bluuebunny/crossref_metadata_2025 huggingface dataset:
GABA in the Nucleus Accumbens Shell Participates in the Central Regulation of Feeding Behavior
Authors: Stratford Thomas R. , Kelley Ann E.
Published: April 2018

We have demonstrated previously that injections of 6,7-dinitroquinoxaline-2,3-dione into the nucleus accumbens shell (AcbSh) elicits pronounced feeding in satiated rats. This glutamate antagonist blocks AMPA and kainate receptors and most likely increases food intake by disrupting a tonic excitatory input to the AcbSh, thus decreasing the firing rate of a population of local neurons. Because the application of GABA agonists also decreases neuronal activity, we hypothesized that administration of GABA agonists into the AcbSh would stimulate feeding in satiated rats. We found that acute inhibition of cells in the AcbSh via administration of the GABAAreceptor agonist muscimol or the GABABreceptor agonist baclofen elicited intense, dose-related feeding without altering water intake. Muscimol-induced feeding was blocked by coadministration of the selective GABAAreceptor blocker bicuculline, but not by the GABABreceptor blocker saclofen. Conversely, baclofen-induced feeding was blocked by coadministration of saclofen, but was not affected by bicuculline. Furthermore, we found that increasing local levels of GABA by administration of a selective GABA-transaminase inhibitor, γ-vinyl-GABA, elicited robust feeding in satiated rats, suggesting a physiological role for endogenous AcbSh GABA in the control of feeding. A mapping study showed that although some feeding can be elicited by muscimol injections near the lateral ventricles, the ventromedial AcbSh is the most sensitive site for eliciting feeding. These findings demonstrate that manipulation of GABA-sensitive cells in the AcbSh can have a pronounced, but specific, effect on feeding behavior in rats. They also constitute the initial description of a novel and potentially important component of the central mechanisms controlling food intake.
Ca2+- and Voltage-Dependent Inactivation of Ca2+Channels in Nerve Terminals of the Neurohypophysis
Authors: Branchaw Janet L. , Banks Matthew I. , Jackson Meyer B.
Published: April 2018

Ca2+channel inactivation was investigated in neurohypophysial nerve terminals by using patch-clamp techniques. The contribution of intracellular Ca2+to inactivation was evaluated by replacing Ca2+with Ba2+or by including BAPTA in the internal recording solution. Ca2+channel inactivation during depolarizing pulses was primarily voltage-dependent. A contribution of intracellular Ca2+was revealed by comparing steady-state inactivation of Ca2+channels with Ca2+current and with intracellular [Ca2+]. However, this contribution was small compared to that of voltage. In contrast to voltage-gated Ca2+channels in other preparations, in the neurohypophysis Ba2+substitution or intracellular BAPTA increased the speed of inactivation while reducing the steady-state level of inactivation. Ca2+channel recovery from inactivation was studied by using a paired-pulse protocol. The rate of Ca2+channel recovery from inactivation at negative potentials was increased dramatically by Ba2+substitution or intracellular BAPTA, indicating that intracellular Ca2+inhibits recovery. Stimulation with trains of brief pulses designed to mimic physiological bursts of electrical activity showed that Ca2+channel inactivation was much greater with 20 Hz trains than with 14 Hz trains. Inactivation induced by 20 Hz trains was reduced by intracellular BAPTA, suggesting an important role for Ca2+-dependent inactivation during physiologically relevant forms of electrical activity. Inhibitors of calmodulin and calcineurin had no effect on Ca2+channel inactivation, arguing against a mechanism of inactivation involving these Ca2+-dependent proteins. The inactivation behavior described here, in which voltage effects on Ca2+channel inactivation predominate at positive potentials and Ca2+effects predominate at negative potentials, may be relevant to the regulation of neuropeptide release.
Cortistatin Is Expressed in a Distinct Subset of Cortical Interneurons
Authors: de Lecea Luis , del Rio José Antonio , Criado José R. , Alcántara Soledad , Morales Marisela , Danielson Patria E. , Henriksen Steven J. , Soriano Eduardo , Sutcliffe J. Gregor
Published: April 2018

Cortistatin is a presumptive neuropeptide that shares 11 of its 14 amino acids with somatostatin. In contrast to somatostatin, administration of cortistatin into the rat brain ventricles specifically enhances slow wave sleep, apparently by antagonizing the effects of acetylcholine on cortical excitability. Here we show that preprocortistatin mRNA is expressed in a subset of GABAergic cells in the cortex and hippocampus that partially overlap with those containing somatostatin. A significant percentage of cortistatin-positive neurons is also positive for parvalbumin. In contrast, no colocalization was found between cortistatin and calretinin, cholecystokinin, or vasoactive intestinal peptide. During development there is a transient increase in cortistatin-expressing cells in the second postnatal week in all cortical areas and in the dentate gyrus. A transient expression of preprocortistatin mRNA in the hilar region at P16 is paralleled by electrophysiological changes in dentate granule cells. Together, these observations suggest mechanisms by which cortistatin may regulate cortical activity.
Contributions of Voltage-Gated Ca2+Channels in the Proximal versus Distal Dendrites to Synaptic Integration in Prefrontal Cortical Neurons
Authors: Seamans Jeremy K. , Gorelova Natalia A. , Yang Charles R.
Published: April 2018

The electrogenesis of synaptically activated dendritic Ca2+-mediated potentials, which may contribute to synaptic signal integration in pyramidal cells, was examined in rat layers V–VI prefrontal cortical (PFC) neuronsin vitro. Intrasomatically recorded suprathreshold synaptic responses evoked by stimulation of the distal dendrites were attenuated by focal Cd2+application to the proximal apical dendritic stem (100–200 μm from soma), but not to the apical dendritic tuft (>500 μm from soma). With use of intracellular QX-314 and Cs+to block Na+and K+currents, intrasomatic recordings revealed that the Cd2+-induced attenuation of synaptic responses was attributable to the blockade of a dendritic Ca2+-mediated “hump” potential and high-threshold Ca2+spike activated by NMDA EPSPs. The hump potential was not blocked by bath application of Ni2+(100 μm) but was blocked by focal application of Cd2+to the proximal but not distal apical dendrites, suggesting that it was generated by Ca2+channels located in the proximal dendrites. Direct patch-clamp recordings made from the distal apical tuft of layers V–VI PFC neurons revealed that layers I–II synaptic stimulation or intradendritic depolarizing current pulses evoked tetrodotoxin- and QX-314-sensitive Na+spikes. Unlike in the stem of the apical dendrite, Ca2+spikes were not easily evoked in the distal apical tuft when Na+channels were blocked. When triggered, the Cd2+-sensitive Ca2+spikes in the dendritic tuft were nonregenerative and had very high activation thresholds (approximately +10 mV). These results suggested that the high voltage-activated Ca2+potentials that amplify distal EPSPs are primarily generated in the proximal stem of the apical dendrite and not within the fine dendritic branches of the apical tuft of layers V–VI PFC neurons.
Mice Lacking the TNF 55 kDa Receptor Fail to Sleep More After TNFα Treatment
Authors: Fang Jidong , Wang Ying , Krueger James M.
Published: April 2018

Tumor necrosis factor (TNF) is a well characterized sleep-regulatory substance. To study receptor mechanisms for the sleep-promoting effects of TNF, sleep patterns were determined in control and TNF 55 kDa receptor knock-out (TNFR-KO) mice with a B6 × 129 background after intraperitoneal injections of saline or murine TNFα. The TNFR-KO mice had significantly less baseline sleep than the controls. TNFα dose-dependently increased non-rapid eye movement sleep (NREMS) in the controls but did not influence sleep in TNFR-KO mice. Although TNFR-KO mice failed to respond to TNFα, they had an increase in NREMS and a decrease in rapid eye movement sleep after interleukin-1β treatment. These results indicate that TNFα affects sleep via the 55 kDa receptor and provide further evidence that TNFα is involved in physiological sleep regulation. Current results also extend the list of species to mice in which TNFα and interleukin-1β are somnogenic.
Excitotoxic Lesions of the Amygdala Fail to Produce Impairment in Visual Learning for Auditory Secondary Reinforcement But Interfere with Reinforcer Devaluation Effects in Rhesus Monkeys
Authors: Málková Ludis̆e , Gaffan David , Murray Elisabeth A.
Published: April 2018

Aspiration lesions of the amygdala were found previously to produce a severe impairment in visual discrimination learning for auditory secondary reinforcement in rhesus monkeys (Gaffan and Harrison, 1987). To determine whether excitotoxic amygdala lesions would also produce this effect, we trained four naive rhesus monkeys on the same task. The monkeys were required to learn 40 new visual discrimination problems per session in a situation in which visual choices were guided by an auditory secondary reinforcer that had been previously associated with food reward. Bilateral excitotoxic lesions of the amygdala had no effect on the rate of learning visual discrimination problems for auditory secondary reinforcement. We also tested the amygdalectomized monkeys on a reinforcer devaluation task and compared their performance with a group of three normal monkeys. The monkeys first learned to discriminate 60 pairs of objects, baited with two different food rewards. Each of the food rewards was then devalued by selective satiation in two separate experimental sessions. Normal controls tended to avoid displacing objects that covered the devalued food to a significantly greater degree than did the amygdalectomized monkeys, indicating that the excitotoxic amygdala damage interfered with reinforcer devaluation effects. Our results are consistent with the idea that the amygdala is necessary for learning the association between stimuli and the value of particular food rewards; however, the amygdala is not necessary for maintaining the value of secondary reinforcers, once they have been learned.
dSLo Interacting Protein 1, a Novel Protein That Interacts with Large-Conductance Calcium-Activated Potassium Channels
Authors: Xia Xiao-ming , Hirschberg Birgit , Smolik Sarah , Forte Michael , Adelman John P.
Published: April 2018

Large-conductance calcium-activated potassium channels (BK channels) are activated by depolarized membrane potential and elevated levels of intracellular calcium. BK channel activity underlies the fast afterhyperpolarization that follows an action potential and attenuates neurotransmitter and hormone secretion. Using a modified two-hybrid approach, the interaction trap, we have identified a novel protein fromDrosophila, dSLIP1 (dSLo interacting protein), which specifically interacts withDrosophilaand human BK channels and has partial homology to the PDZ domain of α1 syntrophin. The dSLIP1 and dSlo mRNAs are expressed coincidently throughout theDrosophilanervous system, the two proteins interactin vitro, and they may be coimmunoprecipitated from transfected cells. Coexpression of dSLIP1 with dSlo or hSlo BK channels inXenopusoocytes results in reduced currents as compared with expression of BK channels alone; current amplitudes may be rescued by coexpression with the channel domain that interacts with dSLIP1. Single-channel recordings and immunostaining of transfected tissue culture cells suggest that dSLIP1 selectively reduces Slo BK currents by reducing the number of BK channels in the plasma membrane.
Reduction of O-LinkedN-Acetylglucosamine-Modified Assembly Protein-3 in Alzheimer’s Disease
Authors: Yao Pamela J. , Coleman Paul D.
Published: April 2018

Abnormal protein processing and modification is associated with Alzheimer’s disease (AD) pathology. The role of phosphorylation in AD has been studied extensively because the presumed abnormal phosphorylation of tau protein is believed to play a role in the formation of paired helical filaments. Glycosylation with O-linkedN-acetylglucosamine (O-GlcNAc) to serine and threonine residues is a dynamic protein modification of intracellular proteins, and it shares similar features with protein phosphorylation. In this study,O-GlcNAc glycosylation of proteins from autopsied human brains with confirmed AD and non-AD age-matched controls was examined.O-GlcNAcylation was demonstrated by labeling protein extracts with [3H]galactose in the presence of galactosyltransferase and subsequent analyses of saccharide–protein linkage and saccharide structure. The number ofO-GlcNAc-containing proteins and the overallO-GlcNAc level do not appear to be different between AD and control brain tissues. The only significant change observed is a marked reduction ofO-GlcNAcylated clathrin assembly protein-3 (AP-3) in AD. The reduction is more evident in brain neocortical regions, and there appears to be a negative correlation between O-glycosylated AP-3 and the density of neurofibrillary tangles. These data suggest a possible association between the O-glycosylated AP-3 and AD pathology.
Astrocytic Gap Junctions Remain Open during Ischemic Conditions
Authors: Cotrina Maria Luisa , Kang Jian , Lin Jane H-C , Bueno Earl , Hansen Thomas W. , He Lili , Liu Yulin , Nedergaard Maiken
Published: April 2018

Gap junctions are highly conductive channels that allow the direct transfer of intracellular messengers such as Ca2+and inositol triphosphate (IP3) between interconnected cells. In brain, astrocytes are coupled extensively by gap junctions. We found here that gap junctions among astrocytes in acutely prepared brain slices as well as in culture remained open during ischemic conditions. Uncoupling first occurred after the terminal loss of plasma membrane integrity. Gap junctions therefore may link ischemic astrocytes in an evolving infarct with the surroundings. The free exchange of intracellular messengers between dying and potentially viable astrocytes might contribute to secondary expansion of ischemic lesions.
Sensory Cells Determine Afferent Terminal Morphology in Cross-Innervated Electroreceptor Organs: Implications for Hair Cells
Authors: Zakon Harold , Lu Ying , Weisleder Pedro
Published: April 2018

Type I and type II hair cells of the vestibular system are innervated by afferents that form calyceal and bouton terminals, respectively. These cannot be experimentally cross-innervated in the inner ear to determine how they influence each other. However, analogous organs are accessible for transplantation and cross-innervation in the brown ghost electric fish. These fish possess three types of electroreceptor organs. Of these, the sensory receptors of the type I tuberous organ are S-100- and parvalbumin-positive with a calbindin-positive afferent that forms a large calyx around the organ. Neither the sensory receptors nor the afferents of the ampullary organs label with these antibodies, and the afferent branches form a single large bouton beneath each receptor cell. In controls, when cut ampullary afferents reinnervate transplanted ampullary organs, they have characteristic calbindin-negative terminals with large boutons. When type I tuberous afferents reinnervate ampullary organs, receptor cells remain S-100- and parvalbumin-negative, and the tuberous afferents still express calbindin. The nerve terminals, however, make large ampullary-like boutons on the receptor cells. These results suggest that (1) afferent terminal morphology is dictated by the receptor organ; (2) expression of calbindin by the afferent is not suppressed by innervation of the incorrect end organ; (3) ampullary organs generate ampullary receptor cells although innervated by tuberous afferents; and (4) ampullary receptor cells can be trophically supported by tuberous afferents.
The Second Messenger cAMP Elicits Eating by an Anatomically Specific Action in the Perifornical Hypothalamus
Authors: Gillard Elizabeth R. , Khan Arshad M. , Grewal Rickinder S. , Mouradi Bara , Wolfsohn Stefany D. , Stanley B. Glenn
Published: April 2018

We have previously shown that a membrane-permeant analog of cAMP, 8-bromo-cAMP (8-br-cAMP), elicits a vigorous eating response when microinjected into the perifornical hypothalamus (PFH) or lateral hypothalamus (LH) of satiated rats, suggesting that increases in cAMP in these areas may be important in the neural control of eating. To determine the locus of this effect, we compared the ability of 8-br-cAMP (1–100 nmol/0.3 μl) to elicit eating after microinjection into the PFH, LH, or the following bracketing areas: the anterior and posterior LH, paraventricular nucleus of the hypothalamus, thalamus, and amygdala. 8-br-cAMP at 50 nmol elicited eating (≥3.4 gm in 2 hr) exclusively in the PFH and LH. At 100 nmol, 8-br-cAMP elicited a larger response in these areas and elicited a smaller, more variable response in the thalamus. We similarly mapped the feeding-stimulatory effects of compounds that increase endogenous cellular cAMP in naive rats. Combined microinjection of matched doses (300 nmol) of 3-isobutyl-1-methylxanthine and 7-deacetyl-7-O-(N-methylpiperazino)-γ-butyryl-forskolin was effective exclusively in the PFH, eliciting an average 2 hr food intake of 8.4 ± 2.0 gm. Collectively, these results suggest that increases in cellular cAMP within a specific brain site, the PFH, may play a role in the neural stimulation of eating.
Facilitative Effects of the Ampakine CX516 on Short-Term Memory in Rats: Enhancement of Delayed-Nonmatch-to-Sample Performance
Authors: Hampson Robert E. , Rogers Gary , Lynch Gary , Deadwyler Sam A.
Published: April 2018

Ampakines are a family of drugs that selectively increase AMPA receptor-gated currents and improve performance on several behavioral tasks. This report describes evidence that ampakines cause a cumulative enhancement of performance in a spatial short-term memory task (Deadwyler et al., 1996). Two groups of rats were trained on a spatial variant of the delayed-nonmatch-to-sample (DNMS) paradigm. One group (n= 12) received the ampakine CX516 (Cortex Pharmaceuticals) alternated with vehicle for 17 consecutive days and then only vehicle for an additional 7 d. The second group (n= 6) received only vehicle injections over the same number of days. CX516 improved performance within sessions, particularly on trials with delays of 6–35 sec. In 9 of 12 rats, the positive effect of the drug was also present on nondrug days between CX516 administration and after cessation of CX516 injections. The animals that received only vehicle injections showed no improvement in DNMS performance over the entire 32 d of testing. Three of the 12 animals given CX516 did not exhibit “carryover” effects of the drug to the intervening (vehicle only) test sessions, but nonetheless exhibited superior performance during the first half of the session on days in which the ampakine was administered. Evaluation of errors suggests that the ampakine eliminated the necessity for a shift in response strategy that produced proactive interference on the following trial. Hippocampal involvement in these ampakine effects is discussed as a prelude to the second article in the series (Hampson et al., 1998).
Facilitative Effects of the Ampakine CX516 on Short-Term Memory in Rats: Correlations with Hippocampal Neuronal Activity
Authors: Hampson Robert E. , Rogers Gary , Lynch Gary , Deadwyler Sam A.
Published: April 2018

In the companion article (Hampson et al., 1998), the ampakine CX516 (Cortex Pharmaceuticals) was shown to produce a marked facilitation of performance of a spatial delayed-nonmatch-to-sample (DNMS) task in rats. Injections of the drug before each daily session produced a marked and progressive improvement in performance at longer delays (>5 sec) that persisted for 7 d after drug treatment was terminated. In most animals (n= 9) the increase in performance carried over to the intervening vehicle for days, whereas in others (n= 3) the effects dissipated within the session according to the pharmacological half-life of CX516. In this article we report firing correlates of simultaneously recorded cells in the CA1 and CA3 fields of the hippocampus over the period in which DNMS performance was facilitated by CX516. Sample and Delay period firing was enhanced by 100–350% under CX516 and increased progressively over days as did DNMS performance. The firing increases were restricted to correct trials only and were largest on trials with long delays. Firing in the intertrial interval was also altered, but in a manner consistent with a previously demonstrated reduction in between-trial proactive interference by CX516. Finally, in animals in which the effects of CX516 were restricted to when the drug was actually present (i.e., no carryover effects), increased cell firing also paralleled the time course of the performance increase. Results are discussed with respect to the actions of ampakines on hippocampal cellular and synaptic processes that underlie DNMS performance.
Dendritic Calcium Spike Initiation and Repolarization Are Controlled by Distinct Potassium Channel Subtypes in CA1 Pyramidal Neurons
Authors: Golding Nace L. , Jung Hae-yoon , Mickus Timothy , Spruston Nelson
Published: April 2018

In CA1 pyramidal neurons of the hippocampus, calcium-dependent spikes occurin vivoduring specific behavioral states and may be enhanced during epileptiform activity. However, the mechanisms that control calcium spike initiation and repolarization are poorly understood. Using dendritic and somatic patch-pipette recordings, we show that calcium spikes are initiated in the apical dendrites of CA1 pyramidal neurons and drive bursts of sodium-dependent action potentials at the soma. Initiation of calcium spikes at the soma was suppressed in part by potassium channels activated by sodium-dependent action potentials. Low-threshold, putative D-type potassium channels [blocked by 100 μm4-aminopyridine (4-AP) and 0.5–1 μmα-dendrotoxin (α-DTX)] played a prominent role in setting a high threshold for somatic calcium spikes, thus restricting initiation to the dendrites. DTX- and 4-AP-sensitive channels were activated during sodium-dependent action potentials and mediated a large component of their afterhyperpolarization. Once initiated, repetitive firing of calcium spikes was limited by activation of putative BK-type calcium-activated potassium channels (blocked by 250 μmtetraethylammonium chloride, 70 nmcharybdotoxin, or 100 nmiberiotoxin). Thus, the concerted action of calcium- and voltage-activated potassium channels serves to focus spatially and temporally the membrane depolarization and calcium influx generated by calcium spikes during strong, synchronous network excitation.
Modulation of the Light Response by cAMP inDrosophilaPhotoreceptors
Authors: Chyb Sylwester , Hevers Wulf , Forte Michael , Wolfgang William J. , Selinger Zvi , Hardie Roger C.
Published: April 2018

Phototransduction inDrosophilais mediated by a G-protein-coupled phospholipase C transduction cascade in which each absorbed photon generates a discrete electrical event, the quantum bump. In whole-cell voltage-clamp recordings, cAMP, as well as its nonhydrolyzable and membrane-permeant analogs 8-bromo-cAMP (8-Br-cAMP) and dibutyryl-cAMP, slowed down the macroscopic light response by increasing quantum bump latency, without changes in bump amplitude or duration. In contrast, cGMP or 8-Br-cGMP had no effect on light response amplitude or kinetics. None of the cyclic nucleotides activated any channels in the plasma membrane. The effects of cAMP were mimicked by application of the non-specific phosphodiesterase inhibitor IBMX and the adenylyl cyclase activator forskolin; zaprinast, a specific cGMP-phosphodiesterase inhibitor, was ineffective. Bump latency was also increased by targeted expression of either an activated Gsα subunit, which increased endogenous adenylyl cyclase activity, or an activated catalytic protein kinase A (PKA) subunit. The action of IBMX was blocked by pretreatment with the PKA inhibitor H-89. The effects of cAMP were abolished in mutants of theninaCgene, suggesting this nonconventional myosin as a possible target for PKA-mediated phosphorylation. Dopamine (10 μm) and octopamine (100 μm) mimicked the effects of cAMP. These results indicate the existence of a G-protein-coupled adenylyl cyclase pathway inDrosophilaphotoreceptors, which modulates the phospholipase C-based phototransduction cascade.
Evidence of Presynaptic Location and Function of the Prion Protein
Authors: Herms Jochen , Tings Tobias , Gall Stefan , Madlung Axel , Giese Armin , Siebert Heike , Schürmann Peter , Windl Otto , Brose Nils , Kretzschmar Hans
Published: April 2018

The prion protein (PrPC) is a copper-binding protein of unknown function that plays an important role in the etiology of transmissible spongiform encephalopathies. Using morphological techniques and synaptosomal fractionation methods, we show that PrPCis predominantly localized to synaptic membranes. Atomic absorption spectroscopy was used to identify PrPC-related changes in the synaptosomal copper concentration in transgenic mouse lines. The synaptic transmission in the presence of H2O2, which is known to be decomposed to highly reactive hydroxyl radicals in the presence of iron or copper and to alter synaptic activity, was studied in these animals. The response of synaptic activity to H2O2was found to correlate with the amount of PrPCexpression in the presynaptic neuron in cerebellar slice preparations from wild-type, Prnp0/0, and PrP gene-reconstituted transgenic mice. Thus, our data gives strong evidence for the predominantly synaptic location of PrPC, its involvement in the regulation of the presynaptic copper concentration, and synaptic activity in defined conditions.
Neonatal Partial Denervation Results in Nodal But Not Terminal Sprouting and a Decrease in Efficacy of Remaining Neuromuscular Junctions in Rat Soleus Muscle
Authors: Lubischer Jane L. , Thompson Wesley J.
Published: April 2018

Mature motoneurons respond to partial denervation of their target muscle by sprouting to reinnervate denervated fibers, thus maintaining muscle strength in the face of motoneuronal loss caused by injury or disease. Neonatal motoneurons, however, do not expand to innervate more muscle fibers. The present work seeks to understand this developmental change in motoneuron response to partial denervation. It has been suggested that neonatal motor units cannot increase in size because they are already at their maximum size (approximately five times larger than in adulthood). We ruled out this explanation by showing that after partial denervation on postnatal day 14 (P14), when motor units have decreased to their adult size, motoneurons still did not sprout to reinnervate as many fibers as in adulthood. Instead, we found evidence supporting an alternative explanation involving terminal Schwann cells. After partial denervation of neonatal (but not adult) muscles, terminal Schwann cells at denervated endplates undergo apoptosis. We found that terminal (but not nodal) sprouting was absent in partially denervated neonatal muscles. This finding suggests that terminal Schwann cells, previously reported to guide terminal sprouts to denervated endplates in adult muscles, are necessary for the formation and growth of terminal sprouts. Moreover, partial denervation on P14 severely weakened the remaining, uninjured synapses, suggesting that neonatal motoneurons may withdraw terminals after the denervation of nearby fibers. These findings have implications for the interpretation of previous studies on synapse elimination and offer insight into the failure of young motor units to expand after partial denervation.
Sonic hedgehogRegulates Proliferation and Inhibits Differentiation of CNS Precursor Cells
Authors: Rowitch David H. , St.-Jacques Benoit , Lee Scott M. K. , Flax Jonathon D. , Snyder Evan Y. , McMahon Andrew P.
Published: April 2018

Activation of the Sonic hedgehog (Shh) signal transduction pathway is essential for normal pattern formation and cellular differentiation in the developing CNS. However, it is also thought to be etiological in primitive neuroectodermal tumors. We adaptedGAL4/UASmethodology to ectopically express full-lengthShhin the dorsal neural tube of transgenic mouse embryos commencing at 10 d postcoitum (dpc), beyond the period of primary dorsal–ventral pattern formation and floorplate induction. Expression ofShhwas maintained until birth, permitting us to investigate effects of ongoing exposure to Shh on CNS precursorsin vivo. Proliferative rates of spinal cord precursors were twice that of wild-type littermates at 12.5 dpc. In contrast, at late fetal stages (18.5 dpc), cells that were Shh-responsive but postmitotic were present in persistent structures reminiscent of the ventricular zone germinal matrix. This tissue remained blocked in an undifferentiated state. These results indicate that cellular competence restricts the proliferative response to Shhin vivoand provide evidence that proliferation and differentiation can be regulated separately in precursor cells of the spinal cord. Thus, Hedgehog signaling may contribute to CNS tumorigenesis by directly enhancing proliferation and preventing neural differentiation in selected precursor cells.
Bovine CNS Myelin Contains Neurite Growth-Inhibitory Activity Associated with Chondroitin Sulfate Proteoglycans
Authors: Niederöst Barbara P. , Zimmermann Dieter R. , Schwab Martin E. , Bandtlow Christine E.
Published: April 2018

The absence of fiber regrowth in the injured mammalian CNS is influenced by several different factors and mechanisms. Besides the nonconducive properties of the glial scar tissue that forms around the lesion site, individual molecules present in CNS myelin and expressed by oligodendrocytes, such as NI-35/NI-250, bNI-220, and myelin-associated glycoprotein (MAG), have been isolated and shown to inhibit axonal growth. Here, we report an additional neurite growth-inhibitory activity purified from bovine spinal cord myelin that is not related to bNI-220 or MAG. This activity can be ascribed to the presence of two chondroitin sulfate proteoglycans (CSPGs), brevican and the brain-specific versican V2 splice variant. Neurite outgrowth of neonatal cerebellar granule cells and of dorsal root ganglion neuronsin vitrowas strongly inhibited by this myelin fraction enriched in CSPGs. Immunohistochemical staining revealed that brevican and versican V2 are present on the surfaces of differentiated oligodendrocytes. We provide evidence that treatment of oligodendrocytes with the proteoglycan synthesis inhibitors β-xylosides can strongly influence the growth permissiveness of oligodendrocytes. β-Xylosides abolished cell surface presentation of brevican and versican V2 and reversed growth cone collapse in encounters with oligodendrocytes as demonstrated by time-lapse video microscopy. Instead, growth cones were able to grow along or even into the processes of oligodendrocytes. Our results strongly suggest that brevican and versican V2 are additional components of CNS myelin that contribute to its nonpermissive substrate properties for axonal growth. Expression of these CSPGs on oligodendrocytes may indicate that they participate in the restriction of structural plasticity and regeneration in the adult CNS.
Methamphetamine-Induced Neurotoxicity Alters Locomotor Activity, Stereotypic Behavior, and Stimulated Dopamine Release in the Rat
Authors: Wallace Tanya L. , Gudelsky Gary A. , Vorhees Charles V.
Published: April 2018

The neurochemical evidence of methamphetamine (MA)-induced toxicity to dopaminergic nerve terminals is well documented; however, the functional consequences are not clearly defined. The present study was designed to investigate whether MA-induced dopamine depletions affect locomotor activity, stereotypic behavior, and/or extracellular dopamine concentrations in the neostriatum. Male rats were treated with a neurotoxic regimen of MA (10 mg/kg, i.p., every 2 hr for four injections) or vehicle and tested for functional effects 1 week later. Animals that had received the neurotoxic regimen of MA showed a reduction in both caudate nucleus and nucleus accumbens dopamine contents of 56 and 30%, respectively. Furthermore, MA-treated rats exhibited a significant attenuation in spontaneous activity, as well as a significant diminution in MA (low dose)-stimulated locomotor activity as compared to vehicle-treated rats. However, there were no differences in the MA (low dose)-induced increases in extracellular dopamine concentrations in the caudate nucleus or the nucleus accumbens core of either group. Interestingly, the acute administration of higher doses of MA elicited a significantly augmented stereotypic response and a significantly attenuated increase in the extracellular concentration of dopamine in the caudate nucleus of rats treated with a neurotoxic regimen of MA as compared to vehicle-treated animals. These data indicate that MA-induced neurotoxicity results in abnormal dopamine-mediated behaviors, as well as a brain region-specific impairment in stimulated dopamine release.
Dopamine Receptors and Groups I and II mGluRs Cooperate for Long-Term Depression Induction in Rat Prefrontal Cortex through Converging Postsynaptic Activation of MAP Kinases
Authors: Otani Satoru , Auclair Nathalie , Desce Jean-Marie , Roisin Marie-Paule , Crépel Francis
Published: April 2018

Tetanic stimuli to layer I–II afferents in rat prefrontal cortex induced long-term depression (LTD) of layer I–II to layer V pyramidal neuron glutamatergic synapses when tetani were coupled to bath application of dopamine. This LTD was blocked by the following metabotropic glutamate receptor (mGluR) antagonists coapplied with dopamine: (S)-α-methyl-4-carboxyphenylglycine (MCPG; group I and II antagonist), (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA; group I antagonist), or (RS)-α-methylserine-O-phosphate monophenyl ester (MSOPPE; group II antagonist). This suggests that the dopamine-facilitated LTD requires synaptic activation of groups I and II mGluRs during tetanus. LTD could also be induced by coupling tetani to bath application of groups I and II mGluR agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD). In the next series of experiments, coapplication of dopamine and 1S,3R-ACPD, but not application of either drug alone, consistently induced LTD without tetani or even single test stimuli during drug application, suggesting that coactivation of dopamine receptors and the mGluRs is sufficient for LTD induction. Immunoblot analyses with anti-active mitogen-activated protein kinases (MAP-Ks) revealed that D1 receptors, D2 receptors, group I mGluRs, and group II mGluRs all contribute to MAP-K activation in prefrontal cortex, and that combined activation of dopamine receptors and mGluRs synergistically or additively activate MAP-Ks. Consistently, LTD by dopamine + 1S,3R-ACPD coapplication, as well as the two other forms of LTD (LTD by dopamine + tetani and LTD by 1S,3R-ACPD + tetani), was blocked by bath application of MAP-K kinase inhibitor PD98059. LTD by dopamine + 1S,3R-ACPD coapplication was also blocked by postsynaptic injection of synthetic MAP-K substrate peptide. Our results suggest that dopamine receptors and groups I and II mGluRs cooperate to induce LTD through converging postsynaptic activation of MAP-Ks.
Subcellular Localization of Tetanus Neurotoxin-Insensitive Vesicle-Associated Membrane Protein (VAMP)/VAMP7 in Neuronal Cells: Evidence for a Novel Membrane Compartment
Authors: Coco Silvia , Raposo Graca , Martinez Sonia , Fontaine Jean-Jacques , Takamori Shigeo , Zahraoui Ahmed , Jahn Reinhard , Matteoli Michela , Louvard Daniel , Galli Thierry
Published: April 2018

The clostridial neurotoxin-insensitive solubleN-ethylmaleimide-sensitive factor attachment protein (SNAP) receptors, tetanus neurotoxin-insensitive (TI)-vesicle-associated membrane protein (VAMP)/VAMP7, SNAP23, and syntaxin 3 have recently been implicated in transport of exocytotic vesicles to the apical plasma membrane of epithelial cells. This pathway had been shown previously to be insensitive to tetanus neurotoxin and botulinum neurotoxin F. TI-VAMP/VAMP7 is also a good candidate to be implicated in an exocytotic pathway involved in neurite outgrowth because tetanus neurotoxin does not inhibit this process in conditions in which it abolishes neurotransmitter release. We have now found that TI-VAMP/VAMP7 has a widespread distribution in the adult rat brain in which its localization strikingly differs from that of nerve terminal markers. TI-VAMP/VAMP7 does not enrich in synaptic vesicles nor in large dense-core granules but is associated with light membranes. In hippocampal neurons developingin vitro, TI-VAMP/VAMP7 localizes to vesicles in the axonal and dendritic outgrowths and concentrates into the leading edge of the growth cone, a region devoid of synaptobrevin 2, before synaptogenesis. After the onset of synaptogenesis, TI-VAMP/VAMP7 is found predominantly in the somatodendritic domain. In PC12 cells, TI-VAMP/VAMP7 does not colocalize with synaptobrevin 2, chromogranin B, or several markers of endocytic compartments. At the electron microscopic level, TI-VAMP/VAMP7 is mainly associated with tubules and vesicles. Altogether, these results suggest that TI-VAMP/VAMP7 defines a novel membrane compartment in neurite outgrowths and in the somatodendritic domain.
Expression of the Voltage-Gated Chloride Channel ClC-2 in Rod Bipolar Cells of the Rat Retina
Authors: Enz Ralf , Ross Brenda J. , Cutting Garry R.
Published: April 2018

Voltage-gated chloride channels (ClC) are highly conserved during evolution and appear to participate in a variety of physiological functions. Recently, ClC-2 was proposed to play a role in stabilizing the chloride equilibrium potential near or below the resting membrane potential in neurons expressing ligand-gated chloride channels. Because rod bipolar cells in mammalian retina express three forms of inhibitory ligand-gated chloride channels, we decided to study ClC-2 localization and function in the rat retina. RNA encoding ClC-1, -2, -3, -4, and -5 was detected by reverse transcription-PCR in the rat retina. ClC-2-specific antibodies identified protein on cell bodies and in synaptic layers. Double-immunofluorescence staining revealed that intense ClC-2 immunoreactivity colocalized with PKC-stained rod bipolar cells. Patch-clamp experiments performed with individual rod bipolar cells demonstrated the presence of a time-dependent, inwardly rectified current activated at hyperpolarizing membrane potentials. This current demonstrated selectivity for different anions (Cl−> I−> gluconate), was inhibited by Cd2+, and was minimally reduced by 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid. These features are consistent with currents generated by ClC-2 channels. Our data indicate that functional ClC-2 channels are present in retinal rod bipolar cells and support a role for ClC-2 in maintaining Cl−homeostasis in neurons with ligand-gated chloride channels.
Development of a Glia-Rich Axon-Sorting Zone in the Olfactory Pathway of the MothManduca sexta
Authors: Rössler Wolfgang , Oland Lynne A. , Higgins Mark R. , Hildebrand John G. , Tolbert Leslie P.
Published: April 2018

Olfactory receptor cells (ORCs) of a particular odor tuning are dispersed in the olfactory epithelium, but their axons converge on distinct glomeruli in primary olfactory centers. As a consequence, axon associations must change to bring axons of ORCs with the same odor specificity together. Studies inManduca sextahave indicated that just before they enter the antennal lobe (AL), ORC axons undergo extreme reorganization, finally entering the AL in fascicles destined for subsets of glomeruli. This axon-sorting zone is heavily populated by glial cells, and ORC axon growth cones often are in close physical contact with the glia. In moths rendered glia deficient, ORC axons fail to fasciculate in this region. Using propidium iodide to label nuclei and 5-bromo-2′-deoxyuridine to monitor proliferation, we found that the glia in the sorting zone arise from the AL, appearing shortly after the first ORC axons arrive. Experimental removal of some or all of the sensory innervation revealed that proliferation of sorting-zone glia is triggered by ORC axons. A second set of glia arises in the antenna and migrates along the antennal nerve toward the brain, populating the nerve after the establishment of the sorting zone. Development of this type of glial cell is independent of contact of the ORC axons with their central targets. We conclude that the sorting zone arises from CNS glia in response to ingrowth of ORC axons, and a critical number of glia must be present in the sorting zone for axons to correctly establish new neighbor–neighbor associations.
The Extracellular Matrix Modulates Olfactory Neurite Outgrowth on Ensheathing Cells
Authors: Tisay Katarina T. , Key Brian
Published: April 2018

Primary olfactory axons grow along a stereotypical pathway from the nasal cavity to the olfactory bulb through an extracellular matrix rich in laminin and heparan sulfate proteoglycans (HSPGs) and bounded by the expression of chondroitin sulfate proteoglycans (CSPGs). This pathway is pioneered by olfactory ensheathing cells, which provide a substrate conducive for axon growth during early development. In the present study, we examined the effect of several extracellular matrix constituents on the spreading and migration, as well as the neurite outgrowth-promoting properties, of olfactory ensheathing cells. Laminin and Matrigel enhanced the spreading and migration of olfactory ensheathing cells and increased their neurite outgrowth-promoting activity. In contrast, HSPG and CSPG had little effect on the spreading and migration of olfactory ensheathing cells and hence did not promote olfactory neurite outgrowth.In vitroolfactory axons grew preferentially on the surface of olfactory ensheathing cells rather than the underlying extracellular matrix. We propose that olfactory ensheathing cells secrete laminin and HSPGs, which together with other cofactors, stimulate these cells to migrate and adopt a neurite outgrowth-promoting phenotype. Expression of CSPGs in the surrounding mesenchyme confines the growth of ensheathing cells, as well as the axons, which grow on the surface of these cells, to a specific pathway. Thus, the ECM indirectly modulates the growth and guidance of olfactory axons during development.
Altered Midline Axon Pathways and Ectopic Neurons in the Developing Hypothalamus of Netrin-1- and DCC-Deficient Mice
Authors: Deiner Michael S. , Sretavan David W.
Published: April 2018

Optic nerve formation in mouse involves interactions between netrin-1 at the optic disk and the netrin-1 receptor DCC (deleted in colorectal cancer) expressed on retinal ganglion cell (RGC) axons. Deficiency in either protein causes RGC pathfinding defects at the disk leading to optic nerve hypoplasia (Deiner et al., 1997). Here we show that further along the visual pathway, RGC axons in netrin-1- or DCC-deficient mice grow in unusually angular trajectories within the ventral hypothalamus. In heterozygousSeyneumice that also have a small optic nerve, RGC axon trajectories appear normal, indicating that the altered RGC axon trajectories in netrin-1 and DCC mutants are not secondarily caused by optic nerve hypoplasia. Intrinsic hypothalamic patterning is also affected in netrin-1 and DCC mutants, including a severe reduction in the posterior axon projections of gonadotropin-releasing hormone neurons. In addition to axon pathway defects, antidiuretic hormone and oxytocin neurons are found ectopically in the ventromedial hypothalamus, apparently no longer confined to the supraoptic nucleus in mutants. In summary, netrin-1 and DCC, presumably via direct interactions, govern both axon pathway formation and neuronal position during hypothalamic development, and loss of netrin-1 or DCC function affects both visual and neuroendocrine systems. Netrin protein localization also indicates that unlike in more caudal CNS, guidance about the hypothalamic ventral midline does not require midline expression of netrin.
BDNF Modulates, But Does Not Mediate, Activity-Dependent Branching and Remodeling of Optic Axon ArborsIn Vivo
Authors: Cohen-Cory Susana
Published: April 2018

The proper development of axon terminal arbors and their recognition of target neurons depend, in part, on neuronal activity. Neurotrophins are attractive candidate signals to participate in activity-dependent development and refinement of neuronal connectivity. In the visual system, brain-derived neurotrophic factor (BDNF) has been shown to modulate the elaboration and refinement of axonal arbors and to participate in the establishment of topographically ordered visual maps. By examiningin vivowith time-lapse microscopy the effects of activity blockade and BDNF on optic axon arborization, I show that the dynamic mechanisms by which neurotrophins and neuronal activity regulate axon arborization differ. Acute retinal activity blockade by intraocular injection of tetrodotoxin (TTX) rapidly and significantly increased branch addition and elimination, thus interfering with axon branch stabilization. The effects of activity blockade on branch dynamics resulted in increased arbor complexity in the long term and were prevented by altering endogenous BDNF levels at the target. BDNF promoted axon arborization by increasing branch addition and lengthening, without affecting branch elimination. Activity blockade, however, did not prevent the growth-promoting effects of BDNF, indicating that BDNF can affect axon arborization even in the absence of activity. Together this evidence indicates that BDNF acts as a modulator, but not as a direct mediator, of activity during the morphological development of neurons. Consequently, neuronal activity and BDNF use distinct but interactive mechanisms to control the development of neuronal connectivity; BDNF modulates axon arborization by promoting growth, neuronal activity participates in axon branch stabilization, and together these two signals converge to shape axon form.
Gaze Direction Modulates Finger Movement Activation Patterns in Human Cerebral Cortex
Authors: Baker Justin T. , Donoghue John P. , Sanes Jerome N.
Published: April 2018

We investigated whether gaze direction modified the pattern of finger movement activation in human cerebral cortex using functional magnetic resonance imaging (MRI). Participants performed a sequential finger-tapping task or made no finger movements while maintaining gaze in the direction of the moving hand (aligned conditions) or away from the location of the moving hand. Functional MR signals, measured in the hemisphere contralateral to the moving hand, revealed finger movement-related activation in primary motor cortex, lateral and medial premotor cortex, and a wide extent of the lateral superior and inferior parietal lobules. In each area, the extent of the finger movement activation increased when static gaze was more aligned with the moving hand compared to when gaze was directed away from the moving hand. These data suggest the existence of large-scale cortical networks related to finger actions and indicate that skeletomotor processing in the cerebral cortex is consistently modified by gaze direction signals.