bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-Voltage-Activated Ca2+Currents Are Generated by Members of the CavT Subunit Family (α1G/H) in Rat Primary Sensory Neurons
Authors: Lambert Régis C. , McKenna Frank , Maulet Yves , Talley Edmund M. , Bayliss Douglas A. , Cribbs Leanne L. , Lee Jung-Ha , Perez-Reyes Edward , Feltz Anne
Published: April 2018

Recently, two members of a new family of Ca2+channel α1 subunits, α1G (or CavT.1) and α1H (or CavT.2), have been cloned and expressed. These α1 subunits generate Ba2+currents similar to the T-type Ca2+currents present in sensory neurons. Here, we use three methods to investigate whether the T currents of nodosus ganglion neurons are encoded by members of the CavT family. PCR detected the presence of mRNA encoding both α1G and α1H, as well as a third highly related sequence, α1I.In situhybridizations performed on nodosus ganglia demonstrate a high expression of α1H subunit RNAs. Transfection of nodosus ganglion neurons with a generic antisense oligonucleotide against this new α1 subunit family selectively suppresses the low-voltage-activated Ca2+current. The antisense oligonucleotide effect increased with time after transfection and reached a maximum 3 d after treatment, indicating a 2–3 d turnover for the α1 proteins. Taken together, these results suggest that the T-type current present in the sensory neurons is mainly attributable to α1H channels. In addition, taking advantage of the high specificity of the antisense ON to the cloned channels, we showed that T-type currents greatly slowed the repolarization occurring during an action potential and were responsible for up to 51% of the Ca2+entry during spikes. Therefore, the antisense strategy clearly demonstrates the role of low-voltage-activated Ca2+current in affecting the afterpotential properties and influencing the cell excitability. Such tools should be beneficial to further studies investigating physiological roles of T-type Ca2+currents.
Localization of Myosin-Iβ near Both Ends of Tip Links in Frog Saccular Hair Cells
Authors: Garcı́a Jesús A. , Yee Ann G. , Gillespie Peter G. , Corey David P.
Published: April 2018

Current evidence suggests that the adaptation motor of mechanoelectrical transduction in vertebrate hair cells is myosin-Iβ. Previously, confocal and electron microscopy of bullfrog saccular hair cells using an anti-myosin-Iβ antibody labeled the tips of stereocilia. We have now done quantitative immunoelectron microscopy to test whether myosin-Iβ is enriched at or near the side plaques of tip links, the proposed sites of adaptation, using hair bundles that were serially sectioned parallel to the macular surface. The highest particle density occurred at stereocilia bases, close to the cuticular plate. Also, stereocilia of differing lengths had approximately the same number of total particles, suggesting equal targeting of myosin-Iβ to all stereocilia. Finally, particles tended to clump in clusters of two to five particles in the distal two-thirds of stereocilia, suggesting a tendency for self-assembly of myosin-Iβ.

As expected from fluorescence microscopy, particle density was high in the distal 1 μm of stereocilia. If myosin-Iβ is the adaptation motor, a difference should exist in particle density between regions containing the side plaque and those excluding it. Averaging of particle distributions revealed two regions with approximately twice the average density: at the upper ends of tip links in a 700-nm-long region centered ∼100 nm above the side plaque, and at the lower ends of tip links within the tip plaques. Controls demonstrated no such increase. The shortest stereocilia, which lack side plaques, showed no concentration rise on their sides. Thus, the specific localization of myosin-Iβ at both ends of tip links supports its role as the adaptation motor.
Endogenous Neurotrophin-3 Regulates Short-Term Plasticity at Lateral Perforant Path–Granule Cell Synapses
Authors: Kokaia Merab , Asztely Fredrik , Olofsdotter Klara , Sindreu Carlos Balet , Kullmann Dimitri M. , Lindvall Olle
Published: April 2018

In the adult brain, neurotrophin-3 (NT-3) is mainly localized in dentate granule cells, and its expression is decreased by various stimuli, e.g., seizure activity. We have examined the role of endogenous NT-3 for excitatory synaptic transmission at lateral perforant path–dentate granule cell synapses using hippocampal slices from NT-3 knock-out (+/−) and wild-type (+/+) mice. Paired-pulse facilitation (PPF) and also short-term synaptic plasticity induced by a brief, high-frequency train of afferent stimulation were reduced, but the expression of long-term potentiation was not affected in the NT-3+/− mice. Incubation of the slices with recombinant NT-3 reversed the deficit in PPF through a mechanism requiringde novoprotein synthesis, implying that the impaired short-term plasticity does not result from a developmental alteration. No changes of overall presynaptic release probability, measured by the progressive block of NMDA receptor-mediated synaptic currents by MK-801, or desensitization of AMPA receptors were detected. Because NT-3 expression is reduced after focal seizures, impaired short-term facilitation may represent a protective response that limits the propagation of epileptiform activity from the entorhinal cortex to the hippocampus.
The Number of Glutamate Transporter Subtype Molecules at Glutamatergic Synapses: Chemical and Stereological Quantification in Young Adult Rat Brain
Authors: Lehre Knut P. , Danbolt Niels C.
Published: April 2018

The role of transporters in shaping the glutamate concentration in the extracellular space after synaptic release is controversial because of their slow cycling and because diffusion alone gives a rapid removal. The transporter densities have been measured electrophysiologically, but these data are from immature brains and do not give precise information on the concentrations of the individual transporter subtypes. Here we show by quantitative immunoblotting that the numbers of the astroglial glutamate transporters GLAST (EAAT1) and GLT (EAAT2) are 3200 and 12,000 per μm3tissue in the stratum radiatum of adult rat hippocampus (CA1) and 18,000 and 2800 in the cerebellar molecular layer, respectively. The total astroglial cell surface is 1.4 and 3.8 m2/cm3in the two regions, respectively, implying average densities of GLAST and GLT molecules in the membranes around 2300 and 8500 μm−2in the former and 4700 and 740 μm−2in the latter region. The total concentration of glial glutamate transporters in both regions corresponds to three to five times the estimated number of glutamate molecules in one synaptic vesicle from each of all glutamatergic synapses. However, the role of glial glutamate transporters in limiting synaptic spillover is likely to vary between the two regions because of differences in the distribution of astroglia. Synapses are completely ensheathed and separated from each other by astroglia in the cerebellar molecular layer. In contrast, synapses in hippocampus (stratum radiatum) are only contacted by astroglia and are often found side by side without intervening glial processes.
Depolarization Selectively Increases the Expression of the Kv3.1 Potassium Channel in Developing Inferior Colliculus Neurons
Authors: Liu Si-qiong J. , Kaczmarek Leonard K.
Published: April 2018

The Kv3.1 channel subunit, when expressed heterologously, gives rise to a high-threshold noninactivating potassium current. Experiments with auditory neurons have suggested that the presence of this channel subunit enables them to fire action potentials at high frequencies. We have found that the expression levels of Kv3.1 transcripts increase in inferior colliculus neurons before the onset of hearing and then remain relatively constant. Because spontaneous neuronal activity plays an important role in modulating neuronal excitability during development, we examined the effects of depolarization with an elevated concentration of external potassium ions on the expression of Kv3.1 channel subunits in immature inferior colliculus neurons. Elevated potassium produced a marked increase in Kv3.1 mRNA levels and in the amplitude of a high-threshold, noninactivating current before the onset of hearing. This increase was prevented by the presence of a calcium channel blocker, indicating that calcium influx mediated the depolarization-induced increase in this current. In contrast, treatment with an elevated external potassium concentration caused only a moderate increase in the peak amplitude of a lower-threshold inactivating current. The repolarization of action potentials in the high-potassium-treated cells was more rapid and complete than in the control cells. Computer simulations confirmed that this change could be explained by a change in Kv3.1-like current of the same magnitude as recorded in voltage-clamp experiments. Thus, depolarization and calcium influx may alter the excitability of immature inferior colliculus neurons by selectively increasing the levels of a Kv3.1-like potassium current.
Extracellular Signal-Regulated Kinase (ERK) Controls Immediate Early Gene Induction on Corticostriatal Stimulation
Authors: Sgambato Véronique , Pagès Christiane , Rogard Monique , Besson Marie-Jo , Caboche Jocelyne
Published: April 2018

Activity-dependent changes in neuronal structure and synaptic remodeling depend critically on gene regulation. In an attempt to understand how glutamate receptor stimulation at the membrane leads to gene regulation in the nucleus, we traced intracellular signaling pathways targeting DNA regulatory elements of immediate early genes (IEGs). For this purpose we used anin vivoelectrical stimulation of the glutamatergic corticostriatal pathway. We show that a transient activation of extracellular signal-regulated kinase (ERK) proteins (detected by immunocytochemistry with an anti-active antibody) is spatially coincident with the onset of IEG induction [c-fos,zif 268, and map kinase phosphatase-1 (MKP-1) detected byin situhybridization] in the striatum, bilaterally. Both Elk-1 and CREB transcription factors (targeting SRE and CRE DNA regulatory elements, respectively) were hyperphosphorylated in register with ERK activation and IEG mRNA induction. However, their hyperphosphorylation occurred in different subcellular compartments: the cytoplasm and the nucleus for Elk-1 and the nucleus for CREB. The role of the ERK signaling cascade in gene regulation was confirmed after intrastriatal and unilateral injection of the specific ERK inhibitor PD 98059, which completely abolished c-fos,zif 268, and MKP-1 mRNA induction in the injected side. Of interest, both Elk-1 and CREB hyperphosphorylation also was impaired after PD 98059 injection. Thus two different ERK modules, one depending on the cytoplasmic activation of Elk-1 and the other one depending on the nuclear activation of CREB, control IEG transcriptional regulation in our model. Our findings provide significant insights into intracellular mechanisms underlying synaptic plasticity in the striatum.
Synaptogenesis Via Dendritic Filopodia in Developing Hippocampal Area CA1
Authors: Fiala John C. , Feinberg Marcia , Popov Viktor , Harris Kristen M.
Published: April 2018

To determine the role of dendritic filopodia in the genesis of excitatory synaptic contacts and dendritic spines in hippocampal area CA1, serial section electron microscopy and three-dimensional analysis of 16 volumes of neuropil from nine male rat pups, aged postnatal day 1 (P1) through P12, were performed. The analysis revealed that numerous dendritic filopodia formed asymmetric synaptic contacts with axons and with filopodia extending from axons, especially during the first postnatal week. At P1, 22 ± 5.5% of synapses occurred on dendritic filopodia, with 19 ± 5.9% on filopodia at P4, 20 ± 8.0% at P6, decreasing to 7.2 ± 4.7% at P12 (p< 0.02). Synapses were found at the base and along the entire length of filopodia, with many filopodia exhibiting multiple synaptic contacts. In all, 162 completely traceable dendritic filopodia received 255 asymmetric synaptic contacts. These synapses were found at all parts of filopodia with equal frequency, usually occurring on fusiform swellings of the diameter. Most synaptic contacts (53 ± 11%) occurred directly on dendritic shafts during the first postnatal week. A smaller but still substantial portion (32 ± 12%) of synapses were on shafts at P12 (p< 0.036). There was a highly significant (p< 0.0002) increase in the proportion of dendritic spine synapses with age, rising from just 4.9 ± 4.3% at P1 to 37 ± 14% at P12. The concurrence of primarily shaft and filopodial synapses in the first postnatal week suggests that filopodia recruit shaft synapses that later give rise to spines through a process of outgrowth.
Developmental Regulation of Apoptosis in Dorsal Root Ganglion Neurons
Authors: Vogelbaum Michael A. , Tong Jianxin X. , Rich Keith M.
Published: April 2018

The survival of dorsal root ganglion (DRG) neurons, bothin vivoandin vitro, is dependent on the availability of nerve growth factor (NGF) for a transient period early in development after which these neurons become independent of NGF for survival. The precise molecular mechanism by which developing DRG neurons gain independence from NGF has not been determined. We used anin vitromodel of DRG neuronal development to test hypotheses that independence from NGF in mature DRG neurons could be caused by developmental regulation of either elements of the NGF withdrawal signal transduction pathway or of proteins important for activation of the apoptosis output pathway.

Interruption of phosphotidylinositol-3 kinase activation, by treatment with the specific inhibitor LY294002, resulted in apoptosis in immature but not mature DRG neurons in a manner similar to that observed with NGF withdrawal. Further downstream along the signal transduction pathway, c-JUN phosphorylation occurred in both immature and mature DRG neurons after NGF withdrawal or treatment with LY294002, despite the fact that the older neurons did not undergo apoptosis. In contrast, the ratio of expression of the proapoptotic genebaxto antiapoptotic genebcl-xLwas many times higher in immature than mature neurons, bothin vivoandin vitro.

Taken together, these results strongly suggest that developmental regulation of NGF withdrawal-induced apoptosis in DRG occurs via control of the relative level of expression of members of thebcl-2gene family.
Task-Dependent Viscoelasticity of Human Multijoint Arm and Its Spatial Characteristics for Interaction with Environments
Authors: Gomi Hiroaki , Osu Rieko
Published: April 2018

Human arm viscoelasticity is important in stabilizing posture, movement, and in interacting with objects. Viscoelastic spatial characteristics are usually indexed by the size, shape, and orientation of a hand stiffness ellipse. It is well known that arm posture is a dominant factor in determining the properties of the stiffness ellipse. However, it is still unclear how much joint stiffness can change under different conditions, and the effects of that change on the spatial characteristics of hand stiffness are poorly examined. To investigate the dexterous control mechanisms of the human arm, we studied the controllability and spatial characteristics of viscoelastic properties of human multijoint arm during different cocontractions and force interactions in various directions and amplitudes in a horizontal plane. We found that different cocontraction ratios between shoulder and elbow joints can produce changes in the shape and orientation of the stiffness ellipse, especially at proximal hand positions. During force regulation tasks we found that shoulder and elbow single-joint stiffness was each roughly proportional to the torque of its own joint, and cross-joint stiffness was correlated with elbow torque. Similar tendencies were also found in the viscosity–torque relationships. As a result of the joint stiffness changes, the orientation and shape of the stiffness ellipses varied during force regulation tasks as well. Based on these observations, we consider why we can change the ellipse characteristics especially in the proximal posture. The present results suggest that humans control directional characteristics of hand stiffness by changing joint stiffness to achieve various interactions with objects.
Segregation of Behavior-Specific Synaptic Inputs to a Vertebrate Neuronal Oscillator
Authors: Juranek Jenifer , Metzner Walter
Published: April 2018

Although essential for understanding the mechanisms underlying sensorimotor integration and motor control of behaviors, very little is known about the degree to which different behaviors share neural elements of the sensorimotor command chain by which they are controlled. Here, we provide, to our knowledge, the first direct physiological evidence that various modulatory premotor inputs to a vertebrate central pattern generator, the pacemaker nucleus in gymnotiform electric fish, carrying distinctly different behavioral information, can remain segregated from their various sites of origin in the diencephalon to the synaptic termination sites on different target neurons in the medullary pacemaker nucleus. During pharmacological activation of each of the premotor inputs originating from the three prepacemaker nuclei so far identified, we determinedin vivothe changes in input resistance in the neuronal elements of the pacemaker nucleus, i.e., relay cells and pacemaker cells. We found that each input yields significantly different effects on these cells; the inputs from the two diencephalic prepacemaker nuclei, PPnC and PPnG, which resulted in increased oscillator activity, caused significantly lower input resistances in relay and pacemaker cells, respectively, exhibiting drastically different time courses. The input from the sublemniscal prepacemaker nucleus, which resulted in reduced oscillator activity, however, caused a significant increase in input resistance only in relay cells. Considering that the sensory pathways processing stimuli yielding these behaviors are separated as well, this study indicates that sensorimotor control of different behaviors can occur in strictly segregated channels from the sensory input of the brain all through to the synaptic input level of the final premotor command nucleus.
Interhemispheric Coordination of Premotor Neural Activity during Singing in Adult Zebra Finches
Authors: Vu Eric T. , Schmidt Marc F. , Mazurek Mark E.
Published: April 2018

The song system, a neural network that mediates the learning and production of song by oscine songbirds, is investigated extensively as a model system for understanding the neural basis of complex skill learning. Part of the complexity of birdsong arises from the coordinated recruitment of multiple groups of muscles on both sides of the body. Although the song system is bilaterally organized, little is known about how premotor activities on the two sides are coordinated during singing. We investigated this by unilaterally recording neural activity in the forebrain song nucleus HVc (also known as the high vocal center) during singing and by forcing the premotor activities in the two hemispheres out of synchrony by perturbing neural activity in the contralateral HVc with electrical stimulation. Perturbing the activity in one HVc at any time during a song led to a short-latency readjustment of activity in the contralateral HVc. This readjustment consisted of a true resetting of the temporal pattern of activity in the contralateral HVc rather than merely a transient activity suppression overlaid on an unaltered pattern of premotor activity. These results strongly suggest that the output of song premotor areas in the forebrain is continuously monitored and that an active mechanism exists for resynchronizing the outputs from the two hemispheres whenever their gross temporal patterns differ significantly. The possible anatomical substrates for these coordinating mechanisms and their potential roles in song learning are discussed.
Slow Oscillations (≤1 Hz) Mediated by GABAergic Interneuronal Networks in Rat Hippocampus
Authors: Zhang Y. , Perez Velazquez J. L. , Tian G. F. , Wu C.-P. , Skinner F. K. , Carlen P. L. , Zhang L.
Published: April 2018

Perfusion of rat brain slices with low millimole CsCl elicits slow oscillations of ≤1 Hz in hippocampal CA1 pyramidal neurons. These oscillations are GABAAreceptor-mediated hyperpolarizations that permit a coherent fire–pause pattern in a population of CA1 neurons. They can persist without the activation of ionotropic glutamate receptors but require adenosine-dependent inhibition of glutamate transmission. In response to external Cs+, multiple interneurons in the CA1 region display rhythmic discharges that correlate with the slow oscillations in CA1 pyramidal neurons. The interneuronal discharges arise spontaneously from the resting potential, and their rhythmicity is regulated by periodic, GABAAreceptor-mediated hyperpolarizations. In addition, interneurons show periodic partial spikes and neurobiotin coupling, and applications of known gap junctional uncouplers interrupt the Cs+-induced slow rhythm in both CA1 pyramidal neurons and interneurons. We propose that these slow oscillations originate from a GABAergic interneuronal network that interacts through reciprocal inhibition and possibly gap junctional connection.
Development of Functional Topography in the Corticorubral Projection: AnIn VivoAssessment Using Synaptic Potentials Recorded from Fetal and Newborn Cats
Authors: Song Wen-Jie , Murakami Fujio
Published: April 2018

In mammals, topographic maps emerge from initially diffuse projections during development. To gain insight into the mechanisms governing the transition from a diffuse projection to a topographic map, we studied topographic specificity of functional connections during development, using the cat corticorubral system as a model. In the adult cat, rubrospinal neurons in the dorsomedial part of the red nucleus (RN) receive input primarily from the forelimb area of the sensorimotor cortex, whereas those in the ventrolateral part receive input primarily from the hindlimb area. During development, axons from the sensorimotor cortex arrive in the RN at embryonic day 50 (E50) (Song et al., 1995a) and are diffusely distributed in the RN until postnatal day 13 (P13) (Higashi et al., 1990). Here, we studied the development of the pattern of functional cortical inputs to individual rubrospinal neurons, using synaptic potentials recordedin vivo. The functional topography in each rubrospinal neuron in developing cats was examined and classified either as adult-like or nonadult-like by comparison with the adult pattern. In preterm kittens from E61 to E65, only about half of the recorded neurons (41%;n= 22) showed adult-like functional topography. This percentage, however, increased to 82% (n= 56) in P1–P8 kittens and to 93% (n= 42) in P13–P28 kittens. These results, in conjunction with the above mentioned anatomical observations, suggest that corticorubral axons make functional synapses nonselectively with rubrospinal neurons before birth. Furthermore, the functional topographic map developed earlier than the anatomical map (P13), suggesting that there is a developmental step of selective promotion of synapse formation and/or selective enhancement of synaptic efficacy in topographically appropriate regions in the RN, before the emergence of the mature anatomical map.
Abstract and Effector-Specific Representations of Motor Sequences Identified with PET
Authors: Grafton Scott T. , Hazeltine Eliot , Ivry Richard B.
Published: April 2018

Positron emission tomography was used to identify neural systems involved in the acquisition and expression of sequential movements produced by different effectors. Subjects were tested on the serial reaction time task under implicit learning conditions. In the initial acquisition phase, subjects responded to the stimuli with keypresses using the four fingers of the right hand. During this phase, the stimuli followed a fixed sequence for one group of subjects (group A) and were randomly selected for another group (group B). In the transfer phase, arm movements were used to press keys on a substantially larger keyboard, and for both groups, the stimuli followed the sequence. Behavioral indices provided clear evidence of learning during the acquisition phase for group A and transfer when switched to the large keyboard. Sequence acquisition was associated with learning-related increases in regional cerebral blood flow (rCBF) in a network of areas in the contralateral left hemisphere, including sensorimotor cortex, supplementary motor area, and rostral inferior parietal cortex. After transfer, activity in inferior parietal cortex remained high, suggesting that this area had encoded the sequence at an abstract level independent of the particular effectors used to perform the task. In contrast, activity in sensorimotor cortex shifted to a more dorsal locus, consistent with motor cortex somatotopy. Thus, activity here was effector-specific. An increase in rCBF was also observed in the cingulate motor area at transfer, suggesting a role linking the abstract sequential representations with the task-relevant effector system. These results highlight a network of areas involved in sequence encoding and retrieval.
Selective Innervation of Neostriatal Interneurons by a Subclass of Neuron in the Globus Pallidus of the Rat
Authors: Bevan Mark D. , Booth Philip A. C. , Eaton Sean A. , Bolam J. Paul
Published: April 2018

A subpopulation of neurons in the globus pallidus projects to the neostriatum, which is the major recipient of afferent information to the basal ganglia. Given the moderate nature of this projection, we hypothesized that the pallidostriatal projection might exert indirect but powerful control over principal neuron activity by targeting interneurons, which comprise only a small percentage of neostriatal neurons. This was tested by the juxtacellular labeling and recording of pallidal neurons in combination with immunolabeling of postsynaptic neurons.

In addition to innervating the subthalamic nucleus and output nuclei, 6 of 23 labeled pallidal neurons projected to the neostriatum. Both the firing characteristics and the extent of the axonal arborization in the neostriatum were variable. However, light and electron microscopic analysis of five pallidostriatal neurons revealed that each neuron selectively innervated neostriatal interneurons. A large proportion of the boutons of an individual axon (19–66%) made contact with parvalbumin-immunoreactive interneurons. An individual parvalbumin-immunoreactive neuron (n= 27) was apposed on average by 6.7 boutons (SD = 6.1) from a single pallidal axon (n= 2). Individual pallidostriatal boutons typically possessed more than one symmetrical synaptic specialization. In addition, 3–32% of boutons of axons from four of five pallidal neurons contacted nitric oxide synthase-immunoreactive neurons. Descending collaterals of pallidostriatal neurons were also found to make synaptic contact with dopaminergic and GABAergic neurons of the substantia nigra. These data imply that during periods of cortical activation, individual pallidal neurons may influence the activity of GABAergic interneurons of the neostriatum (which are involved in feed-forward inhibition and synchronization of principle neuron activity) while simultaneously patterning neuronal activity in basal ganglia downstream of the neostriatum.
Activation of Vagal Afferents after Intravenous Injection of Interleukin-1β: Role of Endogenous Prostaglandins
Authors: Ek Monica , Kurosawa Mieko , Lundeberg Thomas , Ericsson Anders
Published: April 2018

Intravenous administration of interleukin-1 (IL-1) activates central autonomic neuronal circuitries originating in the nucleus of the solitary tract (NTS). The mechanism(s) by which blood-borne IL-1 regulates brain functions, whether by operating across the blood–brain barrier and/or by activating peripheral sensory afferents, remains to be characterized. It has been proposed that vagal afferents originating in the periphery may monitor circulating IL-1 levels, because neurons within the NTS are primary recipients of sensory information from the vagus nerve and also exhibit exquisite sensitivity to blood-borne IL-1. In this study, we present evidence that viscerosensory afferents of the vagus nerve respond to intravenously administered IL-1β. Specific labeling for mRNAs encoding the type 1 IL-1 receptor and the EP3 subtype of the prostaglandin E2 receptor was detectedin situover neuronal cell bodies in the rat nodose ganglion. Moreover, intravenously applied IL-1 increased the number of sensory neurons in the nodose ganglion that express the cellular activation markerc-Fos, which was matched by an increase in discharge activity of vagal afferents arising from gastric compartments. This response to IL-1 administration was attenuated in animals pretreated with the cyclooxygenase inhibitor indomethacin, suggesting partial mediation by prostaglandins. In conclusion, these results demonstrate that somata and/or fibers of sensory neurons of the vagus nerve express receptors to IL-1 and prostaglandin E2 and that circulating IL-1 stimulates vagal sensory activity via both prostaglandin-dependent and -independent mechanisms.
Serotonin Modulation of Sensory Inputs to the Lateral Amygdala: Dependency on Corticosterone
Authors: Stutzmann Grace E. , McEwen Bruce S. , LeDoux Joseph E.
Published: April 2018

The lateral nucleus of the amygdala (LA) receives excitatory (glutamatergic) inputs from thalamic and cortical sensory processing areas and is believed to be involved in evaluation of the affective significance of sensory events. We examined whether serotonin (5-HT) affects excitatory transmission in auditory afferents to the LA and, if so, whether this modulation of sensory transmission is regulated by the stress hormone corticosterone (CORT). Neuronal activity in the LA was elicited via iontophoretic ejection ofl-glutamate or synaptically via electrical stimulation of auditory afferent pathways. In the intact rat, iontophoretically applied 5-HT inhibited both synaptically and glutamate-evoked action potentials in most neurons examined. However, after adrenalectomy (ADX), which eliminates endogenous CORT, 5-HT no longer inhibited evoked activity in the LA. High-CORT doses given to ADX animals reinstated the inhibition of excitatory transmission of 5-HT, whereas low-CORT doses had little effect. Immunocytochemical labeling of the glucocorticoid receptor in the intact rat demonstrated nuclear staining throughout several amygdala regions, including the LA. However, after ADX, no nuclear labeling was visible. With a high replacement dose of CORT (5 or 10 mg) after ADX, dense nuclear staining returned, but with a low replacement dose (1 mg/kg), there was only light nuclear staining. Thus, the ability of 5-HT to modulate glutamatergic activity in auditory pathways to the amygdala is dependent on the presence of CORT and possibly glucocorticoid activation. Via this mechanism, 5-HT modulates the processing of sensory information within the LA and thus may regulate amygdala-related functions.
Long-Lasting Induction of Astrocytic Basic Fibroblast Growth Factor by Repeated Injections of Amphetamine: Blockade by Concurrent Treatment with a Glutamate Antagonist
Authors: Flores Cecilia , Rodaros Demetra , Stewart Jane
Published: April 2018

Repeated administration of stimulant drugs leads to lasting changes in their behavioral and neurochemical effects. These changes are initiated by drug actions in the somatodendritic regions of midbrain dopaminergic neurons in the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) and continue to develop for a period of time after termination of drug treatment. Here we show that repeated administration of amphetamine (3.0 mg/kg, i.p.; three injections, once every other day) results in sustained increases in basic fibroblast growth factor immunoreactivity (bFGF-IR) in both VTA and SNc, 200–500% over that seen in saline-treated animals. Increases were observed 24 hr, 72 hr, 1 week and 1 month after the last drug injection. Because glutamate participates in the development of sensitization to stimulant drugs, we assessed the effect of the glutamate antagonist, kynurenic acid (KYN), on amphetamine-induced bFGF-IR. Coadministration of KYN prevented the increases in bFGF-IR in both VTA and SNc assessed 1 week after the amphetamine treatment. No changes in bFGF-IR were observed in the nucleus accumbens or dorsal striatum. bFGF-IR was found to be associated with astrocytes and not with dopaminergic neurons. These findings suggest that sustained enhancement of astrocytic bFGF expression in DA somatodendritic regions is a mechanism whereby stimulant drugs exert enduring effects on midbrain DA function. We hypothesize that increased glutamatergic activity elicited by amphetamine and other stimulant drugs places excessive demands on the functioning of DA neurons recruiting regulatory and neuroprotective processes that lead to enduring changes in DA neuron functioning and connectivity.
Neuroprotection by Glial Metabotropic Glutamate Receptors Is Mediated by Transforming Growth Factor-β
Authors: Bruno V. , Battaglia G. , Casabona G. , Copani A. , Caciagli F. , Nicoletti F.
Published: April 2018

The medium collected from cultured astrocytes transiently exposed to the group-II metabotropic glutamate (mGlu) receptor agonists (2S,1′R,2′R,3′R)-2-(2,3-dicarboxycyclopropyl)glycine (DCG-IV) or (S)-4-carboxy-3-hydroxyphenylglycine (4C3HPG) is neuroprotective when transferred to mixed cortical cultures challenged with NMDA (Bruno et al., 1997). The following data indicate that this particular form of neuroprotection is mediated by transforming growth factor-β (TGFβ). (1) TGFβ1 and -β2 were highly neuroprotective against NMDA toxicity, and their action was less than additive with that produced by the medium collected from astrocytes treated with DCG-IV or 4C3HPG (GM/DCG-IV or GM/4C3HPG); (2) antibodies that specifically neutralized the actions of TGFβ1 or -β2 prevented the neuroprotective activity of DCG-IV or 4C3HPG, as well as the activity of GM/DCG-IV or GM/4C3HPG; and (3) a transient exposure of cultured astrocytes to either DCG-IV or 4C3HPG led to a delayed increase in both intracellular and extracellular levels of TGFβ. We therefore conclude that a transient activation of group-II mGlu receptors (presumably mGlu3 receptors) in astrocytes leads to an increased formation and release of TGFβ, which in turn protects neighbor neurons against excitotoxic death. These results offer a new strategy for increasing the local production of neuroprotective factors in the CNS.
Slow Closed-State Inactivation: A Novel Mechanism Underlying Ramp Currents in Cells Expressing the hNE/PN1 Sodium Channel
Authors: Cummins Theodore R. , Howe James R. , Waxman Stephen G.
Published: April 2018

To better understand why sensory neurons express voltage-gated Na+channel isoforms that are different from those expressed in other types of excitable cells, we compared the properties of the hNE sodium channel [a human homolog of PN1, which is selectively expressed in dorsal root ganglion (DRG) neurons] with that of the skeletal muscle Na+channel (hSkM1) [both expressed in human embryonic kidney (HEK293) cells]. Although the voltage dependence of activation was similar, the inactivation properties were different. The V1/2for steady-state inactivation was slightly more negative, and the rate of open-state inactivation was ∼50% slower for hNE. However, the greatest difference was that closed-state inactivation and recovery from inactivation were up to fivefold slower for hNE than for hSkM1 channels. TTX-sensitive (TTX-S) currents in small DRG neurons also have slow closed-state inactivation, suggesting that hNE/PN1 contributes to this TTX-S current. Slow ramp depolarizations (0.25 mV/msec) elicited TTX-S persistent currents in cells expressing hNE channels, and in DRG neurons, but not in cells expressing hSkM1 channels. We propose that slow closed-state inactivation underlies these ramp currents. This conclusion is supported by data showing that divalent cations such as Cd2+and Zn2+(50–200 μm) slowed closed-state inactivation and also dramatically increased the ramp currents for DRG TTX-S currents and hNE channels but not for hSkM1 channels. The hNE and DRG TTX-S ramp currents activated near −65 mV and therefore could play an important role in boosting stimulus depolarizations in sensory neurons. These results suggest that differences in the kinetics of closed-state inactivation may confer distinct integrative properties on different Na+channel isoforms.
A Product of theDrosophila stonedLocus Regulates Neurotransmitter Release
Authors: Stimson Daniel T. , Estes Patricia S. , Smith Michiko , Kelly Leonard E. , Ramaswami Mani
Published: April 2018

TheDrosophila stonedlocus encodes two novel gene products termed stonedA and stonedB, which possess sequence motifs shared by proteins involved in intracellular vesicle traffic. A specific requirement forstonedin the synaptic vesicle cycle has been suggested by synthetic genetic interactions betweenstonedandshibire, a gene essential for synaptic vesicle recycling (Petrovich et al., 1993). A synaptic role ofstonedgene products also is suggested by altered synaptic transients in electroretinograms recorded fromstonedmutant eyes (Petrovich et al., 1993). We show here that the stonedA protein is highly enriched atDrosophilanerve terminals. Mutant alleles that affect stonedA disrupt the normal regulation of synaptic vesicle exocytosis at neuromuscular synapses ofDrosophila. Spontaneous neurotransmitter release is enhanced dramatically, and evoked release is reduced substantially in suchstonedmutants. Ultrastructural studies reveal no evidence of major disorganization atstonedmutant nerve terminals. Thus, our data indicate a direct role for stonedA in regulating synaptic vesicle exocytosis. However, genetic and morphological observations suggest additional, subtle effects ofstonedmutations on synaptic vesicle recycling. Remarkably, almost all phenotypes ofstonedmutants are similar to those previously described for mutants of synaptotagmin, a protein postulated to regulate both exocytosis and the recycling of synaptic vesicles. We propose a model in which stonedA functions together with synaptotagmin to regulate synaptic vesicle cycling.
Glutamate Potentiates the Toxicity of Mutant Cu/Zn-Superoxide Dismutase in Motor Neurons by Postsynaptic Calcium-Dependent Mechanisms
Authors: Roy Josée , Minotti Sandra , Dong Lichun , Figlewicz Denise A. , Durham Heather D.
Published: April 2018

Mutations in the Cu/Zn-superoxide dismutase (SOD-1) gene are responsible for a subset of familial cases of amyotrophic lateral sclerosis. Using a primary culture model, we have demonstrated that normally nontoxic glutamatergic input, particularly via calcium-permeable AMPA/kainate receptors, is a major factor in the vulnerability of motor neurons to the toxicity of SOD-1 mutants. Wild-type and mutant (G41R, G93A, or N139K) human SOD-1 were expressed in motor neurons of dissociated cultures of murine spinal cord by intranuclear microinjection of plasmid expression vector. Both a general antagonist of AMPA/kainate receptors (CNQX) and a specific antagonist of calcium-permeable AMPA receptors (joro spider toxin) reduced formation of SOD-1 proteinaceous aggregates and prevented death of motor neurons expressing SOD-1 mutants. Partial protection was obtained by treatment with nifedipine, implicating Ca2+entry through voltage-gated calcium channels as well as glutamate receptors in potentiating the toxicity of mutant SOD-1 in motor neurons. Dramatic neuroprotection was obtained by coexpressing the calcium-binding protein calbindin-D28k but not by increasing intracellular glutathione levels or treatment with the free radical spin trap agent,N-tert-butyl-α-phenylnitrone. Thus, generalized oxidative stress could have contributed in only a minor way to death of motor neurons expressing the mutant SOD-1. These studies demonstrated that the toxicity of these mutants is calcium-dependent and provide direct evidence that calcium entry during neurotransmission, coupled with deficiency of cytosolic calcium-binding proteins, is a major factor in the preferential vulnerability of motor neurons to disease.
Identification of a Signaling Pathway Activated Specifically in the Somatodendritic Compartment by a Heparan Sulfate That Regulates Dendrite Growth
Authors: Calvet Sophie , Doherty Patrick , Prochiantz Alain
Published: April 2018

In two earlier reports we demonstrated that natural heparan sulfate, but not dermatan or chondroitin sulfate glycosaminoglycans, stimulate axonal elongation and inhibit dendrite growthin vitro(Lafont et al., 1992). The latter specific effect on dendrite elongation was reproduced by chemically synthesized heparan sulfates and by SR 80037A, a purified sulfated and hexanoylated heparin fragment (Lafont et al., 1994). Adding radioactive SR 80037A to purified neurons demonstrated the existence, at the neuronal surface, of heparan sulfate-specific and saturable binding sites, suggesting that SR 80037A activates specific signal transduction pathways. In the present study, using rat or mouse neurons from the embryonic cortex, we show that SR 80037A signaling involves one or several G-coupled receptor or receptors, small GTPases ρA and/or ρC, and one or several PKCs. We also demonstrate that the rapid soma rounding elicited by SR 80037A does not require protein synthesis but that the long-term effect on dendrite initiation requires protein synthesis in a short period after the addition of the heparan sulfate. Finally, by preparing membranes from the somatodendritic or axonal compartments we demonstrate that the identified signaling pathway is activated by SR 80037A primarily in the somatodendritic compartment and is not sensitive to the addition of a dermatan sulfate glycosaminoglycan that does not induce the axonal phenotype by impairing dendrite initiation and elongation.
Overexpression in Neurons of Human Presenilin-1 or a Presenilin-1 Familial Alzheimer Disease Mutant Does Not Enhance Apoptosis
Authors: Bursztajn Sherry , DeSouza Richard , McPhie Donna L. , Berman S. A. , Shioi Junichi , Robakis Nikolaos K. , Neve Rachael L.
Published: April 2018

Programmed cell death, or apoptosis, has been implicated in Alzheimer’s disease (AD). DNA damage was assessed in primary cortical neurons infected with herpes simplex virus (HSV) vectors expressing the familial Alzheimer’s disease (FAD) gene presenilin-1 (PS-1) or an FAD mutant of this gene, A246E. After infection, immunoreactivity for PS-1 was shown to be enhanced in infected cells. The infected cells exhibited no cytotoxicity, as evaluated by trypan blue exclusion and mitochondrial function assays. Quantitative analysis of cells that were immunohistochemically labeled using a Klenow DNA fragmentation assay or the TUNEL method revealed no enhancement of apoptosis in PS-1-infected cells. This result was confirmed using assays for chromatin condensation and for DNA fragmentation. Expression of PS-1 protected against induction of apoptosis in the cortical neurons by etoposide or staurosporine. The specificity of this phenotype was demonstrated by the fact that cortical cultures infected with recombinant HSV vectors expressing the amyloid precursor protein (APP-695) showed, in contrast, a significant increase in the number of apoptotic cells and an increase in DNA fragmentation for all parameters tested. Our results indicate that overexpression of wild-type or A246E mutant PS-1 does not enhance apoptosis in postmitotic cortical cells and suggest that the previously reported enhancement of apoptosis by presenilins may be dependent on cell type.
Evidence for the Participation of the Neuron-Specific CDK5 Activator P35 during Laminin-Enhanced Axonal Growth
Authors: Paglini Gabriela , Pigino Gustavo , Kunda Patricia , Morfini Gerardo , Maccioni Ricardo , Quiroga Santiago , Ferreira Adriana , Cáceres Alfredo
Published: April 2018

Cultures of cerebellar macroneurons were used to study the pattern of expression, subcellular localization, and function of the neuronal cdk5 activator p35 during laminin-enhanced axonal growth. The results obtained indicate that laminin, an extracellular matrix molecule capable of selectively stimulating axonal extension and promoting MAP1B phosphorylation at a proline-directed protein kinase epitope, selectively stimulates p35 expression, increases its association with the subcortical cytoskeleton, and accelerates its redistribution to the axonal growth cones. Besides, suppression of p35, but not of a highly related isoform designated as p39, by antisense oligonucleotide treatment selectively reduces cdk5 activity, laminin-enhanced axonal elongation, and MAP1b phosphorylation. Taken collectively, the present results suggest that cdk5/p35 may serve as an important regulatory linker between environmental signals (e.g., laminin) and constituents of the intracellular machinery (e.g., MAP1B) involved in axonal elongation.
The Power Ratio and the Interval Map: Spiking Models and Extracellular Recordings
Authors: Reich Daniel S. , Victor Jonathan D. , Knight Bruce W.
Published: April 2018

We describe a new, computationally simple method for analyzing the dynamics of neuronal spike trains driven by external stimuli. The goal of our method is to test the predictions of simple spike-generating models against extracellularly recorded neuronal responses. Through a new statistic called the power ratio, we distinguish between two broad classes of responses: (1) responses that can be completely characterized by a variable firing rate, (for example, modulated Poisson and gamma spike trains); and (2) responses for which firing rate variations alone are not sufficient to characterize response dynamics (for example, leaky integrate-and-fire spike trains as well as Poisson spike trains with long absolute refractory periods). We show that the responses of many visual neurons in the cat retinal ganglion, cat lateral geniculate nucleus, and macaque primary visual cortex fall into the second class, which implies that the pattern of spike times can carry significant information about visual stimuli. Our results also suggest that spike trains of X-type retinal ganglion cells, in particular, are very similar to spike trains generated by a leaky integrate-and-fire model with additive, stimulus-independent noise that could represent background synaptic activity.
Postural Hand Synergies for Tool Use
Authors: Santello Marco , Flanders Martha , Soechting John F.
Published: April 2018

Subjects were asked to shape the right hand as if to grasp and use a large number of familiar objects. The chosen objects typically are held with a variety of grips, including “precision” and “power” grips. Static hand posture was measured by recording the angular position of 15 joint angles of the fingers and of the thumb. Although subjects adopted distinct hand shapes for the various objects, the joint angles of the digits did not vary independently. Principal components analysis showed that the first two components could account for >80% of the variance, implying a substantial reduction from the 15 degrees of freedom that were recorded. However, even though they were small, higher-order (more than three) principal components did not represent random variability but instead provided additional information about the object. These results suggest that the control of hand posture involves a few postural synergies, regulating the general shape of the hand, coupled with a finer control mechanism providing for small, subtle adjustments. Because the postural synergies did not coincide with grip taxonomies, the results suggest that hand posture may be regulated independently from the control of the contact forces that are used to grasp an object.