bluuebunny/crossref_metadata_2025 huggingface dataset:
Glutamate transporter mRNA expression in proliferative zones of the developing and adult murine CNS
Authors: Sutherland ML , Delaney TA , Noebels JL
Published: April 2018

Neuronal migration, differentiation, and synapse formation are developmental processes within the CNS significantly influenced by ionotropic and metabotropic glutamate receptor activity. Extracellular glutamate concentrations mediating this activity are regulated by transport proteins localized in neuronal and glial cell membranes. We have used in situ hybridization analysis with subtype-specific antisense-oligonucleotides to study the distribution of glia-specific excitatory amino acid transporter (mEAAT1 and mEAAT2) mRNAs during the later stages of embryogenesis and postnatal CNS development. Distinct but overlapping embryonic and postnatal patterns of localization were observed for the two transporter transcripts. Both mEAAT1 and mEAAT2 mRNAs were found during the peak period of gliogenesis (E15-E19) in the telencephalic and mesencephalic CNS proliferative zones. The overall expression of mEAAT1 mRNA diminished after the completion of cell migration, whereas mEAAT2 mRNA expression increased significantly during postnatal development. Interestingly, mEAAT2 transcript expression continued in the subventricular zone postnatally and persisted in this proliferative zone in the adult brain. From PO onward, mEAAT1 mRNA was present predominantly in the cerebellar Purkinje cell layer and at a much lower abundance in the cortex, hippocampus, basal nuclei, and septum, whereas from P7 onward, mEAAT2 mRNA expression increased throughout most of the neuraxis. Postnatally, transcripts for mEAAT1 and mEAAT2 were found in cell bodies, processes, and commissural white matter tracts of the CNS. The divergent temporal and spatial expression of EAAT subtypes and their persistence in mature fiber tracts and radial glia layers reveal that specific EAATs are likely to play multiple distinct roles in the developing and adult CNS, including the regulation of cell proliferation, axon-glia interactions, and neuronal survival.
Context-dependent synaptic action of glycinergic and GABAergic inputs in the dorsal cochlear nucleus
Authors: Golding NL , Oertel D
Published: April 2018

Cartwheel cells are prominent interneurons in the dorsal cochlear nucleus (DCN) that bear considerable homology to cerebellar Purkinje cells. They contact other cartwheel cells as well as fusiform cells, the principal cells of the DCN. In fusiform cells, the inhibition from cartwheel cells interacts with excitation mediated by granule cells and auditory nerve fibers, and shapes the output of the DCN in its ascent to the inferior colliculi. With intracellular recordings from anatomically identified cells in slices, synaptic inputs to fusiform and cartwheel cells were analyzed pharmacologically. Shocks to the auditory nerve and granule cell domains evoked glutamatergic, glycinergic, and GABA(A)ergic postsynaptic potentials (PSPs) in both cartwheel and fusiform cells. The temporal patterns of spontaneous and evoked glycinergic PSPs in fusiform and cartwheel cells were similar and mirrored the pattern of firing of cartwheel cells, probably reflecting the anatomical connections between these cell types and supporting the conclusion that cartwheel cells are glycinergic. In fusiform cells, glycinergic and GABA(A)ergic IPSPs evoked with shocks reversed at -68 mV on average. In marked contrast, glycinergic and GABA(A)ergic PSPs in cartwheel cells, as well as responses to exogenous application of 50–100 mM glycine or 100 microns muscimol, were depolarizing. Reversal potentials of PSPs and responses to glycine and muscimol were similar and averaged -52 mV. Glycinergic and GABA(A)ergic PSPs could elicit firing from cartwheel cells at their resting potentials, but could also reduce rapid firing during strong depolarizations. Thus, the action of glycinergic and GABA(A)ergic inputs on cartwheel cells depends on the electrophysiological context in which they occur.
Photopigment transmittance imaging of the primate photoreceptor mosaic
Authors: Packer OS , Williams DR , Bensinger DG
Published: April 2018

We introduce a new technique for classifying many photoreceptors simultaneously in fresh, excised primate retina on the basis of their absorptance spectra. Primate retina is removed from the pigment epithelium and illuminated under a microscope from the same direction as in the intact eye. To facilitate the guiding of light into the receptor outer segments, the optical axes of the photoreceptors are oriented parallel to the optical axis of the microscope. Photoreceptor outer-segment tips are imaged on a charge-coupled device array, which provides radiometric measurements of the light passing through each photoreceptor. These images are acquired sequentially at three wavelengths chosen to maximize the absorptance differences among the three cone photopigments. After the photopigment is bleached, a second set of three images is acquired. The ratios of the images before and after bleaching at each wavelength are photopigment transmittance maps of the retina. These are combined into a single trichromatic image showing the distribution of photopigment if the retina could be viewed directly in white light without bleaching. We have found patches of receptors in peripheral macaque retina where the measured absorptance at the wavelength of maximum absorptance is consistent with the predicted axial absorptance of th photopigment. The cones in these patches cluster into two groups corresponding to the middle wavelength- sensitive (n = 53, mean absorptance = 0.28) and the long wavelength- sensitive (n = 63, mean absorptance = 0.30) cones. The mean absorptances of 273 macaque and 183 human rods were 0.51 and 0.41, respectively.
Chronic antidepressant administration increases the expression of cAMP response element binding protein (CREB) in rat hippocampus
Authors: Nibuya M , Nestler EJ , Duman RS
Published: April 2018

The present study demonstrates that chronic, but not acute, adminstration of several different classes of antidepressants, including serotonin- and norepinephrine-selective reuptake inhibitors, increases the expression of cAMP response element binding protein (CREB) mRNA in rat hippocampus. In contrast, chronic administration of several nonantidepressant psychotropic drugs did not influence expression of CREB mRNA, demonstrating the pharmacological specificity of this effect. In situ hybridization analysis demonstrates that antidepressant administration increases expression of CREB mRNA in CA1 and CA3 pyramidal and dentate gyrus granule cell layers of the hippocampus. In addition, levels of CRE immunoreactivity and of CRE binding activity were increased by chronic antidepressant administration, which indicates that expression and function of CREB protein are increased along with its mRNA. Chronic administration of the phosphodiesterase (PDE) inhibitors rolipram or papaverine also increased expression of CREB mRNA in hippocampus, demonstrating a role for the cAMP cascade. Moreover, coadministration of rolipram with imipramine resulted in a more rapid induction of CREB than with either treatment alone. Increased expression and function of CREB suggest that specific target genes may be regulated by these treatments. We have found that levels of brain-derived neurotrophic factor (BDNF) and trkB mRNA are also increased by administration of antidepressants or PDE inhibitors. These findings indicate that upregulation of CREB is a common action of chronic antidepressant treatments that may lead to regulation of specific target genes, such as BDNF and trkB, and to the long-term effects of these treatments on brain function.
Stimulus-dependent synchronization of neuronal responses in the visual cortex of the awake macaque monkey
Authors: Kreiter AK , Singer W
Published: April 2018

In visual areas of the cerebral cortex, most neurons exhibit preferences for particular features of visual stimuli, but in general, the tuning is broad. Thus, even simple stimuli evoke responses in numerous neurons with differing but overlapping feature preferences, and it is commonly held that a particular feature is encoded in the pattern of graded responses of the activated population rather than in the optimal responses of individual cells. To decipher this population code, responses evoked by a particular stimulus need to be identified and bound together for further joint processing and must not be confounded with responses to other, nearby stimuli. Such selection of related responses could be achieved by synchronizing the respective discharges at a time scale of milliseconds, as this would selectively and jointly enhance their saliency. This hypothesis predicts that a given set of neurons should exhibit synchronized discharges more often when responding to a single stimulus than when activated by different but simultaneously presented stimuli. To test this prediction, recordings were performed with two electrodes from spatially segregated cells in the middle temporal area (MT) of the awake behaving macaque monkey. It was found that cells with overlapping receptive fields, but different preferences for directions of motion, can engage in synchronous activity if they are stimulated with a single moving bar. In contrast, if the same cells are activated with two different bars, each moving in the direction preferred by the cells at the two respective sites, responses show no or much fewer synchronous epochs. Control experiments exclude that this effect is attributable to changes in response amplitude, the mere presence of two stimuli, or the specific orientation of the bars. The critical variable determining the strength of correlation is the extent to which both sites are activated by a common stimulus or by two different stimuli with different directions of motion.
Attenuation of Astroglial Reactivity by Interleukin-10
Authors: Balasingam Vijayabalan , Yong Voon Wee
Published: April 2018

Prominent responses that follow brain trauma include the activation of microglia, the recruitment of blood-derived macrophages, and astroglial reactivity. Based on evidence that cytokines produced by macrophages/microglia may cause astrocytes to become reactive, the aim of this study was to determine whether astroglial reactivity could be attenuated by interleukin (IL)-10, a potent inhibitor of cytokine synthesis by macrophages/microglia. Four days after the local application of IL-10 to the site of corticectomy in adult mice, the number of reactive astrocytes and their state of hypertrophy was reduced (by 60%) when compared with vehicle controls. In the majority of IL-10-treated mice, but not in any vehicle controls, the tissue in the immediate vicinity of IL-10 application contained viable but nonreactive astrocytes. The mechanism by which IL-10 attenuates astroglial reactivity is likely via the reduction of cytokine production by macrophages/microglia because, based on Mac-1 immunohistochemistry, the macrophages/microglia of IL-10 brains had a decreased activation state compared with vehicle-treated controls. Another macrophage/microglia deactivating agent, macrophage inhibitory factor, also reduced astroglial activityin vivo. Furthermore, IL-10 had no direct effect on purified astrocytes in culture, indicating that itsin vivoaction on astroglial reactivity is likely via indirect mechanisms. Finally, injury resulted in the substantial rise of tumor necrosis factor-α mRNA levels, and this elevation was significantly inhibited by IL-10. The ability to manipulate the extent of astrogliosis should provide a means of addressing the neurotrophic or inhibitory role of reactive astrocytes in neurological recovery.
Whole-Cell Patch-Clamp Recording Reveals Subthreshold Sound-Evoked Postsynaptic Currents in the Inferior Colliculus of Awake Bats
Authors: Covey Ellen , Kauer Julie A. , Casseday John H.
Published: April 2018

The inferior colliculus receives excitatory and inhibitory input from parallel auditory pathways that differ in discharge patterns, latencies, and binaural properties. Processing in the inferior colliculus may depend on the temporal sequence in which excitatory and inhibitory synaptic inputs are activated and on the resulting balance between excitation and inhibition. To explore this issue at the cellular level, we used the novel approach of whole-cell patch-clamp recording in the midbrain of awake bats (Eptesicus fuscus) to record EPSCs or IPSCs. Sound-evoked EPSCs were recorded in most neurons. These EPSCs were frequently preceded by an IPSC, followed by an IPSC, or both. These findings help explain the large latency range and transient responses that characterize inferior colliculus neurons. The EPSC was sometimes followed by long-lasting oscillatory currents, suggesting that a single brief sound sets up a pattern of altered excitability that persists far beyond the duration of the initial sound. In three binaural neurons, ipsilateral sound evoked a large IPSC that partially or totally canceled the EPSC evoked by contralateral sound. In one binaural neuron with ipsilaterally evoked IPSCs, contralaterally evoked IPSCs occurred in response to frequencies above and below the neuron’s best frequency. Thus, both monaural and binaural interactions can occur at single inferior colliculus neurons. These results show that whole-cell patch-clamp recording offers a powerful means of understanding how subthreshold processes determine the responses of auditory neurons.
Chronic 3-Nitropropionic Acid Treatment in Baboons Replicates the Cognitive and Motor Deficits of Huntington’s Disease
Authors: Palfi Stéphane , Ferrante Robert J. , Brouillet Emmanuel , Beal M. Flint , Dolan Robert , Guyot Marie Caroline , Peschanski Marc , Hantraye Philippe
Published: April 2018

We showed recently that chronic administration of the mitochondrial inhibitor 3-nitropropionic acid (3NP) in primates produces various dyskinetic movements and dystonic postures associated with selective striatal lesions displaying many similarities with the pathological features of Huntington’s disease (HD). In the present study, we examined whether such a toxic treatment could also induce frontal-type deficits similar to those observed in HD patients. Cognitive performances of 3NP-treated and control baboons were compared using the object retrieval detour task (ORDT), a test designed to assess the functional integrity of the frontostriatal pathway in human and nonhuman primates. During the same time, the motor function of each animal was assessed under spontaneous “no drug” conditions, and time-sampled neurological observations were used after apomorphine administration. A significant impairment in the ORDT was observed in the 3NP animals after 3–6 weeks of treatment, occurring in the absence of spontaneous abnormal movements but in the presence of apomorphine-inducible dyskinesias. Prolonged 3NP treatment resulted in the progressive appearance of spontaneous abnormal movements. Histological evaluation of these animals showed selective bilateral caudate–putamen lesions with sparing of the cerebral cortex, notably the prefrontal cortex. The present study demonstrates that chronic 3NP treatment replicates in primates the basic pathophysiological triad of HD, including spontaneous abnormal movements, progressive striatal degeneration, and a frontostriatal syndrome of cognitive impairment.
Hormonal Regulation of CREB Phosphorylation in the Anteroventral Periventricular Nucleus
Authors: Gu Guibao , Rojo Anthony A. , Zee Michele C. , Yu Jianhua , Simerly Richard B.
Published: April 2018

The anteroventral periventricular nucleus (AVPV) is a nodal point in neural circuits regulating secretion of gonadotropin and contains sexually dimorphic populations of hormonally regulated dopamine-, dynorphin-, and enkephalin-containing neurons. Because the tyrosine hydroxylase (TH), prodynorphin (PDYN), and proenkephalin (PENK) genes contain cAMP response elements that control their expression in their promoters, we used histochemical methods to determine whether ovarian steroids alter expression of the cAMP response element-binding protein (CREB) in the AVPV. Because the ability of CREB to activate transcription depends on phosphorylation at Ser133, we also evaluated the effects of acute steroid treatment on levels of phosphorylated CREB (pCREB) in AVPV neurons by using an antibody that differentiates between CREB and pCREB. Treatment of ovariectomized rats with estradiol treatments caused a significant induction in the number of pCREB-immunoreactive nuclei within 30 min that was maintained for at least 4 hr, but did not alter CREB immunostaining in the AVPV. Pretreatment with the estrogen antagonist Nafoxidine blocked this induction. In contrast, acute administration of progesterone to estrogen-primed animals suppressed and then increased pCREB staining in the AVPV at 30 and 60 min, respectively; no significant differences between experimental and control animals were apparent by 2 hr after progesterone treatment. Double-labeling experiments showed that pCREB was colocalized with PDYN, PENK, or TH mRNA in the AVPV, suggesting that pCREB may mediate the effect of steroid hormones on gene expression in these neurons.
Cloning and Functional Characterization of a Novel Dopamine Receptor fromDrosophila melanogaster
Authors: Feng Guoping , Hannan Frances , Reale Vincenzina , Hon Yuen Yi , Kousky Christopher T. , Evans Peter D. , Hall Linda M.
Published: April 2018

A cDNA clone is described that encodes a novel G-protein-coupled dopamine receptor (DopR99B) expressed inDrosophilaheads. The DopR99B receptor maps to 99B3–5, close to the position of the octopamine/tyramine receptor gene at 99A10–B1, suggesting that the two may be related through a gene duplication. Agonist stimulation of DopR99B receptors expressed inXenopusoocytes increased intracellular Ca2+levels monitored as changes in an endogenous inward Ca2+-dependent chloride current. In addition to initiating this intracellular Ca2+signal, stimulation of DopR99B increased cAMP levels. The rank order of potency of agonists in stimulating the chloride current is: dopamine > norepinephrine > epinephrine > tyramine. Octopamine and 5-hydroxytryptamine are not active (<100 μm). This pharmacological profile plus the second-messenger coupling pattern suggest that the DopR99B receptor is a D1-like dopamine receptor. However, the hydrophobic core region of the DopR99B receptor shows almost equal amino acid sequence identity (40–48%) with vertebrate serotonergic, α1- and β-adrenergic, and D1-like and D2-like dopaminergic receptors. Thus, thisDrosophilareceptor defines a novel structural class of dopamine receptors. Because DopR99B is the second dopamine receptor cloned fromDrosophila, this work establishes dopamine receptor diversity in a system amenable to genetic dissection.
Regulation of Dendritic Spine Density in Cultured Rat Hippocampal Neurons by Steroid Hormones
Authors: Murphy Diane D. , Segal Menahem
Published: April 2018

The effects of gonadal steroid hormones on dendritic spines were studied in hippocampal neurons that were dissociated and grown in culture for 2–3 weeks. Exposure to estradiol caused up to a twofold increase in dendritic spine density in these neurons. The effect of estradiol was stereospecific and blocked by the steroid antagonist tamoxifen. The estradiol-induced rise in spine density was blocked by the NMDA antagonist APV, but not by the AMPA/KA antagonist DNQX. The estradiol-induced rise in spine density was blocked by the serine/threonine kinase inhibitor H7, but not by the tyrosine kinase inhibitor genestein, and was partially mimicked by PMA, an activator of protein kinase C. Estradiol also caused an increase in the fluorescence intensity of synaptophysin-immunoreactive terminals, corresponding to presynaptic boutons. Finally, estradiol caused a rise in [Ca]ireactivity of the cultured neurons to topical application of glutamate. These studies are the first to examine receptor and second messenger regulation of dendritic spines, and they illustrate the viability of cultured neurons as a powerful test system to address issues related to the regulation of dendritic spine maturation.
Motor Neurons Are Selectively Vulnerable to AMPA/Kainate Receptor-Mediated InjuryIn Vitro
Authors: Carriedo Sean G. , Yin Hong Z. , Weiss John H.
Published: April 2018

The nonphosphorylated neurofilament marker SMI-32 stains motor neurons in spinal cord slices and stains a subset of cultured spinal neurons [“large SMI-32(+) neurons”], which have a morphology consistent with motor neurons identifiedin vitro: large cell body, long axon, and extensive dendritic arborization. They are found preferentially in ventral spinal cord cultures, providing further evidence that large SMI-32(+) neurons are indeed motor neurons, and SMI-32 staining often colocalizes with established motor neuron markers (including acetylcholine, calcitonin gene-related peptide, and peripherin). Additionally, choline acetyltransferase activity (a frequently used index of the motor neuron population) and peripherin(+) neurons share with large SMI-32(+) neurons an unusual vulnerability to AMPA/kainate receptor-mediated injury. Kainate-induced loss of these motor neuron markers is Ca2+-dependent, which supports a critical role of Ca2+ions in this injury. Raising extracellular Ca2+exacerbates injury, whereas removal of extracellular Ca2+is protective. A basis for this vulnerability is provided by the observation that most peripherin(+) neurons, like large SMI-32(+) neurons, are subject to kainate-stimulated Co2+uptake, a histochemical stain that identifies neurons possessing Ca2+-permeable AMPA/kainate receptor-gated channels. Finally, of possibly greater relevance to the slow motor neuronal degeneration in diseases, both large SMI-32(+) neurons and peripherin(+) neurons are selectively damaged by prolonged (24 hr) low-level exposures to kainate (10 μm) or to the glutamate reuptake blockerl-trans-pyrrolidine-2,4-dicarboxylic acid (100 μm). During these low-level kainate exposures, large SMI-32(+) neurons showed higher intracellular Ca2+concentrations than most spinal neurons, suggesting that Ca2+ions are also important in this more slowly evolving injury.
TGF-β-Induced Apoptosis of Cerebellar Granule Neurons Is Prevented by Depolarization
Authors: de Luca Ariane , Weller Michael , Fontana Adriano
Published: April 2018

The regulation of programmed cell death in the developing nervous system involves target-derived survival factors, afferent synaptic activity, and hormone- and cytokine-dependent signaling. Cultured immature cerebellar granule neurons die by apoptosis within several daysin vitrounless maintained in depolarizing (high) concentrations of potassium (25 mmK+). Here we report that transforming growth factors (TGF)-β1, -β2, and -β3accelerate apoptosis of these neurons when maintained in physiological (low) K+medium (5 mmK+) as assessed by measures of viability, quantitative DNA fragmentation, and nuclear morphology. TGF-β-induced apoptosis of these neurons is not blocked by CNTF and LIF, cytokines that enhance neuronal survival when applied alone, or by IGF-I, which prevents apoptosis upon potassium withdrawal. In contrast, neurons that differentiate in high K+medium for several daysin vitroacquire resistance to TGF-β-mediated cell death. Granule neurons maintained in either low or high K+medium produce latent, but not bioactive, TGF-β1and -β2. Because neutralizing TGF-β antibodies fail to augment survival of low K+neurons, the cerebellar neurons are apparently unable to activate latent TGF-β. Thus, apoptosis of low K+neurons is not attributable to endogenous production of TGF-β. Taken together, our data suggest that TGF-β may limit the expansion of postmitotic neuronal precursor populations by promoting their apoptosis but may support survival of those neurons that have maturated, differentiated, and established supportive synaptic connectivity.
Mnemonic Responses of Single Units Recorded from Monkey Inferotemporal Cortex, Accessed via Transcommissural Versus Direct Pathways: A Dissociation between Unit Activity and Behavior
Authors: Sobotka Stanislaw , Ringo James L.
Published: April 2018

Three macaques were trained on a task in which a sequence of single visual images was presented serially, and the monkeys signaled whether the image was a new or a repeated one. The optic chiasm and splenium of the corpus callosum were transected, leaving the anterior commissure as the only path for cortical interhemispheric transfer. Images were presented to only one eye at a time. Re-presentations of images to the same eye were recognized correctly in >95% of trials. A robust stimulus-specific adaptation (i.e., a reduced response to a repeated image) was seen in the population of single units recorded from inferotemporal cortex during these same trials. When an interhemispheric transfer was demanded of the animals (i.e., the re-presentation was made to the other eye), recognition performance was somewhat reduced, to 86% correct. Interestingly, in this situation the stimulus-specific adaptation disappeared completely. The disappearance occurred regardless of whether the transfer direction was from the hemisphere ipsilateral to the recording site to the hemisphere contralateral to the recording site, or vice versa. Thus, stimulus-specific adaptation in inferotemporal cortex units is not required for recognition.
Three-Dimensional Statistical Analysis of Sulcal Variability in the Human Brain
Authors: Thompson Paul M. , Schwartz Craig , Lin Robert T. , Khan Aelia A. , Toga Arthur W.
Published: April 2018

Morphometric variance of the human brain is qualitatively observable in surface features of the cortex. Statistical analysis of sulcal geometry will facilitate multisubject atlasing, neurosurgical studies, and multimodality brain mapping applications. This investigation describes the variability in location and geometry of five sulci surveyed in each hemisphere of six postmortem human brains placed within the Talairach stereotaxic grid. The sulci were modeled as complex internal surfaces in the brain. Heterogeneous profiles of three-dimensional (3D) variation were quantified locally within individual sulci.

Whole human heads, sectioned at 50 μm, were digitally photographed and high-resolution 3D data volumes were reconstructed. The parieto-occipital sulcus, the anterior and posterior rami of the calcarine sulcus, the cingulate and marginal sulci, and the supracallosal sulcus were delineated manually on sagittally resampled sections. Sulcal outlines were reparameterized for surface comparisons. Statistics of 3D variation for arbitrary points on each surface were calculated locally from the standardized individual data. Additional measures of surface area, extent in three dimensions, surface curvature, and fractal dimension were used to characterize variations in sulcal geometry.

Paralimbic sulci exhibited a greater degree of anterior– posterior variability than vertical variability. Occipital sulci displayed the reverse trend. Both trends were consistent with developmental growth patterns. Points on the occipital sulci displayed a profile of variability highly correlated with their 3D distance from the posterior commissure. Surface curvature was greater for the arched paralimbic sulci than for those bounding occipital gyri in each hemisphere. On the other hand, fractal dimension measures were remarkably similar for all sulci examined, and no significant hemispheric asymmetries were found for any of the selected spatial and geometric parameters. Implications of cortical morphometric variability for multisubject comparisons and brain mapping applications are discussed.
Excitatory Actions of GABA after Neuronal Trauma
Authors: van den Pol Anthony N. , Obrietan Karl , Chen Gong
Published: April 2018

GABA is the dominant inhibitory neurotransmitter in the CNS. By opening Cl−channels, GABA generally hyperpolarizes the membrane potential, decreases neuronal activity, and reduces intracellular Ca2+of mature neurons. In the present experiment, we show that after neuronal trauma, GABA, both synaptically released and exogenously applied, exerted a novel and opposite effect, depolarizing neurons and increasing intracellular Ca2+. Different types of trauma that were effective included neurite transection, replating, osmotic imbalance, and excess heat. The depolarizing actions of GABA after trauma increased Ca2+levels up to fourfold in some neurons, occurred in more than half of the severely injured neurons, and was long lasting (>1 week). The mechanism for the reversed action of GABA appears to be a depolarized Cl−reversal potential that results in outward rather than inward movement of Cl−, as revealed by gramicidin-perforated whole-cell patch-clamp recording. The consequent depolarization and resultant activation of the nimodipine sensitive L- and conotoxin-sensitive N-type voltage-activated Ca2+channel allows extracellular Ca2+to enter the neuron. The long-lasting capacity to raise Ca2+may give GABA a greater role during recovery from trauma in modulating gene expression, and directing and enhancing outgrowth of regenerating neurites. On the negative side, by its depolarizing actions, GABA could increase neuronal damage by raising cytosolic Ca2+levels in injured cells. Furthermore, the excitatory actions of GABA after neuronal injury may contribute to maladaptive signal transmission in affected GABAergic brain circuits.
Chemically Mediated Cross-Excitation in Rat Dorsal Root Ganglia
Authors: Amir Ron , Devor Marshall
Published: April 2018

Primary afferent neurons in mammalian dorsal root ganglia (DRGs) are anatomically isolated from one another and are not synaptically interconnected. As such, they are classically thought to function as independent sensory communication elements. However, it has recently been shown that most DRG neurons are transiently depolarized when axons of neighboring neurons of the same ganglion are stimulated repetitively. Here we further characterize this functional coupling. In electrophysiological recordings made from excised rat DRGs, we found that DRG “cross-depolarization” is excitatory in that it is accompanied by an increase in the probability of spiking in response to otherwise subthreshold test pulses delivered intracellularly. Cross-depolarization contributes to this mutual cross-excitation. However, at least as important a contribution comes from a net increase in the neurons’ input resistance (Rin) triggered by the stimulation of neighboring neurons. This change inRinoccurs even when cross-depolarization is absent or is balanced out. The amplitude of cross-depolarization was found to be voltage-dependent, with a reversal potential at approximately −23 mV. Reversibility and the change inRinboth indicate that activity of neighboring neurons causes a membrane conductance change that is chemically mediated. Thus, far from being isolated, most DRG neurons participate in ongoing mutual interactions in which neuronal excitability is continuously modulated by afferent spike activity. This intraganglionic dialog appears to be mediated, at least in part, by an activity-dependent diffusable substance(s) released from neuronal somata and/or adjacent axons, and detected by neighboring cell somata and/or axons.
Involvement of Cytokines in Lipopolysaccharide-Induced Facilitation of CGRP Release from Capsaicin-Sensitive Nerves in the Trachea: Studies with Interleukin-1β and Tumor Necrosis Factor-α
Authors: Hua Xiao-Ying , Chen Ping , Fox Alyson , Myers Robert R.
Published: April 2018

Lipopolysaccharide (LPS), an endotoxin, produces pain behavior, inflammation, and changes in immune function. Many of these effects are secondary to the production of cytokines. In the present study, we investigated the effect of LPS on the releasing function of afferent terminals as measured by calcitonin gene-related peptide (CGRP) release inex vivoperfused rat trachea, and examined the possible role of the cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) as intermediaries in this effect. Systemic injection of LPS (0.75 mg/kg, i.p.) in adult rats induced an increase in body temperature followed by hypothermia, indicating ongoing infection. We observed that capsaicin-induced (0.1 μm) tracheal CGRP release was significantly enhanced in the LPS-treated animals after 5 hr. This enhancement of the peptide release by LPS was blocked by IL-1β tripeptide antagonist Lys-d-Pro-Thr (10 μm) and mimicked by IL-1β and TNF-α (10–100 pg/ml), suggesting that the potentiating effect of LPS on CGRP release is mediated by generation of IL-1β and TNF-α. IL-1β-induced augmentation of CGRP release was blocked by Lys-d-Pro-Thr. Additionally, the cyclooxygenase inhibitor ketorolac (10 μm) significantly attenuated the facilitatory effects of LPS and IL-1β, indicating involvement of prostanoids. These findings suggest that endotoxin treatment generated cytokines such as IL-1β and TNF-α that regulated the peripheral releasing function of primary sensory afferents by sensitizing the terminals and facilitating peptide release. This effect is prostanoid dependent.
Extracellular Synthesis of cADP-Ribose from Nicotinamide-Adenine Dinucleotide by Rat Cortical Astrocytes in Culture
Authors: Pawlikowska Ludmila , Cottrell Susan E. , Harms Matthew B. , Li Ya , Rosenberg Paul A.
Published: April 2018

cADPR is an endogenous calcium-mobilizing agent that in vertebrates is synthesized from nicotinamide-adenine dinucleotide (NAD) by bifunctional enzymes with ADP-ribosyl cyclase and cADPR hydrolase activity. ADP-ribosyl cyclase and cADPR hydrolase activity have been reported in the brain, but the cellular localization of these activities has not been determined previously. In the present study, selective culturing techniques were employed to localize ADP-ribosyl cyclase activity and cADPR hydrolase activity to astrocytes or neurons in cultures derived from rat embryonic cerebral cortex. ADP-ribosyl cyclase activity was determined by incubating cultures with 1 mmNAD in the extracellular medium for 60 min at 37°C and measuring formation of cADPR by bioassay and by HPLC. Astrocyte cultures and mixed cultures of astrocytes and neurons had mean specific activities of 0.84 ± 0.06 and 0.9 ± 0.18 nmol cADPR produced/mg protein/hr, respectively. No detectable ADP-ribosyl cyclase activity was found in neuron-enriched/astrocyte-poor cultures. cADPR hydrolase activity was detectable by incubating cultures with 300 μmcADPR for 60 min at 37°C and assaying loss of cADPR or accumulation of ADPR. The demonstration of extracellular ADP-ribosyl cyclase and cADPR hydrolase activities associated with astrocytes may have important implications for the role of extracellular cADPR in signal transduction and in intercellular communication in the nervous system.
Neuropeptide Y-Mediated Long-Term Depression of Excitatory Activity in Suprachiasmatic Nucleus Neurons
Authors: van den Pol Anthony N. , Obrietan Karl , Chen Gong , B. Belousov Andrei
Published: April 2018

A brief exposure to light can shift the phase of mammalian circadian rhythms by 1 hr or more. Neuropeptide Y (NPY) administration to the hypothalamic suprachiasmatic nucleus, the circadian clock in the brain, also causes a phase shift in circadian rhythms. After a phase shift, the neural clock responds differently to light, suggesting that learning has occurred in neural circuits related to clock function. Thus, certain stimuli can produce effects that last for an extended period, but possible mechanisms of this long-term effect have not been previously examined at the cellular level. Here, we report that NPY caused a long-term depression in both electrical activity and intracellular calcium levels of neurons, as studied with whole-cell patch-clamp recording and Fura-2 digital imaging. In contrast to the immediate (1 sec) recovery after relief from glutamate receptor blockade, a brief single application of NPY (100 nm) depressed cytosolic Ca2+for >1 hr. The mechanism of this long-term calcium depression, a form of cellular learning, is dependent on the simultaneous release of glutamate and activation of NPY receptors, because both the extended response to NPY and any aftereffect were blocked by coapplication of glutamate receptor antagonists. Postsynaptic actions of NPY, mediated by both Y1- and Y2-like receptors, were short term and recovered rapidly. The primary site of long-term NPY actions may be on presynaptic glutamatergic axons, because the frequency of miniature excitatory postsynaptic currents in the presence of tetrodotoxin was reduced by transient exposure to NPY in both cultures and slices.
Immunohistochemical Distribution and Electron Microscopic Subcellular Localization of the Proteasome in the Rat CNS
Authors: Mengual Elisa , Arizti Paz , Rodrigo José , Giménez-Amaya José Manuel , Castaño JoséG.
Published: April 2018

The proteasome multicatalytic proteinase (MCP) is a 20S complex that plays a major role in nonlysosomal pathways of intracellular protein degradation. A polyclonal antibody against rat liver MCP was used to investigate the distribution of MCP in the CNS of the rat and its subcellular localization within the neurons. As expected, MCP immunoreactivity (MCP-IR) was distributed ubiquitously in the rat CNS but not homogeneously. The most intensely stained neurons were the pyramidal cortical neurons of layer 5 and the motor neurons of the ventral horn in the spinal cord, which show an intense nuclear and cytoplasmatic MCP-IR and clearly stained processes. Additionally, some populations of large neurons in the mesencephalon and brainstem also displayed a moderate MCP-IR in their perikarya. The vast majority of neurons in the remaining structures did not show a strong cytoplasmatic MCP-IR, but their nuclei displayed an intense MCP-IR. The subcellular localization also was studied by immunoelectron microscopy. MCP-IR was intense in the neuronal nuclei, and significant staining also was found in the cytoplasm, dendritic, and axonic processes (including some myelinated axons) and in synaptic boutons, as illustrated in the cerebellar cortex. The distribution of MCP in the rat CNS and its subcellular localization are discussed in relation to (1) the distribution of calpain, the other major nonlysosomal cellular protease, and (2) the possible role of MCP in the degradation of regulatory proteins and key transcription factors that are essential in many neuronal responses.
The Role of Monoamine Metabolism in Oxidative Glutamate Toxicity
Authors: Maher Pamela , Davis John B.
Published: April 2018

Glutamate kills neuronal cells by either a receptor-mediated pathway or the inhibition of cystine uptake, the “oxidative pathway.” Antioxidants can block cell death initiated by either pathway, suggesting that toxicity is dependent on the production of free radicals. We provide evidence that in a neuronal cell line, glutamate toxicity via the oxidative pathway requires monoamine metabolism as a source of free radicals. Glutamate toxicity is inhibited by monoamine oxidase (MAO) type-A-specific inhibitors, but only at concentrations much higher than those required to inhibit classical type-A MAO. Toxicity is not inhibited by MAO type-B-specific inhibitors at any concentration. Furthermore, treatment of cells with agents that block monoamine uptake inhibits glutamate toxicity. These results suggest that an enzyme distinct from MAO is involved in monoamine metabolism and demonstrate a relationship between glutamate toxicity and monoamine metabolism. These data also have implications for the understanding and treatment of neurodegenerative disorders in which glutamate toxicity is thought to be involved.
Activity-Independent Segregation of Excitatory and Inhibitory Synaptic Terminals in Cultured Hippocampal Neurons
Authors: Benson Deanna L. , Cohen P. Aryeh
Published: April 2018

Cultured hippocampal neurons were used as a model system to address experimentally the spatial and temporal sequence leading to the appropriate sorting of excitatory and inhibitory synaptic terminals to different cellular target domains and the role of neural activity in this process. By using antibodies against glutamic acid decarboxylase 65 (GAD65) and synaptophysin, we examined the development and segregation of GABAergic and non-GABAergic synaptic terminals on single neurons. Electron microscopy confirmed that GAD65-labeled swellings observed using light microscopy corresponded to synaptic boutons. From the time at which GABAergic terminals first appeared, they developed at a more rapid rate on neuronal somata than non-GABAergic terminals did, such that by 18 d in culture, 60% of the total boutons on somata were GABAergic. By contrast, the majority (70%) of boutons on dendrites were non-GABAergic. These data suggest that inhibitory synaptic terminals are targeted preferentially to or maintained on cell somata at the expense of excitatory terminals. Interestingly, non-GABAergic terminals were not inhibited from forming synapses on cell somata, because in the absence of GABAergic terminals they attained the same total somatic terminal density seen in the presence of GABAergic terminals. Chronic blockade of neuronal activity did not affect the differential targeting of GABAergic and non-GABAergic axons; however, it did reduce the extent of dendritic arborization. Our findings support a two-step model for synaptic segregation whereby the majority of terminals is initially targeted in an activity-independent manner to the appropriate cellular domains, but an additional developmental mechanism serves to further restrict and refine the original synaptic distribution.
Nerve Growth Factor and Neurotrophin-3 Differentially Regulate the Proliferation and Survival of Developing Rat Brain Oligodendrocytes
Authors: Cohen Rick I. , Marmur Ronen , Norton William T. , Mehler Mark F. , Kessler John A.
Published: April 2018

There is increasing evidence that the neurotrophins, particularly nerve growth factor (NGF) and neurotrophin-3 (NT-3), play a role in the regulation of glial development in the CNS. Recent studies have shown that the proliferation of optic nerve-derived O2A progenitors (OLPs) is potentiated by NT-3 in combination with platelet-derived growth factor, whereas NT-3 alone supports the survival of their differentiated progeny (Barres et al., 1994). In this study, we have examined the expression of the high-affinity neurotrophin receptors (trks) and the low-affinity nerve growth factor receptor p75 in developing oligodendrocytes (OLs). In addition, we have examined the effects of NGF and NT-3 on proliferation and survival of OLPs and OLs, respectively. TrkC, the high-affinity NT-3 receptor, and trkA, the high-affinity NGF receptor, are both expressed from the early OLP through the mature OL stage. The truncated form of trkB, lacking the tyrosine kinase domain, and the low-affinity neurotrophin receptor p75 are expressed at low levels in OLPs and are upregulated in mature OLs. NGF and NT-3 both induced the phosphorylation of mitogen-activated protein kinase (MAPK) in OLPs and in OLs. In both OLPs and OLs, NT-3 sustained the activation of MAPK more than NGF. NT-3 enhanced the proliferation of OLPs and supported the survival of OLs. By contrast, unless coadministered with FGF-2, NGF did not exhibit mitogenic effects on OLPs but did enhance the survival of differentiated OLs. Our data demonstrate the presence of functional trkA and trkC in developing OLs and indicate that both NGF and NT-3 have a broad spectrum of developmental actions on cells of the OL lineage.
Basic Fibroblast Growth Factor Increases Functional L-Type Ca2+Channels in Fetal Rat Hippocampal Neurons: Implications for Neurite MorphogenesisIn Vitro
Authors: Shitaka Yoshitsugu , Matsuki Norio , Saito Hiroshi , Katsuki Hiroshi
Published: April 2018

Basic fibroblast growth factor (bFGF) is a potent neurotrophic factor that regulates cell proliferation and differentiation during neuronal development. Here we report that fetal hippocampal neurons chronically treated with bFGF displayed larger [Ca2+]iincreases than nontreated neurons in response to high K+-induced depolarization. This [Ca2+]iresponse was abolished by nicardipine and was little affected by treatments that depleted intracellular Ca2+stores, thus reflecting the activities of L-type voltage-dependent Ca2+channels. Whole-cell recordings also demonstrated increased high-voltage-activated Ca2+currents in bFGF-treated neurons, whereas low-voltage-activated Ca2+currents remained unchanged. bFGF-stimulated increase in Ca2+response was not observed in neurons treated with cycloheximide or actinomycin D, indicating that protein and RNA synthesis were required for this effect. Visualization using a fluorescent dihydropyridine analog revealed that bFGF-treated neurons expressed increased amounts of L-type Ca2+channels on the cell body. In addition, bFGF-treated neurons acquired distinctive morphology of neurites that was characterized by markedly increased neuritic branching. The branching points in neurites were associated with clusters of L-type Ca2+channels and resultant “Ca2+hotspots” that showed large [Ca2+]iincreases in response to membrane depolarization. Concurrent application of nicardipine completely blocked the bFGF-stimulated increase in neuritic branching. Therefore, bFGF enhances the expression of functional L-type Ca2+channels on the cell body and neurites of fetal hippocampal neurons, which may play an important role in the regulation of their differentiation and the establishment of their neurite morphology.
Functional Anatomy of Spatial Mental Imagery Generated from Verbal Instructions
Authors: Mellet Emmanuel , Tzourio Nathalie , Crivello Fabrice , Joliot Marc , Denis Michel , Mazoyer Bernard
Published: April 2018

Positron emission tomography (PET) was used to monitor regional cerebral blood flow variations while subjects were constructing mental images of objects made of three-dimensional cube assemblies from auditorily presented instructions. This spatial mental imagery task was contrasted with both passive listening (LIST) of phonetically matched nonspatial word lists and a silent rest (REST) condition. All three tasks were performed in total darkness. Mental construction (CONS) specifically activated a bilateral occipitoparietal–frontal network, including the superior occipital cortex, the inferior parietal cortex, and the premotor cortex. The right inferior temporal cortex also was activated specifically during this condition, and no activation of the primary visual areas was observed. Bilateral superior and middle temporal cortex activations were common to CONS and LIST tasks when both were compared with the REST condition. These results provide evidence that the so-called dorsal route known to process visuospatial features can be recruited by auditory verbal stimuli. They also confirm previous reports indicating that some mental imagery tasks may not involve any significant participation of early visual areas.