bluuebunny/crossref_metadata_2025 huggingface dataset:
Cellular Localization of the Prohormone Convertases in the Hypothalamic Paraventricular and Supraoptic Nuclei: Selective Regulation of PC1 in Corticotrophin-Releasing Hormone Parvocellular Neurons Mediated by Glucocorticoids
Authors: Dong Weijia , Seidel Bertolt , Marcinkiewicz Mieczyslaw , Chrétien Michel , Seidah Nabil G. , Day Robert
Published: April 2018

The prohormone convertases (PCs) are processing enzymes that activate proproteins via cleavage at specific single or pairs of basic residues. The hypothalamic paraventricular nucleus (PVN) and supraoptic nucleus (SON) are primary sites of biosynthesis of several neuroendocrine hormone precursors, including provasopressin (pro-AVP), pro-oxytocin (pro-OT), and procorticotrophin-releasing hormone (pro-CRH), which require post-translational processing to yield active products. Usingin situhybridization, we observed PC1 and PC5 mRNAs in PVN and SON magnocellular neurons, while PC2 mRNA was observed in both magnocellular and parvocellular PVN neurons as well as magnocellular SON neurons. Similar to furin, PC7 mRNA was expressed throughout the PVN and SON, whereas PACE4 mRNA levels were undetectable. Both immunohistochemical and Western blot studies were performed to demonstrate the presence of PC proteins and forms in the PVN and SON. Using double-labelingin situhybridization, we examined the cellular colocalization of each PC mRNA with pro-AVP, pro-OT, and pro-CRH mRNAs in PVN and SON. PC1 mRNA was colocalized with both AVP and OT mRNA in PVN and SON magnocellular neurons. All AVP, OT, and CRH neurons expressed PC2. In contrast, PC5 mRNA was colocalized only with OT mRNA. We examined the effects of adrenalectomy (ADX) on PVN PC mRNA levels. PC1 mRNA levels were increased selectively within CRH/AVP parvocellular neurons but were unchanged in PVN magnocellular AVP or OT neurons. These results established the anatomical organization of each convertase and proneuropeptide substrates in the PVN and SON and suggested potential roles for each enzyme under resting and stimulated conditions.
Oscillatory γ-Band (30–70 Hz) Activity Induced by a Visual Search Task in Humans
Authors: Tallon-Baudry Catherine , Bertrand Olivier , Delpuech Claude , Pernier Jacques
Published: April 2018

The coherent representation of an object in the visual system has been suggested to be achieved by the synchronization in the γ-band (30–70 Hz) of a distributed neuronal assembly. Here we measure variations of high-frequency activity on the human scalp. The experiment is designed to allow the comparison of two different perceptions of the same picture. In the first condition, an apparently meaningless picture that contained a hidden Dalmatian, a neutral stimulus, and a target stimulus (twirled blobs) are presented. After the subject has been trained to perceive the hidden dog and its mirror image, the second part of the recordings is performed (condition 2). The same neutral stimulus is presented, intermixed with the picture of the dog and its mirror image (target stimulus). Early (95 msec) phase-locked (or stimulus-locked) γ-band oscillations do not vary with stimulus type but can be subdivided into an anterior component (38 Hz) and a posterior component (35 Hz). Non-phase-locked γ-band oscillations appear with a latency jitter around 280 msec after stimulus onset and disappear in averaged data. They increase in amplitude in response to both target stimuli. They also globally increase in the second condition compared with the first one. It is suggested that this γ-band energy increase reflects both bottom-up (binding of elementary features) and top-down (search for the hidden dog) activation of the same neural assembly coding for the Dalmatian. The relationships between high- and low-frequency components of the response are discussed, and a possible functional role of each component is suggested.
The Neuronal Basis of the Behavioral Choice between Swimming and Shortening in the Leech: Control Is Not Selectively Exercised at Higher Circuit Levels
Authors: Shaw Brian K. , Kristan Jr. William B.
Published: April 2018

Swimming and the whole-body shortening reflex are two incompatible behaviors performed by the medicinal leechHirudo medicinalis. We set out to examine the neuronal basis of the choice between these behaviors, taking advantage of the fact that the neuronal circuit underlying swimming is relatively well understood. The leech swim circuit is organized hierarchically and contains three interneuronal levels, including two upper levels of “command-like” neurons. We tested the responses of the swim circuit neurons to stimuli that produced shortening, using reduced preparations in which neurophysiological recording could be performed while behaviors were elicited. We found that the majority of the swim circuit neurons, including most of the command-like cells and all of the cells at the highest hierarchical level of the circuit, were excited by stimuli that produced shortening as well as by stimuli that produced swimming. Only a subset of neurons, at levels below the top, were inhibited during shortening; these included one of the command-like cells and an oscillator cell (an interneuron that is part of the central pattern generator for swimming). These results imply that the control of the choice between swimming and shortening is not exercised selectively at the higher levels of the swim circuit.
Effect of Mutations in Vesicle-Associated Membrane Protein (VAMP) on the Assembly of Multimeric Protein Complexes
Authors: Hao Joe C. , Salem Natalie , Peng Xiao-Rong , Kelly Regis B. , Bennett Mark K.
Published: April 2018

The assembly of multimeric protein complexes that include vesicle-associated membrane protein 2 (VAMP-2) and the plasma membrane proteins syntaxin 1A and synaptosome-associated protein of 25 kDa (SNAP-25) are thought to reflect the biochemical correlates of synaptic vesicle targeting, priming, or fusion. Using a variety of protein–protein interaction assays and a series of deletion and point mutations, we have investigated the domains of VAMP-2 required for the formation of binary complexes with either syntaxin 1A or SNAP-25 and ternary complexes with both syntaxin 1A and SNAP-25. Deletions within the central conserved domain of VAMP-2 eliminated binding to either syntaxin 1A or both syntaxin 1A and SNAP-25. Although all of the deletion mutants were able to form ternary complexes, only some of these complexes were resistant to denaturation in sodium dodecyl sulfate. These results demonstrate that cooperative interactions result in the formation of at least two biochemically distinct classes of ternary complex. Two point mutations previously shown to have effects on the intracellular trafficking of VAMP-2 (M46A, reduced endocytosis and sorting to synaptic vesicles; N49A, enhanced sorting to synaptic vesicles) lie within a domain required for both syntaxin 1A and SNAP-25 binding. Syntaxin 1A and SNAP-25 binding was reduced by the M46A mutation and enhanced by the N49A mutation, suggesting that a correlation exists between the membrane-trafficking phenotype of the two VAMP-2 point mutants and their competence to form complexes with either syntaxin 1A or SNAP-25.
Expression of Neuregulins and their Putative Receptors, ErbB2 and ErbB3, Is Induced during Wallerian Degeneration
Authors: Carroll Steven L. , Miller Michele L. , Frohnert Paul W. , Kim Susanne S. , Corbett John A.
Published: April 2018

Schwann cell dedifferentiation and proliferation is a prerequisite to axonal regeneration in the injured peripheral nervous system. The neuregulin (NRG) family of growth and differentiation factors may play a particularly important role in this process, because these axon-associated molecules are potent Schwann cell mitogens and differentiation factorsin vitro. We have examined Schwann cell DNA synthesis and the expression of NRGs and their receptors, the erbB membrane tyrosine kinases, in rat sciatic nerve, sensory ganglia, and spinal cord 0–30 d postaxotomy. Analysis of NRG cDNAs from these tissues revealed several novel splice variants and showed that cells endogenous to injured nerve express NRG mRNAs. A selective induction of mRNAs encoding the glial growth factor (GGF) subfamily of NRGs occurs in nerve beginning 3 d postaxotomy and thus coincides with the onset of Schwann cell DNA synthesis. In later stages of Wallerian degeneration, however, Schwann cell mitogenesis markedly decreases, whereas elevated GGF expression persists. Of the four known erbB kinases, Schwann cells express both erbB2 and erbB3 receptors over the entire interval studied. Expression of erbB2 and erbB3 is coordinately induced in response to axotomy, indicating that Schwann cell responses to NRGs may be modulated by changes in receptor density. Neuregulin (including transmembrane precursors) and erbB protein are associated with Schwann cells postaxotomy. Thus, in contrast to the concept of NRGs as axon-associated mitogens, our findings suggest that NRGs produced by Schwann cells themselves may be partially responsible for Schwann cell proliferation during Wallerian degeneration, probably acting via autocrine or paracrine mechanisms.
Melatonin Prevents Death of Neuroblastoma Cells Exposed to the Alzheimer Amyloid Peptide
Authors: Pappolla Miguel A. , Sos Melisa , Omar Rawhi A. , Bick Roger J. , Hickson-Bick Diane L. M. , Reiter Russel J. , Efthimiopoulos Spiros , Robakis Nickolaos K.
Published: April 2018

Studies from several laboratories have generated evidence suggesting that oxidative stress is involved in the pathogenesis of Alzheimer’s disease (AD). The finding that the amyloid β protein (Aβ) has neurotoxic properties and that such effects are, in part, mediated by free radicals has provided insights into mechanisms of cell death in AD and an avenue to explore new therapeutic approaches. In this study we demonstrate that melatonin, a pineal hormone with recently established antioxidant properties, is remarkably effective in preventing death of cultured neuroblastoma cells as well as oxidative damage and intracellular Ca2+increases induced by a cytotoxic fragment of Aβ. The effects of melatonin were extremely reproducible and corroborated by multiple quantitative methods, including cell viability studies by confocal laser microscopy, electron microscopy, and measurements of intracellular calcium levels. The importance of this finding is that, in contrast to conventional antioxidants, melatonin has a proposed physiological role in the aging process. Secretion levels of this hormone are decreased in aging and more severely reduced in AD. The reported phenomenon may be of therapeutic relevance in AD.
Pharmacology and Distribution of Norepinephrine Transporters in the Human Locus Coeruleus and Raphe Nuclei
Authors: Ordway Gregory A. , Stockmeier Craig A. , Cason Garrick W. , Klimek Violetta
Published: April 2018

The norepinephrine transporter (NET) is a site of action for tricyclic antidepressant drugs and for drugs of abuse such as amphetamine and cocaine. In this study, the binding of [3H]nisoxetine to NETs in the noradrenergic cell group, the locus coeruleus, and the serotonergic cell groups, the dorsal raphe nuclei, was measured autoradiographically in postmortem human brain. [3H]nisoxetine binding was unevenly distributed along the rostral–caudal axis of the locus coeruleus and correlated positively with numbers of neuromelanin-containing (noradrenergic) cells along the axis of the locus coeruleus within individuals. Binding densities of [3H]nisoxetine in dorsal raphe nuclei were similar to that in the locus coeruleus. [3H]nisoxetine binding was unevenly distributed along the entire rostral–caudal extent of the dorsal raphe, with the highest binding occurring in the interfascicular and ventral nuclei. A moderate amount of [3H]nisoxetine binding was also observed in the median raphe nucleus. The specificity of [3H]nisoxetine binding to NETs in monoaminergic nuclei was assessed by measuring the inhibition of its binding by desipramine, imipramine, or citalopram. The order of affinities of these drugs was identical in the locus coeruleus and dorsal and median raphe and was characteristic of binding to NETs (desipramine > imipramine > citalopram). Thus, high levels of NETs and an uneven distribution of NETs occur in the locus coeruleus as well as in the dorsal raphe nuclei of the human.
Sleep and Sleep Regulation in Normal and Prion Protein-Deficient Mice
Authors: Tobler Irene , Deboer Tom , Fischer Marek
Published: April 2018

Mice are the preferred mammalian species for genetic investigations of the role of proteins. The normal function of the prion protein (PrP) is unknown, although it plays a major role in the prion diseases, including fatal familial insomnia. We investigated its role in sleep and sleep regulation by comparing baseline recordings and the effects of sleep deprivation in PrP knockout mice (129/SV) and wild-type controls (129/SV × C57BL/6), which are the mice used for most gene targeting experiments and whose behavior is not well characterized. Although no difference was evident in the amount of vigilance states, the null mice exhibited a larger degree of sleep fragmentation than the wild-type with almost double the amount of short waking episodes. As in other rodents, cortical temperature closely reflected the time course of waking. The increase of slow-wave activity (SWA; mean EEG power density in the 0.25–4.0 Hz range) at waking to nonrapid eye movement (NREM) sleep transitions was faster and reached a lower level in the null mice than in the wild-type. The contribution of the lower frequencies (0.25–5.0 Hz) to the spectrum was smaller than in other rodents in all three vigilance states, and the distinction between NREM sleep and REM sleep was most marked in the theta band. After the sleep deprivation, SWA was increased, but the changes in EEG power density and SWA were more prominent and lasted longer in the PrP-null mice. Our results suggest that PrP plays a role in promoting sleep continuity.
Inhibition of Transmitter Release Correlates with the Proteolytic Activity of Tetanus Toxin and Botulinus Toxin A in Individual Cultured Synapses ofHirudo medicinalis
Authors: Bruns Dieter , Engers Silke , Yang Clement , Ossig Rainer , Jeromin Andreas , Jahn Reinhard
Published: April 2018

We have studied the effects of tetanus toxin and botulinus toxin A on neurotransmitter release in the Retzius→P-cell synapse of the leech and exploited the unique properties of this system, which allow for combined physiological and biochemical analyses in single-cell pairs. The sequences ofHirudo medicinalissynaptobrevin and synaptosomal-associated protein of 25 kDa (SNAP-25), deduced by cDNA cloning, are 61 and 55% identical, respectively, to their corresponding mammalian homologs. WhereasHirudosynaptobrevin is proteolyzed by tetanus toxin, its SNAP-25 isoform is resistant to botulinus toxin A cleavage because of amino acid substitutions within and around the putative cleavage site. In close correlation, microinjection of tetanus toxin into the presynaptic neuron produced a block of transmitter release, whereas botulinus toxin A had no effect on synaptic transmission. Subsequent immunoblotting of single-cell pairs demonstrated directly that the tetanus toxin-mediated block of exocytosis is accompanied by cleavage of synaptobrevin in the injected neuron, resulting in the generation of a detectable C-terminal cleavage product. Immunoblotting also confirmed the resistance of SNAP-25 to botulinus toxin A cleavagein vivo. Using recombinant proteins, we show that the N-terminal fragment of synaptobrevin released by tetanus toxin, but not its C-terminal membrane-anchored cleavage product, participates with syntaxin and SNAP-25 in synaptic SNAP receptor (SNARE) ternary complex formation inHirudo. Our data demonstrate a direct correlation between the inhibition of transmitter release and the ability of the neurotoxin to proteolyze its target protein and support the view that SNARE ternary complex formation is an important step leading to synaptic vesicle exocytosis.
Experimentally Induced Retinal Projections to the Ferret Auditory Thalamus: Development of Clustered Eye-Specific Patterns in a Novel Target
Authors: Angelucci Alessandra , Clascá Francisco , Bricolo Emanuela , Cramer Karina S. , Sur Mriganka
Published: April 2018

We have examined the relative role of afferents and targets in pattern formation using a novel preparation, in which retinal projections in ferrets are induced to innervate the medial geniculate nucleus (MGN). We find that retinal projections to the MGN are arranged in scattered clusters. Clusters arising from the ipsilateral eye are frequently adjacent to, but spatially segregated from, clusters arising from the contralateral eye. Both clustering and eye-specific segregation in the MGN arise as a refinement of initially diffuse and overlapped projections. The shape, size, and orientation of retinal terminal clusters in the MGN closely match those of relay cell dendrites arrayed within fibrodendritic laminae in the MGN. We conclude that specific aspects of a projection system are regulated by afferents and others by targets. Clustering of retinal projections within the MGN and eye-specific segregation involve progressive remodeling of retinal axon arbors, over a time period that closely parallels pattern formation by retinal afferents within their normal target, the lateral geniculate nucleus (LGN). Thus, afferent-driven mechanisms are implicated in these events. However, the termination zones are aligned within the normal cellular organization of the MGN, which does not differentiate into eye-specific cell layers similar to the LGN. Thus, target-driven mechanisms are implicated in lamina formation and cellular differentiation.
Proteolipid Protein Regulates the Survival and Differentiation of Oligodendrocytes
Authors: Yang Xiaoyi , Skoff Robert P.
Published: April 2018

Proteolipid protein (PLP) has been postulated to play a critical role in the early differentiation of oligodendrocytes (OLs) in addition to its known role as a structural component of myelin. To identify this early function, we blocked the synthesis of PLP in glial cultures with antisense oligodeoxynucleotides that targeted the PLP initiation codon. Primary glial cultures were incubated with phosphorothioate-protected oligodeoxynucleotides (S-ODNs) for up to 11 d. PLP in OLs was reduced >90%. OLs treated with antisense S-ODNs appeared strikingly healthy as judged by (1) immunocytochemical staining for myelin glycolipids and myelin basic protein, (2) their prolonged survival compared with untreated cultures, and (3) their ability to re-establish membrane sheets after removal of the S-ODNs.

Our studies show that PLP is required for elaboration and stability of the myelin membrane sheets made by most OLs, but it is not necessary for the network of processes established by OLs. More importantly, the number of OLs in the antisense-treated cultures was nearly sevenfold greater after a 10–11 d incubation with S-ODNs than in control cultures. The number of proliferating OL progenitors was not increased in the antisense-treated cultures, indicating that the increase in the number of OLs was attributable to prolonged OL survival. The tissue culture studies reveal that the absence of PLP/DM20 has the positive effect of promoting OL survival but the negative effect of preventing their full differentiation. This finding clarifies many of the paradoxical findings seen in the PLP mutants, the PLP overexpressers, and the PLP−animals.
Extracellular ATP Activates Calcium Signaling, Ion, and Fluid Transport in Retinal Pigment Epithelium
Authors: Peterson Ward M. , Meggyesy Chris , Yu Kefu , Miller Sheldon S.
Published: April 2018

The presence of receptors for ATP has not been established in any native preparation of retinal neurons or glia. In the present study, we used conventional electrophysiological and [Ca2+]influorescence imaging techniques to investigate the effects of ATP added to Ringer’s solution perfusing the retinal-facing (apical) membrane of freshly isolated monolayers of bovine retinal pigment epithelium (RPE). ATP (or UTP) produced large, biphasic voltage and resistance changes with aKdof ∼5 μmfor ATP and ∼1 μmfor UTP. Electrical and pharmacological evidence indicates that the first and second phases of the response are attributable to an increase in basolateral membrane Cl conductance and a decrease in apical membrane K conductance, respectively. The ATP-induced responses were not affected by adenosine, but were reduced by the P2-purinoceptor blocker suramin. ATP also produced a large, transient increase in [Ca2+]inthat was blocked by cyclopiazonic acid, an inhibitor of endoplasmic reticulum Ca2+-ATPases. The calcium buffer BAPTA attenuated the voltage effects of ATP. We also found that apical DIDS significantly inhibited the ATP-evoked [Ca2+]inand electrical responses, suggesting that DIDS blocked the purinoceptor. Measurements of fluid movement across the RPE using the capacitance probe technique demonstrated a significant increase in fluid absorption by apical UTP. These data indicate the presence of metabotropic P2Y/P2U-purinoceptors at the RPE apical membrane and implicate extracellular ATPin vivoas a retinal signaling molecule that could help regulate the hydration and chemical composition of the subretinal space.
Nucleus-Specific Chloride Homeostasis in Rat Thalamus
Authors: Ulrich Daniel , Huguenard John R.
Published: April 2018

Synchronous thalamic network activity occurring during slow wave sleep and paroxysmal discharges critically depends on the ability of thalamocortical relay cells and inhibitory neurons of the nucleus reticularis thalami (nRt) to fire bursts of action potentials. Inhibitory synaptic potentials (IPSPs) originating from nRt cells are crucial in deinactivating T-channels and thus promoting burst firing in relay cells, but the functional role of intra-nRt IPSPs is less well understood. A major factor that regulates the net effects of IPSP generation is the chloride equilibrium potential (ECl). Here we applied the perforated patch-clamp technique, using the cation-selective ionophore gramicidin to assess the reversal potential of chloride in nRt and relay cells in brain slices. We found that the reversal potential of GABA-induced membrane currents (EGABA) was significantly more hyperpolarized in relay (−81 ± 2.6 mV), as compared with nRt cells (−71 ± 2.5 mV).EGABAwas not significantly different from the reversal potential of evoked IPSCs (EIPSC; −82 ± 4.4 mV) in relay cells. In both relay and reticular neurons the chloride gradient was collapsed partially by the chloride cation cotransport blocker furosemide, suggesting an active chloride extrusion mechanism in thalamic neurons. Given the relatively hyperpolarized resting potentials (approximately −70 mV) reported for nRt and relay cells duringin vitrothalamic oscillations, we conclude that under these conditions GABAAIPSPs lead to significant hyperpolarization in relay cells. By contrast, intra-nRt inhibition essentially would be shunting, i.e., would produce minimal membrane polarization but still could reduce the amplitude of excitatory events.
Expression of the GABAAReceptor δ Subunit Is Selectively Modulated by Depolarization in Cultured Rat Cerebellar Granule Neurons
Authors: Gault Laura M. , Siegel Ruth E.
Published: April 2018

The levels of several GABAAreceptor subunit mRNAs increase as cerebellar granule neurons migrate to their adult positions and receive excitatory mossy fiber input. Despite the temporal similarity of these increases in transcript expressionin vivo, studies in cultured granule neurons demonstrated that the subunit mRNAs are differentially regulated. To address the possibility that neuronal activity regulates transcript expression, GABAAreceptor subunit mRNA levels were assessed in cultured granule neurons grown in chemically defined, serum-free medium containing either nondepolarizing (5 mM) or depolarizing (25 mm) KCl concentrations. Whereas the δ subunit mRNA was almost undetectable in cultures maintained in nondepolarizing medium, an eightfold increase occurred between days 2 and 4 in cultures grown in depolarizing medium. Furthermore, δ subunit transcript expression was reduced by 76 ± 6% when neurons in depolarizing medium were switched into nondepolarizing medium. The importance of depolarization in the initiation and maintenance of subunit transcript expression in granule neurons was selective for the GABAAreceptor δ subunit. These changes in transcript expression involved calcium entry through L-type calcium channels. Nifedipine treatment (1 μm) both reduced intracellular calcium and decreased δ subunit mRNA expression by 79 ± 4%. Furthermore, inhibition of Ca2+/calmodulin-dependent protein kinases (CaM kinases) by KN-62 (1 μm) also reduced δ subunit transcript expression. These studies demonstrate that KCl-induced depolarization, a condition that mimics the effects of neuronal activity, selectively modulates GABAAreceptor δ subunit mRNA expression through a pathway involving calcium entry and activation of a CaM kinase.
Massive Loss of Mid- and Hindbrain Neurons during Embryonic Development of Homozygous Lurcher Mice
Authors: Cheng Susie So-Wun , Heintz Nathaniel
Published: April 2018

The mouse neurological mutant lurcher (Lc) results from a semidominant mutation. HeterozygousLc/+ mice are viable but ataxic becauseLc/+ Purkinje cells die by apoptosis within the first 3 weeks of life.Lc/Lcmice die shortly after birth. To aid in understanding the function of the lurcher gene product, we have examined the embryonic development of homozygous lurcher animals. The ratio of +/+:Lc/+:Lc/Lcanimals did not deviate significantly from the expected 1:2:1. Homozygous lurcher mice at P0 were found to be normal under gross morphological examination. However, these mice weighed less, lacked milk in their stomach, and died within the first day of life. No resorbed embryos were found at embryonic day (E) 17.5, indicating that all homozygous lurchers survived until birth. Histological examination of P0 animals revealed that in homozygous lurcher mice the patterning of the brain is normal but that there has been a massive loss of hindbrain neurons during embryonic development. A particularly conspicuous consequence of theLc/Lcgenotype at birth is the complete absence of large neurons comprising the trigeminal motor nucleus. These neurons arise normally and are maintained until E15.5. However, beginning at E15.5 large numbers of pyknotic cells are evident in the trigeminal motor nucleus, suggesting that these cells die coincident with their terminal differentiation in the developing hindbrain. Because the trigeminal motor nucleus controls muscles required for suckling, these results suggest an explanation for the neonatal death of homozygousLcanimals. These data demonstrate that the severe and dose-dependent developmental consequences oflurchergene action result from degeneration of distinct neuronal populations on maturation in the developing CNS.
The Establishment of Peripheral Sensory Arbors in the Leech:In VivoTime-Lapse Studies Reveal a Highly Dynamic Process
Authors: Wang Huajun , Macagno Eduardo R.
Published: April 2018

Pressure-sensitive (P) neurons located in the leech CNS form elaborate terminal arbors in the body wall of the animal during mid-embryogenesis. In the experiments discussed here, arbor development in the target region was studied in intact, unanesthetized leech embryos using time-lapse video microscopy of individual, fluorescently stained P neurons. Analysis of time-lapse recordings made over a period of several days revealed that arbor formation is a very dynamic process. At any particular time, most high-order terminal branches were either extending or retracting, in approximately equal numbers and at very similar rates. Many branches underwent several rounds of extension and retraction every hour. Net arbor growth occurred at a much lower rate than the extension and retraction rates of individual branches. Process retraction sometimes resulted in an apparent change in the topological order of processes. Significantly, the initiation of new branches was restricted to a few locations along the parent process, which were termed “hot spots.” Moreover, the capacity to generate high-order branches correlated with parent process stability.

The target region of the growing P cell arbor in the body wall was subsequently examined using confocal microscopy in fixed preparations. The arbor expanded between the longitudinal and circular muscle layers, a region occupied by small unidentified cells. Simultaneous imaging of the dye-labeled terminal arbor and the surrounding tissue at two different wavelengths suggested that the high-order processes were navigating around these cells, which sometimes forced the growing processes to assume a bent form.

These observations suggest that the formation of the P cell arbor can be best described as a “dynamically unstable” process that is constrained by interactions with its environment.
Regulation of Quantal Secretion from Developing Motoneurons by Postsynaptic Activity-Dependent Release of NT-3
Authors: Liou Jau-Cheng , Fu Wen-Mei
Published: April 2018

Neurotrophic factors derived from postsynaptic muscle cells may play important roles in the development of presynaptic neuronal functions. In 3-d-oldXenopusnerve–muscle cultures, embryonic spinal neurons that had made natural contact with co-cultured myocytes exhibited spontaneous release of larger packets of acetylcholine (ACh) quanta than those released by the isolated neurons having no contact with any myocyte. Treatment of isolated neurons with neurotrophin-3 (NT-3) for 2 d increased the average sizes of quantal ACh packets at newly formed nerve–muscle synapses, whereas treatment with antibody against NT-3 or with K252a, a specific inhibitor of tyrosine kinase receptors, decreased the quantal size at existing synapses, which suggests that NT-3 supplied by the postsynaptic muscle cell may be responsible for the development and maintenance of the quantal packets. The muscle effect seems to depend on synaptic activities mediated by postsynaptic ACh receptor channels, because chronic treatment of the culture withd-tubocurarine (d-Tc) for 2 d resulted in a marked reduction of the quantal sizes, when assayed after extensive washing of the culture with Ringer’s solution. The curare treatment did not affect the postsynaptic ACh receptor sensitivity, because iontophoretically applied ACh induced current responses similar to those of control. Finally, co-treatment of the culture with NT-3 andd-Tc reversed the effect ofd-Tc on the quantal size, and this reversal effect was abolished when K252a was also applied concomitantly. Our results suggest that muscle-derived NT-3 participates in the maturation of normal transmitter packets in developing neurons, and the secretion of NT-3 depends on spontaneous synaptic activity.
Cortically Driven Immediate-Early Gene Expression Reflects Modular Influence of Sensorimotor Cortex on Identified Striatal Neurons in the Squirrel Monkey
Authors: Parthasarathy H.B. , Graybiel A.M.
Published: April 2018

Current understanding of basal ganglia function emphasizes their involvement in the focal, context-dependent release of motor and cognitive circuits in the brainstem and frontal lobes. How such selective action can arise despite the existence of massively convergent inputs from the cerebral cortex is unknown. However, anatomical work has suggested that specificity could be achieved in corticostriatal circuits by modular patterns of convergent and divergent cortical inputs to striatal projection neurons. To test for such modular activation of striatal neurons, we electrically microstimulated physiologically identified sites in the primary somatosensory (SI) and primary motor (MI) cortex of the squirrel monkey. We compared the efferent fiber distributions anterogradely traced from these sites to the distributions of striatal neurons activated by microstimulation to express Fos- and Jun B-like immediate-early gene proteins. We show that the microstimulation of sensorimotor cortex induces Fos and Jun B expression in localized cell clusters in the putamen and that these clusters match the anatomical input fiber clusters (matrisomes). The modular activation of striatal neurons by sensorimotor cortex seems likely. Unexpectedly, >75% of the Fos-positive nuclei in densely labeled cell clusters were in enkephalin-immunoreactive neurons. This expression pattern suggests that the primate sensorimotor cortex exerts a differential influence on the enkephalinergic (indirect pathway) as opposed to the substance P/dynorphin (direct pathway) projection neurons of the putamen. The densely labeled clusters of Fos-labeled enkephalinergic neurons occurred within larger zones containing sparsely distributed Fos-labeled parvalbumin neurons. Moreover, when the cortical stimulation induced expression of Fos-like protein only in sparsely distributed neurons, almost every putamenal neuron expressing Fos was a parvalbumin-containing (GABAergic) interneuron. These patterns suggest a model in which the primate sensorimotor cortex can target parvalbumin-containing inhibitory interneurons, which in turn depress the remaining neuronal activity within and around matrisomes in a feed-forward manner until sufficient coherent cortical input can overcome the inhibition to influence selectively enkephalinergic projection neurons in the activated matrisomes. Tuning of cortical input by striatal interneurons thus may be an important mechanism by which broader anatomical connections are dynamically adjusted to achieve selective flow of information through the basal ganglia.
Termination of Epileptic Afterdischarge in the Hippocampus
Authors: Bragin Anatol , Penttonen Markku , Buzsáki György
Published: April 2018

The mechanism of afterdischarge termination in the various hippocampal regions was examined in the rat. Stimulation of the perforant path or the commissural system was used to elicit afterdischarges. Combination of multiple site recordings with silicon probes, current source density analysis, and unit recordings in the awake animal allowed for a high spatial resolution of the field events. Interpretation of the field observations was aided by intracellular recordings from anesthetized rats. Irrespective of the evoking conditions, afterdischarges always terminated first in the CA1 region. Termination of the afterdischarge was heralded by a large DC shift initiated in dendritic layers associated with a low amplitude “afterdischarge termination oscillation” (ATO) at 40 to 80 Hz in the cell body layer. ATOs were also observed in the CA3 region and the dentate gyrus. The DC shift spread at the same velocity (0.1–0.2 mm/sec) in all directions and could cross the hippocampal fissure. All but 1 of the 25 putative interneurons in the CA1 and dentate regions ceased to fire before the onset of ATO. Intracellularly, ATO and the emerging DC potential were associated with fast depolarizing potentials and firing of pyramidal cells and depolarization block of spike initiation, respectively. Both field ATO and the intracellular depolarization shift were replicated by focal microinjection of potassium. We hypothesize that [K+]olost by the intensely discharging neurons during the afterdischarge triggers propagating waves of depolarization in the astrocytic network. In turn, astrocytes release potassium, which induces a depolarization block of spike generation in neurons, resulting in “postictal depression” of the EEG.
Prenatal Stress Induces High Anxiety and Postnatal Handling Induces Low Anxiety in Adult Offspring: Correlation with Stress-Induced Corticosterone Secretion
Authors: Vallée Monique , Mayo Willy , Dellu Françoise , Le Moal Michel , Simon Hervé , Maccari Stefania
Published: April 2018

It is well known that the hypothalamo-pituitary-adrenal (HPA) axis is altered by early environmental experiences, particularly in the perinatal period. This may be one mechanism by which the environment changes the physiology of the animal such that individual differences in adult adaptative capabilities, such as behavioral reactivity and memory performance, are observable. To determine the origin of these behavioral individual differences, we have investigated whether the long-term influence of prenatal and postnatal experiences on emotional and cognitive behaviors in adult rats are correlated with changes in HPA activity. To this end, prenatal stress of rat dams during the last week of gestation and postnatal daily handling of rat pups during the first 3 weeks of life were used as two environmental manipulations. The behavioral reactivity of the adult offspring in response to novelty was evaluated using four different parameters: the number of visits to different arms in a Y-maze, the distance covered in an open field, the time spent in the corners of the open field, and the time spent in the open arms of an elevated plus-maze. Cognitive performance was assessed using a water maze and a two-trial memory test. Adult prenatally stressed rats showed high anxiety-like behavior, expressed as an escape behavior to novelty correlated with high secretion of corticosterone in response to stress, whereas adult handled rats exhibited low anxiety-like behavior, expressed as high exploratory behavior correlated with low secretion of corticosterone in response to stress. On the other hand, neither prenatal stress nor handling changed spatial learning or memory performance. Taken together, these results suggest that individual differences in adult emotional status may be governed by early environmental factors; however, perinatal experiences are not effective in influencing adult memory capacity.
Effects ofm-Chlorophenylpiperazine on Regional Brain Glucose Utilization: A Positron Emission Tomographic Comparison of Alcoholic and Control Subjects
Authors: Hommer Daniel , Andreasen Paul , Rio Daniel , Williams Wendol , Ruttimann Urs , Momenan Reza , Zametkin Alan , Rawlings Robert , Linnoila Markku
Published: April 2018

m-Chlorophenylpiperazine (mCPP) is a mixed serotonin agonist/antagonist used extensively in psychiatric research. Alcoholics show blunted neuroendocrine responses to mCPP, and in some settings mCPP can induce craving for alcohol, particularly among early onset alcoholics. We used 2-[18F]-2-deoxy-d-glucose positron emission tomography to examine the effects of intravenously administered mCPP (0.08 mg/kg) on brain glucose utilization in a group of 18 male alcoholics and 12 healthy male control subjects. Differences between two sequential scans (the first followed placebo and the second followed mCPP) were evaluated statistically with a Gaussian random field-based method. Among healthy volunteers mCPP significantly increased brain glucose metabolism in the right medial and posterior orbital gyrus, the cerebellar hemispheres bilaterally, the left nucleus accumbens, the head of the caudate nucleus bilaterally, the anterior and medial-dorsal nuclei of the thalamus bilaterally, the middle frontal gyrus, the left insular cortex, the left middle temporal gyrus, and the posterior cingulate gyrus. Among alcoholic subjects mCPP significantly increased brain glucose metabolism in larger areas of the cerebellum and posterior cingulate than it did in healthy volunteers, but compared with the healthy volunteers, alcoholics showed a smaller area of mCPP-induced activation in the thalamus, almost no activation in the orbital cortices, and no activation at all in the head of the caudate nucleus or the middle frontal gyrus. These results suggest that a serotoninergic challenge activates basal ganglia circuits involving orbital and prefrontal cortices among healthy volunteers but that the response of these circuits is blunted among alcoholics.
Selective Alteration of Long-Term Potentiation-Induced Transcriptional Response in Hippocampus of Aged, Memory-Impaired Rats
Authors: Lanahan Anthony , Lyford Gregory , Stevenson Gail S. , Worley Paul F. , Barnes Carol A.
Published: April 2018

Normal human aging is associated with selective changes in cognition that are attributable, in part, to dysfunction of hippocampal pathways. Rodents also exhibit age-dependent hippocampal dysfunction that results in spatial memory deficits and a correlated reduction in the maintenance of long-term potentiation (LTP). Although suprathreshold stimulus protocols result in normal LTP induction in aged rats, the ability to sustain this increase in synaptic efficacy is reduced in the old animals. The maintenance phase of LTP is known to be dependent on rapid, transcriptional events, and recent studies have identified signal transduction mechanisms that link glutamate-induced responses at the synapse with transcriptional responses at the nucleus. To examine the integrity of these signaling pathways in aged hippocampus, we monitored the induction of a panel of immediate early genes (IEGs) that are known to be transcriptionally activated after LTP-inducing stimuli, using a “reverse Northern” strategy. Here we report that a broad representation of IEGs are similarly induced in awake, behaving young adult and aged, memory-impaired rats. This indicates a general preservation of these presumptive signaling pathways during the aging process. Induced levels ofc-fosmRNA, however, are significantly higher in the aged animals. These observations suggest that age-dependent hippocampal dysfunction may be associated with a selective change in the dynamic activity of signaling pathways upstream of c-fos, possibly involving calcium regulation.
A Simplified Preparation for Relating Cellular Events to Behavior: Mechanisms Contributing to Habituation, Dishabituation, and Sensitization of theAplysiaGill-Withdrawal Reflex
Authors: Cohen Tracey E. , Kaplan Saul W. , Kandel Eric R. , Hawkins Robert D.
Published: April 2018

To relate cellular events to behavior in a more rigorous fashion, we have developed a simplified preparation for studying the gill-withdrawal reflex ofAplysia, in which it is relatively easy to record the activity of individual neurons during simple forms of learning. Approximately 84% of the reflex in this preparation is mediated through the single motor neuron LDG1, so that changes in the firing of LDG1 can account for most of the changes in behavior. We have used this preparation to investigate cellular mechanisms contributing to habituation, dishabituation, and sensitization by recording evoked firing, the complex postsynaptic potential (PSP), and the monosynaptic component of the complex PSP in LDG1. Our results suggest that habituation is largely attributable to depression at sensory neuron synapses. By contrast, dishabituation and sensitization involve several mechanisms at different loci, including facilitation at sensory neuron synapses, enhancement in the periphery (perhaps attributable to post-tetanic potentiation at the neuromuscular junction), and both facilitation and inhibition of excitatory and inhibitory interneurons. Moreover, these different mechanisms contribute preferentially at different times after training, so that information processing in the neuronal circuit for the reflex is distributed not only in space but also in time. Nonetheless, our results also suggest that the neuronal circuit is not a highly distributed neural network. Rather, plasticity of the reflex can evidently be accounted for by several specific mechanisms and loci of plasticity in a defined neural circuit, including a limited number of neurons, some of which make a large contribution to the behavior.
Distinct Roles for Ceramide and Glucosylceramide at Different Stages of Neuronal Growth
Authors: Schwarz Andreas , Futerman Anthony H.
Published: April 2018

Sphingolipids (SLs) are important structural and regulatory components of neuronal plasma membranes. Previous studies using fumonisin B1, an inhibitor of the synthesis of ceramide, the precursor of all SLs, demonstrated that ceramide synthesis is required to sustain axonal growth in hippocampal neurons (Harel and Futerman, 1993; Schwarz et al., 1995) and dendritic growth in cerebellar Purkinje cells (Furuya et al., 1995). We now show that ceramide plays distinct roles at different stages of neuronal development. (1) During axon growth, ceramide must be metabolized to glucosylceramide (GlcCer) to sustain growth. Thus, whereasd-erythro-ceramide, which is metabolized to GlcCer, is able to antagonize the disruptive effects of fumonisin B1on axon growth,l-threo-ceramide, which is not metabolized to GlcCer, is ineffective. (2) The formation of minor processes from lamellipodia can be stimulated by incubation with short-acyl chain analogs of ceramide that are active in ceramide-mediated signaling pathways, or by generation of endogenous ceramide by incubation with sphingomyelinase. However, GlcCer synthesis is not required for this initial stage of neuronal development. (3) During minor process formation and during axon growth, incubation with high concentrations of ceramide or sphingomyelinase, but not dihydroceramide, induces apoptosis. Together, these observations are consistent with the possibility that minor process formation and apoptosis can be regulated by ceramide-dependent signaling pathways and that the decision whether to enter these diametrically opposed pathways depends on intracellular ceramide concentrations. In contrast, axonal growth requires the synthesis of GlcCer from ceramide, perhaps to support an intracellular transport pathway.
Interleukin-1 Enhances the ATP-Evoked Release of Arachidonic Acid from Mouse Astrocytes
Authors: Stella Nephi , Estellés Angeles , Siciliano Julio , Tencé Martine , Desagher Solange , Piomelli Daniele , Glowinski Jacques , Prémont Joël
Published: April 2018

During neuropathological states associated with inflammation, the levels of cytokines such as interleukin-1β (IL-1β) are increased. Several studies have suggested that the neuronal damage observed in pathogenesis implicating IL-1β are caused by an alteration in the neurochemical interactions between neurons and astrocytes. We report here that treating striatal astrocytes in primary culture with IL-1β for 22–24 hr enhances the ATP-evoked release of arachidonic acid (AA) with no effect on the ATP-induced accumulation of inositol phosphates. The molecular mechanism responsible for this effect involves the expression of P2Y2receptors (a subtype of purinoceptor activated by ATP) and cytosolic phospholipase A2 (cPLA2, an enzyme that mediates AA release). Indeed, P2Y2antisense oligonucleotides reduce the ATP-evoked release of AA only from IL-1β-treated astrocytes. Further, both the amount of cPLA2 (as assessed by Western blotting) and the release of AA resulting from direct activation of cPLA2increased fourfold in cells treated with IL-1β. We also report evidence indicating that the coupling of newly expressed P2Y2receptors to cPLA2is dependent on PKC activity. These results suggest that during inflammatory conditions, IL-1β reveals a functional P2Y2signaling pathway in astrocytes that results in a dramatic increase in the levels of free AA. This pathway may thus contribute to the neuronal loss associated with cerebral ischemia or traumatic brain injury.
ENC-1: A Novel MammalianKelch-Related Gene Specifically Expressed in the Nervous System Encodes an Actin-Binding Protein
Authors: Hernandez Maria-Clemencia , Andres-Barquin Pedro J. , Martinez Salvador , Bulfone Alexandro , Rubenstein John L.R. , Israel Mark A.
Published: April 2018

We have identified and characterized a novel murine gene,Ectoderm-Neural Cortex-1 (ENC-1),that is an early and highly specific marker of neural induction in vertebrates.ENC-1,which encodes a kelch family related protein, is expressed during early gastrulation in the prospective neuroectodermal region of the epiblast and later in development throughout the nervous system (NS).ENC-1expression is highly dynamic and, after neurulation, preferentially defines prospective cortical areas. The only apparent expression ofENC-1outside the NS is restricted to the rostral-most somitomere of the presomitic mesoderm, at the times corresponding to the epithelialization that precedes somite formation. Cellular expression of epitope-tagged ENC-1 shows extensive co-localization of ENC-1 with the actin cytoskeleton, and immunoprecipitation studies demonstrate a physical association between ENC-1 and actin. ENC-1 functions as an actin-binding protein that may be important in the organization of the actin cytoskeleton during neural fate specification and development of the NS.