bluuebunny/crossref_metadata_2025 huggingface dataset:
Sodium, Calcium and Late Potassium Currents are Reduced in Cerebellar Granule Cells Cultured in the Presence of a Protein Complex Conferring Resistance to Excitatory Amino Acids
Authors: Zona Cristina , Ragozzino Davide , Ciotti Maria Teresa , Mercanti Delio , Avoli Massimo , Brancati Aldo , Calissano Pietro
Published: April 2006

Whole‐cell, patch‐clamp recordings were used to study voltage‐gated currents generated by cerebellar granule cells that were cultured in medium containing either 10% fetal calf serum (hereafter termed S + granules) or neurite outgrowth and adhesion complex (NOAC, hereafter called NOAC granules). NOAC is a protein complex found in rabbit serum that renders granules resistant to the excitotoxic action of excitatory amino acids. During depolarizing commands both S+ and NOAC granules generated Na+ and Ca2+ inward currents and an early and a late K+ outward currents. However, Na+ and Ca2+ Inward currents and late outward K+ currents recorded in NOAC granules were smaller than those seen in S+ granules. Furthermore, although of similar amplitude, early K+ currents displayed different kinetics in the two types of neurons. Thus, these data demonstrate that the electrophysiological properties of cerebellar granules, and probably of other neuronal populations, depend upon serum components and raise the possibility that an analogous modulation might be operative in vivo, and play a role in development, synaptic plasticity or neuropathological processes.
Stochastic Geometry and Electrotonic Architecture of Dendritic Arborization of Brain Stem Motoneuron
Authors: Bras H. , Korogod S. , Driencourt Y. , Gogan P. , Tyc‐Dumont S.
Published: April 2006

We describe how the stochastic geometry of dendritic arborization of a single identified motoneuron of the rat affects the local details of its electrotonic structure. After describing the 3D dendritic geometry at high spatial resolution, we simulate the distribution of voltage gradients along dendritic branches under steady‐state and transient conditions. We show that local variations in diameters along branches and asymmetric branchings determine the non‐monotonous features of the heterogeneous electrotonic structure. This is defined by the voltage decay expressed as a function of the somatofugal paths in physical distances (voltage gradient). The fan‐shaped electrotonic structure demonstrates differences between branches which are preserved when simulations are computed from different values of specific membrane resistivity although the absolute value of their voltages is changed. At given distances from soma and over long paths, some branches display similar voltages resulting in their grouping which is also preserved when specific membrane resistivity is changed. However, the mutual relation between branches inside the group is respecified when different values of specific membrane resistivity are used in the simulations. We find that there are some invariant features of the electrotonic structure which are related to the geometry and not to the electrical parameters, while other features are changed by altering the electrical parameters. Under transient conditions, the somatofugal invasion of the dendritic tree by a somatic action potential shifts membrane potentials (above 10 mV) of dendritic paths for unequal distances from the soma during several milliseconds. Electrotonic reconfigurations and membrane shifts might be a mechanism for postsynaptic plasticity.
Antisense Probes Against Mediatophore Block Transmitter Release in Oocytes Primed with Neuronal mRNAs
Authors: Cavalli Antonella , Dunant Yves , Leroy Christine , Meunier François‐Marie , Morel Nicolas , Israël Maurice
Published: April 2006

Antisense oligodesoxynucleotides were used to determine whether the mediatophore proteolipid is necessary for the Ca2+‐dependent release of the neurotransmitter acetylcholine. Xenopus laevis oocytes were injected with poly(A)+ mRNAs extracted from the electric lobes of Torpedo marmorata. The electric lobes contain an homogeneous population of cholinergic neurons homologous to motoneurons. Addition of antisense probes hybridizing to the mediatophore 15 kDa subunit inhibited the expression of both the mediatophore proteolipid in oocyte membranes and the Ca2+‐dependent acetylcholine release. Expression of other neuronal functions such as synthesis of [14C]acetylcholine from [14C]acetate was not inhibited. Another antisense probe specific for the sequence of a related proteolipid cDNA (the 15 kDa subunit of the chromaffin granule protonophore) was used as a control. It did not hybridize with the Torpedo mediatophore mRNA and, injected in addition to electric lobe mRNAs, it did not inhibit either mediatophore expression or acetylcholine release. We showed in addition that the mRNA primed oocytes did not contain a vesicular pool of acetylcholine. It was concluded (i) that the mediatophore proteolipid is essential for Ca2+‐dependent acetylcholine release and (ii) that the cytosolic pool of neurotransmitter seems to be preferentially used in this system.
Low Doses of NMDA Receptor Antagonists Synergistically Increase the Anticonvulsant Effect of the AMPA Receptor Antagonist NBQX in the Kindling Model of Epilepsy
Authors: Löscher Wolfgang , Rundfeldt Chris , Hönack Dagmar
Published: April 2006

Excitatory amino acid transmitters are involved in the initiation of seizures and their propagation. Most attention has been directed to synapses using N‐methyl‐d‐aspartate (NMDA) receptors, although more recent evidence indicates potential roles for the a‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptors as well. In the present experiments in amygdala‐kindled rats, i.e. a model of partial epilepsy, competitive and uncompetitive NMDA antagonists exerted only weak anticonvulsant effects, whereas the AMPA antagonist 2,3‐dihydroxy‐6‐nitro‐7‐sulfamoylbenzo(F)quinoxaline (NBQX) potently increased focal seizure threshold and inhibited seizure spread from the focus. These effects of NBQX were dramatically increased by pretreatment with low doses of NMDA antagonists, whereas adverse effects of NBQX were not potentiated. These data suggest that both non‐NMDA and NMDA receptors are critically involved in the kindled state, and that combinations of AMPA and NMDA receptor antagonists provide a new strategy for treatment of epileptic seizures.
Functional and Structural Topography of Horizontal Inhibitory Connections in Cat Visual Cortex
Authors: Kisvárday Zoltán F. , Eysel Ulf T.
Published: April 2006

The functional organization of long‐horizontal inhibitory connections was studied in cat visual cortical area 17, using a combination of electrophysiological recording and anatomical tracing in the same tissue. Orientation maps were obtained by recording multiunit activity from layer III at regular intervals (100–300μm) in a region of ‐1.3 mm2 of cortex at a depth corresponding to the location of the basket cell axons reconstructed later. Before the physiological mapping, the neuronal tracer biocytin had been iontophoretically injected at one functionally characterized site. On the basis of light microscopic features a total of five biocytin‐labelled large basket axons, BC1 ‐ BC5, were reconstructed from series of horizontal sections of two cats. The parent somata and dendritic fields of three axons (BC1, BC4 and BC5) could also be reconstructed. The axonal field of basket cell BC1 had an overall lateral spread of 1.8 mm. The axons of basket cells BC4 and BC5 spanned a distance of 3.05 and 2.85 mm, respectively. The distribution pattern of histologically reconstructed recording sites and of five labelled basket cell axons were directly compared in the same sections. The results show that a single large basket cell provides input to regions representing the whole range of orientations, i.e. iso‐orientation (±30°), oblique orientation (±[30–60]°) and cross‐orientation (±[60–90]°) to that at the basket cell's soma. Furthermore, the differential effect mediated by the same large basket cell at sites of different orientation preference was numerically estimated for two basket cells (BC4 and BC5) whose preferred orientations could be determined on the basis of recording sites adjacent to their parent somata. We counted the number of axonal terminals of these basket cells at iso‐, oblique‐ and cross‐orientation sites and found no significant difference in the average density of terminals at sites of either orientation preference. The functional topography of large basket cell axons indicates that the same basket cell can mediate iso‐, oblique‐ and cross‐orientation inhibition at different sites. Hence, we assume that large basket cells serve a complex physiological role depending on the location of target cells in the orientation map.
Regional Distribution of Putative NPY Y1 Receptors and Neurons Expressing Y1 mRNA in Forebrain Areas of the Rat Central Nervous System
Authors: Larsen Philip J. , Sheikh Søren P. , Jakobsen Cherine R. , Schwartz Thue W. , Mikkelsen Jens D.
Published: April 2006

Using monoiodinated radioligands of peptide YY (PYY), and the recently introduced neuropeptide Y (NPY) analogue [Leu31,Pro34]NPY, receptor binding sites of the Y1 and Y2 type were localized in the rat brain by quantitative in vitro autoradiography. The binding specificity and affinity of both radiolabeled ligands were analysed by ligand binding studies employing rat brain membrane homogenates from cerebral cortex and hippocampus. Using in situ hybridization histochemistry, the regional distribution and cellular localization of mRNA encoding the Y1 receptor were investigated in rat brain sections and compared to the distribution of Y1‐specific binding sites. PYY binds to both Y1 and Y2 receptors, while long C‐terminal fragments such as NPY13–36 and NPY16–36 bind preferentially to Y2 receptors. [Leu31, Pro34]NPY is a specific agonist for Y1 receptors. Highest densities of [125I]PYY binding sites were found in the cerebral cortex, the thalamus, the lateral septum, the hippocampus and the mesencephalic dopaminergic areas. In order to block putative Y2 receptors, a series of [125I]PYY binding experiments was performed in the presence of NPY13–36 (1 μM), a Y2 preferring C‐terminal fragment. High densities of binding sites remained present in the cerebral cortex, the thalamus and the medial mammillary nucleus when NPY13–36 was present in the incubation medium. Furthermore, these areas were highly enriched with [125l][Leu31, Pro34]NPY binding sites. In contrast, the hippocampal complex had its binding capacity reduced by ‐50%, while the lateral septum and mesencephalic dopaminergic areas had their binding capacities reduced even further. Linear regression analysis showed a high degree of correspondence between [125l][Leu31, Pro34]NPY binding and that obtained with [125I]PYY in the presence of 1 μM NPY13–36, suggesting that the two independent approaches to visualizing Y1 binding sites are comparable. In situ hybridization histochemistry revealed high levels of Y1 mRNA in the granular cell layer of the hippocampal dentate gyrus, several thalamic nuclei and the hypothalamic arcuate nucleus. Moderate levels of Y1 mRNA were seen in the frontoparietal cortex, several thalamic nuclei, the hippocampal pyramidal layers, the subiculum, the olfactory tubercle, the claustrum and a number of hypothalamic nuclei. The mesencephalon, the amygdala and most basal ganglia showed very low levels of hybridization. The present study further clarifies the anatomical distribution of multiple NPY binding sites within the central nervous system of the rat, and extends earlier suggestions that Y1 and Y2 receptor types are present within the central nervous system.
Mouse Barrel Cortex Functionally Compensates for Deprivation Produced by Neonatal Lesion of Whisker Follicles
Authors: Melzer Peter , Crane Alison M. , Smith Carolyn B.
Published: April 2006

In the murine somatosensory pathway, the metabolic whisker map in barrel cortex derived with the autoradiographic deoxyglucose method is spatially in register with the morphological whisker map represented by the barrels. The barrel cortex of adult mice, in which we had removed three whisker follicles from the middle row of whiskers shortly after birth, contained a disorganized zone surrounded by enlarged barrels with partially disrupted borders. With the fully quantitative autoradiographic deoxyglucose method, we investigated in barrel cortex of such mice the magnitude and the pattern of metabolic responses evoked by the deflection of whiskers. Most remarkably, the simultaneous deflection of six whiskers neighbouring the lesion activated not only the territory of the corresponding barrels, but also the unspecifiable area intercalated between the clearly identified barrels. This metabolic whisker map, unpredictable from the morphological ‘barrel’ map, may reflect a functional compensation for the deficit in input.
Precision and Variability in Postsynaptic Target Selection of Inhibitory Cells in the Hippocampal CA3 Region
Authors: Gulyás Attila I. , Mlles Richard , Hájos Norbert , Freund Tamás F.
Published: April 2006

Non‐pyramidal cells were filled intracellularly with biocytin in the CA3 region of the guinea‐pig hippocampus in vitro, within or close to stratum pyramidale. On the basis of camera lucida reconstructions and electron microscopy, six different cell types with distinct laminar distribution of axon terminals could be distinguished. The axon of three axo‐axonic cells, three typical basket cells, and atypical basket cells of two types arborized in the perisomatic and proximal dendritlc region of CA3 pyramidal cells. Two cells with axons innervating the distal dendritlc segments of pyramidal cells were also found; one terminated in stratum radiatum and the other in stratum lacunosum‐moleculare. Electron microscopy demonstrated that symmetrical synapses were formed by the labelled boutons on axon initial segments, somata, and proximal or distal dendrites of mostly pyramidal neurons. Axo‐axonic cells showed absolute target selectivity for axon initial segments, whereas for the other cells the distribution of contacted elements was determined by the laminar distribution of axon terminals. In two cases, where additional cells were labelled with biocytin, multiple (up to nine) light microscopically identified contacts (presumed synaptic contacts) were established by the interneurons on several pyramidal cells and on an axo‐axonic cell. Our results show that a restricted set of inhibitory cells, with somata within or close to CA3 stratum pyramldale, possess variable patterns of axonal arborization. Various types of postsynaptic elements are contacted, but precision in selecting certain targets and ignoring others is maintained within a particular cell type and layer. In contrast to the diversity of axonal arbors the structure of the dendritic trees shows no consistent differences, suggesting that the cells may be activated by a similar set of afferents. It seems probable that the innervation of precise regions of postsynaptic pyramidal cells by different types of interneurons–often in conjunction with particular excitatory afferents (Han et at., Eur. J. Neurosci., 5, 395–410, 1993)–underlies functional differences in inhibitory synaptic actions.
Loss of Layer‐specific Astrocytic Glutamine Synthetase Immunoreactivity in Slice Cultures of Hippocampus
Authors: Derouiche Amin , Heimrich Bernd , Frotscher Michael
Published: April 2006

Glutamine synthetase (GS) supposedly inactivates the excitatory neurotransmitter glutamate. By using immunocytochemistry for GS, we recently demonstrated a layer‐specific, perisynaptic distribution of GS‐immunoreactive astrocytes and their processes in perfusion‐fixed rat hippocampi. Highest levels of immunoreactivity were found in well defined termination zones of glutamatergic hippocampal afferents. In the present study we analysed the developmental aspect of this neuron – glia interaction by using hippocampal slice cultures lacking all extrinsic afferents. Under these conditions, no layer‐specific distribution of astrocytic GS immunoreactivity could be demonstrated. This suggests that the laminated distribution of GS immunoreactivity is formed in parallel with the segregated termination of hippocampal afferents. Thus, there is no predetermined pattern of GS‐containing astrocytes playing a role in the segregation of extrinsic fibres. The ultrastructural localization of GS immunoreactivity in fine astrocytic processes around asymmetric, probably glutamatergic excitatory spine synapses confirms earlier in situ findings, which suggests that this arrangement is a global phenomenon of glutamatergic systems.
Differential Visualization of Dopamine D2 and D3 Receptor Sites in Rat Brain. A Comparative Study Using In Situ Hybridization Histochemistry and Ligand Binding Autoradiography
Authors: Landwehrmeyer B. , Mengod G. , Palacios J. M.
Published: April 2006

At least five members of the dopamine receptor family have been characterized at the gene level. D2, D3 and D4 dopamine receptors are related pharmacologically. In order to visualize the differential expression of D1, D2 and D3 receptors in rat brain we have combined in situ hybridization histochemistry with receptor autoradiography. Regions enriched with D3 messenger RNA (mRNA) included the islands of Calleja (ioC) and nucleus accumbens. Very low or undetectable levels were present in the caudate–putamen. In contrast, no D2 transcripts were observed in the islands of Calleja, but there were high levels in the nucleus accumbens, caudate–putamen (CP) and pyramidal layer of the olfactory tubercle. A comparison of the binding pattern of six dopamine receptor radioligands hitherto regarded as D2 receptor‐selective showed that the islands of Calleja were intensely labelled by [125I]iodosulpride, [3H]CV 205 502 and [3H]SDZ 205 501, while the binding of [3H]spiperone, [3H]raclopride and [3H]YM 09151–2 was much lower or undetectable. Pharmacological analysis of the binding of D2/D3 ligands to the islands of Calleja and caudate–putamen suggests that binding sites in these two regions are of different pharmacology, consistent with the presence of D3 sites in the islands of Calleja and the predominance of D2 sites in the caudate. These results demonstrate the expression of D3 binding sites in the rat brain and provide a procedure to differentiate D2 and D3 receptor populations in binding studies.
Acute and Chronic Phases of Unilateral Inflammation in Rat's Ankle are Associated with an Increase in the Proportion of Calcitonin Gene‐related Peptide‐immunoreactive Dorsal Root Ganglion Cells
Authors: Hanesch Ulrike , Pfrommer Ursula , Grubb Blair D. , Schaible Hans‐Georg
Published: April 2006

Using immunocytochemical methods, the proportion of calcitonin gene‐related peptide immunoreactive perikarya was determined in dorsal root ganglia L4–L6 in four control rats and in ten rats with a unilateral inflammation in the ankle region of the left hindlimb. The inflammation was induced by subdermal injection of Freund's complete adjuvant at the ankle. Swelling and cellular infiltration of the ankle region developed within 2 days, and were stable and restricted to the injected ankle for the duration of the 3‐week study. In control rats ∼24% of 20 419 perikarya showed calcitonin gene‐related peptide (CGRP)‐like immunoreactivity. In rats with unilateral inflammation the proportion of CGRP‐positive neurons was increased on the inflamed side to ∼32% of 11 454 cells at day 2 (P < 0.001 with respect to ganglia in normal rats) and ∼29% of 10 739 perikarya at day 20 post inoculation (P < 0.01). By contrast, no significant changes were found between ganglia in the non‐injected side (∼25% at day 2 and ∼24% at day 20). These results demonstrate that peripheral inflammation is associated with an increase in the proportion of neurons in the dorsal root ganglia that synthetize CGRP. This up‐regulation is already present at an early stage of inflammation but also at later stages, suggesting that the increased synthesis of CGRP is an important neurobiological reaction associated with the acute and chronic phases of inflammation.
Zonal Organization Within the Projection from the Inferior Olive to the Rostral Paramedian Lobule of the Cat Cerebellum
Authors: Trott Judy R. , Apps Richard
Published: April 2006

The projection from the inferior olivary nucleus to the forelimb‐related regions of the c1, c2 and c3 zones within rostral folia of the paramedian lobule of the cat cerebellum was studied using a combined electrophysiological and neuroanatomical tracing technique. In each experiment, the cerebellar cortical zones were identified by their receipt of spino‐olivocerebellar input evoked by percutaneous electrical stimulation of the limbs. A small (15 – 30 nl) injection of wheatgerm agglutinin – horseradish peroxidase (WGA – HRP) was then made into the centre of one of the zones. The olivary regions projecting to each zone were compared with the regions within the olive that have previously been shown to project to the corresponding cortical zones within lobule V of the anterior lobe. The results show that some (but not all) of the paravermal zones in the anterior lobe are also represented in the paramedian lobule (PML). The most medial (c1) zone in rostral PML receives climbing fibre input from an area in the rostral dorsal accessory olive which overlaps partially with the area that projects to the medial half of the C1 zone in lobule V. A zone equivalent to the lateral half of the c1 zone (the cx zone) in lobule V does not appear to be present within rostral PML. A middle (c2) zone within rostral PML receives olivary input from a region within the rostral medial accessory olive that overlaps partially with the area that projects to the c2 zone in lobule V. The presence of a c3 zone within rostral PML was found to be variable between animals and it could be identified electrophysiologically in only two out of a possible nine cases. In summary, the results demonstrate that, although a number of similarities exist between the olivocerebellar projections to corresponding cortical zones in the two forelimb‐receiving regions of the cat paravermal cortex, the differences in olivocerebellar connectivity between the two regions suggest that functional differences between them may also exist.
The Incidence of Bifurcation Among Corticocortical Connections from Area 17 in the Developing Visual Cortex of the Cat
Authors: Price David J. , Ferrer José Manuel R.
Published: April 2006

In newborn kittens, cells in the striate cortex (visual area 17) that project to area 18 (part of extrastriate cortex) are distributed with uniform density in the superficial and in the deep layers. During postnatal weeks 2 – 3, some of these corticocortical connections are removed to generate an adult‐like projection in which association cells are clustered mainly in the superficial layers of area 17. Axonal elimination, without cell death, is the major factor sculpting patches of corticocortical cells in superficial layers. In adult cats, few cells in area 17 (∼5%) have axons that bifurcate to multiple extrastriate areas. We have studied the possibility that the early exuberant innervation of area 18 by neurons in area 17 is largely from the transient collaterals of axons that also project to other visual areas. Kittens aged 2 – 21 days were each injected with a pair of retrogradely transported tracers, either diamidino yellow and fast blue, or diamidino yellow and a carbocyanine dye, at retinotopically corresponding points in area 18 and either area 19 or the posteromedial lateral suprasylvian cortex (PMLS). As for injections in area 18, those in area 19 and PMLS in kittens aged ≥5 days labelled cells in continuous bands in area 17; in older kittens neurons projecting from area 17 to extrastriate regions were in patches, mainly in superficial layers. In each animal, the labelling from the two injections overlapped by 51–92%. However, at all ages, never more than 4% of cells projecting to area 18 branched to PMLS; ≤6% of area 17‐to‐18 cells bifurcated to area 19 in kittens aged ≥15 days, although slightly more (10 – 12%) did so at 3 – 5 days. Thus, as in adults, we found no evidence of frequent collateralization among the axons of cells projecting from area 17 to other extrastriate areas in kittens.
The Structure of Sleep is Related to the Learning Ability of Rats
Authors: Ambrosini M. V. , Mariucci G. , Colarieti L. , Bruschelli G. , Carobi C. , Giuditta A.
Published: April 2006

Using electroencephalographic methods, rats learning or not learning a two‐way active avoidance task were found to differ significantly in the structure of sleep determined the day before training. The main differences concerned (i) synchronized sleep episodes followed by wakefulness, which were longer and fewer in learning rats; (ii) paradoxical sleep episodes, which were longer in learning rats. Significant correlations were present between the number and/or the average duration of synchronized sleep episodes followed by wakefulness or by paradoxical sleep and the number of avoidances or escapes scored in the training session. Power spectral analysis indicated that the relative output in the 6 – 7‐Hz region was higher in learning rats, notably during short episodes of synchronized sleep followed by paradoxical sleep. As two‐way active avoidance training induces comparable modifications in postacquisition sleep (Ambrosini et al., Physiol. Behav., 51, 217 – 226, 1992), the features of preacquisition sleep which prevail in learning rats might directly determine their capacity to learn. Alternatively, they might reflect the existence of a genetic determinant independently conditioning the ability to learn.
The Envelope Glycoprotein of HIV‐1 Alters NMDA Receptor Function
Authors: Sweetnam Paul M. , Saab Omar H. , Wroblewski Jarda T. , Price Christopher H. , Karbon E. William , Ferkany John W.
Published: April 2006

Human immunodeficiency virus (HIV‐1) infection often results in central nervous system (CNS) dysfunction, yet the mechanism(s) of action for HIV‐1 in the CNS are not fully understood. In the present study gp120, the HIV‐1 envelope glycoprotein, was shown to selectively inhibit N‐methyl‐d‐aspartate (NMDA) receptor function. In addition to inhibiting radioligand binding to rat NMDA receptors, gp120 inhibited NMDA‐induced currents in Xenopus oocytes, attenuated NMDA‐stimulated calcium flux and cytotoxicity in cultured cerebellar granule cells, and provided partial protection against NMDA‐induced lethality in vivo. These findings suggest that NMDA receptor complex is a possible site of action of HIV‐1 within the CNS.
Cocaine Enhances the Changes in Extracellular Dopamine in Nucleus Accumbens Associated with Reinforcing Stimuli: A High‐speed Chronoamperometric Study in Freely Moving Rats
Authors: Kiyatkin Eugene A.
Published: April 2006

Numerous data suggest that the mesocorticolimbic dopamine (DA) system is critically involved in the organization and regulation of goal‐directed behaviours of various types as well as in the mediation of the psychogenic effects of cocaine. To test the hypothesis that cocaine not only alters levels of extracellular DA within the mesolimbic DA system, but in addition changes the response of this system to reinforcing environmental stimuli, a study using high‐speed chronoamperometry was done to evaluate the effects of cocaine (15 mg/kg, i.p.) on extracellular DA in the nucleus accumbens and to assess the effects of cocaine on the response evoked by the presentation of tail‐pinch and palatable food. Cocaine was found to induce long‐term biphasic changes in extracellular DA (an increase followed by a decrease) and, more importantly, to enhance DA increases evoked by both tail‐pinch and food. The powerful enhancing action of cocaine on DA release, triggered by significant environmental stimuli and associated with behaviours of different types, is considered to be a possible primary mechanism of its rewarding or euphorigenic effect.
Glutamate‐like Immunoreactivity in Retinal Terminals of the Mouse Suprachiasmatic Nucleus
Authors: Castel M. , Belenky M. , Cohen S. , Ottersen O. P. , Storm‐Mathisen J.
Published: April 2006

With a view to identifying the neurotransmitter content of retinal terminals within the mouse suprachiasmatic nucleus, a highly specific antiserum to glutaraldehyde‐coupled glutamate was used in a postembedding immunogold procedure at the ultrastructural level. Retinal terminals were identified by cholera toxin–horseradish peroxidase transported anterogradely from the retina and reacted with tetramethyl benzidine/tungstate/H2O2, or by their characteristically pale and distended mitochondria with irregular cristae. Controls included model ultrathin sections containing high concentrations of various amino acids. Alternate serial sections were labelled with anti‐glutamate and anti‐γ‐aminobutyric acid (GABA). Data were analysed by computer‐assisted image analysis. Density of glutamate labelling (gold particles per μm2) on whole retinal terminals was > 3 times higher than that on postsynaptic dendrites, and > 5 times higher than that on miscellaneous non‐retinal non‐glutamatergic terminals in the suprachiasmatic nucleus. The overall density of gold particles over retinal terminals was ∼ 3 times higher than that over GABAergic terminals, in which glutamate‐like immunoreactivity was mainly mitochondrial. Labelling of vesicles in retinal terminals was almost 5 times greater than the apparent labelling of vesicles in GABAergic terminals, underscoring the location of transmitter glutamate within synaptic vesicles in retinal terminals. In the retino‐recipient region of the suprachiasmatic nucleus there was also a small population of non‐retinal glutamatergic terminals. Their overall immunoreactivity was similar to or exceeded that of retinal terminals, but morphological features clearly distinguished between these two types of glutamate‐containing terminals. The present results indicate that the vast majority of retinal terminals may use glutamate as a transmitter, in keeping with electrophysiological and neuropharmacological data from other sources. The possibility of cotransmitters within retinal terminals, suggested by the presence of dense‐core vesicles among the glutamate‐containing synaptic vesicles, has still to be addressed.
Potent Analgesia Induced in Rats by Combined Action at PCP and Polyamine Recognition Sites of the NMDA Receptor Complex
Authors: Coderre Terence J.
Published: April 2006

The present study was performed to examine the analgesic effects of the intrathecal administration of agents acting at various sites in the N‐methyl‐d‐aspartic acid (NMDA) receptor complex on the nociceptive responses to s.c. formalin injection in rats. Both the competitive NMDA receptor antagonist 2‐amino‐5‐phosphonovaleric acid (APV) and the non‐competitive NMDA antagonist dizocilpine maleate (MK‐801) produced dose‐dependent analgesic effects in the late, but not the early, phase of the formalin test. The polyamine antagonist ifenprodil, and the strychnine‐insensitive glycine antagonists DCQX and 7‐chlorokynurenic acid, failed to produce any analgesic effects in either the early or the late phase of the formalin test. The analgesic effects of APV were enhanced slightly by combined administration with a non‐analgesic dose of glycine, and the analgesic effects of MK‐801 were dramatically potentiated by combined adminstration of a non‐analgesic dose of the polyamine spermine. The results indicate that much more potent analgesia can be produced in the formalin test by a combination of open channel blockers (such as MK‐801) with agonists acting at the polyamine site, than by a single treatment with antagonists to either glycine allosteric or polyamine sites within the NMDA receptor complex.
Giant GABAB‐mediated Synaptic Potentials Induced by Zinc in the Rat Hippocampus: Paradoxical Effects of Zinc on the GABAB Receptor
Authors: Xie Xinmin , Smart Trevor G.
Published: April 2006

The interaction of zinc with pre‐ and postsynaptic GABAB receptors was studied in adult rat hippocampal slices using intracellular recording in CA1 and CA3 pyramidal neurons. Zinc (50 – 300 μM) antagonized baclofen responses with a variable potency, whereas CGP‐35348 (100 μM) or barium (300 μM) produced a more substantial and consistent inhibition. Zinc also induced giant GABAA‐mediated depolarizing potentials (GDP) in these neurons. After blocking GABAA and excitatory synaptic transmission, monosynaptic hyperpolarizing inhibitory postsynaptic potentials (IPSP) mediated by GABAB receptors (IPSPB) were inhibited by CGP‐35348 or barium; however, zinc increased the latency and prolonged the duration of the IPSPB and also induced the appearance of spontaneous giant GABAB‐mediated hyperpolarizing potentials (GHP). In some cells, IPSPBs in zinc exhibited a multiphasic appearance. The early component was partially inhibited by 300 μM zinc and was followed by a late GHP. CGP‐35348 at 100 μM inhibited the early monosynaptic IPSPB but not the GHP; however, at 300 μM both components were blocked. Paired‐pulse inhibition of the IPSPB was used to assess the effect of zinc on presynaptic GABAB receptors. Neither the zinc‐chelating agent CP94 (400 μM) nor zinc affected this phenomenon. CGP‐35348, barium and polyvalent cations, such as cadmium, copper, cobalt, manganese, iron and aluminium, failed to induce giant potentials in hippocampal neurons. It is concluded that zinc is apparently unique in synchronizing the release of GABA to produce GDPs and GHPs.
Functional Organization of Area V2 in the Alert Macaque
Authors: Peterhans E. , von der Heydt R.
Published: April 2006

We studied the relation between anatomical structure and functional properties of cells in area V2 of the macaque. Visual function was assessed in the alert animal during fixation of gaze. Recording sites were reconstructed with respect to cortical lamination and the cytochrome oxidase pattern. We measured orientation and direction selectivity, end‐stopping, sensitivity to binocular disparity and ocular dominance, and determined more complex functions like sensitivity to anomalous contours and lines defined by coherent motion. Orientation selectivity was found in all parts of area V2, with high frequencies in the pale and thick stripes of the cytochrome oxidase pattern, and with lower frequency in the thin stripes. Representations of anomalous contours were found in the pale and thick stripes with similar frequencies, but generally not in the thin stripes, which have been thought to process colour. Lines defined by coherent motion were most frequently represented in the thick stripes; they were less frequent in the pale stripes, and (as with anomalous contours) were not found in the thin stripes. Sensitivity to binocular disparity was found in all types of stripes, but more frequently in the thick stripes, where the exclusively binocular neurons were also concentrated. By contrast, no segregation was found for direction selectivity and end‐stopping. All neuronal properties were distributed evenly across cortical laminae. We conclude that mechanisms for figure–ground segregation involve the pale and the thick stripes of the cytochrome oxidase pattern, perhaps with greater emphasis on 'shape from motion’and 'stereoscopic depth’in the thick stripes, while more elementary neuronal properties are distributed almost evenly across the stripe pattern.
Functional Organization of the Human First and Second Somatosensory Cortices: a Neuromagnetic Study
Authors: Hari R. , Karhu J. , Hämäläinen M. , Knuutila J. , Salonen O. , Sams M. , Vilkman V.
Published: April 2006

Multichannel neuromagnetic recordings were used to differentiate signals from the human first (SI) and second (SII) somatosensory cortices and to define representations of body surface in them. The responses from contralateral SI, peaking at 20 – 40 ms, arose mainly from area 3b, where representations of the leg, hand, fingers, lips and tongue agreed with earlier animal studies and with neurosurgical stimulations and recordings on convexial cortex in man. Representations of the five fingers were limited to a cortical strip of ∼2 cm in length. Responses from SII peaked 100 – 140 ms after contra‐ and ipsilateral stimuli and varied considerably from one subject to another. Signs of somatotopical organization were seen also in SII. Responses of SII were not fully recovered at interstimulus intervals of 8 s.
Expression of c‐Jun as a Response to Dorsal Root and Peripheral Nerve Section in Damaged and Adjacent Intact Primary Sensory Neurons in the Rat
Authors: Jenkins R. , McMahon S. B. , Bond A. B. , Hunt S. P.
Published: April 2006

It was previously shown that the immediate early gene, c‐jun, was highly expressed over long periods, in both peripheral sensory and motor neurons following axon damage or block of axoplasmic transport. Here we have examined the question of whether the expression of c‐Jun protein is related to axon injury per se or to the process of axon growth. We have examined dorsal root ganglion (DRG) cells subjected to different manipulations which are associated with varying degrees of regrowth, as follows: (i) after peripheral nerve section, where it appears that all damaged neurons make some regenerative effort. 1 – 24 days after sciatic nerve section and ligation most cells in L4/L5 DRG were c‐Jun‐positive; (ii) after section of the central processes of the DRG cells, which then showed a slow and limited regrowth of their axons towards, but not into, the spinal cord. This resulted in a variable, but significant, expression of c‐Jun in a small number of DRG cells; (iii) in intact sensory neurons that were offered the opportunity to sprout into adjacent denervated peripheral tissue. The sciatic nerve was ligated and the response of cells in the L3 ganglia (many of which project to the saphenous nerve) was measured. A small but significant number of cells were c‐Jun‐positive; (iv) in intact sensory neurons that were offered the opportunity to sprout centrally into partialy denervated neuropil of the spinal cord. We examined neurons in the L3 DRG after rhizotomy of the adjacent L4/L5 dorsal roots. Previous work suggests that sensory neurons show at best a very limited growth under these conditions. No significant increase was seen in c‐Jun expression in these cases. These results suggest that c‐Jun expression is closely correlated with growth and regeneration, and not simply a consequence of neuronal injury.
A Phosphorylation Epitope on MAP 1B that is Transiently Expressed in Growing Axons in the Developing Rat Nervous System
Authors: Gordon‐Weeks Phillip R. , Mansfield S. Gary , Alberto Concha , Johnstone Mandy , Moya Fernando
Published: April 2006

We have isolated a monoclonal antibody (150) that recognizes a phosphorylation epitope on the microtubule‐associated protein (MAP) 1B. Immunoblot analysis of the developing rat central nervous system shows that monoclonal antibody 150 is directed against a protein of ∼325 kDa (MAP 1B) that copolymerizes with microtubules through successive cycles of temperature‐dependent assembly and disassembly. Furthermore, immunoprecipitated MAP 1B contains the epitope recognized by monoclonal antibody 150. Removal of phosphate from blotted proteins using alkaline phosphatase abolishes the binding of monoclonal antibody 150 to MAP 1B, indicating that the epitiope is phosphorylated. In the developing rat nervous system, immunohistochemistry with monoclonal antibody 150 shows that the phosphorylation epitope on MAP 1B is transiently expressed in growing axons but not in dendrites. For instance, in the neonatal rat cerebellum, the parallel fibres of granule cells are stained only during elongation and not after synaptogenesis. The monoclonal antibody 150 epitope is also transiently expressed in radial glial fibres and in certain cell nuclei. All immunostaining of sections with monoclonal antibody 150 was completely abolished by alkaline phosphatase treatment. These observations and previous ones made by us in cell culture (Mansfield et al., J. Neurocytol., 20, 654 – 666, 1991) suggest that the phosphorylation epitope on MAP 1B recognized by monoclonal antibody 150, which has not been previously detected in vivo, may be important in axonogenesis.
Distribution and Characterization of Neuropeptide FF‐like Immunoreactivity in the Rat Nervous System with a Monoclonal Antibody
Authors: Lee Che‐Hung , Wasowicz Krzysztof , Brown Robert , Majane Elizabeth A. , Yang Hsiu‐Ying T. , Panula Pertti
Published: April 2006

Monoclonal antibodies against neuropeptide FF were produced and characterized. The antibodies are directed and highly specific to neuropeptide FF, and reactivity requires the C‐terminal dipeptide of neuropeptide FF (Arg‐Phe‐NH2). Tissue extracts from bovine spinal cord, rat spinal cord and hypothalamus were analysed by high‐pressure liquid chromatography coupled with radioimmunoassay using the characterized monoclonal antibody. Only one immunoreactive peptide was detected and it coeluted with authentic neuropeptide FF. Using this highly specific monoclonal antibody, the distribution of neuropeptide FF‐like immunoreactivity was further studied by indirect immunohistochemistry. Immunoreactivity was seen in two major cell groups in the rat brain. The largest cell group was located in the medial hypothalamus between the dorsomedial and ventromedial nuclei. The other one was found in the nucleus of the solitary tract. Fibres immunoreactive for neuropeptide FF were located in the lateral septal nucleus, amygdala, different hypothalamic areas, nucleus of the solitary tract, ventral medulla, trigeminal complex and the dorsal horn of the spinal cord. Spinal and sympathetic ganglia were non‐reactive. No neuropeptide FF immunoreactivity was seen in the gut autonomic nervous system or endocrine cells. The results show that neuropeptide FF‐like immunoreactivity has a clearly more limited distribution in the nervous system than typical brain–gut peptides.
Heterogeneity of Metabotropic Glutamate Receptors in the Striatum: Electrophysiological Evidence
Authors: Calabresi Paolo , Pisani Antonio , Mercuri Nicola B. , Bernardi Giorgio
Published: April 2006

In order to investigate the functional role of metabotropic glutamate receptors (mGluRs) in the striatum we performed extracellular and intracellular recordings from a corticostriatal brain slice preparation. The effects of l‐2‐amino‐3‐phosphopropionic acid (l‐AP3), an antagonist of mGluRs, were studied both on long‐term synaptic depression (LTD) and on presynaptic inhibition of excitatory postsynaptic potentials (EPSPs) induced by different agonists of mGluRs. l‐AP3 produced a dose‐dependent (3 – 30 μM) reduction of the LTD evoked in the striatum by the tetanic stimulation of the corticostriatal pathway. In contrast to this action, l‐AP3 (10 – 100 μM) did not significantly affect the presynaptic inhibitory effect of 1‐amino‐cyclopentyl‐trans‐dicarboxylic acid (t‐ACPD), an agonist of mGluRs, on corticostriatal transmission. Higher concentrations of l‐AP3 (0.3 – 1 mM) reduced by themselves the EPSP amplitude. The inhibitory effect of t‐ACPD on the cortically evoked EPSPs was mimicked either by the active stereoisomer 1S,3R‐ACPD or by amino‐4‐phosphonobutyric acid (l‐AP4), a glutamate autoreceptor agonist. In some neurons, these inhibitory actions were coupled with membrane depolarizations. The depression of synaptic transmission caused by t‐ACPD, 1S,3R‐ACPD and l‐AP4 was not altered following the induction of LTD. Chronic lithium treatment of the animals (60–120 mg/kg i.p. for 10 days) blocked striatal LTD but not presynaptic inhibition mediated by mGluR agonists. The present findings show that the mechanisms underlying LTD and the presynaptic inhibition induced by different agonists of mGluRs exhibit functional and pharmacological differences. These data suggest heterogeneity of mGluRs in the striatum.
Synaptic Excitation Triggers Oscillations During NMDA Receptor Activation in Rat Abducens Motoneurons
Authors: Durand Jacques
Published: April 2006

Rat abducens motoneurons were intracellularly recorded in vivo during synaptic excitation and extracellular microionophoretic application of N‐methyl‐d‐aspartate (NMDA). Trigeminal excitatory post‐synaptic potentials (EPSPs) evoked in abducens motoneurons were studied during intracellular current injection. They were not sensitive to hyperpolarization or depolarization of the membrane potential in the range of –75 mV to –55 mV using current pulse intensities between –3 nA and + 1 nA. Microionophoretic applications of aminophosphonovalerate (APV), MK801 and i.v. injections of MK801 (1 – 3 mg/kg) or ketamine (10 mg/kg) did not modify trigeminal EPSPs, suggesting that NMDA receptors are not involved in this synaptic transmission. However, microionophoretic applications of NMDA on abducens motoneurons enhanced trigeminal EPSPs and gave rise to regenerative oscillations. The co‐activation of NMDA receptors and trigeminal synapses induced these oscillations. The trigeminal EPSP may delay and reset the oscillations depending on where it was evoked in the oscillatory cycle. Depolarizing current pulses intracellularly applied to abducens motoneurons could trigger a post‐hyperpolarization followed by rebound depolarization during NMDA application, confirming the activation of active membrane properties. However, depolarizing current pulses could not trigger oscillations similar to those entrained by the EPSPs. The importance of the location of trigeminal synapses in relation to those of NMDA receptors in the dendritic arborization of abducens motoneurons is discussed. Our results show that the same sensory stimulus may have different post‐synaptic effects on abducens motoneurons during the co‐activation of NMDA receptors. A complete modification of the motor output during NMDA receptor activation strongly supports an active role of abducens motoneurons provided that NMDA receptors are physiologically activated during motor pattern generation.
Monocularly Induced 2‐Deoxyglucose Patterns in the Visual Cortex and Lateral Geniculate Nucleus of the Cat: I. Anaesthetized and Paralysed Animals
Authors: Löwel Siegrid , Singer Wolf
Published: April 2006

Extending previous investigations of the topographic relationship between ocular dominance and orientation columns in the cat visual cortex the two systems were visualized with transneuronally transported [3H]proline and with activity‐dependent uptake of [14C]2‐deoxyglucose, respectively. In addition, we used the 2‐deoxyglucose method for a functional assay of both columnar systems. To this end, cats were injected with [3H]proline in the right eye. Two weeks later, they were stimulated monocularly through this eye by presenting contours of only a single orientation in the left and contours of many different orientations in the right visual hemifield while 2‐deoxyglucose was injected. The patterns of increased 2‐deoxyglucose uptake and of terminal labelling were analysed in flat‐mount sections of the visual cortices and in frontal sections of the lateral geniculate nuclei. In the lateral geniculate nucleus, regions of increased 2‐deoxyglucose uptake are in register with the [3H]proline‐labelled laminae of the open eye. In the visual cortex, the hemispheres stimulated with many different orientations showed a rather homogeneous accumulation of 2‐deoxyglucose over the entire extent and throughout all layers of area 17. The hemispheres stimulated with a single orientation displayed columnar patterns of orientation domains essentially similar to those obtained with binocular presentation of a single orientation. In particular and despite monocular stimulation, regions of increased 2‐deoxyglucose uptake were neither in register with the [3H]proline‐labelled terminals of the stimulated eye in layer IV nor confined to columns of neural tissue above and below these terminals. The maximal horizontal offset between the termination sites of thalamic afferents and activated orientation columns was in the order of 400 μm. These findings suggest several conclusions. (i) In the cat visual cortex, binocular convergence seems to occur so early in cortical processing that monocular stimulation with many orientations leads to a rather homogeneous activation of cortical tissue. (ii) From the termination zones of geniculate afferents activity is apparently distributed already within layer IV to the respective orientation columns. (iii) This horizontal spread of activity could be assured by target cells with radially extending dendrites and/or tangentially oriented fibres.