bluuebunny/crossref_metadata_2025 huggingface dataset:
Blockade of Glutamate-Mediated Activity in the Developing Retina Perturbs the Functional Segregation of ON and OFF Pathways
Authors: Bisti Silvia , Gargini Claudia , Chalupa Leo M.
Published: April 2018

The dendrites of ganglion cells initially ramify throughout the inner plexiform layer of the developing retina before becoming stratified into ON or OFF sublaminae. This ontogenetic event is thought to depend on glutamate-mediated afferent activity, because treating the developing retina with the glutamate analog 2-amino-4-phosphonobutyrate (APB), which hyperpolarizes ON cone bipolar cells and rod bipolar cells, thereby preventing their release of glutamate, effectively arrests the dendritic stratification process. To assess the functional consequences of this manipulation, extracellular recordings were made from single cells in the A laminae of the dorsal lateral geniculate nucleus and from the optic tract in mature cats that had received intraocular injections of APB during the first postnatal month. Such recordings revealed that stimulation of the APB-treated eye evoked both ON as well as OFF discharges in 37% of the cells tested. (As expected, when the normal eye was activated, virtually all cells yielded only ON or OFF responses.) The proportion of ON–OFF cells found here corresponds closely to the incidence of multistratified dendrites observed previously in anatomical studies of APB-treated cat retinas. This suggests that the ganglion cells with multistratified dendrites receive functional inputs from ON as well as OFF cone bipolar cells. This interpretation is further supported by the finding that the proportion of ON–OFF cells was very similar in the geniculate layer innervated by the treated eye and in the optic tract. The cells activated by the APB-treated eye were also found not to show response suppression when flashing stimuli of increasing size were used. This suggests that exposing the developing retina to APB perturbs the neural circuitry mediating the antagonistic center–surround organization found in normal receptive fields. The functional changes evident after treating the developing retina with APB suggest that it should now be feasible to assess how the segregation of ON and OFF retinal pathways relates to organizational features at higher levels of the visual system, such as orientation selectivity in cortical cells.
Response of Thalamocortical Neurons to Hypoxia: A Whole-Cell Patch-Clamp Study
Authors: Erdemli Gül , Crunelli Vincenzo
Published: April 2018

The effect of hypoxia (3–4 min of 95% N2, 5% CO2) on thalamocortical (TC) neurons was investigated using the whole-cell patch-clamp technique in rat dorsal lateral geniculate nucleus slices kept submerged at 32°C. The predominant feature of the response of TC neurons to hypoxia was an increase in input conductance (ΔGN= 117 ± 15%,n= 33) that was accompanied by an inward shift in baseline holding current (IBH) at −65 and −57 mV (ΔIBH= −45 ± 6 pA,n= 18, and −25 ± 8 pA,n= 33, respectively) but not at −40 mV. The hypoxia-induced increase inGN(as well as the shift inIBH) was abolished by procedures that are known to blockIh, i.e., bath application of 4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino)-pyrimidinium chloride (100–300 μm) (ΔGN= 5 ± 13%,n= 11) and CsCl (2–3 mm) (ΔGN= 16 ± 16%,n= 5), or low [Na+]o(ΔGN= 10 ± 10%,n= 5), whereas bath application of BaCl2(0.1–2.0 mm) had no significant effect (ΔGN= 128 ± 14%,n= 8). The hypoxic response was also abolished in low [Ca+2]o(ΔGN= 25 ± 16%, ΔIBH= −6 ± 8 pA,n= 13), but was unaffected by recording with electrodes containing EGTA (10 mm), BAPTA (10–30 mm), Cs+, or Cl−, as well as in the presence of external tetraethylammonium and 4-aminopyridine. Furthermore, preincubation of the slices with botulinum toxin A (100 nm), which is known to reduce Ca2+-dependent transmitter release, blocked the hypoxic response (ΔGN= −3 ± 15%, ΔIBH= 10 ± 5 pA,n= 4).

We suggest that a positive shift in the voltage-dependence ofIhand a change in its activation kinetics, which transforms it into a fast activating current, may be responsible for the hypoxia-induced changes inGNandIBH, probably via an increase in Ca+2-dependent transmitter release.
Hippocampal Neurotoxicity of Δ9-Tetrahydrocannabinol
Authors: Chan Guy Chiu-Kai , Hinds Thomas R. , Impey Soren , Storm Daniel R.
Published: April 2018

Marijuana consumption elicits diverse physiological and psychological effects in humans, including memory loss. Here we report that Δ9-tetrahydrocannabinol (THC), the major psychoactive component of marijuana, is toxic for hippocampal neurons. Treatment of cultured neurons or hippocampal slices with THC caused shrinkage of neuronal cell bodies and nuclei as well as genomic DNA strand breaks, hallmarks of neuronal apoptosis. Neuron death induced by THC was inhibited by nonsteroidal anti-inflammatory drugs, including indomethacin and aspirin, as well as vitamin E and other antioxidants. Furthermore, treatment of neurons with THC stimulated a significant increase in the release of arachidonic acid. We hypothesize that THC neurotoxicity is attributable to activation of the prostanoid synthesis pathway and generation of free radicals by cyclooxygenase. These data suggest that some of the memory deficits caused by cannabinoids may be caused by THC neurotoxicity.
Identification of the Dopamine D3 Receptor in Oligodendrocyte Precursors: Potential Role in Regulating Differentiation and Myelin Formation
Authors: Bongarzone Ernesto R. , Howard Sherrel G. , Schonmann Vilma , Campagnoni Anthony T.
Published: April 2018

Expression of the dopamine D3 receptor (D3r) was found in primary mixed glial cultures from newborn brain and in the corpus callosumin vivoduring the peak of myelination. Expression of the D3r mRNA, but not D2r mRNA, was detected as early as 5 din vitro(DIV) by RT-PCR. Immunoblot studies revealed D3r protein was also expressed in the cultures. Double immunofluorescence analysis for the D3r and for surface markers of specific stages of oligodendrocyte development indicated that D3r expression occurred in precursors and in immature oligodendrocytes but not in mature oligodendrocytes (i.e., A2B5+007−01−and A2B5+007+01−cells but not A2B5−007+01+cells). Confocal microscopic analysis indicated that D3r was associated with cell bodies and cell membranes but not with the processes emanating from cell somas. Immunohistochemistry of brain sections revealed the presence of D3r in some oligodendrocytes located mainly within the genu and radiato of the corpus callosum during the active period of myelination.

Treatment of cultures with 20 μmquinpirole led to decreased numbers of O1+oligodendrocytes possessing myelin-like membranes as well as an increase in the number of precursors in 14 DIV cultures. This effect was prevented by the dopamine antagonist haloperidol. These results show that the D3r expression is not restricted to neurons but it is also expressed in differentiating oligodendrocytes before terminal maturation. It also suggests that dopamine or some other D3r ligand may play a role in oligodendrocyte differentiation and/or the formation of myelin by mature oligodendrocytes.
Patterns of Intracellular Calcium Fluctuation in Precursor Cells of the Neocortical Ventricular Zone
Authors: Owens David F. , Kriegstein Arnold R.
Published: April 2018

Changes in intracellular free calcium concentration ([Ca2+]i) are known to influence a variety of events in developing neurons. Although spontaneous changes of [Ca2+]ihave been examined in immature cortical neurons, the calcium dynamics of cortical precursor cells have received less attention. Using an intact cortical mantle and confocal laser microscopy, we examined the spatiotemporal patterns of spontaneous [Ca2+]ifluctuations in neocortical ventricular zone (VZ) cellsin situ. The majority of activity consisted of single cells that displayed independent [Ca2+]ifluctuations. These events occurred in cells throughout the depth of the VZ. Immunohistochemical staining confirmed that these events occurred primarily in precursor cells rather than in postmitotic neurons. When imaging near the ventricular surface, synchronous spontaneous [Ca2+]iincreases were frequently observed in pairs of adjacent cells. Cellular morphology, time-lapse imaging, and nuclear staining demonstrated that this activity occurred in mitotically active cells. A third and infrequently encountered pattern of activity consisted of coordinated spontaneous increases in [Ca2+]iin groups of neighboring VZ cells. The morphological characteristics of these cells and immunohistochemical staining suggested that the coordinated events occurred in gap junction-coupled precursor cells. All three patterns of activity were dependent on the release of Ca2+from intracellular stores. These results demonstrate distinct patterns of spontaneous [Ca2+]ichange in cortical precursor cells and raise the possibility that these dynamics may contribute to the regulation of neurogenesis.
Leukemia Inhibitory Factor Is an Anti-Inflammatory and Analgesic Cytokine
Authors: Banner Lisa R. , Patterson Paul H. , Allchorne Andrew , Poole Steve , Woolf Clifford J.
Published: April 2018

The mRNA for leukemia inhibitory factor (LIF), a neuroimmune signaling molecule, is elevated during skin inflammation produced by intraplantar injection of complete Freund’s adjuvant (CFA). Moreover, although LIF knock-out mice display normal sensitivity to cutaneous mechanical and thermal stimulation compared with wild-type mice, the degree of CFA-induced inflammation in mice lacking LIF is enhanced in spatial extent, amplitude, cellular infiltrate, and interleukin (IL)-1β and nerve growth factor (NGF) expression. Conversely, local injection of low doses of recombinant LIF diminishes mechanical and thermal hypersensitivity as well as the IL-1β and NGF expression induced by CFA. These data show that upregulation of LIF during peripheral inflammation serves a key, early anti-inflammatory role and that exogenous LIF can reduce inflammatory hyperalgesia.
Behavioral State Control through Differential Serotonergic Inhibition in the Mesopontine Cholinergic Nuclei: A Simultaneous Unit Recording and Microdialysis Study
Authors: Thakkar Mahesh M. , Strecker Robert E. , McCarley Robert W.
Published: April 2018

Cholinergic neurons of the mesopontine nuclei are strongly implicated in behavioral state regulation. One population of neurons in the cholinergic zone of the laterodorsal tegmentum and the pedunculopontine nuclei, referred to as rapid eye movement (REM)-on neurons, shows preferential discharge activity during REM sleep, and extensive data indicate a key role in production of this state. Another neuronal group present in the same cholinergic zone of the laterodorsal tegmentum and the pedunculopontine nuclei, referred to as Wake/REM-on neurons, shows preferential discharge activity during both wakefulness and REM sleep and is implicated in the production of electroencephalographic activation in both of these states. To test the hypothesis of differential serotonergic inhibition as an explanation of the different state-related discharge activity, we developed a novel methodology that enabled, in freely behaving animals, simultaneous unit recording and local perfusion of neuropharmacological agents using a microdialysis probe adjacent to the recording electrodes. Discharge activity of REM-on neurons was almost completely suppressed by local microdialysis perfusion of the selective 5-HT1Aagonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), although this agonist had minimal or no effect on the Wake/REM-on neurons. We conclude that selective serotonergic inhibition is a basis of differential state regulation in the mesopontine cholinergic nuclei, and that the novel methodology combining neurophysiological and neuropharmacological information from the freely behaving animal shows great promise for further insight into the neural basis of behavioral control.
Mice Lacking Ataxin-1 Display Learning Deficits and Decreased Hippocampal Paired-Pulse Facilitation
Authors: Matilla Antoni , Roberson Erik D. , Banfi Sandro , Morales Joanella , Armstrong Dawna L. , Burright Eric N. , Orr Harry T. , Sweatt John D. , Zoghbi Huda Y. , Matzuk Martin M.
Published: April 2018

Spinocerebellar ataxia type 1 (SCA1) is a neurodegenerative disorder characterized by ataxia, progressive motor deterioration, and loss of cerebellar Purkinje cells. To investigate SCA1 pathogenesis and to gain insight into the function of theSCA1gene product ataxin-1, a novel protein without homology to previously described proteins, we generated mice with a targeted deletion in the murineSca1gene. Mice lacking ataxin-1 are viable, fertile, and do not show any evidence of ataxia or neurodegeneration. However,Sca1null mice demonstrate decreased exploratory behavior, pronounced deficits in the spatial version of the Morris water maze test, and impaired performance on the rotating rod apparatus. Furthermore, neurophysiological studies performed in area CA1 of the hippocampus reveal decreased paired-pulse facilitation inSca1null mice, whereas long-term and post-tetanic potentiations are normal. These findings demonstrate that SCA1 is not caused by loss of function of ataxin-1 and point to the possible role of ataxin-1 in learning and memory.
Absence of Fenfluramine-Induced Anorexia and Reduced c-fos Induction in the Hypothalamus and Central Amygdaloid Complex of Serotonin 1B Receptor Knock-Out Mice
Authors: Lucas José J. , Yamamoto Ai , Scearce-Levie Kimberly , Saudou Frédéric , Hen René
Published: April 2018

Fenfluramine, a serotonin releaser and uptake inhibitor, has been widely prescribed as an appetite suppressant. Despite its popular clinical use, however, the precise neural pathways and specific 5-HT receptors that account for its anorectic effect have yet to be elucidated. To test the hypothesis that stimulation of 5-HT1Breceptors is required for the anorectic effect of fenfluramine, we assessed food intake in wild-type and 5-HT1Bknock-out mice. Next, to determine possible brain structures and pathways that may contribute to the 5-HT1B-mediated effects of fenfluramine, we studied by immunohistochemistry the induction of the immediate early gene c-fos. Although the effect of fenfluramine on locomotion was indistinguishable between both wild-type and 5-HT1Bknock-out mice, the anorectic effect of the drug was absent in only the knock-out mice. Furthermore, the induction of c-Fos immunoreactivity found in the paraventricular nucleus of the hypothalamus (PVN) of wild-type mice was substantially reduced in the knock-outs. Induction in the central amygdaloid nucleus (CeA) and in the bed nucleus of the stria terminalis (BNST), although robust in wild-type animals, was completely absent in knock-out animals. The mixed 5-HT1A/1Bagonist RU24969 was able to mimic both the hypophagia and c-fos induction elicited by fenfluramine in wild-type mice, but not in the 5-HT1Bknock-out mice. Our results thus demonstrate that stimulation of 5-HT1Breceptors is required for fenfluramine-induced anorexia and suggest a role for the PVN, CeA, and BNST in mediating this effect.
D2-Like Dopamine Autoreceptor Activation Reduces Quantal Size in PC12 Cells
Authors: Pothos Emmanuel N. , Przedborski Serge , Davila Viviana , Schmitz Yvonne , Sulzer David
Published: April 2018

D2-like dopamine autoreceptors regulate dopamine release and are implicated in important actions of antipsychotic drugs and rewarding behaviors. To directly observe the effects of D2autoreceptors on exocytic neurotransmitter release, we measured quantal release of dopamine from pheochromocytoma PC12 cells that express D2and D4autoreceptors. High potassium-evoked secretion in PC12 cells produced a unimodal population of quantal sizes. We found that exposures to the D2-like agonist quinpirole that inhibited tyrosine hydroxylase activity by ∼50% also reduced quantal size by ∼50%. The reduced quantal size was blocked by the D2antagonist sulpiride and reversed byl-DOPA. Quinpirole also decreased the frequency of stimulation-evoked quantal release. Together, these findings indicate effects on quantal neurotransmission by D2-like dopamine autoreceptors previously distinguished as synthesis-modulating autoreceptors that regulate tyrosine hydroxylase activity versus impulse-regulating autoreceptors that modulate membrane potential. The results also provide an initial demonstration of a receptor-mediated mechanism that alters quantal size.
An Essential Role for a Small Synaptic Vesicle-Associated Phosphatidylinositol 4-Kinase in Neurotransmitter Release
Authors: Wiedemann Claudia , Schäfer Theo , Burger Max M. , Sihra Talvinder S.
Published: April 2018

Glutamate release from nerve terminals is the consequence of Ca2+-triggered fusion of small synaptic vesicles with the presynaptic plasma membrane. ATP dependence of neurotransmitter release has been suggested to be founded, in part, on phosphorylation steps preceding membrane fusion. Here we present evidence for an essential role of phosphatidylinositol phosphorylation in stimulated release of neurotransmitter glutamate from isolated nerve terminals (synaptosomes). Specifically, we show that a phosphatidylinositol 4-kinase (PtdIns 4-kinase) activity resides on nerve terminal-derived small synaptic vesicles (SSVs) and that inhibition of the PtdIns 4-kinase activity in intact synaptosomes leads to attenuation of the evoked release of glutamate. The attenuation of transmitter release is reversible and correlates with respective changes in intrasynaptosomal PtdIns 4-kinase activity. Because only the Ca2+-dependent release of glutamate is affected, regulation appears to be at the level of exocytosis. Taken together, our data imply a mandatory role for PtdIns 4-kinase and phosphoinositide products in the regulated exocytosis of SSV in mammalian nerve terminals.
Imaging Odor-Induced Calcium Transients in Single Olfactory Cilia: Specificity of Activation and Role in Transduction
Authors: Leinders-Zufall Trese , Greer Charles A. , Shepherd Gordon M. , Zufall Frank
Published: April 2018

The possibility that odor stimuli trigger distinct Ca2+elevations within the cilia of vertebrate olfactory receptor neurons (ORNs) is a widely proposed concept. However, because of the small size of the olfactory cilia, the existence and properties of such Ca2+elevations and their role in odor transduction are still unknown. We investigate odor-induced Ca2+changes in individual olfactory cilia from salamander using the Ca2+indicator dye fluo-3 in combination with laser scanning confocal microscopy. Single brief applications of odor ligand produce highly localized Ca2+elevations in individual cilia lasting for several seconds. These Ca2+signals originate in the cilia and depend entirely on Ca2+entry through ciliary cyclic nucleotide-gated ion channels. The odor specificity of the Ca2+rises implies a receptor-operated mechanism underlying odor detection. Each of the cilia on a receptor neuron functions as an independent biochemical compartment that can detect odorants and produce a Ca2+transient with remarkably uniform properties in terms of kinetics and odor specificity. The rate of recovery of the odor-induced Ca2+transients matches recovery from a short-term form of odor adaptation. Application of the membrane-permeant intracellular Ca2+chelator BAPTA AM eliminates this odor adaptation. The results indicate that an olfactory cilium serves as a basic functional unit at the input level of the olfactory system, controlling both the specificity and sensitivity of odor detection.
Readiness of Zebrafish Brain Neurons to Regenerate a Spinal Axon Correlates with Differential Expression of Specific Cell Recognition Molecules
Authors: Becker Thomas , Bernhardt Robert R. , Reinhard Eva , Wullimann Mario F. , Tongiorgi Enrico , Schachner Melitta
Published: April 2018

We analyzed changes in the expression of mRNAs for the axonal growth-promoting cell recognition molecules L1.1, L1.2, and neural cell adhesion molecule (NCAM) after a rostral (proximal) or caudal (distal) spinal cord transection in adult zebrafish. One class of cerebrospinal projection nuclei (represented by the nucleus of the medial longitudinal fascicle, the intermediate reticular formation, and the magnocellular octaval nucleus) showed a robust regenerative response after both types of lesions as determined by retrograde tracing and/orin situhybridization for GAP-43. A second class (represented by the nucleus ruber, the nucleus of the lateral lemniscus, and the tangential nucleus) showed a regenerative response only after proximal lesion. After distal lesion, upregulation of L1.1 and L1.2 mRNAs, but not NCAM mRNA expression, was observed in the first class of nuclei. The second class of nuclei did not show any changes in their mRNA expression after distal lesion. After proximal lesion, both classes of brain nuclei upregulated L1.1 mRNA expression (L1.2 and NCAM were not tested after proximal lesion). In the glial environment distal to the spinal lesion, labeling for L1.2 mRNA but not L1.1 or NCAM mRNAs was increased. These results, combined with findings in the lesioned retinotectal system of zebrafish (Bernhardt et al., 1996), indicate that the neuron-intrinsic regulation of cell recognition molecules after axotomy depends on the cell type as well as on the proximity of the lesion to the neuronal soma. Glial reactions differ for different regions of the CNS.
DOPA Decarboxylase Activity in Attention Deficit Hyperactivity Disorder Adults. A [Fluorine-18]Fluorodopa Positron Emission Tomographic Study
Authors: Ernst Monique , Zametkin Alan J. , Matochik John A. , Jons Peter H. , Cohen Robert M.
Published: April 2018

Converging evidence implicates the dopaminergic system and the prefrontal and nigrostriatal regions in the pathophysiology of attention deficit hyperactivity disorder (ADHD). Using positron emission tomography (PET) with [fluorine-18]fluorodopa (F18-DOPA), we compared the integrity of the presynaptic dopaminergic function between 17 ADHD adults and 23 healthy controls. The ratio of the isotope concentration of specific regions to that of nonspecific regions reflects DOPA decarboxylase activity and dopamine storage processes. Of three composite regions (prefrontal cortex, striatum, and midbrain), only the prefrontal cortex showed significantly different F18-DOPA ratios in ADHD as compared with control adults (p< 0.01). The medial and left prefrontal areas were the most altered (lower F18-DOPA ratios by 52 and 51% in ADHD as compared with controls). Similarly, the interaction [sex × diagnosis] was significant only in the prefrontal cortex (p< 0.02): lower ratios in men than in women in ADHD and vice versa in controls. These findings suggest that a prefrontal dopaminergic dysfunction mediates ADHD symptoms in adults and that gender influences this abnormality. On the basis of previous neuroimaging findings in ADHD showing discrepant findings in adults and adolescents and on evidence for midbrain dopaminergic defect in adolescents, we hypothesize that the prefrontal dopaminergic abnormality in ADHD adults is secondary and results from an interaction of the primary subcortical dopaminergic deficit with processes of neural maturation and neural adaptation.
Region-Specific Regulation of Glutamic Acid Decarboxylase (GAD) mRNA Expression in Central Stress Circuits
Authors: Bowers Garrett , Cullinan William E. , Herman James P.
Published: April 2018

Neurocircuit inhibition of hypothalamic paraventricular nucleus (PVN) neurons controlling hypothalamo–pituitary–adrenocortical (HPA) activity prominently involves GABAergic cell groups of the hypothalamus and basal forebrain. In the present study, stress responsiveness of GABAergic regions implicated in HPA inhibition was assessed byin situhybridization, using probes recognizing the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD65 and GAD67 isoforms). Acute restraint preferentially increased GAD67 mRNA expression in several stress-relevant brain regions, including the arcuate nucleus, dorsomedial hypothalamic nucleus, medial preoptic area, bed nucleus of the stria terminalis (BST) and hippocampus (CA1 and dentate gyrus). In all cases GAD67 mRNA peaked at 1 hr after stress and returned to unstimulated levels by 2 hr. GAD65 mRNA upregulation was only observed in the BST and dentate gyrus. In contrast, chronic intermittent stress increased GAD65 mRNA in the anterior hypothalamic area, dorsomedial nucleus, medial preoptic area, suprachiasmatic nucleus, anterior BST, perifornical nucleus, and periparaventricular nucleus region. GAD67 mRNA increases were only observed in the medial preoptic area, anterior BST, and hippocampus. Acute and chronic stress did not affect GAD65 or GAD67 mRNA expression in the caudate nucleus, reticular thalamus, or parietal cortex. Overall, the results indicate preferential upregulation of GAD in central circuitry responsible for direct (hypothalamus, BST) or multisynaptic (hippocampus) control of HPA activity. The distinct patterns of GAD65 and GAD67 by acute versus chronic stress suggest stimulus duration-dependent control of GAD biosynthesis. Chronic stress-induced increases in GAD65 mRNA expression predict enhanced availability of GAD65 apoenzyme after prolonged stimulation, whereas acute stress-specific GAD67 upregulation is consistent withde novosynthesis of active enzyme by discrete stressful stimuli.
Multitasking in the Olfactory System: Context-Dependent Responses to Odors Reveal Dual GABA-Regulated Coding Mechanisms in Single Olfactory Projection Neurons
Authors: Christensen Thomas A. , Waldrop Brian R. , Hildebrand John G.
Published: April 2018

Studies of olfaction have focused mainly on neural processing of information about the chemistry of odors, but olfactory stimuli have other properties that also affect central responses and thus influence behavior. In moths, continuous and intermittent stimulation with the same odor evokes two distinct flight behaviors, but the neural basis of this differential response is unknown. Here we show that certain projection neurons (PNs) in the primary olfactory center in the brain give context-dependent responses to a specific odor blend, and these responses are shaped in several ways by a bicuculline-sensitive GABA receptor. Pharmacological dissection of PN responses reveals that bicuculline blocks GABAA-type receptors/chloride channels in PNs, and that these receptors play a critical role in shaping the responses of these glomerular output neurons. The firing patterns of PNs are not odor-specific but are strongly modulated by the temporal pattern of the odor stimulus. Brief repetitive odor pulses evoke fast inhibitory potentials, followed by discrete bursts of action potentials that are phase-locked to the pulses. In contrast, the response to a single prolonged stimulus with the same odor is a series of slow oscillations underlying irregular firing. Bicuculline disrupts the timing of both types of responses, suggesting that GABAA-like receptors underlie both coding mechanisms. These results suggest that glomerular output neurons could use more than one coding scheme to represent a single olfactory stimulus. Moreover, these context-dependent odor responses encode information about both the chemical composition and the temporal pattern of the odor signal. Together with behavioral evidence, these findings suggest that context-dependent odor responses evoke different perceptions in the brain that provide the animal with important information about the spatiotemporal variations that occur in natural odor plumes.
Dynamic Regulation of RGS2 Suggests a Novel Mechanism in G-Protein Signaling and Neuronal Plasticity
Authors: Ingi Tatsuya , Krumins Andrejs M. , Chidiac Peter , Brothers Greg M. , Chung Stephen , Snow Bryan E. , Barnes Carol A. , Lanahan Anthony A. , Siderovski David P. , Ross Elliott M. , Gilman Alfred G. , Worley Paul F.
Published: April 2018

Long-term neuronal plasticity is known to be dependent on rapidde novosynthesis of mRNA and protein, and recent studies provide insight into the molecules involved in this response. Here, we demonstrate that mRNA encoding a member of the regulator of G-protein signaling (RGS) family, RGS2, is rapidly induced in neurons of the hippocampus, cortex, and striatum in response to stimuli that evoke plasticity. Although several members of the RGS family are expressed in brain with discrete neuronal localizations, RGS2 appears unique in that its expression is dynamically responsive to neuronal activity. In biochemical assays, RGS2 stimulates the GTPase activity of the α subunit of Gqand Gi1. The effect on Gi1 was observed only after reconstitution of the protein in phospholipid vesicles containing M2 muscarinic acetylcholine receptors. RGS2 also inhibits both Gq- and Gi-dependent responses in transfected cells. These studies suggest a novel mechanism linking neuronal activity and signal transduction.
Altered Ca2+Signaling and Mitochondrial Deficiencies in Hippocampal Neurons of Trisomy 16 Mice: A Model of Down’s Syndrome
Authors: Schuchmann Sebastian , Müller Wolfgang , Heinemann Uwe
Published: April 2018

It has been suggested that augmented nerve cell death in neurodegenerative diseases might result from an impairment of mitochondrial function. To test this hypothesis, we investigated age-dependent changes in neuronal survival and glutamate effects on Ca2+homeostasis and mitochondrial energy metabolism in cultured hippocampal neurons from diploid and trisomy 16 (Ts16) mice, a model of Down’s syndrome. Microfluorometric techniques were used to measure survival rate, [Ca2+]ilevel, mitochondrial membrane potential, and NAD(P)H autofluorescence. We found that Ts16 neurons die more than twice as fast as diploid neurons under otherwise identical culture conditions. Basal [Ca2+]ilevels were elevated in Ts16 neurons. Moreover, in comparison to diploid neurons, Ts16 neurons showed a prolonged recovery of [Ca2+]iand mitochondrial membrane potential after brief glutamate application. Glutamate evoked an initial NAD(P)H decrease that was found to be extended in Ts16 neurons in comparison to diploid neurons. Furthermore, for all age groups tested, glutamate failed to cause a subsequent NAD(P)H overshoot in Ts16 cultures in contrast to diploid cultures. In the presence of cyclosporin A, an inhibitor of the mitochondrial membrane permeability transition, NAD(P)H increase was observed in both diploid and Ts16 neurons. The results support the hypothesis that Ca2+impairs mitochondrial energy metabolism and may play a role in the pathogenesis of neurodegenerative changes in neurons from Ts16 mice.
Regional Selective Neuronal Degeneration after Protein Phosphatase Inhibition in Hippocampal Slice Cultures: Evidence for a MAP Kinase-Dependent Mechanism
Authors: Rundén Elise , Seglen Per O. , Haug Finn-Mogens , Ottersen Ole Petter , Wieloch Tadeusz , Shamloo Mehrdad , Laake Jon Henrik
Published: April 2018

The regional selectivity and mechanisms underlying the toxicity of the serine/threonine protein phosphatase inhibitor okadaic acid (OA) were investigated in hippocampal slice cultures. Image analysis of propidium iodide-labeled cultures revealed that okadaic acid caused a dose- and time-dependent injury to hippocampal neurons. Pyramidal cells in the CA3 region and granule cells in the dentate gyrus were much more sensitive to okadaic acid than the pyramidal cells in the CA1 region. Electron microscopy revealed ultrastructural changes in the pyramidal cells that were not consistent with an apoptotic process. Treatment with okadaic acid led to a rapid and sustained tyrosine phosphorylation of the mitogen-activated protein kinases ERK1 and ERK2 (p44/42mapk). The phosphorylation was markedly reduced after treatment of the cultures with the microbial alkaloid K-252a (a nonselective protein kinase inhibitor) or the MAP kinase kinase (MEK1/2) inhibitor PD98059. K-252a and PD98059 also ameliorated the okadaic acid-induced cell death. Inhibitors of protein kinase C, Ca2+/calmodulin-dependent protein kinase II, or tyrosine kinase were ineffective. These results indicate that sustained activation of the MAP kinase pathway, as seen after e.g., ischemia, may selectively harm specific subsets of neurons. The susceptibility to MAP kinase activation of the CA3 pyramidal cells and dentate granule cells may provide insight into the observed relationship between cerebral ischemia and dementia in Alzheimer’s disease.
Reciprocal Regulation of Ciliary Neurotrophic Factor Receptors and Acetylcholine Receptors during Synaptogenesis in Embryonic Chick Atria
Authors: Wang Xin , Halvorsen Stanley W.
Published: April 2018

Ciliary neurotrophic factor (CNTF) has been implicated in the development, survival, and maintenance of a broad range of neurons and glia in the peripheral nervous system and the CNS. Evidence also suggests that CNTF may affect development of cells outside the nervous system. We have found that functional CNTF and its receptor are expressed in developing embryonic chick heart and may be involved in parasympathetic synapse formation. CNTF and CNTF receptor mRNA levels were highest at embryonic day 11 (E11)–E13, the period of parasympathetic innervation in chick atria. Levels of atrial CNTF receptor mRNA were fourfold greater at E13 than at E6 and at E13 were 2.5-fold higher in atria than in ventricle, corresponding to the higher degree of parasympathetic innervation occurring in atria. Treatment of isolated atria or cultured atrial myocytes with recombinant human or avian CNTF resulted in the tyrosine phosphorylation and nuclear translocation of the signal transducer and activator of transcription STAT3. The developmental increase in atrial CNTF receptor mRNA was enhanced by stimulating muscarinic receptors with carbacholin ovoand was inhibited by blocking muscarinic cholinergic receptors with atropine. Treatment of cultured atrial myocytes with CNTF resulted in a twofold increase in the levels of muscarinic receptors. Thus, CNTF was able to regulate a key component of parasympathetic synapses on atrial myocytes. These results suggest a postsynaptic role for CNTF in the onset of parasympathetic function in the developing heart and provide new clues to molecular mechanisms directing synapse formation at targets of the autonomic nervous system.
Increase in Serotonin-1A Autoreceptors in the Midbrain of Suicide Victims with Major Depression—Postmortem Evidence for Decreased Serotonin Activity
Authors: Stockmeier Craig A. , Shapiro Laura A. , Dilley Ginny E. , Kolli Tamara N. , Friedman Lee , Rajkowska Grazyna
Published: April 2018

It has been hypothesized that a deficit in serotonin may be a crucial determinant in the pathophysiology of major depression. Serotonin-1A receptors are located on serotonin cell bodies in the midbrain dorsal raphe (DR) nucleus, and the activation of these receptors inhibits the firing of serotonin neurons and diminishes the release of this neurotransmitter in the prefrontal cortex. Repeated treatment with some antidepressant medications desensitizes serotonin-1A receptors in the rat midbrain. The present study determined whether the binding of [3H]8-hydroxy-2-(di-n-propyl)aminotetralin (8-OH-DPAT), an agonist at serotonin-1A receptors, is altered in the midbrain of suicide victims with major depression. Radiolabeling of the serotonin-1A receptor in the DR varied significantly along the rostral-to-caudal extent of the human midbrain. The binding of [3H]8-OH-DPAT to serotonin-1A receptors was increased significantly in the midbrain DR of suicide victims with major depression as compared with psychiatrically normal control subjects. In suicide victims with major depression, the increase in the binding of [3H]8-OH-DPAT to serotonin-1A receptors was detected in the entire DR and specifically localized to the dorsal and ventrolateral subnuclei. Enhanced radioligand binding of an agonist to inhibitory serotonin-1A autoreceptors in the human DR provides pharmacological evidence to support the hypothesis of diminished activity of serotonin neurons in suicide victims with major depression.
Food Restriction Enhances the Central Rewarding Effect of Abused Drugs
Authors: Cabeza de Vaca Soledad , Carr Kenneth D.
Published: April 2018

Chronic food restriction increases the systemic self-administration and locomotor-stimulating effect of abused drugs. However, it is not clear whether these behavioral changes reflect enhanced rewarding potency or a CNS-based modulatory process. The purpose of this study was to determine whether food restriction specifically increases the rewarding potency of drugs, as indexed by their threshold-lowering effect on lateral hypothalamic self-stimulation, and whether any such effect can be attributed to an enhanced central response rather than changes in drug disposition. When drugs were administered systemically, food restriction potentiated the threshold-lowering effect of amphetamine (0.125, 0.25, and 0.5 mg/kg, i.p.), phencyclidine (1.0, 2.0, and 3.0 mg/kg, i.p.), and dizocilpine (MK-801) (0.0125, 0.05, and 0.1 mg/kg, i.p.) but not nicotine (0.15, 0.3, 0.45 mg/kg, s.c.). When amphetamine (25.0, 50.0, and 100.0 μg) and MK-801 (5.0, 10.0, and 20.0 μg) were administered via the intracerebroventricular route, food restriction again potentiated the threshold-lowering effects and increased the locomotor-stimulating effects of both drugs. These results indicate that food restriction increases the sensitivity of neural substrates for rewarding and stimulant effects of drugs. In light of work that attributes rewarding effects of MK-801 to blockade of NMDA receptors on medium spiny neurons in nucleus accumbens, the elements affected by food restriction may lie downstream from the mesoaccumbens dopamine neurons whose terminals are the site of amphetamine-rewarding action. Possible metabolic–endocrine triggers of this effect are discussed, as is the likelihood that mechanisms mediating the modulatory effect of food restriction differ from those mediating sensitization by intermittent drug exposure.
Cognitive Channels Computing Action Distance and Direction
Authors: Bhat Raghuram B. , Sanes Jerome N.
Published: April 2018

Visually guided, goal-directed reaching requires encoding action distance and direction from attributes of visual landmarks. We identified a cognitive mechanism that seemingly performs visual motor extension before action initiation and replicated and extended previous results that identified a mechanism for visual motor mental rotation. We find that humans systematically delay action onset while newly planning increasingly distant arm movements beyond a visual landmark, consistent with an internal representation for visual motor extension. Onset times also changed systematically during concurrent mental rotation and visual motor extension computations required to process new directions and distances. Visual motor extension associated with reaching slowed when participants needed to plan action direction within the same time frame, whereas mental rotation efficiency was unaffected by concurrent needs to prepare action distance. In contrast to parallel direction and distance computations needed for direct aiming to a visual target, the planning of new directions and distances likely occurs at distinct times. When considered with previous findings, the current results suggest the existence of an intermediate component of motor preparation that engages a covert mechanism of cognitive motor planning.
Glial Contribution to Glutamate Uptake at Schaffer Collateral–Commissural Synapses in the Hippocampus
Authors: Bergles Dwight E. , Jahr Craig E.
Published: April 2018

Astrocytes in the hippocampus express high-affinity glutamate transporters that are important for lowering the concentration of extracellular glutamate after release at excitatory synapses. These transporters exhibit a permeability to chaotropic anions that is associated with transport, allowing their activity to be monitored in cell-fee patches when highly permeant anions are present. Astrocyte glutamate transporters are highly temperature sensitive, becausel-glutamate-activated, anion-potentiated transporter currents in outside-out patches from these cells exhibited larger amplitudes and faster kinetics at 36°C than at 24°C. The cycling rate of these transporters was estimated by using paired applications of eitherl-glutamate ord-aspartate to measure the time necessary for the peak of the transporter current to recover from the steady-state level. Transporter currents in patches recovered with a time constant of 11.6 msec at 36°C, suggesting that either the turnover rate of native transporters is much faster than previously reported for expressed EAAT2 transporters or the efficiency of these transporters is very low. Synaptically activated transporter currents persisted in astrocytes at physiological temperatures, although no evidence of these currents was found in CA1 pyramidal neurons in response to afferent stimulation.l-glutamate-gated transporter currents were also not detected in outside-out patches from pyramidal neurons. These results are consistent with the hypothesis that astrocyte transporters are responsible for taking up the majority of glutamate released at Schaffer collateral–commissural synapses in the hippocampus.
Rapid Ca2+Entry through Ca2+-Permeable AMPA/Kainate Channels Triggers Marked Intracellular Ca2+Rises and Consequent Oxygen Radical Production
Authors: Carriedo Sean G. , Yin Hong Zhen , Sensi Stefano L. , Weiss John H.
Published: April 2018

The widespread neuronal injury that results after brief activation of highly Ca2+-permeable NMDA channels may, in large part, reflect mitochondrial Ca2+overload and the consequent production of injurious oxygen radicals. In contrast, AMPA/kainate receptor activation generally causes slower toxicity, and most studies have not found evidence of comparable oxygen radical production. Subsets of central neurons, composed mainly of GABAergic inhibitory interneurons, express AMPA/kainate channels that are directly permeable to Ca2+ions. Microfluorometric techniques were performed by using the oxidation-sensitive dye hydroethidine (HEt) to determine whether the relatively rapid Ca2+flux through AMPA/kainate channels expressed on GABAergic neurons results in oxygen radical production comparable to that triggered by NMDA. Consistent with previous studies, NMDA exposures triggered increases in fluorescence in most cultured cortical neurons, whereas high K+(50 mm) exposures (causing depolarization-induced Ca2+influx through voltage-sensitive Ca2+channels) caused little fluorescence change. In contrast, kainate exposure caused fluorescence increases in a distinct subpopulation of neurons; immunostaining for glutamate decarboxylase revealed the responding neurons to constitute mainly the GABAergic population. The effect of NMDA, kainate, and high K+exposures on oxygen radical production paralleled the effect of these exposures on intracellular Ca2+levels when they were monitored with the low-affinity Ca2+-sensitive dye fura-2FF, but not with the high-affinity dye fura-2. Inhibition of mitochondrial electron transport with CN−or rotenone almost completely blocked kainate-triggered oxygen radical production. Furthermore, antioxidants attenuated neuronal injury resulting from brief exposures of NMDA or kainate. Thus, as with NMDA receptor activation, rapid Ca2+influx through Ca2+-permeable AMPA/kainate channels also may result in mitochondrial Ca2+overload and consequent injurious oxygen radical production.
Increased Neurogenesis in the Dentate Gyrus After Transient Global Ischemia in Gerbils
Authors: Liu Jialing , Solway Karen , Messing Robert O. , Sharp Frank R.
Published: April 2018

Neurogenesis in the dentate gyrus of adult rodents is regulated by NMDA receptors, adrenal steroids, environmental stimuli, and seizures. To determine whether ischemia affects neurogenesis, newly divided cells in the dentate gyrus were examined after transient global ischemia in adult gerbils. 5-Bromo-2′-deoxyuridine-5′-monophosphate (BrdU) immunohistochemistry demonstrated a 12-fold increase in cell birth in the dentate subgranular zone 1–2 weeks after 10 min bilateral common carotid artery occlusions. Two minutes of ischemia did not significantly increase BrdU incorporation. Confocal microscopy demonstrated that BrdU immunoreactive cells in the granule cell layer colocalized with neuron-specific markers for neuronal nuclear antigen, microtubule-associated protein-2, and calbindin D28k, indicating that the newly divided cells migrated from the subgranular zone into the granule cell layer and matured into neurons. Newborn cells with a neuronal phenotype were first seen 26 d after ischemia, survived for at least 7 months, were located only in the granule cell layer, and comprised ∼60% of BrdU-labeled cells in the granule cell layer 6 weeks after ischemia. The increased neurogenesis was not attributable to entorhinal cortical lesions, because no cell loss was detected in this region. Ischemic preconditioning for 2 min, which protects CA1 neurons against subsequent ischemic damage, did not prevent increased neurogenesis in the granule cell layer after a subsequent severe ischemic challenge. Thus, ischemia-induced dentate neurogenesis is not attributable to CA1 neuronal loss. Enhanced neurogenesis in the dentate gyrus may be a compensatory adaptive response to ischemia-associated injury and could promote functional recovery after ischemic hippocampal injury.
Basic FGF Increases Communication between Cells of the Developing Neocortex
Authors: Nadarajah B. , Makarenkova H. , Becker D. L. , Evans W. H. , Parnavelas J. G.
Published: April 2018

We have found that basic fibroblast growth factor (bFGF), applied to cortical progenitor cellsin vitro, produces an increase in the expression of the gap junction protein connexin (Cx) 43 and in the mRNA encoding Cx 43. This effect was evident in both proliferating and nonproliferating cells. The elevated levels of mRNA suggest that bFGF is likely to exert its effect by upregulating the rate of transcription of the Cx 43 gene. We have further shown that the increase in Cx 43 expression is mediated through the receptor tyrosine kinase pathway and is associated with enhanced intercellular dye-coupling mediated by gap junctions. These results suggest that gap junction channels provide a direct conduit for mitogens released in response to bFGF to effectively regulate proliferation during corticogenesis.
Interstitial Branches Develop from Active Regions of the Axon Demarcated by the Primary Growth Cone during Pausing Behaviors
Authors: Szebenyi Györgyi , Callaway John L. , Dent Erik W. , Kalil Katherine
Published: April 2018

Interstitial branches arise from the axon shaft, sometimes at great distances behind the primary growth cone. After a waiting period that can last for days after extension of the primary growth cone past the target, branches elongate toward their targets. Delayed interstitial branching is an important but little understood mechanism for target innervation in the developing CNS of vertebrates. One possible mechanism of collateral branch formation is that the axon shaft responds to target-derived signals independent of the primary growth cone. Another possibility is that the primary growth cone recognizes the target and demarcates specific regions of the axon for future branching. To address whether behaviors of the primary growth cone and development of interstitial branches are related, we performed high-resolution time-lapse imaging on dissociated sensorimotor cortical neurons that branch interstitiallyin vivo. Imaging of entire cortical neurons for periods of days revealed that the primary growth cone pauses in regions in which axon branches later develop. Pausing behaviors involve repeated cycles of collapse, retraction, and extension during which growth cones enlarge and reorganize. Remnants of reorganized growth cones are left behind on the axon shaft as active filopodial or lamellar protrusions, and axon branches subsequently emerge from these active regions of the axon shaft. In this study we propose a new model to account for target innervationin vivoby interstitial branching. Our model suggests that delayed interstitial branching results directly from target recognition by the primary growth cone.