bluuebunny/crossref_metadata_2025_split 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

AbstractTotal 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

AbstractIt 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

AbstractThe 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

AbstractProtein 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

AbstractStriatal 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

AbstractSounds 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

AbstractL‐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

AbstractNeurons 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

AbstractSome 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

AbstractDopamine 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

AbstractLow‐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

AbstractIn 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

AbstractCentral 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

AbstractRecent 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.