3.5-fold at 12 hr and reached peak levels 5 d (49.5-fold;p< 0.001) after permanent MCAO. The profile of OPN mRNA induction after transient MCAO (160 min) with reperfusion was essentially the same as that of permanent MCAO.In situhybridization and immunohistochemical studies demonstrated strong induction of OPN in the ischemic cortex, which was localized primarily in a subset of ED-1-positive macrophages that accumulated in the ischemic zone. Moreover, OPN immunoreactivity was detected in the matrix of ischemic brain, suggesting a functional role of the newly deposited matrix protein in cell–matrix interactions and remodeling. Indeed, using a modified Boyden chamber, we demonstrated a dose-dependent chemotactic activity of OPN in C6 astroglia cells and normal human astrocytes. Taken together, these data suggest that the upregulation of OPN after focal brain ischemia may play a role in cellular (glia, macrophage) migration/activation and matrix remodeling that provides for new matrix–cell interaction.
Control of Neural Development and Function in a Thermoregulatory Network by the LIM Homeobox Genelin-11
Authors: Hobert Oliver , D’Alberti Tania , Liu Yanxia , Ruvkun Gary
Published: April 2018

We show here that thelin-11LIM homeobox gene is expressed in nine classes of head, ventral cord, and tail neurons and functions at a late step in the development of a subset of these neurons. In alin-11null mutant, alllin-11-expressing neurons are generated. Several of these neurons, however, exhibit neuroanatomical as well as functional defects. In the lateral head ganglion,lin-11functions in a neural network that regulates thermosensory behavior. It is expressed in the AIZ interneuron that processes high temperature input and is required for the function of AIZ in the thermoregulatory neural network. Another LIM homeobox gene,ttx-3, functions in the antagonistic thermoregulatory interneuron AIY (Hobert et al., 1997). Thus, distinct LIM genes specify the functions of functionally related antagonistic interneurons within a neural network dedicated for thermoregulatory processes. Bothttx-3andlin-11expression are maintained throughout adulthood, suggesting that these LIM homeobox genes play a role in the functional maintenance of this neural circuit. We propose that particular LIM homeobox genes specify the distinct features of functionally related neurons that generate patterned behaviors.