bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Nitrous Oxide on Excitatory and Inhibitory Synaptic Transmission in Hippocampal Cultures
Authors: Mennerick Steven , Jevtovic-Todorovic Vesna , Todorovic Slobodan M. , Shen Weixing , Olney John W. , Zorumski Charles F.
Published: April 2018

Nitrous oxide (N2O; laughing gas) has been a widely used anesthetic/analgesic since the 19th century, although its cellular mechanism of action is not understood. Here we characterize the effects of N2O on excitatory and inhibitory synaptic transmission in microcultures of rat hippocampal neurons, a preparation in which anesthetic effects on monosynaptic communication can be examined in a setting free of polysynaptic network variables. Eighty percent N2O occludes peak NMDA receptor-mediated (NMDAR) excitatory autaptic currents (EACs) with no effect on the NMDAR EAC decay time course. N2O also mildly depresses AMPA receptor-mediated (AMPAR) EACs. We find that N2O inhibits both NMDA and non-NMDA receptor-mediated responses to exogenous agonist. The postsynaptic blockade of NMDA receptors exhibits slight apparent voltage dependence, whereas the blockade of AMPA receptors is not voltage dependent. Although the degree of ketamine and Mg2+blockade of NMDA-induced responses is dependent on permeant ion concentration, the degree of N2O blockade is not. We also observe a slight and variable prolongation of GABAAreceptor-mediated (GABAR) postsynaptic currents likely caused by previously reported effects of N2O on GABAAreceptors. Despite the effects of N2O on both NMDA and non-NMDA ionotropic receptors, glial glutamate transporter currents and metabotropic glutamate receptor-mediated synaptic depression are not affected. Paired-pulse depression, the frequency of spontaneous miniature excitatory synaptic currents, and high-voltage–activated calcium currents are not affected by N2O. Our results suggest that the effects of N2O on synaptic transmission are confined to postsynaptic targets.
Attenuation of Focal Ischemic Brain Injury in Mice Deficient in the ε1 (NR2A) Subunit of NMDA Receptor
Authors: Morikawa Eiharu , Mori Hisashi , Kiyama Yuji , Mishina Masayoshi , Asano Takao , Kirino Takaaki
Published: April 2018

The role of glutamate neurotoxicity in cerebral ischemia has long been advocated but still remains controversial, because various glutamate receptor (GluR) antagonists showed inconsistent protective efficacy in brain ischemia models. To address this central issue of ischemic brain damage more directly, we used mutant mice deficient in the GluRε1 (NR2A) subunit of NMDA receptor with or without additional heterozygous mutation in the GluRε2 (NR2B) subunit. Those mutant mice, as well as their littermates, were subjected to focal cerebral ischemia by introducing a 6–0 nylon suture from left common carotid artery. Brain injury volumes after 2 hr of suture insertion, as evaluated by 2,3,5-triphenyltetrazolium chloride staining at 24 hr after ischemia, revealed significantly smaller injury size in GluRε1 subunit knock-out mice compared with their wild-type littermates. The reduction in injury volume was not attributable to differences in body temperature or in blood flow during ischemia. Additional heterozygous GluRε2 subunit disruption did not result in further reduction in injury volume. These data directly demonstrate relevance of NMDA receptor-mediated tissue injury after brain ischemia and provide evidence that GluRε1 subunit is involved in these injurious mechanisms.
Differentiation of Oligodendroglial Progenitors Derived from Cortical Multipotent Cells Requires Extrinsic Signals Including Activation of gp130/LIFβ Receptors
Authors: Marmur Ronen , Kessler John A. , Zhu Gaofa , Gokhan Solen , Mehler Mark F.
Published: April 2018

We have previously isolated epidermal growth factor (EGF)-responsive multipotent progenitor cells from the early postnatal rodent cerebral cortex independent of generative zones. In this study we have examined the mechanisms regulating the generation of differentiated oligodendrocytes (OLs) from these multipotent cells. Although cultures of primary cortical OL progenitor cells propagated at clonal density spontaneously gave rise to differentiated OLs in defined medium, cultures of multipotent progenitors isolated from identical regions supported the elaboration of OL progenitors but not differentiated OLs. These observations indicate that the terminal maturation of OL progenitors derived from multipotent cells is dependent on signals present within the cellular environment. Application of cytokines such as basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), or neurotrophin 3 (NT3) to clonal density cultures of cortical multipotent progenitors increased the proportion of OL progenitors but failed to support the generation of differentiated OLs. By contrast, application of factors that activate gp130/leukemia inhibitory factor β (LIFβ) heterodimeric receptors, such as ciliary neurotrophic factor (CNTF), activated signal transducers and activators of transcription-3 in these OL progenitor cells and promoted the generation of differentiated OLs. Clonal analysis also demonstrated that CNTF directly targets OL progenitors derived from the multipotent cells. These observations suggest that two distinct progenitor cell pathways contribute to the generation of differentiated OLs during postnatal cortical gliogenesis. Although oligodendroglial maturation of classical OL progenitor cells is driven by cell autonomous mechanisms, our findings demonstrate that the generation of differentiated OLs from cortical multipotent progenitor cells is dependent on environmental cues, including activation of gp130/LIFβ receptors.
Targeted Expression of a Toxin Gene to D1 Dopamine Receptor Neurons byCre-Mediated Site-Specific Recombination
Authors: Drago John , Padungchaichot Poolpol , Wong John Y. F. , Lawrence Andrew J. , McManus Julie F. , Sumarsono Sony H. , Natoli Anthony L. , Lakso Merja , Wreford Nigel , Westphal Heiner , Kola Ismail , Finkelstein David I.
Published: April 2018

Idiopathic Parkinson’s disease involves the loss of midbrain dopaminergic neurons, resulting in the presynaptic breakdown of dopaminergic transmission in the striatum. Huntington’s disease and some neurodegenerative diseases with Parkinsonian features have postsynaptic defects caused by striatal cell death. Mice were generated in which an attenuated form of the diphtheria toxin gene (tox-176) was expressed exclusively in D1 dopamine receptor (D1R)-positive cells with the aim of determining the effect of this mutation on development of the basal ganglia and on the locomotor phenotype. Transgenic mice expressingCre, a site-specific DNA recombinase, were crossed with a second line in which a transcriptionally silencedtox-176gene was inserted into the D1R gene locus by homologous recombination. Young doubly transgenic mutant mice expressing thetox-176gene displayed bradykinesia, dystonia, and had falls caused by myoclonic jerks. The mutant brain had evidence of apoptosis and reactive gliosis and, consistent with the D1R expression pattern, the striatum was reduced in volume, and the Islands of Calleja were absent. In contrast, the cortex was of normal thickness. D1Rs were not detectable in mutants byin situhybridization or ligand autoradiography, whereas D2 dopamine receptor (D2R) mRNA and protein was present in the striatum. In addition, substance P and dynorphin, neuropeptides known to be expressed in D1R-positive striatonigral projection neurons were not detectable. Enkephalin, a marker found in D2-positive striatopallidal projection neurons was expressed in the mutant brain. The mutant represents a novel neurodegenerative disease model with a dramatic extrapyramidal phenotype.
Acetylcholinesterase Gene Expression in Axotomized Rat Facial Motoneurons Is Differentially Regulated by Neurotrophins: Correlation with trkB and trkC mRNA Levels and Isoforms
Authors: Fernandes Karl J.L. , Kobayashi Nao R. , Jasmin Bernard J. , Tetzlaff Wolfram
Published: April 2018

We examined the potential influences of muscle-derived neurotrophins on the acetylcholinesterase (AChE) gene expression of adult rat motoneurons. Seven days after facial nerve transection, both AChE mRNA and enzyme activity levels were markedly reduced in untreated and vehicle-treated facial motoneurons, suggesting positive regulation of motoneuron AChE expression by muscle-derived factors. Because skeletal muscle is a source of neurotrophin-3 (NT-3), NT-4/5, and BDNF, these neurotrophins were individually infused onto the proximal nerve stump for 7 d, beginning at the time of axotomy. The trkB ligands NT-4/5 and BDNF prevented the downregulation of AChE mRNA and enzymatic activity, as determined byin situhybridization, biochemical assay, and histochemical visualization of enzyme activity. In contrast, NT-3 had limited effects, and NGF was without effect. Because motoneurons normally express both trkB and trkC receptors and the trkC ligand NT-3 is the most abundant muscle-derived neurotrophin, we investigated possible reasons for the limited effects of NT-3.In situhybridization and reverse transcription-PCR both revealed a downregulation of trkC mRNA in axotomized motoneurons, which contrasted the upregulation of trkB expression. Furthermore, isoforms of trkC were detected carrying insertions within their kinase domains, known to limit certain trkC-mediated signal transduction pathways. Because the changes in trkB and trkC mRNA levels were not significantly altered by neurotrophin infusions, it is unlikely they were induced by loss of muscle-derived neurotrophins. These results demonstrate that NT-4/5 and BDNF stimulate AChE gene expression in motoneurons and support the concept that muscle-derived trkB ligands modulate the cholinergic phenotype of their innervating motoneurons.
Regulation of Tyrosine Hydroxylase Promoter Activity by Chronic Morphine in TH9.0-LacZ Transgenic Mice
Authors: Boundy Virginia A. , Gold Stephen J. , Messer Chad J. , Chen Jingshan , Son Jin H. , Joh Tong H. , Nestler Eric J.
Published: April 2018

Levels of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, are known to be upregulated in specific brain regions by chronic administration of drugs of abuse. Chronic morphine administration increases TH levels in the locus coeruleus and ventral tegmental area, whereas chronic cocaine administration increases TH levels in the ventral tegmental area only. While such upregulation of TH has been related to behavioral effects of the drugs, the mechanism underlying these adaptations has remained controversial. To study the possibility that upregulation of TH occurs at the transcriptional level, we investigated the effect of chronic morphine or cocaine treatment on the activity of the TH gene promoter (9.0 kb), coupled to the LacZ reporter gene, in transgenic mice. These TH9.0-LacZ mice have been shown to exhibit correct tissue-specific expression and regulation of the reporter gene. We show here that chronic (but not acute) exposure of the TH9.0-LacZ mice to morphine increases the expression of β-galactosidase (which is encoded by the LacZ gene) in the locus coeruleus by twofold compared with sham-treated mice. In contrast, β-galactosidase expression in the ventral tegmental area was decreased 20–25% by chronic morphine and unaffected by chronic cocaine administration. Similar results were obtained after analysis of TH mRNA levels in these brain regions byin situhybridization. These results suggest that chronic morphine upregulates TH expression via transcriptional mechanisms in the locus coeruleus but by post-transcriptional mechanisms in the ventral tegmental area.
Neurotoxic Lesions of the Dorsomedial Thalamus Impair the Acquisition But Not the Performance of Delayed Matching to Place by Rats: a Deficit in Shifting Response Rules
Authors: Hunt Peter R. , Aggleton John P.
Published: April 2018

This study examined the acquisition of a T-maze matching to place task by rats with neurotoxic lesions of the thalamic nucleus medialis dorsalis. This test of spatial working memory also entails learning a task rule that is contrary to the animals’ innate preference. The rats next performed the same matching task over different retention delays. Finally, they were trained on a reversal of the task rule, i.e., to nonmatch to place. Although the lesions produced a clear acquisition impairment on the matching task, there was no evidence of a loss of working memory. A series of control tasks found no appreciable effect on a conditioned cue preference task or on open field activity. The pattern of results shows that medialis dorsalis lesions lead to a selective increase in perseverative behavior that can retard task acquisition. This perseverative deficit closely resembles that observed after prefrontal damage in rats, strongly indicating dysfunction in a common system.
Serotonin1BReceptor Stimulation Enhances Cocaine Reinforcement
Authors: Parsons Loren H. , Weiss Friedbert , Koob George F.
Published: April 2018

The effects of serotonin1B[5-hydroxytryptamine1B(5-HT1B)] receptor activation on cocaine reinforcement were investigated using intravenous cocaine self-administration by rats. The 5-HT1Breceptor agonists 5-methoxy-3-1,2,3,6-tetrahydro-4-pyridinyl-1H-indole (RU 24969) (0.3–3 mg/kg), 3-(1,2,5,6-tetrahydro-4-pyridyl)-5-propoxypyrrolo[3,2-b]pyridine (CP 94,253) (0.3–3 mg/kg), and 3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyridine (CP 93,129) (3 and 10 μg, i.c.v.) each dose-dependently reduced the self-administration of a cocaine dose on the descending limb of the fixed-ratio 5 (FR-5) cocaine dose–effect function, in a manner similar to the effect produced by increasing the unit dose of cocaine. In addition, each of these 5-HT1Bagonists lowered the threshold dose of cocaine that supported self-administration. These results are consistent with a 5-HT1Bagonist-induced potentiation of cocaine reinforcement. On a progressive ratio schedule of reinforcement, RU 24969 and CP 94,253 dose-dependently (0.3–3 mg/kg) increased the highest completed ratio for cocaine self-administration, again by producing behavioral alterations similar to those induced by increasing the unit dose of cocaine. The effect of CP 94,253 was dose-dependently blocked by the 5-HT1B/1Dreceptor partial agonist 2′-methyl-4′-(5-methyl[1,2,4]oxadiazol-3-yl)-biphenyl-4-carboxylic acid[4-methodoxy-3-(4-methyl-piperazin-1-yl)-phenyl]-amide (GR 127,935) (0.3–10 mg/kg) but was unaffected by the 5-HT1Areceptor antagonist 4-iodo-N-[2-[4-(methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl- benzamide (p-MPPI; 1–10 mg/kg). Self-administration behavior was not maintained when either RU 24969 or CP 94,253 was substituted for cocaine, indicating that these 5-HT1Bagonists do not produce significant reinforcing effects alone. Together, these findings indicate that 5-HT1Breceptor stimulation facilitates the reinforcing properties of cocaine. These results are in opposition to recent findings with 5-HT1Breceptor knock-out mice and may have important ontogenic implications in the area of drug abuse research.
Immunocytochemical Localization of the Postsynaptic Density Protein PSD-95 in the Mammalian Retina
Authors: Koulen Peter , Fletcher Erica L. , Craven Sarah E. , Bredt David S. , Wässle Heinz
Published: April 2018

Synapse-associated proteins are the scaffold for the selective aggregation of ion channels at synapses; they provide the link to cytoskeletal elements and possibly are involved with the regulation of synaptic efficacy by electrical activity. The localization of the postsynaptic density protein PSD-95 was studied in different mammalian retinae (rat, monkey, and tree shrew) by using immunocytochemical methods. Immunofluorescence for PSD-95 was most prominent in the outer plexiform layer (OPL). The axon terminals of rods and cones, the rod spherules and cone pedicles, were strongly labeled. Electron microscopy, using preembedding immunocytochemistry, showed PSD-95 localized presynaptically within the photoreceptor terminals. Distinct PSD-95 labeling was also present in the inner plexiform layer (IPL). It had a punctate appearance suggesting the synaptic clustering of PSD-95 in the IPL. Electron microscopy showed that PSD-95 was concentrated in processes that were postsynaptic at bipolar cell ribbon synapses (dyads). As a rule, only one of the two postsynaptic members of the dyad was labeled for PSD-95. Double-labeling experiments were performed for PSD-95 and for SAP 102 or PSD-93, respectively, two other members of the family of synapse-associated proteins. All three were found to be colocalized in the synaptic hot spots in the IPL. In the OPL, however, PSD-95 and PSD-93 were found presynaptically, whereas SAP 102 was located postsynaptically at photoreceptor synapses. Double-labeling experiments also were performed for PSD-95 and for the NR1 subunit of the NMDA receptor. They were found to be colocalized in synaptic hot spots in the IPL.
Mitochondrial Control of Acute Glutamate Excitotoxicity in Cultured Cerebellar Granule Cells
Authors: Castilho Roger F. , Hansson Oskar , Ward Manus W. , Budd Samantha L. , Nicholls David G.
Published: April 2018

Mitochondria within cultured rat cerebellar granule cells have a complex influence on cytoplasmic free Ca2+([Ca2+]c) responses to glutamate. A decreased initial [Ca2+]celevation in cells whose mitochondria are depolarized by inhibition of the ATP synthase and respiratory chain (conditions which avoid ATP depletion) was attributed to enhanced Ca2+extrusion from the cell rather than inhibited Ca2+entry via the NMDA receptor. Even in the presence of elevated extracellular Ca2+, when [Ca2+]cresponses were restored to control values, such cells showed resistance to acute excitotoxicity, defined as a delayed cytoplasmic Ca2+deregulation (DCD) during glutamate exposure. DCD was a function of the duration of mitochondrial polarization in the presence of glutamate rather than the total period of glutamate exposure. Once initiated, DCD could not be reversed by NMDA receptor inhibition. In the absence of ATP synthase inhibition, respiratory chain inhibitors produced an immediate Ca2+deregulation (ICD), ascribed to an ATP deficit. In contrast to DCD, ICD could be reversed by subsequent ATP synthase inhibition with or without additional NMDA receptor blockade. DCD could not be ascribed to the failure of an ATP yielding metabolic pathway. It is concluded that mitochondria can control Ca2+extrusion from glutamate-exposed granule cells by the plasma membrane in three ways: by competing with efflux pathways for Ca2+, by restricting ATP supply, and by inducing a delayed failure of Ca2+extrusion. Inhibitors of the mitochondrial permeability transition only marginally delayed the onset of DCD.
Protein Kinase A Activity May Kinetically Upregulate the Striatal Transporter for Dopamine
Authors: Batchelor Melissa , Schenk James O.
Published: April 2018

The neuronal dopamine transporter (DAT) plays a key role in terminating dopaminergic chemical neurotransmission; thus, the study of the regulation of DAT activity is important in defining parameters relevant to the control of dopaminergic neurotransmission. Interpretation of the results from previous work of this laboratory suggests that occupation of presynaptic autoreceptors increases DAT activity. Second messenger signaling related to kinetic upregulation of DAT has not been examined previously. However, others have shown that protein kinase C activity may downregulate DAT activity, whereas protein kinase A has shown variable results. Herein it is shown that protein kinase A activity mediates the kinetic upregulation of DAT. Quinpirole increased DAT activity that was blocked by sulpiride and the protein kinase A selective inhibitor H-89. Brief incubations with forskolin and 8-bromo-cAMP (8-Br-cAMP) were found to stimulate striatal DAT activity by increasing theVmaxof transport without affecting theKm. Exposures >15 min had no effect. The 8-Br-cAMP-stimulated increases in DAT activity were blocked by pre-exposure to H-89. Thus, second messenger signaling via the cAMP cascade may mediate kinetic upregulation of DAT. Kinetic analyses of the results suggest that either insertion of DAT into the membrane or activation of pre-existing DAT within the membrane mediates the regulation.
Mammalian Nicotinic Receptors with α7 Subunits That Slowly Desensitize and Rapidly Recover from α-Bungarotoxin Blockade
Authors: Cuevas Javier , Berg Darwin K.
Published: April 2018

One of the most abundant nicotinic receptors in the nervous system is a species that contains the α7 gene product, rapidly desensitizes, and binds α-bungarotoxin with great affinity. The receptor has a high relative permeability to calcium and performs a variety of functions including presynaptic modulation of transmitter release and postsynaptic generation of synaptic currents. Fast excitatory transmission in mammalian intracardiac ganglia is mediated primarily by nicotinic receptors, and although intracardiac ganglion neurons express the α7 gene, no toxin-sensitive response has been detected previously in them. We report here that whole-cell patch-clamp recordings from freshly dissociated intracardiac ganglion neurons reveal a nicotinic response that desensitizes slowly and is blocked by α-bungarotoxin in a rapidly reversible manner. The only rat gene previously thought capable of forming such receptors was α9, but no evidence suggests that the α9 gene is expressed in neurons. We find that reverse transcription (RT)–PCR detects α7 but not α9 mRNA in the ganglia. In addition, the pharmacology of the nicotinic response is typical of α7-containing receptors but differs in several respects from that expected for α9. Binding experiments with immunotethered receptors identifies a ganglionic species that contains the α7 gene product. Moreover, intracellular perfusion of the cells with an anti-α7 monoclonal antibody specifically reduces the amplitude of the toxin-sensitive response. The results indicate that α7-containing receptors are responsible for the slowly desensitizing, toxin-reversible response and suggest that the receptors are modified in cell-specific ways to influence their functional properties.
Heteromultimeric Delayed-Rectifier K+Channels in Schwann Cells: Developmental Expression and Role in Cell Proliferation
Authors: Sobko Alexander , Peretz Asher , Shirihai Orian , Etkin Sarah , Cherepanova Vera , Dagan Daniel , Attali Bernard
Published: April 2018

Schwann cells (SCs) are responsible for myelination of nerve fibers in the peripheral nervous system. Voltage-dependent K+currents, including inactivating A-type (KA), delayed-rectifier (KD), and inward-rectifier (KIR) K+channels, constitute the main conductances found in SCs. Physiological studies have shown thatKDchannels may play an important role in SC proliferation and that they are downregulated in the soma as proliferation ceases and myelination proceeds. Recent studies have begun to address the molecular identity of K+channels in SCs. Here, we show that a large repertoire of K+channel α subunits of theShaker(Kv1.1, Kv1.2, Kv1.4, and Kv1.5),Shab(Kv2.1), andShaw(Kv3.1b and Kv3.2) families is expressed in mouse SCs and sciatic nerve. We characterized heteromultimeric channel complexes that consist of either Kv1.5 and Kv1.2 or Kv1.5 and Kv1.4. In postnatal day 4 (P4) sciatic nerve, most of the Kv1.2 channel subunits are involved in heteromultimeric association with Kv1.5. Despite the presence of Kv1.1 and Kv1.2 α subunits, the K+currents were unaffected by dendrotoxin I (DTX), suggesting that DTX-sensitive channel complexes do not account substantially for SCKDcurrents. SC proliferation was found to be potently blocked by quinidine or 4-aminopyridine but not by DTX. Consistent with previous physiological studies, our data show that there is a marked downregulation of allKDchannel α subunits from P1–P4 to P40 in the sciatic nerve. Our results suggest thatKDcurrents are accounted for by a complex combinatorial activity of distinct K+channel complexes and confirm thatKDchannels are involved in SC proliferation.
p21 Ras and Phosphatidylinositol-3 Kinase Are Required for Survival of Wild-Type and NF1 Mutant Sensory Neurons
Authors: Klesse Laura J. , Parada Luis F.
Published: April 2018

Nerve growth factor (NGF) is a required differentiation and survival factor for sympathetic and a majority of neural crest-derived sensory neurons in the developing vertebrate peripheral nervous system. Although much is known about the function of NGF, the intracellular signaling cascade that it uses continues to be a subject of intense study. p21 ras signaling is considered necessary for sensory neuron survival. How additional intermediates downstream or in parallel may function has not been fully understood yet. Two intracellular signaling cascades, extra cellular regulated kinase (erk) and phosphatidylinositol-3 (PI 3) kinase, transduce NGF signaling in the pheochromocytoma cell line PC12. To elucidate the role these cascades play in survival and differentiation, we used a combination of recombinant adenoviruses and chemical inhibitors to perturb these pathways in sensory neurons from wild-type mice and mice deficient for neurofibromin in which the survival and differentiation pathway is constitutively active. We demonstrate that ras activity is both necessary and sufficient for the survival of embryonic sensory neurons. Downstream of ras, however, the erk cascade is neither required nor sufficient for neuron survival or overall differentiation. Instead, the activity of PI 3 kinase is necessary for the survival of the wild-type and neurofibromin-deficient neurons. Therefore, we conclude that in sensory neurons, NGF acts via a signaling pathway, which includes both ras and PI 3 kinase.
Segmental Specificity of Chick Sympathetic Preganglionic Projections Is Influenced by Preganglionic Neurons from Neighboring Spinal Cord Segments
Authors: Yip Joseph W. , Yip Yee Ping L. , Capriotti Christine
Published: April 2018

Sympathetic preganglionic neurons of the chick are located between the brachial and lumbosacral enlargements of the spinal cord. Their axons exit the spinal cord via their adjacent ventral roots and project rostrally or caudally along the sympathetic trunk to innervate sympathetic ganglia. The projections of sympathetic preganglionic neurons are segmentally specific. Neurons from the 16th cervical (C16) and the first thoracic (T1) spinal cord segments project predominantly in the rostral direction, whereas those from the fifth thoracic (T5) to the first lumbar (L1) spinal segments project predominantly in the caudal direction. Neurons from intervening spinal cord segments (T2–T4) project in rostral and caudal directions. In the present study, neural tube manipulations show that the direction of preganglionic projections is altered by both the elimination and addition of preganglionic neurons projecting into the sympathetic trunk from neighboring segments. The present study also compares the projections of preganglionic neurons from transplants of multiple neural tube segments with those from transplants of single neural tube segments reported in a previous study (Yip, 1987). In the previous study when single thoracic neural tube segments were transplanted to the cervical level, preganglionic neurons did not maintain their original projection patterns. The present study found that, when contiguous neighboring segments were transplanted to the cervical level, preganglionic neurons maintained projection patterns characteristic of their original segmental levels. These results indicate that the direction of preganglionic projections can be influenced by neurons from neighboring segments, suggesting that the formation of segmentally specific preganglionic projections during embryogenesis may involve the interactions of preganglionic neurons with those from neighboring spinal cord segments.
A Role for Transforming Growth Factor α as an Inducer of Astrogliosis
Authors: Rabchevsky Alexander G. , Weinitz Juno M. , Coulpier Muriel , Fages Christiane , Tinel Marina , Junier Marie-Pierre
Published: April 2018

TGFα is a member of the epidermal growth factor (EGF) family with which it shares the same receptor, the EGF receptor (EGFR). Synthesis of TGFα and EGFR in reactive astrocytes developing after CNS insults is associated with the differentiative and mitogenic effects of TGFα on cultured astrocytes. This suggests a role for TGFα in the development of astrogliosis. We evaluated this hypothesis using transgenic mice bearing the human TGFα cDNA under the control of the zinc-inducible metallothionein promoter. Expression levels of glial fibrillary acidic protein (GFAP) and vimentin and morphological features of astrocytes were used as indices of astroglial reactivity in adult transgenic versus wild-type mice provided with ZnCl2in their water for 3 weeks. In the striatum, the hippocampus, and the cervical spinal cord, the three CNS areas monitored, transgenic mice displayed enhanced GFAP mRNA and protein levels and elevated vimentin protein levels. GFAP-immunoreactive astrocytes exhibited numerous thick processes and hypertrophied somata, which are characteristic aspects of reactive astrocytes. Their number increased additionally in the striatum and the spinal cord, but no astrocytic proliferation was observed using bromodeoxyuridine immunohistochemistry. Neither the morphology nor the number of microglial cells appeared modified. A twofold increase in phosphorylated EGFR was detected in the striatum and was associated with the immunohistochemical detection of numerous GFAP-positive astrocytes bearing the EGFR, suggesting a direct action of TGFα on astrocytes. Altogether, these results demonstrate that enhanced TGFα synthesis is sufficient to trigger astrogliosis throughout the CNS, whereas microglial metabolism is unaffected.
Calcium Currents of Rhythmic Neurons Recorded in the Isolated Respiratory Network of Neonatal Mice
Authors: Elsen Frank Peter , Ramirez Jan-Marino
Published: April 2018

To obtain a quantitative characterization of voltage-activated calcium currents in respiratory neurons, we performed voltage-clamp recordings in the transverse brainstem slice of mice from neurons located within the ventral respiratory group. It is assumed that this medullary region contains the neuronal network responsible for generating the respiratory rhythm. This study represents one of the first attempts to analyze quantitatively the currents in respiratory neurons. The inward calcium currents of VRG neurons consisted of two components: a high voltage-activated (HVA) and a low voltage-activated (LVA) calcium current. The activation threshold of the HVA current was at −40 mV. It was fully activated (peak voltage) between −10 and 0 mV. The half-maximal activation (V50) was at −27.29 mV ± 1.15 (n= 24). The HVA current was inactivated completely at a holding potential of −35 mV and fully deinactivated at a holding potential of −65 mV (V50, −52.26 mV ± 0.27;n= 18). The threshold for the activation of the LVA current was at −65 mV. This current had its peak voltage between −50 and −40 mV (mean,V50= −59.15 mV ± 0.21;n= 15). The LVA current was inactivated completely at a holding potential of −65 mV and deinactivated fully at a holding potential of −95 mV (mean,V50= −82.40 mV ± 0.32;n= 38). These properties are consistent with other studies suggesting that the LVA current is a T-type current. The properties of these inward currents are discussed with respect to their role in generating Ca2+potentials that may contribute to the generation of the mammalian respiratory rhythm.
Control of Grip Force When Tilting Objects: Effect of Curvature of Grasped Surfaces and Applied Tangential Torque
Authors: Goodwin Antony W. , Jenmalm Per , Johansson Roland S.
Published: April 2018

When we manipulate objects in everyday tasks, there are variations in the shape of the grasped surfaces, and the loads that potentially destabilize the grasp include time-varying linear forces and torques tangential to the grasped surfaces. Previous studies of the control of fingertip forces for grasp stability have dealt principally with flat grip surfaces and linear force loads. Here, we studied the regulation of grip force with changes in curvature of grasped surfaces and changes in tangential torque applied by the index finger and thumb when humans lifted an object and rotated it about the horizontal grip axis through an angle of 65°. The curvatures of the matched pair of spherical surfaces varied from −50 m−1(concave with radius 20 mm) to 200 m−1(convex with radius 5 mm). The applied tangential torque at the orientation of 65° was varied sixfold. Regardless of the values of curvature and end torque, grip force and tangential torque were coordinated, increasing in parallel throughout the tilt with an approximately linear relationship; the slope of the line increased progressively with increasing surface curvature. This parametric scaling of grip force was directly related to the minimum grip force required to prevent rotational slip, resulting in an adequate safety margin against slip in all cases. We conclude that surface curvature parametrically influences grip force regulation when the digits are exposed to torsional loads. Furthermore, the sensorimotor programs that control the grip force apparently predict the effect of the total load comprising linear forces and tangential torques.
Perinatal Gonadectomy Exerts Regionally Selective, Lateralized Effects on the Density of Axons Immunoreactive for Tyrosine Hydroxylase in the Cerebral Cortex of Adult Male Rats
Authors: Kritzer M. F.
Published: April 2018

The catecholamine innervation of the cerebral cortex is essential for its normal operations and is implicated in cortical dysfunction in mental illness. Previous studies in rats have shown that the maturational tempo of these afferents is highly responsive to changes in gonadal hormones. The present findings show that perinatal hormone manipulation also has striking, region- and hemisphere-specific consequences for cortical catecholamines in adulthood.

The effect of perinatal gonadectomy on catecholamines was examined in representative sensory, motor, and association cortices of adult male rats by combining hormone manipulation with immunocytochemistry for tyrosine hydroxylase, a rate-limiting enzyme in catecholamine biosynthesis. Qualitative and quantitative comparison of immunoreactivity in rats perinatally gonadectomized or sham-operated revealed complex changes in gonadectomized subjects; in cingulate cortex, TH immunoreactivity was strongly and bilaterally diminished, in sensory and motor cortices, axon density was decreased in left hemispheres, but was minimally affected on the right, and in a premotor cortex, gonadectomy was without significant effect in either hemisphere. Corresponding analyses in gonadectomized rats supplemented with testosterone revealed a protective influence, albeit one in which TH immunoreactivity so showed regional and hemispheric variability in responsiveness to hormone replacement. These complex patterns of TH sensitivity suggest highly asymmetric hormone stimulation of cortical catecholamines. Such discriminative action may contribute to sex differences in the functional maturation and lateralization of the cortex and may also have bearing on disorders such as dyslexia, which show sexual dimorphisms, and in which functional laterality of the cortex may be particularly at issue.
Contrasting Role of Presenilin-1 and Presenilin-2 in Neuronal DifferentiationIn Vitro
Authors: Hong Chang-Sook , Caromile Leslie , Nomata Yasuhiro , Mori Hiroshi , Bredesen Dale E. , Koo Edward H.
Published: April 2018

Presenilin-1 (PS1) and presenilin-2 (PS2), the major genes of familial Alzheimer’s disease, are homologous tosel-12, aCaenorhabditis elegansgene involved in cell fate decision during development. Recently, wild-type and mutant presenilins have been associated also with apoptotic cell death. By using stable transfection of antisense cDNAs, we studied the functions of PS1 and PS2 during neuronal differentiation in the NTera2 human teratocarcinoma (NT2) cell line. Expression of antisense PS1 resulted in a failure of the clones to differentiate into neurons after retinoic acid induction, whereas cells transfected with antisense PS2 differentiated normally. Concomitantly, antisense PS1 clones were associated with increased apoptosis both under basal conditions and during the early period of neuronal differentiation after retinoic acid treatment. Overexpression ofbcl-2in antisense PS1 clones reduced cell death and resulted in a recovery of neuronal differentiation. These studies suggest that PS1 plays a role in differentiation and cell death and that PS1 and PS2 have differing physiological roles in this experimental paradigm.
A Role for MAPK/ERK in Sympathetic Neuron Survival: Protection against a p53-Dependent, JNK-Independent Induction of Apoptosis by Cytosine Arabinoside
Authors: Anderson Christopher N. G. , Tolkovsky Aviva M.
Published: April 2018

The antimitotic nucleoside cytosine arabinoside (araC) causes apoptosis in postmitotic neurons for which two mechanisms have been suggested: (1) araC directly inhibits a trophic factor-maintained signaling pathway required for survival, effectively mimicking trophic factor withdrawal; and (2) araC induces apoptosis by a p53-dependent mechanism distinct from trophic factor withdrawal. In rat sympathetic neurons, we found that araC treatment for 12 hr induced ∼25% apoptosis without affecting NGF-maintained signaling; there was neither reduction in the activity of mitogen actived protein kinase/extracellular signal-regulated kinase (MAPK/ERK) or protein kinase B/Akt, a kinase implicated in NGF-mediated survival, nor was there c-Jun N-terminal kinase (JNK) activation or c-Jun N-terminal phosphorylation, events implicated in apoptosis induced by NGF withdrawal. However, araC treatment, but not NGF-withdrawal, elevated expression of p53 protein before and during apoptosis. Additionally, araC-induced apoptosis was suppressed in sympathetic neurons from p53 null mice. Although MAPK/ERK activity is not necessary for NGF-induced survival, it protected against toxicity by araC, because inhibition of the MAPK pathway by PD98059 resulted in a significant increase in the rate of apoptosis induced by araC in the presence of NGF. Consistent with this finding, ciliary neurotrophic factor, which does not cause sustained activation of MAPK/ERK, did not protect against araC toxicity. Our data show that, in contrast to NGF deprivation, araC induces apoptosis via a p53-dependent, JNK-independent mechanism, against which MAPK/ERK plays a substantial protective role. Thus, NGF can suppress apoptotic mechanisms in addition to those caused by its own deprivation.
Molecular Diversity of the Calcium Channel α2δ Subunit
Authors: Klugbauer Norbert , Lacinová Lubica , Marais Elsé , Hobom Muriel , Hofmann Franz
Published: April 2018

Sequence database searches with the α2δ subunit as probe led to the identification of two new genes encoding proteins with the essential properties of this calcium channel subunit. Primary structure comparisons revealed that the novel α2δ-2 and α2δ-3 subunits share 55.6 and 30.3% identity with the α2δ-1 subunit, respectively. The number of putative glycosylation sites and cysteine residues, hydropathicity profiles, and electrophysiological character of the α2δ-3 subunit indicates that these proteins are functional calcium channel subunits. Coexpression of α2δ-3 with α1Cand cardiac β2a or α1Eand β3 subunits shifted the voltage dependence of channel activation and inactivation in a hyperpolarizing direction and accelerated the kinetics of current inactivation. The kinetics of current activation were altered only when α2δ-1 or α2δ-3 was expressed with α1C. The effects of α2δ-3 on α1Cbut not α1Eare indistinguishable from the effects of α2δ-1. Using Northern blot analysis, it was shown that α2δ-3 is expressed exclusively in brain, whereas α2δ-2 is found in several tissues.In situhybridization of mouse brain sections showed mRNA expression of α2δ-1 and α2δ-3 in the hippocampus, cerebellum, and cortex, with α2δ-1 strongly detected in the olfactory bulb and α2δ-3 in the caudate putamen.
Lipopolysaccharide Injected into the Cerebral Ventricle Evokes Fever through Induction of Cyclooxygenase-2 in Brain Endothelial Cells
Authors: Cao Chunyu , Matsumura Kiyoshi , Ozaki Masashi , Watanabe Yasuyoshi
Published: April 2018

Activation of the arachidonic acid cascade is an essential step for the development of fever during brain inflammation. We investigated the brain sites where this activation takes place by use of a rat model of brain inflammation. Intracerebroventricular administration of lipopolysaccharide but not of its vehicle evoked fever. The fever was markedly suppressed when the rats had been pretreated with a cyclooxygenase-2-specific inhibitor.In situhybridization and immunohistochemical studies revealed that cyclooxygenase-2 mRNA and its protein were induced by lipopolysaccharide in blood vessels near the cerebral ventricles and in those in the subarachnoidal space. Double immunohistochemical staining revealed that these cyclooxygenase-2-positive cells were mostly endothelial cells. The time course of fever and that of cyclooxygenase-2 induction in the endothelial cells were in parallel. Cyclooxygenase-2 mRNA in a certain type of telencephalic neurons was also upregulated by the intracerebroventricular administration, but this neuronal response occurred both in vehicle-injected rats and in lipopolysaccharide-injected ones to the same extent. Therefore, the neuronal response was not essential to the development of fever. These results suggest that brain endothelial cells play a crucial role in the development of fever during brain inflammation by activating their arachidonic acid cascade.
ATP Stimulates Sympathetic Transmitter Release via Presynaptic P2X Purinoceptors
Authors: Boehm Stefan
Published: April 2018

ATP is a fast transmitter in sympathetic ganglia and at the sympathoeffector junction. In primary cultures of dissociated rat superior cervical ganglion neurons, ATP elicits noradrenaline release in an entirely Ca2+-dependent manner. Nevertheless, ATP-evoked noradrenaline release was only partially reduced (by ∼50%) when either Na+or Ca2+channels were blocked, which indicates that ATP receptors themselves mediated transmembrane Ca2+entry. An “axonal” preparation was obtained by removing ganglia from explant cultures, which left a network of neurites behind; immunostaining for axonal and dendritic markers revealed that all of these neurites were axons. In this preparation, ATP raised intraaxonal Ca2+and triggered noradrenaline release, and these actions were not altered when Ca2+channels were blocked by Cd2+. Hence, Ca2+-permeable ATP-gated ion channels, i.e., P2X purinoceptors, are located at presynaptic sites and directly mediate Ca2+-dependent transmitter release. These presynaptic P2X receptors displayed a rank order of agonist potency of ATP ≥ 2-methylthio-ATP > ATPγS ≫ α,β-methylene-ATP ≈ β,γ-methylene-l-ATP and were blocked by suramin or PPADS. ATP, 2-methylthio-ATP, and ATPγS also evoked inward currents measured at neuronal somata, but there these agonists were equipotent. Hence, presynaptic P2X receptors resemble the cloned P2X2 subtype, but they appear to differ from somatodendritic P2X receptors in terms of agonist sensitivity. Suramin reduced depolarization-evoked noradrenaline release by up to 20%, when autoinhibitory mechanisms were inactivated by pertussis toxin. These results indicate that presynaptic P2X purinoceptors mediate a positive, whereas G-protein-coupled P2Y purinoceptors mediate a negative, feedback modulation of sympathetic transmitter release.
Evidence for a Role of Truncated trkC Receptor Isoforms in Mouse Development
Authors: Palko Mary Ellen , Coppola Vincenzo , Tessarollo Lino
Published: April 2018

ThetrkClocus encodes several receptors for neurotrophin-3, including the well studied full-length tyrosine kinase isoform, in addition to receptor isoforms lacking the kinase active domain. TrkC receptors are widely expressed throughout mouse development in many different organs. To investigate the function of truncated receptorsin vivoand to identify cell types that are biologically responsive to this gene product, we have overexpressed a physiological truncated trkC isoform in the mouse. Mice overexpressing this receptor develop to term but die in the first postnatal days. High levels of transgene expression result in severe developmental defects in the peripheral nervous system and in the heart. The severity of neuronal losses observed in these animals suggests that truncated receptors may act by sequestering neurotrophin, thus, closely relating this mouse model to the neurotrophin-3-deficient one. Lower levels of exogenous truncated receptor in transgenic mice result in a more modest phenotype and, in some neuronal populations, do not cause neural deficits. Taken together, these data suggest that truncated trkC receptor isoforms may have modulatory functions in development.
Lhx9: A Novel LIM-Homeodomain Gene Expressed in the Developing Forebrain
Authors: Rétaux Sylvie , Rogard Monique , Bach Ingolf , Failli Vieri , Besson Marie-Jo
Published: April 2018

A novel LIM-homeodomain gene,Lhx9, was isolated by degenerate RT-PCR followed by mouse embryonic library screening.Lhx9cDNA encodes a protein that is most closely related toDrosophilaapterous and rodent Lhx2 proteins. TheLhx9spatiotemporal pattern of expression during embryogenesis was similar but distinct fromLhx2. Highest expression levels were found in the diencephalon, telencephalic vesicles, and dorsal mesencephalon. Domains of expression respected the proposed neuromeric boundaries (Puelles and Rubenstein, 1993).Lhx9was also expressed in the spinal cord, forelimb and hindlimb mesenchyme, and urogenital system. AlthoughLhx9expression was sustained in diencephalon and mesencephalon from embryonic day 10.5 (E10.5) to postnatal stages, it was transient in the future cerebral cortex, where it was turned off between E14.5 and E16.5.Lhx9expression was highest if not exclusively located (depending on the region of interest) in the intermediate and mantle zones, as opposed to the mitotic ventricular zone. Lhx9 protein was tested for interaction with the recently discovered cofactors of LIM-homeodomain proteins and was found to interact strongly both with CLIM1 and CLIM2. The expression pattern and structural characteristics ofLhx9suggest that it encodes a transcription factor that might be involved in the control of cell differentiation of several neural cell types. Furthermore, Lhx9 protein could act in a combinatorial manner with other LIM-homeodomain factors expressed in overlapping pattern.
Tenascin-R Inhibits the Growth of Optic FibersIn VitroBut Is Rapidly Eliminated during Nerve Regeneration in the SalamanderPleurodeles waltl
Authors: Becker Catherina G. , Becker Thomas , Meyer Ronald L. , Schachner Melitta
Published: April 2018

Tenascin-R is a multidomain molecule of the extracellular matrix in the CNS with neurite outgrowth inhibitory functions. Despite the fact that in amphibians spontaneous axonal regeneration of the optic nerve occurs, we show here that the molecule appears concomitantly with myelination during metamorphosis and is present in the adult optic nerve of the salamanderPleurodeles waltlby immunoblots and immunohistochemistry.In vitro, adult retinal ganglion cell axons were not able to grow from retinal explants on a tenascin-R substrate or to cross a sharp substrate border of tenascin-R in the presence of laminin, indicating that tenascin-R inhibits regrowth of retinal ganglion cell axons. After an optic nerve crush, immunoreactivity for tenascin-R was reduced to undetectable levels within 8 d. Immunoreactivity for the myelin-associated glycoprotein (MAG) was also diminished by that time. Myelin was removed by phagocytosing cells at 8–14 d after the lesion, as demonstrated by electron microscopy. Tenascin-R immunoreactivity was again detectable at 6 months after the lesion, correlated with remyelination as indicated by MAG immunohistochemistry. Regenerating axons began to repopulate the distal lesioned nerve at 9 d after a crush and grew in close contact with putative astrocytic processes in the periphery of the nerve, close to the pia, as demonstrated by anterograde tracing. Thus, the onset of axonal regrowth over the lesion site was correlated with the removal of inhibitory molecules in the optic nerve, which may be necessary for successful axonal regeneration in the CNS of amphibians.