bluuebunny/crossref_metadata_2025 huggingface dataset:
Conditioned medium from cultures of embryonic neurons contains a high molecular weight factor which induces acetylcholine receptor aggregation on cultured myotubes
Authors: Schaffner AE , Daniels MP
Published: April 2018

The developmental mechanisms involved in the formation of stable arrays of postsynaptic neurotransmitter receptors near sites of neurotransmitter release are essentially unknown. However, several recent studies have shown that cells or tissues of neural origin produce macromolecular factors which induce an increase in the number of acetylcholine (ACh) receptors or the number of receptor aggregates on cultured embryonic myotubes. We have tested primary cultures of embryonic neurons and other cell types for the release of an ACh receptor aggregation factor. Conditioned medium from the cultures was applied to cultures of embryonic rat myotubes for 1 day; ACh receptors on the myotubes were stained with tetramethylrhodamine-labeled alpha- bungarotoxin and ACh receptor aggregation activity, defined as the change in the number of receptor aggregates per myotube, was assayed. Aggregation activity with a molecular weight greater than or equal to 50,000 was released by cultures of neurons from sympathetic ganglia, dorsal root ganglia, spinal cord, and cerebellum. Little or no activity was released by glial or other non-neuronal cultures. Release of aggregation activity by different neuronal cell types varied by up to an order of magnitude; however, this variation was not well correlated with the differences in ACh synthesis. The factor(s) in neuronal cell conditioned medium induced a rearrangement of pre-existing receptors at the cell surface, and its action was not dependent on new protein synthesis. The results of this study are consistent with the idea that one or more receptor aggregation factors secreted by neurons are involved in the organization of neurotransmitter receptors during synapse formation in vivo.
Study of Receptor-Mediated Neurotoxins Released by HIV-1-Infected Mononuclear Phagocytes Found in Human Brain
Authors: Giulian Dana , Yu Jiahan , Li Xia , Tom Donald , Li Jun , Wendt Elaine , Lin Shen-Nan , Schwarcz Robert , Noonan Christine
Published: April 2018

Although there is growing evidence that neurotoxic molecules produced by HIV-1-infected mononuclear phagocytes damage neurons, the precise mechanisms of neuronal attack remain uncertain. One class of cytotoxin involves neuronal injury mediated via the NMDA receptor. We examined blood monocytes and brain mononuclear cells isolated at autopsy from HIV-1-infected individuals for the ability to release NMDA-like neuron-killing factors. We found that a neurotoxic amine, NTox, was produced by blood monocytes and by brain mononuclear phagocytes infected with retrovirus.In vivoinjections of minute quantities of NTox produced selective damage to hippocampal pyramidal neurons. NTox can be extracted directly from brain tissues infected with HIV-1 and showed structural features similar to wasp and spider venoms. In contrast to NTox, HIV-1 infection did not increase the release of the NMDA excitotoxin quinolinic acid (QUIN) from mononuclear cells. Although we found modest elevations of QUIN in the CSF of HIV-1-infected individuals, the increases were likely attributable to entry through damaged blood–brain barrier. Taken together, our data pinpoint NTox, rather than QUIN, as a major NMDA receptor-directed toxin associated with neuro-AIDS.
Clustering of Gephyrin at GABAergic but Not Glutamatergic Synapses in Cultured Rat Hippocampal Neurons
Authors: Craig Ann Marie , Banker Gary , Chang Weiru , McGrath Maureen E. , Serpinskaya Anna S.
Published: April 2018

The molecular mechanisms underlying the establishment of a postsynaptic receptor mosaic on CNS neurons are poorly understood. One protein thought to be involved is gephyrin, a peripheral membrane protein that binds to the inhibitory glycine receptor and functions in clustering this receptor at synapses in cultured rat spinal cord neurons. We investigated the possible association of gephyrin with synapses in cultured rat hippocampal neurons, where glutamate and GABA but not glycine are the principal transmitters. Gephyrin immunoreactivity was detected in axons as well as dendrites, changing from a predominantly axonal to a more dendritic distribution with time in culture. Gephyrin staining was not distributed uniformly, but always took the form of clusters. Small clusters of gephyrin (0.2 μm2), present throughout development, were distributed widely and not restricted to synaptic sites. Larger clusters of gephyrin (0.4–10.0 μm2, sometimes composed of groups of small clusters), which developed in older cells, were localized to a subset of contacts between axons and dendrites. These large clusters were not present at glutamatergic synapses (marked by immunostaining for GluR1), but were closely associated with GABAergic synapses (marked by immunostaining for GABA and glutamic acid decarboxylase). These results, together with previous findings, suggest that gephyrin may function to anchor GABA and glycine receptors, but not glutamate receptors, at postsynaptic sites on central neurons. They also raise the possibility that gephyrin has additional functions, independent of its role at synapses.
Restoration of Normal Conduction Properties in Demyelinated Spinal Cord Axons in the Adult Rat by Transplantation of Exogenous Schwann Cells
Authors: Honmou Osamu , Felts Paul A. , Waxman Stephen G. , Kocsis Jeffery D.
Published: April 2018

Although remyelination of demyelinated CNS axons is known to occur after transplantation of exogenous glial cells, previous studies have not determined whether cell transplantation can restore the conduction properties of demyelinated axons in the adult CNS. To examine this issue, the dorsal columns of the adult rat spinal cord were demyelinated by x-irradiation and intraspinal injections of ethidium bromide. Cell suspensions of cultured astrocytes and Schwann cells derived from neonatal rats transfected with the (β-galactosidase) reporter gene were injected into the glial-free lesion site. After 3–4 weeks nearly all of the demyelinated axons were remyelinated by the transplanted Schwann cells. The dorsal columns were removed and maintained in anin vitrorecording chamber; conduction properties were studied using field potential and intra-axonal recording techniques. The demyelinated axons exhibited conduction slowing and block, and a reduction in their ability to follow high-frequency stimulation. Axons remyelinated by transplantation of cultured Schwann cells exhibited restoration of conduction through the lesion, with reestablishment of normal conduction velocity. The axons remyelinated after transplantation showed enhanced impulse recovery to paired-pulse stimulation and greater frequency-following capability as compared with both demyelinated and control axons. These results demonstrate the functional repair of demyelinated axons in the adult CNS by transplantation of cultured myelin-forming cells from the peripheral nervous system in combination with astrocytes.
The Ganglionic Eminence May Be an Intermediate Target for Corticofugal and Thalamocortical Axons
Authors: Métin Christine , Godement Pierre
Published: April 2018

In the nervous system of many species, growing axons associate transiently with cellular groupings along their path. Whether this mechanism applies to the development of corticothalamic and thalamocortical projections is unknown. Using carbocyanine dyes, we studied the early growth of both corticofugal and thalamocortical fibers in hamster embryos. At embryonic day 11.5 (E11.5), corticofugal fibers invade the lateral ganglionic eminence (LGE), and thalamocortical fibers invade the medial ganglionic eminence (MGE). At this age, both sets of fibers are not yet in contact with each other. At the same time, neurons in each subdivision of the GE grow toward the cortex and thalamus. During the next 24 hr, corticofugal and thalamocortical fibers remain within the confines of the GE, where they course at different radial levels and bear large and complex growth cones. In the LGE, corticofugal fibers are often found in close association with cells that are likely to be neuronal. Starting on E13.5, both early projections from the GE decrease, and corticothalamic and thalamocortical fibers invade their definitive target regions. To test whether the GE specifically orients the growth and trajectories of cortical fibers even in the absence of the reciprocal thalamic projection, we cocultured explants of cortex and GE from either hamster or mouse embryos. These experiments showed that the GE, but not other tested brain regions, is able specifically to orient the growth of cortical axons. We therefore suggest that the GE may be an intermediate target in the pathfinding of axons between the cortex and the thalamus.
Microtubule Stability Decreases Axon Elongation but Not Axoplasm Production
Authors: Rochlin M. William , Wickline Karen M. , Bridgman Paul C.
Published: April 2018

Microtubules are a primary cytoskeletal constituent of axons and growth cones. In addition to serving as a scaffolding for axon assembly, they also provide a means of transport of organelles that are essential for outgrowth and maintenance of synaptic function. Pharmacological manipulations that disrupt net assembly of microtubules also interfere with growth cone advance and axon extension. Less is known about the effects of disrupting microtubule dynamics without affecting net assembly. To investigate this, we studied the effects of low doses of nocodazole on axon extension and microtubule organization in rat superior cervical ganglion neurons. We report that 165–330 nmnocodazole significantly reduces axon extension rate and increases axon diameter without affecting the rate of production of axoplasm or microtubule polymer, and without decreasing the average length or number of microtubules. Two observations suggested that microtubule dynamics were depressed by this dose of nocodazole. First, this treatment eliminated the highly divergent lengths and positions of microtubules characteristic of normal growth cones, inducing an array in which each microtubule terminated at roughly the same position in the proximal regions of the growth cone. Second, there was a decrease in the proportion of microtubule length containing mostly tyrosinated (newly assembled) α-tubulin and an increase in the proportion of microtubule length containing mostly acetylated (older, more stable) α-tubulin. Together, these data suggest that a decrease in dynamic instability of microtubules is sufficient to disrupt axon extension but does not interfere with axoplasm production.
Experience-Dependent Plasticity of Binocular Responses in the Primary Visual Cortex of the Mouse
Authors: Gordon Joshua A. , Stryker Michael P.
Published: April 2018

An activity-dependent form of synaptic plasticity underlies the fine tuning of connections in the developing primary visual cortex of mammals such as the cat and monkey. Studies of the effects of manipulations of visual experience during a critical period have demonstrated that a correlation-based competitive process governs this plasticity. The cellular mechanisms underlying this competition, however, are poorly understood. Transgenic and gene-targeting technologies have led to the development of a new category of reagents that have the potential to help answer questions of cellular mechanism, provided that the questions can be studied in a mouse model. The current study attempts to characterize a developmental plasticity in the mouse primary visual cortex and to demonstrate its relevance to that found in higher mammals. We found that 4 d of monocular lid suture at postnatal day 28 (P28) induced a maximal loss of responsiveness of cortical neurons to the deprived eye. These ocular dominance shifts occurred during a well-defined critical period, between P19 and P32. Furthermore, binocular deprivation during this critical period did not decrease visual cortical responses, and alternating monocular deprivation resulted in a decrease in the number of binocularly responsive neurons. Finally, a laminar analysis demonstrated plasticity of both geniculocortical and intracortical connections. These results demonstrate that an activity-dependent, competitive form of synaptic plasticity that obeys correlation-based rules operates in the developing primary visual cortex of the mouse.
A Novel Entorhinal Projection to the Rat Dentate Gyrus: Direct Innervation of Proximal Dendrites and Cell Bodies of Granule Cells and GABAergic Neurons
Authors: Deller Thomas , Martinez Albert , Nitsch Robert , Frotscher Michael
Published: April 2018

Entorhinal fibers to the fascia dentata originating from layer II stellate neurons are known to terminate exclusively in the outer two thirds of the molecular layer, where they innervate distal dendritic portions of dentate neurons. Using anterograde tracing withPhaseolus vulgarisleucoagglutinin, we unraveled a previously unknown entorhinal projection that directly innervates proximal dendritic portions and somata of granule cells and GABAergic neurons. This projection originates from neurons located in entorhinal layers IV–VI of the medial entorhinal area. These fibers enter the outer two thirds of the molecular layer, traverse the inner molecular layer (IML) and granule cell layer, where they form numerous boutons, and finally arborize subjacent to the granule cells. Correlated light and electron microscopy revealed that the boutons formed by these fibers establish asymmetric synapses on dendrites in the IML, on spines and somata of granule cells, and on spineless dendrites subjacent to the granule cell layer. Postembedding immunogold staining indicates that this entorhino-dentate projection is not GABAergic and that it also terminates on GABAergic inhibitory neurons. These data demonstrate that not all entorhino-dentate fibers display a similar high laminar specificity for the outer molecular layer (OML). Although fibers from the superficial layers of the entorhinal cortex terminate exclusively in the OML, entorhinal fibers arising from deeper layers are not confined to laminar boundaries. Finally, the possibility that these supposedly excitatory entorhinal afferents may monosynaptically activate proximal dendrites and somata of dentate neurons needs to be incorporated into contemporary concepts of the hippocampal network.
Interneurons Containing Calretinin Are Specialized to Control Other Interneurons in the Rat Hippocampus
Authors: Gulyás Attila I. , Hájos Norbert , Freund Tamás F.
Published: April 2018

Spine-free calretinin-immunoreactive (CR-IR) interneurons form a subpopulation of GABAergic cells in the rat hippocampus. A characteristic feature of these cells—located in all areas and layers—is the frequent dendro-dendritic and axo-dendritic contacts they form with each other. In this study we examined in detail the connectivity of these neurons by reconstructing their dendritic and axonal arbor and by identifying their postsynaptic targets.

Radially running dendrites of CR-IR cells, located in different layers, intermingled into long braids. An average cell was in contact with dendrites of three to seven other CR-IR cells. Reconstruction of the dendritic trees from six consecutive sections demonstrated that at least 15 cells may participate in a dendro-dendritically connected cluster. Electron microscopical examination revealed that regularly spaced zonula adherentia connect the touching dendrites.

The postsynaptic targets of CR-IR neurons have been examined using postembedding immunogold staining for GABA. CR-containing GABA-immunoreactive axons of local origin formed multiple symmetrical synaptic contacts (two to five) exclusively on GABAergic dendrites (CR-negative as well as CR-positive). Two to 10 CR-IR axons may converge onto a single CR-IR neuron, often from cells belonging to the same dendro-dendritically connected cluster. Using double immunocytochemistry, CR-IR cells were shown to heavily innervate calbindin D28k-containing interneurons and VIP-containing basket cells but avoided the parvalbumin-containing basket and axo-axonic cells.

The unique connectivity of CR-IR cells may enable them to play a crucial role in the generation of synchronous, rhythmic hippocampal activity by controlling other interneurons terminating on different dendritic and somatic compartments of principal cells.
Nucleus-Specific Expression of GABAAReceptor Subunit mRNAs in Monkey Thalamus
Authors: Huntsman M. M. , Leggio M. G. , Jones E. G.
Published: April 2018

Expression of 10 GABAAreceptor subunit genes was examined in monkey thalamus byin situhybridization using cRNA probes specific for α1, α2, α3, α4, α5, β1, β2, β3, γ1, and γ2subunit mRNAs. These displayed unique hybridization patterns with significant differences from rodents. α1, β2, and γ2transcripts were expressed at high levels in all dorsal thalamic nuclei, but expression was significantly higher in sensory relay nuclei—especially the dorsal lateral geniculate nucleus. Other transcripts showed nucleus-specific differences in levels of expression and in the range expressed. α5and α4subunit transcripts were expressed in all nuclei except the intralaminar nuclei. Levels of α2, α3, β1, β3, and γ1expression were very low, except in intralaminar nuclei. In the reticular nucleus, most subunit transcripts were not expressed, and only γ2transcripts were consistently detected at modest levels. Thalamic GABAAreceptors may be assembled from nucleus-specific groupings of subunit polypeptides.
Identification and Characterization of a 47 Base Pair Activity-Dependent Enhancer of the Rat Nicotinic Acetylcholine Receptor δ-Subunit Promoter
Authors: Walke Wade , Xiao Guozhi , Goldman Daniel
Published: April 2018

Nicotinic acetylcholine receptor (nAChR) genes are regulated by muscle electrical activity. E-box sequences found in their promoters are necessary for this regulation. However, many muscle genes contain E-boxes, yet are not regulated by muscle depolarization. This suggests that other elements are necessary, perhaps working in conjunction with E-boxes, to confer depolarization-dependent control onto promoter activity. We have used direct DNA injection into muscle as anin vivoassay to identify and characterize these additional elements. Mutagenesis and expression assays identified multiple elements within the first 81 base pairs (bp) of the nAChR δ-subunit promoter that contribute to its regulation by muscle electrical activity. Within this 81 bp sequence, two regions of DNA were identified that were capable of conferring activity-dependent regulation onto a heterologous promoter. The stronger of these two putative enhancers was characterized further. It is a 47 bp sequence that contains an E-box along with sequences similar to the SV40 core enhancer and an SP1 site. Site-directed mutagenesis identified residues within each of these sequences that were necessary for enhancer activity. Furthermore, methylation interference DNA footprinting assays showed increased nuclear protein binding to sequences within both these enhancers after muscle denervation, and this pattern of binding was very similar to that observed with nuclear protein isolated from myotube extracts. These latter results suggest that similar mechanisms may mediate increased nAChR expression during muscle development and after muscle denervation.
Dopamine Receptor Agonists Regulate Levels of the Serotonin 5-HT2AReceptor and its mRNA in a Subpopulation of Rat Striatal Neurons
Authors: Laprade Nathalie , Radja Fatiha , Reader Tomás A. , Soghomonian Jean-Jacques
Published: April 2018

The effects of dopamine receptor agonists on the levels of the striatal serotonin 5-HT2Areceptor and its mRNA were investigated in rats lesioned with 6-OHDA as neonates. The mRNA encoding for the 5-HT2Areceptor was detected byin situhybridization histochemistry and the binding to 5-HT2Areceptors was revealed with [125I](2,5-dimethoxy-4-iodophenyl)2-aminopropane ([125I]DOI). In adult control unlesioned rats, labeling with the 5-HT2AcRNA probe and with [125I]DOI was concentrated in medial sectors of the striatum. In 6-OHDA-lesioned rats, labeling with the 5-HT2AcRNA probe or with [125I]DOI was increased in the striatum, particularly in its lateral subdivisions. These increases were abolished after chronic systemic administration of the dopamine receptor agonists apomorphine or SKF-38393. The mRNA levels encoding for the 5-HT2Areceptor were further measured in individual striatal neurons after double-labeling of sections with a 5-HT2Aand a preproenkephalin (PPE) cRNA probe. In control unlesioned rats, 5-HT2AmRNA labeling was distributed in PPE-labeled as well as in PPE-unlabeled striatal neurons. In 6-OHDA-lesioned rats, increased 5-HT2AmRNA labeling was found only in PPE-unlabeled neurons and it was abolished after apomorphine or SKF-38393 administration. These results demonstrate that agonists of dopamine receptors inhibit the expression of 5-HT2Areceptors in a subpopulation of presumed striato-nigral neurons. We propose that this regulation plays an important role in the control of motor activity by dopamine and 5-HT in the basal ganglia.
Network Analysis of Positron Emission Tomography Regional Cerebral Blood Flow Data: Ensemble Inhibition during Episodic Memory Retrieval
Authors: Nyberg Lars , McIntosh Anthony R. , Cabeza Roberto , Nilsson Lars-Göran , Houle Sylvain , Habib Reza , Tulving Endel
Published: April 2018

Two important objectives in the neuroscience of memory are (1) identification of neural pathways involved in memory processes; and (2) characterization of the pattern of interactions between these pathways. Functional neuroimaging can contribute to both of these goals. Using image subtraction analysis of regional cerebral blood flow data measured with positron emission tomography, we identified brain regions that changed activity during episodic memory retrieval (visual word recognition). Relative to a baseline reading task, decreased activity was observed in bilateral prefrontal, bilateral anterior and posterior temporal, and posterior cingulate cortices. Brain regions showing increased activity were the right prefrontal (different from deactivated regions), left anterior cingulate, and left occipital cortices, and vermis of cerebellum. We then performed a network analysis with structural equation modeling to test the hypothesis that regional decreases came about through active inhibition by regions showing increased activity during retrieval. This analysis demonstrated that the influence of activated regions on deactivated regions was more negative during retrieval than during reading, confirming the inhibition hypothesis. Such confirmation could not have been made from the subtraction analysis alone because decreases can come about, at the very least, through reduction of functional influences as well as by active inhibition. The concepts of ensemble excitation and inhibition, as defined through network analysis, are introduced. We argue that it is critical to examine the combined pattern of excitatory and inhibitory influences to fully appreciate the neural basis of episodic memory.
Synchronous GABA-Mediated Potentials and Epileptiform Discharges in the Rat Limbic SystemIn Vitro
Authors: Avoli Massimo , Barbarosie Michaela , Lücke Anne , Nagao Takeki , Lopantsev Valeri , Köhling Rüdiger
Published: April 2018

Application of 4-aminopyridine (4AP, 50 μm) to combined slices of adult rat hippocampus–entorhinal cortex-induced ictal and interictal epileptiform discharges, as well as slow field potentials that were abolished by the μ-opioid agonist [d-Ala2,N-Me-Phe4,Gly-ol5] enkephalin (DAGO, 10 μm) or the GABAAreceptor antagonist bicuculline methiodide (BMI, 10 μm); hence, they represented synchronous GABA-mediated potentials. Ictal discharges originated in the entorhinal cortex and propagated to the hippocampus, whereas interictal activity of CA3 origin was usually recorded in the hippocampus. The GABA-mediated potentials had no fixed site of origin or modality of propagation; they closely preceded (0.2–5 sec) and thus appeared to initiate ictal discharges. Only ictal discharges were blocked by the antagonist of the NMDA receptor 3,3-(2-carboxypiperazine-4-yl)propyl-1-phosphonate (CPP, 10 μm), whereas the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 μm) abolished all epileptiform activities. The GABA-mediated potentials continued to occur synchronously in all regions even after concomitant application of CNQX and CPP. [K+]oelevations were recorded in the entorhinal cortex during the ictal discharge (peak values = 13.9 ± 0.9 mm) and the synchronous GABA-mediated potentials (peak values = 4.2 ± 0.1 mm); the latter increases were presumably attributable to postsynaptic GABAA-receptor activation because they were abolished by DAGO or BMI. Their role in initiating ictal activity was demonstrated by using DAGO, which abolished both GABA-mediated synchronous potentials and ictal discharges. These data indicate that NMDA-mediated ictal discharges induced by 4AP originate in the entorhinal cortex; such a conclusion is in line with clinical evidence obtained in temporal lobe epilepsy patients. 4AP also induces GABA-mediated potentials that spread within the limbic system when excitatory transmission is blocked and may play a role in initiating ictal discharge by increasing [K+]o.
A Dynamic Network Simulation of the Nematode Tap Withdrawal Circuit: Predictions Concerning Synaptic Function Using Behavioral Criteria
Authors: Wicks Stephen R. , Roehrig Chris J. , Rankin Catharine H.
Published: April 2018

The nematode tap withdrawal reflex demonstrates several forms of behavioral plasticity. Although the neural connectivity that supports this behavior is identified (Integration of mechanosensory stimuli inCaenorhabditis elegans, Wicks and Rankin, 1995, J Neurosci 15:2434–2444), the neurotransmitter phenotypes, and hence whether the synapses in the circuit are excitatory or inhibitory, remain uncharacterized. Here we use a novel strategy to predict the polarity configuration, i.e., the array of excitatory and inhibitory connections, of the nematode tap withdrawal circuit using an anatomically and physiologically justifiable dynamic network simulation of that circuit. The output of the modeled circuit was optimized to the behavior of animals, which possessed circuits altered by surgical ablation by exhaustively enumerating an array of synaptic signs that constituted the modeled circuit. All possible polarity configurations were then compared, and a statistical analysis was used to determine whether, for a given synaptic class, a particular polarity was associated with a good fit to behavioral data. The results from four related experiments were used to predict the polarities of seven of the nine cell classes of the tap withdrawal circuit. In addition, the model was used to assess possible roles for two novel mechanosensory integration neurons: DVA and PVD.
Functional Mapping of Human Learning: A Positron Emission Tomography Activation Study of Eyeblink Conditioning
Authors: Blaxton Teresa A. , Zeffiro Thomas A. , Gabrieli John D. E. , Bookheimer Susan Y. , Carrillo Maria C. , Theodore William H. , Disterhoft John F.
Published: April 2018

Regional cerebral blood flow (rCBF) was measured using positron emission tomography during eyeblink conditioning in young adults. Subjects were scanned in three experimental conditions: delay conditioning, in which binaural tones preceded air puffs to the right eye by 400 msec; pseudoconditioning, in which presentations of tone and air puff stimuli were not correlated in time; and fixation rest, which served as a baseline control. Compared with fixation, pseudoconditioning produced rCBF increases in frontal and temporal cortex, basal ganglia, left hippocampal formation, and pons. Learning-specific activations were observed in conditioning as compared with pseudoconditioning in bilateral frontal cortex, left thalamus, right medial hippocampal formation, left lingual gyrus, pons, and bilateral cerebellum; decreases in rCBF were observed for bilateral temporal cortex, and in the right hemisphere in putamen, cerebellum, and the lateral aspect of hippocampal formation. Blood flow increased as the level of learning increased in the left hemisphere in caudate, hippocampal formation, fusiform gyrus, and cerebellum, and in right temporal cortex and pons. In contrast, activation in left frontal cortex decreased as learning increased. These functional imaging results implicate many of the same structures identified by previous lesion and recording studies of eyeblink conditioning in animals and humans and suggest that the same brain regions in animals and humans mediate multiple forms of associative learning that give meaning to a previously neutral stimulus.
Laminar Localization, Morphology, and Physiological Properties of Pyramidal Neurons that Have the Low-Threshold Calcium Current in the Guinea-Pig Medial Frontal Cortex
Authors: de la Peña Elvira , Geijo-Barrientos Emilio
Published: April 2018

One of the several types of ionic currents present in central neurons is the low-threshold, or T-type calcium current (LTCC). This current is responsible for the firing of low-threshold calcium spikes (LTS) and participates in the generation of rhythmic activity and bursts of action potentials in several brain nuclei. We have studied the distribution and properties of pyramidal neurons recorded from the guinea-pig medial frontal cortex that have this calcium current. Pyramidal neurons were recorded in anin vitroslice preparation using either current clamp or single-electrode voltage-clamp recording. Pyramidal neurons that generated LTS or had the LTCC were found only between 500 mm from the pial surface and the white matter (approximately layers V/VI) and were absent in more superficial layers. All pyramidal neurons that fired LTS or had the LTCC were characterized as regular spiking and had some important morphological and physiological differences from the rest of the pyramidal neurons studied. This group of neurons had shorter and less complex apical dendritic arbors, fired action potentials of lower amplitude and longer duration, and were the only type of pyramidal neurons able to generate bursts of action potentials. In addition, the inhibitory synaptic potentials elicited by stimulation of layer I were more powerful in this group of neurons. This research provides new evidence for the presence of the LTCC in subsets of cortical pyramidal neurons, which have specific and well defined morphological and physiological properties.
Mice Lacking Brain-Derived Neurotrophic Factor Exhibit Visceral Sensory Neuron Losses Distinct from Mice Lacking NT4 and Display a Severe Developmental Deficit in Control of Breathing
Authors: Erickson Jeffery T. , Conover Joanne C. , Borday Veronique , Champagnat Jean , Barbacid Mariano , Yancopoulos George , Katz David M.
Published: April 2018

The neurotrophins brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT4) act via the TrkB receptor and support survival of primary somatic and visceral sensory neurons. The major visceral sensory population, the nodose–petrosal ganglion complex (NPG), requires BDNFandNT4 for survival of a full complement of neurons, providing a unique opportunity to compare gene dosage effects between the two TrkB ligands and to explore the possibility that one ligand can compensate for loss of the other. Analysis of newborn transgenic mice lacking BDNF or NT4, or BDNFandNT4, revealed that survival of many NPG afferents is proportional to the number of functional BDNF alleles, whereas onlyonefunctional NT4 allele is required to support survival of all NT4-dependent neurons. In addition, subpopulation analysis revealed that BDNF and NT4 can compensate for the loss of the other to support a subset of dopaminergic ganglion cells. Together, these data demonstrate that the pattern of neuronal dependencies on BDNF and NT4in vivois far more heterogeneous than predicted from previous studies in culture. Moreover, BDNF knockout animals lack a subset of afferents involved in ventilatory control and exhibit severe respiratory abnormalities characterized by depressed and irregular breathing and reduced chemosensory drive. BDNF is therefore required for expression of normal respiratory behavior in newborn animals.
Stoichiometry of a Recombinant GABAAReceptor
Authors: Chang Yongchang , Wang Ruoping , Barot Sonal , Weiss David S.
Published: April 2018

GABA is the main inhibitory neurotransmitter in the mammalian brain. The postsynaptic GABAAreceptor/pore complex is presumed to be a pentamer typically composed of a combination of α, β, and γ subunits, although the stoichiometry remains controversial. We probed the stoichiometry of the GABAAreceptor by site-directed mutagenesis of a conserved leucine (to serine) in the putative second membrane-spanning domain of the rat α1(αL263S), β2(αL259S), and γ2(αL274S) subunit isoforms. Coexpression of wild-type and mutant subunits of each class (e.g., α and αL263S), along with their wild-type counterparts (e.g., β and γ), inXenopus laevisoocytes resulted in mixed populations of receptors with distinct GABA sensitivities. This is consistent with the interpretation that the leucine mutation increased the GABA sensitivity in proportion to the number of incorporated mutant subunits. The apparent number of incorporated subunits for each class (α, β, and γ) could then be determined from the number of components comprising the compound GABA dose–response relationships. Using this approach, we conclude that the recombinant α1β2γ2 GABAAreceptor is a pentamer composed of two α subunits, two β subunits, and one γ subunit.
Astrocyte Growth, Reactivity, and the Target of the Antiproliferative Antibody, TAPA
Authors: Geisert Jr. Eldon E. , Yang LiJuan , Irwin Michael H.
Published: April 2018

Reactive astrocytes form a scar after injury to the CNS that many investigators believe contributes to the lack of functional regeneration. In the present study, we identify an astrocytic membrane protein that appears to play an important role in reactive gliosis and scar formation. Cultures of rat astrocytes were used as a model system to produce and to screen monoclonal antibodies that would alter cell growth. One antibody, AMP1, was identified that depresses the mitotic activity of cultured glial cells and alters their morphology. Expression cloning reveals that the antigen on the external surface of the cultured glial cells has a high degree of homology with the human lymphocyte protein called Target of the Anti-Proliferative Antibody (TAPA-1; this rat protein will be referred to as rTAPA). rTAPA is a member of the tetramembrane-spanning superfamily of proteins and, as with other members of this family of proteins, rTAPA is associated with the regulation of cellular interactions and mitotic activity. After an injury to the cerebral cortex, there is a dramatic increase in AMP1 immunoreactivity that is spatially restricted to the reactive astrocytes at the glial scar. This change represents an upregulation of a membrane protein, rTAPA, that is approximately equal to the increase observed for glial fibrillary acidic protein. The high levels of rTAPA at the site of CNS injury and the AMP1 antibody perturbation studies indicate that rTAPA may play a prominent role in the response of astrocytes to injury and in glial scar formation.
Evidence for Differential Control of Posterior Hypothalamic, Supramammillary, and Medial Mammillary Theta-Related Cellular Discharge by Ascending and Descending Pathways
Authors: Kirk Ian J. , Oddie Scott D. , Konopacki Jan , Bland Brian H.
Published: April 2018

Single-unit discharge was recorded from cells in the posterior hypothalamic nucleus (PH), supramammillary nucleus (SuM), and medial mammillary nucleus (MM) during hippocampal theta (θ) elicited by stimulation of the reticular nucleus pontis oralis (RPO). In agreement with previously published work, θ-related cells in the PH (12 cells) were all classified as tonic θ-ON (increased tonic discharge rate during hippocampal θ), whereas those in the SuM (9 cells) and MM (15 cells) were all classified as phasic θ-ON (rhythmic discharge, in phase with ongoing θ). The effect of RPO stimulation on cell discharge was tested after hippocampal θ was abolished by infusion of procaine into the medial septum/vertical limb of the diagonal band. The RPO-elicited discharge patterns of all PH tonic θ-ON cells and all SuM phasic θ-ON cells survived septal procaine infusion. Further, the discharge rate of PH cells and the frequency of burst discharge of SuM cells during RPO stimulation both increased after the infusion. In contrast, septal procaine infusion abolished the RPO-elicited rhythmic discharge pattern in MM phasic θ-ON cells and attenuated their discharge rates. These results indicate that the PH and SuM form parts of an ascending system mediating hippocampal θ, whereas the MM receives (and perhaps relays to other parts of the limbic system) rhythmic input descending from the septo-hippocampal system. In addition, PH and SuM receive descending inputs that limit the discharge rates of their θ-related cells during hippocampal θ.
Reduced Growth Cone Motility in Cultured Neurons fromDrosophilaMemory Mutants with a Defective cAMP Cascade
Authors: Kim Yun-Taik , Wu Chun-Fang
Published: April 2018

Drosophilamemory mutantsdunce (dnc)andrutabaga (rut)are known to have altered intracellular cAMP levels, nerve terminal growth, and plasticity of synaptic transmission. Because the growth cone is responsible for neurite outgrowth and synaptogenesis, video microscopy was used to examine growth cone morphology and behavior of mutant neurons in larval CNS cultures. We found that growth cone exploratory movement was nearly arrested by both mutations, even though they change cAMP levels in opposite directions. Thedncphenotype could be mimicked by normal neurons when perfused with dibutyryl cAMP (db-cAMP) or forskolin. In contrast,rutgrowth cones became active when perfused with db-cAMP. Furthermore, motility was also restored by counterbalancing the effects of the two genes in double mutants, indicating that dynamic control of growth cone motility in developingDrosophilaneurons requires optimal cAMP levels within an operational range. These findings represent the first demonstration of altered growth cone properties in learning and memory mutants and establish in a natural setting the role of cAMP in growth cone motility and neuronal plasticity.
Modulation of Excitatory Synaptic Transmission by Adenosine Released from Single Hippocampal Pyramidal Neurons
Authors: Brundege James M. , Dunwiddie Thomas V.
Published: April 2018

Adenosine is a potent neuromodulator in the CNS, but the mechanisms that regulate adenosine concentrations in the extracellular space remain unclear. The present study demonstrates that increasing the intracellular concentration of adenosine in a single hippocampal CA1 pyramidal neuron selectively inhibits the excitatory postsynaptic potentials in that cell. Loading neurons with high concentrations of adenosine via the whole-cell patch-clamp technique did not affect the GABAA-mediated inhibitory postsynaptic potentials, the membrane resistance, or the holding current, whereas it significantly increased the adenosine receptor-mediated depression of excitatory postsynaptic currents. The effects of adenosine could not be mimicked by an agonist at the intracellular adenosine P-site, but the effects could be antagonized by a charged adenosine receptor antagonist and by adenosine deaminase, demonstrating that the effect was mediated via adenosine acting at extracellular adenosine receptors. The effect of adenosine loading was not blocked by BaCl2and therefore was not caused by an adenosine-activated postsynaptic potassium conductance. Adenosine loading increased the paired-pulse facilitation ratio, demonstrating that the effect was mediated by presynaptic adenosine receptors. Finally, simultaneous extracellular field recordings demonstrated that the increase in extracellular adenosine was confined to excitatory synaptic inputs to the loaded cell. These data demonstrate that elevating the intracellular concentration of adenosine in a single CA1 pyramidal neuron induces the release of adenosine into the extracellular space in such a way that it selectively inhibits the excitatory inputs to that cell, and the data support the general conclusion that adenosine is a retrograde messenger used by pyramidal neurons to regulate their excitatory input.
Determinants of the Time Course of Facilitation at the Granule Cell to Purkinje Cell Synapse
Authors: Atluri Pradeep P. , Regehr Wade G.
Published: April 2018

Short-term facilitation is a widely observed form of synaptic enhancement that is not well understood. Although presynaptic calcium has long been implicated in this process, its role is unclear, particularly at synapses in the mammalian brain. We tested the role of presynaptic residual free calcium ([Ca]res) in facilitation of synapses between granule cells and Purkinje cells in rat cerebellar slices. Paired-pulse facilitation of synaptic currents resulted in an approximately 2.5-fold enhancement that decayed with a time constant of ∼200 msec, as assessed by voltage-clamp recordings. Measurements of [Ca]resusing fluorescent calcium-sensitive indicators revealed that [Ca]resdecayed more rapidly than did facilitation. Manipulation of [Ca]resdynamics by introducing EGTA into presynaptic terminals sped the decays of [Ca]resand facilitation in a dose-dependent manner. When [Ca]reswas reduced to a brief impulse lasting several milliseconds, facilitation was still present, although reduced in amplitude and duration. Facilitation decayed with an intrinsic time constant of ∼40 msec. These results suggest that facilitation at this synapse is produced by a calcium-driven process with a high affinity and a slow effective off-rate. A combination of [Ca]resdynamics and the properties of a calcium-driven reaction determine the time course and amplitude of facilitation.
Distribution of Networks Generating and Coordinating Locomotor Activity in the Neonatal Rat Spinal CordIn Vitro: A Lesion Study
Authors: Kjaerulff Ole , Kiehn Ole
Published: April 2018

The isolated spinal cord of the newborn rat contains networks that are able to create a patterned motor output resembling normal locomotor movements. In this study, we sought to localize the regions of primary importance for rhythm and pattern generation using specific mechanical lesions. We used ventral root recordings to monitor neuronal activity and tested the ability of various isolated parts of the caudal thoracic-lumbar cord to generate rhythmic bursting in a combination of 5-HT and NMDA. In addition, pathways mediating left/right and rostrocaudal burst alternation were localized. We found that the isolated ventral third of the spinal cord can generate normally coordinated rhythmic activity, whereas lateral fragments resulting from sagittal sections showed little or no rhythmogenic capability compared with intact control preparations. The ability to generate fast and regular rhythmic activity decreased in the caudal direction, but the rhythm-generating network was found to be distributed over the entire lumbar region and to extend into the caudal thoracic region. The pathways mediating left/right alternation exist primarily in the ventral commissure. As with the rhythmogenic ability, these pathways were distributed along the lumbar enlargement. Both lateral and ventral funiculi were sufficient to coordinate activity in the rostral and caudal regions. We conclude that the networks organizing locomotor-related activity in the spinal cord of the newborn rat are distributed.
Emotional and Behavioral Correlates of Mediodorsal Thalamic Neurons during Associative Learning in Rats
Authors: Oyoshi Tatsuki , Nishijo Hisao , Asakura Tetsuhiko , Takamura Yusaku , Ono Taketoshi
Published: April 2018

Neuronal activity was recorded from the mediodorsal thalamic nucleus (MD) of behaving rats that were trained to lick a protruding spout just after a conditioned stimulus to obtain reward or to avoid shock. Conditioned stimuli included both elemental (auditory or visual stimuli) and configural (simultaneous presentation of auditory and visual stimuli predicting reward outcome opposite that predicted by each stimulus presented alone) stimuli. Of 122 MD neurons responding during the task, the activity of 13 increased just before licking only during the task, but not before spontaneous licking during the intertrial interval (conditioned behavior related). These conditioned behavior-related neurons were located mainly in the lateral MD, which has intimate anatomical connections with motor-related areas such as anterior cingulate and striatum. The activity of the other 109 neurons was related to conditioned stimulation (conditioned stimulus related). Most of these neurons responded differentially to both elemental and configural stimuli in terms of reward contingency, and also changed their responses during extinction and relearning trials. Conditioned stimulus-related neurons with latencies <300 msec were located mainly in the rostromedial MD, which receives afferents from the basolateral nucleus of the amygdala in which sensory information from various sources converge. Furthermore, most differential neurons that were tested responded during the delay period in a reward task in which a delay was imposed between the conditioned stimulus and reward delivery. The present results, along with previous anatomical studies, suggest the existence of two limbic circuits: anterior cingulate–striatum–lateral MD (motor) and amygdala–medial MD–orbital prefrontal cortex (short-term memory/emotion).
Intracellular Characterization of Song-Specific Neurons in the Zebra Finch Auditory Forebrain
Authors: Lewicki Michael S.
Published: April 2018

Auditory neurons in the forebrain nucleus HVc (hyperstriatum ventrale pars caudale) are highly sensitive to the temporal structure of the bird’s own song. These “song-specific” neurons respond strongly to forward song, weakly to the song with the order of the syllables reversed, and little or not at all to reversed song. To investigate the cellular mechanisms underlying these responses,in vivointracellular recordings were made from adult HVc neurons. Song-specific cells could be divided into those that responded strongly throughout autogenous song (tonic cells) and those that responded with bursts of action potentials at specific points during the song (phasic cells). Phasic cells were hyperpolarized during autogenous song, even though this stimulus also elicited the strongest response. Less hyperpolarization was seen to the same song with the syllables in reverse order, and none was seen to reversed song. The responses of both types of song-specific cells contained high-frequency bursts of action potentials. The bursts of the phasic cells showed attenuation of the action potential height and lack of full repolarization after each spike. This type of bursting was significantly correlated with the amount of hyperpolarization before each burst in phasic cells and nonauditory cells that generated such bursts spontaneously. These data suggest that song-specific neurons use long-lasting hyperpolarization as a mechanism to integrate auditory context, an important component of temporal order selectivity. Hyperpolarization also may increase the precision of spike timing, which could be important for the neural code subserving song learning and production.