bluuebunny/crossref_metadata_2025 huggingface dataset:
Axonal Sprouting of CA1 Pyramidal Cells in Hyperexcitable Hippocampal Slices of Kainate‐treated Rats
Authors: Perez Yaël , Morin France , Beaulieu Clermont , Lacaille Jean‐Claude
Published: April 2006

CA1 pyramidal cells become hyperexcitable following hippocampal kainate lesions. To examine if axonal sprouting contributes to this epileptiform activity, the local axonal arborization of CA1 pyramidal cells was examined after intracellular labelling with biocytin in hippocampal slices from control rats and in hyperexcitable slices obtained from rats treated with kainate (bilateral intracerebroventricular injections) 2‐4 weeks previously. Biocytin‐labelled cells with an axon that could be followed from the soma to the alveus were drawn and reconstructed with a camera lucida (15 cells from control slices and 14 cells from hyperexcitable slices). Local axonal arborizations were more extensive in cells of hyperexcitable slices. This increase in axon collaterals was generally seen in the alveus and in stratum oriens, but changes were more prominent in the latter. In stratum oriens, cells from hyperexcitable slices showed a significant increase in mean total axon length (1035 versus 373 μm in control), in mean number of branching points (6.50 versus 0.67 in control) and in mean number of segment orders per axon (3.07 versus 1.47 in control). Their first‐order axon segments were similar in length to those of control cells (236 versus 338 pm in control), but with significantly more branching points (2.86 versus 0.53 in control). Their second‐order axon segments were significantly longer (381 versus 63 μm in control) and also showed more branching points (2.71 versus 0.13 in control). Their third‐ and fourth‐order axon segments were also longer and with more branching points. Under high‐power light microscopic examination, biocytin‐labelled axonal varicosities in cells of hyperexcitable slices were often seen in close apposition with their own dendrites, presumably making synaptic contact (five of nine cells examined). No such appositions were seen in any of the control cells (seven cells examined). These results indicate that, following kainate lesions, there is sprouting of local axon collaterals of CA1 pyramidal cells in stratum oriens and in the alveus. This local increase in axon collaterals may contribute to the epileptiform activity in the CA1 area by providing recurrent excitation via newly formed synaptic, and perhaps even autaptic, contacts with pyramidal cell dendrites.
Regional Distribution of the Anticonvulsant and Behavioural Effects of Muscimol Injected into the Substantia Nigra of Rats
Authors: Shehab Safa , Simkins Marion , Dean Paul , Redgrave Peter
Published: April 2006

Previous anatomical investigations have reported a direct projection from substantia nigra pars lateralis to the dorsal midbrain anticonvulsant zone. The present study tested the hypothesis that the anticonvulsant properties of nigral inhibition previously attributed to substantia nigra pars reticulata were, in fact, due to the suppression of neural activity in the adjacent pars lateralis. Using the electroshock model of epilepsy, a systematic map of the anticonvulsant effects of bilateral injections of muscimol (60 ng/0.5 μI per side) into different parts of substantia nigra was constructed. Electroshock (1 s of 40 mA 50 Hz AC) was administered via ear‐clip electrodes 5 or 60 min following injections of muscimol, or 60 min after control injections of saline. To provide insight into the functional mechanisms whereby nigral inhibition might suppress tonic seizures the behavioural effects elicited by muscimol were also noted. No evidence supporting the experimental prediction was found. The most sensitive region of substantia nigra for suppressing tonic hindlimb extension was caudal pars reticulata. These data indicate a serious mismatch between the results of microinjection mapping studies and underlying patterns of anatomical connectivity. The behavioural reaction most closely associated with tonic seizure suppression was stereotyped locomotion; both were obtained maximally from caudal pars reticulata. Rostral substantia nigra was associated more with oral stereotypy, while a raised head position was observed at lateral injection sites and a lowered positioning of the head at medial locations. These data suggest that the rat substantia nigra may contain a functional organization based on a form of somatomotor topography. This organization may influence which part of the substantia nigra is most effective in suppressing seizures expressed by different muscle groups of the body.
Distinct Effects of Recombinant Tenascin‐R Domains in Neuronal Cell Functions and Identification of the Domain Interacting with the Neuronal Recognition Molecule F3/11
Authors: Xiao Zhi‐cheng , Taylor Joanne , Montag Dirk , Rougon Geneviève , Schachner Melitta
Published: April 2006

We have identified distinct domains of the rat extracellular matrix glycoprotein tenascin‐R using recombinant fragments of the molecule that confer neuronal cell functions. In short‐term adhesion assays (0.5 h), cerebellar neurons adhered best to the fragment representing the fibrinogen knob (FG), but also the fibronectin type Ill (FN) repeats 1‐2 and 6‐8. FG, FN1‐2 and FN3‐5 were the most repellent fragments for neuronal cell bodies. Neurites and growth cones were strongly repelled from areas coated with fragments containing the cysteine‐rich stretch and the EGF‐like domains (EGF‐L), FN1‐2, FN3‐5 and FG. Polarization of morphology of hippocampal neurons was exclusively associated with FG, while EGF‐L prevented neurite outgrowth altogether. The binding site of the neuronal receptor for tenascin‐R, the immunoglobulin superfamily adhesion molecule F3/11, was localized to EGF‐L. The combined observations show distinct, but also overlapping functions for the different tenascin‐R domains. They further suggest the existence of multiple neuronal tenascin‐R receptors which influence the response of neurons to their extracellular matrix environment.
Novelty‐related Rapid Locomotor Effects of Corticosterone in Rats
Authors: Sandi Carmen , Venero César , Guaza Carmen
Published: April 2006

Glucocorticoids modulate brain function and behaviour through different mechanisms. Although classical effects are mediated through intracellular receptors that modulate gene transcription, recent evidence supports the existence of rapid, nongenomic steroid effects through the neuronal membrane. In this study, we explored possible rapid behavioural effects of corticosterone in the rat, which could provide a model to characterize further the mechanisms involved in rapid corticosteroid nongenomic actions. We found that a corticosterone injection, at doses (2.5 or 5 mg/kg) that mimic plasma concentrations produced by substantial stress, rapidly increases (within 7.5 min of its systemic administration) the locomotor response displayed by rats in a novel environment (activity cage). A lower dose of 1 mg/kg failed to induce this effect. In addition, corticosterone failed to increase locomotion when administered to rats that had been previously exposed to the activity cage. Corticosterone‐induced increased locomotion in a novelty situation was not counteracted by either the intracerebroventricular administration of the protein synthesis inhibitor cycloheximide, or by the intracerebroventricular administration of specific antagonists for each type of intracellular corticosteroid receptor, i.e. RU28318, a mineralocorticoid receptor antagonist and RU38486, a glucocorticoid receptor antagonist. Further studies supported the viability of the receptor antagonists to display an anti‐corticosteroid action interfering, as previously reported, with the behavioural swimming test. Therefore, the rapid actions of corticosterone in locomotor activity described here, which appear to be nongenomic, might provide a model for future research on the elucidation of the mechanisms involved in steroid‐membrane interactions.
Evidence for Modulation of DoDamine‐neuronal Function by Tachykinin NK3 Receptor Stimulation in Gerbil Mesencephalic Cell Cultures
Authors: Alonso R. , Fournier M. , Carayon P. , Petitpretre G. , Le Fur G. , Soubrié P.
Published: April 2006

Primary cultures of gerbil mesencephalon were used for studying the modulation exerted by tachykinin NK3 receptor activation on the activity of dopamine (DA) neurons. Dopamine neurons were identified by their ability to take up [3H]DA in a nomifensine‐dependent manner. Moreover, tyrosine hydroxylase immunohistochemistry revealed that these neurons accounted for 5–7% of the total cell population. The NK3 receptor agonists, senktide (EC50= 0.58 nM) and [MePhe7]neurokinin B (EC50= 3 nM), increased spontaneous [3H]DA release in a concentration‐dependent manner. In contrast, tested at a supramaximal concentration (10‐7 M), neither septide nor substance P were found to affect [3H]DA release. The senktide‐evoked [3H]DA release was not observed when extracellular Ca2+ was chelated, but was unaffected by nomifensine. This indicates that this increase in [3H]DA outflow resulted more from an exocytotic process than from reversal of carrier‐mediated DA uptake. Moreover, the senktide effect was unaffected by the Na+ channel blocker tetrodotoxin, a result suggesting a direct action of senktide on DA neurons. The non‐peptide NK3 receptor antagonist, SR 142801, shifted or blocked (ICs0 = 0.89 nM) the senktide‐evoked [3H]DA release, while its (‐)‐antipode, SR 142806, was 80‐fold less potent, in agreement with binding data. Selective antagonists for NK, (SR 140333) or NK2 (SR 48968) receptors failed to reduce the senktide effect. Light scanning microscopic analysis of mesencephalic cells loaded with the Ca2+ sensitive dye, fluo‐3, showed that senktide induced a rise in cytosolic Ca2+ in 8‐10% of the cell population. The senktide‐induced elevation in intracellular Ca2+ was rapid in onset and transient (at lo4 M) or more sustained with no further increase in fluorescence intensity (at 10‐7 M). The proportion of senktide‐responsive cells was not significantly modified when extracellular Ca2+ was chelated, but was reduced by 87% in the presence of SR 142801 and by 75% in cultures that were pre‐treated with the DA neurotoxin l‐methyl‐4‐phenylpyridinium. The present study shows that enhancement of spontaneous [3H]DA release and intracellular Ca2+ mobilization may be observed after NK3 receptor stimulation and that both biochemical events are likely to occur in DA neurons.
Changes in Synaptic Excitability in the Lateral Septum Associated with Contextual and Auditory Fear Conditioning in Mice
Authors: Garcia René , Jaffard Robert
Published: April 2006

Synaptic excitability in the lateral septum (LS) was assessed electrophysiologically in freely moving mice either submitted to a painful stimulus (shock) or tested on two forms of conditioned fear: contextual conditioning and auditory cue conditioning. Only the amplitude of the N3 component of the two negative waves (N2 and N3) evoked by fimbrial stimulation displayed significant changes in these tests. Experiment 1 showed that both the painful stimulus and subsequent re‐exposure (24 h later) to the conditioning foreground context induced significant and context specific decrease in the N3 amplitude. In Experiment 2, a phasic tone (conditioned stimulus: CS) was paired (paired group) with the footshock (unconditioned stimulus: US) or not (unpaired group) and, 24 h later, animals were re‐exposed successively to the auditory cue and to the context. During the auditory cue test, only the paired group displayed significant freezing and this occurred only during presentation of the CS. In this group, however, a significant reduction in the N3 amplitude was only observed immediately after the cessation of the CS. During the context test, the percentage and time‐course of freezing across the 10 min session were similar in each group. However, in the unpaired group the N3 amplitude reduction was significant and outlasted the duration of the freezing behaviour itself. These results show that alterations in LS synaptic excitability may be dissociated from fear‐induced freezing behaviour. We suggest that LS synapses are part of a brain circuit that predict if and when the US is going to occur.
Regulation of Motoneuronal Calcitonin Gene–related Peptide (CGRP) During Axonal Growth and Neuromuscular Synaptic Plasticity Induced by Botulinum Toxin in Rats
Authors: Tarabal Olga , Calderó Jordi , Ribera Joan , Sorribas Albert , López Ricard , Molgó Jordi , Esquerda Josep E.
Published: April 2006

The aim of this study was to examine whether changes in rat motoneuronal calcitonin gene–related peptide (CGRP) can be correlated with axonal growth and plasticity of neuromuscular synapses. Nerve terminal outgrowth was induced by local paralysis with botulinum toxin. Normal adult soleus and tibialis anterior did not show detectable CGRP content at the motor endplates. Following botulinum toxin injection there was a progressive, transient and bimodal increase in CGRP in both motoneuron cell bodies which innervated poisoned muscles and their motor endplates. CGRP content was moderately increased 1 day after paralysis and, after an initial decline, reached a peak 20 days after injection. This was followed by a gradual decrease and a return to normal levels at the 200th day. CGRP changes in intoxicated endplates were less evident in the tibialis anterior than in the soleus muscle. The CGRP content in motoneurons was positively correlated with the degree of intramuscular nerve sprouting found by silver staining. In situ hybridization revealed an increase in CGRP mRNA in spinal cord motoneurons 20 days after toxin administration. We conclude that motoneurons regulate their CGRP in situations in which peripheral synapse remodelling and plasticity occur.
Involvement of the NMDA Receptor in a Non–cholinergic Action of Acetylcholinesterase in Guinea–pig Substantia Nigra Pars Compacta Neurons
Authors: Webb C. P. , Nedergaard S. , Giles K. , Greenfield S. A.
Published: April 2006

Evidence is accumulating that a soluble, secretory form of acetylcholinesterase may have novel, non–cholinergic functions in certain brain regions, such as the substantia nigra. In this study, application of human recombinant acetylcholinesterase (rhAChE) to pars compacta neurons in the rostral substantia nigra resulted in a sustained hyperpolarization that was not only mimicked by application of N‐methyl–D–aSpartate (NMDA) but also blocked by the NMDA receptor antagonists MK801 and 2–amino–5phosphonopentanoic acid. Neither the rhAChE–nor the NMDA–induced hyperpolarization was seen when the calcium chelator BAPTA was injected into the neuron; hence the effect is mediated by accumulation of intracellular calcium. This intracellular calcium appears sufficient to compromise neuronal metabolism since the rhAChE–induced hyperpolarization was reversed by application of the K–ATP channel antagonist tolbutamide. Butyrylcholinesterase, a protein of similar molecular weight to acetylcholinesterase, which also hydrolyses acetylcholine, had no effect whatsoever. The results suggest that, independent of its normal catalytic function, acetylcholinesterase can act via the NMDA receptor complex to enhance calcium entry into nigral neurons and jeopardize cell metabolism. This non–classical action of acetylcholinesterase might thus be an important factor in the mechanisms underlying parkinsonian neurodegeneration.
Transience of Astrocytes In the Newborn Macaque Monkey Retina
Authors: Distler C. , Kirby M.A.
Published: April 2006

We investigated the morphology and spatial distribution of retinal astrocytes in newborn and early postnatal macaque monkeys. As in adults, retinal astrocytes in neonatal animals were closely associated with ganglion cell axons and blood vessels. However, in contrast with adults, astrocytes transiently occupied the fovea and perifoveal region in newborns and, to a lesser degree, also in early postnatal animals. The density of the perifoveal astrocytes rapidly declined during the first 2‐3 months of life. The results are discussed in relationship to foveal development.
Immunocytochemical Visualization of the mG1uR1 a Metabotropic Glutamate Receptor at Synapses of Corticothalamic Terminals Originating from Area 17 of the Rat
Authors: Vidnyánszky Zoltán , Görcs Tamás J. , Négyessy László , Borostyánköi Zsolt , Kuhn Rainer , Knöpfel Thomas , Hámori József
Published: April 2006

Pre‐embedding immunogold histochemistry was combined with Phaseolus vulgaris leucoagglutinin anterograde tract tracing in order to analyse the relationship between the subcellular localization of the mGluR1a metabotropic glutamate receptors and the distribution of corticothalamic synapses in the dorsal lateral geniculate nucleus (dLGN) and the lateral posterior nucleus (LP) of the rat. The injection of the tracer into area 17 labelled two types of corticothalamic terminals: (i) the small boutons constituting the majority of the labelled fibres which form asymmetrical synapses both in the dLGN and LP; and (ii) the giant terminals typically participating in glomerulus‐like synaptic arrangements and found exclusively in the lateral posterior nucleus. The small corticothalamic terminals often established synapses with mGluR1a‐immunopositive dendrites, with immunometal particles concentrated at the periphery of their postsynaptic membranes. In contrast, the synapses formed by giant boutons in the lateral posterior nucleus were always mGluR1a‐immunonegative. We conclude that the corticothalamic fibres forming the small synaptic terminals are the most likely candidates for the postulated mGluR‐mediated modulation of visual information flow by corticothalamic feedback mechanisms.
A Cholecystokinin‐B Receptor Antagonist Potentiates GABAergic and Glycinergic Inhibition in the Nucleus of the Solitary Tract of the Rat
Authors: McLean H. A. , Champagnat J. , Denavit‐Saubié M.
Published: April 2006

In both rodent and primate in vivo models, cholecystokininB (CCKB) antagonists such as PD134,308 have anxiolytic effects that may involve the potentiation of GABAergic transmission. We have investigated this interaction using exogenous application of GABA and whole cell patch recording techniques in neurons of the nucleus of the solitary tract (NTS) in brainstem slice preparations. In the presence of PD134, 308 the magnitude of the GABA‐evoked decrease in membrane input resistance was enhanced by 41.2 ± 3.1% and the duration of the response was prolonged by 34.8 ± 2.2%. Also, PD134, 308 potentiated glycine‐evoked decreases in membrane input resistance, increasing the amplitude of the response by 62.8 ± 4.8% and prolonging the duration of the response by 23.5 ± 3.6%. The effect of PD134, 308 persisted in the presence of tetrodotoxin, after reversal of the transmembrane gradient to chloride ions and under conditions of exaggerated GABAA receptor desensitization. Our results demonstrate that at least part of the functional link between PD134,308 and the GABAA response occurs postsynaptically.
Synergistic Neurite‐outgrowth Promoting Activity of Two Related Axonal Proteins, Bravo/Nr‐CAM and G4/Ng‐CAM in Chicken Retinal Explants
Authors: Morales Gracia , Sánhez‐Puelles Jose Maria , Schwarz Uli , de la Rosa Enrique J.
Published: April 2006

In the developing chicken retina, optic fibres migrating to the tectum express on their surfaces several cell adhesion molecules, including Bravo/Nr‐CAM and G4/Ng‐CAM. We have previously described differential distribution along the retinotectal projection and differential modulation by environmental cues for Bravo and G4 and here we further compare the characteristics of these immunoglobulin superfamily molecules. From day 6 of embryonic development (E6) to day 20 (E20), Bravo and G4 were found to coexist in the retinal optic fibre layer. However, while G4 staining was confined to that layer, as development proceeded Bravo staining spread to the plexiform layers and some radial structures of the retina. G4 displayed a dose‐dependent neurite‐outgrowth promoting activity for E6 retinal explants, while Bravo did not support neurite growth. Surprisingly, when the retinal explants were grown on mixtures of the two molecules, a much more vigorous growth of neurites was seen, revealing a synergistic effect. We propose that Bravo and G4, as well as other axonal surface molecules, affect axonal growth in different ways when they are present in combination than when they are alone.
Peripheral, but not Central, Nervous System Abnormalities are Reversed by Pancreatic Islet Transplantation in Diabetic Lewis Rats
Authors: Morano S. , Sensi M. , Di Gregorio S. , Pozzessere G. , Petrucci A. F. G. , Valle E. , Pugliese G. , Caltabiano V. , Vetri M. , Di Mario U. , Purrello F.
Published: April 2006

Neuroelectrophysiological recordings represent a non‐invasive and reproducible method of detecting central and peripheral nervous system alterations in diabetes mellitus. In order to evaluate whether the normalization of metabolic control obtained by pancreatic islet transplantation could reverse diabetic neuroelectrophysiological alterations, or prevent further deterioration, we used an experimental model in which pancreatic islets (n= 1200) were injected into the portal vein of inbred Lewis rats (used as islet donors as well as recipients). Islets were injected 4 months after diabetes induction, since previous work had shown functional but not morphological damage at the nervous tissue level at this stage of the disease. Visual (V), brainstem auditory (BA) and somatosensory (S) evoked potentials (EPs) were measured in streptozotocin‐induced, islet‐recipient diabetic rats (n= 7), streptozotocin‐induced diabetic rats (n= 16) and non‐diabetic control rats (n= 12). Metabolic parameters and electrophysiological recordings were evaluated before diabetes induction, before transplantation and 4 months later. After transplantation, glycaemic levels returned to normal values within 1 week and remained so until the end of the study, as confirmed by a normal oral glucose tolerance test and by an increase in body weight. Electrophysiological recordings were altered in diabetic animals before transplantation. Four months after transplantation EP recordings improved, with a detectable gradient from the peripheral to the central structures. SEPs were significantly improved in the peripheral tarsus‐16 tract and the L6‐cortex tract (P < 0.005 and P < 0.01 versus diabetic rats) and were ameliorated without achieving statistical significance in the central T6‐cortex tract. BAEP latency values tended to improve in transplanted rats, but the differences versus non‐transplanted diabetic animals failed to reach significance. VEP values remained clearly pathological and even deteriorated after transplantation. These results show that normalization of metabolic control by pancreatic islet transplantation can reverse some of the already established neuroelectrophysiological alterations at the peripheral nervous system level, but does not affect other alterations at the central nervous system level.
Potentiated cAMP Rise in Metabotropically Stimulated Rat Cultured Astrocytes by a Ca2+‐related Al/k2 Adenosine Receptor Cooperation
Authors: Ogata Tadanori , Nakamura Yoichi , Schubert Peter
Published: April 2006

Adenosine agonists favoured an intracellular Ca2+ rise in cultured type 1 astrocytes if the metabotropic glutamate receptors were concomitantly stimulated by (2S,1′s, 2′s)‐2‐(carboxycyclopropyl) glycine (l‐CCG‐I; group II agonist), quisqualate (group I agonist) or 1 ‐aminocyclopentane‐trans‐1,3‐dicarboxylic acid (t‐ACPD; group VII agonist). Since the generation of a Ca2+ signal reflected a newly adopted adenosine A1 receptor action, we tested the possible consequence that the established opposing control of the cellular cAMP content by inhibitory A1 and stimulatory A2 receptor activation was also altered. During metabotropic receptor stimulation by L‐CCG‐I, quisqualate or t‐ACPD, the non‐selective adenosine agonist 2‐chloroadenosine (CI‐adenosine) caused a potentiated cAMP increase which markedly exceeded that produced by CI‐adenosine alone. This cAMP potentiation resulted from altered and Ca2+‐dependent A1/A2 receptor cooperation. It was abolished by A1 receptor blockade and could not be achieved in the presence of t‐ACPD by the A1 agonist R(‐)N6‐(2‐phenylisopropyl)‐adenosine or by the A2 agonist 5′‐N‐ethyl carboxyamidoadenosine alone, but was obtained using their combination. The cAMP potentiation was blocked by intracellular Ca2+ chelation and the required A1 receptor action could be mimicked by a Ca2+ signal generated by the P2y receptor agonist adenosine 5β‐(β‐thio) diphosphate. The results support the conclusion that nanomolar concentrations of adenosine may influence astrocyte reactions by stimulating the Ca2+ and cAMP‐dependent signalling cascade.
Growth of Callosal Terminal Arbors in Primary Visual Areas of the Cat
Authors: Aggoun‐Zouaoui Djamila , Kiper Daniel C. , Innocenti Giorgio M.
Published: April 2006

In kittens ranging in age between postnatal day (P) 5 and P150, callosal axons originating near the 17/18 border were anterogradely labelled with biocytin and reconstructed from serial sections. At the end of the first postnatal week most of the axons begin to invade the cortex near the 17/18 border with multiple branches; some axons already span the grey matter up to layer I. Branches tend to grow into the grey matter in loose bundles ≤l00 μm in diameter, separated by empty spaces of comparable width. In the following weeks additional branches are produced in the grey matter; this appears to blur the initial bundled distribution, although by the end of the first postnatal month the branches are distributed in discrete patches similar to the adult terminal columns. Although a few boutons (presumably synaptic boutons) are found in the white matter/subplate region at earlier ages, they appear in the grey matter from P12 onwards. Their number per axon increases with age, reaching adult values about the end of the first month. Subsequently the number of boutons continues to increase and remains above adult values at P50, P65 and P80; it then decreases, reaching adult levels by P150. During the first month boutons tend to be more numerous in the infragranular layers, but then the trend reverses in favour of the supragranular layers. In most cases, the distribution of boutons spares layer IV partially or completely. From the onset boutons are distributed in radial‘columns’whose diameter increases with age. They maintain selective laminar and columnar distributions through the period of rapid and exuberant increase. These distributions do not appear to be sharpened further by the reduction in the number of boutons to adult levels. On the whole, callosal terminal arbors differentiate through stages of exuberant, albeit progressively constrained, growth involving both progressive and regressive events. Comparisons with previous work suggest that visual activity might finely shape the arbor, from the onset of synaptogenesis onwards.
Activation of Nucleotide Receptors Inhibits High‐threshold Calcium Currents in NG108‐15 Neuronal Hybrid Cells
Authors: Filippov A. K. , Brown D. A.
Published: April 2006

A P2U(UTP‐sensitive) nucleotide receptor has previously been cloned from NG108‐15 neuroblastoma × glioma hybrid cells and it has been shown that activation of this receptor inhibits the M‐type K+‐current. We now report that UTP also inhibits Ca2+‐currents in differentiated NG 108‐15 cells, but probably through a different nucleotide receptor. UTP (100 μM) inhibited the peak of the high‐threshold current by 28.4 ± 3.1% (n= 38) with no effect on the low‐threshold current. Two components of high‐threshold current were identified: one inhibited by 100 nM ω‐conotoxin (CgTx) and one inhibited by 2 μM nifedipine and enhanced by 1 μM BAY K8644. UTP inhibited the former by 31.0 ± 3.1%, with an IC50of 2.8 ± 1.1 μM, and the latter by 34.2 ± 6.1% with an IC50of 1.7 ± 1.3 μM. Pertussis toxin pretreatment prevented inhibition of the CgTx‐sensitive, nifedipine‐resistant but not CgTx‐resistant current. Inhibition was not prevented by intracellular BAPTA (20 mM) or CAMP (1 mM). Effects of UTP on both currents were imitated by UDP, ATP, ADP, AP4A and ATPγS but weakly or not at all by 2‐MeSATP, GTP, AMP‐CPP or ITP. Since the receptors which inhibit Ca2+‐currents are activated by ATP, it is suggested that they might mediate auto‐inhibition of transmitter release by ATP if present on purinergic nerve terminals.
Inability of Rhesus Monkey Area V1 to Discriminate Between Self‐induced and Externally Induced Retinal Image Slip
Authors: IIg Uwe J. , Thier Peter
Published: April 2006

Retinal image slip can result from an eye movement across a stationary object or alternatively from motion of the object while the eyes are stationary. The ability to discriminate between these two kinds of retinal image slip is necessary for the perception of a stable visual world. In order to determine if this ability is already present in monkey visual area V1, we asked if single V1 units are able to differentiate between externally and self‐induced retinal image slip. Externally induced retinal image slip was realized in the‘object motion’condition (OMC) by moving a behaviourally irrelevant visual stimulus (‘object’: a bar or a large random dot pattern) across the receptive field while the monkey fixated a small, stationary target. Conversely, self‐induced retinal image slip of comparable size was evoked in the‘ego motion’condition (EMC) by asking the monkey to pursue the target, moving at the speed of the object in the OMC, while the object was kept stationary. We recorded 221 units from visual area V1, 51 (23%) of them directionally selective, and compared their responses to self‐induced and externally induced retinal image slip. Many of them seemed to give some preference to externally induced retinal image slip. However, on closer examination it became clear that this seeming preference could be attributed to the fact that oculomotor performance was less precise in the EMC than in the OMC, causing a larger deviation from the optimal retinal image trajectory in the EMC. We show that the impact of eye position errors can be eliminated by the use of a position‐invariant stimulus, such as large‐field random dot patterns. We then show that the impact of both eye position errors and deviation of eye velocity from target velocity in the EMC can be eliminated by moving the stimulus in a given OMC trial according to an inverted replica of the eye movement trajectory in the preceding EMC trial, guaranteeing identical retinal stimulation in the OMC and the EMC. If identical retinal stimulation was ensured, none of the V1 units tested was able to differentiate between externally and self‐induced retinal image slip. We conclude that V1 does not contribute to the perception of a world which is stable despite eye movements.
BDNF and NT‐3, but not NGF, Prevent Axotomy‐induced Death of Rat Corticospinal Neurons In Vivo
Authors: Giehl Klaus M. , Tetzlaff Wolfram
Published: April 2006

Brain‐derived neurotrophic factor (BDNF) and neurotrophin‐3 (NT‐3) have been identified as survival factors for adult axotomized rat corticospinal neurons (CSN) in vivo. Axotomy of corticospinal neurons at the level of the internal capsule induced death of 46% of the CSN within the first week after axotomy. The surviving population of CSN displayed severe atrophy with mean cross‐sectional area 49% of their unlesioned contralateral counterparts 7 days after axotomy. Using in situ hybridization to assess the expression of the receptors for the family of neurotrophins, we found trkB and trkC but not trkA mRNA expression in CSN. Intraparenchymal application of BDNF or NT‐3 at doses of 12 μg/day for 7 days via an osmotic minipump fully prevented the axotomy‐induced death of CSN. Interestingly, no neuronal atrophy was seen after BDNF application while NT‐3 had only a partial effect on the size of the axotomized CSN. Nerve growth factor did not prevent death or cell atrophy, consistent with the lack of trkA mRNA expression in these neurons. These findings show that BDNF and NT‐3 are survival factors for adult rat CSN in vivo, and may contribute to the development of therapeutic strategies aiming at the prevention of CSN degeneration in human motor neuron diseases.
Blockade of A2a Adenosine Receptors Positively Modulates Turning Behaviour and c‐Fos Expression Induced by D1 Agonists in Dopamine‐denervated Rats
Authors: Pinna A. , Di Chiara G. , Wardas J. , Morelli M.
Published: April 2006

In rats with unilateral 6‐hydroxydopamine lesions of the dopaminergic nigrostriatal pathway, administration of the A2a adenosine antagonist SCH 58261 alone did not induce any motor asymmetry but strongly potentiated the contralateral turning behaviour induced by the dopamine D1 agonist SKF 38393. SCH 58261 also increased the number of Fos‐like positive nuclei induced by SKF 38393 in the 6‐hydroxydopamine‐lesioned striatum. Intense potentiation of D1‐dependent turning behaviour and c‐Fos expression was also observed after administration of the A2a/A1 antagonist CGS 15943. Administration of the A1 adenosine receptor antagonist DPCPX induced a small potentiation of D1‐mediated contralateral turning while c‐Fos expression induced by SKF 38393 was not modified. The results suggest that endogenous adenosine acting on A2a receptors can exert an inhibitory influence on the functional expression of D1‐mediated responses in dopamine‐denervated rats, and propose new possible therapeutic approaches in the treatment of Parkinson's disease.
Differential Long‐lasting Potentiation of the NMDA and Non‐NMDA Synaptic Currents Induced by Metabotropic and NMDA Receptor Coactivation in Cerebellar Granule Cells
Authors: Rossi Paola , D'Angelo Egidio , Taglietti Vanni
Published: April 2006

Whole‐cell patch‐clamp recordings in rat cerebellar slices were used to investigate the effect of metabotropic glutamate receptor activation on mossy fibre‐granule cell synaptic transmission. Transient application of 20 μM 1 S, 3R‐1 ‐aminocyclopentane‐1,3‐dicarboxylic acid simultaneously with low‐frequency NMDA receptor activation induced long‐lasting non‐decremental potentiation of both NMDA and non‐NMDA receptor‐mediated synaptic transmission. Potentiation could be prevented by application of the metabotropic glutamate receptor antagonist (+)‐O‐methyl‐4‐carboxyphenyl‐glycine at 500 μM. Characteristically, NMDA potentiation was two to three times as large as non‐NMDA current potentiation, occurred only in a slow subcomponent, and was voltage independent. This result demonstrates a pivotal role of NMDA receptors in the metabotropic potentiation of transmission, which may be important in regulating cerebellar information processing.
Calcium Signalling in Mouse Bergmann Glial Cells Mediated by α1‐adrenoreceptors and H1 Histamine ‐ Receptors
Authors: Kirischuk Sergej , Tuschick Sebastian , Verkhratsky Alexej , Kettenmann Helmut
Published: April 2006

The presence of adrenergic and histaminergic receptors in Bergmann glial cells from cerebellar slices from mice aged 20–25 days was determined using fura‐2 Ca2+ microfluorimetry. To measure the cytoplasmic concentration of Ca2+ ([Ca2+]i), either individual cells were loaded with the Ca2+‐sensitive probe fura‐2 using the whole‐cell patch‐clamp technique or slices were incubated with a membrane‐permeable form of the dye (fura‐2/AM) and the microfluorimetric system was focused on individual cells. The monoamines adrenalin and noradrenalin (0.1‐10 μM) and histamine (10‐100 μM) triggered a transient increase in [Ca2+]i. The involvement of the α1‐adrenoreceptor was inferred from the observations that monoamine‐triggered [Ca2+]i responses were blocked by the selective α1‐adreno‐antagonist prazosin and were mimicked by the α1‐adreno‐agonist phenylephrine. The monoamine‐induced [Ca2+]i signals were not affected by β‐ and α2‐adrenoreceptor antagonists (propranolol and yohimbine), and were not mimicked by β‐ and α2‐adrenoreceptor agonists (isoproterenol and clonidine). Histamine‐induced [Ca2+]i responses demonstrated specific sensitivity to only H1 histamine receptor modulators. [Ca2+]i responses to monoamines and histamine did not require the presence of extracellular Ca2+ and they were blocked by preincubation of slices with thapsigargin (500 nM), indicating that the [Ca2+]i increase is due to release from intracellular pools. No [Ca2+]i responses were recorded after application of aspartate, bradykinin, dopamine, GABA, glycine, oxytocin, serotonin, somatostatin, substance P, taurine or vasopressin. We conclude that cerebellar Bergmann glial cells are endowed with α1 ‐adrenoreceptors and H1 histamine receptors which induce the generation of intracellular [Ca2+]i signals via activation of Ca2+ release from inositol‐l,4,5‐trisphosphate‐sensitive intracellular stores.
Pre‐exposure to Subtoxic Levels Prevents Kainic Acid Lesions in Organotypic Hippocampal Slice Cultures: Effects of Kainic Acid on Parvalbumin‐immunoreactive Neurons and Expression of Heat Shock Protein 72 Following the Induction of Tolerance
Authors: Best N. , Sundström L. E. , Mitchell J. , Wheal H. V.
Published: April 2006

The effects of kainic acid on the survival of principal neurons and parvalbumin‐immunoreactive (PARV‐IR) neurons, and on the expression of heat shock protein 72 immunoreactivity (HSP72‐IR) were investigated in organotypic hippocampal slice cultures. Untreated cultures displayed an organotypic organization and the development and morphology of PARV‐IR neurons in the hippocampus paralleled that reported to occur in vivo, with the exception of the hilar region of the dentate gyrus which exhibited a marked lack of PARV‐IR neurons. No constitutive expression of HSP72 was found in untreated cultures. The lesion of CA3 neurons and the reduction in numbers of PARV‐IR neurons in both CA3 and CA1 after chronic exposure to 5 μM kainic acid were similar to those reported to occur in vivo. Exposure to 1 μM doses of kainic acid resulted in a widespread appearance of HSP72‐IR and the induction of tolerance to a previously toxic dose of kainic acid. These results suggest the presence of endogenous neuroprotective mechanisms, activated by a stress response which induces HSP72, and is reminiscent of the induced tolerance reported to occur after a mild ischaemic insult.
BDN F Down‐regulates Neurotrophin Responsiveness, TrkB Protein and TrkB mRNA Levels in Cultured Rat Hippocampal Neurons
Authors: Frank Lone , Ventimiglia Roseann , Anderson Keith , Lindsay Ronald M. , Rudge John S.
Published: April 2006

Regulation of Trk receptors by their ligands, the neurotrophins, was investigated in dissociated cultures of embryonic day 18 rat hippocampal neurons. Cultures were exposed to brain‐derived neurotrophic factor (BDNF), neurotrophin‐3 (NT‐3) or NT‐4/5 for 24 h upon plating followed by factor washout. As determined by immunohistochemical staining and phosphotyrosine blotting, the functional responses to acute stimulation with BDNF, NT‐3 and NT‐4/5, including c‐Fos induction and phosphorylation of Trk and extracellular signal‐regulated kinase (ERK) proteins, were significantly decreased after 6 days in culture by prior exposure to BDNF. As determined by Western and Northern blot analysis respectively, there was a parallel down‐regulation of TrkB protein as well as of trkB and trkC mRNA levels in BDNF‐pretreated cultures. Exposure to NT‐3 or NT‐4/5 at the same concentrations as BDNF did not down‐regulate any of the measured cellular responses or TrkB protein and/or trkB and trkC mRNA levels. Regulation of hippocampal neuronal TrkB protein does not appear to be just a developmental phenomenon, as infusion of BDNF into the hippocampus of adult rats for 6 days produced an 80% decrease in levels of full‐length TrkB protein. We thus show that exposure of hippocampal neurons to BDNF, both in culture and in the adult brain, results in down‐regulation of TrkB. At least in vitro, this leads to long‐term functional desensitization to BDNF. NT‐3 and NT‐4/5. as well as down‐regulation of trkB and trkC mRNA.
Lemniscal Input to Identified Neurons of the Central Nucleus of Mouse Inferior Colliculus: an Intracellular Brain Slice Study
Authors: Wagner Thomas
Published: April 2006

Intracellular recordings were performed in 34 neurons in the central nucleus of the inferior colliculus in brain slice preparations of the mouse. Sixteen neurons recorded were stained intracellularly by injection of biocytin and identified as multipolar. After electrical stimulation of the lateral lemniscus, 32 of 34 neurons exhibited postsynaptic potentials (PSPs). Onset latencies of the PSPs were 5.0±2.8 ms (range 2‐12 ms), presumably reflecting the lack of a significant monosynaptic input to most of the neurons recorded. An excitatory PSP (EPSP), often followed by a late inhibitory PSP (IPSP), was present in all neurons which received synaptic input. The IPSPs usually had a reversal potential positive to the cell's resting membrane potential, thus working as shunting inhibitors. Superfusion of the slice with the GABAA antagonist bicuculline resulted in blockade of the IPSP and pronounced prolongation of the EPSP. In 50% of these cases, paroxysmal depolarizing shifts were observed in the presence of bicuculline. Blocking the non‐NMDA glutamate receptors with 6,7‐dinitroquinoxaline‐2,3‐dione resulted not only in the total disappearance of EPSPs but also of late IPSPs, indicating that the latter depend on the glutamatergic EPSPs. Furthermore, all neurons recorded must receive substantial innervation from sources within the inferior colliculus, together constituting a complex neuronal network in the inferior colliculus with an important role of the inhibitory neurotransmitter GABA in controlling network properties.
GAP‐43 mRNA in Mouse Motoneurons Undergoing Axonal Sprouting in Response to Muscle Paralysis or Partial Denervation
Authors: Bisby M. A. , Tetzlaff W. , Brown M. C.
Published: April 2006

To test the hypothesis that collateral sprouting of motoneurons can occur without the intervention of metabolic changes in the cell body, we examined the levels of growth‐associated protein 43 (GAP‐43) mRNA in mouse motoneurons induced to sprout by muscle inactivity (following marcaine or botulinum toxin treatment) or by partial denervation. GAP‐43 mRNA was selected as an appropriate marker for cell body metabolic changes because it is expressed at low levels in mature motoneurons, but is strongly expressed during developmental or regenerative axonal growth in motoneurons. Sprouting motoneurons were identified by retrograde labelling with fluorescent tracers applied to the muscle in which sprouting occurred. Both a full‐length cDNA probe and an oligonucleotide probe were used for in situ hybridization. We were unable to detect any significant increases in GAP‐43 mRNA levels in fluorescent motoneurons after any treatment, except 4 days after partial denervation (but not at 2 or 8 days). This amounted to a 1.6‐fold increase in signal level compared to control motoneurons, while presumed axotomized motoneurons in the same spinal cords displayed on average an 8.7‐fold increase. We conclude that collateral sprouting can occur in motoneurons without a detectable increase in cell body levels of GAP‐43 mRNA. The modest increase observed in the 4‐day partial denervation situation may be a response to the more vigorous and extensive nodal axonal sprouting occurring in these motoneurons. Our results do not deny a role for pre‐existing GAP‐43 in collateral sprouting, but support the hypothesis that sprouting can occur in motoneurons without necessarily requiring increased GAP‐43 mRNA levels in the cell body.
The Extraneuronal Transporter for Monoamine Transmitters Exists in Cells Derived from Human Central Nervous System Glia
Authors: Russ Hermann , Staudt Kerstin , Martel Fátima , Gliese Martin , Schömig Edgar
Published: April 2006

From studies on sympathetically innervated peripheral tissues it is well known that both neuronal and nonneuronal transport systems contribute to the inactivation of released monoamine transmitters. The close proximity between synapses and glia cell processes in the CNS leads to the so far unresolved question whether non‐neuronal transporters are involved in the inactivation of centrally released monoamine transmitters such as noradrenaline, dopamine and 5‐hydroxytryptamine. 1‐Methyl‐4‐phenylpyridinium (MPP+) is a prototypical substrate of the extraneuronal monoamine transporter (uptake2). [3H]MPP+ was found to accumulate in various human glioma cell lines. [3H]MPP+transport was characterized in more detail in HTZ146 human glioma cells. The Ki values of various compounds for the inhibition of initial rates of [3H]MPP+ transport into HTZ146 cells were closely correlated with the known Ki values for the inhibition of the extraneuronal monoamine transporter (P < 0.001, r= 0.991, n= 7). The rank order of inhibitory potencies was decynium 22 > corticosterone > cyanine 863 > O‐methylisoprenaline > quinine > clonidine > quinidine. [3H]MPP+ accumulation was investigated not only in various CNS tumour cell lines but also in primary cultures of human astrocytes and rat cerebral cortex slices. In all tested experimental systems, accumulation was sensitive to cyanine‐related inhibitors of the extraneuronal monoamine transporter. These findings suggest that the extraneuronal monoamine transporter exists in glia cells. Furthermore, it was shown that MPP+ is able to make use of the extraneuronal monoamine transporter not only to enter but also to leave glia cells. This finding suggests that the extraneuronal monoamine transporter may play a key role in the mechanism of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) neurotoxicity.
Diversity of Postsynaptic Amplitude and Failure Probability of Unitary Excitatory Synapses between CA3 and CA1 Cells in the Rat Hippocampus
Authors: Raastad Morten , Lipowski Rupert
Published: April 2006

Different CA3 cells may have dissimilar effects on a CA1 pyramidal cell. In order to test this idea, we studied the amplitude distribution of excitatory postsynaptic currents (EPSCs) in response to weak electrical stimulation of presynaptic axons in the rat hippocampal slice. We accepted the response populations as representative for the effect of, in most cases, a single axon when the EPSCs appeared at a certain threshold stimulation strength, with the subsequent lack of increase in amplitude with further stimulation increase. By comparing the EPSC amplitude distributions obtained from different synaptic inputs to the same CA1 cell, we found differences in the failure probability and the EPSC amplitude, each of which contributed to differences in the mean response amplitude. We conclude that not only the number but also the specific subset of active CA3 cells is important for the synaptically driven discharge of a given CA1 cell.
Noradrenalin Enhances the Activity of Cochlear Nucleus Neurons in the Rat
Authors: Ebert Ulrich
Published: April 2006

The cochlear nucleus of rats is heavily innervated by noradrenergic fibres from the locus coeruleus. The physiological meaning of this innervation is poorly understood. Therefore, iontophoretically applied noradrenalin was tested on single neurons of the cochlear nucleus in urethane‐anaesthetized rats. Iontophoresis of noradrenalin had a dual effect. During application noradrenalin led to moderate inhibition of tone‐evoked activity in 37% of the tested neurons. In contrast, ∼20‐30 s after the onset of iontophoresis a long‐lasting increase in discharge activity was found in most neurons. Data from iontophoresis of the α1‐receptor agonist phenylephrine and the α2‐receptor agonist clonidine suggest that the fast moderate inhibition is mediated by α2‐receptors while the pronounced long‐lasting elevated neuronal firing is mediated by α1‐receptors. However, these data do not exclude the possibility that part of the response to noradrenalin is also mediated by β‐receptors. Electrical stimulation of the locus coeruleus resulted in an increase in discharge activity comparable with iontophoresis of noradrenalin or phenylephrine. Thus, activation of the locus coeruleus predominantly increases spontaneous and tone‐evoked neuronal firing in the cochlear nucleus of the rat. This α1‐receptor‐mediated enhanced discharge activity may serve to increase the sensitivity of acoustic processing mechanisms or to lower the threshold for short‐latency acoustic reflexes.