bluuebunny/crossref_metadata_2025 huggingface dataset:
TRKB signalling controls the expression of N‐methyl‐d‐aspartate receptors in the visual cortex
Authors: Margotti Elisa , Covaceuszach Sonia , Tongiorgi Enrico , Cattaneo Antonino , Domenici Luciano
Published: March 2003

NMDA receptors (NMDARs) are multimeric proteins, the biological and functional characteristics of which depend on differential subunit assembly during postnatal development. In the present paper, we investigated whether the expression of NMDAR subunits NR1, NR2A, NR2B is influenced by neurotrophins in rat visual cortex. We used a soluble form of the TrkB receptor engineered as an immunoadhesin (TrkB‐IgG) in order to block TrkB ligands. TrkB‐IgG was released through a cannula implanted in the occipital pole and connected to a mini‐osmotic pump. TrkB‐IgG was continuously released from postnatal day 20–21 (P20–21) to P36–37. In a different group of animals used as controls, osmotic pumps were filled with saline. Different antibodies were used to stain neurons expressing NR1, NR2A and NR2B. We counted the number of neurons stained for NR2A and NR2B subunits and expressed this as percentage with respect to the total number of cresyl‐violet stained neurons in each cortical layer. In the visual cortex of TrkB‐IgG‐treated rats, the percentage of neurons expressing NR2A was significantly increased in all cortical layers. Concerning the NR2B subunit, the percentage of stained neurons was not significantly different between TrkB‐IgG‐treated and control rats. The staining level for both NR2A and NR2B, but not NR1, was reduced in all cortical layers in TrkB‐IgG‐treated animals. In agreement with this result, the endogenous levels of NR2A and NR2B subunits were reduced in TrkB‐IgG‐treated animals as shown by Western blotting. Thus, TrkB signalling controls the cellular expression of NMDAR subunits in visual cortical neurons during postnatal development.
Evidence for a direct projection from the paraventricular nucleus of the hypothalamus to putative serotoninergic neurons of the nucleus paragigantocellularis involved in the control of erection in rats
Authors: Bancila M. , Giuliano F. , Rampin O. , Mailly P. , Brisorgueil M.‐J. , Calas A. , Vergé D.
Published: March 2003

In the male rat, serotoninergic neurons of the ventrolateral medulla send direct projections onto spinal preganglionic neurons that innervate the penis. The role of the paraventricular nucleus of the hypothalamus in the control of penile erection is well recognized. Our aim was to demonstrate anatomical relation between paraventricular neurons and medullary serotoninergic neurons innervating the penis. In adult male rats, stereotaxic iontophoretic injections of Phaseolus vulgaris leuco‐agglutinin were performed in the paraventricular nucleus. Neurons in the ventrolateral medulla were retrogradely labelled using transneuronal retrograde transport of pseudorabies virus injected in the corpus cavernosum. Sections of the ventro‐lateral medulla were processed for double immunofluorescence to reveal both Phaseolus vulgaris leuco‐agglutinin and pseudorabies virus using specific antibodies. Sections were also processed for the simultaneous detection of pseudorabies virus and serotonin. Pseudorabies virus‐infected neurons in the ventrolateral medulla were present in the nucleus paragigantocellularis, reticular formation of the medulla, raphe pallidus and raphe magnus. In the nucleus paragigantocellularis, all pseudorabies virus‐infected‐neurons were immunoreactive for serotonin. Some of them received Phaseolus vulgaris leuco‐agglutinin‐labelled varicose fibres that ran along the soma of pseudorabies virus‐infected neurons. Confocal microscopy suggested the presence of several close appositions between them, which were demonstrated using three‐dimensional reconstruction of serial optical sections. Our results show that paraventricular neurons send direct projections in the nucleus paragigantocellularis onto neurons that innervate the penis. They suggest a possible role of the paraventricular nucleus in penile erection through the control of descending serotoninergic raphe‐spinal neurons. The neurotransmitter used in this pathway remains to be determined.
The postnatal reorganization of primary afferent input and dorsal horn cell receptive fields in the rat spinal cord is an activity‐dependent process
Authors: Beggs Simon , Torsney Carole , Drew Liam J. , Fitzgerald Maria
Published: March 2003

The dorsal horn of the spinal cord in the newborn rat is characterized by large cutaneous mechanoreceptive fields, a predominance of A‐fibre synaptic inputs and diffuse primary afferent A‐fibre projections, all of which are gradually reduced and refined over the first postnatal weeks. This may be partly responsible for the reduction in cutaneous flexion reflex sensitivity of rats over the postnatal period. Here we show that chronic, local exposure of the dorsal horn of the lumbar spinal cord to the NMDA antagonist MK801 from birth prevents the normal functional and structural reorganization of A‐fibre connections. Dorsal horn cells in spinal MK801‐treated animals, investigated at eight weeks of age by in vivo electrophysiological recording, had significantly larger cutaneous mechanoreceptive fields and greater A‐fibre evoked responses than vehicle controls. C‐fibre evoked responses were unaffected. Chronic MK801 also prevented the normal structural reorganization of A‐fibre terminals in the spinal cord. The postnatal withdrawal of superficially projecting A‐fibre primary afferents to deeper laminae did not occur in treated animals although C‐fibre afferent terminals and cell density in the dorsal horn were apparently unaffected. Spinal MK801‐treated animals also had significantly reduced behavioural reflex thresholds to mechanical stimulation of the hindpaw compared to naïve and vehicle‐treated animals, whereas noxious heat thresholds remained unaffected. The results indicate that the normal postnatal structural and functional development of A‐fibre sensory connectivity within the spinal cord is an activity‐dependent process requiring NMDA receptor activation.
Characterization of the mouse adenylyl cyclase type VIII gene promoter: regulation by cAMP and CREB
Authors: Chao Jennifer R. , Ni Yan G. , Bolaños Carlos A. , Rahman Zia , DiLeone Ralph J. , Nestler Eric J.
Published: March 2003

Adenylyl cyclase (AC) type VIII has been implicated in several forms of neural plasticity, including drug addiction and learning and memory. In the present study, we directly examined the role for the transcription factor CREB (cAMP response element binding protein) in regulating ACVIII expression by cloning a 5.2 kilobase region upstream of the translation start site of the mouse ACVIII gene. Analysis of this fragment revealed consensus elements for several transcription factors, including a canonical cAMP response element (CRE) in close proximity to the transcription initiation region. Next, ACVIII promoter activity was studied in two neural‐derived cell lines and in primary cultures of rat striatal neurons. Activation of the cAMP pathway by forskolin treatment increased promoter activity, and a series of deletion and point mutants demonstrated that this activation is mediated specifically via the canonical CRE site. Gel shift assays confirmed that this site can bind CREB and several CREB family proteins. Further, activation of the ACVIII promoter by forskolin was potentiated by expression of a constitutively active form of CREB, CREB‐VP16, whereas it was inhibited by expression of a dominant‐negative form of CREB, A‐CREB. Finally, over‐expression of CREB in vivo, by viral‐mediated gene transfer, induced ACVIII promoter activity in the brains of ACVIII‐LacZ transgenic mice. These results suggest that the ACVIII gene is regulated by CREB in vitro and in vivo and that this regulation may contribute to CREB‐dependent neural plasticity.
Neural correlates of the motivational and somatic components of naloxone‐precipitated morphine withdrawal
Authors: Frenois François , Cador Martine , Caillé Stéphanie , Stinus Luis , Le Moine Catherine
Published: March 2003

In morphine‐dependent rats, low naloxone doses have been shown to induce conditioned place aversion, which reflects the negative motivational component of opiate withdrawal. In contrast, higher naloxone doses are able to induce a ‘full’ withdrawal syndrome, including overt somatic signs. The c‐fos gene is commonly used as a marker of neuronal reactivity to map the neural substrates that are recruited by various stimuli. Using in situ hybridization, we have analysed in the brain of morphine‐dependent rats the effects of acute withdrawal syndrome precipitated by increasing naloxone doses on c‐fos mRNA expression. Morphine dependence was induced by subcutaneous implantation of slow‐release morphine pellets for 6 days and withdrawal was precipitated by increasing naloxone doses inducing the motivational (7.5 and 15 µg/kg) and somatic (30 and 120 µg/kg) components of withdrawal. Our mapping study revealed a dissociation between a set of brain structures (extended amygdala, lateral septal nucleus, basolateral amygdala and field CA1 of the hippocampus) which exhibited c‐fos mRNA dose‐dependent variations from the lowest naloxone doses, and many other structures (dopaminergic and noradrenergic nuclei, motor striatal areas, hypothalamic nuclei and periaqueductal grey) which were less sensitive and recruited only by the higher doses. In addition, we found opposite dose‐dependent variations of c‐fos gene expression within the central (increase) and the basolateral (decrease) amygdala after acute morphine withdrawal. Altogether, these results emphasize that limbic structures of the extended amygdala along with the lateral septal nucleus, the basolateral amygdala and CA1 could specifically mediate the negative motivational component of opiate withdrawal.
Amygdala norepinephrine levels after training predict inhibitory avoidance retention performance in rats
Authors: McIntyre Christa K. , Hatfield Tammy , McGaugh James L.
Published: March 2003

Previous findings indicate that footshock and several drugs that modulate memory consolidation alter norepinephrine (noradrenaline) release in the amygdala, as assessed byin vivomicrodialysis and high‐performance liquid chromatography. Such findings suggest that norepinephrine release in the amygdala may be critical for regulating memory consolidation. The present study was the first to examine the relationship between norepinephrine release in the amygdala assessed after inhibitory avoidance training and 24‐h retention performance within individual animals. Norepinephrine levels increased to > 300% of pretraining baseline 30 min after training and remained elevated for 2 h. In individual rats, the increase in norepinephrine levels after training correlated highly with 24‐h retention performance. These findings indicate that the degree of activation of the noradrenergic system within the amygdala in response to a novel, emotionally arousing experience predicts the extent of long‐term memory for that experience.
Cellular architecture of the nucleus reuniens thalami and its putative aspartatergic/glutamatergic projection to the hippocampus and medial septum in the rat
Authors: Bokor Hajnalka , Csáki Ágnes , Kocsis Katalin , Kiss József
Published: March 2003

Little is known about the neurochemical features of the nucleus reuniens thalami (RE). In the present study, immunocytochemical experiments were performed to characterize the expression pattern of certain neurochemical markers, e.g. the calcium‐binding proteins calbindin and calretinin and several neuropeptides. Colocalization studies revealed that half of the calbindin‐positive cells express calretinin, and numerous calretinin‐immunoreactive neurons contain calbindin. In contrast, immunolabelling for neuropeptides did not reveal cell bodies in the RE. The RE establishes widespread connections with several limbic structures. To correlate these projection patterns with the neurochemical characteristics of RE neurons, the retrograde tracer [3H]d‐aspartate, which is selectively taken up by high affinity uptake sites that use glutamate as neurotransmitter, and the nonselective retrograde tracer wheatgerm agglutinin‐conjugated colloidal gold was injected into the stratum lacunosum moleculare of the hippocampal CA1 subfield and into the medial septum. The results provide direct anatomical demonstration of aspartatergic/glutamatergic projection from the RE to the hippocampus and to the medial septum. Nearly all of the projecting neurons proved to be calbindin‐immunopositive and many of them expressed calretinin. Both retrograde labelling techniques revealed that neurons projecting to the hippocampus were located in clusters in the dorsolateral part of the RE, whereas neurons projecting to the medial septum were mainly distributed in the ventromedial portion of the nucleus, indicating that different cell populations project to these limbic areas. These results suggest that neurons in the RE are heterogeneous and contribute to the excitatory innervation of the septo‐hippocampal system.
Attentional demands reflect learning‐induced alterations of bimanual coordination dynamics
Authors: Temprado J. J. , Monno A. , Zanone P. G. , Kelso J. A. S.
Published: March 2003

This study aimed to investigate the effects of practice on bimanual coordination dynamics and attentional demands. Participants were asked to perform a dual‐task associating a cyclic antiphase bimanual pattern and a discrete reaction time task. A pretest determined each individual critical transition frequency. In the training session, participants practised 120 trials. They were instructed to maintain the antiphase coordination pattern at the critical transition frequency. The training session was interrupted and followed by an intermediate test (after 60 trials) and a post‐test (30 min after 120 trials), respectively. A retention test was performed 7 days after the end of the training session. Results showed that: (i) the number of transitions decreased as a consequence of practice; and (ii), subjects were able to maintain the antiphase pattern at a higher frequency than in the pretest. Analysis of the trade‐off between relative phase variability and reaction time showed that participants were able to maintain a higher level of stability at the same (intermediate and post‐test) or a lower attentional cost (retention test). These findings show that phase transition dynamics and pattern stability can be significantly modified as a result of practice. Changes in the trade‐off between pattern stability and cost with learning confirm that the attentional cost incurred by the central nervous system to maintain pattern stability decreased with practice. In line with recent neurobiological studies, the present study provides new insights regarding relationships between brain processes, attentional demands and coordinated behaviour in learning bimanual patterns.
Decreased glucocorticoid receptor mRNA and dysfunction of HPA axis in rats after removal of the cholinergic innervation to hippocampus.
Authors: Han Jung‐Soo , Bizon Jennifer L. , Chun Hyun‐Ja , Maus Courtney E. , Gallagher Michela
Published: March 2003

Excess exposure to glucocorticoids can have deleterious effects on physiology and cognition. Glucocorticoids acting via receptors located in hippocampal neurons contribute to negative feedback after stress by terminating the further release of glucocorticoids. The current study investigated the effects of selective immunolesions of septo‐hippocampal cholinergic neurons on hippocampal corticosterone receptor mRNA and on hypothalamic‐pituitary‐adrenal (HPA) activity. As evaluated by in situ hybridization, hippocampal glucocorticoid receptor (GR) mRNA, but not mineralocorticoid receptor (MR) mRNA, was significantly decreased in lesioned rats compared to controls. In a companion study, the peak corticosterone response to one hour of restraint stress did not differ between lesion and control groups but the post‐stress decline of corticosterone was more protracted in the lesioned rats. These findings are discussed in terms of their possible relevance to ageing as age‐related degeneration of the basal forebrain cholinergic system may contribute to the commonly observed dysfunction of the HPA axis in older animals.
The effects of genetic and pharmacological blockade of the CB1 cannabinoid receptor on anxiety
Authors: Haller J. , Bakos N. , Szirmay M. , Ledent C. , Freund T. F.
Published: March 2003

The aim of this study was to compare the effects of the genetic and pharmacological disruption of CB1 cannabinoid receptors on the elevated plus‐maze test of anxiety. In the first experiment, the behaviour of CB1‐knockout mice and wild‐type mice was compared. In the second experiment, the cannabinoid antagonist SR141716A (0, 1, and 3 mg/kg) was administered to both CB1‐knockout and wild type mice. Untreated CB1‐knockout mice showed a reduced exploration of the open arms of the plus‐maze apparatus, thus appearing more anxious than the wild‐type animals, however no changes in locomotion were noticed. The vehicle‐injected CB1‐knockout mice from the second experiment also showed increased anxiety as compared with wild types. Surprisingly, the cannabinoid antagonist SR141716A reduced anxiety in both wild type and CB1 knockout mice. Locomotor behaviour was only marginally affected. Recent evidence suggests the existence of a novel cannabinoid receptor in the brain. It has also been shown that SR141716A binds to both the CB1 and the putative novel receptor. The data presented here supports these findings, as the cannabinoid receptor antagonist affected anxiety in both wild type and CB1‐knockout mice. Tentatively, it may be suggested that the discrepancy between the effects of the genetic and pharmacological blockade of the CB1 receptor suggests that the novel receptor plays a role in anxiety.
Fibroblast growth factor‐2 increases functional excitatory synapses on hippocampal neurons
Authors: Li Ai‐Jun , Suzuki Seigo , Suzuki Masashi , Mizukoshi Eiichi , Imamura Toru
Published: March 2003

The effect of fibroblast growth factor‐2 (FGF‐2) on synapse formation was investigated using rat cultured hippocampal neurons. Treatment with FGF‐2 (0.4–10 ng/mL) for 6 days enhanced synaptogenesis on these neurons by ∼50%, as determined by counting puncta immunostained for presynaptic‐ or postsynaptic‐specific proteins. This enhancement was statistically significant, and was abolished by a specific inhibitor of mitogen‐activated protein kinase (MAPK). The majority of neurons expressed FGF receptors (types 1–3) abundantly on the membrane of somata, dendrites, and growth cones, and in these regions phosphorylation of MAPK was enhanced after FGF‐2 application. Furthermore, our experiments showed that the majority of synapses formed in cultures containing FGF‐2 were positive both for presynaptic proteins and postsynaptic excitatory synapse‐specific proteins, and that these synapses had a similar capacity to recycle the fluorescent styryl dye FM4‐64 as those in the control culture. These results indicate that: (i) FGF‐2 increases excitatory synapses on hippocampal neurons by activating MAPK activity through FGF receptors; and (ii) synapses formed in FGF‐2‐treated culture are capable of cycling vesicles.
Synaptic plasticity in the acoustic startle pathway: the neuronal basis for short‐term habituation?
Authors: Weber Maruschka , Schnitzler Hans‐Ulrich , Schmid Susanne
Published: March 2003

The aim of the present study was to analyse the cellular mechanism underlying short‐term habituation of the acoustic startle response (ASR). We explored distinct synapses of the neuronal startle pathway in rat brain slices by patch‐clamp recordings of giant neurons in the caudal pontine reticular formation. Presynaptic stimulation of auditory afferents by repeated bursts at 0.1 and 1 Hz led to an exponential decay of EPSC magnitudes. This homosynaptic depression (HSD) was reversible and repeatedly inducible after recovery. Many parameters of HSD in vitro match those of ASR habituation in vivo. The mechanisms underlying HSD are distinct from classical short‐term plasticity: paired‐pulse as well as paired‐burst stimulation revealed a facilitation of the second EPSC, occurring in a much smaller time window up to interstimulus intervals of 200 ms. Pharmacological experiments demonstrated that HSD could be completely blocked by the group II and III metabotropic glutamate receptor antagonist MPPG. Similar results were obtained by CPPG, another group II and III antagonist. In contrast, HSD was not affected by the group I and II antagonist MCPG. We conclude that we found a form of synaptic depression in synapses within the primary startle pathway which correlates in many respects with short‐term habituation of the ASR and which is presumably mediated by group III metabotropic glutamate receptors.
Time course of motor cortex reorganization following botulinum toxin injection into the vibrissal pad of the adult rat
Authors: Franchi G.
Published: March 2003

The present experiment studies representation patterns in the motor cortex (M1) of adult rats, 1, 3, 6, and 12 days after unilateral injection of Botulinum Toxin (BTX) into the vibrissa pad. Intracortical microstimulation (ICMS) was used to evidence changes in the representation over time and in the current thresholds required to evoke movements inside the disconnected vibrissa region. After 1 day, isolated as well as contiguous negative sites were observed within the motor cortex corresponding to the disconnected vibrissa region. Thereafter the percentage of unresponsive sites decreased so that after 6 days, the number of unresponsive sites was not significantly higher than those in the control hemispheres. Within the disconnected vibrissa region, electrical stimulation elicited forelimb, eye, ipsilateral vibrissa and neck movements. Following BTX injection, the enlargement of the forelimb representation into the disconnected vibrissa representation began during the first day and stabilized during the second week after injection. In the first days, stimulation thresholds in expanded forelimb sites were higher than those required for similar movement in normal M1 forelimb representation. These thresholds then declined so that in ∼6 days they were similar to normal. There was no clear evidence that stimulation of sites in the medial part of disconnected vibrissa‐cortex evoked eye movements during the first 6 days after BTX injection. After this time, thresholds required to evoke eye movement in expanded sites were generally similar to, and never higher than, those needed to evoke this movement in control sites. Intermingled ipsilateral vibrissa and neck movement occupies part of the medial vibrissa region. Over the 12 days, extension of the ipsilateral vibrissa representation shrank while the representation of neck movement remained unchanged. Throughout the entire time there was no change in the excitability of these sites and the thresholds remained higher than that needed to elicit the vibrissa movement normally represented in this cortical region. No significant differences in threshold were found over time for any of the other movement categories represented in M1. These results indicate that, over time, the new movements inside the disconnected vibrissa region develop differently in M1 following peripheral motor disconnection. The implications for mechanisms involved in cortical plasticity are discussed.
Indirect projections from the suprachiasmatic nucleus to the ventrolateral preoptic nucleus: a dual tract‐tracing study in rat
Authors: Deurveilher Samuel , Burns Joan , Semba Kazue
Published: March 2003

The suprachiasmatic nucleus (SCN) contains a master clock for most circadian rhythms in mammals, including daily sleep–wake cycles. The ventrolateral preoptic nucleus (VLPO) plays a key role in sleep generation and, as such, might be an important target of the SCN circadian signal. However, direct SCN projections to the VLPO are limited, suggesting that most of the SCN output to the VLPO might be conveyed indirectly. We examined this possibility by microinjecting selected known major targets of SCN efferents with biotinylated dextran‐amine and/or cholera toxin B subunit, followed by analyses of retrograde labelling in the SCN and anterograde labelling in the VLPO. Retrograde labelling results confirmed that the medial preoptic area, subparaventricular zone, dorsomedial hypothalamic nucleus and posterior hypothalamic area all received projections from the SCN; these projections arose predominantly from the shell, as opposed to the core, of the SCN. Anterograde labelling results indicated that these same nuclei also projected to the VLPO, mainly its medial and ventral aspects. Comparison of the results of injections of similar sizes across different target groups indicated that the rostral part of the medial preoptic area and the caudal part of the dorsomedial hypothalamic nucleus were particularly noteworthy for the abundance of both SCN source neurons and efferent fibres and terminals in the VLPO. These results suggest that the SCN might provide indirect input to the VLPO via the medial preoptic area and the dorsomedial hypothalamic nucleus, and that these indirect neuronal pathways might play a major role in circadian control of sleep–wake cycles.
Differential excitability and voltage‐dependent Ca2+ signalling in two types of medial entorhinal cortex layer V neurons
Authors: Egorov Alexei V. , Heinemann Uwe , Müller Wolfgang
Published: March 2003

The entorhinal cortex (EC) is a key structure in memory formation, relaying sensory information to the hippocampal formation and processed information to the neocortex. EC neurons in the deep layers modulate the transfer of sensory information by the superficial layers and the dentate gyrus, and form the output to the neocortex. Here we characterize two types of EC layer V neurons by their fluorescence morphology, electrophysiology and intracellular Ca2+ signalling using intracellular recording and Ca2+ imaging. Pyramidal neurons show, in response to depolarizing current pulses, regular firing with strong adaptation and a fast and medium afterhyperpolarization (AHP) which are separated by a depolarizing notch and, with hyperpolarizing current injection, a transient sag. Multipolar cells respond to depolarization with delayed firing with very weak adaptation and have no depolarizing notch between fast and medium AHP and no sag with hyperpolarization. The delayed firing was blocked by 30 µm 4‐aminopyridine, indicating mediation by the D‐type potassium current. Subthreshold depolarization evoked membrane potential oscillations of 2–5 Hz in both cell types and an increase in [Ca2+]i of 37 nm in pyramidal and 59 nm in multipolar neurons. Repetitive firing at 10 Hz for 30 s increased [Ca2+]i in pyramidal and multipolar neurons by 194 and 295 nm, respectively. Differential temporal firing and Ca2+ signalling suggest specific information processing and synaptic memory storage possibilities in these two layer V cell types of the EC.
Brain‐derived neurotrophic factor induces long‐lasting Ca2+‐activated K+ currents in rat visual cortex neurons
Authors: Mizoguchi Yoshito , Monji Akira , Nabekura Junichi
Published: March 2003

Brain‐derived neurotrophic factor (BDNF) increases postsynaptic intracellular Ca2+ and modulates synaptic transmission in various types of neurons. Ca2+‐activated K+ currents, opened mainly by intracellular Ca2+ elevation, contribute to hyperpolarization following action potentials and modulate synaptic transmission. We asked whether BDNF induces Ca2+‐activated K+ currents by postsynaptic elevation of intracellular Ca2+ in acutely dissociated visual cortex neurons of rats. Currents were analysed using the nystatin‐perforated patch clamp technique and imaging of intracellular Ca2+ mobilization with fura‐2. At a holding potential of −50 mV, BDNF application (20 ng/mL) for 1–2 min induced an outward current (IBDNF‐OUT; 80.0 ± 29.0 pA) lasting for more than 90 min without attenuation in every neuron tested. K252a (200 nm), an inhibitor of Trk receptor tyrosine kinase, and U73122 (3 μm), a specific phospholipase C (PLC)‐γ inhibitor, suppressed IBDNF‐OUT completely. IBDNF‐OUT was both charybdotoxin‐ (600 nm) and apamin‐ (300 nm) sensitive, suggesting that this current was carried by Ca2+‐activated K+ channels. BAPTA‐AM (150 μm) gradually suppressed IBDNF‐OUT. Fura‐2 imaging revealed that a brief application of BDNF elicited a long‐lasting elevation of intracellular Ca2+. These results show that BDNF induces long‐lasting Ca2+‐activated K+ currents by sustained intracellular Ca2+ elevation in rat visual cortex neurons. While BDNF, likely acting through the Trk B receptor, was necessary for the induction of long‐lasting Ca2+‐activated K+ currents via intracellular Ca2+ elevation, BDNF was not necessary for the maintenance of this current.
Astrocytes enhance lipopolysaccharide‐induced nitric oxide production by microglial cells
Authors: Solà Carme , Casal Carme , Tusell Josep M. , Serratosa Joan
Published: March 2003

Several stimuli result in glial activation and induce nitric oxide (NO) production in microglial and astroglial cells. The bacterial endotoxin lipopolysaccharide (LPS) has been widely used to achieve glial activation in vitro, and several studies show that both microglial and, to a lesser extent, astroglial cell cultures produce NO after LPS treatment. However, NO production in endotoxin‐treated astrocyte cultures is controversial. We characterized NO production in microglial, astroglial and mixed glial cell cultures treated with lipopolysaccharide, measured as nitrite accumulation in the culture media. We also identified the NO‐producing cells by immunocytochemistry, using specific markers for the inducible NO synthase (iNOS) isoform, microglial and astroglial cells. Only microglial cells showed iNOS immunoreactivity. Thus, contaminating microglial cells were responsible for NO production in the secondary astrocyte cultures. We then analysed the effect of astrocytes on NO production by microglial cells using microglial–astroglial cocultures, and we observed that this production was clearly enhanced in the presence of astroglial cells. Soluble factors released by astrocytes did not appear to be directly responsible for such an effect, whereas nonsoluble factors present in the cell membrane of LPS‐treated astrocytes could account, at least in part, for this enhancement.
Expression and regulation of interleukin‐10 and interleukin‐10 receptor in rat astroglial and microglial cells
Authors: Ledeboer Annemarie , Brevé John J. P. , Wierinckx Anne , Van Der Jagt Saskia , Bristow Adrian F. , Leysen Josée E. , Tilders Fred J. H. , Van Dam Anne‐Marie
Published: March 2003

Activated glial cells crucially contribute to brain inflammatory responses. Interleukin‐10 (IL‐10) is an important modulator of glial cell responses in the brain. In the present study we describe the expression of IL‐10 and the IL‐10 receptor (IL‐10R1) in primary cocultures of rat microglial and astroglial cells. Using quantitative RT‐PCR and ELISA, we show that IL‐10 mRNA expression and subsequent IL‐10 secretion is time‐dependently induced by lipopolysaccharide (LPS). IL‐10R1, however, is constitutively expressed in glial cell cocultures, as shown by RT‐PCR and immunocytochemistry. Radioligand binding studies using 125I‐IL‐10 reveal that rat glial cells express a single binding site with an apparent affinity of approximately 600 pm for human IL‐10. Observations in enriched cultures of either microglial or astroglial cells indicate that both cell types express IL‐10 mRNA and are capable of secreting IL‐10. Both cell types also express IL‐10R1 mRNA and protein. However, in glial cell cocultures immunoreactive IL‐10R1 protein is predominantly observed in astrocytes, suggesting that microglial expression of IL‐10R1 in cocultures is suppressed by astrocytes. In addition, exogenous IL‐10 is highly potent in down‐regulating LPS‐induced IL‐1β and IL‐10 mRNA, and, at a higher dose, IL‐10R1 mRNA in untreated and LPS‐treated cultures, suggesting that IL‐10 autoregulates its expression and inhibits that of IL‐1β at the transcriptional level. Together the findings support the concept that IL‐10, produced by activated microglial and astroglial cells, modulates glia‐mediated inflammatory responses through high‐affinity IL‐10 receptors via paracrine and autocrine interactions.
Stimulation of cortical acetylcholine release following blockade of ionotropic glutamate receptors in nucleus accumbens
Authors: Neigh‐McCandless Gretchen , Kravitz B. Adar , Sarter Martin , Bruno John P.
Published: March 2003

In vivo microdialysis techniques were used to determine the ability of glutamate receptors within the nucleus accumbens to trans‐synaptically modulate the basal forebrain cortical cholinergic system. Rats were implanted with a dialysis probe in the medial prefrontal cortex to measure changes in cortical acetylcholine efflux and in the ipsilateral nucleus accumbens to locally manipulate glutamate receptor activity. Intra‐accumbens perfusion of the broad spectrum ionotropic glutamate receptor antagonist kynurentate (1.0, 5.0 mm) led to a dose‐dependent increase (maximum of 200%) in cortical acetylcholine efflux. This stimulated efflux was reproduced with the intra‐accumbens perfusion of the AMPA/kainate antagonist DNQX (0.1, 0.25, 2.5 mm; maximum increase of 200%) or the NMDA antagonist D‐CPP (10.0, 100.0, 200 µM; maximum increase of 400%). These results reveal a significant glutamatergic tone within the accumbens of awake rats and support the hypothesis that accumbens efferents to basal forebrain modulate the excitability of the basal forebrain cortical cholinergic system.
Caspase‐mediated death of newly formed neurons in the adult rat dentate gyrus following status epilepticus
Authors: Ekdahl Christine T. , Mohapel Paul , Weber Ekkehard , Bahr Ben , Blomgren Klas , Lindvall Olle
Published: March 2003

A large proportion of cells that proliferate in the adult dentate gyrus under normal conditions or in response to brain insults exhibit only short‐term survival. Here, we sought to determine which cell death pathways are involved in the degeneration of newly formed neurons in the rat dentate gyrus following 2 h of electrically induced status epilepticus. We investigated the role of three families of cysteine proteases, caspases, calpains, and cathepsins, which can all participate in apoptotic cell death. Status epilepticus increased the number of bromodeoxyuridine (BrdU)‐positive proliferated cells in the subgranular zone of the dentate gyrus. At the time of maximum cell proliferation, immunohistochemical analyses revealed protein expression of active caspase‐cleaved poly (ADP‐ribose) polymerase (PARP) in ≈ 66% of the BrdU‐positive cells, while none of them expressed cathepsin B or the 150‐kDa calpain‐produced fodrin breakdown product. To evaluate the importance of cysteine proteases in regulating survival of the newly formed neurons, we administered intracerebroventricular infusions of a caspase inhibitor cocktail (zVAD‐fmk, zDEVD‐fmk and zLEHD‐fmk) over a 2‐week period, sufficient to allow for neuronal differentiation, starting 1 week after the epileptic insult. Increased numbers of cells double‐labelled with BrdU and neuron‐specific nuclear protein (NeuN) marker were detected in the subgranular zone and granule cell layer of the caspase inhibitor‐treated rats. Our data indicate that caspase‐mediated cell death pathways are active in progenitor cell progeny generated by status epilepticus and compromise survival during neuronal differentiation.
Descending pathways controlling visually guided updating of reaching in cats
Authors: Pettersson L.‐G. , Perfiliev S.
Published: March 2003

This study uses a previously described paradigm (Pettersson et al., 1997) to investigate the ability of cats to change the direction of ongoing reaching when the target is shifted sideways; the effect on the switching latency of spinal cord lesions was investigated. Large ventral lesions transecting the ventral funicle and the ventral half of the lateral funicle gave a 20–30 ms latency prolongation of switching in the medial (right) direction, but less prolongation of switching directed laterally (left), and in one cat the latencies of switching directed laterally were unchanged. It may be inferred that the command for switching in the lateral direction can be mediated by the dorsally located cortico‐ and rubrospinal tracts whereas the command for short‐latency switching in the medial direction is mediated by ventral pathways. A restricted ventral lesion transecting the tectospinal pathway did not change the switching latency. Comparison of different ventral lesions revealed prolongation of the latency if the lesion included a region extending dorsally along the ventral horn and from there ventrally as a vertical strip, so it may be postulated that the command for fast switching, directed medially, is mediated by a reticulospinal pathway within this location. A hypothesis is forwarded suggesting that the visual control is exerted via ponto‐cerebellar pathways.
Inhibition of tonic spinal glutamatergic activity induces antinociception in the rat
Authors: Tambeli Claudia H. , Parada Carlos A. , Levine Jon D. , Gear Robert W.
Published: March 2003

Inhibition of tonic activity in spino‐supraspinal projection neurons induces heterosegmental antinociception that is mediated by opioid receptors in nucleus accumbens. To investigate the origin of this tonic activity, we evaluated the ability of inhibiting neurotransmission in the spinal cord to produce heterosegmental antinociception in the trigeminal nociceptive jaw‐opening reflex (JOR) in the rat. Spinal intrathecal administration of calcium channel blockers attenuated the JOR, suggesting that the tonic spinal activity depends on synaptic input. To identify the excitatory neurotransmitter receptors involved, selective antagonists for AMPA/kainate, mGluR1, NMDA or NK1 receptors were administered intrathecally to the spinal cord. The AMPA/kainate and mGluR1 receptor antagonists, but not the NMDA or NK1 receptor antagonists, induced antinociception, which was antagonized by intra‐accumbens administration of the selective µ‐opioid receptor antagonist CTOP. Thus, inhibition of tonic spinal glutamatergic activity resulted in supraspinally mediated antinociception. As this antinociception occurred in the absence of interventions that would produce a facilitated nociceptive state, this tonic glutamatergic activity is important in setting nociceptive threshold.
Dynamic patterns of BDNF expression in injured sensory neurons: differential modulation by NGF and NT‐3
Authors: Karchewski L. A. , Gratto K. A. , Wetmore C. , Verge V. M. K.
Published: March 2003

It has been suggested that altered retrograde neurotrophin support contributes to the phenotypic switch observed in BDNF expression in injured sensory neurons. Thus, modulatory influences of NGF and NT‐3 on BDNF expression in injured adult rat DRG neurons were examined using in situ hybridization and immunohistochemical approaches. Quantitative analysis reveals a biphasic response to sciatic nerve injury, whereby in the first day following injury, BDNF expression is up‐regulated in ≈83% of injured neurons including all small neurons, and a larger pool of trkB expressing neurons than in intact. By 1 week and up to 3 weeks later expression is still seen in ≈66% of injured neurons, but the characteristic phenotypic switch in the subpopulations expressing BDNF occurs, whereby expression in the trkA population is reduced and expression in trkB‐ and in trkC‐positive neurons is elevated. NGF infusion results in elevated levels of BDNF expression in both intact and injured trkA‐positive neurons, accompanied by reduced trkB expression. NT‐3 acts in an opposite fashion effecting a down‐regulation in BDNF expression in intact neurons and preventing/reducing the injury‐associated increases in BDNF expression in both trkC‐ and nontrkC‐expressing subpopulations of injured neurons. These effects suggest NGF can regulate BDNF expression in trkA‐expressing neurons regardless of the axonal state and that elevated levels of BDNF may contribute to the down‐regulation in trkB expression associated with these states. Furthermore, the findings demonstrate that NT‐3 can act in an antagonistic fashion to NGF in the regulation of BDNF expression in intact neurons, and mitigate BDNF's expression in injured neurons.
Visual–vestibular interactive responses in the macaque ventral intraparietal area (VIP)
Authors: Bremmer Frank , Klam François , Duhamel Jean‐René , Ben Hamed Suliann , Graf Werner
Published: March 2003

Self‐motion detection requires the interaction of a number of sensory systems for correct perceptual interpretation of a given movement and an eventual motor response. Parietal cortical areas are thought to play an important role in this function, and we have thus studied the encoding of multimodal signals and their spatiotemporal interactions in the ventral intraparietal area of macaque monkeys. Thereby, we have identified for the first time the presence of vestibular sensory input to this area and described its interaction with somatosensory and visual signals, via extracellular single‐cell recordings in awake head‐fixed animals. Visual responses were driven by large field stimuli that simulated either backward or forward self‐motion (contraction or expansion stimuli, respectively), or movement in the frontoparallel plane (visual increments moving simultaneously in the same direction). While the dominant sensory modality in most neurons was visual, about one third of all recorded neurons responded to horizontal rotation. These vestibular responses were typically in phase with head velocity, but in some cases they could signal acceleration or even showed integration to position. The associated visual responses were always codirectional with the vestibular on‐direction, i.e. noncomplementary. Somatosensory responses were in register with the visual preferred direction, either in the same or in the opposite direction, thus signalling translation or rotation in the horizontal plane. These results, taken together with data on responses to optic flow stimuli obtained in a parallel study, strongly suggest an involvement of area VIP in the analysis and the encoding of self‐motion.
Heading encoding in the macaque ventral intraparietal area (VIP)
Authors: Bremmer Frank , Duhamel Jean‐René , Ben Hamed Suliann , Graf Werner
Published: March 2003

We recorded neuronal responses to optic flow stimuli in the ventral intraparietal area (VIP) of two awake macaque monkeys. According to previous studies on optic flow responses in monkey extrastriate cortex we used different stimulus classes: frontoparallel motion, radial stimuli (expansion and contraction) and rotational stimuli (clockwise and counter‐clockwise). Seventy‐five percent of the cells showed statistically significant responses to one or more of these optic flow stimuli. Shifting the location of the singularity of the optic flow stimuli within the visual field led to a response modulation in almost all cases. For the majority of neurons, this modulatory influence could be approximated in a statistically significant manner by a two‐dimensional linear regression. Gradient directions, derived from the regression parameters and indicating the direction of the steepest increase in the responses, were uniformly distributed. At the population level, an unbiased average response for the stimuli with different focus locations was observed. By applying a population code, termed ‘isofrequency encoding’, we demonstrate the capability of the recorded neuronal ensemble to retrieve the focus location from its population discharge. Responses to expansion and contraction stimuli cannot be predicted based on quantitative data on a neuron's frontoparallel preferred stimulus direction and the location and size of its receptive field. These results, taken together with data on polymodal motion responses in this area, suggest an involvement of area VIP in the analysis and the encoding of heading.
Calcium‐dependent acetylcholine release from Xenopus oocytes: simultaneous ionic currents and acetylcholine release recordings
Authors: Aleu Jordi , Blasi Joan , Solsona Carles , Marsal Jordi
Published: March 2003

The fusion of synaptic vesicles with presynaptic membranes is controlled by a complex network of protein–protein and protein–lipid interactions. SNAP‐25, syntaxin and synaptobrevin (SNARE complex) are thought to participate in the formation of the core of the membrane fusion machine but the molecular basis of SNARE interactions is not completely understood. Thus, it would be interesting to design experiments to test those relationships in a new model. Xenopus laevis oocytes are valuable tools for studying the molecular structure and function of ionic channels and neurotransmitter receptors. Here we show that SNARE proteins are present in native Xenopus oocytes and that those oocytes injected with acetylcholine and presynaptic plasma membranes extracted from the electric organ of Torpedo marmorata assume some of the functions of a cholinergic nerve terminal. Neurotransmitter release and macroscopic currents were recorded and analysed simultaneously in a single oocyte electrically depolarized: acetylcholine release was detected using a chemiluminiscent method and calcium entry was measured by exploiting the endogenous Ca2+‐activated chloride current of the oocyte with a two‐electrode voltage‐clamp system. Neurotransmitter release was calcium‐ and voltage‐dependent and partially reduced in the presence of several calcium channel blockers. Clostridial neurotoxins, both holotoxin and injected light‐chain forms, also inhibited acetylcholine release. We also studied the role of the SNARE complex in synaptic transmission and membrane currents by using monoclonal antibodies against SNAP‐25, syntaxin or VAMP/synaptobrevin. The use of antibodies against VAMP/synaptobrevin, SNAP‐25 and syntaxin inhibited acetylcholine release, as did clostridial toxins. However, macroscopic currents were only modified either by syntaxin antibody or by Botulinium‐C1 neurotoxin. This model constitutes a new approach for understanding the vesicle exocytosis processes.
Bilateral parieto‐frontal network for verbal working memory: an interference approach using repetitive transcranial magnetic stimulation (rTMS)
Authors: Mottaghy Felix M. , Döring Tobias , Müller‐Gärtner Hans‐Wilhelm , Töpper Rudolf , Krause Bernd J.
Published: March 2003

Verbal working memory has been attributed to a left‐dominant neuronal network, including parietal, temporal and prefrontal cortical areas. The current study was designed to evaluate the contribution of these brain regions to verbal working memory processes and to assess possible hemispheric asymmetry. The effect of repetitive transcranial stimulation (rTMS) on performance in a verbal working memory task both during, and after an rTMS train (110% of individual motor threshold, 4 Hz) over nine different scalp locations was studied [bilateral middle frontal gyrus (MFG), bilateral supramarginal gyrus (SMG), bilateral inferior parietal cortex (IP) and three different midline control sites]. Significant performance deterioration was observed during rTMS over the left and right MFG and left and right IP. There was no consistent interference effect across subjects over the left or right SMG and the three different midline control sites. The interference effect with the given stimulation parameters did not last beyond the rTMS train itself. The data provide evidence for a symmetrical, bilateral parieto‐frontal verbal working memory network. The data are discussed with respect to the competing ideas of a parieto‐frontal central executive network vs. a network that processes the inherent semantic and object features of the visually presented verbal stimuli in parallel.