bluuebunny/crossref_metadata_2025 huggingface dataset:
Single‐channel Activity in Cultured Cortical Neurons of the Rat in the Presence of a Toxic Dose of Glutamate
Authors: Backus Kurt Harald , Trube Gerhard
Published: April 2006

Rat cortical neurons grown in cell culture were exposed to 500 μM glutamate for 5 min during continuous current recording from cell‐attached patches. The Ca2+‐dependence and ion selectivity of the membrane channels activated during and after glutamate application were studied in inside‐out patches. Glutamate blocked spontaneous action potential firing. In 77% of the experiments glutamate activated several types of ion channels indirectly, i.e. via a change of cytoplasmic factors. Channel activity did not disappear after removing glutamate from the bath. A K+ channel requiring intracellular calcium ([Ca2+]i) was activated in 44% of the experiments (conductance for inward currents in cell‐attached patches 118 ± 6 pS;‘BK channel'). Another Ca2+‐dependent channel permeable for Cl‐ (conductance for outward currents in cell‐attached patches 72±17 pS), acetate and methanesulphonate appeared in 26% of the patches. Other K+ channels of smaller conductance were infrequently observed. During and after glutamate application the activity of the BK channel showed an initial increase followed by a transient decay and a second rise to a plateau, probably reflecting a similar time course of changes in [Ca2+]i. Both phases of increasing channel activity required the presence of extracellular Ca2+ suggesting that [Ca2+]i was mainly increased by Ca2+ influx. The N‐methyl‐d‐aspartate (NMDA) antagonists dizocilpine (MK‐801, 10 μM) and dl‐2‐amino‐5‐phosphonovaleric acid (AP5; 100 μM), added within 5 min after glutamate application, stopped BK channel activity and restored the spontaneous action potential firing. We conclude that the influx of Ca2+ through NMDA receptor channels causes a strong activation of Ca2+‐dependent K+ channels, which is likely to result in pronounced loss of intracellular K+. NMDA receptor channels seem to remain active for a long time (>10 min) after the end of glutamate application.
Electrophysiological and Pharmacological Characterization of Vestibular Inputs to Identified Frog Abducens Motoneurons and Internuclear Neurons In Vitro
Authors: Straka Hans , Dieringer Norbert
Published: April 2006

Synaptic vestibular inputs of antidromically identified motoneurons and internuclear neurons in the abducens nucleus were studied electrophysiologically and pharmacologically in the isolated brain of grass frogs (Rana temporaria). The prevailing response pattern of abducens motoneurons (AbMOT) following stimulation of the VIIIth nerve was crossed disynaptic excitation and uncrossed disynaptic inhibition. A few AbMOT (five of 46), however, exhibited uncrossed excitation instead of inhibition. Abducens internuclear neurons (AbINT), identified by antidromic activation following stimulation of the contralateral medial longitudinal fascicle, exhibited disynaptic response patterns to stimulation of the VIIIth nerve that were very similar in latency and rise time to those of AbMOT except for the absence of uncrossed disynaptic inhibition. Bath application of strychnine (50 μM), a glycine antagonist, blocked the uncrossed inhibitory vestibular input to AbMOT and AbINT completely and reversibly, whereas picrotoxin (100 μM), a GABA (γ‐aminobutyric acid) antagonist, had no detectable effect on these disynaptic potentials. These results suggest glycine as the transmitter of inhibitory vestibular projections onto AbMOT and AbINT. The pharmacology of the excitatory vestibular input of these neurons was studied by electrical stimulation of the vestibular nuclear complex. Crossed monosynaptic excitatory inputs in AbMOT and AbINT were blocked completely by CNQX (6‐cyano‐7‐nitroquinoxaline‐2,3‐dione) (10 μM), an antagonist of AMPA (α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid) receptors, indicating glutamatergic excitation. Comparison of these results with those in the cat suggests the presence of a basic horizontal vestibulo‐ocular reflex that is very similarly organized, and corroborates the hypothesis that major behavioural differences in the performance of compensatory eye movements between species result from the properties of supplementary networks and not from differences in a common‘three‐neuron’vestibulo‐ocular arc.
Decrease in the Reactivity of Locus Coeruleus Neurons to Hypotension after an Increase in their Tyrosine Hydroxylase Content: A Subregional In Vivo Voltammetry Study in the Rat
Authors: Vachette Cédric , Bourde Odile , Gillon Jean‐Yves , Pujol Jean‐François , Renaud Bernard
Published: April 2006

The aim of the present work was to determine if noradrenergic neurons of the anterior and the posterior subregions of the locus coeruleus exhibit a difference in reactivity in response to sodium nitroprusside‐induced arterial hypotension, and if the pharmacological induction of tyrosine hydroxylase by RU24722 modifies the reactivity of locus coeruleus neurons to this hypotensive stimulus. Previous findings have demonstrated that administration of RU24722 increases the concentration of tyrosine hydroxylase in the rat locus coeruleus by two different mechanisms in the anterior and in the posterior locus coeruleus subregions. The goal of the present study was to measure in vivo the changes in catecholaminergic metabolism in the locus coeruleus after treatment with RU24722 using differential normal pulse voltammetry (DNPV). In vehicle‐treated rats, arterial hypotension increased catecholaminergic metabolism with the same pattern in the two locus coeruleus subregions. However, the changes in the magnitude of the catechol oxidation current throughout the recording period were significantly smaller in the posterior subregion (P < 0.001). In the RU24722‐pretreated rats, there was a 39% increase in tyrosine hydroxylase and dihydroxyphenylacetic acid in the locus coeruleus. The functional reactivity to hypotension measured by DNPV was significantly decreased (P < 0.001) in both the anterior and posterior locus coeruleus subregions with RU24722 treatment. Therefore, this study suggests that the response of locus coeruleus cells to a hypotensive stimulus depends upon the intracellular tyrosine hydroxylase concentration both in the basal condition and during pharmacological induction of tyrosine hydroxylase gene expression.
Neurons in the Primate Superior Colliculus are Active Before and During Arm Movements to Visual Targets
Authors: Werner Wilfried
Published: April 2006

The activity of single neurons in the superior colliculus was recorded while a rhesus monkey made arm movements to visual targets located on a screen in front of him. It was found that the activity of a subpopulation of cells was clearly related to these arm movements. The neurons began to discharge either with the onset of the movement, during the movement period, or well before the onset of electromyogram (EMG) activity and movement, and could be active for the entire duration of EMG activity. While the discharge pattern of some of these‘reach’neurons was not different for movements to different target positions, other cells showed graded changes in activity depending on the direction of movement. The peak discharge rate could rise to > 100 impulses/s. Some units received somatosensory input; other reach cells exhibited a visual response and/or presaccadic activity. It is likely that the primate superior colliculus is not only involved in the initiation and control of orientating movements of the eyes but also in reaching movements of the arms.
Reversal of Rigidity and Improvement in Motor Performance by Subthalamic High‐frequency Stimulation in MPTP‐treated Monkeys
Authors: Benazzouz Abdelhamid , Gross Christian , Féger Jean , Boraud Thomas , Bioulac Bernard
Published: April 2006

In Parkinson's disease the loss of dopaminergic neurons in the substantia nigra is associated with global disorganization of basal ganglia activity and, in particular, with increased activity of the excitatory glutamatergic neurons of the subthalamic nucleus. Recent experimental studies have shown that parkinsonian symptoms can be alleviated by selective lesioning of the subthalamic nucleus in monkeys treated with 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP). We measured the effect of high‐frequency stimulation of the subthalamic nucleus in two unilaterally MPTP‐treated monkeys in order to determine whether it was possible to obtain reversible, gradual and controllable functional impairment of this structure. Clinical, mechanographic and electromyographic results demonstrate that this technique can alleviate parkinsonian rigidity and bradykinesia without causing dyskinesia or hemiballismus. This study supports the hypothesis that the subthalamic nucleus and its excitatory projections have an important role in the mechanisms sustaining the expression of parkinsonian motor changes, and suggests that high‐frequency stimulation of the subthalamic nucleus could be included in treatment for parkinsonism.
Axonal Transport of Dopamine‐containing Vesicles Labelled In Vivo with [3H] Reserpine
Authors: Lechardeur D. , Castel M. N. , Reibaud M. , Scherman D. , Laduron P. M.
Published: April 2006

Axonal transport of the vesicular monoamine transporter was assayed in the rat brain by in vivo binding of the specific ligand [3H] reserpine. Because of the marked localization of reserpine binding sites in dopaminergic cell bodies and nerve terminals, the dopaminergic nigrostriatal pathway was chosen for the study of the axonal transport of the monoamine carrier present in the membrane of synaptic vesicles. When labelled reserpine was injected into the substantia nigra, a delayed accumulation of radioactivity in the ipsilateral striatum was observed ∼4 h after the injection. Similarly, injection into the right striatum was followed by a substantial accumulation of radioactivity in the ipsilateral substantia nigra, which was prevented by peripheral injection of unlabelled reserpine or tetrabenazine. This process was rapid and dependent on microtubules. In senescent rats, the amount of retrogradely transported [3H] reserpine was significantly reduced. These results demonstrate that labelled reserpine may be used to monitor in vivo fast axonal transport in central neurons.
In Vitro Phosphorylation in Isolated Horizontal Cells of the Fish Retina: Effects of the State of Light Adaptation
Authors: Janssen‐Bienhold Ulrike , Nagel Heinz , Weiler Reto
Published: April 2006

Horizontal cells, which are second‐order neurons of the vertebrate retina, exhibit synaptic plasticity governed by light and dark adaptation. We have investigated the alterations in the protein phosphorylation patterns of isolated carp (Cyprinus carpio) horizontal cells in relation to their state of light adaptation by using an in vitro phosphorylation assay and compared the resulting data with protein synthesis patterns of the whole retina. Phosphoproteins and [35S]methionine‐labelled proteins were analysed by one‐ and two‐dimensional gel electrophoresis followed by autoradiography. The state of light adaptation significantly affected the in vitro phosphorylation of horizontal cell proteins with molecular weights of 68, 56/58, 47, 28 and 15 kDa, but had no effect on the protein synthesis of retinal proteins. In the light the most prominent increase of 32P incorporation was observed in the 47 kDa protein. The biochemical properties of this protein closely resembled those of the growth‐associated GAP‐48, found in the fish retina. In addition, the phosphorylation of horizontal cell homogenates in the presence of protein kinase activators such as cyclic AMP, calcium, calmodulin and phospholipids revealed that horizontal cells of the fish retina contain cyclic AMP‐, calcium/calmodulin‐ and calcium/phospholipid‐dependent protein kinase activity resulting in the phosphorylation of several horizontal cell proteins, including the phosphoproteins which were affected by the state of light adaptation.
The Proximal Region of the MBP Gene Promoter is Sufficient to Induce Oligodendroglial‐specific Expression in Transgenic Mice
Authors: Goujet‐Zalc C. , Babinet Ch. , Monge M. , Timsit S. , Cabon F. , Gansmüller A. , Miura M. , Sanchez M. , Pournin S. , Mikoshiba K. , Zalc B.
Published: April 2006

To characterize regulatory DNA sequences involved in oligodendroglial expression of myelin basic protein (MBP), transgenic mice carrying a 256 bp fragment of the mouse MBP promoter fused to an Escherichia coli lacZ gene were generated. Of four transgenic families, two (lines 2 and 4) expressed β‐galactosidase activity in the nervous system but not in most other tissues. Histochemical and immunohistochemical analysis of adult brain from these two lines showed oligodendroglial‐specific expression of the transgene. In line 2, only a small proportion of oligodendrocytes expressed the transgene, and in labelled cells the product of the enzymatic reaction with β‐galactosidase was confined to a small round vesicle in the vicinity of the nucleus. In contrast, in tissue sections from line 4 adult brain and spinal cord β‐galactosidase activity was much more intense and at least 80 – 90% of oligodendrocytes expressed the transgene. Detection of the MBP‐lacZ transcript by in situ hybridization showed that the transgene mRNA was confined to the oligodendrocyte cell body. These results suggest that cis‐acting regulatory elements, specifying oligodendrocytes identity, are located within 256 bp upstream from the MBP gene.
Developmentally Regulated Expression of CGRP in the Mouse Olfactory Pathway
Authors: Denis‐Donini S. , Chini B. , Vitadello M.
Published: April 2006

The pattern of expression of the neuropeptide CGRP and its encoding mRNA has been determined by immunohistochemistry and in situ hybridization in the mouse olfactory pathway during development. Specific CGRP transcripts are first detected at E13 followed by the appearance of the peptide at E15. Both peptide and transcript are present until birth; their expression then appears to be down‐regulated since postnatally the peptide is only observed in some olfactory receptor neurons. A monoclonal antibody that specifically recognizes the neurofilament subunit NF‐M has been used in order to identify olfactory and trigeminal axons. Our results demonstrate that CGRP is expressed in olfactory neurons and their axons during development, thus supporting further its role as a differentiation factor during olfactory bulb ontogenesis.
Changes in the Mechanical Tuning Characteristics of the Hearing Organ Following Acoustic Overstimulation
Authors: Ulfendahl Mats , Khanna Shyam M. , Löfstrand Paula
Published: April 2006

An in vitro preparation of the guinea‐pig temporal bone was used to study the effects of acoustic overstimulation on the mechanical tuning characteristics of the inner ear. Using laser heterodyne interferometry, the vibratory responses of selected sensory and supporting cells within the hearing organ were measured in response to acoustic signals applied to the ear to obtain mechanical tuning curves before and after applying acoustic overstimulation. Following overstimulation the frequency at which the maximal vibration response occurred moved towards lower frequencies, the vibration amplitude generally increased and the shape of the mechanical tuning curves became considerably flatter. These effects were seen within minutes of overstimulation. The micromechanical changes were accompanied by distinct morphological changes mainly affecting the first row of outer hair cells, which were swollen and shortened. Hensen bodies and swelling of the subsurface cisternae were observed in the affected cells. Apart from this, most of the shortened cells looked structurally intact, had undamaged sensory hair bundles and made synaptic contacts to both afferent and efferent nerve fibres. The results demonstrate that the outer hair cells play a key role in determining the tuning of the hearing organ.
Differential Responses of Single Reticulospinal Cells to Spatially Localized Stimulation of the Optic Tectum in a Teleost Fish, Salmo trutta
Authors: Bosch T. J. , Paul D. H.
Published: April 2006

To determine whether the topographically organized retinal input to the optic tectum is subsequently mapped onto the reticular formation, the responses of antidromically identified reticulospinal cells to tectal surface stimulation were investigated in 45 decerebrated, paralysed trout. The tectum was stimulated through a silver ball surface electrode at 24 different locations, and extracellular recordings were made from the rhombencephalic brainstem with glass microelectrodes filled with a 10% solution of horseradish peroxidase (HRP) in Tris buffer (pH 7.4). After recording, the HRP was, in some cases, iontophoretically expelled from the pipette to identify its location and visualized in histological sections by a modified Hanker‐Yates method. Individual reticulospinal neurons discharged 1 – 4 spikes at short latency in response to stimulation of each of the 24 tectal locations. From one tectal location per cell, this initial response was followed by a late, sustained burst. With a short stimulus train (6 pulses, 55 Hz) the burst could last for over a second with discharge rates of up to 500 Hz. Sometimes this burst could be evoked from neighbouring tectal locations, but only by greatly increasing the stimulus strength. We conclude that the reticular formation receives a highly divergent monosynaptic connection from all locations of the tectum and that the longer latency, sustained burst response is due to a mapped connection between the tectum and the reticular formation. Since the late burst could be preceded by a silent period lasting for ∼32 ms, we cannot rule out a dependence on interneurons situated between the tectum and the reticulospinal cells.
In vitro and In vivo Analysis of a Rat Bipotential O – 2A Progenitor Cell Line Containing the Temperature‐sensitive Mutant Gene of the SV40 Large T Antigen
Authors: Barnett Susan C. , Franklin Robin J. M. , Blakemore William F.
Published: April 2006

Primary cultures from neonatal rat optic nerve contain pluripotential O – 2A progenitor cells that are capable of differentiating into oligodendrocytes, type‐2 astrocytes or adult O – 2A progenitors (O – 2Aadult). Since primary optic nerve cultures contain a mixture of glial cell types of which only a small number are O – 2A progenitors, experiments on cell lineage and differentiation carried out using these cultures are both intrinsically limited and difficult to interpret. Ideally, cells from a clonal cell population would provide the optimal starting material for biological studies. In this paper we describe the creation of an O – 2A progenitor cell line using a retrovirus carrying a temperature‐sensitive mutant SV40 large T antigen gene. This cell line has provided sufficient numbers of cells to allow analysis of their in vitro properties and their behaviour following transplantation into an in vivo environment. At the non‐permissive temperature (39°C), these cells differentiate into oligodendrocytes and type‐2 astrocytes in a similar fashion to O – 2A progenitor cells from primary cultures (O – 2Aprim). When grown in media containing platelet‐derived growth factor and basic fibroblast growth factor, the cell numbers can be expanded in culture without differentiating, consistent with the behaviour of O – 2Aprim progenitor cells. By exploiting this property, it has been possible to culture large numbers of O – 2A progenitors for in vivo analysis. In this study we have shown that transplantation of this O – 2A cell line into glia‐free areas in adult rat spinal cord results in differentiation of a proportion of cells into oligodendrocytes which are capable of myelinating axons. Furthermore, differentiation of O – 2A cells into astrocytes was also observed, indicating that the bipotentiality of these cells in vitro can also be demonstrated in vivo.
Methoxyverapamil Reduction of Nicotine‐induced Catecholamine Release Involves Inhibition of Nicotinic Acetylcholine Receptor Currents
Authors: Boehm Stefan , Huck Sigismund
Published: April 2006

The mechanism by which the putative Ca2+ channel blocker methoxyverapamil (D600) inhibits nicotine‐induced catecholamine release was investigated in bovine adrenal chromaffin cells and in neurons from paravertebral sympathetic ganglia of chick embryos. We found D600 to prevent catecholamine release evoked by 30 s applications of nicotine with a significantly higher potency than the release induced either by 30 s K+ depolarizations or by electrical field stimulation of sympathetic neurons. Like the use‐dependent action of D600 upon Ca2+ channels, the magnitude of inhibition of the K+‐evoked secretion depended on the duration of stimulation (10 s to 5 min). Data on catecholamine release were supplemented by patch‐clamp recordings. We found whole‐cell currents in chromaffin cells evoked by (extrapolated) 0.5 s applications of nicotine to be significantly more sensitive to D600 than Ca2+ currents induced by a 0.5 s depolarization from ‐80 to 0 mV. In both instances, the potency of D600 depended on the duration of the (nicotinic and depolarizing) stimuli. Our data suggest that D600 inhibits nicotine‐induced catecholamine release by reducing nicotinic acetylcholine receptor currents rather than voltage‐gated Ca2+ currents. Hence, in chromaffin cells as well as in sympathetic neuronal preparations, D600 does not appear to be a suitable tool to investigate the part voltage‐activated Ca2+ currents play in cellular events induced by nicotine.
A Study of the Barium‐sensitive and ‐insensitive Components of the Action of Thyrotropin‐releasing Hormone on Lumbar Motoneurons of the Rat Isolated Spinal Cord
Authors: Fisher N. D. , Nistri A.
Published: April 2006

The electrophysiological action of thyrotropin‐releasing hormone (TRH) on rat spinal motoneurons was studied in vitro using single‐electrode voltage‐ and current‐clamp techniques. In current‐clamp conditions TRH elicited a slowly developing depolarization, associated with a large input resistance increase and sustained neuronal firing; the primary metabolites of TRH were ineffective. Under voltage‐clamp conditions in the presence of tetrodotoxin, TRH evoked a large inward current (ITRH; peaking at approximately –40 mV) associated with a large input conductance fall. Only 44% of cells displayed ITRH reversal; when the chord conductance values of these cells were plotted against membrane potential, a bell‐shaped relation occurred, indicating voltage‐dependent block by TRH of a persistent conductance active over a wide range of membrane potentials. ITRH reversal values were shifted to more positive levels in high K+ solution in Nernstian fashion; hence a large proportion of the TRH response is suggested to be mediated by the block of a K+ conductance (IK(T)). IK(T) (and its voltage‐dependent block by TRH) was resistant to certain K+ channel antagonists (tetraethylammonium, Cs+, 4‐aminopyridine or apamin), but was depressed by Ba2+. The Ba2+‐resistant fraction of ITRH was attenuated by Cd2+, Mn2+ or Co2+, indicating that it probably involved a Ca2+‐sensitive inward current. Concomitant application of Ba2+ and Cd2+ induced a near‐total block of the response to TRH. It is suggested that suppression of IK(T), associated with the onset of a Ca2+‐sensitive current, can explain the excitatory effect of TRH on rat spinal motoneurons.
Cysteine Sulphinate and Cysteate: Mediators of Cysteine Toxicity in the Neonatal Rat Brain?
Authors: Lehmann Anders , Hagberg Henrik , Orwar Owe , Sandberg Mats
Published: April 2006

Excitotoxic amino acids contain two acidic groups, but cysteine represents an exception to this rule. The hypothesis that cysteine toxicity is mediated by the oxidized and diacidic metabolites cysteine sulphinate and/or cysteate was tested in the present study. The issue was approached in three different ways. Firstly, the distribution of brain injury after subcutaneous administration of cysteine (1 mg/g) to 4‐day‐old rats was compared with that caused by cysteine sulphinate (3 mg/g). Secondly, the effects of excitatory amino acid receptor antagonists on cysteine and cysteine sulphinate toxicity were investigated. Thirdly, the cerebral concentrations of cysteine sulphinate were determined after cysteine administration and compared with those obtained after cysteine sulphinate injection. The cerebral cortex was the region most vulnerable to cysteine toxicity, followed by the hippocampus (especially the medial subicular neurons), amygdala, caudoputamen, cerebellum and septum. Pronounced extravasation of red blood cells was observed in lesioned areas. One day after cysteine administration, the injury was infarction‐like and sharply demarcated. Cysteine sulphinate‐induced damage resembled cysteine‐induced lesions in some respects: the anterior cingulate and retrosplenial cortices, as well as medial subicular cells, were quite vulnerable. However, the differences prevailed. Cysteine sulphinate, but not cysteine, killed neurons of the superficial part of the tectum, the medial habenula, the ventromedial hypothalamus and the arcuate nucleus. Further, while cysteine toxicity was prominent in deep cortical layers, cysteine sulphinate preferentially damaged superficial cortical neurons. Cysteine toxicity was abolished by pretreatment with MK‐801, a selective NMDA antagonist, but not by 2,3‐dihydroxy‐6‐nitro‐7‐sulphamoyl‐benzo(F)quinoxaline, a selective AMPA receptor blocker. In contrast, the considerably smaller lesion seen after cysteine sulphinate administration was only partially prevented by MK‐801. Large (19‐fold) increases in cortical cysteine sulphinate concentration were noted after injection of a toxic dose of cysteine. This corresponds to 90 nmol cysteine sulphinate/g protein. The cysteate concentration was not increased above the detection limit. Injection of a toxic dose of cysteine sulphinate elevated cysteine sulphinate concentration in the frontomedial cortex (a region consistently injured by cysteine sulphinate) almost three orders of magnitude more than that observed after cysteine administration. Taken together, these results strongly suggest that neither cysteine sulphinate nor cysteate alone mediate cysteine toxicity. Possible candidates for such a role include cysteine carbamate and S‐sulpho‐cysteine. Another alternative is that the sulphydryl group of cysteine sensitizes the NMDA receptor complex and thereby enhances the effect of glutamate and/or some other endogenous NMDAmimetics.
Covariations Between Hippocampal Mossy Fibres and Working and Reference Memory in Spatial and Non‐spatial Radial Maze Tasks in Mice
Authors: Crusio Wim E. , Schwegler Herbert , Brust Ingrid
Published: April 2006

Male mice from nine inbred mouse strains were tested at the age of 3 months in either a spatial or a non‐spatial version of the radial maze. Only four out of eight arms contained food rewards, permitting simultaneous assessment of working and reference memory in both situations. Other animals from the same strains were processed histologically to estimate the strain‐specific extents of the mossy fibre projections. No significant between‐task correlations were obtained for either working or reference memory. However, measures of working and reference memory correlated with each other within tasks. This suggests that these concepts may perhaps not be validly used in the mouse. Large, positive correlations of the size of the intra‐ and infrapyramidal mossy fibre projection with both working and reference memory were obtained in the spatial radial maze task, but not in the non‐spatial one. We conclude that heritable variations of the hippocampal intra‐ and infrapyramidal mossy fibre projection influence processes related to spatial learning capabilities in radial mazes.
Interleukin‐6 and Transforming Growth Factor‐β1 mRNAs are Induced in Rat Facial Nucleus Following Motoneuron Axotomy
Authors: Kiefer Reinhard , Lindholm Dan , Kreutzberg Georg W.
Published: April 2006

Transection of the rat facial nerve leads to a rapid activation of both astrocytes and microglia around axotomized motoneurons. The factors involved in glial activation in vivo are poorly defined but cytokines have been implicated as major regulators of glial activity in vitro. In the present study we have investigated the expression of cytokine mRNAs in the axotomized facial nucleus that might be involved in glial activation. Eight hours after axotomy unilateral transection of the facial nerve had already induced a rapid accumulation of interleukin (IL)‐6‐mRNA, with a peak at 24 hours. No IL‐6 mRNA was detected on the unoperated control side. Transforming growth factor (TGF)‐β1 mRNA was detected at low levels in the normal facial nucleus, increasing to three times the normal level 2 days after axotomy. After day 7 TGF‐β1 mRNA levels gradually declined, with a second minor peak 21 days after axotomy. In situ hybridization experiments, 4 and 21 days after axotomy, localized TGF‐β1 mRNA to activated microglial cells around regenerating motoneurons, as well as probably some astrocytes. Motoneurons did not express TGF‐β1 mRNA. TGF‐β3 was found to be normally expressed in the facial nucleus but was not regulated by axotomy. No mRNA for IL‐1, tumour necrosis factor‐α or interferon‐γ was found in the regenerating facial nucleus at any point in time. Our data indicate that IL‐6 might act as an early activating signal for glial cells in response to motoneuron axotomy, and that TGF‐β1 expressed by activated glial cells might provide a long‐lasting negative feedback signal to control glial activation.
High External Potassium Induces an Increase in the Phosphorylation of the Cytoskeletal Protein MAP2 in Rat Hippocampal Slices
Authors: Díaz‐Nido Javier , Montoro Rafael J. , López‐Barneo José , Avila Jesús
Published: April 2006

Depolarization induced in rat hippocampal slices by a high concentration of extracellular K+ leads to an increase in the phosphorylation of microtubule‐associated protein MAP2. The comparison of the major phosphopeptides derived from in situ and in vitro phosphorylated MAP2 suggests the implication of calcium‐dependent protein kinases, including calcium/calmodulin‐dependent protein kinase type II and protein kinase C, in the up‐phosphorylation of MAP2. In particular, a peptide containing the tubulin‐binding domain of the MAP2 molecule may be phosphorylated by protein kinase C. As the association of MAP2 with the cytoskeleton may be regulated by phosphorylation, we suggest that changes in the phosphorylation level bf MAP2 might be involved in synaptic remodelling in hippocampal neurons.
Cytokines Regulate L‐Arginine‐Dependent Cyclic GMP Production in Rat Glial Cells
Authors: Simmons Martha L. , Murphy Sean
Published: April 2006

We have previously demonstrated that primary astrocyte cultures from neonatal rat cortex and C6 glioma cells express a calcium‐independent nitric oxide synthase (NOS) on induction with bacterial endotoxin (lipopolysaccharide, LPS). One hypothesis regarding the mechanism of the LPS induction is that it causes release of cytokines from these cells which then induce the enzyme directly. Such cytokine induction of NOS has been demonstrated in many extraneural cell types. l‐Arginine‐dependent increases in cyclic GMP correlate with smaller increases in accumulation of nitrite, the major oxidation product of nitric oxide, and hence can serve as a more sensitive measure of nitric oxide production. Here we provide evidence that interferon‐γ (IFN‐γ), interleukin (IL)‐1β and tumour necrosis factor‐α induce l‐arginine‐dependent cyclic GMP synthesis in C6 cells and that a combination of IFN‐γ and IL‐1β induce l‐arginine‐dependent cyclic GMP synthesis in astrocyte cultures, indicating that these cytokines induce NOS. In both cell types the induction by cytokines was less sensitive to inhibition by dexamethasone, IL‐10 and IL‐4 than was induction by LPS. These data suggest that cytokines can also induce a NOS in glial cells and that the mechanism of this induction may be more direct than that of LPS, since it is less sensitive to modulation by immunosuppressors. Due to the close associations of astrocytes with neurons and microvasculature, cytokine‐induced NOS could have potentially important pathophysiological effects in the central nervous system.
Sulphhydryl‐modifying Reagents Alter Ototoxin Block of Muscarinic Receptor‐linked Phosphoinositide Turnover in the Cochlea
Authors: Bartolami Sylvain , Planche Myriam , Pujol Rémy
Published: April 2006

In the 12‐day‐old rat cochlea, the synthesis of inositol phosphates (IPs) can be activated via M3 cholinoceptors. This stimulation is blocked by ototoxins (mercury, ethacrynate, cisplatin, neomycin), drugs with side effects that lead to damage of hair cells and strial cells. As these toxic effects can be reversed in vivo by thiol molecules, we investigated whether modifications of thiol compounds could be involved in ototoxin‐induced inhibition of the IP turnover in the cochlea. For this purpose, we assessed whether the sulphhydryl‐modifying reagents N‐ethylmaleimide and cadmium modify the carbachol‐stimulated formation of IPs in the 12‐day‐old rat cochlea. Both molecules inhibit the carbachol effect on a dose‐dependent way without altering the basal metabolism of IPs. As cadmium may block some calcium channels, the effect of verapamil, another calcium channel antagonist, was tested. Verapamil (1 –50 μM) does not alter carbachol‐evoked IP formation, suggesting that the inhibitory effect of cadmium is not due to a calcium influx block. Binding experiments with the muscarinic ligand quinuclidinyl benzylate (QNB) showed that the sulphhydryl‐modifying reagents do not displace QNB from binding sites. Combining ototoxins and reagents shows that N‐ethylmaleimide acts synergistically with all ototoxins but ethacrynate while cadmium does so only with mercury. Both N‐ethylmaleimide and cadmium have additive effects with ethacrynate. As a supplement, disulphide bond‐modifying agents do not alter the carbachol‐enhanced metabolism of IPs. These results suggest that molecules having thiol‐modifying properties inhibit the carbachol‐induced turnover of IPs without acting at the muscarinic sites. Since thiol modifiers and ethacrynate share similar features in both QNB binding and IP response it is hypothesized that they strike common targets, possibly G proteins.
Differential Regulation of Preprotachykinin‐A mRNA Expression in Striatum by Excitation of Hippocampal Neurons
Authors: Brené Stefan , Lindefors Nils , Herrera‐Marschitz Mario , Persson Håkan
Published: April 2006

In this report we have studied the influence of hippocampal neurons on neuropeptide mRNA expression in both dorsal and ventral striatum in the rat. Intrahippocampal unilateral kainic acid injections were performed in control animals and in animals with a unilateral 6‐hydroxydopamine‐induced dopamine deafferentation of the striatum. In situ hybridization combined with quantitative image analysis was used to study the expression of preprotachykinin A mRNA encoding the neuropeptides substance P and neurokinin A. The 6‐hydroxydopamine‐induced lesion caused a decrease of preprotachykinin A mRNA levels in the ipsilateral dorsal striatum and in both sides of the ventral striatum. In normal rats, the intrahippocampal kainic acid injection caused a twofold increase in preprotachykinin A mRNA in the limbic parts of the striatum, which are innervated by the hippocampus. No effect of the kainic acid injection was seen in the lateral parts of the dorsal striatum, a region which does not appear to be innvervated by the hippocampus. Animals with a 6‐hydroxydopamine lesion showed a similar kainic acid‐mediated increase in preprotachykinin A mRNA in parts of the ventral striatum. In the dopamine‐lesioned dorsal striatum and ventral striatum the decreased preprotachykinin A mRNA levels were normalized by the intrahippocampal kainic acid injection. These results show that kainic acid‐mediated excitation of hippocampal neurons causes a dopamine‐independent induction of preprotachykinin A mRNA expression in parts of the ventral striatum, and reverses the dopamine deafferentation‐induced decrease of preprotachykinin A mRNA in both dorsal and ventral striatum. Combined, our results suggest that hippocampal neurons can regulate preprotachykinin A mRNA expression in both the ventral and the dorsal striatum.
Functional Organization of Auditory Cortex in the Mongolian Gerbil (Meriones unguiculatus). I. Electrophysiological Mapping of Frequency Representation and Distinction of Fields
Authors: Thomas Hardy , Tillein Jochen , Heil Peter , Scheich Henning
Published: April 2006

The frequency representation within the auditory cortex of the anaesthetized Mongolian gerbil (Meriones unguiculatus) was studied using standard microelectrode (essentially multiunit) mapping techniques. A large tonotopically organized primary auditory field (AI) was identified. High best frequencies (BFs) were represented rostrally and low BFs caudally along roughly dorsoventrally oriented isofrequency contours. Additional tonotopic representations were found adjacent to AI. Rostral to AI was a smaller field with a complete tonotopic gradient reversed with respect to that in AI (mirror image representation) and was termed the anterior auditory field (AAF). BFs in the range from 0.1 to 43 kHz, apparently covering the hearing range of the Mongolian gerbil, were found in AI and AAF. Units in these two core fields responded to narrow frequency ranges with short latencies. Ventral to the common high‐frequency border to AAF and AI, a rapid transition to very low BFs suggested the presence of a ventral field (V). Caudal to AI two small tonotopically organized fields were identified, a dorsoposterior field (DP) and a ventroposterior field (VP). The VP showed a tonotopic organization mirror imaged to that of AI, i.e. low frequencies were represented rostrally near the caudal border of AI, and high frequencies caudally. The DP showed a concentric frequency organization with high BFs located in the centre. Units in DP and VP fired less strongly, with considerably longer latencies, and responded to a broader range of frequencies than units in AI and AAF. Dorsocaudal to AI a dorsal field (D) was identified, harbouring units that responded to very broad ranges of frequencies. A tonotopic organization of field D could not be discerned. In the border region of AI and D, low‐frequency responses were similar to those found in parts of AI and AAF, but without a clear‐cut tonotopic organization. This region was termed Aid. The two core fields AI and AAF appeared to be located within the koniocortex, while the remaining fields lay outside. Our data show that the organization of the gerbil auditory cortex is highly elaborate, with parcellation into fields as complex as in cat or primates.
Spatiotemporal Induction of Immediate Early Genes in the Rat Brain after Limbic Seizures: Effects of NMDA Receptor Antagonist MK‐801
Authors: Gass Peter , Herdegen Thomas , Bravo Rodrigo , Kiessling Marika
Published: April 2006

Fos, jun and krox belong to multigene families coding for transcription factors. These cellular immediate early genes (IEGs) are thought to be involved in coupling neuronal excitation to changes of target gene expression. Immunocytochemistry with specific antisera was used to assess regional levels of six IEG‐encoded proteins (c‐Fos, Fos B, Krox‐24, c‐Jun, Jun B, Jun D) in the rat forebrain after kainic acid‐induced limbic seizures. The results demonstrate a complex spatial pattern of IEG induction and/or suppression in limbic and non‐limbic structures. The sequence of induction within hippocampal subpopulations was identical for all IEGs investigated, following the order dentate gyrus, CA1 and CA3, and irrespective of different temporal profiles for individual transcription factors. Since Fos and Jun proteins act via homo‐ and heterodimer complexes at specific DNA sites, our data imply that the postictal combinatorial changes of these dimers allow a sequential and differential regulation of target gene expression in specific forebrain regions. Pretreatment with the non‐competitive NMDA receptor antagonist MK‐801 did not affect kainate‐induced expression of IEGs in the limbic system, indicating that IEG induction in these regions is mediated by high‐affinity kainate and AMPA receptors rather than NMDA receptors. In contrast, MK‐801 abolished IEG induction in the somatosensory cortex and striatum, suggesting that IEG expression in non‐limbic neurons occurs transsynaptically and is mediated by NMDA receptors.
Propagation of Epileptiform Activity During Development of Amygdala Kindling in Rats: Linear and Non‐linear Association Between lpsi‐ and Contralateral Sites
Authors: Beldhuis Hans J. A. , Suzuki Takanori , Pijn Jan Pieter M. , Teisman Ard , da Silva Fernando H. Lopes , Bonus Béla
Published: April 2006

The relationship between ipsi‐ and contralateral epileptiform electroencephalographic (EEG) activity was investigated in rats that were kindled daily in the amygdala. Two types of relationship—linear and non‐linear associations—were studied and used to estimate time delays of EEG activity between homotopic amygdalar sites during consecutive tetanizations. The progressive development of epileptiform EEG and convulsive behaviour was accompanied by an increase in association. Maximal association values of the non‐linear function were significantly higher than linear association values. The gradual development of motor seizure severity was correlated with increased non‐linearity. Time delays between the two amygdalae were estimated comparably with the linear and non‐linear function: 30.0±3.3 and 24.6±1.7 ms (ipsilateral leading contralateral), respectively. However, in rats displaying exclusively bilaterally generalized motor convulsions, maximal values of both functions decreased but were still significantly higher than control values of phaserandomized EEG. Corresponding positive as well as negative interhemispheric time delays were recorded during the afterdischarge. These results demonstrated a strengthened association between the ipsi‐and contralateral amygdala during primary epileptogenesis induced by amygdala kindling. In contrast, development of a secondary focus in the contralateral homotopic region resulted in a weakened interhemispheric association. Secondary bilateral synchrony between the ipsi‐ and contralateral amygdala occurred during the evoked epileptiform EEG activity.
GABAA Receptor Function in the Early Period After Transient Forebrain Ischaemia in the Rat
Authors: Verheul H. B. , de Leeuw F.‐E. , Scholten G. , Tulleken C. A. F. , da Silva F. H. Lopes , Ghijsen W. E. J. M.
Published: April 2006

The purpose of this study was to evaluate the function of the GABAA receptor following transient forebrain ischaemia. The GABA‐stimulated chloride (36Cl−) uptake into synaptoneurosomes was determined as an indicator of GABAA receptor function. Synaptoneurosomes were isolated from control rats and rats in which the forebrain was made ischaemic by way of the two‐vessel occlusion model. Animals subjected to ischaemia were killed at the end of the ischaemic insult and at 30 min or 2 or 5 h of recirculation. The results showed a reduction of 75% in GABA‐mediated 36Cl− uptake in synaptoneurosomes isolated from animals shortly (<0.5 h) after the ischaemic episode (P < 0.01). After longer recirculation periods the GABA‐mediated 36Cl− uptake reached preischaemic control levels. To investigate whether alterations in 36Cl− uptake were related to the synaptoneurosomal metabolic status, the synaptoneurosomal ATP content was measured. The time course of the ATP recovery correlated with the recovery of the GABA‐mediated 36Cl− uptake (r= 0.7, P < 0.001). To investigate the importance of ATP in GABA‐mediated 36Cl−uptake more directly, synaptoneurosomes isolated from control rats were exposed to chemically induced ATP depletion with rotenone, an inhibitor of oxidative phosphorylation. This resulted in similar reductions in both ATP level and GABA‐stimulated 36Cl− uptake as observed after in vivo ischaemia. These findings indicate that GABAA receptor function is transiently impaired in the early postischaemic period in a way which is closely related to alterations in cellular energy metabolism. The relevance of these findings to the development of ischaemic cell death is discussed.
Interaction of the Amygdala with the Frontal Lobe in Reward Memory
Authors: Gaffan D. , Murray E. A. , Fabre‐Thorpe M.
Published: April 2006

Five cynomolgus monkeys (Macaca fascicularis) were assessed for their ability to associate visual stimuli with food reward. They learned a series of new two‐choice visual discriminations between coloured patterns displayed on a touch‐sensitive monitor screen; the feedback for correct choice was delivery of food. Normal learning in this task is known to be dependent on the amygdala. The monkeys received brain lesions which were designed to disconnect the amygdala from interaction with other brain structures thought to be involved in this memory task. All the monkeys received an amygdalectomy in one hemisphere and lesions in the other hemisphere of some of the projection targets of the amygdala, namely the ventral striatum, the mediodorsal thalamus and the ventromedial prefrontal cortex. The rate of learning new problems was assessed before and after each operation. Disconnection of the amygdala from the ventral striatum was without effect on learning rate. An earlier study had shown that disconnection of the amygdala from either the mediodorsal thalamus or the ventromedial prefrontal cortex produced only a mild impairment, significantly less severe than that produced by bilateral lesions of any of these three structures. The present results show, however, that disconnection of the amygdala from both the mediodorsal thalamus and the ventromedial prefrontal cortex in the same animal, by crossed unilateral lesions of the amygdala in one hemisphere and of both the mediodorsal thalamus and the ventromedial prefrontal cortex in the other hemisphere, produces an impairment as severe as that which follows bilateral lesions of any of these three structures. These results show that, in stimulus – reward associative memory, the role of the amygdala is entirely dependent on its interaction with the frontal lobe, either by direct projections or by indirect subcortical pathways including the mediodorsal nucleus of the thalamus; and that there are at least two partially independent pathways by which the amygdala can influence the frontal lobe.
Serotonin Differentially Modulates Responses Mediated by Specific Excitatory Amino Acid Receptors in the Rat Locus Coeruleus
Authors: Charléty P. J. , Chergui K. , Akaoka H. , Saunier C. F. , Buda M. , Aston‐Jones G. , Chouvet G.
Published: April 2006

Microiontophoretic application of selective agonists for the three major excitatory amino acid receptors, N‐methyl‐d‐aspartate (NMDA), quisqualate and kainate, increased the discharge rate of noradrenergic locus coeruleus (LC) neurons in vivo. NMDA activation was selectively attenuated by iontophoretic application of 2‐amino‐5‐phosphonopentanoate (AP5), an antagonist at NMDA receptors, whereas kainate‐ and quisqualate‐evoked responses were attenuated by both NMDA and non‐NMDA antagonists iontophoresis. NMDA‐ and quisqualate‐evoked responses were significantly decreased by co‐iontophoresis of serotonin (5‐HT). When the NMDA receptor‐mediated component of the response to kainate was blocked with AP5 iontophoresis, 5‐HT increased the response of LC neurons to kainate. These results revealed that 5‐HT differentially modulates the responsiveness of LC neurons to excitatory amino acids, depending on the receptor subtypes responsible for the neuronal activation.