bluuebunny/crossref_metadata_2025 huggingface dataset:
The Extracellular Matrix Molecule Tenascin: Expression in the Developing Chick Retinotectal System and Substrate Properties for Retinal Ganglion Cell Neurites In vitro
Authors: Bartsch Susanne , Husmann Knut , Schachner Melitta , Bartsch Udo
Published: April 2006

To investigate the molecular mechanisms involved in the outgrowth of retinal ganglion cell axons in the tectum, the expression of the extracellular matrix molecule tenascin was analysed in the tectum and retina of chickens by immunocytochemistry and in situ hybridization. Tissue was analysed between embryonic days 4 and 12, just before and during the period when retinal ganglion cell axons innervate their target region, the optic tectum. In the tectum, tenascin immunoreactivity becomes detectable at the anterior pole at embryonic day 4, 2 days before retinal ganglion cell axons arrive, and spreads caudally with increasing age. At early stages, tenascin is predominantly accumulated in the stratum opticum, the zone of ingrowing retinal ganglion cell axons, and along their prospective pathway. In the stratum opticum, the molecule is associated with radial glial fibres, glial endfeet and retinal ganglion cell axons located in the immediate neighbourhood of radial glial fibres. At all ages investigated, tenascin mRNA is mainly restricted to cells located in the periventricular region, suggesting that the molecule is synthesized by radial glial cells. In the retina, tenascin is expressed by amacrine, displaced amacrine and horizontal cells but not by retinal ganglion cells. To investigate whether the accumulation of tenascin in the developing and prospective pathway of retinal ganglion cell axons may affect their rate of growth we assayed the substrate properties of tenascin for retinal ganglion cell neurites in vitro. When retinal ganglion cell suspensions from 6–day‐old chick embryos were maintained on homogeneous mouse or chick tenascin/ polyornithine substrates, neurite length was significantly increased when compared to polyornithine substrates at coating concentrations of 10 or 20 μg/ml. Higher coating concentrations (35 or 70 μg/ml) resulted in neurite lengths comparable to control values. Together, these observations suggest that tenascin in the developing and prospective stratum opticum might serve as a preformed pathway to support growth of retinal ganglion cell axons in the tectum.
A Combined Retrograde Tracer and GABA‐immunocytochemical Study of the Projection from Nucleus Interpositus Posterior to the Posterior Lobe c2 Zone of the Cat Cerebellum
Authors: Kolston Jacqueline , Apps Richard , Trott Judy R.
Published: April 2006

The extent to which the cells of origin of the cerebellar nucleocortical pathway are immunopositive for γ‐aminobutyric acid (GABA) was investigated in four cats using retrograde labelling of nucleocortical neurons in combination with immunocytochemistry. Neurons were retrogradely labelled by injection of fluorescent (coumarin)‐tagged latex microspheres into the c2 zone in the rostral part of the paramedian lobule. The zone was identified electrophysiologically by the characteristics of the climbing fibre responses evoked on the cerebellar surface by percutaneous stimulation applied to the left and right forepaws in pentobarbitone‐anaesthetized animals. Sections of the cerebellum containing the retrogradely labelled neurons were processed for GABA immunocytochemistty using a fluorescent (rhodamine)‐tagged immunoglobulin. When viewed with epifluorescence microscopy and appropriate filter blocks the retrogradely labelled nucleocortical neurons could be visualized in the same sections as the GABA‐immunopositive neurons. Almost all of a total of 254 labelled nucleocortical neurons were located in nucleus interpositus posterior, where a total of 711 GABAergic neurons were also found. None of these cells contained coumarin‐tagged beads and displayed immunoreactivity for GABA (i.e. none was double‐labelled). When compared by area of their cell body, the nucleocortical and GABA‐immunopositive neurons appeared to form two partially overlapping populations. The mean cell area of the nucleocortical neurons was 620 ± 233 pm2 (SD), whereas the GABA‐immunopositive neurons were much smaller, with a mean cell area of 220 ± 115 pm2. The results suggest that GABA does not play a major role in the nucleocortical pathway to the c2 zone of the rostral paramedian lobule of the cat cerebellum.
Marginal Cells in the Spinal Cord of Four Elasmobranchs (Torpedo marmorata, T. torpedo, Raja undulata and Scyliorhinus canicula): Evidence for Homology with Lamprey lntraspinal Stretch Receptor Neurons
Authors: Anadón Ramon , Molist Pilar , Pombal Manuel Angel , Rodríguez‐Moldes Isabel , Rodicio Maria Celina
Published: April 2006

This study reports for the first time the presence of marginal cells, probably with stretch receptor function, in the spinal cord of four elasmobranch species, two electric rays, Torpedo marmorata and T. torpedo, the skate Raja undulata and the dogfish Scyliorhinus canicula. In all four species, the marginal cells were located close to the lateroventral surface of the cord and possessed thick dendrites which formed part of characteristic glomerular structures. In vitro retrograde labelling of the spinal cord of the dogfish with horseradish peroxidase (HRP) showed that some of these cells have contralateral projections. Ultrastructural study of normal and retrograde HRP‐labelled material showed that the glomerular dendrites of marginal cells give rise to numerous fingerlike structures and are associated with a rich plexus of nerve terminals. Characteristically, these dendrites contain numerous mitochondria. Immunocytochemical studies revealed a rich plexus of somatostatin‐ and GABA‐immunoreactive fibres in the glomeruli. These results strongly suggest that the marginal cells of the elasmobranch spinal cord are stretch receptors homologous to lamprey edge cells and to the marginal nucleus cells of the spinal cord of urodeles and snakes. We discuss the possible role of these cells in the modulation of swimming movements.
Gene Expression and In Vitro Release of Galanin in Rat Hypothalamus During Development
Authors: Giorgi S. , Forloni G. , Baldi G. , Consolo S.
Published: April 2006

The expression and distribution of the mRNA coding for galanin precursor, preprogalanin (ppGAL), were analysed in several rat hypothalamic nuclei (periventricular, paraventricular, supraoptic, dorsomedial and arcuate nuclei and the lateral hypothalamic area) during development by an in situ hybridization technique and computer‐assisted grain counting over individual cells. ppGAL mRNA (expressed as number of grains/100 pm2) was detectable from postnatal day (PD) 1 in all the nuclei considered, and the amount of transcript per cell was 6–11 times less than in the adult. ppGAL mRNA progressively increased from PD8 to 14 to 21. The level of ppGAL mRNA in all the nuclei at PD21 was about half that in adulthood, except in the dorsomedial nucleus, where the difference was no more than 20%. As an index of the activity of galanin‐containing neurons, we measured the basal and K+‐evoked in vitro release of galanin‐like immunoreactivity from hypothalamic slices of PD14, 21 and 90 rats by radioimmunoassay. Basal release of galanin‐like immunoreactivity remained at the same level from PD14 to PD90, but the response to KCI (50 mM) stimulation was lower at PD14 (‐90%) and PD21 (>200%) than at PD90 (350%). Basal and K+‐evoked release was sensitive to tetrodotoxin, indicating a neuronal origin. This study provides the first evidence that the increase in ppGAL mRNA during the ontogeny of hypothalamic nuclei is associated with an increase in galaninergic neuronal function.
Expression of Endopeptidase‐24.11 (Common Acute Lymphoblastic Leukaemia Antigen CDI0) in the Sciatic Nerve of the Adult Rat After Lesion and During Regeneration
Authors: Kioussi Chrissa , Mamalaki Avgi , Jesse Kristjan , Mirsky Rhona , Hersh Louis B. , Matsas Rebecca
Published: April 2006

Endopeptidase‐24.11, which is identical with the common acute lymphoblastic leukaemia antigen CD1O (CALLA), is a cell surface Zn2+ metalloprotease that regulates peptide‐induced responses in different tissues, including the nervous and immune systems. In the peripheral nervous system, high levels of the enzyme are present in all neonatal and early postnatal Schwann cells, while as myelination proceeds it is gradually suppressed in the majority of cells that form myelin but retained in non‐myelin‐forming cells in the adult animal. In the present study we have investigated the effects of transection, crush and regeneration of the adult rat sciatic nerve on the expression of the endopeptidase by Schwann cells in situ. Endopeptidase‐24.11 was monitored by immunocytochemistry using the monoclonal anti‐endopeptidase antibody 23811. For comparison, a parallel study was carried out with a monoclonal antibody directed against the rat nerve growth factor receptor. We found that (i) all Schwann cells of the distal segment re‐expressed endopeptidase‐24.11 as early as 4 days after axotomy, the level of immunostaining reaching a maximum after 2 weeks, (ii) axonal regeneration repressed Schwann cell expression of endopeptidase‐24.11, and (iii) the induction of the nerve growth factor receptor followed a similar pattern to that of endopeptidase‐24.11 in the transected and crushed nerve. Enzymatic amplification of endopeptidase‐24.11 cDNA from normal and axotomized adult rat sciatic nerve confirmed the expression of endopeptidase‐24.11 in these tissues. Our results show that the expression of endopeptidase‐24.11 in Schwann cells, as is the case with the nerve growth factor receptor, is induced by the loss of the normal axon‐Schwann cell contact. The significant increase in the expression of endopeptidase‐24.11 by Schwann cells after axonal damage suggests that the enzyme could play a role in axonal regeneration.
Cholecystokinin Octapeptide In Vitro and Ex Vivo Strongly Modulates Striatal Dopamine D2 Receptors in Rat Forebrain Sections
Authors: Li X.‐M. , Hedlund P. B. , Fuxe K.
Published: April 2006

Receptor autoradiographic experiments together with the filter wipe‐off technique were performed to investigate the effects of cholecystokinin octapeptide (CCK‐8) on dopamine D2 receptors. In vitro studies showed that 1 nM CCK‐8 significantly increased the KD value of binding sites for the D2 agonist [3H]N‐propylnorapomorphine (NPA) in the rostral and caudal parts of the nucleus accumbens by 48 and 148% respectively. In contrast, 1 nM CCK‐8 significantly decreased the IC50 value of dopamine for binding sites for the D2 antagonist [125I]iodosulpride in the rostral and caudal parts of the caudate‐putamen by 46 and 56% respectively, and in the rostral and caudal parts of the nucleus accumbens (areas of CCK‐dopamine coexistence) by 57 and 75% respectively. Ex vivo studies demonstrated that 30 min after an intraventricular injection of 1 nmol/rat CCK‐8 the KD value of [3H]NPA binding sites in the caudal part of the forebrain and the IC50 value of dopamine for [125I]iodosulpride binding sites in the caudal part of the nucleus accumbens were significantly increased by 160% and decreased by 77% respectively. These results indicate for the first time that in sections CCK‐8 in vitro and ex vivo can strongly regulate D2 receptor affinity in the striatum. The present studies also provide evidence for stronger modulation of D2 receptors by CCK‐8 in the area of CCW‐dopamine coexistence in the nucleus accumbens than in other basal ganglion areas, supporting the existence of CCWD2 receptor interactions in cotransmission. The stronger interactions found in sections than in membrane preparations may indicate the requirement of intracellular mechanisms and/or a more intact membrane structure for optimal receptor‐receptor interactions.
Evidence for Cis Interaction and Cooperative Signalling by the Heat‐stable Antigen Nectadrin (murine CD24) and the Cell Adhesion Molecule L1 in Neurons
Authors: Kadmon Guni , von Bohlen und Halbach Friedrich , Horstkorte Rüdiger , Eckert Marion , Altevogt Peter , Schachner Melitta
Published: April 2006

L1 is a transmembranal hornophilic cell adhesion molecule of the immunoglobulin superfamily expressed by neural and lymphoid cells. The heat‐stable antigen (HSA, murine CD24) nectadrin is a highly and heterogeneously glycosylated glycophosphatidylinositol‐linked differentiation antigen of haematopoietic and neural cells. L1 and nectadrin have been shown to mediate cell adhesion and intracellular Ca2+ signals in neurons and B lymphoblasts, respectively. Here we show that nectadrin is co‐expressed with L1 in murine cerebellar granule cell neurons and neuroblastoma N2A cells. Purified nectadrin bound to L1 with an apparent binding ratio of five nectadrin molecules to one L1 molecule at saturation. Binding between nectadrin and purified N‐CAM was not observed. In co‐capping experiments nectadrin co‐redistributed with L1 and N‐CAM. Since in these cells N‐CAM and L1 cohere by cis binding nectadrin appears to join the L1‐N‐CAM complex through binding to L1. Antibodies to each L1 and nectadrin evoked small increases in the intracellular Ca2+ concentration. However, when both antibodies were added together or in tandem to the cells, a strong intracellular Ca2+ signal was measured that was at least 6‐ and 10‐fold stronger than the signal separately induced by L1 and nectadrin antibodies respectively. Such a cooperative effect was not observed in B lymphoblasts, using the same antibodies, or in neurons, using a combination of L1 and Thy‐1 antibodies. Both the weak Ca2+ signal mediated by L1 alone and the enhanced signal jointly triggered by antibodies to L1 and nectadrin were inhibited by phorbol 12‐myristate 13‐acetate and were not significantly affected by Ni2+ and Cd2+ cations, suggesting that they are related to one another and involve recruitment of intracellular Ca2+. Nectadrin therefore appears to join a functional complex of neuronal adhesion molecules and to potentiate the signal transduction pathway of L1, possibly in response to neuron‐neuron contact formation.
AMPA‐induced Lesions of the Basal Forebrain Differentially Affect Cholinergic and Non‐cholinergic Neurons: Lesion Assessment Using Quantitative In Situ Hybridization Histochemistry
Authors: Page Keith J. , Sirinathsinghji D. J. S. , Everitt Barry J.
Published: April 2006

The direct and transynaptic effects of lesions of the basal forebrain induced by α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid (AMPA) and ibotenic acid were investigated using quantitative in situ hybridization histochemistry. Probes complementary to the sequences of choline acetyltransferase mRNA, glutamate decarboxylase mRNA and preproenkephalin mRNA were used to assess direct lesion effects within the basal forebrain and probes for postsynaptic M‐1 and M‐3 muscarinic receptors were used to assess long‐term changes in neocortical muscarinic receptor mRNA expression following cholinergic deafferentation. AMPA‐induced basal forebrain lesions destroyed significantly more neurons that expressed choline acetyltransferase mRNA than ibotenic acid‐induced lesions (90 versus 60%), but significantly fewer neurons which expressed either glutamate decarboxylase or preproenkephalin mRNA (61 versus 83% reduction in glutamate decarboxylase mRNA and 56 versus 79% reduction in preproenkephalin mRNA). AMPA‐induced lesions did, however, destroy a significant proportion of the neurons which expressed glutamate decarboxylase and preproenkephalin mRNA (‐60%). The neurons spared following AMPA‐induced lesions were typically situated dorsolaterally within the dorsal pallidum, although neurons expressing glutamate decarboxylase or preproenkephalin mRNA were frequently observed within the areas of greatest cholinergic neuronal loss, i.e. the region of the nucleus basalis magnocellularis. These findings suggest that there is a population of non‐cholinergic pallidal neurons which are insensitive to AMPA but not to ibotenic acid, reflecting a possibly heterogeneous distribution of NMDA and non‐NMDA subtypes of glutamate receptors within the rat basal forebrain. AMPA‐induced lesions of the basal forebrain were, however, without significant effect on the levels of expression of M‐1 and M‐3 muscarinic receptor mRNAs in the cerebral neocortex.
The Distribution of Neurons Coexpressing Immunoreactivity to AMPA‐sensitive Glutamate Receptor Subtypes (GluR1‐4) and Nerve Growth Factor Receptor in the Rat Basal Forebrain
Authors: Page Keith J. , Everitt Barry J.
Published: April 2006

The regional distribution of neurons containing a‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid (AMPA) receptor (GluR1‐4) subunit immunoreactivity, relative to the distribution of cholinergic neurons within the basal forebrain of rats, was assessed using single‐ and dual‐antigen immunocytochemistry. Analysis of serial sections stained with antibodies to nerve growth factor receptor (NGFr) and antibodies against each of the AMPA receptor subunits, GluR1‐4, revealed a regional codistribution between NGFr‐ and GluR1‐ and GluR4‐immunoreactive neurons in the medial septum, diagonal band nuclei and nucleus basalis magnocellularis. Quantitative dual‐labelling immunocytochemistry using NGFr in combination with each of the GluR antibodies revealed >65% colocalization between NGFr and GluR4 in each of the major cholinergic nuclei in the basal forebrain and 10–15% colocalization between NGFr, GluR1 and GluR2‐3. The reticular nucleus of the thalamus, a structure known to be highly susceptible to AMPA‐induced neurotoxicity, expressed GluR4 immunoreactivity exclusively. The observation that cholinergic neurons of the basal forebrain are also highly sensitive to AMPA and express the GluR4 subunit suggests that GluR4 may be important in AMPA receptor‐mediated excitotoxicity.
The Effects of AMPA‐induced Lesions of the Medial Septum and Vertical Limb Nucleus of the Diagonal Band of Broca on Spatial Delayed Non‐matching to Sample and Spatial Learning in the Water Maze
Authors: McAlonan Gráinne M. , Dawson Gerard R. , Wilkinson Lynn O. , Robbins Trevor W. , Everitt Barry J.
Published: April 2006

These experiments investigated in the rat the impact on spatial delayed non‐matching to sample and on acquisition of the Morris water maze of (i) AMPA‐induced lesions of the medial septal nucleus, which produced a marked reduction of hippocampal choline acetyltransferase activity and acetylcholine levels (measured using in vivo dialysis) together with lesser reductions in cholinergic markers in the cingulate cortex and (ii) similar AMPA‐induced lesions of the vertical limb nucleus of the diagonal band of Broca (vDB), which produced more marked reductions in cholinergic markers in the cingulate cortex than in the hippocampus. Medial septal lesions produced a delay‐dependent deficit in spatial working memory, while lesions of the vDB resulted in a delay‐independent performance deficit. In addition, rats with vDB lesions adopted biased response strategies during the imposition of long delays. Neither lesion significantly affected the acquisition of a spatial reference memory task, the Morris water maze. The results are discussed in terms of cholinergic‐ and GABAergic‐dependent functions of the hippocampal formation and cingulate cortex in spatial short‐term and reference memory.
Cerebral Achromatopsia in Monkeys
Authors: Heywood C. A. , Gaffan D. , Cowey A.
Published: April 2006

In human cerebral achromatopsia, extrastriate cortical damage produces a severe or complete loss of colour vision, with relative sparing of non‐chromatic vision. The critical lesion appears to be in a medial occipito‐temporal area, occupying the lingual and caudal fusiform gyri; positron emission tomography has shown that this cortical region is one of several activated in normal human observers during colour vision tasks. Attempts to find an analogous ‘colour centre’ in the cortex of monkeys have not been successful. In particular, ablation of cortical area V4, sometimes thought on physiological grounds to be more involved in wavelength and colour coding than any other visual cortical area, produces only mild impairments in colour discrimination. In the present study we tested the colour vision of monkeys after cortical ablations that mainly or entirely spared area V4. One group of monkeys (group AT) received ablations in the temporal lobe anterior to area V4, and a second group (group MOT) received ablations in a medial occipito‐temporal area roughly corresponding in cranial location to the lesion that produces human cerebral achromatopsia. The animals in group MOT showed no impairment of their colour vision. Group AT, in contrast, had a severe impairment in chromatic vision, with a relative sparing of non‐chromatic vision. Their behaviour was indistinguishable from that of a human patient with total cerebral achromatopsia who had been tested on the same tasks. These results show that area V4 in macaque monkeys is not analogous, and probably not homologous, to the human colour centre. Instead, they suggest that the area of the monkey's brain corresponding to the colour area in the human brain is in the temporal cortex, anterior to area V4.
Peripheral Myelin Protein‐22 is Expressed in Rat and Mouse Brain and Spinal Cord Motoneurons
Authors: Parmantier E. , Cabon F. , Braun C. , D'Urso D. , Müller H. W. , Zalc B.
Published: April 2006

Peripheral myelin protein PMP‐22 is expressed by Schwann cells and is a constituent of peripheral nervous system (PNS) myelin. Two PMP‐22 transcripts, SR73 and CD25, differing in their 5’non‐coding sequences have been described. SR73 is present both in the PNS and in non‐neural tissue, whereas CD25 mRNA is almost exclusively expressed in Schwann cells. PMP‐22 mRNA is also present in the central nervous system (CNS), but at much lower levels than in the PNS. We have investigated the regional distribution of PMP‐22 mRNA in the rat and mouse CNS by the reverse transcriptase‐polymerase chain reaction method, using oligonucleotide primers specific for the SR73 or CD25 transcripts. SR73 mRNA was detected in all the CNS regions analysed, whereas the CD25 message was present only in the brainstem and the spinal cord. Localization of the PMP‐22 transcripts, determined by in situ hybridization in 21 day‐old animals, showed selective expression in the motor nuclei. The PMP‐22 signal was very weak in the nuclei of the oculomotor and trochlear nerves and absent in the nucleus of the abducens nerve. A strong PMP‐22 signal was observed in the motor nuclei of the trigeminal, facial, ambigus, vagus, hypoglossal and accessory spinal nerves and in the ventral horn of the spinal cord. The PMP‐22‐positive cells were identified as motoneurons on the basis of topographic and morphological criteria, as well as immunolabelling with neuron‐specific antibodies. Immunostaining with specific anti‐PMP‐22 antibodies demonstrated that neurons expressing the PMP‐22 message also expressed the corresponding protein in their cell bodies and axons. In contrast, neurons in the sensory nuclei of cranial nerves and dorsal root ganglion neurons were PMP‐22‐negative. In the trembler mouse, a PNS dysmyelinating mutant with a missense mutation in PMP‐22, the motoneuronal expression of PMP‐22 mRNA was either normal or increased.
Long‐lasting Potentiation of a Direct Central Connection between Identified Motor Neurons in the Locust
Authors: Parker David
Published: April 2006

The plasticity of the direct central connection between the fast extensor and the posterior fast flexor tibiae motor neurons in the locust (Schistocerca gregaria) metathoracic ganglion was studied. An action potential in the fast extensor results in a monosynaptic excitatory postsynaptic potential (EPSP) in the flexor motor neuron. Antidromic stimulation of the fast extensor at 100 Hz for 3.5 s resulted in a long‐lasting potentiation of the EPSP amplitude. The potentiation was not dependent on feedback caused by movement of the tibia, and was associated with an increase in the input resistance of the flexor motor neuron. The potentiation was heterosynaptic, and was not affected by bath application of the N‐methyl‐D‐aspartate receptor antagonist 2‐amino‐5‐phosphonovaleric acid. The potentiation was voltage dependent, as hyperpolarizing the flexor motor neuron during the stimulation blocked the development of the potentiation whereas depolarizing the flexor in the absence of presynaptic activity caused potentiation of subsequent fast extensor‐evoked EPSPs. The depolarization‐induced potentiation was calcium dependent. Antidromic stimulation of the fast extensor at 100 Hz for 3.5 s also caused modulation of the presynaptic action potential. The spike duration was increased and the amplitude of the afterhyperpolarization reduced. These effects were dependent on movement of the tibia. Bath application of the 5‐hydroxytryptamine (5‐HT) receptor antagonist ketanserin blocked the changes in the presynaptic spike. The modulation was probably due to the release of 5‐HT from proprioceptive afferents that monitor movement of the tibia about the femur. The modulation of the presynaptic action potential increases transmitter release onto the flexor motor neurons, and this acts in synergy with the postsynaptic modulation to potentiate the connection.
Synaptic Vesicle Depletion in Reticulospinal Axons is Reduced by 5‐hydroxytryptamine: Direct Evidence for Presynaptic Modulation of Glutamatergic Transmission
Authors: Shupliakov O. , Pieribone V. A. , Gad H. , Brodin L.
Published: April 2006

5‐hydroxytryptamine (5‐HT; serotonin) is known to depress glutamatergic synaptic transmission in the spinal cord of vertebrates. To test directly whether 5‐HT inhibits synaptic glutamate release, we examined its effect on the ultrastructure of synaptic vesicle clusters in giant reticulospinal axons in a lower vertebrate (lamprey; Lampetra fluviatilis). The size of these axons makes it possible to selectively expose only a part of the presynaptic element to 5‐HT, while another part of the same axon is maintained in control solution. Action potential stimulation at 20 Hz for 20 min caused a marked reduction in the number of synaptic vesicles in active zones maintained in control solution, while in the part exposed to 5‐HT (20 μM) the number of synaptic vesicles per active zone was ‐3‐fold higher. In contrast, 5‐HT had no effect on the number of vesicles in resting axons. To examine whether 5‐HT acts by reducing presynaptic Ca2+ influx, intra‐axonal recordings of Ba2+ potentials were performed. No reduction of the axonal Ba2+ potential could be detected after application of 20 or 200 pM 5‐HT. The present results show that 5‐HT reduces the rate of synaptic exocytosis in reticulospinal axons. The effect appears to be mediated by a mechanism distinct from the presynaptic Ca2+ channels.
Trans‐synaptic Modulation of Striatal ACh Release In Vivo by the Parafascicular Thalamic Nucleus
Authors: Baldi Gianni , Russi Giovanni , Nannini Luca , Vezzani Annamaria , Consolo Silvana
Published: April 2006

Electrical stimulation of the parafascicular but not the ventrolateral or dorsomedial thalamic nucleus (ten 0.5 ms, 10 V pulses, 140 pA) of freely moving rats induced a frequency‐dependent (2.5, 5,10 and 20 Hz) increase in the extracellular acetylcholine (ACh) content of the dorsal striatum, assessed by trans‐striatal microdialysis. The time‐dependent effect of 10 Hz stimulation was studied. The peak increase, 39% above baseline, was attained during 4 min of stimulation. This was blocked by coperfusion with 5 pM tetrodotoxin, indicating that the release we measured represents a physiological process. The facilitatory effect of parafascicular nucleus stimulation does not appear to be associated with indirect action through the cerebral frontal cortex because acute lesion of the excitatory corticostriatal afferents, which by itself reduced basal ACh release by 40%, did not modify the effect of 10 Hz stimulation. The possible involvement of the fasciculus retroflexus in the facilitation of ACh release was also ruled out. The non‐competitive NMDA‐type receptor antagonist MK‐801, applied by reversed dialysis (30 pM) or systemically injected (0.2 mg/kg), significantly reduced the basal ACh output and prevented the tetanus‐evoked increase in ACh release. The results provide in vivo evidence that the activity of the cholinergic neurons in the dorsal striatum is trans‐synaptically modulated by parafascicular nucleus excitatory afferents through activation of the NMDA subtype of glutamate receptors that is probably located in the striatum.
Comparing Localization of Conventional Functional Magnetic Resonance Imaging and Magnetoencephalography
Authors: Beisteiner R. , Gomiscek G. , Erdler M. , Teichtmeister C. , Moser E. , Deecke L.
Published: April 2006

The technique of functional magnetic resonance imaging (FMRI) allows the measurement of functional cerebral blood flow changes occurring with specific tasks. However, the spatial relationship between neuronal activity and functional cerebral blood flow changes is not kno'wn yet. This study compares the centre of neuronal activation (measured by magnetoencephalography) with that of the blood flow response (measured by FMRI) to unilateral motor stimulation in eight subjects. The results show a mean localization difference of 1.6 cm and demand application of methodological improvements as recently suggested.
Involvement of Serotonin in Developmental Plasticity of Kitten Visual Cortex
Authors: Gu Qiang , Singer Wolf
Published: April 2006

During a critical period of postnatal development, neuronal connections in the kitten visual cortex are susceptible to experience‐dependent modifications. These modifications are facilitated by the neuromodulators noradrenaline and acetylcholine. To address the question of whether serotonin (5‐hydroxytryptamine; 5‐HT), the other major neuromodulator in the cerebral cortex, also plays a role in developmental plasticity, we investigated whether interference with serotoninergic transmission in the kitten visual cortex affects ocular dominance (OD) plasticity. The serotonin neurotoxin 5,7‐dihydroxytryptamine or the serotonin receptor blockers ketanserin and methysergide were infused into the visual cortex of kittens undergoing monocular deprivation. We found that both methods of disrupting serotoninergic transmission reduced OD plasticity. However, to be effective, the receptor blockers ketanserin and methysergide had to be applied in combination, suggesting that coactivation of serotonin receptor subtypes of both the 5‐HT1 and 5‐HT2 families have a permissive function in OD plasticity. Since activation of 5‐HT2 receptors stimulates phosphoinositide hydrolysis, our data suggest that second messengers from the phospholipid pathway may play an important role in developmental plasticity of visual cortex.
Failure of Axon Regeneration in Postnatal Rat Entorhino‐hippocampal Slice Coculture is Due to Maturation of the Axon, not that of the Pathway or Target
Authors: Li D. , Field P. M. , Raisman G.
Published: April 2006

Horizontal slices which included the entorhinal area in continuity with the hippocampus were taken from the ventral levels of the cerebral hemispheres of rat pups from two age groups, from the 6th to the 8th postnatal days (‘young') and the 12th to the 15th days (‘old’). The slices were divided into an entorhinal part and a hippocampal part (which consisted of the hippocampus proper, dentate gyrus and subiculum) by a knife cut passing through the deep white matter of the entorhinal area. The slices were recombined in their normal orientation by matching the cut edges in the following age combinations: young/young, old/old, young/old and old/young. After 14 days in culture, crystals of biocytin were placed on the superficial layers of the entorhinal area. In the young/young combination the same placement of biocytin simultaneously labelled projections passing in both directions across the interface, i.e. (i) orthograde transport of biocytin taken up by entorhinal projection neurons resulted in labelling of axons passing from the entorhinal area across the interface between the cocultures to reach the correct terminal zone in the outer molecular layer of the dentate gyrus, and (ii) retrograde transport of biocytin taken up by axons and their terminals in the entorhinal area labelled the slender subicular and adjacent hippocampal field CA1 pyramidal cells whose axons project to the entorhinal area. In the old/old cocultures there were no projections in either direction. In the mixed age combinations, young entorhinal cortical tissue projected correctly across the interface to old dentate gyrus, but old entorhinal tissue did not project to young dentate gyrus. Conversely, the pyramids of young subicular tissue projected across the interface to old entorhinal tissue, but old subicular tissue did not project to young entorhinal cortex. Therefore, the crucial factor in the age‐related failure of the formation of projections was the age of the axons of the projecting neurons. The fail‐age for the formation of entorhino‐dentate projections was the same as that for the formation of the subiculo‐entorhinal projections passing in the opposite direction across the same interface. Thus the greater age of the pathway and the target fields did not prevent the younger axons from successfully finding their routes through the tissue and recognizing the correct terminal fields. General tissue factors, such as the formation of scar tissue and the onset of myelination (which occurs in the perforant path around the 10th day of life), also did not affect the outcome, since in the young/old and old/young combinations the projection failed in one direction across the interface while it succeeded in the opposite direction across the same interface.
5′‐Nucleotidase Activates and an Inhibitory Antibody Prevents Neuritic Differentiation of PC12 Cells
Authors: Heilbronn Alev , Zimmermann Herbert
Published: April 2006

Ecto‐5′‐nucleotidase catalyses the hydrolysis of AMP at the surface of a variety of cells whereas it is absent from others. In addition to its catalytic activity, a function in neural development and also its interaction with extracellular matrix proteins has been reported. In order to further elucidate the biological function of ecto‐5′‐nucleotidase we have investigated the effect of 5′‐nucleotidase on nerve growth factor‐induced differentiation of PC12 cells. Furthermore, we compared the effect of an inhibitory versus a non‐inhibitory monospecific antibody against the enzyme on neuritic differentiation and survival of PC12 cells that constitutively express the enzyme. When coverslips are coated with the soluble form of ecto‐5′‐nucleotidase in addition to collagen, there is a considerable increase in nerve growth factor‐induced neurite length during the first 24 h of culture. Addition of an antibody to a culture medium that inhibits 5′‐nucleotidase activity to 33% of control values dramatically reduces the number of neurites per cell within 3 days of culture. The cells round up, cluster and eventually die. On the contrary, another antibody that had no significant effect on enzyme activity affected neither nerve growth factor‐induced neurite formation nor survival of PC12 cells. Addition of adenosine (200 nM, 10 or 20 μM) to the culture medium did not influence PC12 cell differentiation. The effects induced by the inhibitory antibody could be only partially prevented by simultaneous application of adenosine. Our results suggest that 5′‐nucleotidase is essential for nerve growth factor‐induced neurite outgrowth and survival of PC12 cells. The results obtained cannot be simply explained on the basis of the availability and extracellular production of adenosine.
Response to Novelty and its Rapid Habituation in Locus Coeruleus Neurons of the Freely Exploring Rat
Authors: Vankov Andrey , Hervé‐Minvielle Anne , Sara Susan J.
Published: April 2006

Activity of single units of the noradrenergic nucleus locus coeruleus was recorded in rats during active exploration of a novel environment. Novelty was controlled by the placement of objects in given holes in a hole board. The basic protocol included a habituation session in which the holes were empty and an object session in which a novel object was placed in one of the two holes. During the habituation session, when the whole environment was unfamiliar, there was a phasic response the first time the rat visited any hole, which habituated after one visit. During the second session, when one of the holes contained an object, the cell fired when the rat encountered the novel object. There was no response to empty holes in this session. The neuronal response was markedly diminished or entirely absent on the second and subsequent visits to object‐containing holes, indicative of rapid habituation. In some rats it was possible to run a second object session, when a new object was introduced into a previously empty hole. Visits to this hole elicited a robust response, which again habituated after one single visit. The results show that the responses of locus coeruleus to novelty or change, which has been demonstrated in formal learning situations, occurs in freely behaving rats while they are learning about a new environment. Moreover, the response to novelty and change in the environment is short‐lived, rapidly habituating after one or two encounters with the stimulus.

This research was supported by grants from the Ministere de la Recherche et de la Technologie (MRT; 91C0956) and the CNRS Cognisciences Programme (ATIPE) to S. J. S., and by a collaborative grant from the European Neuroscience Programme of the European Science Foundation. A. V. is a visiting scientist from the Brain Research Institute of the Bulgarian Academy of Sciences, Sofia, and was supported by postdoctoral fellowships from the Fondation Pour La Recherche Medicale and from the CNRS. A. H. M. was supported by a predoctoral fellowship from the MRT. Gerard Dutrieux provided technical assistance in the development of the hole board apparatus.
Glycine‐ and GABA‐activated Currents in Identified Glial Cells of the Developing Rat Spinal Cord Slice
Authors: Pastor Andrea , Chvátal Alexandr , Syková Eva , Kettenmann Helmut
Published: April 2006

In the neonatal rat spinal cord, four types of glial cells, namely astrocytes, oligodendrocytes and two types of precursor cells, can be distinguished based on their membrane current patterns and distinct morphological features. In the present study, we demonstrate that these cells respond to the inhibitory neurotransmitters glycine and GABA, as revealed with the whole‐cell recording configuration of the patch‐clamp technique. All astrocytes and glial precursor cells and a subpopulation of oligodendrocytes responded to glycine. The involvement of glycine receptors was inferred from the observation that the response was blocked by strychnine and that the induced current reversed close to the Cl‐ equilibrium potential. GABA induced large membrane currents in astrocytes and precursor cells while oligodendrocytes showed only small responses. The GABA‐activated current was due to the activation of GABAA receptors since muscimol mimicked and bicuculline blocked the response; moreover, the reversal potential was close to the Cl‐ equilibrium potential. Besides the increase in a Cl‐ conductance, GABAA receptor activation also induced a block of the resting K+ conductance, as observed previously in Bergmann glial cells. Our experiments show that while glial GABAA receptors are found in many brain regions and the spinal cord, glial glycine receptors have so far been detected only in the spinal cord. The restricted coexpression of glial and neuronal glycine receptors in a defined central nervous system grey matter area implies that such glial receptors may be involved in synaptic transmission.
Effects of Nigrostriatal Denervation and L‐Dopa Therapy on the GABAergic Neurons of the Striatum in MPTP‐treated Monkeys and Parkinson's Disease: An In Situ Hybridization Study of GAD67 mRNA
Authors: Levy R. , Herrero M. T. , Ruberg M. , Villares J. , Faucheux B. , Guridi J. , Guillen J. , Luquin M. R. , Javoy‐Agid F. , Obeso J. A. , Agid Y. , Hirsch E. C.
Published: April 2006

The effects of nigrostriatal denervation and L‐dopa therapy on GABAergic neurons were analysed in patients with Parkinson's disease and in monkeys rendered parkinsonian by MPTP intoxication. The expression of the messenger RNA coding for the 67 kDa isoform of glutamic acid decarboxylase (GAD67 mRNA), studied by quantitative in situ hybridization, was used as an index of the GABAergic activity of the striatal neurons. A significant increase in GAD67 mRNA expression, generalized to all GABAergic neurons, was observed in MPTP‐treated monkeys compared to control monkeys in the putamen and caudate nucleus (+44 and +67% respectively), but not in the ventral striatum. L‐Dopa therapy significantly reduced GAD67 mRNA expression in the putamen and caudate nucleus to levels similar to those found in control monkeys. However, the return to normal of GAD67 mRNA expression was not homogeneous across all neurons since it was followed by an increase of labelling in one subpopulation of GABAergic neurons and a decrease in another. These data suggest that in MPTP‐treated monkeys the degeneration of nigrostriatal dopaminergic neurons results in a generalized increase in GABAergic activity in all the GABAergic neurons of the striatum, which is partially reversed by L‐dopa therapy. As the expression of GAD67 mRNA is less intense in the ventral than in the dorsal striatum, this increase in striatal GABAergic activity may be related to the severity of nigrostriatal denervation. In parkinsonian patients who had been chronically treated with L‐dopa, GAD67 mRNA expression was significantly decreased in all GABAergic neurons, in the caudate nucleus (by 44%), putamen (by 43.5%) and ventral striatum (by 26%). The opposite variation of GAD67 mRNA in patients with Parkinson's disease, compared with MPTP‐treated monkeys, might be explained by the combination of chronic nigrostriatal denervation and long‐term L‐dopa therapy.
Pattern Formation in the Mammalian Forebrain: Striatal Patch and Matrix Neurons Intermix Prior to Compartment Formation
Authors: Krushel Leslie A. , Fishell Gord , van der Kooy Derek
Published: April 2006

The striatum of the mammalian forebrain is divided into two compartments: the patches and the matrix. Neurons of the patch compartment in the rat striatum become postmitotic earlier in neurogenesis than neurons of the matrix compartment. The selective adhesion of patch neurons to one another has been suggested previously to be an important developmental mechanism of striatal compartmentation. We asked if the selective adhesion of patch neurons is expressed before or after the migration of the majority of the matrix neurons into the striatum. Patch neurons were labelled in vivo by a fluorescent retrograde tracer injected into the substantia nigra on embryonic day 19, which almost exclusively labelled patch neurons. Matrix neurons were labelled with a maternal injection of bromodeoxyuridine at embryonic day 18. When animals were killed at embryonic day 20, the majority of the retrogradely labelled patch neurons were intermixed with the bromodeoxyuridine‐labelled matrix neurons, although there appeared to be clustering of some of the patch neurons. However, by postnatal day 2 there was a complete segregation of the clusters of the retrogradely labelled patch neurons from the bromodeoxyuridine‐labelled matrix neurons in the striatum. This process was modelled in vitro. The patch and matrix compartments were labelled in vivo at embryonic day 13 and 18 respectively, with different birthdate markers ([3H]thymidine or bromodeoxyuridine). At embryonic day 20 the striatal tissue was removed, dissociated and reaggregated in suspension cultures. After 1 day in vitro, labelled patch and matrix neurons were randomly intermixed within the reaggregates. Examination of the cultures at 2.5 and 4 days in vitro revealed clumping of the labelled patch neurons towards the centres of the reaggregates. Over this same period, the labelled matrix neurons did not clump and were dispersed towards the periphery of the reaggregates. The results suggest that patch neuron adhesiveness may appear relatively soon after these neurons become postmitotic, but that this adhesiveness is unable to overcome the initial force produced by the massive migration of matrix neurons into the striatum. We hypothesize that a migratory phase of embryonic striatal development exists, when fated patch and matrix neurons intermix. After this migratory phase, patch neuron adhesiveness can produce the mature segregation of the striatal compartments.
Desensitization of AMPA Receptors Limits the Amplitude of EPSPs and the Excitability of Motoneurons of the Rat Isolated Spinal Cord
Authors: Ballerini Laura , Bracci Enrico , Nistri Andrea
Published: April 2006

Intracellular recording was used to study the effect of cyclothiazide, a selective blocker of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA) receptor desensitization, on lumbar motoneurons of the rat isolated spinal cord. Cyclothiazide (25 μM) enhanced the responses to AMPA in a tetrodotoxin‐insensitive fashion, without affecting those produced by N‐methyl‐D‐aspartate or γ‐aminobutyric acid. Excitatory postsynaptic potentials (EPSPs) evoked by dorsal root stimulation were strongly potentiated in amplitude while paired‐pulse depression (produced by applying pairs of pulses at 2 s interval) of the EPSP was decreased. In the presence of cyclothiazide the frequency of spontaneous synaptic events was greatly increased and network‐driven bursting activity developed with eventual loss of electrical excitability. The present results suggest that pharmacological block of AMPA receptor desensitization led to strong excitation of motoneurons and indicate a physiological role of desensitization in protecting these nerve cells from overactivity.
Lines of Murine Oligodendroglial Precursor Cells Immortalized by an Activated neu Tyrosine Kinase Show Distinct Degrees of Interaction with Axons In Vitro and In Vivo
Authors: Jung M. , Krämer E. , Grzenkowski M. , Tang K. , Blakemore W. , Aguzzi A. , Khazaie K. , Chlichlia K. , von Blankenfeld G. , Kettenmann H. , Trotter J.
Published: April 2006

Replication‐defective retroviruses expressing the t‐neu oncogene, or a hybrid protein with the neu tyrosine kinase linked to the external region of the human epidermal growth factor receptor (egfr‐neu), were used to establish lines of murine oligodendroglial precursor cells. Differentiation of the t‐neu lines into myelin‐associated glycoprotein (MAG)‐positive oligodendrocytes was induced by dibutyryl cAMP, and the egfr‐neu line showed limited differentiation in vitro upon withdrawal of epidermal growth factor. Cerebellar granule cell neurons expressed mitogens for the cell lines. Upon transplantation into demyelinated lesions, t‐neu line cells engaged with the demyelinated axons whereas the egfr‐neu line cells differentiated further and ensheathed the axons. These cell lines thus interact with neurons in vitro and in vivo and can be used as tools to define the molecules involved in different stages of neuron‐glia interaction.
Role of Bcl‐2 in the Brain‐derived Neurotrophic Factor Survival Response
Authors: Allsopp Timothy E. , Kiselev Sergei , Wyatt Sean , Davies Alun M.
Published: April 2006

Developing neurons die if they fail to obtain an adequate supply of neurotrophins from their targets but how neurotrophins suppress cell death is not known. Although over‐expression of exogenous Bcl‐2 can prevent the death of cultured neurons deprived of members of the nerve growth factor family of neurotrophins it is not known if this effect is physiologically relevant. To determine if Bcl‐2 participates in the neurotrophin survival response we used antisense bcl‐2 RNA to inhibit endogenous Bcl‐2 expression. Here we show that brain‐derived neurotrophic factor (BDNF)‐dependent neurons are killed by antisense bcl‐2 RNA in the presence of BDNF. However, when these neurons were supported with ciliary neurotrophic factor (CNTF) their survival was not affected by antisense bcl‐2 RNA. Likewise, the survival of CNTF‐dependent ciliary neurons was not affected by antisense bcl‐2 RNA. Our findings suggest that Bcl‐2 is required for the BDNF survival response and that alternative, Bcl‐2‐independent survival mechanisms operate in sensory and parasympathetic neurons exposed to CNTF.