bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of "reconstructed" motor synapses of the garter snake
Authors: Wilkinson RS , Lunin SD
Published: April 2018

We have developed a technique, called synaptic reconstruction, that permits nerve terminals of living vertebrate neuromuscular junctions (NMJs) to be isolated and then manually recombined with vacant endplate sites to form functional synapses. By reconstructing NMJs with various combinations of pre- and postsynaptic partners, or with varying degrees of pre- to postsynaptic alignment, the functional properties of the three anatomical components of the NMJ--nerve terminal, endplate, and the alignment between them--may be studied independently. Our experiments thus far indicate, surprisingly, that reconstructed NMJs function nearly normally. Thus, one feature of the intact vertebrate NMJ, precise alignment between presynaptic active zones and postsynaptic secondary folds, is either unnecessary for normal function or, alternatively, is spontaneously reestablished when an isolated terminal and vacant endplate site are placed in contact. We have also utilized synaptic reconstruction to examine a recently described property of NMJs: the regulation of quantal size among motor synapses in one muscle so that larger muscle fibers receive larger single quantal currents. Quantal size appears to be a postsynaptic attribute, suggesting that its regulation is achieved by a postsynaptic mechanism.
Opposite responses of mesolimbic dopamine system to controllable and uncontrollable aversive experiences
Authors: Cabib S , Puglisi-Allegra S
Published: April 2018

It has been previously shown that rodents exposed to stressful experiences show a biphasic response of the mesolimbic dopamine (DA) system, that is, initial increase of DA release followed by a decrease below control levels (Puglisi-Allegra et al., 1991). Evidence is now presented showing that mice exposed to a series of foot shocks show an increase of DA release in the nucleus accumbens septi (NAS) if they are allowed to control the shock experience (shocked condition) and a decrease of DA release in this brain area if they are not allowed to exert any control (yoked condition). These results indicate that escapable/controllable and inescapable/uncontrollable aversive experiences elicit opposite responses from the mesolimbic DA system. Mice exposed to the apparatus without receiving shock (sham condition) show a time-dependent biphasic evolution mesolimbic DA release in line with previous reports indicating that confinement in an unknown environment represents a stressful experience for mice. Moreover, exposure to the sham condition for a time comparable to the duration of shock and yoked exposure induces a mesolimbic DA response only quantitatively different from the response of the yoked group but qualitatively different from the response of the shocked mice. These results suggest that in environmental conditions that allow behavioral control, enhanced mesolimbic DA release is maintained regardless of the intensity of the aversive stimuli. On the other hand, evaluation of changes in acid DA metabolites levels in the frontal cortex (FC) of mice exposed to the shocked, yoked, and sham conditions suggests that stressful experiences characterized by a different intensity of the aversive stimuli could elicit graded responses in the FC DA system.(ABSTRACT TRUNCATED AT 250 WORDS)
Signaling by insulin-like growth factors in paralyzed skeletal muscle: rapid induction of IGF1 expression in muscle fibers and prevention of interstitial cell proliferation by IGF-BP5 and IGF-BP4
Authors: Caroni P , Schneider C
Published: April 2018

In the absence of muscle activity, muscle fibers, muscle interstitial cells, and intramuscular nerves display characteristic reactions presumably aimed at restoring a functioning neuromuscular system and avoiding degenerative events. In partially denervated muscle these include proliferation of interstitial cells, followed by nerve sprouting. The same reactions can be induced in intact muscle by elevation of intramuscular insulin-like growth factor (IGF) levels. To determine whether IGFs may participate in the initiation of restorative reactions in inactivated muscle we analyzed the expression of IGF1 and IGF2 mRNA in botulinum toxin-paralyzed and in denervated rat skeletal muscle, and interfered with the activity of IGFs by locally applying the IGF-binding proteins IGF-BP5 and IGF-BP4. To obtain a resolution of the in situ hybridization signals at the cellular level, a nonradioactive method based on digoxigenin-labeled probes was applied. We found that muscle fiber IGF1 mRNA increased rapidly and transiently in inactivated muscle. The time course of this response was similar to that reported for ACh receptor subunits and myogenins. A similar behavior was observed for the corresponding IGF1 protein. The IGF1 response coincided with the transient muscle interstitial cell proliferation reaction. Local application of recombinant IGF-BP5 or IGF- BP4, which are endogenous and specific extracellular ligands of IGFs, prevented the stimulation of interstitial cell proliferation in paralyzed muscle. Our data demonstrate the elevated production of the growth factor IGF1 among early reactions in electrically inactive skeletal muscle fibers and indicate that muscle IGFs are required for the induction of intramuscular interstitial cell proliferation. These findings support the hypothesis that in the neuromuscular system IGF1 plays an important role in initiating cellular reactions in the vicinity of inactive muscle fibers.
Neural Mechanisms of Visual Working Memory in Prefrontal Cortex of the Macaque
Authors: Miller Earl K. , Erickson Cynthia A. , Desimone Robert
Published: April 2018

Prefrontal (PF) cells were studied in monkeys performing a delayed matching to sample task, which requires working memory. The stimuli were complex visual patterns and to solve the task, the monkeys had to discriminate among the stimuli, maintain a memory of the sample stimulus during the delay periods, and evaluate whether a test stimulus matched the sample presented earlier in the trial. PF cells have properties consistent with a role in all three of these operations. Approximately 25% of the cells responded selectively to different visual stimuli. Half of the cells showed heightened activity during the delay after the sample and, for many of these cells, the magnitude of delay activity was selective for different samples. Finally, more than half of the cells responded differently to the test stimuli depending on whether they matched the sample. Because inferior temporal (IT) cortex also is important for working memory, we compared PF cells with IT cells studied in the same task. Compared with IT cortex, PF responses were less often stimulus-selective but conveyed more information about whether a given test stimulus was a match to the sample. Furthermore, sample-selective delay activity in PF cortex was maintained throughout the trial even when other test stimuli intervened during the delay, whereas delay activity in IT cortex was disrupted by intervening stimuli. The results suggest that PF cortex plays a primary role in working memory tasks and may be a source of feedback inputs to IT cortex, biasing activity in favor of behaviorally relevant stimuli.
Identification of a Novel Repressive Element That Contributes to Neuron-Specific Gene Expression
Authors: Weber Joseph R. M. , Skene J. H. Pate
Published: April 2018

Multiple signaling pathways are thought to control the selective expression of genes over the course of neuronal differentiation. One approach to elucidating these pathways is to identify specificcis-acting elements that serve as the final targets for these signaling pathways in neural-specific genes. We now identify a novel repressive element from the growth-associated protein 43 (GAP-43) gene that can contribute to neuron-specific gene expression by inhibiting transcription in a wide range of non-neuronal cell types. This repressive element is located downstream of the GAP-43 TATA box and is highly position-dependent. When transferred to viral promoters this element preferentially inhibits transcription in non-neuronal cells. Electrophoretic mobility shift assays show that the repressive element comprises at least two protein recognition sites. One of these is a novel sequence motif that we designate the SNOG element, because it occurs downstream of the TATA boxes of the synaptosomal-associated protein of 25 kDa and neuronal nitric oxide synthase genes, as well as the GAP-43 gene. The GAP-43 repressive element is distinct in sequence and position dependence from the repressor element 1/neuron-restrictive silencer element previously described in other neural genes and therefore is a likely target for a distinct set of signaling pathways involved in the control of neuronal differentiation.
The Brain Chondroitin Sulfate Proteoglycan Brevican Associates with Astrocytes Ensheathing Cerebellar Glomeruli and Inhibits Neurite Outgrowth from Granule Neurons
Authors: Yamada Hidekazu , Fredette Barbara , Shitara Kenya , Hagihara Kazuki , Miura Ryu , Ranscht Barbara , Stallcup William B. , Yamaguchi Yu
Published: April 2018

Brevican is a nervous system-specific chondroitin sulfate proteoglycan that belongs to the aggrecan family and is one of the most abundant chondroitin sulfate proteoglycans in adult brain. To gain insights into the role of brevican in brain development, we investigated its spatiotemporal expression, cell surface binding, and effects on neurite outgrowth, using rat cerebellar cortex as a model system. Immunoreactivity of brevican occurs predominantly in the protoplasmic islet in the internal granular layer after the third postnatal week. Immunoelectron microscopy revealed that brevican is localized in close association with the surface of astrocytes that form neuroglial sheaths of cerebellar glomeruli where incoming mossy fibers interact with dendrites and axons from resident neurons.In situhybridization showed that brevican is synthesized by these astrocytes themselves. In primary cultures of cerebellar astrocytes, brevican is detected on the surface of these cells. Binding assays with exogenously added brevican revealed that primary astrocytes and several immortalized neural cell lines have cell surface binding sites for brevican core protein. These cell surface brevican binding sites recognize the C-terminal portion of the core protein and are independent of cell surface hyaluronan. These results indicate that brevican is synthesized by astrocytes and retained on their surface by an interaction involving its core protein. Purified brevican inhibits neurite outgrowth from cerebellar granule neuronsin vitro, an activity that requires chondroitin sulfate chains. We suggest that brevican presented on the surface of neuroglial sheaths may be controlling the infiltration of axons and dendrites into maturing glomeruli.
Transforming Growth Factor-α Null and Senescent Mice Show Decreased Neural Progenitor Cell Proliferation in the Forebrain Subependyma
Authors: Tropepe Vincent , Craig Constance G. , Morshead Cindi M. , van der Kooy Derek
Published: April 2018

The adult mammalian forebrain subependyma contains neural stem cells and their progeny, the constitutively proliferating progenitor cells. Using bromodeoxyuridine labeling to detect mitotically active cells, we demonstrate that the endogenous expression of transforming growth factor-α (TGFα) is necessary for the full proliferation of progenitor cells localized to the dorsolateral corner of the subependyma and the full production of the neuronal progenitors that migrate to the olfactory bulbs. Proliferation of these progenitor cells also is diminished with age (in 23- to 25-months-old compared with 2- to 4-months-old mice), likely because of a lengthening of the cell cycle. Senescence or the absence of endogenous TGFα does not affect the numbers of neural stem cells isolatedin vitroin the presence of epidermal growth factor. These results suggest that endogenous TGFα and the effects of senescence may regulate the proliferation of progenitor cells in the adult subependyma, but that the number of neural stem cells is maintained throughout life.
Acute Morphogenic and Chemotropic Effects of Neurotrophins on Cultured EmbryonicXenopusSpinal Neurons
Authors: Ming Guo-li , Lohof Ann M. , Zheng James Q.
Published: April 2018

Neurotrophins constitute a family of trophic factors with profound effects on the survival and differentiation of the nervous system. Addition of brain-derived neurotrophic factor (BDNF) or neurotrophin-3 (NT-3), but not nerve growth factor (NGF), increased the survival of embryonicXenopusspinal neurons in culture, although all three neurotrophins enhanced neurite outgrowth. Here we report that neurotrophins also exert acute actions on the morphology and motility of 1-day-old culturedXenopusspinal neurons. Bath application of BDNF induced extensive formation of lamellipodia simultaneously at multiple sites along the neurite shaft as well as at the growth cone. The BDNF-induced lamellipodia appeared within minutes, rapidly protruded to their greatest extent in about 10 min, and gradually disappeared thereafter, leaving behind newly formed thin lateral processes. When applied as microscopic concentration gradients, both BDNF and NT-3, but not NGF, induced the growth cone to grow toward the neurotrophin source. Our results suggest that neurotrophic factors, when delivered to responsive neurons, may serve as morphogenic and chemotropic agents during neuronal development.
Apparent Position of Visual Targets during Real and Simulated Saccadic Eye Movements
Authors: Morrone M. Concetta , Ross John , C. Burr David
Published: April 2018

It is now well established that briefly flashed single targets are mislocalized in space, not only during saccades but also before them. We show here by several techniques (including a vernier judgment that did not require absolute location in space) that errors appear up to 100 msec before saccades are made and are maximal just before they start. The size and even the sign of errors depend strongly on position in the visual field, the complete pattern of errors suggesting a compression of visual space around the initial fixation point and the target of the impending saccade. The compression was confirmed by displaying multiple rather than single targets and was found to be powerful enough to reduce or even to remove vernier offset for pairs of bars shown simultaneously and to create offsets for colinear bars separated in time by 75 msec. It also reduced the apparent number of parallel bars. When saccades were simulated by moving the display at saccadic speed, there were sometimes errors of location, but only for tasks requiring absolute judgment of position. The pattern of errors differed greatly from that during saccades and, in particular, showed no signs of compression. We can model our saccade results by assuming a shift in the point in space associated with eye position compression of eccentricity along the axis of saccades.
Activation of Protein Kinase A Contributes to the Expression But Not the Induction of Long-Term Hyperexcitability Caused by Axotomy ofAplysiaSensory Neurons
Authors: Liao Xiaogang , Gunstream John D. , Lewin Matthew R. , Ambron Richard T. , Walters Edgar T.
Published: April 2018

Nociceptive sensory neurons (SNs) inAplysiaprovide useful models to study both memory and adaptive responses to nerve injury. Induction of long-term memory in many species, includingAplysia, is thought to depend on activation of cAMP-dependent protein kinase (PKA). BecauseAplysiaSNs display similar alterations in models of memory and after nerve injury, a plausible hypothesis is that axotomy triggers memory-like modifications by activating PKA in damaged axons. The present study disproves this hypothesis. SN axotomy was produced by (1) dissociation of somata from the ganglion [which is shown to induce long-term hyperexcitability (LTH)], (2) transection of neurites of dissociated SNs growingin vitro, or (3) peripheral nerve crush. Application of the competitive PKA inhibitor Rp-8-CPT-cAMPS at the time of axotomy failed to alter the induction of LTH by each form of axotomy, although the inhibitor antagonized hyperexcitability produced by 5-HT application. Strong activation of PKA in the nerve by coapplication of a membrane-permeant analog of cAMP and a phosphodiesterase inhibitor was not sufficient to induce LTH of either the SN somata or axons. Furthermore, nerve crush failed to activate axonal PKA or stimulate its retrograde transport. Therefore, PKA activation plays little if any role in the induction of LTH by axotomy. However, the expression of LTH was reduced by intracellular injection of the highly specific PKA inhibitor PKI several days after nerve crush. This suggests that long-lasting activation of PKA in or near the soma contributes to the maintenance of long-term modifications produced by nerve injury.
Ciliary Neurotrophic Factor is a Regulator of Muscular Strength in Aging
Authors: Guillet Catherine , Auguste Patrick , Mayo Willy , Kreher Paul , Gascan Hugues
Published: April 2018

Ciliary neurotrophic factor (CNTF) participates in the survival of motor neurons and reduces the denervation-induced atrophy of skeletal muscles. Experiments performed in rats show a decrease in peripheral CNTF synthesis during aging, associated with an overexpression of its α-binding receptor component by skeletal muscles. Measurement of sciatic nerve CNTF production and of the muscular performance developed by the animals revealed a strong correlation between the two studied parameters (r= 0.8;p< 0.0003). Furthermore, the twitch and tetanic tensions measured in the isolated soleus skeletal muscle in 24-month-old animals increased 2.5-fold by continuousin vivoadministration of CNTF. Analyses of the activation level of leukemia inhibitory factor receptor β- and signal transducer and activator of transcription 3-signaling molecules in response to exogenous CNTF revealed an increased tyrosine phosphorylation positively correlated with the twitch tension developed by the soleus muscle of the animals.
Mutation in Neurofilament Transgene Implicates RNA Processing in the Pathogenesis of Neurodegenerative Disease
Authors: Cañete-Soler Rafaela , Silberg Debra G. , Gershon Michael D. , Schlaepfer William W.
Published: April 2018

A mouse neurofilament light subunit (NF-L) transgene with a 36 bpc-mycinsert at the end of the coding region was found to have neuropathic effects on enteric and motor neurons of transgenic mice. The severity of phenotype was related directly to the levels of transgenic mRNA expression. High levels of transgene expression were lethal to newborn pups, causing profound alterations in the development of the enteric nervous system and extensive vacuolar changes in motor neurons. Lower levels of transgene expression led to a transient stunting of growth and focal alterations of enteric and motor neurons. Because the positioning of thec-mycinsert coincided with the location of the major stability determinant of the NF-L mRNA (Cañete-Soler et al., 1998a,b), additional studies were undertaken. These studies showed that thec-mycinsert alters the ribonucleoprotein (RNP) complexes that bind to the stability determinant and disrupts their ability to regulate the stability of the transcripts. The findings indicate that expression of an NF-L transgene with a mutant mRNA stability determinant is highly disruptive to enteric and motor neurons and implicate alterations in RNA processing in the pathogenesis of a neurodegenerative condition.
Lysophosphatidic Acid Stimulates Neurotransmitter-Like Conductance Changes that Precede GABA and l-Glutamate in Early, Presumptive Cortical Neuroblasts
Authors: Dubin Adrienne E. , Bahnson Tristram , Weiner Joshua A. , Fukushima Nobuyuki , Chun Jerold
Published: April 2018

During neurogenesis in the embryonic cerebral cortex, the classical neurotransmitters GABA andl-glutamate stimulate ionic conductance changes in ventricular zone (VZ) neuroblasts. Lysophosphatidic acid (LPA) is a bioactive phospholipid producing myriad effects on cells including alterations in membrane conductances (for review, see Moolenaar et al., 1995). Developmental expression patterns of its first cloned receptor gene,lpA1/vzg-1(Hecht et al., 1996; Fukushima et al., 1998) in the VZ suggested that functional LPA receptors were synthesized at these early times, and thus, LPA could be an earlier stimulus to VZ cells than the neurotransmitters GABA andl-glutamate. To address this possibility, primary cultures of electrically coupled, presumptive cortical neuroblast clusters were identified by age, morphology, electrophysiological profile, BrdU incorporation, and nestin immunostaining. Single cells from cortical neuroblast cell lines were also examined. Whole-cell variation of the patch-clamp technique was used to record from nestin-immunoreactive cells after stimulation by local administration of ligands. After initial plating at embryonic day 11 (E11), cells responded only to LPA but not to GABA orl-glutamate. Continued growth in culture for up to 12 hr produced more LPA-responsive cells, but also a growing population of GABA- orl-glutamate-responsive cells. Cultures from E12 embryos showed LPA as well as GABA andl-glutamate responses, with LPA-responsive cells still representing a majority. Overall, >50% of cells responded to LPA with depolarization mediated by either chloride or nonselective cation conductances. These data implicate LPA as the earliest reported extracellular stimulus of ionic conductance changes for cortical neuroblasts and provide evidence for LPA as a novel, physiological component in CNS development.
Selective Inhibition of Kindling Development by Intraventricular Administration of TrkB Receptor Body
Authors: Binder Devin K. , Routbort Mark J. , Ryan Terence E. , Yancopoulos George D. , McNamara James O.
Published: April 2018

Recent work has shown that neurotrophin gene expression is increased after seizures evoked in the kindling model of epilepsy, but whether neurotrophins regulate kindling development is as yet unclear. In this study, we attempted to block selectively the activation of distinct neurotrophin receptors throughout kindling development in the rat via chronic intracerebroventricular administration of trk receptor bodies. The efficacy and selectivity of the trk receptor bodies were established by inhibition of neurotrophin-induced trk receptor phosphorylation in pheochromocytoma (PC12) cells and primary cultures of cortical neurons. The intracerebroventricular infusion of trkB receptor body (trkB–Fc) inhibited development of kindling in comparison with that seen with saline or human IgG controls, trkA–Fc, or trkC–Fc. These results imply that activation of trkB receptors contributes to the development of kindling, a form of activity-dependent behavioral plasticity in the adult mammalian brain.
Filopodial Adhesion Does Not Predict Growth Cone Steering EventsIn Vivo
Authors: Isbister Carolyn M. , O’Connor Timothy P.
Published: April 2018

Migration of growth cones is in part mediated by adhesive interactions between filopodia and the extracellular environment, transmitting forces and signals necessary for pathfinding. To elucidate the role of substrate adhesivity in growth cone pathfinding, we developed anin vivoassay for measuring filopodial–substrate adhesivity using the well-characterized Ti pioneer neuron pathway of the embryonic grasshopper limb. Using time-lapse imaging and a combination of rhodamine-phalloidin injections and DiI labeling, we demonstrate that the filopodial retraction rate after treatment with cytochalasin D or elastase reflects the degree of filopodial–substrate adhesivity. Measurements of filopodial retraction rates along regions of known differing substrate adhesivities confirmed the use of this assay to examine filopodial–substrate adhesion duringin vivopathfinding events. We analyzed 359 filopodia from 22 Ti growth cones and found that there is no difference between the retraction rates of filopodia extending toward the correct target (on-axis) and filopodia extending away from the correct target (off-axis). These results indicate on-axis and off-axis filopodia have similar substrate adherence. Interestingly, we observed a 300% increase in the extension rates of on-axis filopodia during Ti growth cone turning events. Therefore, in addition to providing filopodia with important guidance information, regional cues are capable of modulating the filopodial extension rate. The homogeneity in filopodial retraction rates, even among these turning growth cones in which differential adhesivity might be expected to be greatest, strongly establishes that differential adhesion does not govern Ti pioneer neuron migration rate or pathfinding. We propose that the presence of local differences in receptor-mediated second messenger cascades and the resulting assembly of force-generating machinery may underlie the ability of filopodial contacts to regulate growth cone steeringin vivo.
Stimulus-Dependent Translocation of κ Opioid Receptors to the Plasma Membrane
Authors: Shuster Samuel J. , Riedl Maureen , Li Xinren , Vulchanova Lucy , Elde Robert
Published: April 2018

We examined the cellular and subcellular distribution of the cloned κ opioid receptor (KOR1) and its trafficking to the presynaptic plasma membrane in vasopressin magnocellular neurosecretory neurons. We used immunohistochemistry to show that KOR1 immunoreactivity (IR) colocalized with vasopressin-containing cell bodies, axons, and axon terminals within the posterior pituitary. Ultrastructural analysis revealed that a major fraction of KOR1-IR was associated with the membrane of peptide-containing large secretory vesicles. KOR1-IR was rarely associated with the plasma membrane in unstimulated nerve terminals within the posterior pituitary. A physiological stimulus (salt-loading) that elicits vasopressin release also caused KOR1-IR to translocate from these vesicles to the plasma membrane. After stimulation, there was a significant decrease in KOR1-IR associated with peptide-containing vesicles and a significant increase in KOR1-IR associated with the plasma membrane. This stimulus-dependent translocation of receptors to the presynaptic plasma membrane provides a novel mechanism for regulation of transmitter release.
Choline and Selective Antagonists Identify Two Subtypes of Nicotinic Acetylcholine Receptors that Modulate GABA Release from CA1 Interneurons in Rat Hippocampal Slices
Authors: Alkondon Manickavasagom , Pereira Edna F. R. , Eisenberg Howard M. , Albuquerque Edson X.
Published: April 2018

Neuronal nicotinic receptors (nAChR) are known to control transmitter release in the CNS. Thus, this study was aimed at exploring the diversity and localization of nAChRs present in CA1 interneurons in rat hippocampal slices. The use of a U-tube as the agonist delivery system was critical for the reliable detection of nicotinic responses induced by brief exposure of the neurons to ACh or to the α7 nAChR-selective agonist choline. The present study demonstrated that CA1 interneurons, in addition to expressing functional α7 nAChRs, also express functional α4β2-like nAChRs and that activation of both receptors facilitates an action potential-dependent release of GABA. Depending on the experimental condition, one of the following nicotinic responses was recorded from the interneurons by means of the patch-clamp technique: a nicotinic whole-cell current, depolarization accompanied by action potentials, or GABA-mediated postsynaptic currents (PSCs). Responses mediated by α7 nAChRs were short-lasting, whereas those mediated by α4β2 nAChRs were long-lasting. Thus, phasic or tonic inhibition of CA1 interneurons may be achieved by selective activation of α7 or α4β2 nAChRs, respectively. It can also be suggested that synaptic levels of choline generated by hydrolysis of AChin vivomay be sufficient to control the activity of the α7 nAChRs. The finding that methyllycaconitine and dihydro-β-erythroidine (antagonists of α7 and α4β2 nAChRs, respectively) increased the frequency and amplitude of GABAergic PSCs suggests that there is an intrinsic cholinergic activity that sustains a basal level of nAChR activity in these interneurons.
Patterns of Spontaneous Purkinje Cell Complex Spike Activity in the Awake Rat
Authors: Lang Eric J. , Sugihara Izumi , Welsh John P. , Llinás Rodolfo
Published: April 2018

The olivocerebellar system is known to generate periodic synchronous discharges that result in synchronous (to within 1 msec) climbing fiber activation of Purkinje cells (complex spikes) organized in parasagittally oriented strips. These results have been obtained primarily in anesthetized animals, and so the question remains whether the olivocerebellar system generates such patterns in the awake animal. To this end, multiple electrode recordings of crus 2a complex spike activity were obtained in awake rats conditioned to execute tongue movements in response to a tone. After removal of all movement- and tone-related activity, the remaining data were examined to characterize spontaneous complex spike activity in the alert animal. Spontaneous complex spikes occurred at an average firing rate of 1 Hz and a clear ≈10 Hz rhythmicity. Analysis of the autocorrelograms using a rhythm index indicated that the large majority of Purkinje cells displayed rhythmicity, similar to that in the anesthetized preparation. In addition, the patterns of synchronous complex spike activity were also similar to those observed in the anesthetized preparation (i.e., simultaneous activity was found predominantly among Purkinje cells located within the same parasagittally oriented strip of cortex). The results provide unequivocal evidence that the olivocerebellar system is capable of generating periodic patterns of synchronous activity in the awake animal. These findings support the extrapolation of previous results obtained in the anesthetized preparation to the waking state and are consistent with the timing hypothesis concerning the role of the olivocerebellar system in motor coordination.
Network Oscillations Generated by Balancing Graded Asymmetric Reciprocal Inhibition in Passive Neurons
Authors: Manor Yair , Nadim Farzan , Epstein Steven , Ritt Jason , Marder Eve , Kopell Nancy
Published: April 2018

We describe a novel mechanism by which network oscillations can arise from reciprocal inhibitory connections between two entirely passive neurons. The model was inspired by the activation of the gastric mill rhythm in the crab stomatogastric ganglion by the modulatory commissural ganglion neuron 1 (MCN1), but it is studied here in general terms. One model neuron has a linear current–voltage (I–V) curve with a low (L) resting potential, and the second model neuron has a linear current–voltage curve with a high (H) resting potential. The inhibitory connections between them are graded. There is an extrinsic modulatory excitatory input to the L neuron, and the L neuron presynaptically inhibits the modulatory neuron. Activation of the extrinsic modulatory neuron elicits stable network oscillations in which the L and H neurons are active in alternation. The oscillations arise because the graded reciprocal synapses create the equivalent of a negative-slope conductance region in theI–Vcurves for the cells. Geometrical methods are used to analyze the properties of and the mechanism underlying these network oscillations.
Parallel Information Processing in the Dorsal Striatum: Relation to Hippocampal Function
Authors: Devan Bryan D. , White Norman M.
Published: April 2018

We investigated the effects of localized medial and lateral CPu lesions and fornix/fimbria lesions on responses to a local cue and to behavior based on cognitive–spatial information in the water maze. Rats were trained concurrently on the cue (visible platform) and spatial (submerged platform) components of the task, followed by a test in which responses to the two types of information were dissociated by a measure of competing response tendencies. Bilateral lesions of lateral CPu did not affect acquisition of either cue or spatial responding but produced a preference for the spatial response on the competition test. Bilateral lesions of the medial CPu retarded but did not prevent learning both components and produced a preference for the cue response on the competition test. The latter effect was accompanied by increased thigmotaxis (swimming in the periphery of the pool), primarily during the early acquisition trials, which was attributed to an impaired ability to respond to learned spatial information. Fornix/fimbria lesions prevented spatial but not cue learning and produced a preference for the cue response on the competition test. Asymmetric lesions (unilateral hippocampus and contralateral medial CPu) produced mild retardation of acquisition of both the cue and spatial tasks and a preference for the cue response on the competition test. These findings dissociate the functions of the lateral and medial CPu and suggest that the hippocampus and medial CPu may be parts of a system that promotes responding based on learned cognitive–spatial information, particularly in competitive cue–place response situations.
Photolytic Manipulation of [Ca2+]iReveals Slow Kinetics of Potassium Channels Underlying the Afterhyperpolarization in Hipppocampal Pyramidal Neurons
Authors: Sah Pankaj , Clements John D.
Published: April 2018

The identity of the potassium channel underlying the slow, apamin-insensitive component of the afterhyperpolarization current (sIAHP) remains unknown. We studied sIAHPin CA1 pyramidal neurons using simultaneous whole-cell recording, calcium fluorescence imaging, and flash photolysis of caged compounds. Intracellular calcium concentration ([Ca2+]i) peaked earlier and decayed more rapidly than sIAHP. Loading cells with low concentrations of the calcium chelator EGTA slowed the activation and decay of sIAHP. In the presence of EGTA, intracellular calcium decayed with two time constants. When [Ca2+]iwas increased rapidly after photolysis of DM-Nitrophen, both apamin-sensitive and apamin-insensitive outward currents were activated. The apamin-sensitive current activated rapidly (<20 msec), whereas the apamin-insensitive current activated more slowly (180 msec). The apamin-insensitive current was reduced by application of serotonin and carbachol, confirming that it was caused by sIAHPchannels. When [Ca2+]iwas decreased rapidly via photolysis of diazo-2, the decay of sIAHPwas similar to control (1.7 sec). All results could be reproduced by a model potassium channel gated by calcium, suggesting that the channels underlying sIAHPhave intrinsically slow kinetics because of their high affinity for calcium.
Region-Specific Regulation of RGS4 (Regulator of G-Protein–Signaling Protein Type 4) in Brain by Stress and Glucocorticoids:In VivoandIn VitroStudies
Authors: Ni Yan G. , Gold Stephen J. , Iredale Philip A. , Terwilliger Rose Z. , Duman Ronald S. , Nestler Eric J.
Published: April 2018

The present study demonstrates that the regulator of G-protein–signaling protein type 4 (RGS4) is differentially regulated in the locus coeruleus (LC) and the paraventricular nucleus (PVN) of the hypothalamus by chronic stress and glucocorticoid treatments. Acute or chronic administration of corticosterone to adult rats decreased RGS4 mRNA levels in the PVN but increased these levels in the LC. Similarly, chronic unpredictable stress decreased RGS4 mRNA levels in the PVN but had a strong trend to increase these levels in the LC. Chronic stress also decreased RGS4 mRNA levels in the pituitary. The molecular mechanisms of RGS4 mRNA regulation were further investigatedin vitroin the LC-like CATH.a cell line and the neuroendocrine AtT20 cell line using the synthetic corticosterone analog dexamethasone. Consistent with the findingsin vivo, dexamethasone treatment caused a dose- and time-dependent decrease in RGS4 mRNA levels in AtT20 cells but a dose- and time-dependent increase in CATH.a cells. RGS4 mRNA regulation seen in these two cell lines seems to be attributable, at least in part, to opposite changes in mRNA stability. The differential regulation of RGS4 expression in the LC and in key relays of the hypothalamic–pituitary–adrenal axis could contribute to the brain’s region-specific and long-term adaptations to stress.
Encephalopsin: A Novel Mammalian Extraretinal Opsin Discretely Localized in the Brain
Authors: Blackshaw Seth , Snyder Solomon H.
Published: April 2018

We have identified a mammalian opsin, encephalopsin, that shows strong and specific expression in the brain. Encephalopsin defines a new family of opsins and shows highest homology to vertebrate retinal and pineal opsins. Encephalopsin is highly expressed in the preoptic area and paraventricular nucleus of the hypothalamus, both regions implicated in encephalic photoreception in nonmammalian vertebrates. In addition, encephalopsin shows highly patterned expression in other regions of the brain, being enriched in selected regions of the cerebral cortex, cerebellar Purkinje cells, a subset of striatal neurons, selected thalamic nuclei, and a subset of interneurons in the ventral horn of the spinal cord. Rostrocaudal gradients of encephalopsin expression are present in the cortex, cerebellum, and striatum. Radial stripes of encephalopsin expression are seen in the cerebellum. In the cortex and cerebellum, encephalopsin expression is considerably higher and more highly patterned in the adult than in the neonate. Encephalopsin is the first putative extraocular opsin identified in mammals and may play a role in encephalic photoreception.
A Current Activated on Depletion of Intracellular Ca2+Stores Can Regulate Exocytosis in Adrenal Chromaffin Cells
Authors: Fomina Alla F. , Nowycky Martha C.
Published: April 2018

Exocytosis in excitable cells is strongly coupled to Ca2+entry through voltage-gated channels but can be evoked by activation of membrane receptors that release Ca2+from inositol 1,4,5-trisphosphate-sensitive internal stores. In many cell types, depletion of Ca2+stores activates Ca2+influx across the plasma membrane, a process known as capacitative or store-operated Ca2+entry. This influx is mediated by a number of voltage-independent, Ca2+-selective currents. In addition to replenishing Ca2+stores, these currents are hypothesized to play an important role in agonist-evoked secretion in nonexcitable cells, although this has not been confirmed experimentally. The existence and physiological function of such currents in excitable cells is not known. Using the capacitance detection technique to monitor exocytosis, we provide direct experimental evidence that a similar mechanism exists in bovine adrenal chromaffin cells. Depletion of intracellular Ca2+stores with thapsigargin, a SERCA pump inhibitor, or with BAPTA, an exogenous Ca2+chelator, activates a small-amplitude, voltage-independent current that is carried by Ca2+and Na+ions. Ca2+entry through this pathway is sufficient to stimulate exocytosis at negative membrane potentials. In addition, depolarization-evoked exocytosis is markedly facilitated on activation of the current. These data suggest that excitable cells possess a store-operated Ca2+influx mechanism that may both directly trigger exocytosis and modulate excitation–secretion coupling.
Gene Expression in the Brain across the Hibernation Cycle
Authors: O’Hara Bruce F. , Watson Fiona L. , Srere Hilary K. , Kumar Himanshu , Wiler Steven W. , Welch Susan K. , Bitting Louise , Heller H. Craig , Kilduff Thomas S.
Published: April 2018

The purpose of this study was to characterize changes in gene expression in the brain of a seasonal hibernator, the golden-mantled ground squirrel,Spermophilus lateralis, during the hibernation season. Very little information is available on molecular changes that correlate with hibernation state, and what has been done focused mainly on seasonal changes in peripheral tissues. We produced over 4000 reverse transcription-PCR products from euthermic and hibernating brain and compared them using differential display. Twenty-nine of the most promising were examined by Northern analysis. Although some small differences were observed across hibernation states, none of the 29 had significant changes. However, a more direct approach, investigating expression of putative hibernation-responsive genes by Northern analysis, revealed an increase in expression of transcription factors c-fos, junB, and c-Jun, but not junD, commencing during late torpor and peaking during the arousal phase of individual hibernation bouts. In contrast, prostaglandin D2 synthase declined during late torpor and arousal but returned to a high level on return to euthermia. Other genes that have putative roles in mammalian sleep or specific brain functions, including somatostatin, enkephalin, growth-associated protein 43, glutamate acid decarboxylases 65/67, histidine decarboxylase, and a sleep-related transcript SD464 did not change significantly during individual hibernation bouts. We also observed no decline in total RNA or total mRNA during torpor; such a decline had been previously hypothesized. Therefore, it appears that the dramatic changes in body temperature and other physiological variables that accompany hibernation involve only modest reprogramming of gene expression or steady-state mRNA levels.
Enhanced Amphetamine- and K+-Mediated Dopamine Release in Rat Striatum after Repeated Amphetamine: Differential Requirements for Ca2+- and Calmodulin-Dependent Phosphorylation and Synaptic Vesicles
Authors: Kantor Lana , Hewlett G. H. Keikilani , Gnegy Margaret E.
Published: April 2018

After cessation of repeated, intermittent amphetamine, we detected an emergent Ca2+-dependent component of amphetamine-induced dopamine release and an increase in calmodulin and Ca2+- and calmodulin-dependent protein kinase activity in rat striatum. This study examined the involvement of calmodulin-dependent protein kinase II (CaM kinase II) and synaptic vesicles in the enhanced Ca2+-dependent dopamine release in response to amphetamine or K+in rat striatum. Rats were pretreated for 5 d with 2.5 mg/kg amphetamine or saline and withdrawn from drug for 10 d. The selective CaM kinase II inhibitor KN-93 (1 μm), but not the inactive analog KN-92, attenuated the Ca2+-dependent amphetamine-mediated dopamine release from amphetamine-pretreated rats but had no effect in saline-pretreated controls. [3H]Dopamine uptake was unaltered by repeated amphetamine or KN-93 and was Ca2+independent. Striatal dopamine release stimulated by 50 mmKCl was enhanced twofold after repeated amphetamine compared with that in saline controls but was unaffected by KN-93. To examine the requirement for dopaminergic vesicles in the Ca2+-dependent dopamine release, we administered reserpine to saline- and amphetamine-pretreated rats 1 d before killing. Reserpine pretreatment did not affect amphetamine-mediated dopamine release from either pretreatment group but completely ablated K+-mediated dopamine release. Reserpine did not disrupt the ability of 1 μmKN-93 to block the Ca2+-dependent amphetamine-mediated dopamine release from amphetamine-pretreated rats. The results indicate that the enhanced dopamine release elicited by amphetamine from chronically treated rats is dependent on Ca2+- and calmodulin-dependent phosphorylation and is independent of vesicular dopamine storage. On the contrary, the enhanced depolarization-mediated vesicular dopamine release is independent of Ca2+- and calmodulin-dependent phosphorylation.
Spontaneous Activity in Developing Turtle Retinal Ganglion Cells: Pharmacological Studies
Authors: Sernagor Evelyne , Grzywacz Norberto M.
Published: April 2018

Extracellular recordings were obtained from the ganglion cell (GC) layer during correlated spontaneous bursting activity (SBA) in the immature turtle retina. Pharmacological agents were bath-applied, and their effects on burst and correlation parameters were determined.

SBA requires synaptic transmission. It was blocked in the presence of curare and mecamylamine, two cholinergic nicotinic antagonists, and enhanced with neostigmine, a cholinesterase inhibitor. SBA was profoundly inhibited during blockade of glutamatergic receptors with the broad spectrum antagonist kynurenate and it vanished with 6,7-dinitroquinoxaline-2–3-dione (DNQX) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), two AMPA/kainate receptor antagonists. Blockade of NMDA receptors withd(−)-2-amino-5-phosphonopentanoic acid (d-AP-5) led only to a modest reduction in SBA. Blockade of GABAAreceptors with bicuculline prolonged the duration of the bursts. Inhibition of GABA uptake with nipecotic acid led to a decrease in burst rate. Blockade of K+channels with cesium (Cs+) and tetraethylammonium (TEA) led to a dramatic decrease in excitability. Burst propagation between neighboring GCs was reduced by K+channel blockade. Gap junction blockade had no consistent effect on bursts or correlation parameters. None of these drugs had a strong effect on the refractory period between bursts.

We conclude that correlated SBA in immature turtle GCs requires both cholinergic nicotinic and glutamatergic (mainly through AMPA/kainate receptors) synaptic transmission. GABAergic activity modulates the intensity and the duration of the bursts. Extracellular K+is involved in lateral activity propagation and increases retinal excitability, which may be required for burst generation.
Song-Induced Phosphorylation of cAMP Response Element-Binding Protein in the Songbird Brain
Authors: Sakaguchi Hironobu , Wada Kazuhiro , Maekawa Masao , Watsuji Toshikazu , Hagiwara Masatoshi
Published: April 2018

We have investigated the participation of cAMP response element-binding protein (CREB) in the response of the songbird brain to a natural auditory stimulus, a conspecific song. The cells in the two song control nuclei, the higher vocal center (HVC) and area X of zebra finches (Taeniopygia guttata), were intensely stained with an anti-CREB monoclonal antibody. Double-labeling studies showed that CREB immunoreactivity was detected only in area X-projecting neurons in the HVC. The cloned CREB cDNA from zebra finches (zCREB) is highly homologous to mammalian δ CREB. Phosphorylation of zCREB at Ser119in area X-projecting HVC neurons was induced by hearing tape-recorded conspecific songs of zebra finches, but not by birdsongs of another species or white noise. These results raise the possibility that zCREB plays a crucial role in the sensory process of song learning.