bluuebunny/crossref_metadata_2025 huggingface dataset:
Blockade of the NPY Y5 receptor potentiates circadian responses to light: complementaryin vivoandin vitrostudies
Authors: Yannielli P. C. , Brewer J. McKinley , Harrington M. E.
Published: February 2004

Neuropeptide Y (NPY) is delivered to the suprachiasmatic nuclei (SCN) circadian pacemaker via an input from the thalamic intergeniculate leaflet. NPY can inhibit light‐induced responses of the circadian system of Syrian hamsters. Here we studied whether an antagonist to NPY receptors can be used to potentiate photic phase shifts late in the subjective night. First we determined byin situhybridization that both NPY Y1 and Y5 receptor mRNA are expressed in the SCN of Syrian hamsters. Second, similar to our previous findings at Zeitgeber time 14 (ZT 14, where ZT 12 was the time of lights off), we found that NPY applied at ZT 18.5 onto the SCN region of brain slices maintainedin vitrocould block NMDA‐induced phase advances of the spontaneous firing rate rhythm, and this blocking effect was probably mediated by the Y5 receptor, since co‐application of Y5 receptor antagonists completely reversed the effect of NPY, while application of a Y1 receptor antagonist had no effect under the same conditions. Third, we found that co‐treatment with a Y5 receptor antagonistin vivo(s.c., 10 mg/kg) not only reversed the effect of NPY applied to the SCNin vivothrough a cannula but also significantly potentiated the light‐induced phase advance in the absence of NPY. This is the first report of a NPY receptor antagonist having such an effect, and indicates that NPY Y5 receptor antagonists could be clinically useful for potentiating circadian system responses to light.
Olfactory bulb neurons express functional, entrainable circadian rhythms
Authors: Granados‐Fuentes Daniel , Saxena Meera T. , Prolo Laura M. , Aton Sara J. , Herzog Erik D.
Published: February 2004

Circadian pacemakers drive many daily molecular, physiological and behavioural rhythms. We investigated whether the main olfactory bulb is a functional circadian pacemaker in rats. Long‐term, multielectrode recordings revealed that individual, cultured bulb neurons expressed near 24‐h oscillations in firing rate. Real‐time recordings of Period1 gene activity showed that a population of cells within the bulb expressed synchronized rhythmicity starting on embryonic day 19. This rhythmicity was intrinsic to the mitral, and not the granule, cell layer, entrainable to physiological temperature cycles and temperature compensated in its period. However, removal of the olfactory bulbs had no effect on running wheel behaviour. These results indicate that individual mitral/tufted cells are competent circadian pacemakers which normally synchronize to each other. The daily rhythms in gene expression and firing rate intrinsic to the olfactory bulb are not required for circadian patterns of locomotion, indicating that they are involved in rhythms outside the canonical circadian system.
Spatiotemporal properties of cytoplasmic cyclic AMP gradients can alter the turning behaviour of neuronal growth cones
Authors: Munck Sebastian , Bedner Peter , Bottaro Thierry , Harz Hartmann
Published: February 2004

Growth cones, the terminal structures of elongating neurites, use extracellular guidance information in order to navigate to appropriate target cells. The directional information of guidance cues is transduced to a cytoplasmic gradient of messenger molecules across the growth cone leading to rearrangements of the cytoskeleton. One messenger molecule regulating growth cone turning is cAMP, which is also known to be sufficient to direct growth cone attraction. Cytoplasmic cAMP gradients have been generated in the present study by photolysing caged cAMP with UV light focused on one side of growth cones of chick sensory neurons. Using this method we show that only specific time patterns of pulsed cAMP release are capable of inducing growth cone turning whereas others, which release the same amount of cAMP, are ineffective. Theoretical calculations show that diverse time patterns produce different intracellular gradients, which were visualized directly in HeLa cells expressing cAMP‐sensitive ion channels as a reporter system. Together these data indicate that the spatiotemporal properties of the intracellular gradient are crucial for growth cone turning.
Long‐ and short‐range reward expectancy in the primate orbitofrontal cortex
Authors: Hikosaka Kazuo , Watanabe Masataka
Published: February 2004

The orbitofrontal cortex (OFC) is important in motivation and emotion. We previously reported reward expectancy‐related delay activities during a delayed reaction time task in primate OFC neurons. To further investigate the significance of the OFC in motivational operations, we examined pre‐instruction, baseline activities of OFC neurons in relation to reward expectancy during the delayed reaction time task. In this task, an instruction cue indicated whether reward would be present or absent in the trial. Each set of four consecutive trials constituted one block within which three different kinds of rewards and one trial with no reward were given in a fixed order that differed from the monkey's reward preference. We identified two types of OFC neurons with reward expectancy‐related pre‐instruction activities: Step‐type neurons showed stepwise changes (increase or decrease) in pre‐instruction activity toward the trial with a particular outcome, which usually was the most or least attractive within a block; Pref‐type neurons showed pre‐instruction activity changes according to the monkey's preference for each trial's outcome. We propose that Step‐type and Pref‐type neurons are related to long‐range and short‐range reward expectancies of a particular outcome, respectively. The OFC is considered to play important roles in goal‐directed behaviour by adjusting the motivational level toward a certain (current or future) outcome of a particular motivational significance based on the two kinds of reward expectancy processes. Impairments in goal‐directed behaviour by OFC patients may be caused by a lack of long‐range expectancy or by a deficit in compromising between short‐range and long‐range expectancies.
Peripheral nerve injury induces trans‐synaptic modification of channels, receptors and signal pathways in rat dorsal spinal cord
Authors: Yang Liang , Zhang Fang‐Xiong , Huang Fen , Lu Yin‐Jing , Li Guo‐Dong , Bao Lan , Xiao Hua‐Sheng , Zhang Xu
Published: February 2004

Peripheral tissue injury‐induced central sensitization may result from the altered biochemical properties of spinal dorsal horn. However, peripheral nerve injury‐induced modification of genes in the dorsal horn remains largely unknown. Here we identified strong changes of 14 channels, 25 receptors and 42 signal transduction related molecules in Sprague–Dawley rat dorsal spinal cord 14 days after peripheral axotomy by cDNA microarray. Twenty‐nine genes were further confirmed by semiquantitative RT‐PCR, Northern blotting, in situ hybridization and immunohistochemistry. These regulated genes included Ca2+ channel α1E and α2/δ1 subunits, α subunits for Na+ channel 1 and 6, Na+ channel β subunit, AMAP receptor GluR3 and 4, GABAA receptor α5 subunit, nicotinic acetylcholine receptor α5 and β2 subunits, PKC α, βI and δ isozymes, JNK1–3, ERK2–3, p38 MAPK and BatK and Lyn tyrosine‐protein kinases, indicating that several signal transduction pathways were activated in dorsal spinal cord by peripheral nerve injury. These results demonstrate that peripheral nerve injury causes phenotypic changes in spinal dorsal horn. Increases in Ca2+ channel α2/δ1 subunit, GABAA receptor α5 subunit, Na+ channels and nicotinic acetylcholine receptors in both dorsal spinal cord and dorsal root ganglia indicate their potential roles in neuropathic pain control.
Distributed neuronal networks for encoding category‐specific semantic information: the mismatch negativity to action words
Authors: Shtyrov Yury , Hauk Olaf , Pulvermüller Friedemann
Published: February 2004

Mismatch negativity (MMN), an index of experience‐dependent memory traces, was used to investigate the processing of action‐related words in the human brain. Responses to auditorily presented movement‐related English words were recorded in a non‐attend odd‐ball protocol using a high‐density electroencephalographic (EEG) set‐up. MMN was calculated using responses to the same words presented as standard and deviant stimuli in different sessions to avoid contamination from phonetic–acoustic differences. The topography of the mismatch negativity to action words revealed an unusual centro‐posterior distribution of the responses, suggesting that activity was at least in part generated posterior to usually observed frontal MMNs. Moreover, responses to hand‐related word stimulus (pick) had a more widespread lateral distribution, whereas leg‐related stimulus (kick) elicited a more focal dorsal negativity. These differences, remarkably reminiscent of sensorimotor cortex topography, were further assessed using distributed source analysis of the EEG signal (L2 minimum‐norm current estimates). The source analysis also confirmed differentially distributed activation for the two stimuli. We suggest that these results indicate activation of distributed neuronal assemblies that function as category‐specific memory traces for words and may involve sensorimotor cortical structures for encoding action words.
VIP and PACAP induce selective neuronal differentiation of mouse embryonic stem cells
Authors: Cazillis Michèle , Gonzalez Bruno J. , Billardon Claude , Lombet Alain , Fraichard Alexandre , Samarut Jacques , Gressens Pierre , Vaudry Hubert , Rostène William
Published: February 2004

The capacity of embryonic stem cells (ES cells) to differentiate into neuronal cells represents a potential source for neuronal replacement and a model for studying factors controlling early stages of neuronal differentiation. Various molecules have been used to induce such differentiation but so far neuropeptides acting via functional G‐protein‐coupled receptors (GPCRs) have not been investigated. Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase‐activating polypeptide (PACAP) are neuropeptides expressed in early development which affect neuronal precursor proliferation and neuronal differentiation. VIP and PACAP share two common receptors (VPAC1 and VPAC2 receptors) while only PACAP binds with high affinity to PAC1 receptors. The aim of the study was to determine whether VIP and PACAP could produce functional neuronal differentiation of ES cells. Mouse ES cells were allowed to aggregate in embryoid bodies (EBs) in the presence or not of VIP and PACAP for 1 week. VIP and PACAP potently increased the proportion of EB‐derived cells expressing specifically a neuronal phenotype shown by immunocytochemistry and neurite outgrowth without altering glial cell number. Binding and RT‐PCR analyses demonstrated the presence of VPAC2 and PAC1 receptors on ES cells. Accordingly, both peptides increased cyclic AMP and intracellular calcium. In contrast, EB‐derived cells only expressed a functional PAC1 receptor, suggesting a switch in GPCR phenotype during ES cell differentiation. These original data demonstrate that functional GPCRs for VIP and PACAP are present on ES cells and that these neuropeptides may induce their differentiation into a neuronal phenotype. It opens an exciting new field for neuropeptide regulation of tissue ontogenesis.
Risk factors for dopaminergic neuron loss in human α‐synuclein transgenic mice
Authors: Thiruchelvam M. J. , Powers J. M. , Cory‐Slechta D. A. , Richfield E. K.
Published: February 2004

Genetic background, pesticide exposure, age, gender, diet and lifestyle are implicated risk factors in Parkinson's disease. We demonstrate dopamine neuron loss and other features of Parkinsonism based on the interaction of several of these human risk factors in transgenic mice expressing human α‐synuclein. Mice expressing different forms of human α‐synuclein had progressive declines in locomotor activity and abnormal responses to apomorphine that were modified by transgenic status. Stereological counts of tyrosine hydroxylase‐positive neurons significantly declined with age only in the transgenic lines, consistent with a constant or decreasing risk, with the line expressing a double‐mutant form of human α‐synuclein more severely affected than the line expressing wild‐type human α‐synuclein. Treatment with Mn2+‐ethylenebisdithiocarbamate and paraquat resulted in significantly greater effects in the double‐mutant line than the other lines. Inclusions were not identified in the transgenic lines. Overexpression of human α‐synuclein had adverse effects on substantia nigra pars compacta dopaminergic neurons that were modified by risk factors interacting in humans, including human α‐synuclein mutations, ageing, and exposure to pesticides.
Alteration of dopamine D1 receptor‐mediated motor inhibition and stimulation during development in rats is associated with distinct patterns of c‐fos mRNA expression in the frontal‐striatal circuitry
Authors: Diaz Heijtz Rochellys , Scott Lena , Forssberg Hans
Published: February 2004

Dopamine D1 receptors have been implicated in various neurodevelopmental disorders, including attention‐deficit/hyperactivity disorder. However, little is known about potential late maturational changes of the motor inhibitory and stimulatory role of these receptors. Here, we investigated the effects of a full and selective D1 receptor agonist, SKF‐81297, on motor activity and expression of the plasticity‐associated gene, c‐fos, in the prefrontal cortex and striatum of juvenile and adolescent male rats. In general, SKF‐81297 produced a biphasic effect on motor activity (locomotor and rearing activity), which consisted of an initial short inhibition followed by a long‐lasting stimulation. These effects were dose‐ and age‐ dependent. The inhibitory phase was more pronounced in adolescent than in juvenile rats whereas the opposite was true for the stimulatory phase. During the initial inhibitory phase of the drug, c‐fos mRNA expression was increased in the prefrontal cortex of juvenile rats but reduced in adolescent rats. There was also an increase in c‐fos mRNA expression in the medial‐dorsal striatum and olfactory tubercle, which was more evident in juvenile rats. In contrast, during the stimulatory phase, c‐fos mRNA expression was increased in both the dorsal and ventral striatum, especially in the nucleus accumbens, as well as in the prefrontal cortex, in both age groups. The increase of c‐fos mRNA in the dorsal striatum, however, was more pronounced in juvenile rats. These results indicate the presence of two distinct D1 receptor populations within the frontal‐striatal circuitry, which have opposite effects on motor activity, and which have different maturational profiles.
Light‐ and clock‐dependent regulation of ribosomal S6 kinase activity in the suprachiasmatic nucleus
Authors: Butcher Greg Q. , Lee Boyoung , Hsieh Fortune , Obrietan Karl
Published: February 2004

Recent work has revealed that signalling via the p42/44 mitogen‐activated protein kinase (MAPK) pathway couples light to entrainment of the circadian clock located in the suprachiasmatic nucleus (SCN). Given that many effects of the MAPK pathway are mediated by intermediate kinases, it was of interest to identify kinase targets of ERK in the SCN. One potential target is the family of 90‐kDa ribosomal S6 kinases (RSKs). In this study, we examined light‐induced regulation of RSK‐1 in the SCN. Immunohistochemical and Western analysis were used to show that photic stimulation during the early and late night triggered the phosphorylation of RSK‐1 at two sites that are targeted by ERK. This increase in the phosphorylation state of RSK‐1 corresponded with an approximate fourfold increase in kinase activity. Light exposure during the subjective day did not increase the phosphorylated form of RSK‐1, indicating that the capacity of light to stimulate RSK‐1 activation is phase‐restricted. Double immunofluorescent labelling of SCN tissue revealed the colocalized expression of the activated form of ERK with the phosphorylated form of RSK‐1 following a light pulse. In vivo pharmacological inhibition of light‐induced MAPK pathway activation blocked RSK‐1 phosphorylation, indicating that RSK‐1 activity is regulated by the MAPK pathway. PDK‐1, a coregulator of RSK‐1, is also expressed in the SCN and is likely to contribute to RSK‐1 activity. RSK‐1 phosphorylation was also rhythmically regulated within a subset of phospho‐ERK‐expressing cells. Together these results identify RSK‐1 as a light‐ and clock‐regulated kinase and raise the possibility that it contributes to entrainment and timing of the circadian pacemaker.
Neuron–glial trafficking of NH4+ and K+: separate routes of uptake into glial cells of bee retina
Authors: Marcaggi Païkan , Jeanne Marion , Coles Jonathan A.
Published: February 2004

Ammonium (NH4+ and/or NH3) and K+ are released from active neurons and taken up by glial cells, and can modify glial cell behaviour. Study of these fluxes is most advanced in the retina of the honeybee drone, which consists essentially of identical neurons (photoreceptors) and identical glial cells (outer pigment cells). In isolated bee retinal glial cells, ammonium crosses the membrane as NH4+ on a Cl− cotransporter. We have now investigated, in the more physiological conditions of a retinal slice, whether the NH4+‐Cl− cotransporter can transport K+ and whether the major K+ conductance can transport NH4+. We increased [NH4+] or [K+] in the superfusate and monitored uptake by recording from the glial cell syncytium or from interstitial space with microelectrodes selective for H+ or K+. In normal superfusate solution, ammonium acidified the glial cells but, after 6 min superfusion in low [Cl−] solution, ammonium alkalinized them. In the same low [Cl−] conditions, the rise in intraglial [K+] induced by an increase in superfusate [K+] was unchanged, i.e. no K+ flux on the Cl− cotransporter was detected. Ba2+ (5 mm) abolished the glial depolarization induced by K+ released from photoreceptors but did not reduce NH4+uptake. We estimate that when extracellular [NH4+] is increased, 62–100% is taken up by the NH4+‐Cl− cotransporter and that when K+ is increased, 77–100% is taken up by routes selective for K+. This separation makes it possible that the glial uptake of NH4+ and of K+, and hence their signalling roles, might be regulated separately.
Bombesin/gastrin‐releasing peptide receptors in the basolateral amygdala regulate memory consolidation
Authors: Roesler Rafael , Lessa Daniela , Venturella Roberta , Vianna Mônica R. M. , Luft Tatiana , Henriques João Antônio Pegas , Izquierdo Ivan , Schwartsmann Gilberto
Published: February 2004

Several receptor and intracellular signalling systems in the basolateral amygdala (BLA) regulate memory formation. In the present study, we show that bombesin/gastrin‐releasing peptide (GRP) receptors in the BLA are involved in the consolidation of affectively motivated memory. Adult male rats were trained in a single‐trial step‐down inhibitory avoidance task and tested for retention 24 h later. Post‐training systemic injection of the bombesin/GRP receptor antagonist (D‐Tpi6, Leu13 psi[CH2NH]‐Leu14) bombesin (6–14) (RC‐3095) impaired memory retention. In rats implanted under thionembutal anaesthesia with guide cannulae aimed at the BLA, post‐training bilateral infusion of RC‐3095 into the BLA dose‐dependently impaired retention. Pre‐training unilateral muscimol inactivation of the BLA blocked the memory‐impairing effect of post‐training systemic administration of RC‐3095. The results suggest that bombesin/GRP receptors in the BLA are involved in the consolidation of aversive memory, and the BLA mediates the memory‐impairing effect of systemic bombesin/GRP receptor blockade.
Modulation of oscillatory brain activity and evoked potentials in a repetition priming task in the human EEG
Authors: Gruber Thomas , Malinowski Peter , Müller Matthias M.
Published: February 2004

Cortical object representations seem to require the formation of neural cell assemblies. The physiological correlate of cell assembly activity may be seen in synchronized neural activity in the gamma band range. The improvement in perceiving and identifying an object by experience is commonly referred to as repetition priming. One possible neural mechanism for repetition priming is ‘repetition suppression’ within a cell assembly coding the stimulus. The present electroencephalogram study was designed to investigate oscillatory brain activity when line drawings of concrete objects were repeated either immediately after a first presentation or after intervening a number of different stimuli. Results showed a broad posterior distribution of induced gamma band responses (GBRs) after the initial picture presentation. Repeated presentations of the same picture led to a significant decrease of induced gamma power. Furthermore, repeated presentations of the same object resulted in a decrease in phase synchrony between distant electrode sites. No significant repetition effects were found in the alpha or beta frequency range. The event‐related potential (ERP), which was also modulated by priming, showed a different scalp distribution compared with induced GBRs. In addition, ERP repetition effects decayed at larger intervals between initial and repeated presentations, whereas induced GBRs were not modulated as a function of stimulus lag. We concluded that the decrease in amplitude of induced GBRs and the reduction of gamma phase synchrony between pairs of electrodes after repeated picture presentations might be linked to a ‘sharpening’ mechanism within a cell assembly representing an object.
Nitric oxide acts as a slow‐down and search signal in developing neurites
Authors: Trimm Kevin R. , Rehder Vincent
Published: February 2004

Nitric oxide (NO) has been demonstrated to act as a signaling molecule during neuronal development, but its precise function is unclear. Here we investigate whether NO might function at the neuronal growth cone to affect growth cone motility. We have previously demonstrated that growth cones of identified neurons from the snail Helisoma trivolvis show a rapid and transient increase in filopodial length in response to NO, which was regulated by soluble guanylyl cyclase (sGC) [S. Van Wagenen and V. Rehder (1999) J. Neurobiol., 39, 168–185]. Because in vivo studies have demonstrated that growth cones have longer filopodia and advance more slowly in regions where pathfinding decisions are being made, this study aimed to establish whether NO could function as a combined ‘slow‐down and search signal’ for growth cones by decreasing neurite outgrowth. In the presence of the NO donor NOC‐7, neurites of B5 neurons showed a concentration‐dependent effect on neurite outgrowth, ranging from slowing at low, stopping at intermediate and collapsing at high concentrations. The effects of the NO donor were mimicked by directly activating sGC with YC‐1, or by increasing its product with 8‐bromo‐cGMP. In addition, blocking sGC in the presence of NO with NS2028 blocked the effect of NO, suggesting that NO affected outgrowth via sGC. Ca2+ imaging of growth cones with Fura‐2 indicated that [Ca2+]i increased transiently in the presence of NOC‐7. These results support the hypothesis that NO can function as a potent slow/stop signal for developing neurites. When coupled with transient filopodia elongation, this phenomenon emulates growth cone searching behavior.
Left and right superior parietal lobule in tactile object discrimination
Authors: Stoeckel M. C. , Weder B. , Binkofski F. , Choi H.‐J. , Amunts K. , Pieperhoff P. , Shah N. J. , Seitz R. J.
Published: February 2004

Tactile object discrimination is one of the major manual skills of humans. While the exploring finger movements are not perceived explicitly, attention to the movement‐evoked kinaesthetic information gates the tactile perception of object form. Using event‐related functional magnetic resonance imaging in seven healthy subjects we found one area in the right superior parietal cortex, which was specifically activated by kinaesthetic attention during tactile object discrimination. Another area with similar location in the left hemisphere was related to the maintenance of tactile information for subsequent object discrimination. We conclude that kinaesthetic information is processed in the anterior portion of the superior parietal cortex (aSPL) with a right hemispheric predominance for discrimination and a left hemispheric predominance for information maintenance.
Cocaine‐induced vs. behaviour‐related alterations of spontaneous and evoked discharge of somatosensory cortical neurons
Authors: Drouin Candice , Waterhouse Barry D.
Published: February 2004

While the abuse potential of cocaine stems mainly from its ability to increase dopaminergic transmission in limbic regions, drug actions on other monoamine‐innervated circuits may contribute to the development and maintenance of cocaine addiction. Previous extracellular recordings in anaesthetized rats revealed a facilitatory influence of cocaine on primary sensory pathways, which could influence the processing of drug‐related stimuli during the development of cocaine addiction. We further analysed these sensory effects of cocaine in freely behaving rats (n = 9). Using an array of eight microelectrodes chronically implanted in infragranular layers of primary somatosensory cortex, we recorded the basal activity of 40 single‐ and 64 multiunits and their response to electrical stimulation of the whisker pad before and after incremental doses of cocaine (0.25–2 mg/kg i.v.). Both spontaneous and cocaine‐induced explorations were associated with elevated basal firing of the cortical neurons and suppression of their short‐latency excitation and postexcitatory inhibition in response to the whisker‐pad stimulation. In addition to exploration‐related alterations, the administration of cocaine enhanced the long‐latency rebound excitation induced by the whisker‐pad stimulation. This component of the sensory response, which is more labile and does not seem to convey information about the physical characteristics of the stimulus, may participate in the processing of drug‐related sensory stimuli.
GAP‐43 overexpression in adult mouse Purkinje cells overrides myelin‐derived inhibition of neurite growth
Authors: Gianola Sara , Rossi Ferdinando
Published: February 2004

Up‐regulation of growth‐associated proteins in adult neurons promotes axon regeneration and neuritic elongation onto nonpermissive substrates. To investigate the interaction between these molecules and myelin‐related inhibitory factors, we examined transgenic mice in which overexpression of the growth‐associated protein GAP‐43 is driven by the Purkinje cell‐specific promoter L7. Contrary to their wild‐type counterparts, which have extremely poor regenerative capabilities, axotomized transgenic Purkinje cells exhibit profuse sprouting along the intracortical neurite and at the severed stump [Buffo et al. (1997) J. Neurosci., 17, 8778–8791]. Here, we investigated the relationship between such sprouting axons and oligodendroglia to ask whether GAP‐43 overexpression enables Purkinje neurites to overcome myelin‐derived inhibition. Intact transgenic Purkinje axons display normal morphology and myelination. Following injury, however, many GAP‐43‐overexpressing neurite stumps are devoid of myelin cover and sprout into white matter regions containing densely packed myelin and Nogo‐A‐ or MAG‐immunopositive oligodendrocytes. The intracortical segments of these neurites show focal accumulations of GAP‐43, which are associated with disrupted or retracted myelin sheaths. Numerous sprouts originate from such demyelinated segments and spread into the granular layer. Some myelin loss, though not axon sprouting, is also evident in wild‐type mice, but this phenomenon is definitely more rapid and extensive in transgenic cerebella. Thus, GAP‐43‐overexpressing Purkinje axons are endowed with enhanced capabilities for growing into nonpermissive territories and show a pronounced tendency to lose myelin. Our observations suggest that accumulation of GAP‐43 along precise axon segments disrupts the normal axon–glia interaction and enhances the retraction of oligodendrocytic processes to facilitate the outgrowth of neuritic sprouts.
Enhancement of steady‐state auditory evoked magnetic fields in tinnitus
Authors: Diesch Eugen , Struve Maren , Rupp Andre , Ritter Steffen , Hülse Manfred , Flor Herta
Published: February 2004

The steady‐state auditory evoked magnetic field and the Pbm, the magnetic counterpart of the second frontocentrally positive middle latency component of the transitory auditory evoked potential, were measured in ten tinnitus patients using a 122‐channel gradiometer system. The patients had varying degrees of hearing loss. In all patients, the tinnitus frequency was located above the frequency of the audiometric edge, i.e. the location on the frequency axis above which hearing loss increases more rapidly. Stimuli were amplitude‐modulated sinusoids with carrier frequencies at the tinnitus frequency, the audiometric edge, two frequencies below the audiometric edge, and two frequencies between the audiometric edge and the tinnitus frequency. Below the audiometric edge, the root‐mean‐square field amplitude of the steady‐state response computed across the whole head as well as the contralateral and the ipsilateral dipole moment decreased as a function of carrier frequency. With carrier frequency above the audiometric edge, the steady‐state response increased again. The amplitudes of the transitory Pbm component were patterned in a qualitatively similar way, but without the differences being significant. For the steady‐state response, both whole‐head root‐mean‐square field amplitude and the dipole moment of the sources at the tinnitus frequency showed significant positive correlations with subjective ratings of tinnitus intensity and intrusiveness. These correlations remained significant when the influence of hearing loss was partialled out. The observed steady‐state response amplitude pattern likely reflects an enhanced state of excitability of the frequency region in primary auditory cortex above the audiometric edge. The relationship of tinnitus to auditory cortex hyperexcitability and its independence of hearing loss is discussed with reference to loss of surround inhibition in and map reorganization of primary auditory cortex.
Second messenger cascade of glial responses evoked by interneuron activity and by a myomodulin peptide in the leech central nervous system
Authors: Britz Frank C. , Hirth Ingolf C. , Deitmer Joachim W.
Published: February 2004

The giant glial cell in the neuropil of segmental ganglia of the leech Hirudo medicinalis responds to the activity of the Leydig interneuron and to a peptide of the myomodulin family, the presumed transmitter mediating the Leydig neuron‐to‐giant glial cell transmission, with a membrane hyperpolarization due to an increased membrane K+ conductance [Britz et al. (2002) Glia, 38, 215–227]. We have now studied the second messenger cascade initiated by Leydig neuron stimulation and by the endogenous myomodulin (MMHir) in the voltage‐clamped giant glial cell. Glial responses to both stimuli are mediated by a G‐protein‐coupled receptor linked to adenylyl cyclase by the following criteria: (i) injection of GDP‐β‐S, but not GDP, resulted in an irreversible decrease of the glial responses to both stimuli; (ii) the responses to both stimuli were reversibly inhibited by the adenylyl cyclase inhibitor SQ22,536; and (3) bath‐applied di‐butyryl‐cyclic AMP, but not di‐butyryl‐cyclic GMP, elicited an outward current, which reduced the responses elicited by neuronal stimulation or myomodulin. A cocktail of protein kinase (PK) inhibitors (H‐8, KT5720), the PKA antagonist Rp‐cAMPS, or presumed inhibitors of cyclic nucleotide channels, LY83583 and l‐cis‐diltiazem, had no effect on the glial responses. Our results suggest that Leydig neuron stimulation and MMHir activate a cAMP‐mediated K+ conductance in the glial cell, which appeared neither to be due to the activation of PKA nor of known cyclic nucleotide‐gated channels directly.
Adaption of the serotoninergic neuronal phenotype in the absence of 5‐HT autoreceptors or the 5‐HT transporter: involvement of BDNF and cAMP
Authors: Rumajogee Prakasham , Vergé Daniel , Hanoun Naïma , Brisorgueil Marie‐Jeanne , Hen René , Lesch Klaus‐Peter , Hamon Michel , Miquel Marie‐Christine
Published: February 2004

Serotonin 5‐HT1A and 5‐HT1B receptors and the 5‐HT transporter are key regulators of the serotoninergic neuronal phenotype. We show here that genetic deletion of any of these elements differentially regulates 5‐HT neuronal number in rostral raphe cultures from E14 mice. Serotonin neuronal number was increased by almost four‐fold and 1.8‐fold in cultures from 5‐HT1AR−/− and 5‐HT1BR−/− mice, respectively. In contrast, the lack of serotonin transporter expression was associated with a 50% decrease in 5‐HT neuronal number. In raphe cultures from the rat, BDNF and cAMP have been shown to up‐regulate the neuronal serotoninergic phenotype through TrkB‐dependent mechanisms [Rumajogee et al. (2002) J. Neurochem., 83, 1525–1528]. Similar tyrosine kinase‐dependent up‐regulating effects, in the absence of serotoninergic key‐elements are reported here, on both 5‐HT neuronal number and neurites length. However, the extents of BDNF‐triggered and cAMP‐triggered effects on serotoninergic neuritic length were approximately 1.5‐fold higher in 5‐HT1AR−/− mutants. These findings show that the up‐regulatory mechanisms triggered by BDNF on serotoninergic neuronal number and neurite extension are different and that the latter are partially linked to 5‐HT, probably through 5‐HT1A autoreceptors. Together, these data suggest that serotonin autoreceptors, mainly 5‐HT1A but also 5‐HT1B, may be responsible for a tonic auto‐inhibitory effect of 5‐HT itself on the serotoninergic neuronal phenotype during embryonic development, particularly marked in the absence of the 5‐HT transporter.
Somatodendritic localization of the mRNA for EFA6A, a guanine nucleotide exchange protein for ARF6, in rat hippocampus and its involvement in dendritic formation
Authors: Sakagami Hiroyuki , Matsuya Shigetsune , Nishimura Hideki , Suzuki Ryoji , Kondo Hisatake
Published: February 2004

EFA6A is a guanine nucleotide exchange protein (GEP) that can specifically activate ADP‐ribosylation factor 6 (ARF6) in vitro. A recent study has demonstrated that ARF6 is involved in the dendritic formation of developing hippocampal neurons [Hernandez‐Deviez et al. (2002) Nature Neurosci., 5, 623–624]. This study examined a potential role for EFA6A in hippocampal development in Wistar rats. Our results provided definitive evidence for somatodendritic localization of EFA6A mRNA in both cultured and in vivo hippocampal neurons by nonradioactive in situ hybridization. During postnatal development, EFA6A mRNA was dramatically increased and its dendritic localization was most evident between P7 and P14. In contrast, ARF6 mRNA was confined to the neuronal layers of the hippocampus throughout development. In addition, the overexpression of a GEP‐defective mutant of EFA6A enhanced the dendritic formation of the primary hippocampal neurons. The present findings suggest that EFA6A is intimately involved in the regulation of the dendritic development of hippocampal neurons.
Activation of P‐type calcium channel regulates a unique thapsigargin‐sensitive calcium pool in embryonic motoneurons
Authors: Scamps Frédérique , Roig Anne , Boukhaddaoui Hassan , André Sylvain , Puech Sylvie , Valmier Jean
Published: February 2004

By regulating voltage‐dependent Ca2+ influx and intracellular Ca2+ homeostasis, electrical activity plays a central role in motoneuron development. Dissociated cultures of purified embryonic rat motoneurons were used to explore the molecular mechanisms by which Ca2+ influx control [Ca2+]i transients in these neurons. Thapsigargin (250 nm) and cyclopiazonic acid (10 µm), which deplete Ca2+ stores in the endoplasmic reticulum, decrease by 30% the depolarization‐induced [Ca2+]i transients in motoneurons without affecting voltage‐activated calcium currents. This thapsigargin‐sensitive intracellular Ca2+ pool differs from other previous described Ca2+ stores that are sensitive to ryanodine or caffeine, inositol triphosphate, insulin and from mitochondrial Ca2+ pools. Thapsigargin affected the Cav2.1 P‐type Ca2+ channel component of the depolarization‐induced [Ca2+]i transient in motoneurons but spared [Ca2+]i transient induced by Cav1 L‐type and Cav2.2 N‐type Ca2+ channel components, suggesting a close functional relationship between Cav2.1 subunit and this unique thapsigargin‐sensitive Ca2+ store. Altogether the present results demonstrate a new pathway, used by embryonic motoneurons, to regulate Ca2+ signalling through voltage‐activated (Cav2.1) Ca2+ channels.
Endothelins regulate astrocyte gap junctions in rat hippocampal slices
Authors: Blomstrand F. , Venance L. , Sirén A.‐L. , Ezan P. , Hanse E. , Glowinski J. , Ehrenreich H. , Giaume C.
Published: February 2004

Gap junctional communication (GJC) is a typical feature of astrocytes proposed to contribute to the role played by these glial cells in brain physiology and pathology. In acutely isolated hippocampal slices from rat (P11–P19), intercellular diffusion of biocytin through gap junction channels was shown to occur between hundreds of cells immuno‐positive for astrocytic markers studied in the CA1/CA2 region. Single‐cell RT‐PCR demonstrated astrocytic mRNA expression of several connexin (Cx) subtypes, the molecular constituent of gap junction channels, whereas immunoblotting confirmed that Cx43 and Cx30 are the main gap junction proteins in hippocampal astrocytes. In the brain, astrocytes represent a major target for endothelins (Ets), a vasoactive family of peptides. Our results demonstrate that Ets decrease the expression of phosphorylated Cx43 forms and are potent inhibitors of GJC. The Et‐induced effects were investigated using specific Et receptor agonists and antagonists, including Bosentan (Tracleer™), an EtA/B receptor antagonist, and using hippocampal slices and cultures from EtB‐receptor‐deficient rats. Interestingly, the pharmacological profile of Ets effects did not follow the classical profile established in cardiovascular systems. The present study therefore identifies Ets as potent endogenous inhibitory regulators of astrocyte networks. As such, the action of these peptides on astrocyte GJC might be involved in the contribution of astrocytes to neuroprotective processes and have a therapeutic potential in neuropathological situations.
Depolarization, exocytosis and amino acid release evoked by hyposmolarity from cortical synaptosomes
Authors: Tuz Karina , Peña‐Segura Claudia , Franco Rodrigo , Pasantes‐Morales Herminia
Published: February 2004

External osmolarity reduction (20%) led to labelled glutamate, GABA and taurine release from rat brain cortical synaptosomes. A Cl–‐independent, Na+‐dependent, La3+‐sensitive and tetrodotoxin (TTX) reduced depolarization of synaptosomes occurred upon hyposmolarity, suggestive of Na+ entry through nonselective cation channels. This depolarization, together with cytosolic Ca2+ ([Ca2+]I) increase, resulted in exocytosis, monitored by FM1‐43. The release fraction resulting from these phenomena was estimated, by its decrease, by La3+, EGTA‐AM and tetanus toxin (TeTX), as 34–44% for glutamate, 21–29% for GABA and 18–22% for taurine. Protein kinase C (PKC) activation by phorbol‐12‐myristate‐13‐acetate (PMA) increased the hyposmolarity‐elicited exocytosis and this activation increased glutamate (80%), GABA (51%) and taurine (42%) hyposmotic efflux. Inhibition by chelerythrine reduced glutamate, GABA and taurine efflux by 64%, 50% and 24%, respectively. The Na+‐dependence of amino acid release (glutamate 63%, GABA 46% and taurine 29%) may result from both, prevention of the depolarization‐exocytosis efflux, and blockade of the carrier reversal operation. Carrier blockade by dl‐threo‐β‐benzyloxy aspartate (TBOA) and NO‐711 resulted in 37% and 28% reduction of glutamate and GABA release, respectively. Contribution of the osmolyte leak pathway to amino acid release, estimated by the influence of Cl– (NPPB) and tyrosine kinase (AG18) blocker, was up to 55% for taurine, but only 10–18% for GABA, with apparently no contribution for glutamate. The predominant osmolyte‐type mechanism of taurine release suggest its function in volume control in nerve endings, while glutamate and GABA respond to events concurrent with hyposmolarity by a neurotransmitter‐like release mechanism. The hyposmolarity‐induced amino acid efflux from nerve endings may have consequences for neuronal excitability during hyponatremia.
Amygdalar circuits required for either consolidation or extinction of taste aversion memory are not required for reconsolidation
Authors: Bahar Amir , Dorfman Nimrod , Dudai Yadin
Published: February 2004

Recent reports have revitalized the debate on whether, for each item in memory, consolidation occurs just once, or whether, upon their activation in retrieval, items in memory undergo reconsolidation. Further, it has been recently reported that following retrieval in the absence of reinforcer, the activated memory can either reconsolidate or extinguish, depending on the training history. This raises the question whether consolidation, extinction and reconsolidation share neuronal mechanisms, and moreover, whether reconsolidation recapitulates consolidation. In conditioned taste aversion (CTA), consolidation depends on protein synthesis in the central nucleus of the amygdala, whereas extinction depends on protein synthesis in the basolateral nuclei of the amygdala. Here we show that inhibition of protein synthesis in either of these nuclei has no effect on CTA memory under conditions that initiate reconsolidation. This implies that reconsolidation does not recapitulate consolidation, and that consolidation, reconsolidation and extinction are different processes.
Role of “fibrin” cuffs in chronic nonspecific oral ulceration
Authors: Joshi Ameeta , Sloan Philip
Published: February 2004

We report the novel finding of matrix‐rich “fibrin” cuffs in chronic nonspecific oral ulceration and propose a possible role for these lesions. Pericapillary cuffs are typically found in chronic venous ulceration. Vascular cuffs, which form in the base and margins of leg ulcers, have been reported to contain fibrin, laminin, fibronectin, tenascin, and types I and III collagen. Histologically identical vascular cuffs are present in oral ulcers of unusually prolonged chronicity and their occurrence in the oral cavity suggests that chronic venous insufficiency and backpressure are not essential to their formation. It is proposed that the matrix‐rich pericapillary cuffs may act as a scaffold for angiogenesis in ulceration of prolonged duration.
Effects of a CDK inhibitor on lens regeneration
Authors: Tsonis Panagiotis A. , Madhavan Mayur , Call Mindy K. , Gainer Sarah , Rice Audie , Del Rio‐Tsonis Katia
Published: February 2004

Lens regeneration in adult newts is always initiated from the dorsal iris by transdifferentiation of the pigment epithelial cells. One of the most important early events should be the ability of pigment epithelial cells to dedifferentiate and re‐enter the cell cycle. As a first step in an attempt to study this event, we have decided to examine the effects of a cyclin‐dependent kinase‐2 inhibitor on lens regeneration. At the appropriate concentration, this inhibitor completely abolished the ability of pigment epithelial cells to form a new lens, but it did not stop them from dedifferentiating and forming a small lens vesicle. The effects of this inhibitor seem to be mediated by its opposite effects on cell proliferation and apoptosis. The inhibitor significantly reduced cell proliferation and enhanced apoptosis of pigment epithelial cells both in vitro and in vivo and of the regenerating lens in vivo.
Transplantation of the urinary bladder and other organs in the subcutaneous tissue induces cyst formation and epithelialization: its potential usefulness in regenerative medicine
Authors: Sawada Hajime , Esaki Michiyo , Sheng Hong‐Ming , Kita Asami , Yoshida Toyokazu
Published: February 2004

Certain hollow organs are known to form cysts when heterologously transplanted. In order to examine the usefulness of the phenomenon for regenerative medicine, rat urinary bladders and other organs were allo‐transplanted under the subcutaneous tissue of the back. These transplanted tissues very often formed cysts covered with epithelia. The epithelia covered an area about twice the original size. In the case of the urinary bladder, the epithelium started moving from the edge of the transplants around day 3 after the operation, and as time proceeded, the tela submucosa and tunica muscularis also moved to encircle the epithelium, and formed the wall of the cyst. The basal laminae were formed under the newly expanded epithelium slightly behind the leading tip. All of the organs tested had the capability of cyst formation and epithelialization, although their rate differed between organs. The results are discussed with reference to the potential use of cyst formation for regenerating damaged organs.
Effect of cytokine growth factors on the prevention of acute wound failure
Authors: Robson Martin C. , Dubay Derek A. , Wang Xue , Franz Michael G.
Published: February 2004

Cytokine growth factor treatment of chronic wounds has met with mixed results. The chronic wound presents a hostile environment to peptides such as growth factors. Cytokine growth factors have not been studied extensively in acute wounds. However, incisional hernias are a major example of acute wound failure that has not been solved by various mechanical approaches. A biological approach to acute wound failure by use of cytokine growth factors may offer a new strategy. A rodent incisional hernia model was used. Seventy‐six rats underwent 3‐cm midline celiotomies and were closed with fine, fast‐absorbing sutures to induce intentional acute wound failure. Group 1 received no other treatment. The midline fascia in Groups 2–10 was infiltrated with 100 µl of vehicle alone or vehicle containing various test cytokine growth factors. Necropsy was performed on postoperative day 28 and the wounds were examined for herniation. Incisional hernias developed in 83 percent (13/16) of untreated incisional and 88 percent (7/8) and 83 percent (5/6) of the two vehicle‐treated incisions (PBS and carboxymethylcellulose). Hernia incidences were decreased by priming of the fascial incision with transforming growth factor‐β2 (12%, 1/8), basic fibroblast growth factor (25%, 2/8) and interleukin‐1β (50%, 3/6) (p < 0.05). Aqueous platelet‐derived growth factor, becaplermin, insulin‐like growth factor, and granulocyte macrophage‐colony stimulating factor did not significantly decrease the incidence of acute wound failure (p > 0.05). A biological approach to acute wound failure as measured by incisional hernia formation can be useful in reducing the incidence of this complication. Transforming growth factor‐β2, basic fibroblast growth factor, and interleukin 1β all eliminated or significantly reduced the development of incisional hernias in the rat model.