bluuebunny/crossref_metadata_2025 huggingface dataset:
Restoration of circadian behavior by anterior hypothalamic heterografts
Authors: Sollars PJ , Kimble DP , Pickard GE
Published: April 2018

The suprachiasmatic nucleus (SCN) of the anterior hypothalamus (AH) is a circadian oscillator and an important component of the mammalian circadian system. To determine whether the SCN is the dominant circadian pacemaker responsible for generating a species-typical characteristic of circadian rhythms [i.e., period length (tau)], neural transplantation was conducted using fetal AH donors of different species and SCN-lesioned (SCNx) hosts. The circadian behavior of each of the three donor species is clearly distinguishable by its species- typical tau. The extent of SCN pacemaker autonomy was assessed by noting whether the period of the restored circadian rhythm following heterograft transplantation was characteristic of the donor or the host, or whether an atypical circadian period was established. Hamsters rendered arhythmic by SCN ablation were implanted with AH tissue from fetal hamsters (E13-E14, homograft controls) or fetal mice or rats (E15- E17). The AH homografts restored circadian activity rhythms with a tau similar to that of intact hamsters, and fetal mouse AH heterografts restored circadian rhythmicity with a tau similar to that of the donor mouse strain. However, fetal rat AH tissue implanted into SCNx hamsters renewed circadian rhythmicity with a period significantly shorter than either the species-typical tau of the rat donor or the hamster host. In both the mouse and rat AH heterograft experiments, immunocytochemical analysis performed with species-specific monoclonal antibodies revealed extensive fiber outgrowth from the implant into the host hypothalamus, evident up to 7 months postimplantation. The rat implants were consistently larger, more fully vascularized and exhibited less necrosis than the implanted mouse tissue. The histological appearance of the grafts, thus, provides no explantation for the difference in efficacy of the grafts to restore species-typical behavior. However, several interpretations are considered that are consistent with the combined behavioral results observed.
Long-term modulation of inward currents in O2 chemoreceptors by chronic hypoxia and cyclic AMP in vitro
Authors: Stea A , Jackson A , Macintyre L , Nurse CA
Published: April 2018

In mammals, ventilatory acclimatization to hypoxia is associated with an enhanced chemosensitivity of the O2-sensing carotid body, resulting in an increased respiratory drive. To test whether this sensitization involves long-term modulation of ion channel function in endogenous O2 chemoreceptors, i.e., type 1 cells, we exposed cultures of dissociated rat carotid body to chronic hypoxia (6% O2) for 1–2 weeks, before monitoring the electrophysiological properties of type 1 cells using whole-cell, perforated patch recording. Chronic hypoxia augmented voltage-dependent inward Na+ and Ca2+ currents in type 1 cells, without significant changes in voltage dependence of activation or steady-state inactivation. However, after normalizing for the concomitant increase in cell size, indicated by the whole-cell capacitance, only the Na+ current density was significantly enhanced. The Na+ current was sensitive to tetrodotoxin (TTX; 0.5–1 microM) or choline substitution, whereas most of the Ca2+ current was sensitive to the L-type calcium channel blocker, nifedipine (10 microM). Several of these effects of hypoxia were mimicked qualitatively by growing normoxic cultures in the presence of agents that elevate intracellular cyclic AMP, including dibutyryl cAMP (db-cAMP; 200 microM-1 mM) and forskolin (10 microM); treatment with similar concentrations of dibutyryl cyclic GMP was ineffective. Na+ channel induction by db-cAMP was abolished by the protein synthesis inhibitor, cycloheximide (90–180 microM). In current- clamp mode, these altered chemoreceptors had typical resting potentials of approximately -55 mV, and following depolarization often fired multiple spikes that appeared to consist of both short-duration Na+ and long-duration Ca2+ components. We propose that chronic hypoxia, acting in part through cAMP-dependent pathways, increases electrical excitability and calcium mobilization in type 1 cells, and these adaptations may help enhance chemosensitivity during hypoxic acclimatization.
Lesion-induced sprouting of commissural/associational axons and induction of GAP-43 mRNA in hilar and CA3 pyramidal neurons in the hippocampus are diminished in aged rats
Authors: Schauwecker PE , Cheng HW , Serquinia RM , Mori N , McNeill TH
Published: April 2018

Removal of synaptic connections following a partial deafferentation lesion results in a sprouting of remaining afferents that terminate near the denervated area. However, while the ability to form new synapses in response to injury has been reported in both young and aged rats, previous studies have suggested that the injury-induced response in the hippocampus of aged rats may be delayed and/or not as extensive as compared to young adults. Given that growth associated proteins are central for the regulation of neurite outgrowth during both development and regeneration, we were interested in determining if the magnitude and time course of the sprouting response of hippocampal neurons to deafferentation might correlate with induction of growth associated proteins and whether these parameters could be modulated with age. For our studies we used the Holmes fiber stain to determine the expansion of the C/A fiber plexus following denervation and compared the time course of the sprouting response with that observed by in situ hybridization for the neurite outgrowth proteins, growth associated protein-43 (GAP-43), superior cervical ganglion-10 (SCG-10), and neurofilament-68 (NF-68) at various time points after the lesion for each age group. We found that the commissural/associational (C/A) fiber plexus expanded by 45% in young adult rats at 30 and 45 d postlesion and was accompanied by a significant increase in expression of GAP-43 mRNA in both ipsilateral and contralateral hilar and CA3 pyramidal neurons, the cell bodies of origin for the C/A pathway. In contrast, a dampened sprouting response was observed in aged rats at all time points postlesion and coincided with a lack of induction of any of the growth-associated proteins. These results suggest that GAP-43 is involved in outgrowth of C/A axons in the hippocampus in response to a partial deafferentation lesion. However, factors that stimulate neurite outgrowth and upregulate GAP-43 mRNA in response to a partial deafferentation lesion diminish with age.
Gene structure and glial expression of the glycine transporter GlyT1 in embryonic and adult rodents
Authors: Adams RH , Sato K , Shimada S , Tohyama M , Puschel AW , Betz H
Published: April 2018

Na+/Cl(-)-dependent glycine transporters are crucial for the termination of neurotransmission at glycinergic synapses. Two different glycine transporter genes, GlyT1 and GlyT2, have been described. Several isoforms differing in their 5′ ends originate from the GlyT1 gene. We have determined the genomic structure of the murine GlyT1 gene to elucidate the genetic basis underlying the different isoforms. Analysis of cDNA 5′-ends revealed that the GlyT1a and 1b/1c mRNAs are transcribed from two different promoters. During murine embryonic development GlyT1 mRNAs were detectable by RNase protection assays as early as embryonic day E9 and reached maximal levels between E13 and E15. In situ hybridization revealed GlyT1 expression in the developing spinal cord mainly in the ventral part of the ventricular zone at E12. At later stages (E15) transcripts were also found in the lateral half of the basal and intermediate gray matter. In contrast, the second glycine transporter gene GlyT2 displayed a completely different expression pattern. At E11 it is expressed in the mantle zone, and at later stages throughout the ventral horns. In the adult rat brain and spinal cord, GlyT1 hybridization signals were found exclusively in glial cells. Our data indicate that GlyT1 is an early marker of neural development and encodes glia-specific transporter proteins.
A Novel Subunit for Shal K+Channels Radically Alters Activation and Inactivation
Authors: Jegla Timothy , Salkoff Lawrence
Published: April 2018

Shal (Kv4) potassium channel genes encode classical subthreshold A-currents, and their regulation may be a key factor in determining neuronal firing frequency. The inactivation rate of Shal channels is increased by a presently unidentified class of proteins in bothDrosophilaand mammals. We have cloned a novel Shal channel subunit (jShalγ1) from the jellyfishPolyorchis penicillatusthat alters Shal currents from both invertebrates and vertebrates. When co-expressed with the conserved jellyfish Shal homolog jShal1, jShalγ1 dramatically changes both the rate of inactivation and voltage range of activation and steady-state inactivation. jShalγ1 provides fast inactivation by a classic N-type mechanism, which is independent of its effects on voltage dependence. jShalγ1 forms functional channels only as a heteromultimer, and jShalγ1 + jShal1 heteromultimers are functional only in a 2:2 subunit stoichiometry.
Prostaglandin F2αIs Required for NMDA Receptor-Mediated Induction of c-fosmRNA in Dentate Gyrus Neurons
Authors: Lerea Leslie S. , Carlson Noel G. , Simonato Michele , Morrow Jason D. , Roberts Jack L. , McNamara James O.
Published: April 2018

Activation of NMDA receptors has been linked to a diversity of lasting physiological and pathological changes in the mammalian nervous system. The cellular and molecular mechanisms underlying permanent modifications of nervous system structure and function after brief episodes of neuronal activity are unknown. Immediate-early genes (IEGs) have been implicated in the conversion of short-term stimuli to long-term changes in cellular phenotype by regulation of gene expression. The intracellular signaling pathways coupling activation of receptors at the cell surface with induction of IEGs in the nucleus are incompletely understood. NMDA produces a striking increase in the IEG c-fosin dentate gyrus (DG) neuronsin vitro; this induction is dependent, in part, on the arachidonic acid cascade. Here we show that NMDA receptor activation triggers the synthesis of the prostaglandins PGF2αand PGE2, but not PGD2, in rat cerebral cortical neuronsin vitro. We further demonstrate that PGF2α, but not PGE2or PGD2, is necessary but not sufficient for NMDA induction of c-fosmRNA in DG neurons. These findings provide insight into the molecular events coupling activation of the NMDA receptor with regulation of the IEG c-fosand identify the diffusable messenger PGF2αas obligatory for NMDA receptor-mediated transcription of a nuclear IEG.
Essential Role fordlgin Synaptic Clustering of Shaker K+ChannelsIn Vivo
Authors: Tejedor Francisco J. , Bokhari Amr , Rogero Oscar , Gorczyca Michael , Zhang Jiangwen , Kim Eunjoon , Sheng Morgan , Budnik Vivian
Published: April 2018

The assemblage of specific ion channels and receptors at synaptic sites is crucial for signaling between pre- and postsynaptic cells. However, the mechanisms by which proteins are targeted to and clustered at synapses are poorly understood. Here we show that the product of theDrosophila discs-largegene, DLG, is colocalized with Shaker K+channels, which are clustered at glutamatergic synapses at the larval neuromuscular junction. In heterologous cells, DLG can cluster Shaker-type K+channels, and, in the yeast two-hybrid system, the DLG PDZ1–2 domains bind directly to the C-terminal tail of Shaker proteins. We also demonstrate that DLG-Shaker interactions are requiredin vivofor Shaker clustering at the neuromuscular junction. Synaptic clustering of Shaker channels is abolished not only by mutations indlgbut also by a mutation inShakerthat deletes its C-terminal DLG binding motif. Analyses of variousdlgmutant alleles suggest that channel clustering and synaptic targeting functions depend on distinct DLG domains. These studies demonstrate for the first time that DLG plays an important role in synaptic organizationin vivothat correlates with its ability to bind directly to specific membrane proteins of the synapse.
Specialized Membrane Domains for Water Transport in Glial Cells: High-Resolution Immunogold Cytochemistry of Aquaporin-4 in Rat Brain
Authors: Nielsen Søren , Arnulf Nagelhus Erlend , Amiry-Moghaddam Mahmood , Bourque Charles , Agre Peter , Petter Ottersen Ole
Published: April 2018

Membrane water transport is critically involved in brain volume homeostasis and in the pathogenesis of brain edema. The cDNA encoding aquaporin-4 (AQP4) water channel protein was recently isolated from rat brain. We used immunocytochemistry and high-resolution immunogold electron microscopy to identify the cells and membrane domains that mediate water flux through AQP4. The AQP4 protein is abundant in glial cells bordering the subarachnoidal space, ventricles, and blood vessels. AQP4 is also abundant in osmosensory areas, including the supraoptic nucleus and subfornical organ. Immunogold analysis demonstrated that AQP4 is restricted to glial membranes and to subpopulations of ependymal cells. AQP4 is particularly strongly expressed in glial membranes that are in direct contact with capillaries and pia. The highly polarized AQP4 expression indicates that these cells are equipped with specific membrane domains that are specialized for water transport, thereby mediating the flow of water between glial cells and the cavities filled with CSF and the intravascular space.
Postnatal Development of Corticospinal Projections from Motor Cortex to the Cervical Enlargement in the Macaque Monkey
Authors: Armand J. , Olivier E. , Edgley S. A. , Lemon R. N.
Published: April 2018

The postnatal development of corticospinal projections was investigated in 11 macaques by means of the anterograde transport of wheat germ agglutin–horseradish peroxidase injected into the primary motor cortex hand area. Although the fibers of the corticospinal tract reached all levels of the spinal cord white matter at birth, their penetration into the gray matter was far from complete. At birth, as in the adult, corticospinal projections were distributed to the same regions of the intermediate zone, although they showed marked increases in density during the first 5 months. The unique feature of the primate corticospinal tract, namely direct cortico-motoneuronal projections to the spinal motor nuclei innervating hand muscles, was not present to a significant extent at birth. The density of these cortico-motoneuronal projections increased rapidly during the first 5 months, followed by a protracted period extending into the second year of life. The densest corticospinal terminations occupied only 40% of the hand motor nuclei in the first thoracic segment at 1 month, 73% at 5 months, and 75.5% at 3 years. A caudo-rostral gradient of termination density within the hand motor nuclei was present throughout development and persisted into the adult. As a consequence, the more caudal the segment within the cervical enlargement, the earlier the adult pattern of projection density was reached. No transitory corticospinal projections were found. The continuous postnatal expansion of cortico-motoneuronal projections to hand motor nuclei in primates is in marked contrast to the retraction of exuberant projections that characterizes the development of other sensory and motor pathways in subprimates.
Age-Related Differences in Neural Activity during Memory Encoding and Retrieval: A Positron Emission Tomography Study
Authors: Cabeza Roberto , Grady Cheryl L. , Nyberg Lars , McIntosh Anthony R. , Tulving Endel , Kapur Shitij , Jennings Janine M. , Houle Sylvain , Craik Fergus I. M.
Published: April 2018

Positron emission tomography (PET) was used to compare regional cerebral blood flow (rCBF) in young (mean 26 years) and old (mean 70 years) subjects while they were encoding, recognizing, and recalling word pairs. A multivariate partial-least-squares (PLS) analysis of the data was used to identify age-related neural changes associated with (1) encoding versus retrieval and (2) recognition versus recall. Young subjects showed higher activation than old subjects (1) in left prefrontal and occipito-temporal regions during encoding and (2) in right prefrontal and parietal regions during retrieval. Old subjects showed relatively higher activation than young subjects in several regions, including insular regions during encoding, cuneus/precuneus regions during recognition, and left prefrontal regions during recall. Frontal activity in young subjects was left-lateralized during encoding and right-lateralized during recall [hemispheric encoding/retrieval asymmetry (HERA)], whereas old adults showed little frontal activity during encoding and a more bilateral pattern of frontal activation during retrieval. In young subjects, activation in recall was higher than that in recognition in cerebellar and cingulate regions, whereas recognition showed higher activity in right temporal and parietal regions. In old subjects, the differences in blood flow between recall and recognition were smaller in these regions, yet more pronounced in other regions. Taken together, the results indicate that advanced age is associated with neural changes in the brain systems underlying encoding, recognition, and recall. These changes take two forms: (1) age-related decreases in local regional activity, which may signal less efficient processing by the old, and (2) age-related increases in activity, which may signal functional compensation.
An Increase in Lactate Output by Brain Tissue Serves to Meet the Energy Needs of Glutamate-Activated Neurons
Authors: Schurr Avital , Miller James J. , Payne Ralphiel S. , Rigor Benjamin M.
Published: April 2018

Aerobic energy metabolism uses glucose and oxygen to produce all the energy needs of the brain. Several studies published over the last 13 years challenged the assumption that the activated brain increases its oxidative glucose metabolism to meet the increased energy demands. Neuronal function in rat hippocampal slices supplied with 4 mmglucose could tolerate a 15 min activation by a 5 mmconcentration of the excitatory neurotransmitter glutamate (Glu), whereas slices supplied with 10 mmglucose could tolerate a 15 min activation by 20 mmGlu. However, in slices in which neuronal lactate use was inhibited by the lactate transporter inhibitor a-cyano-4-hydroxycinnamate (4-CIN), activation by Glu elicited a permanent loss of neuronal function, with a twofold to threefold increase in tissue lactate content. Inhibition of glycolysis with the glucose analog 2-deoxy-d-glucose (2DG) during the period of exposure to Glu diminished normal neuronal function in the majority of slices and significantly reduced the number of slices that exhibited neuronal function after activation. However, when lactate was added with 2DG, the majority of the slices were neuronally functional after activation by Glu. NMDA, a nontransportable Glu analog by the glial glutamate transporter, could not induce a significant increase in slice lactate level when administered in the presence of 4-CIN. It is suggested that the heightened energy demands of activated neurons are met through increased glial glycolytic flux. The lactate thus formed is a crucial aerobic energy substrate that enables neurons to endure activation.
A Mathematical Model for the Intracellular Circadian Rhythm Generator
Authors: Scheper Tjeerd olde , Klinkenberg Don , Pennartz Cyriel , van Pelt Jaap
Published: April 2018

A mathematical model for the intracellular circadian rhythm generator has been studied, based on a negative feedback of protein products on the transcription rate of their genes. The study is an attempt at examining minimal but biologically realistic requirements for a negative molecular feedback loop involving considerably faster reactions, to produce (slow) circadian oscillations. The model included mRNA and protein production and degradation, along with a negative feedback of the proteins upon mRNA production. The protein production process was described solely by its total duration and a nonlinear term, whereas also the feedback included nonlinear interactions among protein molecules. This system was found to produce robust oscillations in protein and mRNA levels over a wide range of parameter values. Oscillations were slow, with periods much longer than the time constants of any of the individual system parameters. Circadian oscillations were obtained for realistic values of the parameters. The system was readily entrainable to external periodic perturbations. Two distinct classes of phase response curves were found, viz. with or without a time domain within the circadian cycle in which external perturbations fail to induce a phase shift (“dead zone”). The delay and nonlinearity in the protein production and the cooperativity in the negative feedback (Hill coefficient) were for this model found to be necessary and sufficient to generate robust circadian oscillations. The similarities between model outcomes and empirical findings establish that circadian rhythmicity at the cellular level can plausibly emerge from interactions among molecular systems which are not in themselves rhythmic.
Mechanisms and Structural Determinants of HIV-1 Coat Protein, gp41-Induced Neurotoxicity
Authors: Adamson D. Cory , Kopnisky Kathy L. , Dawson Ted M. , Dawson Valina L.
Published: April 2018

Of the individuals with human immunodeficiency virus type 1 (HIV-1) infection, 20–30% will develop the neurological complication of HIV-associated dementia (HAD). The mechanisms underlying HAD are unknown; however, indirect immunologically mediated mechanisms are theorized to play a role. Recently, the HIV-1 coat protein gp41 has been implicated as a major mediator of HAD through induction of neurocytokines and subsequent neuronal cell death. Using primary mixed cortical cultures from neuronal nitric oxide synthase (NOS) null (nNOS−/−) mice and immunological NOS null (iNOS−/−) mice, we establish iNOS-derived NO as a major mediator of gp41 neurotoxicity. Neurotoxicity elicited by gp41 is markedly attenuated in iNOS−/−cultures compared with wild-type and nNOS−/−cultures. The NOS inhibitorl-nitroarginine methyl ester is neuroprotective in wild-type and nNOS−/−cultures, confirming the role of iNOS-derived NO in gp41 neurotoxicity. Confirming that iNOS−/−cultures lack iNOS, gp41 did not induce iNOS in iNOS−/−cultures, but it markedly induced iNOS in wild-type and nNOS−/−cultures. We elucidate the region of gp41 that is critical for iNOS induction and neuronal cell death by monitoring iNOS induction with overlapping peptides spanning gp41. We show that the N-terminal region of gp41, which we designate as the neurotoxic domain, induces iNOS protein activity and iNOS-dependent neurotoxicity at picomolar concentrations in a manner similar to recombinant gp41 protein. Our experiments suggest that gp41 is eliciting the induction of iNOS through potential cell surface receptors or binding sites because the induction of iNOS is dose dependent and saturable and occurs at physiologically relevant concentrations. These data confirm that the induction of iNOS by gp41 and the production of NO are primary mediators of neuronal damage and identify a neurotoxic domain of gp41 that may play an important role in HAD.
Thecat-1Gene ofCaenorhabditis elegansEncodes a Vesicular Monoamine Transporter Required for Specific Monoamine-Dependent Behaviors
Authors: Duerr Janet S. , Frisby Dennis L. , Gaskin Jennifer , Duke Angie , Asermely Karen , Huddleston David , Eiden Lee E. , Rand James B.
Published: April 2018

We have identified theCaenorhabditis eleganshomolog of the mammalian vesicular monoamine transporters (VMATs); it is 47% identical to human VMAT1 and 49% identical to human VMAT2.C. elegansVMAT is associated with synaptic vesicles in ∼25 neurons, including all of the cells reported to contain dopamine and serotonin, plus a few others. WhenC. elegansVMAT is expressed in mammalian cells, it has serotonin and dopamine transport activity; norepinephrine, tyramine, octopamine, and histamine also have high affinity for the transporter. The pharmacological profile ofC. elegansVMAT is closer to mammalian VMAT2 than VMAT1. TheC. elegansVMAT gene iscat-1;cat-1knock-outs are totally deficient for VMAT immunostaining and for dopamine-mediated sensory behaviors, yet they are viable and grow relatively well. Thecat-1mutant phenotypes can be rescued byC. elegansVMAT constructs and also (at least partially) by human VMAT1 or VMAT2 transgenes. It therefore appears that the function of amine neurotransmitters can be completely dependent on their loading into synaptic vesicles.
Heparin-Binding Epidermal Growth Factor-Like Growth Factor in Hippocampus: Modulation of Expression by Seizures and Anti-Excitotoxic Action
Authors: Opanashuk Lisa A. , Mark Robert J. , Porter Julie , Damm Deborah , Mattson Mark P. , Seroogy Kim B.
Published: April 2018

The expression of heparin-binding epidermal growth factor-like growth factor (HB-EGF), an EGF receptor ligand, was investigated in rat forebrain under basal conditions and after kainate-induced excitotoxic seizures. In addition, a potential neuroprotective role for HB-EGF was assessed in hippocampal cultures.In situhybridization analysis of HB-EGF mRNA in developing rat hippocampus revealed its expression in all principle cell layers of hippocampus from birth to postnatal day (P) 7, whereas from P14 through adulthood, expression decreased in the pyramidal cell layer versus the dentate gyrus granule cells. After kainate-induced excitotoxic seizures, levels of HB-EGF mRNA increased markedly in the hippocampus, as well as in several other cortical and limbic forebrain regions. In the hippocampus, HB-EGF mRNA expression increased within 3 hr after kainate treatment, continued to increase until 24 hr, and then decreased; increases occurred in the dentate gyrus granule cells, in the molecular layer of the dentate gyrus, and in and around hippocampal pyramidal CA3 and CA1 neurons. At 48 hr after kainate treatment, HB-EGF mRNA remained elevated in vulnerable brain regions of the hippocampus and amygdaloid complex. Western blot analysis revealed increased levels of HB-EGF protein in the hippocampus after kainate administration, with a peak at 24 hr. Pretreatment of embryonic hippocampal cell cultures with HB-EGF protected neurons against kainate toxicity. The kainate-induced elevation of [Ca2+]iin hippocampal neurons was not altered in cultures pretreated with HB-EGF, suggesting an excitoprotective mechanism different from that of previously characterized excitoprotective growth factors. Taken together, these results suggest that HB-EGF may function as an endogenous neuroprotective agent after seizure-induced neural activity/injury.
The Role of the Intergeniculate Leaflet in Entrainment of Circadian Rhythms to a Skeleton Photoperiod
Authors: Edelstein Kim , Amir Shimon
Published: April 2018

Mammalian circadian rhythms are synchronized to environmental light/dark (LD) cycles via daily phase resetting of the circadian clock in the suprachiasmatic nucleus (SCN). Photic information is transmitted to the SCN directly from the retina via the retinohypothalamic tract (RHT) and indirectly from the retinorecipient intergeniculate leaflet (IGL) via the geniculohypothalamic tract (GHT). The RHT is thought to be both necessary and sufficient for photic entrainment to standard laboratory light/dark cycles. An obligatory role for the IGL–GHT in photic entrainment has not been demonstrated. Here we show that the IGL is necessary for entrainment of circadian rhythms to a skeleton photoperiod (SPP), an ecologically relevant lighting schedule congruous with light sampling behavior in nocturnal rodents. Rats with bilateral electrolytic IGL lesions entrained normally to lighting cycles consisting of 12 hr of light followed by 12 hr of darkness, but exhibited free-running rhythms when housed under an SPP consisting of two 1 hr light pulses given at times corresponding to dusk and dawn. Despite IGL lesions and other damage to the visual system, the SCN displayed normal sensitivity to the entraining light, as assessed by light-induced Fos immunoreactivity. In addition, all IGL-lesioned, free-running rats showed masking of the body temperature rhythm during the SPP light pulses. These results show that the integrity of the IGL is necessary for entrainment of circadian rhythms to a lighting schedule like that experienced by nocturnal rodents in the natural environment.
Velocity Invariance of Receptive Field Structure in Somatosensory Cortical Area 3b of the Alert Monkey
Authors: DiCarlo James J. , Johnson Kenneth O.
Published: April 2018

This is the second in a series of studies of the neural representation of tactile spatial form in cortical area 3b of the alert monkey. We previously studied the spatial structure of 330 area 3b neuronal receptive fields (RFs) on the fingerpad with random dot patterns scanned at one velocity (40 mm/sec; DiCarlo et al., 1998). Here, we analyze the temporal structure of 84 neuronal RFs by studying their spatial structure at three scanning velocities (20, 40, and 80 mm/sec). As in the previous study, most RFs contained a single, central, excitatory region and one or more surrounding or flanking inhibitory regions. The mean time delay between skin stimulation and its excitatory effect was 15.5 msec. Except for differences in mean rate, each neuron’s response and the spatial structure of its RF were essentially unaffected by scanning velocity. This is the expected outcome when excitatory and inhibitory effects are brief and synchronous. However, that interpretation is consistent neither with the reported timing of excitation and inhibition in somatosensory cortex nor with the third study in this series, which investigates the effect of scanning direction and shows that one component of inhibition lags behind excitation. We reconcile these observations by showing that overlapping (in-field) inhibition delayed relative to excitation can produce RF spatial structure that is unaffected by changes in scanning velocity. Regardless of the mechanisms, the velocity invariance of area 3b RF structure is consistent with the velocity invariance of tactile spatial perception (e.g., roughness estimation and form recognition).
A Novel Nervous System β Subunit that Downregulates Human Large Conductance Calcium-Dependent Potassium Channels
Authors: Weiger Thomas M. , Holmqvist Mats H. , Levitan Irwin B. , Clark Frederick T. , Sprague Scott , Huang Wann-Jeng , Ge Pei , Wang Chichung , Lawson Deborah , Jurman Mark E. , Glucksmann M. Alexandra , Silos-Santiago Inmaculada , DiStefano Peter S. , Curtis Rory
Published: April 2018

The pore-forming α subunits of many ion channels are associated with auxiliary subunits that influence channel expression, targeting, and function. Several different auxiliary (β) subunits for large conductance calcium-dependent potassium channels of the Slowpoke family have been reported, but none of these β subunits is expressed extensively in the nervous system. We describe here the cloning and functional characterization of a novel Slowpoke β4 auxiliary subunit in human and mouse, which exhibits only limited sequence homology with other β subunits. This β4 subunit coimmunoprecipitates with human and mouse Slowpoke. β4 is expressed highly in human and monkey brain in a pattern that overlaps strikingly with Slowpoke α subunit, but in contrast to other Slowpoke β subunits, it is expressed little (if at all) outside the nervous system. Also in contrast to other β subunits, β4 downregulates Slowpoke channel activity by shifting its activation range to more depolarized voltages and slowing its activation kinetics. β4 may be important for the critical roles played by Slowpoke channels in the regulation of neuronal excitability and neurotransmitter release.
Cell Contact Regulates Fate Choice by Cortical Stem Cells
Authors: Tsai Robert Y. L. , McKay Ronald D. G.
Published: April 2018

Cell fate is determined by intrinsic programs and external cues, such as soluble signals and cell–cell contact. Previous studies have demonstrated the roles of soluble factors in the proliferation and differentiation of cortical stem cells and cell–cell contact in maintaining stem cells in a proliferative state. In the present study, we focused on the effect of cell–cell interaction on cell-fate determination. We found that density could exert a strong influence on the cell-type composition when cortical stem cells differentiate. Multipotent stem cells, which normally gave rise to neurons, astrocytes, and oligodendrocytes under high-density culture condition, differentiated almost exclusively into smooth muscle at low density. Clonal analysis indicated that smooth muscle and astrocytes were derived from a common precursor and that the density effect on cell types used an instructive mechanism on the choice of fate rather than an effect of selective survival and/or proliferation. This instructive mechanism depended on the local and not the average density of the cells. This local signal could be mimicked by membrane extract. These findings demonstrate the importance of membrane-bound signals in specifying lineage and provide the first evidence for a short-range regulatory mechanism in cortical stem cell differentiation.
Olivocerebellar Climbing Fibers in the Granuloprival Cerebellum: Morphological Study of Individual Axonal Projections in the X-Irradiated Rat
Authors: Sugihara I. , Bailly Y. , Mariani J.
Published: April 2018

Elimination of cerebellar granule cells early during postnatal development produces abnormal neural organization that retains immature characteristics in the adult, including innervation of each Purkinje cell by multiple climbing fibers from the inferior olive. To elucidate mechanisms underlying development of the olivocerebellar projection, we studied light-microscopic morphology of single olivocerebellar axons labeled with biotinylated dextran amine in adult rats rendered agranular by a single postnatal X-irradiation.

Each reconstructed olivocerebellar axon gave off ∼12 climbing fibers, approximately twice as many as in normal rats. Terminal arborizations of climbing fibers made irregular tufts in most areas, whereas they were arranged vertically in a few mildly affected areas. Each climbing fiber terminal arborization innervated only part of the dendritic arbor of a Purkinje cell, and multiple climbing fibers innervated a single Purkinje cell. These climbing fibers originated either from the same olivocerebellar axon (pseudomultiple innervation) or from distinct axons (true multiple innervation). Abundant non-climbing fiber thin collaterals projected to all cortical layers. Although the longitudinal pattern of the zonal olivocerebellar projection was generally observed, lateral branching, including bilateral projections, was relatively frequent.

These results suggest that the granule cell-parallel fiber system induces several important features of olivocerebellar projection: (1) organization of the climbing fiber terminal arborization tightly surrounding Purkinje cell dendrites, (2) elimination of pseudo- and true multiple innervations establishing one-to-one innervation, (3) retraction of non-climbing fiber thin collaterals from the molecular layer, and (4) probable refinement of the longitudinal projection domains by removing aberrant transverse branches.
Progressive Transneuronal Changes in the Brainstem and Thalamus after Long-Term Dorsal Rhizotomies in Adult Macaque Monkeys
Authors: Woods Timothy M. , Cusick Catherine G. , Pons Tim P. , Taub Edward , Jones Edward G.
Published: April 2018

This study deals with a potential brainstem and thalamic substrate for the extensive reorganization of somatosensory cortical maps that occurs after chronic, large-scale loss of peripheral input. Transneuronal atrophy occurred in neurons of the dorsal column (DCN) and ventral posterior lateral thalamic (VPL) nuclei in monkeys subjected to cervical and upper thoracic dorsal rhizotomies for 13–21 years and that had shown extensive representational plasticity in somatosensory cortex and thalamus in other experiments. Volumes of DCN and VPL, number and sizes of neurons, and neuronal packing density were measured by unbiased stereological techniques. When compared with the opposite, unaffected, side, the ipsilateral cuneate nucleus (CN), external cuneate nucleus (ECN), and contralateral VPL showed reductions in volume: 44–51% in CN, 37–48% in ECN, and 32–38% in VPL. In the affected nuclei, neurons were progressively shrunken with increasing survival time, and their packing density increased, but there was relatively little loss of neurons (10–16%). There was evidence for loss of axons of atrophic CN cells in the medial lemniscus and in the thalamus, with accompanying severe disorganization of the parts of the ventral posterior nuclei representing the normally innervated face and the deafferented upper limb. Secondary transneuronal atrophy in VPL, associated with retraction of axons of CN neurons undergoing primary transneuronal atrophy, is likely to be associated with similar withdrawal of axons from the cerebral cortex and should be a powerful influence on reorganization of somatotopic maps in the somatosensory cortex.
Cholinergic Excitation of Septohippocampal GABA But Not Cholinergic Neurons: Implications for Learning and Memory
Authors: Wu Min , Shanabrough Marya , Leranth Csaba , Alreja Meenakshi
Published: April 2018

The medial septum/diagonal band (MSDB), which gives rise to the septohippocampal pathway, is a critical locus for the mnemonic effects of muscarinic drugs. Infusion of muscarinic cholinergic agonists into the MSDB enhance learning and memory processes both in young and aged rats and produce a continuous theta rhythm in the hippocampus. Intraseptal muscarinic agonists also alleviate the amnesic syndrome produced by systemic administration of muscarinic receptor antagonists. It has been presumed, but not proven, that the cellular mechanisms underlying the effects of muscarinic agonists in the MSDB involve an excitation of septohippocampal cholinergic neurons and a subsequent increase in acetylcholine (ACh) release in the hippocampus. Using a novel fluorescent labeling technique to selectively visualize live septohippocampal cholinergic neurons in rat brain slices, we have found that muscarinic agonists do not excite septohippocampal cholinergic neurons, instead they inhibit a subpopulation of cholinergic neurons. In contrast, unlabeled neurons, confirmed to be noncholinergic, septohippocampal GABA-type neurons using retrograde marking and double-labeling techniques, are profoundly excited by muscarine. Thus, the cognition-enhancing effects of muscarinic drugs in the MSDB cannot be attributed to an increase in hippocampal ACh release. Instead, disinhibitory mechanisms, caused by increased impulse flow in the septohippocampal GABAergic pathway, may underlie the cognition-enhancing effects of muscarinic agonists.
Fos-Related Antigen 2: Potential Mediator of the Transcriptional Activation in Rat Adrenal Medulla Evoked by Repeated Immobilization Stress
Authors: Nankova Bistra B. , Rivkin Mark , Kelz Max , Nestler Eric J. , Sabban Esther L.
Published: April 2018

The precise mechanisms by which beneficial responses to acute stress are transformed into long-term pathological effects of chronic stress are largely unknown. Western blot analyses revealed that members of the AP1 transcription factor family are differentially regulated by single and repeated stress in the rat adrenal medulla, suggesting distinct roles in establishing stress-induced patterns of gene expression in this tissue. The induction of c-fos was transient, whereas marked elevation of long-lasting Fos-related antigens, including Fra2, was observed after repeated immobilization. We investigated DNA protein interactions at the AP1-like promoter elements of two stress-responsive genes, tyrosine hydroxylase and dopamine β-hydroxylase. Increased DNA-binding activity was displayed in adrenomedullary extract from repeatedly stressed rats, which was predominantly composed of c-Jun- and Fra2-containing dimers. The induction of Fra2 and increased AP1-like binding activity was reflected in sustained transcriptional activation of tyrosine hydroxylase and dopamine β-hydroxylase genes after repeated episodes of stress. The functional link between Fra2 and regulation of tyrosine hydroxylase and dopamine β-hydroxylase transcription was confirmed in PC12 cells coexpressing this factor and the corresponding promoter–reporter gene constructs. These studies emphasize the potential importance of stress-evoked increases in the expression of the Fra2 gene forin vivoadaptations of the adrenal catecholamine producing system.
Viral Gene Transfer of Dominant-Negative Kv4 Construct Suppresses an O2-Sensitive K+Current in Chemoreceptor Cells
Authors: Pérez-Garcı́a M. Teresa , López-López José Ramón , Riesco Armenia M. , Hoppe Uta C. , Marbán Eduardo , González Constancio , Johns David C.
Published: April 2018

Hypoxia initiates the neurosecretory response of the carotid body (CB) by inhibiting one or more potassium channels in the chemoreceptor cells. Oxygen-sensitive K+channels were first described in rabbit CB chemoreceptor cells, in which a transient outward K+current was reported to be reversibly inhibited by hypoxia. Although progress has been made to characterize this current with electrophysiological and pharmacological tools, no attempts have been made to identify which Kv channel proteins are expressed in rabbit CB chemoreceptor cells and to determine their contribution to the native O2-sensitive K+current. To probe the molecular identity of this current, we have used dominant-negative constructs to block the expression of functional Kv channels of theShaker(Kv1.xDN) or theShal(Kv4.xDN) subfamilies, because members of these two subfamilies contribute to the transient outward K+currents in other preparations. Delivery of the constructs into chemoreceptor cells has been achieved with adenoviruses that enabled ecdysone-inducible expression of the dominant-negative constructs and reporter genes in polycistronic vectors. In voltage-clamp experiments, we found that, whereas adenoviral infections of chemoreceptor cells with Kv1.xDN did not modify the O2-sensitive K+current, infections with Kv4.xDN suppressed the transient outward current in a time-dependent manner, significantly depolarized the cells, and abolished the depolarization induced by hypoxia. Our work demonstrate that genes of theShalK+channels underlie the transient outward, O2-sensitive, K+current of rabbit CB chemoreceptor cells and that this current contributes to the cell depolarization in response to low pO2.
Depletion of a Microtubule-Associated Motor Protein Induces the Loss of Dendritic Identity
Authors: Yu Wenqian , Cook Crist , Sauter Carley , Kuriyama Ryoko , Kaplan Paul L. , Baas Peter W.
Published: April 2018

Dendrites are short stout tapering processes that are rich in ribosomes and Golgi elements, whereas axons are long thin processes of uniform diameter that are deficient in these organelles. It has been hypothesized that the unique morphological and compositional features of axons and dendrites result from their distinct patterns of microtubule polarity orientation. The microtubules within axons are uniformly oriented with their plus ends distal to the cell body, whereas microtubules within dendrites are nonuniformly oriented. The minus-end-distal microtubules are thought to arise via their specific transport into dendrites by the motor protein known as CHO1/MKLP1. According to this model, CHO1/MKLP1 transports microtubules with their minus ends leading into dendrites by generating forces against the plus-end-distal microtubules, thus creating drag on the plus-end-distal microtubules. Here we show that depletion of CHO1/MKLP1 from cultured neurons causes a rapid redistribution of microtubules within dendrites such that minus-end-distal microtubules are chased back to the cell body while plus-end-distal microtubules are redistributed forward. The dendrite grows significantly longer and thinner, loses its taper, and acquires a progressively more axon-like organelle composition. These results suggest that the forces generated by CHO1/MKLP1 are necessary for maintaining the minus-end-distal microtubules in the dendrite, for antagonizing the anterograde transport of the plus-end-distal microtubules, and for sustaining a pattern of microtubule organization necessary for the maintenance of dendritic morphology and composition. Thus, we would conclude that dendritic identity is dependent on forces generated by CHO1/MKLP1.
Eye Position Signal Modulates a Human Parietal Pointing Region during Memory-Guided Movements
Authors: DeSouza Joseph F. X. , Dukelow Sean P. , Gati Joseph S. , Menon Ravi S. , Andersen Richard A. , Vilis Tutis
Published: April 2018

Using functional magnetic resonance imaging, we examined the signal in parietal regions that were selectively activated during delayed pointing to flashed visual targets and determined whether this signal was dependent on the fixation position of the eyes. Delayed pointing activated a bilateral parietal area in the intraparietal sulcus (rIPS), rostral/anterior to areas activated by saccades. During right-hand pointing to centrally located targets, the left rIPS region showed a significant increase in activation when the eye position was rightward compared with leftward. As expected, activation in motor cortex showed no modulation when only eye position changed. During pointing to retinotopically identical targets, the left rIPS region again showed a significant increased signal when the eye position was rightward compared with leftward. Conversely, when pointing with the left arm, the right rIPS showed an increase in signal when eye position was leftward compared with rightward. The results suggest that the human parietal hand/arm movement region (rIPS), like monkey parietal areas (Andersen et al., 1985), exhibits an eye position modulation of its activity; modulation that may be used to transform the coordinates of the retinotopically coded target position into a motor error command appropriate for the wrist.
Occlusion and the Interpretation of Visual Motion: Perceptual and Neuronal Effects of Context
Authors: Duncan Robert O. , Albright Thomas D. , Stoner Gene R.
Published: April 2018

Visual motion can be represented in terms of the dynamic visual features in the retinal image or in terms of the moving surfaces in the environment that give rise to these features. For natural images, the two types of representation are necessarily quite different because many moving features are only spuriously related to the motion of surfaces in the visual scene. Such “extrinsic” features arise at occlusion boundaries and may be detected by virtue of the depth-ordering cues that exist at those boundaries. Although a number of studies have provided evidence of the impact of depth ordering on the perception of visual motion, few attempts have been made to identify the neuronal substrate of this interaction. To address this issue, we devised a simple contextual manipulation that decouples surface motion from the motions of visual image features. By altering the depth ordering between a moving pattern and abutting static regions, the perceived direction of motion changes dramatically while image motion remains constant. When stimulated with these displays, many neurons in the primate middle temporal visual area (area MT) represent the implied surface motion rather than the motion of retinal image features. These neurons thus use contextual depth-ordering information to achieve a representation of the visual scene consistent with perceptual experience.