bluuebunny/crossref_metadata_2025 huggingface dataset:
Corticothalamic Projections from the Cortical Barrel Field to the Somatosensory Thalamus in Rats: A Single‐fibre Study Using Biocytin as an Anterograde Tracer
Authors: Bourassa Jacques , Pinault Didier , Deschênes Martin
Published: April 2006

This study investigated the pattern of axonal projections of single corticothalamic neurons from the cortical barrel field representing the vibrissae in the rat. Microiontophoretic injections of biocytin were performed in cortical layers V and VI to label small pools of corticothalamic cells and their intrathalamic axonal projections. After a survival period of 48 h, the animals were perfused and the tissue was processed for biocytin histochemistry. On the basis of the intrathalamic distribution of axonal fields and of the types of terminations found in the thalamus, four types of corticothalamic projections were identified, (i) Cells of the upper part of layer VI projected exclusively to the ventral posteromedial (VPm) nucleus, where they arborized in long rostrocaudally oriented bands or‘rods’, (ii) All cells of the lower part of layer VI projected to the medial part of the thalamic posterior group (Pom) but the vast majority of them also collateralized in VPm where they participated in the formation of rods, (iii) A minority of corticothalamic cells in the lower portion of layer VI, possibly located under the interbarrel spaces (septae), arborized exclusively in Pom. (iv) The corticothalamic projection of layer V cells originated from collaterals of corticofugal cells whose main axons ran caudally towards the brainstem. These collaterals arborized exclusively in Pom or in the central lateral nucleus. All corticothalamic cells from layer VI displayed the same type of axonal network, made of long branches decorated by terminal buttons emitted en passant at the tip of fine stalks. Corticothalamic fibres arising from layer V pyramids, however, remained smooth as they ran across the lateral thalamus and they generated in Pom one or two clusters of large boutons. All corticothalamic axons derived from layer VI cells, but not those derived from layer V cells, gave off collaterals as they traversed the thalamic reticular complex. These observations are discussed in the light of previous studies bearing on the topological organization and function of corticothalamic projections to VPm and Pom in rats. The possibility that a similar cellular specificity and a similar organizational plan may characterize corticothalamic relationships in other sensory systems is also considered.
Effect of SR33557 on Intramembrane Charge Movement in Normal and‘Muscular Dysgenesis’Mouse Skeletal Muscle Cells
Authors: Strube Caroline , Shimahara Takeshi , Bournaud Roland
Published: April 2006

It has been reported that the indolizinsulphone SR33557, which binds to a site on the α1 subunit of the dihydropyridine receptor, blocks both L‐type calcium channel activity and contraction in skeletal muscle. Moreover, we know that charge movement plays a key role in the mechanism of excitation‐contraction coupling and in controlling the opening of L‐type calcium channels. We demonstrate here that SR33557 reduces intramembrane charge movement in skeletal muscle from normal mice with an IC50 of ‐10 nM. The drug does not completely inhibit charge movement since ‐20% of total charge movement persists even in the presence of 30 μM SR33557. However, the SR33557‐sensitive charge component is more important than the dihydropyridine‐sensitive one. Surprisingly, SR33557 also reduces intramembrane charge movement in dysgenic myotubes which are characterized by a very strong reduction of the number of dihydropyridine binding sites. In these muscles, 10 μM SR33557 reduces ‐40% of total charge movement. These observations suggest the presence of a new component of charge movement which is sensitive to SR33557 but insensitive to nifedipine. This component is also present in dysgenic myotubes, and it could be produced by the lower molecular weight α1, subunit described by Malouf, N. N., McMahon, D. K., Hainsworth, C. N. and Kay, B. K. (1992) (Neuron, 8, 899–906).
Receptors and Second Messengers Involved in Long‐term Depression in Rat Cerebellar Slices In Vitro: a Reappraisal
Authors: Hémart Nathalie , Daniel Hervé , Jaillard Danielle , Crépel Francis
Published: April 2006

In patch‐clamped Purkinje cells (PCs), bath application of the ionotropic glutamate receptor antagonist, 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) prevents induction of long‐term depression (LTD) of parallel fibre (PF)‐mediated EPSPs by a pairing protocol between Ca2+ spike firing and PF stimulation whereas bath application of (RS)‐α‐methyl‐4‐carboxyphenylglycine (MCPG), a metabotropic glutamate (mGLU) receptor antagonist, does not. On the other hand, LTD can be also induced by pairing direct depolarization of PCs with activation of mGLU receptors by 1 S,3R‐aminocyclopentyl‐dicarboxylate (1S, 3R‐ACPD), even in the presence of CNQX. In this case, LTD induction is not consistently blocked by bath application of the nitric oxide synthase inhibitor, NG‐methyl‐l‐arginine (l‐NMMA), whereas it is strongly blocked when the protein kinase C inhibitor peptide 19‐36 is dialysed into PCs. These results are at variance with LTD induced by a pairing protocol between Ca2+ spikes and PF‐mediated EPSPs which depends to the same extent on both cascades. Finally, thapsigargin, which depletes most intracellular Ca2+ pools, does not block induction of LTD by a pairing protocol between Ca2+ spikes and PF‐mediated EPSPs whereas it prevents the induction of LTD depending on strong mGLU receptor activation.
Synchronous High‐frequency Oscillations in Cat Area 18
Authors: Brosch Michael , Bauer Roman , Eckhorn Reinhard
Published: April 2006

The present study extends knowledge of the basic properties of correlated oscillatory activity patterns in the visual cortex of anaesthetized cats. Recordings with multiple electrodes were performed in area 18 and the correlations of multi‐unit activity in the frequency range 35‐80 Hz were determined using the coherence function. Statistical analysis revealed that the multi‐unit correlations depended on the cortical distance between the recording sites, the orientation selectivity of the neurons and their cortical layer. On average, correlations dropped to chance level within several millimetres and were higher in lower than in upper cortical layers. Similar results were found by analysing the correlations of oscillatory patterns in local field potentials recorded from the same electrodes. Correlations of neurons with similar orientation preferences were higher than those of neurons with different orientation preferences. Comparison to a matched sample from area 17 showed that the correlations in areas 18 and 17 depended on similar properties of the neurons. The dependences of correlated oscillations resembled the known pattern and specificity of intra‐areal fibre connections, suggesting that the correlations were intracortically established. Since correlations were specifically and not randomly related to the response properties of cortical neurons and were prominent in a visual area other than area 17, the findings suggest that correlated oscillatory activity provides a potential neural code supporting sensory information processing.
Developmentally Regulated Expression of mRNA for Neurotrophin High‐Affinity (trk) Receptors within Chick Trigeminal Sensory Neurons
Authors: Williams R. , Bäckström A. , Kullander K. , Hallböök F. , Ebendal T.
Published: April 2006

To investigate the distribution of neurons within the developing trigeminal sensory system which express mRNA for each of the three known high‐affinity neurotrophin receptors (trk, trkB and trkC), we have performed in situ hybridization histochemistry on serial sections through the trigeminal ganglion and trigeminal mesencephalic nucleus at various ages of development using specific antisense oligonucleotide probes. We show that trkC mRNA is first expressed in the chicken embryo at stage 13, in presumptive neurons prior to the formation of the ganglion, that trkB mRNA labelling is initially observed within peripheral neurons slightly later, at stage 19, and that trk mRNA expression is not detectable until around embryonic day 3.5 (stage 21/22). The neurons which exhibit mRNA labelling for each of the high‐affinity receptors occupy discrete regions within the ganglion, indicating that the ganglion comprises distinct neuronal subpopulations, each of which has a different capacity to respond to the different neurotrophins. Neurons which express trk mRNA are confined to the proximal region of the ganglion, whereas those which express trkB mRNA and trkC mRNA are located in two distinct regions within the distal aspect and also within the trigeminal mesencephalic nucleus. From the estimation of the number of neurons which exhibit labelling between embryonic days 9 and 18, we determined that the expression of mRNA for the high‐affinity receptors changes during embryonic development of the ganglion. This is consistent with the observed differences in the response to neurotrophins in vitro.
Evidence for the Existence of a Functional Polysynaptic Pathway From Trigeminal Afferents to Lumbar Motoneurons in the Neonatal Rat
Authors: Vinay Laurent , Cazalets Jean‐René , Clarac François
Published: April 2006

Stimulation of trigeminal afferents has been reported to have powerful effects on the spinal cord in adult animals of several species. In the present study, the pathway transmitting these influences was investigated in the neonatal rat. Experiments were performed on in vitro brainstem/spinal cord preparations. Stimulation of the trigeminal nerve evoked bilateral polysynaptic discharges in lumbar ventral roots. Intracellular recordings from lumbar motoneurons showed mainly excitatory responses, although a few inhibitory responses were also observed. Experiments with perfusion of different parts of the preparation with general or selective synaptic blockers revealed a synaptic relay under GABAergic control in the brainstem, and at least one synapse in the cervical and in the thoracic spinal cord. The involvement of lumbar interneurons was established by perfusing the lumbar enlargement with saline containing either a high concentration of divalent ions or mephenesin in order to reduce transmission along polysynaptic pathways. The contribution of excitatory amino acid transmission was evaluated and was found to evoke mixed receptor responses. The course of the pathway was traced by using different lesions to the brainstem and spinal cord. The pathway was found to be ipsilateral in the brainstem and to become bilateral in the spinal cord. The results of the present study demonstrate that polysynaptic sensorimotor pathways are present at birth. The results are discussed in relation to the pontomedullary locomotor strip, which has been thought to share many features with the trigeminal system.
Mitosis of Schwann Cells and Demyelination are Induced by the Amyloid Precursor Protein and Other Protease Inhibitors in the Rat Sciatic Nerve
Authors: Alvarez Jaime , Moreno Ricardo D. , Inestrosa Nibaldo C.
Published: April 2006

We studied the cytological alterations produced in the rat sciatic nerve by the amyloid precursor protein (APP) containing the Kunitz insert (APP K+) and other protease inhibitors. Conditioning of nerve segments with APP K+, aprotinin or leupeptin for 5 days or more resulted in mitosis of Schwann cells, demyelination of fibres, and a <10‐fold increase in Schwann cells, associated with demyelinated fibres. Altered fibres nevertheless involved a small part of the population. Nerve segments proximal and distal to the conditioned region showed almost no alteration. Conditioning with saline, heated APP K+, or APP without the Kunitz insert was not effective. We conclude that APP K+ and other protease inhibitors induce Schwann cells to enter the cell cycle, and once committed to proliferate they resorb their myelin. These functional properties of APP may be relevant to the pathogenesis of Alzheimer's disease.
Functional Neuroanatomy of the Human Visual Fixation System
Authors: Petit Laurent , Tzourio Nathalie , Orssaud Christophe , Pietrzyk Uwe , Berthoz Alain , Mazoyer Bernard
Published: April 2006

The regional cerebral blood flow correlates of the active fixation of an imagined target were studied in five healthy humans using the positron emission tomography activation paradigm. The fixation task was contrasted to a passive control condition, both tasks being performed in total darkness. Blood flow increases were observed in the frontal eye fields and supplementary eye fields and in the median cingulate gyrus. We suggest that the network of these activated regions mediates the interactions between ocular fixation, eye movements and directed visual attention.
Cholecystokinin Excites Neostriatal Neurons in Rats via CCKA or CCKB Receptors
Authors: Davidowa H. , Albrecht D. , Gabriel H.‐J. , Heublein S. , Wetzel K.
Published: April 2006

The effect of iontophoretically applied cholecystokinin (CCK) on neurons of the neostriatum was studied in rats anaesthetized with urethane. The most frequently observed effect of the sulphated octapeptide (CCK‐8S) on striatal neurons was excitation. Spontaneously active neurons responded more often to CCK‐8S than quiescent cells. Silent, primarily non‐responsive neurons could often be stimulated with CCK‐8S using glutamate to induce an ongoing discharge. Thus, 45.8% of the 177 neurons studied changed their discharge rate by more than 30%. Certain CCK receptor antagonists could prevent the effect of CCK‐8S, fully or at least partly, in the majority of CCK‐responsive neurons. The data suggest that cholecystokinin modulates the firing of active neostriatal neurons via the CCKA or the CCKB receptor type. Furthermore, we compared neuronal responses to glutamate with those recorded during concomitant administration of CCK‐8S in order to study the interaction of both transmitters, which may be colocalized in striatal afferents. CCK‐8S mainly enhanced the excitatory effect of glutamate on striatal neurons, but in several neurons the response to glutamate was reduced. The CCKB receptor antagonist could prevent CCK‐8S from increasing the glutamate‐induced activation.
Intraperitoneal Administration of Bacterial Endotoxin Enhances Noradrenergic Neurotransmission in the Rat Preoptic Area: Relationship with Body Temperature and Hypothalamic‐Pituitary‐Adrenocortical Axis Activity
Authors: Linthorst Astrid C. E. , Flachskamm Cornelia , Holsboer Florian , Reul Johannes M. H. M.
Published: April 2006

A combined in vivo microdialysis/biotelemetry method in freely moving rats was used to study the effects of an endotoxic challenge on brain neurotransmission, hypothalamic‐pituitary‐adrenocortical (HPA) axis activity, autonomic functions and behaviour. Rats were equipped with a microdialysis probe in the preoptic area and a transmitter for biotelemetry in the peritoneal cavity. Time‐dependent changes in noradrenergic and serotonergic neurotransmission, and HPA axis activity were monitored by measuring noradrenaline, serotonin, their metabolites and free corticosterone concentrations in dialysates. Core body temperature, heart rate and locomotion were measured simultaneously by biotelemetry. In addition, total behavioural activity was scored by measuring the time during which rats were active. Intraperitoneal administration of endotoxin (lipopolysaccharide; 100 μg/kg body weight) caused a pronounced increase in preoptic extracellular concentrations of noradrenaline and its metabolite 3‐methoxy‐4‐hydroxyphenylglycol (MHPG; 500 and 400% of baseline respectively). No effect was found on preoptic concentrations of serotonin, although the levels of its metabolite 5‐hydroxyindoleacetic acid were slightly elevated (120% of baseline). Intraperitoneal lipopolysaccharide caused a marked increase in corticosterone levels, a decline in behavioural activity, and biphasic rises in body temperature and heart rate. Analysis of the time curves revealed that noradrenaline rose in parallel with the first increase in body temperature and the increase in corticosterone levels. Moreover, maximum noradrenaline levels were reached ˜60 min earlier than the peak in body temperature and corticosterone concentrations. Intraperitoneal pretreatment with the cyclo‐oxygenase inhibitor indomethacin prevented the lipopolysaccharide‐induced changes in body temperature, heart rate and behavioural activity, whereas the changes in noradrenaline, MHPG and corticosterone were largely, but not completely, reduced. Taken together, the results show that an endotoxic challenge results in a highly differentiated response in brain neurotransmission. We postulate that the profound increase in preoptic noradrenergic neurotransmission may be related to the lipopolysaccharide‐evoked induction of fever and/or activation of the HPA axis.
Eye Position Influence on the Parieto‐occipital Area PO (V6) of the Macaque Monkey
Authors: Galletti C. , Battaglini P. P. , Fattori P.
Published: April 2006

The aim of this work was to study the effect of eye position on the activity of neurons of area PO (V6), a cortical region located in the most posterior part of the superior parietal lobule. Experiments were carried out on three awake macaque monkeys. Animals sat in a primate chair in front of a large screen, and fixated a small spot of light projected in different screen locations while the activity of single neurons was extracellularly recorded. Both visual and non‐visual neurons were found. About 48% of visual and 32% of non‐visual neurons showed eye position‐related activity in total darkness, while in ˜61% of visual neurons the visual response was modulated by eye position in the orbit. Eye position fields and/or gain fields were different from cell to cell, going from large and quite planar fields up to peak‐shaped fields localized in more or less restricted regions of the animal's field of view. The spatial distribution of fixation point locations evoking peak activity in the eye position‐sensitive population did not show any evident laterality effect, or significant top/bottom asymmetry. Moreover, the cortical distribution of eye position‐sensitive neurons was quite uniform all over the cortical region studied, suggesting the absence of segregation for this property within area PO (V6). In the great majority of visual neurons, the receptive field‘moved’with gaze according to eye displacements, remaining at the same retinotopic coordinates, as is usual for visual neurons. In some cases, the receptive field did not move with gaze, remaining anchored to the same spatial location regardless of eye movements (‘real‐position cells'). A model is proposed suggesting how eye position‐sensitive visual neurons might build up real‐position cells in local networks within area PO (V6). The presence in area PO (V6) of real‐position cells together with a high percentage of eye position‐sensitive neurons, most of them visual in nature, suggests that this cortical area is engaged in the spatial encoding of extrapersonal visual space. Since lesions of the superior parietal lobule in humans produce deficits in visual localization of targets as well as in arm‐reaching for them, and taking into account that the monkey's area PO (V6) is reported to be connected with the premotor area 6, we suggest that area PO (V6) supplies the premotor cortex with the visuo‐spatial information required for the visual control of arm‐reaching movements.
The Coat Protein gp120 of HIV‐1 Inhibits Astrocyte Uptake of Excitatory Amino Acids via Macrophage Arachidonic Acid
Authors: Dreyer Evan B. , Lipton Stuart A.
Published: April 2006

The human immunodeficiency virus coat protein gp120 injures central mammalian neurons both in vitro and in vivo, and this observation may contribute, at least in part, to the neurological dysfunction associated with the acquired immunodeficiency syndrome. Recent work suggests that gp 120 mediates neuronal damage predominantly via an indirect route involving activation of brain macrophages. We have previously shown that the stimulation of N‐methyl‐D‐aspartate receptors by excitatory amino acids is essential for the neuronal injury observed with gp 120. Here we show that gp 120 impairs astrocyte uptake of excitatory amino acids and the excess glutamate thus engendered may contribute to the increased neuronal damage. We also studied the mechanism whereby gp 120 inhibits the uptake of excitatory amino acids by astrocytes. We present data suggesting that at least one pathway involves a direct effect of gp120 on macrophages, which in turn release arachidonic acid, a known inhibitor of excitatory amino acid uptake by astrocytes. Our findings suggest that the observed effects on glia and neurons of gp120 may be secondary, at least in part, to its initial activation of macrophages.
Alternative Splicing at the C‐terminal but not at the N‐terminal Domain of the NMDA Receptor NR1 is Altered in the Kindled Hippocampus
Authors: Vezzani Annamaria , Speciale Carmela , Vedova Franco Della , Tamburin Monica , Benatti Luca
Published: April 2006

Several lines of evidence suggest that N‐methyl‐D‐aspartate (NMDA) receptors significantly contribute to the development of kindling. In addition, a lasting enhancement of the NMDA receptor function has been suggested to play a significant role in the chronic hyperexcitability occurring in the hippocampus after kindling epileptogenesis. We have investigated whether hippocampal kindling induces changes in the NMDA receptor at the molecular level by assessing the expression of mRNAs of the different spliced variants at the N‐terminal (exon 5) and C‐terminal (exon 21) position of the NMDA receptor 1 (NR1) gene by means of the reverse transcription‐polymerase chain reaction. Alternative splicing at exon 5 confers different sensitivity of the NMDA receptor to polyamines while exon 21 encodes a 37‐amino acid insert containing the major phosphorylation sites for protein kinase C. One week after the acquisition of stage 5 of kindling in rats (generalized tonic‐clonic seizures), the relative abundance of the two alternatively spliced forms at the C‐terminal domain, respectively containing (+) or lacking (−) exon 21, was reversed compared to controls (implanted with electrodes but not stimulated) in the dorsal hippocampus ipsilateral and contralateral to the electrical stimulation. The exon 21+/exon 21− mRNA ratio for controls was 1.3 ± 0.04 (mean ± SE); for ipsilaterally kindled rats it was 0.64 ± 0.05 (P < 0.05), and for contralaterally kindled rats it was 0.48 ± 0.07 (P < 0.01). Similar bilateral effects were observed in the ventral hippocampus (temporal pole). No changes were found 4 weeks after stage 5 seizures and 1 week after the induction of a single afterdischarge. No significant alterations were induced by kindling in the relative abundance of the spliced variants containing or lacking exon 5. Our findings show selective changes in alternative splicing of the NR1 gene after repeated application of an epileptogenic stimulus. This may generate receptors with different functional properties, which may contribute to the increased sensitivity for the induction of generalized seizures during kindling.
Regional Hypometabolism in an Acute Model of Focal Epileptic Activity in the Rat
Authors: Brueh C. , Kloiber O. , Hossman K. A. , Dorn T. , Witte O. W.
Published: April 2006

Focal epileptic activity can be expected to influence distant brain areas via far reaching connections. To investigate such interactions the effects of focal epileptic activity on the metabolism of the brain were investigated in the rat cortex. Focal epileptic activity was induced by the application of penicillin onto the motor cortex. The focus, and to a lesser extent homotopic contralateral brain areas, showed an increase in the regional cerebral metabolic rate of glucose (rCMRGIc) as measured by [14C]deoxyglucose autoradiography. This focal hypermetabolism was accompanied by widespread hypometabolism lateral to the focus. The decrease of rCMRGIc occurred in somatosensory cortical areas but not in the motor cortex behind or in front of the focus, the perirhinal cortex or the occipital cortex. It was associated with an increase in metabolic rate in the ventrolateral, ventroposteromedial, ventroposterolateral and, in particular, posterior nuclei of the thalamus. It is hypothesized that the widespread reduction of rCMRGIc in the somatosensory cortical areas is due to inhibition via thalamic nuclei caused by activity in the motor cortex.
The NeurotroDhins BDNF, NT‐3 and NT‐4/5 Promote Survival and Morphological and Biochemical Differentiation of Striatal Neurons In Vitro
Authors: Ventimiglia Roseann , Mather Pamela E. , Jones Bruce Edward , Lindsay Ronald M.
Published: April 2006

The neurotrophins, brain‐derived neurotrophic factor (BDNF), neurotrophin‐3 (NT‐3), neurotrophin 4/5 (NT‐4/5) and nerve growth factor (NGF), were compared for their effects on the survival and differentiation of embryonic rat striatal neurons grown in low‐density cultures. Treatment with BDNF for 8 days resulted in a 40% increase in overall neuronal survival, a 3‐ to 5‐fold increase in the number of calbindin‐immunoreactive neurons, and an 80% increase in GABA‐positive neurons. Treatment with NT‐3 or NT‐4/5 produced a 2‐ to 3‐fold increase in the number of calbindin‐positive neurons and an increase in GABA‐positive cell number similar to that induced by BDNF. BDNF treatment produced a striking morphological differentiation of striatal GABAergic neurons, which was characterized by a doubling of the number of neurite branch points, the total area of arborization and the perikaryal area compared to control cultures. All three of these factors increased high‐affinity GABA uptake 2‐fold. NGF had no effect on any of the parameters examined. Our results show that BDNF, NT‐3 and NT‐4/5 promote the survival and/or differentiation of calbindin‐immunopositive and GABAergic striatal neurons.
Comparison of the Effects of the Neurotrophins on the Morphological Structure of Dopaminergic Neurons in Cultures of Rat Substantia Nigra
Authors: Studer Lorenz , Spenger Christian , Seiler Rolf W. , Altar C. Anthony , Lindsay Ronald M. , Hyman Carolyn
Published: April 2006

The effect of the various neurotrophin family members on the morphological structure of dopaminergic neurons was compared in dissociated cultures of embryonic rat ventral mesencephalon. Cultures were maintained in vitro in the presence of brain‐derived neurotrophic factor (BDNF), neurotrophin‐3 (NT‐3), neurotrophin‐4/5 (NT‐4/5), nerve growth factor (NGF) or no added growth factors. Three‐dimensional reconstructions of 48 neurons were made in each of the experimental groups following immunocytochemical staining for tyrosine hydroxylase to detect dopaminergic neurons. In addition [3H]mazindol binding analyses were carried out in replicate cultures in order to quantify the effects of the neurotrophins on the number of dopamine uptake sites. Among the neurotrophins tested, NT‐4/5 influenced the proximal morphological parameters most, as determined by a 36% increase in the soma profile area and 35% in the number of stem neurites. Analysis of neuritic size and complexity in these cultures revealed that combined neuritic length and number of segments/cell were increased by 45 and 40% respectively. A change in neurite complexity in the NT‐4/5 treated cultures was further confirmed using Scholl's concentric sphere analysis. In addition, relative to the control, NT‐4/5 increased the neuronal differentiation as evidenced by increases in varicosity density and [3H]mazindol binding by 114 and 101% respectively. BDNF and, to a lesser extent, NT‐3 also increased both proximal parameters and parameters of differentiation, but were without effect on parameters of neuritic size and Complexity. No effects on neuronal structure were observed in NGF treated cultures. These findings demonstrate that BDNF, NT‐3 and NT‐4/5 influence the morphological differentiation of dopaminergic neurons in vitro, suggesting they may play a role in the structural development and plasticity of these neurons in the mesencephalon.
Synergistic Differentiation by Chronic Exposure to Cyclic AMP and Nerve Growth Factor Renders Rat Phaeochromocytoma PC12 Cells Totally Dependent upon Trophic Support for Survival
Authors: Michel Patrick P. , Vyas Sheela , Agid Yves
Published: April 2006

Chronic dibutyryl cAMP (dbcAMP) treatment was observed not only to potentiate the differentiating actions of nerve growth factor (NGF) in PC12 cells, but to render them completely dependent on trophic support for survival even in the presence of serum proteins. When both NGF and dbcAMP were withdrawn from doubly differentiated PC12 cultures, degenerative events occurred after a lag period of 12–18 h, and by 48 h ≤ 5–10% of the cells remained viable. Reduction in [3H]dopamine uptake, an index of cell function and neurite integrity, paralleled cell demise. At the cellular level, ∼20–30% of the nuclei exhibited clear signs of chromatin fragmentation, as characterized by propidium iodide staining, suggesting that degeneration occurred by apoptosis. The cells could be rescued completely from degeneration by dbcAMP or by other cAMP analogues, whereas NGF and depolarization were also effective, but only partially. Phorbol 12‐myristate‐13‐acetate failed to afford protection. If deprivation was interrupted, cell demise could be stopped by restoration of initial culture conditions. Degenerative changes produced by deprivation and recovery processes were not inhibited by macromolecular synthesis inhibitors, e.g. cycloheximide and actinomycin‐D. However, chronic addition of cycloheximide prior to deprivation greatly impaired the differentiation of NGF/dbcAMP cells, allowing these cells to withstand trophic support withdrawal. Altogether our results indicate that the cAMP transduction pathway plays a crucial role not only in the differentiation but also in the survival of NGF/dbcAMP PC12 cells.
Accelerated Structural Maturation Induced by Synapsin I at Developing Neuromuscular Synapses of Xenopus laevis
Authors: Valtorta Flavia , Lezzi Numa , Benfenati Fabio , Lu Bai , Poo Mu‐ming , Greengard Paul
Published: April 2006

The role of synapsin I, a synaptic vesicle‐associated phosphoprotein, in the maturation of nerve–muscle synapses was investigated in nerve–muscle co‐cultures prepared from Xenopus embryos loaded with the protein by the early blastomere injection method. The stage of maturation of the synapses was analysed by electron microscopy as well as by whole‐cell patch‐clamp recording. The acceleration in the functional maturation of neuromuscular synapses induced by synapsin I was accompanied by a profound rearrangement in the ultrastructure of the nerve terminal. Nerve terminals formed by synapsin I‐loaded neurons were characterized by a higher number of small synaptic vesicles organized in clusters and predominantly localized close to the nerve terminal plasma membrane, a smaller number of large dense‐core vesicles and no significant change in the number of coated vesicles. Precocious development of active zone‐like structures as well as deposition of basal lamina into the synaptic cleft were also observed at these synapses. These results support a role for synapsin I in the architectural changes which occur during synaptogenesis and lead to the maturation of quantal neurotransmitter release mechanisms.
Kainic Acid‐induced Heat Shock Protein‐70, mRNA and Protein Expression is Inhibited by MK‐801 in Certain Rat Brain Regions
Authors: Planas Anna M. , Soriano Marc A. , Ferrer Isidre , Farré Eduard Rodríguez
Published: April 2006

The regional expression of inducible 72 kDa heat shock protein (HSP‐70), HSP‐70 mRNA and the neuropathological outcome of their expression were examined in the rat brain following systemic administration of kainic acid (9 mg/kg), and also after pretreatment with the non‐competitive N‐methyl‐D‐aspartate antagonist MK‐801 (1 mg/kg). Five hours after administration of kainic acid alone, dense expression of HSP‐70 mRNA was found within the limbic system, mainly in the hippocampus, piriform and entorhinal cortices, amygdaloid complex, thalamic nuclei, subiculum and in other cortical areas in rats that had shown convulsive behaviour. At 24 h, HSP‐70 immunoreactivity was seen in most areas previously expressing HSP‐70 mRNA, except the piriform and entorhinal cortices and several ventral nuclei of the amygdaloid complex. Histopathological examination at 24 h revealed marked cell loss in these latter regions and less severe histopathological changes in other areas of the limbic system in brains of convulsive rats. No alterations were apparent in non‐convulsive rats. The percentage of rats showing convulsive behaviour with kainic acid was reduced from 74 to 4% following pretreatment with MK‐801. In addition, MK‐801 inhibited the kainic acid‐induced expression of HSP‐70 mRNA and protein in certain brain regions, notably the cortex, the pyramidal cell layer of CA1, and discrete thalamic nuclei. However, HSP‐70 mRNA induction was sustained in the pyramidal cell layer of CA3, the amygdaloid complex and the subiculum, despite the fact that none of these rats convulsed. MK‐801 prevented necrosis in all rats examined except the single rat that had shown convulsive behaviour. These results show that early regional expression of inducible HSP‐70 mRNA allows the visualization of regions affected by kainic acid and maps regions inhibited by MK‐801. In addition, the results identify brain regions putatively involved in the manifestation of limbic convulsions. Furthermore, these data illustrate that the induction of HSP‐70 mRNA is not predictive of cell death or survival.
Evidence for Glutamate as Neurotransmitter in Trigemino‐ and Spinothalamic Tract Terminals in the Nucleus Submedius of Cats
Authors: Ericson Ann‐Charlott , Blomqvist Anders , (Bud) Craig A. D. , Ottersen Ole P. , Broman Jonas
Published: April 2006

The nucleus submedius in the medial thalamus of cats is an important termination site for lamina I trigemino‐ and spinothalamic tract (TSTT) neurons, many of which are nociceptive‐specific, and the nucleus submedius has been proposed to be a dedicated nociceptive substrate involved in the affective aspect of pain. In the present study, the distribution of glutamate was examined by immunocytochemical methods in order to evaluate the possible role of this amino acid as a neurotransmitter in TSTT terminals in the nucleus submedius. TSTT terminals were identified by anterograde transport of horseradish peroxidase and wheatgerm agglutinin‐horseradish peroxidase conjugate from the spinal cord or the medullary dorsal horn. Quantitative analysis of immunogold labelling revealed that TSTT terminals contain about twice the tissue average of glutamate‐like immunoreactivity. A strong positive correlation was found between the density of synaptic vesicles and the density of gold particles in these terminals, whereas no relationship was seen between these variables in GABAergic presynaptic dendrites. Enrichment of glutamate‐like immunoreactivity (∼250% of the tissue average) was also observed in terminals of presumed cortical origin. Presynaptic dendrites and neuron cell bodies in the nucleus submedius were found to contain relatively low levels of glutamate‐like immunoreactivity, at or below the tissue average. These observations provide evidence that glutamate is a neurotransmitter in lamina I TSTT terminals in the nucleus submedius. The findings also suggest glutamatergic neurotransmission between cortical afferents and nucleus submedius neurons. Glutamate is therefore likely to be an important mediator of nociceptive processing in the medial thalamus.
The Stimulation of Thalamic Neurite Outgrowth by Cortex‐derived Growth Factors In Vitro: The Influence of Cortical Age and Activity
Authors: Lotto R. Beau , Price David J.
Published: April 2006

Recent in vitro experiments have provided useful insights into the development of connections between the thalamus and the cortex. While most of these previous studies focused on neurite guidance and target recognition, our experiments used a serum‐free culture system to examine the possible roles of unidentified diffusible cortex‐derived growth factors. We demonstrated that occipital cortical explants release diffusible growth factors that enhance neurite outgrowth from explants of the posterior thalamus (the region around the developing lateral geniculate nucleus). The amount of thalamic outgrowth was dependent on the age of the cocultured cortical slices. Our results suggest that there is an overall increase in the release of cortex‐derived growth factors during the first three postnatal weeks in mice; this parallels known postnatal increases in the production of several identified growth factors. We found evidence for two peaks in the release of cortex‐derived growth factors during the general upward trend, the first at around postnatal day 6 (shortly after thalamocortical innervation of layer 4) and a second between postnatal days 14 and 18 (just after eye‐opening). The increased release of cortex‐derived growth factors was not found when cortical slices were from mice that had been dark‐reared from birth, suggesting that neural activity may be important for enhancing release. Other regions of the central nervous system, including the cerebellum and medulla, were also capable of stimulating some thalamic outgrowth; neither additional explants of the thalamus nor hepatic explants enhanced outgrowth. Fibroblast growth factor is one substance that is distributed preferentially among those tissues that were stimulatory in our experiments. Its level of transcription is known to increase in the brain during the first three postnatal weeks and to be influenced by neural activity. At low doses, fibroblast growth factor greatly increased outgrowth from isolated posterior thalamic explants. Nerve growth factor, another candidate molecule, was less effective. Overall, our results complement the in vivo observations of others on the synthesis of identified growth factors in the cortex and the factors that influence their production. They suggest that growth factors may influence thalamic neurons, and indicate that fibroblast growth factor, and possibly nerve growth factor, are two candidates for molecules mediating the in vitro effects.
Selective Lesioning of the Basal Forebrain Cholinergic System by Intraventricular 192 IgG–saporin: Behavioural, Biochemical and Stereological Studies in the Rat
Authors: Leanza G. , Nilsson O. G. , Wiley R. G. , Björklund A.
Published: April 2006

The elucidation of the functional role of the basal forebrain cholinergic system will require access to a highly specific and efficient cholinergic neurotoxin. Recently, selective depletion of the nerve growth factor (NGF) receptor‐bearing cholinergic neurons in the rat basal forebrain and a dramatic loss of cholinergic innervation in the related cortical regions have been obtained following intraventricular injection of a newly introduced immunotoxin, 192 IgG‐saporin. Here we extend these initial findings and report that administration of increasing doses (1.25, 2.5, 5.0 or 10 μg) of the 192 IgG‐saporin conjugate into the lateral ventricles of adult rats induced dose‐dependent impairments in the water maze task and passive avoidance retention, but only weak and inconsistent effects on locomotor activity. These behavioural changes were paralleled by a reduction in choline acetyltransferase activity in hippocampus and several cortical areas (up to 97%) and selective depletions of NGF receptor‐positive cholinergic neurons in the septal‐diagonal band area and nucleus basalis magnocellularis (up to 99%). By contrast, the non‐cholinergic parvalbumin‐containing neurons in the septum were completely spared, and other cholinergic projection systems (such as in the striatum, thalamus, brainstem and spinal cord) were unaffected even at the highest dose. The observed changes in the water maze and passive avoidance tasks, as well as the cholinergic cell loss, were maintained up to at least 8 months following the intraventricular injection of a single dose (5 μg) of the immunotoxin. The results confirm the usefulness of the 192 IgG‐saporin toxin for selective and profound lesions of the basal forebrain cholinergic neurons and provide further support for a role of the basal forebrain cholinergic system in cognitive functions.
Neutralizing Anti‐p21ras Fabs Suppress Rat Sympathetic Neuron Survival Induced by NGF, LIF, CNTF and cAMP
Authors: Nobes Catherine D. , Tolkovsky Aviva M.
Published: April 2006

In purified cultures of newly isolated rat sympathetic neurons plated on laminin, apoptosis is suppressed by the cytokines leukaemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF), by the permeant cAMP analogue 8‐(4‐chlorophenylthio)cAMP, and by nerve growth factor. Whilst nerve growth factor, 8‐(4‐chlorophenylthio) cAMP and LIF/CNTF initiate survival by using different kinases, in each case survival is inhibited by a Fab fragment of Y13‐259, a neutralizing antibody to p2lras proteins, but not by rat IgG Fab. The inhibitory effect of Y13‐259 could be partially attenuated by cotrituration of the Fab with T′24(inactive)ras. Thus, prevention of apoptosis in rat sympathetic neurons by several different survival factors appears to be critically dependent on p21 ras protein activity.
Divalent Cation Entry in Cultured Rat Cerebellar Granule Cells Measured Using Mn2+ Quench of Fura 2 Fluorescence
Authors: Simpson P. B. , Challiss R. A. J. , Nahorski S. R.
Published: April 2006

In this study the rate of Mn2+ quench of fura‐2 fluorescence evoked by glutamatergic and cholinergic agonists, depolarization and Ca2+ store modulators was measured in cultured cerebellar granule cells, in order to study their effects on Ca2+ entry in isolation from effects on Ca2+ store release. The rate of fluorescence quench by 0.1 mM Mn2+ was markedly increased by 25 mM K+‐ evoked depolarization or by 200 μM N‐methyl‐D‐aspartate (NMDA), with a significantly greater increase occurring during the rapid‐onset peak phase compared to the plateau phase of the K+‐ or NMDA‐evoked [Ca2+]i response. The stimulatory effect of NMDA on Mn2+ quench was abolished by dizocilpine (10 μM), but nitrendipine (2 μM), while decreasing the rate of basal quench, did not affect NMDA‐stimulated Mn2+ entry. This suggests that nitrendipine may not act on NMDA channels in granule cells, at least under these conditions, and that voltage‐operated Ca2+ channels are involved in control quench whereas the NMDA‐evoked quench is dependent on entry through the receptor channel. The t1/2 of quench was unaffected by α‐amino‐hydroxyisoxazole propionic acid (200 μM) and carbamyl choline (1 mM). Neither thapsigargin (10 μM) nor dantrolene (30 μM) significantly affected the rate of quench under control or NMDA‐ or K+‐stimulated conditions, which confirms that the previously reported inhibitory effects on [Ca2+]i elevations evoked by these agents are due to actions on Ca2+ stores. However, thapsigargin elevated [Ca2+Ii in the presence of normal [Ca2+]i, but not in nominally Ca2+‐free medium, indicating that it evokes Ca2+ entry in cerebellar granule cells, probably subsequent to store depletion, which appears to be either too small to be detected by Mn2+ quench or to occur via Mn2+‐impermeant channels.
Induction of MMP9 (92 kDa Gelatinase) Activity and Expression of Tissue In hibitor of Metalloproteinase‐2 mRNA (TIMP‐2) in Primitive Neuroectodermal Cells Infected with Retrovirus HTLV‐I
Authors: Giraudon P. , Thomasset N. , Bernard A. , Verrier B. , Belin M. F.
Published: April 2006

Matrix‐degrading proteases, including metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs), are involved in modulation of the extracellular matrix, which participates in neural cell differentiation, brain morphogenesis and tissue integrity. Metalloproteinases and TlMPs are associated with inflammatory and degenerative processes in the central nervous system and are regulated by cytokines. Human retroviral infections are frequently associated with neurological disturbances. In the present paper, we have studied the changes occurring in human primitive neuroectodermal cells following infection with human T cell lymphotropic virus type 1 (HTLV‐I), a retrovirus responsible for HTLV‐I‐associated myelopathy. Infected neural cells were found to have high metalloproteinase 9 (MMP9–92 kDa gelatinase) activity. MMP9 induction is dependent on HTLV‐I infection of neural cells. In addition, soluble factors, especially tumour necrosis factor α, secreted by infected cells, act as mediators of induction. HTLV‐I infection also induces expression of RNA coding for tissue inhibitor of metalloproteinase 2. These observations indicate that HTLV‐I infection selectively modulates the expression of molecules involved in the dynamic equilibrium between the synthesis and degradation of the neural cell matrix and leads to its remodelling, which modifies cell‐cell interactions and cellular function.
Physiological Characterization of Pretectal Neurons Projecting to the Lateral Posterior‐Pulvinar Complex in the Cat
Authors: Sudkamp S. , Schmidt M.
Published: April 2006

Pretectal neurons projecting to the lateral posterior‐pulvinar complex (LP‐P) in cats were electrophysiologically identified by their antidromic activation from the LP‐P. Their responses to various visual stimuli and to electrical stimulation of the optic chiasm and the lateral geniculate nucleus (LGN) were characterized. In retrograde double‐labelling experiments, the pretectal projections to the LP‐P and to the LGN were tested for possible overlap. Forty‐five neurons were antidromically activated from the LP‐P; 55 % of them could also be activated orthodromically from the optic chiasm. Most antidromically activated neurons responded to rapid movements of large textured visual stimuli as well as to ‘on’ or ‘off’ visual stimulation with short bursts. When stimulated with a slowly moving, large, structured visual stimulus, most cells showed a slight but significant activity increase. None of the neurons projecting to the LP‐P was also activated antidromically from the LGN. Thus, the two populations are separate. This is supported by the results from the retrograde double‐labelling experiments. None of the LP‐P projecting neurons showed any directional selectivity to slow movements of large visual stimuli, a property by which pretectal neurons projecting to the inferior olive are characterized. Thus, neurons projecting to the LP‐P do not bifurcate to the inferior olive. Response properties of neurons projecting to the LP‐P were very similar to those of the ‘jerk’ neurons described by Schweigart and Hoffmann (Exp. Brain Res., 91, 273–283, 1992); therefore we believe them to be identical. Jerk neurons are known to react not only to rapid image shifts with short high‐frequency bursts, but also to saccadic eye movements in the light. As a possible function of LP‐P projecting neurons, the transfer of information about image displacement during saccades or fast‐moving objects in the visual scene is discussed.