bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of dark rearing on phosphorylation of neurotrophin Trk receptors
Authors: Viegi Alessandro , Cotrufo Tiziana , Berardi Nicoletta , Mascia Laura , Maffei Lamberto
Published: March 2003

Total lack of visual experience (dark rearing, DR) is known to affect development of mammalian visual cortex (VC) and to prolong the critical period of visual cortical plasticity. Neurotrophins (NTs) have been proposed to play a relevant role in activity dependent processes important for the final shaping of cortical visual connections. Neurotrophin supply or antagonism of endogenous NT action profoundly affect visual cortical development and plasticity; in particular, exogenous supply of NTs counteracts DR effects on VC development. However, the effects of DR on NT expression are still debated and mounting evidence reports a mismatch between BDNF mRNA and protein expression in DR animals. To gain insight into the effects of DR on expression of nerve growth factor (NGF) and the functional state of NT signalling pathways, we assessed the phosphorylation state of Trk receptors in light‐reared animals (LR), in dark‐reared animals (DR), in DR animals briefly exposed to light and in DR animals with exogenous supply of NTs [NGF, brain‐derived neurotrophic factor (BDNF) and NT‐4] in the VC. We report that DR increases the expression of NGF but reduces the phosphorylation of TrkA and TrkB receptors with respect to LR; normal phosphorylation is rapidly rescued by a brief exposure to light. Exogenous supply of NGF, BDNF or NT4 in DR animals also rescues the phosphorylation of their receptors.
Effects of cholinergic enhancement on conditioning‐related responses in human auditory cortex
Authors: Thiel C. M. , Bentley P. , Dolan R. J.
Published: March 2003

It has previously been shown that cholinergic blockade attenuates conditioning‐related neuronal responses in human auditory cortex. The present study was conducted to investigate the effect of cholinergic enhancement on such experience‐dependent cortical responses. The cholinesterase inhibitor physostigmine, or a placebo control, were continuously infused into healthy young volunteers, during differential aversive conditioning whilst brain activity was measured using event‐related functional magnetic resonance imaging (fMRI). Volunteers were presented with two tones, one of which (CS+) was conditioned by pairing with an electrical shock whereas the other was always presented without the shock (CS–). Conditioning‐related activations, expressed as an enhanced blood oxygenation level dependent (BOLD) response to the salient CS+, were evident in left auditory cortex under placebo but not under physostigmine. This absence of conditioning‐related activations under physostigmine was due to enhanced responses to the CS– under physostigmine as compared to placebo. We suggest that an overactive cholinergic system leads to increased processing of behaviourally irrelevant stimuli and thus attenuates differential conditioning‐related cortical activations.
Metabotropic glutamate receptor 2/3‐dependent long‐term depression in the nucleus accumbens is blocked in morphine withdrawn mice
Authors: Robbe David , Bockaert Joël , Manzoni Olivier J.
Published: March 2003

The nucleus accumbens (NAc) plays a crucial role in addiction. We have recently shown that activation of presynaptic metabotropic glutamate 2/3 receptors (mGlu2/3) induces long‐term depression (LTD) at glutamatergic synapses in the mouse nucleus accumbens (NAc) through the long lasting inhibition of P/Q‐type Ca2+ channels and the cAMP/protein kinase A (PKA) pathway. Because presynaptic mGlu2/3 functions are augmented in the ventral tegmental area of morphine‐withdrawn rats, we have evaluated the consequences of opiate treatment on mGlu2/3 LTD at prelimbic NAc glutamatergic synapses. Here we report that mGlu2/3 LTD is abolished after 1 week of withdrawal from chronic morphine treatment; in the morphine‐withdrawn group LTD measured 5.99 ± 4.84% (P < 0.05) compared with 21.13 ± 5.42% in the sham group. In contrast, chronic morphine treatment did not alter the mechanisms normally underlying mGlu2/3 LTD, such as the cAMP/PKA pathway or P/Q‐type Ca2+ channels. This study shows that one long‐term consequence of morphine treatment is an alteration of synaptic plasticity at glutamatergic synapses in the NAc. Considering that mGlu2/3 agonists (e.g. LY‐354740 used in the present study to induce LTD) reduce behavioural symptoms of morphine withdrawal, these findings could be important in the understanding of the cellular events underlying the dependence‐inducing properties of opiates.
Diversity, developmental regulation and distribution of murine PR55/B subunits of protein phosphatase 2A
Authors: Schmidt Karsten , Kins Stefan , Schild Andreas , Nitsch Roger M. , Hemmings Brian A. , Götz Jürgen
Published: March 2003

Protein phosphatase (PP2A) 2A is a hetero‐trimeric holoenzyme that consists of a core dimer composed of a catalytic subunit that is tightly complexed with the scaffolding subunit PR65/A. This core dimer associates with variable regulatory subunits of the PR55/B, PR61/B′, PR72/B′′ and PR93/PR110/B′′′ families. As PP2A holoenzymes containing PR55/B have been shown to be involved in the pathogenesis of Alzheimer's disease, we characterized the PR55/B family with particular emphasis on its distribution and expression in the brain. We determined the genomic organization of all members of the PR55/B family and cloned their murine cDNAs. Thereby, two novel splice variants of PR55/Bβ were identified. In addition, Northern blot analysis revealed multiple transcripts for the different PR55 subunits, suggesting a higher variability within the PR55 family. In situ hybridization analysis revealed that all PR55/B subunits were widely expressed in the brain. PR55/Bα and Bβ protein expression varies significantly in areas of the brain affected by neurodegenerative diseases such as the hippocampus or cerebellum. At the cellular level, PR55/Bβ protein expression was confined to neurons, whereas PR55/Bα was also expressed in activated astrocytes indicating that the PR55 isoforms confer a different function to the holoenzyme complex. As PP2A dysfunction has been demonstrated to contribute to various human diseases, dissecting the PP2A holoenzyme and its particular function in different cell types will assist in the development of novel therapeutic strategies.
AMPA receptor antagonist LY293558 reverses preproenkephalin mRNA overexpression in the striatum of 6‐OHDA‐lesioned‐rats treated with l‐dopa
Authors: Périer Céline , Marin Concepció , Bonastre Mercè , Tolosa Eduardo , Hirsch Etienne C.
Published: March 2003

Striatal neurons that contain GABA and enkephalin and project to the external segment of the pallidum are thought to be overactive in Parkinson's disease. Furthermore, it has been shown that the appearance of l‐dopa‐induced dyskinesias is correlated to an increase of preproenkephalin (PPE) mRNA expression and that some antagonists of glutamate receptors can prevent and reverse l‐dopa‐induced dyskinesias in parkinsonian rats. The aim of this study was therefore to analyse the effect of a systemic treatment with glutamate receptor antagonists, alone or in combination with l‐dopa, on the PPE mRNA level in rats with a 6‐hydroxydopamine‐induced unilateral lesion of the nigrostriatal pathway. In vehicle‐treated animals, PPE mRNA levels were markedly increased in the striatum on the lesioned side. Sub‐chronic l‐dopa treatment, with bi‐daily injections for 22 days, induced a further increase in PPE mRNA expression in the denervated striatum. Administration of the AMPA receptor antagonist, LY293558, partially reversed the lesion‐induced and l‐dopa‐induced increases in PPE mRNA expression. However, although the administration of the NMDA receptor antagonist MK801 showed a tendency to decrease this l‐dopa induced overexpression, it did not reach significance. This study provides evidence that glutamatergic antagonists, and particularly AMPA antagonists, tend to reverse PPE neurochemical changes at the striatal level induced by l‐dopa in hemiparkinsonian rats.
Human cortical representation of virtual auditory space: differences between sound azimuth and elevation
Authors: Fujiki Nobuya , Riederer Klaus A.J. , Jousmäki Veikko , Mäkelä Jyrki P. , Hari Riitta
Published: March 2003

Sounds convolved with individual head‐related transfer functions and presented through headphones can give very natural percepts of the three‐dimensional auditory space. We recorded whole‐scalp neuromagnetic responses to such stimuli to compare reactivity of the human auditory cortex to sound azimuth and elevation. The results suggest that the human auditory cortex analyses sound azimuth, based on both binaural and monaural localization cues, mainly in the hemisphere contralateral to the sound, whereas elevation in the anterior space and in the lateral auditory space in general, both strongly relying on monaural spectral cues, are analyzed in more detail in the right auditory cortex. The binaural interaural time and interaural intensity difference cues were processed in the auditory cortex around 100–150 ms and the monaural spectral cues later around 200–250 ms.
Calcium‐dependent inactivation and depletion of synaptic cleft calcium ions combine to regulate rod calcium currents under physiological conditions
Authors: Rabl Katalin , Thoreson Wallace B.
Published: March 2003

L‐type Ca2+ currents (ICa) in rod photoreceptors exhibit Ca2+‐dependent inactivation. Perforated‐patch whole‐cell recordings were obtained from isolated rods of the tiger salamander using 1.8 mm Ca2+ in the bathing medium to determine the extent of Ca2+‐dependent inactivation of ICa with physiological [Ca2+] and endogenous buffering. ICa was measured with voltage ramps applied before and after 5‐s steps to −40, −30, −20, or −10 mV. Long depolarizing steps in isolated rods produced inactivation of ICa ranging from 15% at −40 mV to > 80% at −10 mV. Because, in addition to Ca2+‐dependent inactivation, depletion of synaptic cleft Ca2+ accompanying activation of ICa can reduce presynaptic ICa at calycal synapses, we investigated whether a similar mechanism worked at the invaginating rod synapse. Rods from retinal slices with intact synapses were compared with isolated rods in which synaptic cleft depletion is absent. ICa was more strongly depressed by depolarization of rods in retinal slices, with ICa reduced by 47% following voltage steps to −40 mV. The depression of currents by depolarization was also greater for rods from retinal slices than isolated rods when Ca2+ was replaced with Ba2+ to reduce Ca2+‐dependent inactivation. The stronger depolarization‐evoked inhibition of ICa in retinal slices compared to isolated rods probably reflects depletion of synaptic cleft Ca2+ arising from sustained Ca2+ influx. Inactivation of ICa exhibited slow onset and recovery. These findings suggest that Ca2+‐dependent inactivation and depletion of synaptic cleft Ca2+ may combine to regulate ICa in response to light‐evoked changes in rod membrane potential.
The effect of moving textures on the responses of cells in the cat's dorsal lateral geniculate nucleus
Authors: Girardin Cyrille C. , Kiper Daniel C. , Martin Kevan A. C.
Published: March 2003

Neurons in the dorsal lateral geniculate nucleus (dLGN) of the anaesthetized cat were activated with test stimuli (flashing spots, counterphased gratings and moving bars) in the presence of a moving background texture. Moving texture alone produced mild excitation, as a result of stimulation of the receptive field centre. Fast moving coarse textures were more effective than fine slow moving textures. The predominant effect of texture motion, however, was to reduce the response to all test stimuli displayed in the receptive field centre. The effects were similar for X‐ and Y‐like cells. In the case of flashed spots, the sustained response was more strongly suppressed than the transient response. The direction of motion of the texture and differences in the relative motion of bar and texture had no influence on the degree of suppression. These observations are similar to effects seen on cat retinal ganglion cells, and are probably a form of gain control. Such suppressive effects are transmitted to the cortex and are likely to be evoked by large gratings, textures and by natural stimuli, all of which activate extensive regions of the receptive field surround.
Object‐based visual neglect: a computational hypothesis
Authors: Deco Gustavo , Rolls Edmund T.
Published: March 2003

Some patients with damage to the right parietal cortex show neglect for the left half of each of a series of objects shown in a horizontal row in the visual field. The neglect is thus not based on failure to see objects in any part of left visual space, but is object‐based. We show that in a model of attention with separate V1, object (inferior temporal cortex, IT) and spatial (posterior parietal cortex, PP) modules the effect can arise after graded damage increasing towards the right of the PP module when the lateral inhibition between neurons in the PP and V1 modules is short‐range. The local lateral inhibition produces high contrast effects at the edges of each object, and it is when this interacts with gradually increasing damage through the left visual field that the visibility of the left half of each object is especially impaired. This result was found in a formal model completely specified by mean field equations to quantify the dynamical interactions between the modules. This is the first quantitative account of object‐based neglect found in humans with right parietal cortex damage, and provides evidence that the model of attention we describe can account for even detailed and extraordinary phenomena that can occur in visual perception.
Molecular phenotype of rat striatal neurons expressing the dopamine D5 receptor subtype
Authors: Rivera Alicia , Alberti Israel , Martín Ana B. , Narváez José A. , De La Calle Adelaida , Moratalla Rosario
Published: March 2003

Dopamine is one of the principal neurotransmitters in the basal ganglia, where it plays a critical role in motor control and cognitive function through its interactions with the specific dopamine receptors D1 to D5. Although the activities mediated by most dopamine receptor subtypes have already been determined, the role of the D5 receptor subtype in the basal ganglia has still not been established. Furthermore, it is often difficult to distinguish between dopamine D5 and D1 receptors as they are stimulated by the same ligands, and they have a similar molecular structure and pharmacology. In an effort to understand the differences between these two receptor subtypes, we have studied the distribution of neurons containing D5 receptors in the striatum, and their molecular phenotype. As a result, we show that the D5 receptor subtype is present in two different populations of striatal neurons, projection neurons and interneurons. Overall, the abundance of this receptor subtype in the striatum is low, particularly in striatal projection neurons of both the direct and indirect projection pathways. In contrast, the expression of D5 receptors in striatal interneurons (cholinergic, somatostatin‐ or parvalbumin‐positive neurons) is high, while low to moderate expression was observed in calretinin‐positive neurons. Our results demonstrate the presence of D5 receptors in all the striatal cell populations so far described, although at different intensities in each. The fact that a large number of striatal neurons express the D5 receptor subtype suggests that this receptor fulfils an important function in the process of integrating information in the striatum.
Vagal motor neurons in rats respond to noxious and physiological gastrointestinal distention differentially
Authors: Zhang Xueguo , Jiang Chunhui , Tan Zhenjun , Fogel Ronald
Published: March 2003

Low‐pressure gastrointestinal distention modulates gastrointestinal function by a vago‐vagal reflex. Noxious visceral distention, as seen in an obstruction of the gastrointestinal tract, causes abdominal pain, vomiting and affective changes. Using single neuron recording and intracellular injection techniques, we characterized the neuronal responses of neurons in the dorsal motor nucleus of the vagus (DMNV) to low‐ and high‐pressure distentions of stomach and duodenum. Low‐pressure gastric distention inhibited the mean activity of the DMNV neurons whereas high‐pressure gastric distention excited many neurons. Of 47 DMNV neurons, low‐pressure gastric distention inhibited 39, excited four, and did not affect four neurons. High‐pressure gastric distention inhibited 26, excited 20, and left one unaffected. Thirteen of the 39 DMNV neurons inhibited by low‐pressure distention of the stomach reversed their response to excitation during high‐pressure gastric distention. Among 47 DMNV neurons, low‐pressure duodenal distention inhibited 30, excited 10, and did not affect the remaining seven neurons. High‐pressure distention of the duodenum inhibited 25 and excited 22 neurons. Eight DMNV neurons inhibited by low‐pressure duodenal distention were excited in early response to high‐pressure distention of the duodenum. High‐pressure duodenal distention caused an early excitation and late inhibition in the mean activity of the DMNV neurons while low‐pressure duodenal distention only produced late inhibition. These results suggest that different reflexes are present between physiological distention and noxious stimulation of gastrointestinal tract.
Water maze performance, exploratory activity, inhibitory avoidance and hippocampal plasticity in aged superior and inferior learners
Authors: Schulz D. , Huston J. P. , Jezek K. , Haas H. L. , Roth‐Härer A. , Selbach O. , Luhmann H. J.
Published: March 2003

In 28‐ to 30‐month‐old rats, in vitro short‐term and long‐term potentiation (STP and LTP) were measured in area CA1 of the hippocampus in seven superior and seven inferior learners, that were selected from a pool of 40 rats based on water maze escape performance over a period of 9 days. The aim was to examine whether levels of STP and LTP could account for group differences in learning of water maze escape, spatial preference and wall (thigmotaxis)‐avoidance and in short‐term retention of an inhibitory avoidance task. There was no significant group difference in open‐field exploration, i.e. the number of rearings. In contrast to expectation, the superior and inferior learners did not differ significantly from each other in levels of STP and LTP. However, variability in escape and spatial learning, but not thigmotaxis‐avoidance learning, was significantly predicted by variability in STP and LTP in the superior group. Also, open‐field exploratory rearings were significantly correlated with STP and LTP as well as with maze escape learning in the superior group. The results show that, in the aged superior group, levels of CA1 STP and LTP coincided with residual water maze escape and spatial preference learning as well as open‐field exploration, i.e. behavioural expressions known to be related to hippocampal functioning, but not with learning to avoid thigmotaxis in the maze. The lack of such correlations in the inferior group may be due to the severe impairment in escape and spatial preference learning and/or the influence of yet unknown third variables on these relationships.
Neuro–glia interaction effects on GFAP gene: a novel role for transforming growth factor‐β1
Authors: De Sampaio e Spohr Tânia Cristina Leite , Martinez Rodrigo , Da Silva Elen Federowicz , Neto Vivaldo Moura , Gomes Flávia Carvalho Alcantara
Published: March 2003

Central nervous system (CNS) development is highly guided by microenvironment cues specially provided by neuron–glia interactions. By using a transgenic mouse bearing part of the gene promoter of the astrocytic maturation marker GFAP (glial fibrillary acidic protein) linked to the β‐galactosidase (β‐Gal) reporter gene, we previously demonstrated that cerebral cortical neurons increase transgenic β‐Gal astrocyte number and activate GFAP gene promoter by secretion of soluble factors in vitro. Here, we identified TGF‐β1 as the major mediator of this event. Identification of TGF‐β1 in neuronal and astrocyte extracts revealed that both cell types might synthesize this factor, however, addition of neurons to astrocyte monolayers greatly increased TGF‐β1 synthesis and secretion by astrocytes. Further, by exploiting the advantages of cell culture system we investigated the influence of neuron and astrocyte developmental stage on such interaction. We demonstrated that younger neurons derived from 14 embryonic days wild‐type mice were more efficient in promoting astrocyte differentiation than those derived from 18 embryonic days mice. Similarly, astrocytes also exhibited timed‐schedule developed responsiveness to neuronal influence with embryonic astrocytes being more responsive to neurons than newborn and late postnatal astrocytes. RT‐PCR assays identified TGF‐β1 transcripts in young but not in old neurons, suggesting that inability to induce astrocyte differentiation is related to TGF‐β1 synthesis and secretion. Our work reveals an important role for neuron–glia interactions in astrocyte development and strongly implicates the involvement of TGF‐β1 in this event.
Prominent expression of Narp in central vestibular pathways: selective effect of labyrinth ablation
Authors: Reti Irving M. , Minor Lloyd B. , Baraban Jay M.
Published: March 2003

Recent in vitro studies demonstrated that Narp, a secreted immediate early gene (IEG) product, induces AMPA receptor clustering. Accordingly, Narp has been implicated in mediating activity‐dependent changes in synaptic efficacy. To help define the role of Narp in vivo, we conducted immunohistochemical studies of Narp in rat brain. Unexpectedly, we found robust Narp expression in several discrete areas linked to the vestibular system: the anterodorsal nucleus (ADN) of the thalamus, which relays head orientation information to the cortex, the lateral vestibulospinal (Deiters′) nucleus and Purkinje cells in the flocculonodular lobe of the cerebellum. Although strong Narp expression in Deiters' nucleus and the cerebellum was present consistently, Narp expression in the ADN displayed a high degree of variability among animals. To check if this variability in ADN Narp expression reflects its dependence on fluctuating levels of vestibular input, we monitored Narp immunostaining following bilateral labyrinth ablation. This procedure significantly suppressed Narp immunostaining in the ADN, indicating that it is stimulated by naturally occurring vestibular input. In contrast, labyrinth ablation did not affect Narp staining in Deiters' nucleus or the flocculonodular lobe of the cerebellum, presumably because these areas are driven by inputs from multiple systems. As previous studies implicate Narp in synaptic plasticity, these findings suggest that this IEG may mediate ongoing adjustments in synaptic strength or connectivity in several pathways linked to the vestibular system.
Involvement of medullary A2 noradrenergic neurons in the activation of oxytocin neurons after conditioned fear stimuli
Authors: Zhu Lingling , Onaka Tatsushi
Published: March 2003

Fear‐related stimuli activate oxytocin neurons in the hypothalamus and facilitate oxytocin release from the pituitary. Oxytocin neurons in the supraoptic nucleus receive direct noradrenergic innervations from the A1 and A2 cell groups in the medulla oblongata. In the present study, we investigated the role of hypothalamic‐projecting noradrenergic neurons in controlling oxytocin cell activity following fear‐related stimuli in rats. An unconditioned fear stimulus (intermittently applied footshock) or conditioned fear stimulus induced expression of Fos protein, a protein product of an immediate‐early gene, in magnocellular oxytocin neurons in the supraoptic or paraventricular nucleus. A neurotoxin, 5‐amino‐2,4‐dihydroxy‐α‐methylphenylethylamine, microinjected into the vicinity of the supraoptic nucleus, selectively depleted the noradrenaline contents of the nucleus and blocked the Fos expression in the supraoptic nucleus after the unconditioned or conditioned fear stimulus. In the medulla oblongata, the unconditioned fear stimulus induced expression of Fos protein in both A2/C2 and A1/C1 catecholaminergic neurons. On the other hand, the conditioned fear stimulus induced expression of Fos protein preferentially in the A2/C2 neurons. Furthermore, the unconditioned fear stimulus induced Fos expression in the A1/C1 and A2/C2 catecholaminergic neurons labelled with retrograde tracers previously injected into the supraoptic nucleus. The conditioned fear stimulus induced Fos expression preferentially in the A2/C2 catecholaminergic neurons labelled with the retrograde tracers. These data suggest that the conditioned fear‐induced oxytocin cell activity is mediated by the A2 noradrenergic neurons projecting to oxytocin neurons, while the unconditioned fear response is mediated by both A2 and A1 noradrenergic neurons.
Developmental event‐related gamma oscillations: effects of auditory attention
Authors: Yordanova Juliana , Kolev Vasil , Heinrich Hartmut , Woerner Wolfgang , Banaschewski Tobias , Rothenberger Aribert
Published: March 2003

This study describes maturational changes in topographical patterns, stability, and functional reactivity of auditory gamma band (31–63 Hz) responses (GBRs) as brain electrical correlates relevant for cognitive development during childhood. GBRs of 114 healthy children from 9 to 16 years were elicited in an auditory focused attention task requiring motor responding to targets, and analyzed by means of the wavelet transform (WT). The effects of age and task variables (attended side and stimulus type relevance) were examined for GBR power and phase‐locking within 120 ms after stimulation. Similar to the spontaneous gamma band power, the power and phase‐synchronization of GBRs did not depend on the age. However, the functional reactivity of GBRs at specific locations changed in the course of development. In 9–12‐year‐old children, GBRs at frontal locations were larger and better synchronized to target than to nontarget stimulus type, and were larger over the left hemisphere (contralateral to the responding hand), thus manifesting sensitivity to external stimulus features and motor task. In 13–16‐year‐old adolescents, GBRs at parietal sites were enhanced by active attending to the side of stimulation, thus being associated with a maintenance of attentional focus to stimulus location. The results indicate that (i) specific aspects of task‐stimulus processing engage distinct spatially localized gamma networks at functionally relevant areas, and (ii) the neuronal substrates of gamma band networks and the ability to synchronize them in relation to task‐specific processes are available in all age groups from 9 to 16 years. However, the mode and efficiency with which gamma networks can be entrained depends on the age. This age‐dependent reactivity of GBRs to different task variables may reflect a transition in processing strategies emerging at approximately 12–13 years in relation to the maturation of cognitive and executive brain functions.
Interferon‐γ differentially modulates the release of cytokines and chemokines in lipopolysaccharide‐ and pneumococcal cell wall‐stimulated mouse microglia and macrophages
Authors: Häusler Karl Georg , Prinz Marco , Nolte Christiane , Weber Joerg R. , Schumann Ralf R. , Kettenmann Helmut , Hanisch Uwe‐Karsten
Published: March 2003

During bacterial infections of the CNS, activated microglia could support leucocyte recruitment to the brain through the synthesis of cyto‐ and chemokines. In turn, invading leucocytes may feedback on microglial cells to influence their chemokine release pattern. Here, we analyzed the capacity of interferon‐γ (IFNγ) to serve as such a leucocyte‐to‐microglia signal. Production of cyto‐ and chemokines was stimulated in mouse microglia cultures by treatments with lipopolysaccharide (LPS) from Gram‐negative Escherichia coli or cell walls from Gram‐positive Streptococcus pneumoniae (PCW). IFNγ presence during the stimulation (0.1–100 ng/mL) modulated the patterns of LPS‐ and PCW‐induced cyto‐ and chemokine release in a dose‐dependent, potent and complex manner. While amounts of TNFα and IL‐6 remained nearly unchanged, IFNγ enhanced the production of IL‐12, MCP‐1 and RANTES, but attenuated that of KC, MIP‐1α and MIP‐2. Release modulation was obtained with IFNγ preincubation (treatment of cells before LPS or PCW administration), coincubation and even delayed addition to an ongoing LPS or PCW stimulation. Together the changes observed for the microglial chemokine release under IFNγ would shift the chemoattractive profile from favouring neutrophils to a preferential attraction of monocytes and T lymphocyte populations – as actually seen during the course of bacterial meningitis. The findings support the view of activated microglia as a major intrinsic source for an instant production of a variety of chemokines and suggest that leucocyte‐derived IFNγ could potentially regulate the microglial chemokine release pattern.
Effects of polyunsaturated fatty acids on voltage‐gated K+ and Na+ channels in rat olfactory receptor neurons
Authors: Seebungkert Benchamaporn , Lynch Joseph W.
Published: March 2003

Although the polyunsaturated fatty acids arachidonic acid (AA) and docosahexaenoic acid (DHA) are enriched in the olfactory mucosa, their possible contribution to olfactory transduction has not been investigated. This study characterized their effects on voltage‐gated K+ and Na+ channels of rat olfactory receptor neurons. Physiological (3–10 µm) concentrations of AA and DHA potently and irreversibly inhibited the voltage‐gated K+ current in a voltage‐independent manner. In addition, both compounds significantly reduced the inhibitory potency of the odorants acetophenone and amyl acetate at these channels. By comparison, the steady‐state effects of both AA and DHA on the voltage‐gated Na+ channel were relatively weak, with half‐maximal inhibition requiring ≈ 35 µm of either compound. However, a surprising finding was that the initial application of 3 µm AA to a naïve neuron caused a strong but transient inhibition of the Na+ current. The channels became almost completely resistant to this inhibition within 1 min, and a 2‐min wash in control solution was insufficient to restore the strong inhibitory effect. These observations suggest that polyunsaturated fatty acids have the potential to strongly influence the coding of odorant information by olfactory receptor neurons.
Cholinergic modulation of nucleus accumbens medium spiny neurons
Authors: De Rover Mischa , Lodder Johannes C. , Kits Karel S. , Schoffelmeer Anton N. M. , Brussaard Arjen B.
Published: March 2003

The rat nucleus accumbens contains acetylcholine‐releasing interneurons, presumed to play a regulatory role in the electrical activity of medium spiny output neurons. In order to examine this issue in detail, we made electrophysiological recordings in rat nucleus accumbens slices. These experiments showed that γ‐aminobutyric acid‐mediated inhibition of the output neurons might be facilitated by activation of nicotinic acetylcholine receptors, in addition to being suppressed via activation of muscarinic acetylcholine receptors. In contrast, glutamatergic excitation of output neurons appeared to be inhibited by activation of muscarinic acetylcholine receptors and to be insensitive to activation of nicotinic acetylcholine receptors. The spontaneous firing frequency of cholinergic neurons appeared to be under control of both a muscarinic and a nicotinic pathway in a bi‐directional manner. Finally, we made paired recordings in which the functional connection between cholinergic neurons and output neurons was monitored. Driving the cholinergic neurons at physiological firing frequencies stimulated γ‐aminobutyric acid‐mediated inhibition of the output neurons, via activation of nicotinic acetylcholine receptors. The onset of this effect was slow and lacked a fixed delay. These data indicate that activation of nicotinic acetylcholine receptors in rat nucleus accumbens may mediate the facilitation of γ‐aminobutyric acid‐mediated inhibition of medium spiny output neurons. Possible mechanisms of neurotransmission, mediating this cholinergic modulation are discussed.
Silymarin protects dopaminergic neurons against lipopolysaccharide‐induced neurotoxicity by inhibiting microglia activation
Authors: Wang Mei‐Jen , Lin Wan‐Wan , Chen Huan‐Lian , Chang Ying‐Hsin , Ou Hsio‐Chung , Kuo Jon‐Son , Hong Jau‐Shyong , Jeng Kee‐Ching G.
Published: March 2003

An inflammatory response in the central nervous system mediated by activation of microglia is a key event in the early stages of the development of neurodegenerative diseases. Silymarin is a polyphenolic flavanoid derived from milk thistle that has anti‐inflammatory, cytoprotective and anticarcinogenic effects. In this study, we first investigated the neuroprotective effect of silymarin against lipopolysaccharide (LPS)‐induced neurotoxicity in mesencephalic mixed neuron–glia cultures. The results showed that silymarin significantly inhibited the LPS‐induced activation of microglia and the production of inflammatory mediators, such as tumour necrosis factor‐α and nitric oxide (NO), and reduced the damage to dopaminergic neurons. Therefore, the inhibitory mechanisms of silymarin on microglia activation were studied further. The production of inducible nitric oxide synthase (iNOS) was studied in LPS‐stimulated BV‐2 cells as a model of microglia activation. Silymarin significantly reduced the LPS‐induced nitrite, iNOS mRNA and protein levels in a dose‐dependent manner. Moreover, LPS could induce the activation of p38 mitogen‐activated protein kinase (MAPK) and c‐jun N‐terminal kinase but not extracellular signal‐regulated kinase. The LPS‐induced production of NO was inhibited by the selective p38 MAPK inhibitor SB203580. These results indicated that the p38 MAPK signalling pathway was involved in the LPS‐induced NO production. However, the activation of p38 MAPK was not inhibited by silymarin. Nevertheless, silymarin could effectively reduce LPS‐induced superoxide generation and nuclear factor kappaB (NF‐κB) activation. It suggests that the inhibitory effect of silymarin on microglia activation is mediated through the inhibition of NF‐κB activation.
Activity‐dependent modulation of GABAergic synapses in developing rat spinal networks in vitro
Authors: Rosato‐Siri Marcelo , Grandolfo Micaela , Ballerini Laura
Published: March 2003

The role of activity‐dependent plasticity in modulating inhibitory synapses was investigated in embryonic rat spinal cord slice cultures, by chronic exposure to non‐NMDA receptor blockers. GABAergic synaptic efficacy in control and chronic‐treated cultures was investigated by patch‐recordings from visually identified spinal interneurons. In both culture groups proximal stimulation induced the appearance of postsynaptic currents (PSCs), which were fully antagonized by 20 µM bicuculline application and reverse polarity at potential values close to those reported for spontaneous GABAergic PSCs. In chronically treated cells GABAergic evoked PSCs displayed a larger failure rate and a smaller coefficient of variation of mean PSC amplitude, when compared to controls. As opposed to controls, chronic GABAergic evoked PSCs did not facilitate upon paired‐pulse stimulation. Facilitation at chronic synapses was observed when extracellular calcium levels were decreased below physiological values (< 2 mM). Kainate was used to disclose any functional differences between control and treated slices. In accordance with the presynaptic action of kainate, the application of this drug along with GYKI, an AMPA receptor selective antagonist, changed, with analogous potency, short‐term plasticity of GABAergic synapses from control and treated cultures. Nevertheless, in chronic cultures, the downstream effects of such activation unmasked short‐term depression. Ultrastructural analysis of synapses in chronically treated cultures showed a reduction both in symmetric synapses and in the number of vesicles at symmetric terminals. Thus, based on electrophysiological and ultrastructural data, it could be suggested that during the development of spinal circuits, GABAergic synapses are modulated by glutamatergic transmission, and thus implying that excitatory transmission regulates the strength of GABAergic synapses.
Substance P mobilizes intracellular calcium and activates a nonselective cation conductance in rat spiral ganglion neurons
Authors: Ito Ken , Rome Claire , Bouleau Yohan , Dulon Didier
Published: March 2003

We demonstrate the expression of functional tachykinin receptors in rat spiral ganglion neurons (SGNs) using calcium signal measurement and whole‐cell patch clamp recording. Substance P (SP; 10 µm, 1 s application) induced a transient increase in intracellular calcium. The SP dose–response study showed an EC50 of 18.8 µm and a Hill slope of 0.77. Comparison between specific agonists for the three tachykinin receptor (NKR) types showed the potency NKR3 > NKR1 > NKR2 at 10 µm. The Ca2+ response could be evoked in Ca2+‐free medium and was blocked by N‐ethylmaleimide and U‐73122, indicating that Ca2+ was released from intracellular stores via a G‐protein and phospholipase C pathway. Under whole‐cell voltage clamp recording at a holding potential of −50 mV, SP (10 µm, 1 s) evoked a slowly developing transient inward current. The current reversed near to 0 mV and ionic permeability experiments revealed a cation nonselective conductance also permeable to large organic cations such as N‐methyl‐d‐glucamine and tetraethylammonium. Neither removing extracellular calcium nor chelating intracellular calcium with 10 mm BAPTA could block the SP‐evoked current. This conductance appeared coupled to G‐protein activation as intracellular GDP‐βS blocked the SP‐evoked current. Mutual desensitization and occlusion studies with acetylcholine and ATP showed that the SP‐evoked conductance share effector channels and/or intracellular processes with the purinergic/cholinergic conductance. In SGNs, SP could have both a trophic action, via a calcium response, and a neuromodulatory role, by a depolarizing action through the activation of nonselective cation channels.
Chemoreceptor activity is normal in mice lacking the NK1 receptor
Authors: Rigual Ricardo , Rico Alberto J. , Prieto‐Lloret Jesus , De Felipe Carmen , González Constancio , Donnelly David F.
Published: March 2003

Substance P has been proposed to be an important neurotransmitter in the carotid body with the neurokinin 1 (NK1) receptor, mediating excitation between the glomus cells and afferent nerve endings. In order to better understand the role of substance P, this study examined chemoreceptor afferent activity, in vitro, and tissue catecholamine levels and release in adult, wild‐type mice and mice lacking the gene for the NK1 receptor (NK1‐KO). Groups did not differ significantly in body weight, carotid body dopamine content or carotid body norepinephrine content. In wild‐type mice, single unit activity increased from 0.59 ± 0.14 Hz to 19.78 ± 2.27 Hz during superfusion with strong hypoxia (PO2 ≈ 25 Torr). Chemoreceptor activity in NK1‐KO mice, increased from 0.71 ± 0.23 to 21.50 ± 3.62 Hz, and neither baseline or peak frequencies were significantly different from the wild‐type group. Less severe hypoxia (PO2≈ 45 torr), evoked peak activities of 12.50 ± 1.88 and 10.64 ± 3.72 Hz in wild‐type and NK1‐KO mice, which were also not significantly different. In response to severe hypoxia, free‐tissue catecholamine increased to 4.92 ± 0.85 µm in wild‐type mice and 4.26 ± 0.63 µm in NK1‐KO mice, which were also not significantly different. It may therefore be concluded that loss of NK1 receptors has little effect on chemoreceptor function in the mouse, and thus they play, at best, a minor role in the hypoxic chemoreception process.
Reduced stress‐induced hyperthermia in mGluR5 knockout mice
Authors: Brodkin J. , Bradbury M. , Busse C. , Warren N. , Bristow L. J. , Varney M. A.
Published: March 2003

It hs been suggested that metabotropic glutamate receptor subtype 5 (mGluR5) play a role in the expression of anxiety, based on anxiolytic‐like effects of the selective mGluR5 antagonist MPEP (2‐methyl‐6‐(phenylethynyl)pyridine) in rodent models of anxiety, including stress‐induced hyperthermia (SIH). To examine the suggested role of mGlu5 receptors in the expression of anxiety, we examined the stress response in mice lacking mGluR5 in several variations of the SIH procedure. In this paradigm, stress causes a mild increase in body temperature that can be blocked by known anxiolytic agents. Three procedures were employed: classical SIH using rectal‐probe measurement of body temperature, and radiotelemetric measurement of body temperature in response to either saline injection or to the introduction of an intruder into the home cage. In all three procedures the mGluR5‐knockout mice displayed a significant attenuation of the hyperthermic response to stress compared to littermate wild‐type control mice. To confirm that our observations were likely to be due to the absence of mGluR5 in the knockout mice we also tested the effect of the recently described selective mGluR5 antagonist MTEP (3‐[(2‐methyl‐1,3‐thiazol‐4‐yl)ethynyl]pyridine) in both the wild‐type and mGluR5 knockout mice. Administration of MTEP in the wild‐type mice, but not the mGluR5 knockout mice, attenuated SIH. That the mGluR5 knockout mice displayed an anxiolytic‐like phenotype and that the mGluR5 antagonist, MTEP, showed a anxiolytic‐like effect only in mice possessing mGluR5 further supports the suggestion that mGluR5 antagonists may be useful in the treatment of anxiety.
Task‐induced modulation of motor evoked potentials in upper‐leg muscles during human gait: a TMS study
Authors: Bonnard Mireille , Camus Mickaël , Coyle Thelma , Pailhous Jean
Published: March 2003

The aim of this study was to determine the relative involvement of the corticospinal (CS) pathway in voluntarily controlled walking compared to unconstrained walking. In the voluntarily controlled walking condition, subjects had to walk at the same speed as in unconstrained walking with a mechanical constraint, which is known to affect specifically the upper‐leg muscles. The motor cortex was activated transcranially using a focal magnetic stimulation coil in order to elicit motor evoked potentials (MEPs) in the rectus femoris (RF) and the biceps femoris (BF). The magnetic stimulation was delivered at the end of the swing (at 90% of the cycle duration), when the EMG backgrounds were similar in the two experimental conditions. For each subject in each condition, MEPs were measured for several stimulus intensities in order to establish the input/output (I/O) curve (MEPs amplitude plotted against stimulus strength). The results showed a significant increase in the MEPs amplitude of both the RF and BF in voluntarily controlled walking compared to unconstrained walking, which is the first evidence of cofacilitation of MEPs in antagonist upper‐leg muscles during human gait. In conclusion, although a lot of studies have emphasized a privileged input of the corticospinal pathway to the distal lower‐leg muscles, this study shows that, if a locomotory task requires fine control of the proximal upper‐leg muscles, a selective facilitation of MEPs is observed in these muscles.
Neurotensin modulates the amplitude and frequency of voltage‐activated Ca2+ currents in frog pituitary melanotrophs: implication of the inositol triphosphate/protein kinase C pathway
Authors: Belmeguenai Amor , Leprince Jérôme , Tonon Marie‐Christine , Vaudry Hubert , Louiset Estelle
Published: March 2003

Many excitatory neurotransmitters and neuropeptides regulate the activity of neuronal and endocrine cells by modulating voltage‐operated Ca2+ channels. Paradoxically, however, excitatory neuromediators that provoke mobilization of intracellular calcium from inositol trisphosphate (IP3)‐sensitive stores usually inhibit voltage‐gated Ca2+ currents. We have recently demonstrated that neurotensin (NT) stimulates the electrical and secretory activities of frog pituitary melanotrophs, and increases intracellular calcium concentration in these cells. In the present study, we have investigated the effects of NT on Ca2+ currents in cultured frog melanotrophs by using the perforated patch‐clamp technique. Frog neurotensin (f NT) reduced the amplitude and facilitated the inactivation of both L‐ and N‐type Ca2+ currents. Application of the membrane‐permeant Ca2+ chelator BAPTA‐AM, the sarcoendoplasmic reticulum Ca2+‐ATPase inhibitor thapsigargin, or the IP3 receptor antagonist 2‐APB suppressed the reduction of Ca2+ currents induced by f NT. Incubation of melanotrophs with the diacylglycerol analogue PMA, which causes desensitization of protein kinase C (PKC), or with the PKC inhibitors chelerythrine and calphostin C, reduced the inhibitory effect of f NT. The NT‐induced action potential waveforms, applied as voltage‐clamp commands, decreased the amplitude of Ca2+ currents, and enhanced Ca2+ influx by increasing the Ca2+ spike frequency. Altogether, these data indicate that the inhibitory effect of f NT on Ca2+ currents results from activation of the IP3/PKC pathway. The observation that NT controls Ca2+ signalling through both amplitude and frequency modulations of Ca2+ currents suggests that NT might induce spacial and temporal changes of intracellular Ca2+ concentration leading to stimulation of exocytosis.
Mitochondrial oxidative metabolism in motor neuron degeneration (mnd) mouse central nervous system
Authors: Bertamini M. , Marzani B. , Guarneri R. , Guarneri P. , Bigini P. , Mennini T. , Curti D.
Published: March 2003

The mnd mouse spontaneously develops slowly evolving motoneuron pathology leading to progressive motor impairment. There is strong evidence that a complex interplay between oxidative stress, mitochondria abnormalities and alteration of glutamate neurotransmission plays an important role in the pathogenesis of motor neuron diseases. Therefore, we investigated the presence of mitochondrial dysfunction in frontal, central (comprising the motor area) and occipital regions of the cerebral cortex and in the spinal cord of 35‐week‐old mnd mice. Lipid peroxide derivatives reacting with thiobarbituric acid (TBARS) were measured in the cervical, thoracic and lumbar spinal cord. In addition biochemical and behavioural analyses were carried out in mnd mice chronically treated with l‐carnitine from the 11th to the 34th week of life (mndT mice). Slight but significant alterations of mitochondrial enzyme activities were seen in the mnd cortical regions. The central area was the most affected and both complex I, IV and citrate synthase were decreased with respect to controls. The rate of oxygen consumption (QO2) was markedly decreased in both the upper (cervical + upper portion of the thoracic region) and lower (lumbar + lower portion of the thoracic region) mnd spinal cord. The level of TBARS showed a rostro‐caudal trend to increase, being 30% higher in the lumbar tract of mnd mice in comparison with controls. l‐carnitine treatment increased the mitochondrial enzyme activities in cortical regions towards control value and was effective in enhancing QO2 and decreasing TBARS levels in the spinal cord of mndT. Behavioural testing showed that l‐carnitine significantly delayed the onset of motor behaviour impairment. This beneficial effect was declining at 35 week of age, when the biochemical measurements were performed.