bluuebunny/crossref_metadata_2025 huggingface dataset:
Increased β‐Amyloid Precursor Protein Expression in Astrocytes in the Gerbil Hippocampus Following Ischaemia: Association with Proliferation of Astrocytes
Authors: Palacios G. , Mengod G. , Tortosa A. , Ferrer I. , Palacios J. M.
Published: April 2006

Increases in β‐amyloid precursor proteins (APP), which include the β‐amyloid senile plaque protein present in patients with Alzheimer's disease, have been shown to occur in models of neuronal damage and neurotoxic cell injury. This observation led us to examine the expression of these proteins after transient ischaemic episodes in the gerbil. Animals were killed 2–28 days after ischaemia and APP were detected by immunocytochemistry at the light and electron microscopic levels with an antibody raised against the C‐terminal region of these proteins. The gliotic reaction was also examined using glial fibrillary acid protein (GFAP) immunoreactivity. Two days after ischaemia, neuronal cell death was observed in the hippocampal CA1 region accompanied by astrocyte hypertrophy. These hypertrophic astrocytes were found to be GFAP positive but stained weakly for APP. Seven days after ischaemia both astrocyte hypertrophic and hyperplasia, with identified mitotic figures, were observed. These hyperplasic astrocytes were intensely stained by the APP antibody, and were observed up to 28 days after ischaemia. This shows that neuronal cell death produced by transient ischaemia is followed by an increased APP expression which appears to be associated with the hyperplasic astrocytes but not with the initial hypertrophy of this cell population. These results, when taken together with those obtained in other models of neuronal damage or death, clearly suggest that APP expression follows neuronal death and is associated with astrocyte proliferation.
Crucial Role for the Myelin‐associated Glycoprotein in the Maintenance of Axon‐Myelin Integrity
Authors: Fruttiger M. , Montag D. , Schachner M. , Martini R.
Published: April 2006

It has recently been shown that mice deficient in the gene for myelin‐associated glycoprotein develop normal myelin sheaths in the peripheral nervous system. Here we report that in mutant mice older than 8 months the maintenance of axon‐myelin units is disturbed, resulting in both axon and myelin degeneration. Morphological features include those typically seen in human peripheral neuropathies, where demyelination‐induced Schwann cell proliferation and remyelination lead to the formation of so‐called onion bulbs. Expression of tenascin‐C, a molecule indicative of peripheral nerve degeneration, was up‐regulated by axon‐deprived Schwann cells and regenerating axons were occasionally seen. Myelin‐associated glycoprotein thus appears to play a crucial role in the long‐term maintenance of the integrity of both myelin and axons.
Basic Fibroblast Growth Factor Opens Calcium‐Permeable Channels in Quail Mesencephalic Neural Crest Neurons
Authors: Distasi Carla , Munaron Luca , Laezza Fernanda , Lovisolo Davide
Published: April 2006

In order to investigate the action of basic fibroblast growth factor (bFGF) in the nervous system, we have studied the ionic signals elicited by this peptide in cultured quail mesencephalic neural crest neurons using patch‐clamp and cytofluorimetric techniques. In this preparation stimulation with bFGF induced, with a delay of some tens of seconds, an inward cationic current. Single‐channel experiments provided evidence for the activation of a calcium‐permeable channel. In single‐cell cytofluorimetric measurements, a sustained rise in [Ca2+Ii was observed, which was dependent on the presence of external calcium. These events may play a role in the developmental effects of bFGF.
Biphasic Expression of the Fos and Jun Families of Transcription Factors Following Transient Forebrain Ischaemia in the Rat. Effect of Hypothermia
Authors: Kamme Fredrik , Campbell Kenneth , Wieloch Tadeusz
Published: April 2006

Transient global ischaemia induces the expression of immediate early genes. Using in situ hybridization, the expression of c‐fos, fosB, fra‐1, fra‐2, c‐jun and junB was studied after 15 min of normothermic and hypothermia (33°C) transient forebrain ischaemia in the rat, induced by common carotid occlusion combined with systemic hypotension. Two phases of induction of the immediate early genes were observed. The early phase, peaking at 1–2 h of reperfusion, was dominated by marked expression in the dentate gyrus. The second phase, with maximal expression at 12–36 h of reperfusion, was observed particularly in the vulnerable CA1 and CA3 regions. Hypothermia increased the early induction of one of the genes studied, signifying a differential effect of hypothermia upon the signal transduction mechanisms activating these genes. The late induction occurred earlier after hypothermic than after normothermic ischaemia. The early expression of immediate early genes is due to the rapid activation of cytosolic response elements caused by the ischaemic insult. We suggest that the late induction is a stress signal for activation of repair processes, analogous to the cellular response seen after UV light‐induced DMA damage. The relatively fast induction of the immediate early genes following hypothermic ischaemia may reflect a faster resumption of normal intracellular signalling, enhancing neuronal recovery.
pH‐dependent Facilitation of Synaptic Transmission by Histamine in the CA1 Region of Mouse Hippocampus
Authors: Yanovsky Y. , Reymann K. , Haas H. L.
Published: April 2006

The action of histamine on excitatory synaptic transmission in the CA1 region of the mouse hippocampus was investigated. In a medium at pH 7.4 population spikes were increased for ‐60 min after a brief (5 min) perfusion with histamine (5 μM) but excitatory postsynaptic potentials (EPSPs) were unaffected, as previously reported in the rat. At pH 7.0, however, a late component of extra‐ and intracellularly registered EPSPs was enhanced in two phases: a shorter (by 30%) and a longer lasting one (<1 h by 10%). The NMDA antagonist amino‐phosphonovalerate (60 μM) blocked this late component and prevented the EPSP broadening by histamine. In some cells histamine induced burst‐firing and prolonged EPSPs. The actions on EPSPs were not mediated by any of the known histamine receptors as they were not mimicked by histamine H1, H2 and H3 agonists or blocked by H1, H2 or H3 antagonists. We conclude that histamine enhances a late (NMDA) component of hippocampal EPSPs when protonization is increased by a slight shift of the pH in the acidic direction. Such shifts occur during intense nervous discharges, e.g. in epileptic tissue or following tetanic stimulation, and in hypoxic conditions.
Down‐regulation of Glial Glutamate Transporters after Glutamatergic Denervation in the Rat Brain
Authors: Levy L. M. , Lehre K. P. , Walaas S. I. , Storm‐Mathisen J. , Danbolt N. C.
Published: April 2006

Membrane‐localized transporter proteins, expressed in both neurons and glial cells, are responsible for removal of extracellular glutamate in the mammalian CNS. The amounts and activities of these transporters may be under regulatory control. We demonstrate here that cortical lesions, which decrease striatal glutamate uptake in synaptosome‐containing homogenates by ∼50%, also decrease the striatal concentrations of the astrocytic glutamate transporter proteins, GLT‐1 and GLAST by ∼20–30%. Since GABA uptake activity was not decreased and glial fibrillary acidic protein was increased in the same samples, the lesion‐induced losses of GLT‐1 and GLAST were not caused by a general impairment of neuronal or glial function. The observed reduction in the two astrocytic glutamate transporters after corticostriatal nerve terminal degeneration indicates that their levels of expression are dependent on glutamatergic innervation.
Differential Effects of Forebrain 5‐Hydroxytryptamine Depletions on Pavlovian Aversive Conditioning to Discrete and Contextual Stimuli in the Rat
Authors: Wilkinson Lawrence S. , Humby Trevor , Robbins Trevor W. , Everitt Barry J.
Published: April 2006

The experiments examined the effects of depleting forebrain 5‐hydroxytryptamine (5HT) on Pavlovian aversive conditioning to discrete and contextual stimuli. Rats were lesioned with intracerebroventricular injections of the neurotoxin 5,7‐dihydroxytryptamine and then conditioned in a distinctive environment (termed the context) to a 30 s auditory stimulus. In 50% of animals the interval between the offset of the discrete auditory stimulus and the reinforcer, a mild foot‐shock (0.5 mA, 0.5 s), was 5 s (the short‐trace group) and in the other 50%, 30 s (the long‐trace group). Theory predicts that animals in the short‐trace condition will learn more about the discrete stimulus as a predictor of shock and become strongly conditioned, while those in the long‐trace condition learn relatively more about the context. The extent of conditioning to the discrete and contextual stimuli was assessed separately, in extinction, using lick‐suppression and place‐preference measures respectively. Under these conditions sham subjects exhibited the expected dissociation with respect to trace interval. However, lesioned animals exhibited a specific impairment in contextual conditioning. The results are discussed in terms of the behavioural, neurochemical and neuroanatomical specificity of 5HT function in aversive conditioning and the implications for general theories of the role of 5HT in aversive processes.
Expression of NMDA Receptor mRNAs in Rat Motoneurons is Down‐regulated after Axotomy
Authors: Piehl Fredrik , Tabar Gabriella , Cullheim Staffan
Published: April 2006

The cytotoxic effects of glutamate via the N‐methyl‐D‐aspartate (NMDA) receptor have been suggested to take part in the events leading to death of motoneurons after neonatal axotomy. By the use of in situ hybridization and immunohistochemistry we have investigated motoneuron mRNA expression of the NMDA receptor subunits NR1, NR2B and NR2D and of the NR1 subunit protein in two lesion models leading to partial motoneuron death: sciatic nerve transection early postnatally in the rat and ventral root avulsion in the adult rat. The results were compared with a lesion model with no subsequent death of motoneurons, i.e. sciatic nerve transection in the adult rat. All lesions were followed by down‐regulation of the mRNAs for all studied subunits in severed motoneuron populations; down‐regulation was detectable already at early stages postoperatively before any significant death had taken place. The strongest down‐regulation was in fact seen in the lesion with the largest loss of motoneurons (ventral root avulsion). The reduction in the expression of NR1 mRNA was paralleled by a decrease in NR1 subunit protein. We conclude that down‐regulation of NMDA receptor subunit expression is part of the acute response to axonal injury in motoneurons, whether or not neuronal death follows, and that the susceptibility of lesioned motoneurons to excitotoxic effects should be highest early after axonal injury.
A Critical Period for Axon Regrowth Through a Lesion in the Developing Mammalian Retina
Authors: MacLaren R. E. , Taylor J. S. H.
Published: April 2006

Although the central nervous system of mature mammals is incapable of regeneration, certain elements present in the developing system must permit and promote the growth of new axons to their initial targets. We investigate whether the environment of a developing visual system is capable of supporting regeneration in the Brazilian opossum Monodelphis domestica, in which the retinofugal system develops postnatally. Retinae were lesioned up to the 16th postnatal day and analysed for regeneration after a further 7–10 days. Anterograde tracing with Dil showed axons to have regrown from the axotomized area of retina directly through the lesion. Retrograde tracing with horseradish peroxidase injected into the superior colliculus confirmed that axons from the lesioned area of retina had grown to an appropriate position in the midbrain. The proportion of retinae in which axonal continuity was restored across the lesion decreased as the visual system matured, falling to zero after the 12th postnatal day. Thus a critical period exists in the postnatal opossum in which a retinal lesion permits axon passage. Correlating these results to the known pattern of retinofugal pathway development provides an insight into factors that may restrict this critical period to the 12th postnatal day, and suggests that at least some of the axotomized neurons are regenerating.
Activation of p44 and p42 MAP Kinases is not Essential for the Survival of Rat Sympathetic Neurons
Authors: Virdee Kanwar , Tolkovsky Aviva M.
Published: April 2006

We have examined whether activation of MAP kinases [or extracellular signal‐regulated kinases (ERKs)] is required for the survival of rat sympathetic neurons by comparing the actions of three survival factors whose survival‐promoting actions can be blocked by neutralizing Fab fragments to p21 ras (Nobes and Tolkovsky, 1995, Eur. J. Neurosci., 7, 344–350), nerve growth factor (NGF), the cytokines ciliary neurotrophic factor (CNTF) and leukaemia inhibitory factor (LIF), and the cyclic AMP analogue 4‐(8‐chlorophenylthio)cAMP (CPTcAMP). NGF‐induced survival was accompanied by an intense (15‐ to 30‐fold) and steady (>24 h) activation of p44 and p42 ERKs which waned rapidly (t1/2∼30 min) upon NGF withdrawal. However, concentrations of NGF that induced a weak (4‐ to 5‐fold) stimulation of the ERKs were not sufficient to maintain long‐term survival. Moreover, prolonged and intense stimulation of the ERKs by NGF for up to 15.5 h was unable to confer long‐term survival, since withdrawal of NGF after this time resulted in neuronal death that was kinetically indistinguishable from the death of neurons that had not been exposed to NGF. By contrast, CNTF and LIF continued to support survival for up to 3 days after eliciting only transient (<30 min and 1 h respectively) activation of p44 and p42 ERKs, while CPTcAMP induced survival for several days without any measurable activation of the ERKs. Taken together, these data suggest that ERK activation perse is neither necessary nor sufficient for survival and that alternative pathways exist for effecting long‐term survival of rat sympathetic neurons.
Synaptic Input of Horizontal Interneurons in Stratum Oriens of the Hippocampal CA1 Subfield: Structural Basis of Feed‐back Activation
Authors: Blasco‐Ibáñez J. M. , Freund T. F.
Published: April 2006

The synaptic input of interneurons with horizontal dendrites in stratum oriens of the CA1 region was investigated, with particular attention to the portion of synapses originating from local pyramidal cells. Most of these GABAergic interneurons are known to contain somatostatin, and terminate on pyramidal dendrites in conjunction with entorhinal afferents in stratum lacunosum‐moleculare. A smaller number of horizontal cells in this layer are immunoreactive for calbindin, and project to the medial septum. Selective ischaemic degeneration was used to label local axon collaterals of CA1 pyramidal cells, and immunostaining for mGluR1 or calbindin to visualise somatostatin‐ and calbindin‐containing horizontal interneurons, respectively, at the stratum oriens‐alveus border. The number of degenerating and intact synaptic boutons was counted on mGluR1‐ as well as on calbindin‐positive dendrites and somata, whereas in another group of animals the proportion of GABA‐immunoreactive synapses was estimated on calbindin‐positive dendrites. On average, >60% of the total presynaptic elements of both cell types were degenerating, i.e. originated from CA1 pyramidal cells, whereas GABA‐positive boutons, which are known to survive ischaemia, are likely to account for a large proportion of non‐degenerating boutons. Thus the vast majority of presumed excitatory synapses on somatostatin‐ and calbindin‐containing horizontal neurons derives from local collaterals of CA1 pyramidal cells. The remaining GABA‐negative synapses surviving ischaemia may also originate from CA1 pyramidal cells, e.g. from those in the ventral hippocampus, which are rarely damaged by global forebrain ischaemia. Alternative sources may include subcortical afferents known to innervate interneurons, or ipsi‐ and contralateral CAS pyramidal cells, which, according to the present results, may account only for a negligible number of synapses on these interneuron types. We conclude that somatostatin‐containing neurons at the oriens‐alveus border of CA1, which are likely to mediate an inhibitory control of the efficacy and/or plasticity of entorhinal synapses on pyramidal cell dendrites, are driven primarily in a feed‐back manner. The source of afferent excitation for calbindin‐containing horizontal neurons in this region is very similar, suggesting that the GABAergic hippocamposeptal feed‐back is also activated by local pyramidal cell collaterals.
Immunohistochemical Localization of Five Members of the KV1 Channel Subunits: Contrasting Subcellular Locations and Neuron‐specific Co‐localizations in Rat Brain
Authors: Veh Rüdiger W. , Lichtinghagen Ralf , Sewing Sabine , Wunder Frank , Grumbach Isabella M. , Pongs Olaf
Published: April 2006

A large variety of potassium channels is involved in regulating integration and transmission of electrical signals in the nervous system. Different types of neurons, therefore, require specific patterns of potassium channel subunit expression and specific regulation of subunit coassembly into heteromultimeric channels, as well as subunit‐specific sorting and segregation. This was investigated by studying in detail the expression of six different α‐subunits of voltage‐gated potassium channels in the rat hippocampus, cerebellum, olfactory bulb and spinal cord, combiningin situhybridization and immunocytochemistry. Specific polyclonal antibodies were prepared for five α‐subunits (KV1.1, KV1.2, KV1.3, KV1.4, KV1.6) of theShaker‐related subfamily of rat Kvchannels, which encode delayed‐rectifier type and rapidly inactivating A‐type potassium channels. Their distribution was compared to that of an A‐type potassium channel (KV3.4), belonging to theShaw‐related subfamily of rat Kvchannels. Our results show that these Kvchannel α‐subunits are differentially expressed in rat brain neurons. We did not observe in various neurons a stereotypical distribution of Kvchannel α‐subunits to dendritic and axonal compartments, but a complex differential subcellular subunit distribution. The different Kvchannel subunits are targeted either to presynaptic or to postsynaptic domains, depending on neuronal cell type. Thus, distinct combinations of Kv1 α‐subunits are co‐localized in different neurons. The implications of these findings are that both differential expression and assembly as well as subcellular targeting of Kvchannel α‐subunits may contribute to Kvchannel diversity and thereby to presynaptic and postsynaptic membrane excitability.
NADPH Diaphorase Expression in the Rat Retina after Axotomy—a Supportive Role for Nitric Oxide?
Authors: Huxlin Krystel R. , Bennett Max R.
Published: April 2006

The large majority of mammalian retinal ganglion cells degenerate following section of their axons in the optic nerve. It has been suggested that some axotomized retinal ganglion cells die because of toxic agents produced within their immediate environment. Our hypothesis was that nitric oxide might be one of the toxic factors implicated in the death of adult retinal ganglion cells post‐axotomy. In the first instance, we determined whether there were any changes in the retinal expression of NADPH diaphorase both 3 and 14 days following intraorbital section of the optic nerve in adult rats. Secondly, if nitric oxide was indeed implicated in the death of ganglion cells, then trophic factors which rescue these neurons might do so by decreasing the expression of nitric oxide synthase. Recently, we found that a collicular proteoglycan purified from the major target of retinal ganglion cells, the superior colliculus, rescued a greater proportion of adult ganglion cells from axotomy‐induced death than most other known trophic factors. We thus injected this proteoglycan intraocularly after section of the optic nerve and examined its effect on the expression of NADPH diaphorase in the retina. Thirdly, an inhibitor of nitric oxide synthetase was repeatedly injected into the eye following the section of the optic nerve in order to determine if such a treatment might improve the survival of retinal ganglion cells. The present results indicate that section of the optic nerve does not alter the overall levels of NADPH diaphorase within the adult rat retina. Intraocular injections of the collicular proteoglycan actually increased the number of neurons expressing NADPH diaphorase, particularly in the ganglion cell layer. Finally, inhibition of nitric oxide synthetase following axotomy resulted in increased loss of retinal ganglion cells over a 2 week period when compared with controls. Our findings indicate that, rather than being toxic, small amounts of nitric oxide may be important for the survival of a proportion of injured retinal ganglion cells.
BC1 RNA and Vasopressin mRNA in Rat Neurohypophysis: Axonal Compartmentalization and Differential Regulation during Dehydration and Rehydration
Authors: Trembleau Alain , Melia Kathleen R. , Bloom Floyd E.
Published: April 2006

Brain cytoplasmic 1 (BC1) RNA is a small non‐translated RNA polymerase III transcript. Because this RNA can be detected in the rat posterior pituitary with 35S in situ hybridization autoradiography, it has been hypothesized that this RNA might be transported in the axons of hypothalamo‐neurohypophyseal neurons. In the present study, we aimed to determine the cellular localization of BC1 more precisely by using non‐radioactive in situ hybridization of BC1 RNA at both the light and electron microscopic levels. Our studies revealed that BC1 RNA was indeed located intra‐axonally. Furthermore, BC1 RNA was abundant within a subset of axonal swellings and/or terminals, and was also found in discrete cytoplasmic domains of undilated axonal segments. Using a semiquantitative in situ hybridization approach, we have measured and compared the changes in BC1 RNA and arginine vasopressin (AVP) mRNA during dehydration (chronic salt‐loading) and rehydration. Chronic salt‐loading significantly increased both BC1 RNA and AVP mRNA. The increase in BC1 RNA labelling (2.5‐fold), however, was modest and somewhat less enduring than the increase in AVP mRNA labelling (13‐fold). Upon rehydration, both the BC1 and vasopressin transcripts in the posterior pituitary rapidly returned to control values. In conclusion, like vasopressin mRNA, BC1 RNA is transported in axons of the hypothalamo‐neurohypophyseal system where it aggregates in a subset of axonal swellings, and its axonal transport is similarly regulated. Therefore, we propose that BC1 RNA might be involved in the axonal targeting, docking and/or transport of AVP or other axonal mRNAs.
Lesions of the Superior Temporal Cortical Motion Areas Impair Speed Discrimination in the Macaque Monkey
Authors: Orban Guy A. , Saunders Richard C. , Vandenbussche Erik
Published: April 2006

The effects of circumscribed lesions of the superior temporal cortical motion areas on speed discrimination were tested in three macaque monkeys using both moving random‐textured patterns and moving bars. The lesions, which included the middle temporal visual area, the adjacent medial superior temporal visual area and the fundus superior temporal visual area, produced a severe and lasting deficit in speed discrimination when tested with the random patterns. In contrast, deficits were smaller when tested with moving bars. Control lesions of the inferior temporal cortex in two monkeys had little effect on speed discrimination. There was no clear deficit following inferior temporal or superior temporal sulcus lesions on a vernier acuity task. These experiments indicate that the middle temporal and adjacent areas play a crucial role in speed discrimination and that lesion effects depend on the cues available to the animals.
Müller Glia Stabilizes Cell Columns During Retinal Development: Lateral Cell Migration but not Neuropil Growth is Inhibited in Mixed Chick‐Quail Retinospheroids
Authors: Willbold Elmar , Reinicke Michael , Lance‐Jones Cynthia , Lagenaur Carl , Lemmon Vance , Layer Paul G.
Published: April 2006

Radial columnar organization of cell clones is a characteristic feature of vertebrate retinae that is structurally not understood. Here we provide in vitro evidence that Müller glia processes stabilize cells within columns. Dissociated embryonic chick retinal plus pigmented cells regenerate in vitro into fully laminated stratospheroids. After reaggregating chick and quail cells, quail‐derived spheroid areas are detected as isolated sectors, as shown by a quail‐specific antibody. Each sector contains one or multiple cell columns. The radial borders separating chick and quail sectors are fully congruent with the extension of 3A7‐labelled Müller glia processes. While cell somata do not show any lateral interspecies mixing, quail‐derived neuropil extends within the inner plexiform areas far into chick sectors. After selective damage of Müller cells by the gliotoxin dl‐α‐aminoadipic acid, the columnar organization is destabilized, as evidenced by a decrease in vimentin expression and by the migration of individual neurons out of their cell column. These data demonstrate that Müller cells actively stabilize cells within their columns, while neuritic growth is not hindered.
HIV‐1 Envelope Proteins gp120 and gp160 Potentiate NMDA‐induced [Ca2+]i Increase, Alter [Ca2+]i Homeostasis and Induce Neurotoxicity in Human Embryonic Neurons
Authors: Lannuzel Annie , Lledo Pierre‐Marie , Lamghitnia Hassan Ould , Vincent Jean‐Didier , Tardieu Marc
Published: April 2006

The envelope glycoprotein gp120 of the human immunodeficiency virus HIV‐1 has been proposed to cause neuron death in developing murine hippocampal cultures and rat retinal ganglion cells. In the present study, cultured human embryonic cerebral and spinal neurons from 8‐ to 10‐week‐old embryos were used to study the neurotoxic effect of gp120 and gp160. Electrophysiological properties as well as N‐methyl‐d‐aspartate (NMDA)‐induced currents were recorded from neurons maintained in culture for 10–30 days. Neither voltage‐activated sodium or calcium currents nor NMDA‐induced currents were affected by exposure of neurons to 250 pM gp120 or gp160. In contrast, when neurons were subjected to photometric measurements using the calcium dye indo‐1 to monitor the intracellular free Ca2+ concentration ([Ca2+]i), gp120 and gp160 (20–250 pM) potentiated the large rises in [Ca2+]i induced by 50 μM NMDA. The potentiation of NMDA‐induced Ca2+ responses required the presence of Ca2+ in the medium, and was abolished by the NMDA antagonist d‐2‐amino‐5‐phosphonovalerate (AP5) and the voltage‐gated Ca2+ channel inhibitor nifedipine. Moreover, exposure of a subpopulation of spinal neurons (25% of the cells tested) to 20–250 pM gp120 or gp160 resulted in an increase in [Ca2+]i that followed three patterns: fluctuations not affected by AP5, a single peak, and the progressive and irreversible rise of [Ca2+]i. The neurotoxicity of picomolar doses of gp120 and gp160 cultures was estimated by immuno‐fluorescence and colorimetric assay. Treatment of cultures with AP5 or nifedipine reduced gp120‐induced toxicity by 70 and 100% respectively.
Distribution of GLP‐1 Binding Sites in the Rat Brain: Evidence that Exendin‐4 is a Ligand of Brain GLP‐1 Binding Sites
Authors: Göke Rüdiger , Larsen Philip J. , Mikkelsen Jens D. , Sheikh Søren P.
Published: April 2006

The distribution and biochemical properties of glucagon‐like peptide (GLP)‐1(7–36)amide (GLP‐1) binding sites in the rat brain were investigated. By receptor autoradiography of tissue sections, the highest densities of [125I]GLP‐1 binding sites were identified in the lateral septum, the subfornical organ (SFO), the thalamus, the hypothalamus, the interpenduncular nucleus, the posterodorsal tegmental nucleus, the area postrema (AP), the inferior olive and the nucleus of the solitary tract (NTS). Binding studies with [125I][Tyr39]exendin‐4, a GLP‐1 receptor agonist, showed an identical distribution pattern of binding sites. Binding specificity and affinity was investigated using sections of the brainstem containing the NTS. Binding of [125I]GLP‐1 to the NTS was inhibited concentration‐dependently by unlabelled GLP‐1 and [Tyr39]exendin‐4 with K1 values of 3.5 and 9.4 nM respectively. Cross‐linking of hypothalamic membranes with [125I]GLP‐1 or [125I][Tyr39]exendin‐4 identified a single ligand‐binding protein complex with a molecular mass of 63 000 Da. The fact that no GLP‐1 binding sites were detected in the cortex but that they were detected in the phylogenetically oldest parts of the brain emphasizes that GLP‐1 may be involved in the regulation of vital functions. In conclusion, the biochemical data support the idea that the central GLP‐1 receptor resembles the peripheral GLP‐1 receptor. Furthermore, the presence of GLP‐1 binding sites in the circumventricular organs suggests that these may be receptors which act as the target for both peripheral blood‐borne GLP‐1 and GLP‐1 in the nervous system.
Postsynaptic Targets of Purkinje Cell Terminals in the Cerebellar and Vestibular Nuclei of the Rat
Authors: De Zeeuw C. I. , Berrebi A. S.
Published: April 2006

The cerebellar and vestibular nuclei consist of a heterogeneous group of inhibitory and excitatory neurons. A major proportion of the inhibitory neurons provides a GABAergic feedback to the inferior olive, while the excitatory neurons exert more direct effects on motor control via non‐olivary structures. At present it is not clear whether Purkinje cells innervate all types of neurons in the cerebellar and vestibular nuclei or whether an individual Purkinje cell axon can innervate different types of neurons. In the present study, we studied the postsynaptic targets of Purkinje cell axons in the rat using a combination of pre‐embedding immunolabelling of the Purkinje cell terminals by L7, a Purkinje cell‐specific marker, and postembedding GABA and glycine immunocytochemistry. In the cerebellar nuclei, vestibular nuclei and nucleus prepositus hypoglossi Purkinje cell terminals were found apposed to GABAergic and glycinergic neurons as well as to larger non‐GABAergic, non‐glycinergic neurons. In the cerebellar and vestibular nuclei individual Purkinje cell terminals innervated both the inhibitory and excitatory neurons. Both types of neurons were contacted not only by GABAergic Purkinje cell terminals but also by GABA‐containing terminals that were not labelled for L7 and by non‐GABAergic, non‐glycinergic terminals that formed excitatory synapses. Glycine‐containing terminals were relatively scarce (<2% of the GABA‐containing terminals) and frequently contacted the larger non‐GABAergic, non‐glycinergic neurons. To summarize, Purkinje cell axons evoke their effects through different types of neurons present in the cerebellar and vestibular nuclear complex. The observation that individual Purkinje cells can innervate both excitatory and inhibitory neurons suggests that the excitatory cerebellar output system and the inhibitory feedback to the inferior olive are controlled simultaneously.
Morphine Withdrawal Syndrome and G Protein Expression: a Study of the Time Course in the Rat Central Nervous System
Authors: Rubino Tiziana , Parenti Marco , Patrini Gabriela , Massi Paola , Parolaro Daniela
Published: April 2006

We followed the changes in G protein α subunit expression and levels throughout the brain during the naltrexone‐precipitated withdrawal syndrome in morphine‐dependent rats. Intraperitoneally injected naltrexone (10 mg/kg) in rats made tolerant to morphine resulted in sustained withdrawal. Additional naltrexone doses 6, 24 and 72 h later still induced a significant abstinence syndrome. At the fifth naltrexone injection (8 days later) counted signs were completely resolved but checked ones were not. Besides the behavioural modifications, opiate withdrawal affected G protein expression in the central nervous system. In situ hybridization showed that Gαs and Gαo mRNA, whose levels are increased in tolerance, changed further during opiate withdrawal. Specifically, the αs mRNA in the hypothalamus was reduced after the first naltrexone injection and reached the control level with subsequent doses. However, αo mRNA expression in the olfactory system remained elevated after repeated naltrexone injections, declining to the control value only after the fifth dose. The amounts of Gαs and Gαo protein closely followed the time course of mRNA. The relationship between behavioural and biochemical parameters is discussed, together with the regional selectivity of the modifications.
Distribution of a Brain‐specific Proteoglycan, Neurocan, and the Corresponding mRNA During the Formation of Barrels in the Rat Somatosensory Cortex
Authors: Watanabe Eiji , Aono Sachiko , Matsui Fumiko , Yamada Yasukazu , Naruse Ichiro , Oohira Atsuhiko
Published: April 2006

Neurocan is a developmentally regulated chondroitin sulphate proteoglycan in the rat brain. In the present study, spatiotemporal patterns of expression of neurocan and the corresponding mRNA were examined in the developing cortical barrel field of the rat brain by using a monoclonal antibody that was highly specific to neurocan and a riboprobe for a portion of the mRNA. Immunohistochemical analysis revealed that neurocan was distributed throughout the cerebral cortex during early postnatal development but was excluded from the centres of cortical barrels at the time of entry and arborization of thalamocortical axons. At this developmental stage, expression of neurocan mRNA was shown by in situ hybridization to be down‐regulated in the barrel centres. When a row of whisker follicles was laser‐cauterized on postnatal day 1, the pattern of expression of neurocan was disturbed in the row of barrels that corresponded to the lesioned whisker follicles in the contralateral somatosensory cortex. From these observations, it appears that neuronal stimuli through early thalamocortical fibres from the sensory periphery cause reduced expression of neurocan mRNA in neurocan‐producing cells in the presumptive barrel centres. Our findings also suggest that the pattern of distribution of neurocan in early postnatal barrel fields may be due mainly to the down‐regulation of expression of neurocan mRNA.
Dopaminergic Agonists Have Both Presynaptic and Postsynaptic Effects on the Guinea‐pig's Medial Vestibular Nucleus Neurons
Authors: Vibert Nicolas , Serafin Mauro , Crambes Olivier , Vida1 Pierre‐Paul , Mühlethaler Michel
Published: April 2006

A number of studies have indicated a possible interaction between dopamine and the vestibular system. Using intracellular recordings in brainstem slices, we have tested the effects of dopamine and other dopaminergic compounds on guinea‐pig medial vestibular nucleus (MVN) neurons. In normal medium, MVN neurons were depolarized by dopamine as well as by (‐)quinpirole and piribedil, which are selective D2 dopaminergic agonists. The dependence of this effect on the presence of D2 receptors was confirmed by using (‐)sulpiride, a D2 antagonist which blocked the depolarizing effect of dopamine. Dopaminergic D1 receptors were apparently not involved in this effect since a selective D1 agonist, SKF‐38393, had no effect on MVN neurons and the D1 antagonist (+) SCH‐23390 could not block the effect of dopamine. These depolarizing responses to dopamine must be due to a presynaptic action on terminals that normally release GABA spontaneously on MVN neurons, and tonically maintain them in a state of hyperpolarization. Indeed, such a spontaneous release was demonstrated to occur in the slice since application of bicuculline, a GABAA antagonist, depolarized MVNneurons in normal saline, but not in a high Mg2+/low Ca2+ solution known to block synaptic transmission. When dopamine was applied in conditions in which no GABAA‐dependent transmission could occur (either in the presence of bicuculline or in a high Mg2+/low Ca2+ solution) only a hyperpolarizing, most probably postsynaptic, effect occurred. These results indicate that dopamine might exert in vivo a significant modulatory action on the vestibular system, either by a direct action on the vestibular neurons or by modulation of GABAergic transmission.
MK‐801 Blockade of Fos and Jun Expression Following Passive Avoidance Training in the Chick
Authors: Freeman Fiona M. , Rose Steven P. R.
Published: April 2006

Training chicks on a one‐trial passive avoidance task results in transient up‐regulation of the N‐methyl‐d‐aspartate (NMDA) receptor in the left intermediate medial hyperstriatum ventrale (IMHV) of the forebrain 30 min post‐training. Injection of the non‐competitive NMDA receptor inhibitor, (+)‐5‐methyl‐10, 11‐dihydro‐5H‐dibenzo‐ (a.d)‐cyclohepten 5, 10‐imine maleate (MK‐801), around the time of training renders chicks amnesic for the task. Training also results in enhanced expression of the immediate early gene (IEG) c‐fos in the IMHV. To determine the relationship between NMDA receptor up‐regulation and IEG induction during memory formation we have examined the expression of Fos, Jun and their related proteins 1 h following training in the presence/absence of the putative amnestic agent MK‐801. Western blotting of IMHV samples revealed two protein bands with immunoreactivity to the Fos antibody at 47 and 54 kDa. Using an antibody to Jun, two immunoreactive bands were revealed at 39 and 54 kDa. All bands were enhanced in the left IMHV following passive avoidance training. Post‐training intraperitoneal injections of MK‐801 (75 mM) produced amnesia in ∼50% of the birds when tested 1 h after training. Injection of MK‐801 significantly attenuated expression of these proteins in birds rendered amnesic, but not in those that recalled the task. We conclude that NMDA receptor activation precedes immediate early gene expression in the memory formation cascade.
Auditory Cortex of the Rufous Horseshoe Bat: 1. Physiological Response Properties to Acoustic Stimuli and Vocalizations and the Topographical Distribution of Neurons
Authors: Radtke‐Schuller S. , Schuller G.
Published: April 2006

The extent and functional subdivisions of the auditory cortex in the echolocating horseshoe bat, Rhinolophus rouxi, were neurophysiologically investigated and compared to neuroarchitectural boundaries and projection fields from connectional investigations. The primary auditory field shows clear tonotopic organization with best frequencies increasing in the caudorostral direction. The frequencies near the bat's resting frequency are largely over‐represented, occupying six to 12 times more neural space per kHz than in the lower frequency range. Adjacent to the rostral high‐frequency portion of the primary cortical field, a second tonotopically organized field extends dorsally with decreasing best frequencies. Because of the reversed tonotopic gradient and the consistent responses of the neurons, the field is comparable to the anterior auditory field in other mammals. A third tonotopic trend for medium and low best frequencies is found dorsal to the caudal primary field. This area is considered to correspond to the dorsoposterior field in other mammals. Cortical neurons had different response properties and often preferences for distinct stimulus types. Narrowly tuned neurons (Q10dB < 20) were found in the rostral portion of the primary field, the anterior auditory field and in the posterior dorsal field. Neurons with double‐peaked tuning curves were absent in the primary area, but occurred throughout the dorsal fields. Vocalization elicited most effectively neurons in the anterior auditory field. Exclusive response to pure tones was found in neurons of the rostral dorsal field. Neurons preferring sinusoidal frequency modulations were located in the primary field and the anterior and posterior dorsal fields adjacent to the primary area. Linear frequency modulations optimally activated only neurons of the dorsal part of the dorsal field. Noise‐selective neurons were found in the dorsal fields bordering the primary area and the extreme caudal edge of the primary field. The data provide a survey of the functional organization of the horseshoe bat's auditory cortex in real coordinates with the support of cytoarchitectural boundaries and connectional data.
Chondroitin Sulphate Proteoglycans in the Rat Brain: Candidates for Axon Barriers of Sensory Neurons and the Possible Modification by Laminin of their Actions
Authors: Katoh‐Semba R. , Matsuda M. , Kato K. , Oohira A.
Published: April 2006

The addition of chondroitin sulphate proteoglycans (CSPGs), purified from the rat brain, to the culture medium of PC12D cells inhibited their proliferation and neurite outgrowth. Therefore, we investigated the effects of several extracellular components on the inhibitory actions of CSPGs on PC12D cells, as well as their immunocytochemical distribution in the rat embryo to determine whether the findings in vitro could be reproduced in vivo. Coating of the substratum with polylysine was necessary for the appearance of the inhibitory effects of brain CSPGs on PC12D cells. The additional pretreatment of polylysine‐coated dishes with laminin or fibronectin promoted the outgrowth of neurites from PC12D cells. Laminin and fibronectin, but not collagen (types I and IV) and CELL‐TAK (cell adhesion molecules), prevented the inhibitory effects of brain CSPGs in a concentration‐dependent manner. Doses producing 50% reduction by laminin (or fibronectin) of the CSPG effects were 1.5 (or 25) μg/ml for neurite outgrowth and 2.2 (or 28) μg/ml for proliferation. The ratio of dish‐attached CSPGs to laminin necessary for 50% reduction was about ∼50:l (wt/wt). Laminin from any source had the same effect. Brain CSPGs also obviously impeded the growth of fibres from dorsal root ganglion explants and primary cultured dorsal root ganglion neurons. Neurocan (a major CSPG in the brain)‐like immunoreactivity was detected in the boundary caps and roof plate in the rat embryo at 13.5 days of gestation, when DRG neurons were extending their axons to the neural tube. The distributions of laminin and tenascin appeared, respectively, to be slightly and considerably different from that of neurocan. These results suggest that brain CSPGs can generate barriers to the growth of axons from the dorsal root ganglion and that the ratio of CSPGs to laminin may be important in regulating such growth.
Molecular Cloning, Functional Expression and Pharmacological Characterization of the Human Metabotropic Glutamate Receptor Type 2
Authors: Flor P. J. , Lindauer K. , Püttner I. , Rüegg D. , Lukic S. , Knöpfel T. , Kuhn R.
Published: April 2006

A cDNA encoding the human metabotropic glutamate receptor type 2 (hmGluR2) was isolated from human brain cDNA libraries by cross‐hybridization with rat mGluR2 probes. The deduced amino acid sequence of the human mGluR2 receptor consists of 872 residues and shows a sequence identity of 97% to the amino acid sequence of rat mGluR2. Northern blot analyses showed that hmGluR2 is widely expressed in different regions of the adult brain as well as in fetal human brain. Genomic Southern blotting localized the mGluR2 gene to human chromosome 3. Chinese hamster ovary (CHO) cells stably transfected with the cloned hmGluR2 cDNA exhibit agonist induced depression of forskolin‐stimulated cAMP accumulation. A direct comparison of CHO cells stably expressing human and rat mGluR2 with five agonists revealed the same rank order of potency [(2S,3S,4S)‐α‐(carboxycyclopropyl)‐glycine » (1S,3R)‐1‐aminocyclopentane‐1,3‐dicarboxylic acid =l‐glutamate » quisqualate =l‐2‐amino‐4‐phosphonobutyric acid] and similar EC50 values for both homologous receptors. (R.S)‐a‐methyl‐4‐carboxyphenylglycine, a reported antagonist at some mGluR subtypes, reduced the depression of forskolin‐induced cAMP accumulation by (1S,3R)‐ACPD in both human and rat mGluR2.
Synergistic Trophic Actions on Rat Basal Forebrain Neurons Revealed by a Synthetic NGF/BDNF Chimaeric Molecule
Authors: Friedman W. J. , Black I. B. , Persson H. , Ibáñez C. F.
Published: April 2006

Basal forebrain cholinergic neurons, which degenerate in Alzheimer's disease, respond to multiple trophic factors, including the neurotrophins, nerve growth factor (NGF) and brain‐derived neurotrophic factor (BDNF). This dual responsiveness prompted us to investigate the effects of a synthetic chimaeric molecule, containing the active domains of both NGF and BDNF. The NGF/BDNF chimaeric factor exhibited synergistic actions, and was 100‐fold more potent than wild‐type BDNF in enhancing survival of cultured dissociated basal forebrain cholinergic neurons. This effect was apparently due to true BDNF/NGF synergy, since addition of the two wild‐type trophins simultaneously reproduced the effect of the chimaera. Synergy was selective for neurons which respond to both factors; substantia nigra dopaminergic neurons, which respond to BDNF but not NGF, exhibited no potentiation. The chimaeric factor thus revealed a synergy that may normally occur in the brain, and constitutes a potentially novel therapeutic agent with greater potency than naturally occurring individual trophins.
BDNF Produces Analgesia in the Formalin Test and Modifies Neuropeptide Levels in Rat Brain and Spinal Cord Areas Associated With Nociception
Authors: Siuciak Judith A. , Wong Vivien , Pearsall Denise , Wiegand Stanley J. , Lindsay Ronald M.
Published: April 2006

Previous studies have demonstrated an antinociceptive effect of brain‐derived neurotrophic factor (BDNF) following infusion into the midbrain, near the periaqueductal grey and dorsal raphe nuclei. BDNF administration attenuated the behavioural response in the tail‐flick and hot‐plate tests, two models employing a phasic, thermal high‐intensity nociceptive stimulus; the present studies extend our previous findings to include a model of moderate, continuous pain resulting from a chemical stimulus, the formalin test. Midbrain infusion of BDNF decreased the behavioural paw flinch response to subcutaneous formalin injection in both the early and late phases of the test. As our previous studies showed that BDNF‐induced analgesia was reversible by naloxone, we have examined the effects of BDNF administration on brain and spinal cord levels of neuropeptides involved in the modulation of nociceptive information, including the endogenous opioid peptides, met‐enkephalin and P‐endorphin, as well as substance P and neuropeptide Y (NPY). At the site of infusion, within the PAG and dorsal raphe, BDNF increased the level of β‐endorphin by 63%, but had no effect on substance P, metenkephalin or NPY levels. In the dorsal spinal cord, substance P (113% increase), β‐endorphin (97% increase) and NPY (64% increase) were elevated, although ventral spinal cord levels of these peptides remained unchanged. These studies demonstrate a modulatory effect of BDNF on relevant neuropeptides within areas of the brain and spinal cord involved in the processing of nociceptive information.