bluuebunny/crossref_metadata_2025 huggingface dataset:
Are the Interlaminar Zones of the Ferret Dorsal Lateral Geniculate Nucleus Actually Part of the Perigeniculate Nucleus?
Authors: Sanchez-Vives Maria V. , Bal Thierry , Kim Uhnoh , von Krosigk Marcus , McCormick David A.
Published: April 2018

The ferret dorsal lateral geniculate nucleus (LGNd) contains interneurons within the interlaminar zones situated between the laminae corresponding to the ipsi- and contralateral eyes. We found that a subset of these neurons exhibits electrophysiological properties similar to those previously reported for perigeniculate (PGN) neurons, including the generation of rhythmic sequences of rebound low-threshold Ca2+spikes at a frequency of 1–4 Hz after the intracellular injection of a hyperpolarizing current pulse. These “PGN-like” interlaminar interneurons innervated restricted regions of the A-laminae, inhibited thalamocortical cells through GABAA, and perhaps GABAB, receptors, and were excited by axon collaterals from thalamocortical cells. This reciprocal relationship is identical to that formed by PGN cells and allowed the PGN-like interlaminar neurons to participate in the generation of spindle waves and other network oscillations. Pharmacologically, PGN-like interlaminar interneurons were also similar to PGN neurons: both generated a prolonged depolarization in response to the local application of serotonin, 1S,3R-ACPD, and CCK8S, and a rapid depolarization followed by a more prolonged hyperpolarization in response to acetylcholine.

Examination of parvalbumin and calbindin staining in the ferret LGNd revealed that both PGN and a subset of interlaminar neurons were parvalbumin-positive. In contrast, calbindin-positive cells were relatively absent in the PGN and sparsely present in the interlaminar zones, but were numerous in the A and C laminae. Our results indicate that the interlaminar zone in between laminae A and A1 and A1 and C in the ferret LGNd possesses a cell type that is electrophysiologically, pharmacologically, anatomically, immunocytochemically, and functionally similar to neurons in the PGN.
Metabotropic Glutamate Receptors Activate G-Protein-Coupled Inwardly Rectifying Potassium Channels inXenopusOocytes
Authors: Saugstad Julie A. , Segerson Thomas P. , Westbrook Gary L.
Published: April 2018

Receptor-mediated activation of a G-protein-coupled inwardly rectifying potassium channel (GIRK) is a common mechanism for synaptic modulation in the CNS. However, evidence for metabotropic glutamate receptor (mGluR) activation of GIRK is virtually nonexistent, despite the widespread and overlapping distribution of these proteins. We examined this apparent paradox by coexpressing mGluRs 1a, 2, and 7 with the GIRK subunits Kir3.1 and Kir3.4 inXenopusoocytes. Functional expression of GIRK was confirmed by coexpression with the D2 dopamine receptor that is known to activate GIRK in neurons. Agonist activation of each of the three mGluRs evoked inward potassium currents in symmetrical KCl solutions. The current amplitudes evoked by mGluR1a, mGluR2, and D2 were comparable, whereas mGluR7 currents were somewhat smaller. mGluR1a-evoked GIRK currents were not blocked in BAPTA-treated oocytes, demonstrating that GIRK activation was distinct from phospholipase C-mediated activation of the endogenous calcium-dependent chloride current (ICaCl). Pertussis toxin (PTX) treatment significantly reduced both the mGluR and D2 receptor-evoked GIRK currents. In oocytes in which mGluR2 and D2 were coexpressed, activation of mGluR2 occluded additional D2 receptor current, indicating that mGluR2 and D2 receptor coupling to GIRK involves a common G-protein. The efficient coupling of mGluRs to GIRK in oocytes suggests either that mGluR activation of GIRK has been overlooked in neurons or possibly that mGluRs are excluded from GIRK-containing microdomains.
Peptidergic Modulation of Synaptic Transmission in the Parabrachial NucleusIn Vitro: Importance of Degradative Enzymes in Regulating Synaptic Efficacy
Authors: Saleh Tarek M. , Kombian Samuel B. , Zidichouski Jeffrey A. , Pittman Quentin J.
Published: April 2018

This study examined the effects of substance P (SP) and calcitonin gene-related peptide (CGRP) on synaptic transmission in a pontine slice containing the parabrachial nucleus (PBN). Stimulation of the ventral, external lateral portion of the PBN elicited glutamate-mediated EPSCs in cells recorded using the nystatin perforated-patch recording technique in the external lateral, external medial, and central lateral subnuclei of the PBN. Bath application of SP or CGRP dose-dependently and reversibly attenuated the evoked EPSC. The attenuation of the EPSC induced by both of these peptides was not accompanied by changes in input resistance of PBN cells over a wide voltage range, nor did these peptides alter the inward current induced by a brief bath application of AMPA. The combined application of subthreshold concentrations of these peptides revealed a synergistic interaction in reducing the evoked EPSC. The substance P neurokinin-1 receptor antagonist CGP49823 completely and reversibly blockedboththe SP- and the CGRP-induced attenuation of the EPSC. However, the rat CGRP receptor antagonist human-CGRP8-37did not block the actions of CGRP or SP on the EPSC. Using a metabolically stable analog of SP, SP(5–11), or an endopeptidase inhibitor, phosphoramidon, we were able to demonstrate that CGRP enhances the SP effect by inhibiting an SP endopeptidase. Application of phosphoramidon also revealed an endogenous SP “tone” apparently made effective by blockade of the endopeptidase. These results suggest that SP (and CGRP indirectly through an inhibition of the SP endopeptidase) acts on presynaptic NK-1 receptors to cause an inhibition of excitatory transmission in the PBN. These results indicate an important role of endopeptidases in regulating synaptic modulation by peptides.
Neuron Death in the Substantia Nigra of Weaver Mouse Occurs Late in Development and Is Not Apoptotic
Authors: Oo Tinmarlar F. , Blazeski Richard , Harrison Susan M. W. , Henchcliffe Claire , Mason Carol A. , Roffler-Tarlov Suzanne K. , Burke Robert E.
Published: April 2018

Weaveris a spontaneous mutation in mice characterized by the postnatal loss of external granule cells in the cerebellum and dopaminergic neurons of the midbrain, especially in the substantia nigra. We have shown previously that natural cell death with the morphology of apoptosis occurs in the substantia nigra of normal rodents during postnatal development. We therefore sought to determine whether the loss of dopaminergic neurons in homozygous weaver mice occurs during the period of natural cell death in the substantia nigra and whether it has the morphology of apoptosis. We have found, using a silver stain technique, that although apoptotic cell death does occur early postnatally in homozygous weaver substantia nigra, it also does so with equal magnitude in wild-type and heterozygous weaver littermates. Unique to homozygous weavers is the occurrence of degenerating neurons in the nigra that are not apoptotic. These degenerating neurons are observed at postnatal day 7, and they are most abundant on postnatal days 24–25. The nonapoptotic nature of this cell death is confirmed by negativein situend labeling of nuclear DNA fragmentation and by ultrastructural analysis. Ultrastructural studies reveal irregular chromatin aggregates in the nucleus, as well as marked cytoplasmic changes, including the formation of vacuoles and distinctive stacks of dilated cisternae of endoplasmic reticulum. We interpret these changes as indicative of either a variant morphology of programmed cell death or a pathological degenerative process mediated by an as yet unknown mechanism related to the recently described mutation in the GIRK2 potassium channel.
Hair Cell Differentiation in Chick Cochlear Epithelium after Aminoglycoside Toxicity:In VivoandIn VitroObservations
Authors: Stone Jennifer S. , Leaño Sharon G. , Baker Lauren P. , Rubel Edwin W
Published: April 2018

Inner ear epithelia of mature birds regenerate hair cells after ototoxic or acoustic insult. The lack of markers that selectively label cells in regenerating epithelia and of culture systems composed primarily of progenitor cells has hampered the identification of cellular and molecular interactions that regulate hair cell regeneration. In control basilar papillae, we identified two markers that selectively label hair cells (calmodulin and TUJ1 β tubulin antibodies) and one marker unique for support cells (cytokeratin antibodies). Examination of regenerating epithelia demonstrated that calmodulin and β tubulin are also expressed in early differentiating hair cells, and cytokeratins are retained in proliferative support cells. Enzymatic and mechanical methods were used to isolate sensory epithelia from mature chick basilar papillae, and epithelia were cultured in different conditions. In control cultures, hair cells are morphologically stable for up to 6 d, because calmodulin immunoreactivity and phalloidin labeling of filamentous actin are retained. The addition of an ototoxic antibiotic to cultures, however, causes complete hair cell loss by 2 din vitroand generates cultures composed of calmodulin-negative, cytokeratin-positive support cells. These cells are highly proliferative for the first 2–7 d after plating, but stop dividing by 9 d. Calmodulin- or TUJ1-positive cells reemerge in cultures treated with antibiotic for 5 d and maintained for an additional 5 d without antibiotic. A subset of calmodulin-positive cells was also labeled with BrdU when it was continuously present in cultures, suggesting that some cells generated in culture begin to differentiate into hair cells.
The Leaving or Q Fraction of the Murine Cerebral Proliferative Epithelium: A General Model of Neocortical Neuronogenesis
Authors: Takahashi Takao , Nowakowski Richard S. , Caviness Verne S.
Published: April 2018

Neurons of neocortical layers II–VI in the dorsomedial cortex of the mouse arise in the pseudostratified ventricular epithelium (PVE) through 11 cell cycles over the six embryonic days 11–17 (E11–E17). The present experiments measure the proportion of daughter cells that leave the cycle (quiescent or Q fraction or Q) during a single cell cycle and the complementary proportion that continues to proliferate (proliferative or P fraction or P; P = 1 − Q). Q and P for the PVE become 0.5 in the course of the eighth cycle, occurring on E14, and Q rises to ∼0.8 (and P falls to ∼0.2) in the course of the 10th cycle occurring on E16. This indicates that early in neuronogenesis, neurons are produced relatively slowly and the PVE expands rapidly but that the reverse happens in the final phase of neuronogenesis. The present analysis completes a cycle of analyses that have determined the four fundamental parameters of cell proliferation: growth fraction, lengths of cell cycle, and phases Q and P. These parameters are the basis of a coherent neuronogenetic model that characterizes patterns of growth of the PVE and mathematically relates the size of the initial proliferative population to the neuronal population of the adult neocortex.
Functional Anatomic Studies of Memory Retrieval for Auditory Words and Visual Pictures
Authors: Buckner Randy L. , Raichle Marcus E. , Miezin Francis M. , Petersen Steve E.
Published: April 2018

Functional neuroimaging with positron emission tomography was used to study brain areas activated during memory retrieval. Subjects (n = 15) recalled items from a recent study episode (episodic memory) during two paired-associate recall tasks. The tasks differed in that PICTURE RECALL required pictorial retrieval, whereas AUDITORY WORD RECALL required word retrieval. Word REPETITION and REST served as two reference tasks.

Comparing recall with repetition revealed the following observations. (1) Right anterior prefrontal activation (similar to that seen in several previous experiments), in addition to bilateral frontal-opercular and anterior cingulate activations. (2) An anterior subdivision of medial frontal cortex [pre-supplementary motor area (SMA)] was activated, which could be dissociated from a more posterior area (SMA proper). (3) Parietal areas were activated, including a posterior medial area near precuneus, that could be dissociated from an anterior parietal area that was deactivated. (4) Multiple medial and lateral cerebellar areas were activated. Comparing recall with rest revealed similar activations, except right prefrontal activation was minimal and activations related to motor and auditory demands became apparent (e.g., bilateral motor and temporal cortex). Directly comparing picture recall with auditory word recall revealed few notable activations.

Taken together, these findings suggest a pathway that is commonly used during the episodic retrieval of picture and word stimuli under these conditions. Many areas in this pathway overlap with areas previously activated by a different set of retrieval tasks using stem-cued recall, demonstrating their generality. Examination of activations within individual subjects in relation to structural magnetic resonance images provided anatomic information about the location of these activations. Such data, when combined with the dissociations between functional areas, provide an increasingly detailed picture of the brain pathways involved in episodic retrieval tasks.
GAT-3, a High-Affinity GABA Plasma Membrane Transporter, Is Localized to Astrocytic Processes, and It Is Not Confined to the Vicinity of GABAergic Synapses in the Cerebral Cortex
Authors: Minelli Andrea , DeBiasi Silvia , Brecha Nicholas C. , Vitellaro Zuccarello Laura , Conti Fiorenzo
Published: April 2018

The termination of GABA synaptic action by high-affinity, Na+-dependent, neuronal, and glial plasma membrane transporters plays an important role in regulating neuronal activity in physiological and pathological conditions. We have investigated the cellular localization and distribution in the cerebral cortex of adult rats of one GABA transporter (GAT), GAT-3, by immunocytochemistry with affinity-purified polyclonal antibodies directed to its predicted C terminus that react monospecifically with a protein of ∼70 kDa.

Light microscopic studies revealed specific GAT-3 immunoreactivity (ir) in small punctate structures, and it was never observed in fibers or cell bodies. No changes in immunostaining were observed in sections incubated with GAT-3 antibodies preadsorbed with the related rat GAT-1 or mouse GAT-2/BGT-1 C-terminal peptides, whereas in sections incubated with GAT-3 antibodies preadsorbed with rat GAT-3 C-terminal peptide, ir was not present. The highest number of GAT-3-positive puncta was in layer IV and in a narrow band corresponding to layer Vb, followed by layers II and III. Many GAT-3-positive puncta were in close association with pyramidal and nonpyramidal neuron cell bodies. Ultrastructural studies showed that GAT-3 ir was localized exclusively to astrocytic processes, which were found in the neuropil and adjacent to axon terminals having either symmetric or asymmetric specializations. In sections processed by both preembedding labeling for GAT-3 and postembedding immunogold labeling for GABA, only some of the GAT-3-positive astrocytic processes were found close to GABAergic profiles.

These findings on the localization of GAT-3 in the cerebral cortex indicate that this transporter mediates GABA uptake into glial cells, and suggest that glial GABA uptake may function to limit the spread of GABA from the synapse, as well as to regulate overall GABA levels in the neuropil.
Decoding Synapses
Authors: Sen Kamal , Jorge-Rivera J. C. , Marder Eve , Abbott L. F.
Published: April 2018

The strength of many synapses is modified by various use and time-dependent processes, including facilitation and depression. A general description of synaptic transfer characteristics must account for the history-dependence of synaptic efficacy and should be able to predict the postsynaptic response to any temporal pattern of presynaptic activity. To generate such a description, we use an approach similar to the decoding method used to reconstruct a sensory input from a neuronal firing pattern. Specifically, a mathematical fit of the postsynaptic response to an isolated action potential is multiplied by an amplitude factor that depends on a time-dependent function summed over all previous presynaptic spikes. The amplitude factor is, in general, a nonlinear function of this sum. Approximate forms of the time-dependent function and the nonlinearity are extracted from the data, and then both functions are constructed more precisely by a learning algorithm. This approach, which should be applicable to a wide variety of synapses, is applied here to several crustacean neuromuscular junctions. After training on data from random spike sequences, the method predicts the postsynaptic response to an arbitrary train of presynaptic action potentials. Using a model synapse, we relate the functions used in the fit to underlying biophysical processes. Fitting different neuromuscular junctions allows us to compare their responses to sequences of action potentials and to contrast the time course and degree of facilitation or depression that they exhibit.
AMPA Receptor Flip/Flop Mutants Affecting Deactivation, Desensitization, and Modulation by Cyclothiazide, Aniracetam, and Thiocyanate
Authors: Partin Kathryn M. , Fleck Mark W. , Mayer Mark L.
Published: April 2018

AMPA receptor GluRA subunits with mutations at position 750, a residue shown previously to control allosteric regulation by cyclothiazide, were analyzed for modulation of deactivation and desensitization by cyclothiazide, aniracetam, and thiocyanate. Point mutations from Ser to Asn, Ala, Asp, Gly, Gln, Met, Cys, Thr, Leu, Val, and Tyr were constructed in GluRAflip. The last four of these mutants were not functional; S750D was active only in the presence of cyclothiazide, and the remaining mutants exhibited altered rates of deactivation and desensitization for control responses to glutamate, and showed differential modulation by cyclothiazide and aniracetam. Results from kinetic analysis are consistent with aniracetam and cyclothiazide acting via distinct mechanisms. Our experiments demonstrate for the first time the functional importance of residue 750 in regulating intrinsic channel-gating kinetics and emphasize the biological significance of alternative splicing in the M3–M4 extracellular loop.
Age-Dependent Neuronal and Synaptic Degeneration in Mice Transgenic for the C Terminus of the Amyloid Precursor Protein
Authors: Oster-Granite Mary Lou , McPhie Donna L. , Greenan Jane , Neve Rachael L.
Published: April 2018

The molecular basis for the degeneration of neurons and the deposition of amyloid in plaques and in the cerebrovasculature in Alzheimer’s disease (AD) is incompletely understood. We have proposed that one molecule common to these abnormal processes is a fragment of the Alzheimer amyloid precursor protein (APP) comprising the C-terminal 100 amino acids of this molecule (APP-C100). We tested this hypothesis by creating transgenic mice expressing APP-C100 in the brain. We report here that aging (18–28 month) APP-C100 transgenic mice exhibit profound degeneration of neurons and synapses in Ammon’s horn and the dentate gyrus of the hippocampal formation. Of the 106 transgenic mice between 8 and 28 months of age that were examined, all of those older than 18 months displayed severe hippocampal degeneration. The numerous degenerating axonal profiles contained increased numbers of neurofilaments, whorls of membrane, and accumulations of debris resembling secondary lysosomes near the cell body. The dendrites of degenerating granule and pyramidal cells contained disorganized, wavy microtubules. Cerebral blood vessels had thickened refractile basal laminae, and microglia laden with debris lay adjacent to larger venous vessels. Mice transgenic for Flag-APP-C100 (in which the hydrophilic Flag tag was fused to the N terminus of APP-C100) showed a similar degree of neurodegeneration in the hippocampal formation as early as 12 months of age. The 45 control mice displayed only occasional necrotic cells and no extensive cell degeneration in the same brain regions. These findings show that APP-C100 is capable of causing some of the neuropathological features of AD.
Differential Regulation of NMDAR1 mRNA and Protein by Estradiol in the Rat Hippocampus
Authors: Gazzaley Adam H. , Weiland Nancy G. , McEwen Bruce S. , Morrison John H.
Published: April 2018

Estradiol treatment increases the number of NMDA receptor binding sites, and changes evoked synaptic currents in a manner consistent with a steroid-induced functional enhancement of NMDA receptors in rat hippocampus. In this study, we investigate the cellular mechanisms of estradiol-induced NMDA receptor regulation at the protein and mRNA levels in ovariectomized rats treated with ovarian steroids using immunocytochemical andin situhybridization techniques. Confocal laser scanning microscopy was used to quantify alterations in immunofluorescence intensity levels of NMDAR1 subunit proteins within neuronal somata and dendrites of discrete hippocampal fields, whereas in parallel,in situhybridization was used to examine NMDAR1 mRNA levels in corresponding hippocampal regions. The data indicate that estradiol treatment in ovariectomized rats significantly increases immunofluorescence intensity levels in comparison with nonsteroid treated ovariectomized rats within the somata and dendrites of CA1 pyramidal cells and, to a lesser extent, within the granule cell somata of the dentate gyrus. In contrast, such alterations in immunofluorescence intensity occur without concomitant changes in mRNA hybridization levels. Thus, these data suggest that estradiol modulates NMDA receptor function via post-transcriptional regulation of the NMDAR1 subunit protein. The increase in immunofluorescence intensity may reflect an increase in the concentration of the subunit protein, which could account for estrogen-induced changes in pharmacological and physiological properties of the NMDA receptor.
Expression of Hepatocyte Growth Factor/Scatter Factor, Its Receptor,c-met, and Tissue-Type Plasminogen Activator during Development of the Murine Olfactory System
Authors: Thewke Douglas P. , Seeds Nicholas W.
Published: April 2018

The expression of hepatocyte growth factor/scatter factor (HGF/SF) and its receptor, thec-metproto-oncogene product, was examined byin situhybridization in the developing and adult murine olfactory system and compared with the expression of a known activator of HGF/SF, tissue-type plasminogen activator (tPA). In the developing olfactory canal, expression of bothc-metand tPA was observed in the olfactory neuroepithelium, whereas HGF/SF expression appeared to be confined to the mucosa adjacent to the neuroepithelium. During development of the olfactory bulb, HGF/SF and tPA were expressed within the rostral migratory pathway leading to the olfactory bulb, whereasc-metexpression was observed in the mitral cell layer (MCL) of the olfactory bulb and in the anterior olfactory nucleus. In the adult olfactory bulb, expression of HGF/SF was restricted to the periglomerular region of the glomerular layer, whereasc-metwas expressed in the MCL and olfactory nerve fiber layers (ONL). tPA expression in the adult olfactory bulb was observed in the ONL, MCL, and granule cell layers. Therefore, tPA expression was relatively coincident with the expression of HGF/SF and/orc-metin the appropriate projection patterns of the developing and adult olfactory system. In addition, antibodies against tPA inhibited the olfactory bulb extract-mediated cleavage of single-chain HGF/SF. These results suggest that tPA may play a regulatory role in the development and maintenance of the olfactory system by activating HGF/SF in the immediate vicinity of its receptor.
Local and Distributed Effects of Apomorphine on Fronto-Temporal Function in Acute Unmedicated Schizophrenia
Authors: Fletcher Paul C. , Frith Christopher D. , Grasby Paul M. , Friston Karl J. , Dolan Raymond J.
Published: April 2018

We used positron emission tomography (PET) to measure brain activity in healthy control subjects and unmedicated patients with schizophrenia. Subjects were scanned in the context of a combined psychological and pharmacological challenge, and we examined the effects of apomorphine, a drug acting on dopamine receptors, on brain systems engaged by a paced verbal fluency task. This factorial design enabled comparison of control subjects and schizophrenics in terms of the activations engendered by the cognitive task and the pharmacological challenge and the interaction of the two. We report a failure of cognitive task-related activation in anterior cingulate cortex and of task-related deactivation in the left superior temporal gyrus in the schizophrenic subjects. Compared with controls, the impaired cingulate activation was significantly reversed by apomorphine. Additionally, there was a trend for the abnormal fronto-temporal pattern of activation in schizophrenic subjects to be normalized by the drug. Overall, in schizophrenic subjects the effect of apomorphine, which we interpret in terms of a net dopaminergic antagonism, was to modify the brain activity, making the pattern more akin to that seen in control subjects. The results indicate both a regionally specific abnormality of brain function in schizophrenia and an abnormal pattern of fronto-temporal interactions.
Gonadal Steroids Exert Facilitating and “Buffering” Effects on Glucocorticoid-Mediated Transcriptional Regulation of Corticotropin-Releasing Hormone and Corticosteroid Receptor Genes in Rat Brain
Authors: Patchev Vladimir K. , Almeida Osborne F. X.
Published: April 2018

Gonadal steroids profoundly influence several brain functions and are apparently responsible for gender-specific differences in the regulation of hypothalamic–pituitary–adrenal (HPA) secretions. In this study, we examined the so-called “activational” effects of gonadal steroids on the glucocorticoid-mediated regulation of the gene transcription of corticotropin-releasing hormone (CRH) and corticosteroid receptors in brain areas of relevance for the control of pituitary–adrenal secretion. The efficacy of adrenalectomy (ADX) and chronic treatment with high doses of corticosterone (B) to regulate the gene transcription of CRH and corticosteroid receptors in the hypothalamic paraventricular nucleus (PVN) and hippocampus was studied in male and female rats under the conditions of deprivation of gonadectomy (GDX) and replacement with different gonadal steroids, such as estradiol (E2), progesterone (P), and dihydrotestosterone (DHT). In both sexes, ADX alone or in combination with GDX increased, and B treatment suppressed, the steady-state levels of CRH and corticosteroid receptor mRNAs, whereas GDX alone failed to affect any of the parameters studied. Administration of gonadal hormones to steroid-deprived (ADX/GDX) animals partially attenuated the upregulation of mRNAs encoding corticosteroid receptors in the hippocampus. Supplementation with gonadal steroids modified the effects of B on the gene transcription of CRH and corticosteroid receptors. Whereas P alone or in combination with E2counteracted the B-induced downregulation of GR and CRH gene transcription in females, DHT and E2administration further potentiated the effects of B on these parameters in a sex-specific manner. Taken together, the results indicate that gonadal steroids have minor influence on MR, GR, and CRH gene transcription under basal conditions, exert “glucocorticoid-like” effects on the transcription of corticosteroid receptors in the hippocampus of steroid-deprived animals, and interact with glucocorticoid-mediated mechanisms of regulation in the HPA axis through gender-specific “buffering” and “potentiating” effects.
Translational Machinery in Dendrites of Hippocampal Neurons in Culture
Authors: Tiedge Henri , Brosius Jürgen
Published: April 2018

In neurons, several mRNAs are selectively delivered to dendritic domains where they are presumably translated by local protein synthetic machinery. Although electron microscopy has identified polyribosomes in dendrites, in particular in postsynaptic dendritic compartments, the functional composition of the local protein synthetic apparatus and the scope of its translational capacity have not been analyzed. To ascertain the translational competence of dendrites, we have probed hippocampal neurons in primary culture for various integral and associated factors of the translational apparatus. We report here that dendrites of such neurons are equipped with a spectrum of translational machinery components, including ribosomes, tRNAs, initiation and elongation factors, and elements of the cotranslational signal recognition mechanism. These components are differentially and nonuniformly distributed in dendritic arbors. Their dendritic location illustrates the soma-independent potential of dendrites to synthesize selected proteins in local domains.
Detection of Ligands in Regions Anatomically Connected to Neurons Expressing the Eph Receptor Bsk: Potential Roles in Neuron–Target Interaction
Authors: Zhang Jian-Hua , Cerretti Douglas P. , Yu Tian , Flanagan John G. , Zhou Renping
Published: April 2018

Neuron–target interaction is a key feature in the establishment of neuronal networks. However, the underlying mechanism remains unclear. We have shown that at the time of target innervation, Bsk, an eph family receptor, is expressed at high levels in several brain regions including the hippocampus, olfactory bulb, and retina. To study whether the ligands are expressed in the target tissues, we investigated the expression of Bsk ligands using a ligand-affinity probe, Bsk-AP, which consisted of the extracellular domain of Bsk fused in frame with a human placental alkaline phosphatase. These analyses showed that the ligands were expressed at high levels in the developing septum, hypothalamus, olfactory neural epithelium, and tectum.In situhybridization studies revealed that at least three different factors were responsible for the Bsk-AP binding. In the septum, Elf-1, Lerk3 (Efl-2), and AL-1/Lerk7 were transcribed. In the hypothalamus, AL-1/Lerk7 was the ligand detected by Bsk-AP. In the olfactory system, high levels of Lerk3 were detected in the sensory neurons. Both Elf-1 and AL-1/Lerk7 were present in the tectum. These ligand-positive areas are known to be anatomically connected to Bsk-expressing regions. These observations strongly suggest that Bsk and the ligands participate in neuron–target interactions in multiple systems and provide support for their involvement in topographic projection.
A Role in Migration for the αvβ1 Integrin Expressed on Oligodendrocyte Precursors
Authors: Milner Richard , Edwards Gwynneth , Streuli Charles , ffrench-Constant Charles
Published: April 2018

Myelination of the CNS requires the migration of oligodendrocyte precursors throughout the CNS from restricted regions within the ventricular and subventricular zones. In light of the significant effects of cell–extracellular matrix (ECM) interactions on cell migration in other developing systems, we have analyzed the role of integrins in oligodendrocyte precursor migration. We have shown previously that oligodendrocyte precursorsin vitroexpress a limited repertoire of integrins, including α6β1, αvβ1, and αvβ3, and that differentiation is associated with downregulation of αvβ1 and upregulation of αvβ5. Using a migration assay based on the movement of cells away from an agarose drop containing a high-density cell suspension, we find that RGD peptides (that block αv but not α6 integrins) and anti-β1 antibodies block migration on an astrocyte-derived ECM, whereas anti-β3 antibodies have little effect. These re- sults suggest that αvβ1 but not α6β1 plays a role in oligodendrocyte precursor migration, and this is confirmed by the use of blocking monoclonal antibodies that distinguish these two integrins. In keeping with the results of others, we find that differentiated oligodendrocytes lose migratory potential and that the timing of this loss correlates with downregulation of αvβ1. Taken together with the work of others showing that ECM ligands for αvβ1 are expressed within the CNS, we propose that this integrin plays a significant role in the migration of oligodendrocyte precursorsin vivoand that its downregulation during differentiation could be an important factor regulating the migratory phenotype of these cells.
An Explanation for Reflex Blink Hyperexcitability in Parkinson’s Disease. II. Nucleus Raphe Magnus
Authors: Basso Michele A. , Evinger Craig
Published: April 2018

Hyperexcitable reflex blinks are a cardinal sign of Parkinson’s disease. The first step in the circuit linking the basal ganglia and brainstem reflex blink circuits is the inhibitory nigrostriatal pathway (Basso et al., 1996). The current study reports the circuits linking the superior colliculus (SC) to trigeminal reflex blink circuits. Microstimulation of the deep layers of the SC suppresses subsequent reflex blinks at a latency of 5.4 msec. This microstimulation does not activate periaqueductal gray antinociceptive circuits. The brainstem structure linking SC to reflex blink circuits must suppress reflex blinks at a shorter latency than the SC and produce the same effect on reflex blink circuits as SC stimulation, and removal of the structure must block SC modulation of reflex blinks. Only the nucleus raphe magnus (NRM) meets these requirements. NRM microstimulation suppresses reflex blinks with a latency of 4.4 msec. Like SC stimulation, NRM microstimulation reduces the responsiveness of the spinal trigeminal nucleus. Finally, blocking the receptors for the NRM transmitter serotonin eliminates SC modulation of reflex blinks, and muscimol inactivation of the NRM transiently prevents SC modulation of reflex blinks. Thus, the circuit through which the basal ganglia modulates reflex blinking is (1) the substantia nigra pars reticulata inhibits SC neurons, (2) the SC excites tonically active NRM neurons, and (3) NRM neurons inhibit spinal trigeminal neurons involved in reflex blink circuits.
Ultrastructural Localization of Dendritic Messenger RNA in Adult Rat Hippocampus
Authors: Martone Maryann E. , Pollock John A. , Jones Ying Zhang , Ellisman Mark H.
Published: April 2018

An ultrastructural examination of mRNA within adult rat CA1 hippocampal dendrites was conducted using two different methods. The messages for the α and β forms of the calcium–calmodulin-dependent protein kinase II were localized in ultracryosections using silver-intensified gold detection of isoform-specific oligonucleotide probes. Labeling for both isoforms was observed within the cell bodies and proximal dendrites of pyramidal neurons, but only the α form was observed in more distal dendrites. Unfortunately, the morphological preservation of the tissue was not sufficient to determine the localization of labeling relative to subcellular features such as denritic spines. To address this issue, a preembedding peroxidase-based method was developed, resulting in better preservation of the neuropil. The total population of polyadenylated [poly(A)] mRNA was localized in hippocampus using a biotinylated poly(dT) probe. Poly(A) mRNA was present in the nucleus and throughout the cell body of all hippocampal cells and within isolated dendrites and glial processes within the neuropil. Within pyramidal neurons, labeling was distributed in a longitudinal pattern in proximal apical dendrites. More distally, the amount of labeling diminished, and smaller foci of labeling were observed, particularly near the plasma membrane. Concentrated labeling was present at the base of dendritic spines and, less frequently, near synapses onto the dendritic shaft. These results suggest that dendritic mRNA is found in the vicinity of postsynaptic sites and provide additional evidence that local protein synthesis may play an important role in establishing and maintaining synaptic specializations.
NMDA Receptor Activation Inhibits Neuronal Volume Regulation after Swelling Induced by Veratridine-Stimulated Na+Influx in Rat Cortical Cultures
Authors: Churchwell Kevin B. , Wright Stephen H. , Emma Francesco , Rosenberg Paul A. , Strange Kevin
Published: April 2018

Neurons and glia experience rapid fluctuations in transmembrane solute and water fluxes during normal brain activity. Cell volume must be regulated under these conditions to maintain optimal neural function. Almost nothing is known, however, about how brain cells respond to volume challenges induced by changes in transmembrane solute flux. As such, we characterized the volume-regulatory mechanisms of cultured cortical neurons swollen by veratridine-stimulated Na+influx. Exposure of cortical neurons to 100 μmveratridine for 10–15 min caused a 1.8- to 2-fold increase in cell volume that persisted for at least 90 min. This volume increase was blocked by extracellular Na+removal or by exposure to 5 μmtetrodotoxin, indicating that swelling is a result of Na+entry via Na+channels. Treatment of cells with veratridine together with various NMDA receptor antagonists had no effect on the magnitude of swelling. NMDA receptor antagonist-treated cells, however, underwent nearly complete volume recovery within 50–70 min after veratridine exposure. This recovery suggests that NMDA receptor activation disrupts neuronal osmoregulatory pathways. Volume regulation was blocked by Ba2+, quinidine, or 5-nitro-2-(3-phenylpropylamino) benzoic acid, indicating that swelling activates volume regulatory K+and Cl−channels. Veratridine also caused a rapid, transient increase in intracellular Ca2+. Extracellular Ca2+removal or intracellular Ca2+chelation prevented or dramatically reduced veratridine-induced increases in intracellular Ca2+and completely blocked volume recovery. These findings indicate that increases in Ca2+during cell swelling induced by Na+influx are required for activation of neuronal volume-regulatory pathways.
Direct Measurement of AMPA Receptor Desensitization Induced by Glutamatergic Synaptic Transmission
Authors: Otis Thomas , Zhang Su , Trussell Laurence O.
Published: April 2018

Although almost all ionotropic neurotransmitter receptors undergo desensitization, the onset and recovery of desensitization at a synapse have never been observed directly. We have found changes in postsynaptic AMPA receptor sensitivity in neurons of the chick cochlear nucleus, the nucleus magnocellularis (nMAG), by photolysis of caged glutamate immediately after activation of a single synaptic input. Additionally, synaptic desensitization was demonstrated via competition between synaptically released glutamate and an exogenous nondesensitizing agonist, kainate. Both approaches indicated that at least 35–40% of the receptors were desensitized after a single synaptic stimulus. Miniature synaptic currents were depressed after an evoked synaptic current, indicating that desensitization led to a reduction in the response to individual transmitter quanta. Stimulation of adjacent glutamatergic inputs to the same cell demonstrated that nearby terminals did not depress one another, suggesting that the desensitizing level of glutamate is restricted to each axon terminal. These findings confirm that postsynaptic neurons may use desensitization to regulate the strength of transmission on a synapse-specific basis.
Modulation of Inhibitory Transmission by Dopamine in Rat Basal Forebrain Nuclei: Activation of Presynaptic D1-like Dopaminergic Receptors
Authors: Momiyama Toshihiko , Sim J. A.
Published: April 2018

The effects of dopamine (DA) on inhibitory transmission onto identified magnocellular neurons were examined in rat basal forebrain slices using whole-cell recording. IPSCs evoked by focal stimulation within basal forebrain nuclei were reversibly blocked by 10 μmbicuculline and had a decay time constant of 20.1 ± 0.77 msec in the presence of 6-cyano-7-nitroquinoxalline-2,3-dione (5 μm). Bath application of DA reduced the amplitude of IPSCs up to 71.1 ± 1.49% in a concentration-dependent manner between 0.003 and 1 mm(the IC50value being 6.6 μm), without any effect on the holding current at −70 mV. DA (10 μm) reduced the frequency of miniature IPSCs (mIPSCs) recorded in the presence of TTX (0.5 μm), without affecting their mean amplitude, rise time, and decay time constant. Furthermore, the DA-induced effect on mIPSCs remained unaffected by 100 μmcadmium, suggesting a presynaptic mechanism independent of calcium influx. SKF 81297, a D1-like agonist, mimicked DA-induced effect on evoked IPSCs (IC50, 10.9 μm), whereas R(−)-TNPA or (−)-quinpirole, D2-like agonists (30 μm), had little or no effect on the amplitude of evoked IPSCs. R(+)-SCH 23390, a D1-like antagonist, antagonized the DA-induced effect on IPSCs (KB0.82 μm), whereas S(−)-eticlopride, a D2-like antagonist, showed slight antagonism (KB7.8 μm). Forskolin (10 μm) reduced the amplitude of evoked IPSCs to ∼58% of the control and occluded the inhibitory effect of DA. These findings indicate that DA reduces inhibitory transmission onto magnocellular basal forebrain neurons by activating presynaptic D1-like receptors.
Expression of Presenilin 1 and 2 (PS1 and PS2) in Human and Murine Tissues
Authors: Lee Michael K. , Slunt Hilda H. , Martin Lee J. , Thinakaran Gopal , Kim Grace , Gandy Samuel E. , Seeger Mary , Koo Edward , Price Donald L. , Sisodia Sangram S.
Published: April 2018

Mutations in genes encoding related proteins, termed presenilin 1 (PS1) and presenilin 2 (PS2), are linked to the majority of cases with early-onset familial Alzheimer’s disease (FAD). To clarify potential function(s) of presenilins and relationships of presenilin expression to pathogenesis of AD, we examined the expression of PS1 and PS2 mRNA and PS1 protein in human and mouse. Semi-quantitative PCR of reverse-transcribed RNA (RT-PCR) analysis revealed that PS1 and PS2 mRNA are expressed ubiquitously and at comparable levels in most human and mouse tissues, including adult brain. However, PS1 mRNA is expressed at significantly higher levels in developing brain.In situhybridization studies of mouse embryos revealed widespread expression of PS1 mRNA with a neural expression pattern that, in part, overlaps that reported for mRNA encoding specific Notch homologs.In situhybridization analysis in adult mouse brain revealed that PS1 and PS2 mRNAs are enriched in neurons of the hippocampal formation and entorhinal cortex. Although PS1 and PS2 mRNA are expressed most prominently in neurons, lower but significant levels of PS1 and PS2 transcripts are also detected in white matter glial cells. Moreover, cultured neurons and astrocytes express PS1 and PS2 mRNAs. Using PS1-specific antibodies in immunoblot analysis, we demonstrate that PS1 accumulates as ∼28 kDa N-terminal and ∼18 kDa C-terminal fragments in brain. Immunocytochemical studies of mouse brain reveal that PS1 protein accumulates in a variety of neuronal populations with enrichment in somatodendritic and neuropil compartments.
Transcription Factor AP-2 Regulates Human Apolipoprotein E Gene Expression in Astrocytoma Cells
Authors: Garcı́a Miguel A. , Vázquez Jesús , Giménez Cecilio , Valdivieso Fernando , Zafra Francisco
Published: April 2018

Apolipoprotein E (apoE), one of the major plasma lipoproteins, also is expressed in a variety of cell types, including the glial cells of the nervous system. apoE is involved in processes of degeneration and regeneration after nerve lesions as well as in the pathogenesis of Alzheimer’s disease (AD). Glial synthesis of apoE is activated in response to injury both in the peripheral and central nervous system. We now report that the activity of the proximal apoE promoter in astrocytes is upregulated by cAMP and retinoic acid, which act synergistically. Sequence analysis of the apoE promoter indicated the presence of several AP-2 consensus sequences that could mediate the stimulatory effect of cAMP and retinoic acid. The possible functional role of AP-2 was examined by cotransfection of AP-2-deficient HepG2 cells with an apoE promoter construct and a human AP-2 expression construct. Cotransfection with AP-2 significantly elevated apoE promoter activity. DNase I footprinting technique revealed the existence of two binding sites for recombinant AP-2 in regions from −48 to −74 and from −107 to −135 of the apoE promoter. Mutations in these regions markedly impaired the trans-stimulatory effect of AP-2. These results indicate the existence of functional AP-2 sites in the promoter region of apoE that could contribute to the complex regulation of this gene in developmental, degenerative, and regenerative processes of the nervous system.
Neurotrophin-3 Is a Survival FactorIn Vivofor Early Mouse Trigeminal Neurons
Authors: Wilkinson George A. , Fariñas Isabel , Backus Carey , Yoshida Cathleen K. , Reichardt Louis F.
Published: April 2018

Mice lacking neurotrophin-3 (NT-3) have been shown previously to be born with severe sensory deficits. This study characterizes the developmental course of this deficit in the trigeminal sensory ganglion, which in NT-3 homozygous mutants contains only 35% of the normal number of neurons at birth. At embryonic day 10.5 (E10.5), normal numbers of neurons, as assessed by expression of neurofilament protein and of total cells, are present in the ganglia of mutant homozygotes. During the next 3 d (E10.5–E13.5), virtually all of the deficit develops, after which mutant animals retain only ∼30% the normal number of neurons. Quantification of neuronal and neuronal precursor numbers in normal and mutant animals reveals that neurons are specifically depleted in the absence of NT-3. A deficiency in precursor proliferation is only seen after most of the neuronal deficit has developed. Numbers of apoptotic cells in the ganglia of mutant animals are elevated during this same interval, indicating that the neuronal deficit is caused, in large part, by increased cell death of embryonic neurons.

To determine sources of NT-3 in the trigeminal system, we examined the expression pattern of β-galactosidase in mice, in which lacZ has replaced the NT-3 coding exon. E10.5–E11.5 embryos exhibit intense reporter expression throughout the mesenchyme and epithelia of the first branchial arch. β-galactosidase expression in E13.5 embryos is largely confined to the oral epithelium and the mesenchyme underlying the skin. Throughout the E10.5–E13.5 interval, the trigeminal ganglion and its targets in the CNS do not express reporter activity.

We conclude that NT-3 acts principally as a peripherally derived survival factor for early trigeminal neurons.
Visual Response Properties of Striate Cortical Neurons Projecting to Area MT in Macaque Monkeys
Authors: Movshon J. Anthony , Newsome William T.
Published: April 2018

We have previously shown that some neurons in extrastriate area MT are capable of signaling the global motion of complex patterns; neurons randomly sampled from V1, on the other hand, respond only to the motion of individual oriented components. Because only a small fraction of V1 neurons projects to MT, we wished to establish the processing hierarchy more precisely by studying the properties of those neurons projecting to MT, identified by antidromic responses to electrical stimulation of MT. The neurons that project from V1 to MT were directionally selective and, like other V1 neurons, responded only to the motion of the components of complex patterns. The projection neurons were predominantly “special complex,” responsive to a broad range of spatial and temporal frequencies, and sensitive to very low stimulus contrasts. The projection neurons thus comprise a homogeneous and highly specialized subset of V1 neurons, consistent with the notion that V1 acts as clearing house of basic visual measurements, distributing information appropriately to higher cortical areas for specialized analysis.