bluuebunny/crossref_metadata_2025 huggingface dataset:
The Neural Correlates of the Noradrenergic Modulation of Human Attention, Arousal and Learning
Authors: Coull J. T. , Frith C. D. , Dolan R. J. , Frackowiak R. S. J. , Grasby P. M.
Published: April 2006

The prefrontal cortex has been suggested as a site of action for the noradrenergic modulation of cognition. In healthy volunteers attentional deficits can be induced by the α2 adrenoceptor agonist clonidine, without impairment of more explicit tests of frontal lobe function. It is therefore possible that the effects of noradrenaline cannot be localized to a specific brain area such as the prefrontal cortex, but instead involve structures in a more widespread attentional network. A 1.5 μg/kg dose of clonidine or placebo was administered to 13 healthy male volunteers performing the rapid visual information processing task, which places demands on both sustained attention and working memory. Twelve positron emission tomography measurements of regional cerebral blood flow (rCBF) were collected during performance of this task and also during a rest state. A second experiment in 12 healthy volunteers examined the effects of a 1.3 μg/kg dose of clonidine on the rCBF changes associated with performance of a paired associates learning task compared with passive listening to word pairs. Comparison of each of the experimental tasks with its respective control replicated previous findings. A significant drug × task interaction, common to the two studies, was found in the right thalamus. Inspection of the adjusted rCBF values showed that the effect was due to attenuation of thalamic rCBF during the control states rather than to any effects of clonidine during performance of the cognitive tasks, although the effect was stronger in the rapid visual information processing study than in the paired associates learning study. The significant effect of clonidine during the control as opposed to the ‘cognitive’ activation state is consistent with previous findings in animals and humans demonstrating greater effects of clonidine during states of relatively low arousal. The results suggest neuroanatomical dissociation of the noradrenergic modulation of arousal (via the thalamus) and attention.
Follicular Tissues Reduce Drug Effects on Ion Channels in Oocytes of Xenopus laevis
Authors: Madeja Michael , Musshoff Ulrich , Speckmann Erwin‐Josef
Published: April 2006

The influence of follicular tissues on drug effects on ion channels in Xenopus oocytes was tested by investigating the pharmacological properties of a cloned potassium channel in oocytes with and without follicular tissues. The data show that the efficacy of blocking agents (ranging from metal ions to peptides) is drastically reduced by the follicular tissues (reductions by as much as 90% and increases of the IC50 values up to 30–fold). Furthermore, the time course of the blocking effect was slowed down by the tissues (increases of the t50 values up to 40–fold). The described impairment could be mitigated, but not abolished by partial removal of the follicular tissues (so‐called defolliculation, leaving only the vitelline envelope and part of the follicle cells on the oocyte surface). The results indicate that the follicular tissues can induce significant errors in pharmacological measurements on membrane proteins in Xenopus oocytes.
Anatomical Evidence for Rod Input to the Parvocellular Pathway in the Visual System of the Primate
Authors: Grünert Ulrike
Published: April 2006

The question whether midget bipolar cells in macaque monkey retina receive input from rods was investigated using double‐label immunocytochemistry. Flat midget bipolar cells (labelled with antibodies against recoverin) were found to be pre‐ and postsynaptic to All amacrine cells (labelled with antibodies against calretinin). These results support physiological evidence that rod photoreceptor signals could reach the parvocellular pathway at an early stage of visual processing.
Transient Up‐regulation of Ciliary Neurotrophic Factor Receptor‐α mRNA in Axotomized Rat Septa1 Neurons
Authors: Lee Mun‐Yong , Naumann Thomas , Kirsch Matthias , Frotscher Michael , Hofmann Hans‐Dieter
Published: April 2006

Using non‐radioactive in situ hybridization we investigated the effect of fimbria‐fornix transection on the expression of ciliary neurotrophic factor receptor α (CNTFRα) mRNA in axotomized septohippocampal neurons of the rat septal complex. Whereas CNTFRα expression was undetectable in the medial septal nucleus/diagonal band complex (MSDB) of control animals, specific up‐regulation was observed in MSDB neurons after fimbria‐fornix transection. CNTFRα expression was maximal 7–10 days after the lesion and had returned to control levels after 3 weeks. Following unilateral fimbria‐fornix transection, CNTFRα up‐regulation was restricted to the MSDB ipsilateral to the lesion. When cholinergic septal neurons were selectively eliminated by immunolesioning with 192 IgG‐saporin prior to fimbria‐fornix transection, the lesion‐induced expression of CNTFRα was still observed in many medial septal nucleus neurons. These results demonstrate that after fimbria‐fornix transection CNTFRα expression is transiently induced in axotomized, non‐cholinergic neurons of the medial septal nucleus, suggesting a postlesion function of locally supplied CNTF.
Relation Between Dendritic Ca2+ Levels and the Polarity of Synaptic Long‐term Modifications in Rat Visual Cortex Neurons
Authors: Hansel Christian , Artola Alain , Singer Wolf
Published: April 2006

Long‐term changes of synaptic efficacy, in particular when they are use‐dependent, are candidate mechanisms for the storage of information in the nervous system. In a variety of brain structures, including the neocortex and hippocampus, synapses are susceptible to long‐term potentiation (LTP) and long‐term depression (LTD). It has been hypothesized that the polarity of the synaptic gain change depends on the amplitude of the postsynaptic [Ca2+]i rise, the threshold for the induction of LTD being lower than that for the induction of LTP. To test this assumption, we characterized Ca2+ signals in layer II/III pyramidal cells of rat visual cortex slices, using the fluorescent Ca2+ indicator fura‐2, during application of stimulation protocols that had been adjusted to reliably induce either LTP or LTD in cells not loaded with fura‐2. At dendritic sites activated by the stimulated afferents the intracellular [Ca2+] concentration ([Ca2+]i) reached higher amplitudes and decayed more slowly with stimuli inducing LTP than with those inducing LTD. To directly analyse the functional significance of the observed difference in the Ca2+ signal amplitude, we examined whether a tetanization protocol suitable for the induction of LTP can be converted into a protocol inducing LTD by injecting the postsynaptic cells with Ca2+ chelators that reduce the concentration of effective free Ca2+. In the presence of fura‐2 or BAPTA [bis(2‐aminophenoxy) ethane‐N,N,N′,N′‐tetraacetate], the stimulation protocol that would normally produce LTP induced either LTD or failed to induce synaptic modifications altogether. These results support the hypothesis that the amplitude of the postsynaptic rise in [Ca2+]i is a key factor in the determination of the polarity of synaptic gain change.
Deafferentation Weakens Excitatory Synapses in the Developing Central Auditory System
Authors: Kotak Vibhakar C. , Sanes Dan H.
Published: April 2006

Decreased excitatory synaptic activity during development often leads to pre‐ and postsynaptic atrophy, as assessed anatomically. The present study considers the effect of decreased excitatory transmission on the maturation of synaptic strength. Towards this end, cochlear nucleus neurons, which project to the ipsilateral lateral superior olive (LSO), were denervated in gerbils at postnatal day 7, before the onset of hearing. This manipulation was intended to disrupt spontaneous glutamatergic transmission in the LSO while sparing the glycinergic afferents from the medial nucleus of the trapezoid body (MNTB). Afferent‐evoked synaptic activity was assessed 1–6 days after ablation in a brain slice preparation using whole‐cell current‐ and voltage‐clamp recordings. In control animals, ipsilaterally evoked excitatory postsynaptic potentials (EPSPs) were present in 91% of neurons tested, but were observed in only 60% of neurons following cochlea removal. The maximum EPSP amplitude was significantly smaller in manipulated neurons compared with controls, and this was accompanied by a higher incidence of ipsilaterally evoked inhibitory postsynaptic potentials (IPSPs). To study the efficacy of excitatory synapses in greater detail, voltage‐clamp recordings were made in the presence of strychnine and AP‐5 [d(O)‐2‐amino‐5‐phosphonopentanoic acid]. The minimum excitatory postsynaptic current (EPSC) amplitude, presumed to reflect the efficacy of a single glutamatergic afferent, was ∼40% smaller in manipulated neurons. In contrast, MNTB‐evoked IPSPs were similar in neurons from control and ablated animals. However, manipulated neurons often exhibited a rebound depolarization after a hyperpolarizing current pulse or an afferent‐evoked IPSP. In 70% of manipulated neurons, synaptically evoked rebound depolarizations were reduced, but not eliminated, by glutamate receptor antagonists. The glycine receptor antagonist strychnine did eliminate the IPSP‐associated depolarization in these neurons. Collectively, these results suggest that functional denervation of excitatory afferents decreases their synaptic efficacy as result of both cell loss as well as decreased strength of individual surviving synapses.
Regulation of Cholinesterase Gene Expression Affects Neuronal Differentiation as Revealed by Transfection Studies on Reaggregating Embryonic Chicken Retinal Cells
Authors: Robitzki Andrea , Mack Alexandra , Hoppe Ulrike , Chatonnet Arnaud , Layer Paul G.
Published: April 2006

In the embryonic chicken neuroepithelium, butyrylcholinesterase (BChE) as a proliferation marker and then acetylcholinesterase (AChE) as a differentiation marker are expressed in a mutually exclusive manner. These and other data indicate a coregulation of cholinesterase expression, and also possible roles of cholinesterases during neurogenesis. Here, both aspects are investigated by two independent transfection protocols of dissociated retina cells of the 6‐day‐old chick embryo in reaggregation culture, both protocols leading to efficient overexpression of AChE protein. The effect of the overexpressed AChE protein on the re‐establishment of retina‐like three‐dimensional networks (so‐called retinospheroids) was studied. In a first approach, we transfected retinospheroids with a pSVK3 expression vector into which a cDNA construct encoding the entire rabbit AChE gene had been inserted in sense orientation. As detected at the mRNA level, rabbit AChE was heterologously overexpressed in chicken retinospheroids. Remarkably, this was accompanied by a strong increase in endogenous chicken AChE protein, while the total AChE activity was only slightly increased. This increase was due to chicken enzyme, as shown by species‐specific inhibition studies using fasciculin. Clearly, total AChE activity is regulated post‐translationally. As an alternative method of AChE overexpression, transfection of spheroids was performed with an antisense‐5′‐BChE vector, which not only resulted in the down‐regulation of BChE expression, but also strongly increased chicken AChE transcripts, protein and enzyme activity. Histologically, a higher concentration of AChE protein (as a consequence of either AChE overexpression or BChE suppression) was associated with an advanced degree of tissue differentiation, as detected by immunostaining for the cytoskeletal protein vimentin.
Blockade of Basic Fibroblast Growth Factor Retards Recovery from Motor Cortex Injury in Rats
Authors: Rowntree Sharon , Kolb Bryan
Published: April 2006

The endogenous expression of basic fibroblast growth factor (bFGF) was blocked by neutralizing antibodies following unilateral suction lesions of the motor cortex. Rats with control treatment (saline, goat IgG) after motor cortex lesions showed slow recovery of forelimb manipulatory abilities. Rats with blockade of bFGF expression showed little recovery. Anatomically, the control‐treated lesioned rats showed an acute increase in bFGF and glial fibrillary acidic protein (GFAP) reactivity, and chronically they had normal dendritic arborization and spine density in layer V pyramidal cells in the remaining motor cortex. In contrast, rats treated with antibodies to bFGF showed little bFGF reactivity, normal GFAP reactivity, and atrophy of dendritic arbor and decreased spine density in layer V pyramidal cells. These results demonstrate the importance of endogenous bFGF release in processes related to functional recovery after cortical injury.
Comparison of the Expression of c‐fos, nur77 and egr1 mRNAs in Rat Hypothalamic Magnocellular Neurons and their Putative Afferent Projection Neurons: Cell‐ and Stimulus‐specific Induction
Authors: Luckman Simon M.
Published: April 2006

Hypothalamic magnocellular neurons and their afferent inputs provide a model system in which to study the regulation of inducible transcription factors in the brain in vivo. Osmotic stimulation of rats produced by graded infusions of saline at different tonicities was found to lead to the induction of c‐fos, nur77 and egr1 mRNAs in magnocellular neurons, as well as in putative afferent neurons, including those in structures of the forebrain (subfornical organ, median preoptic nucleus and organum vasculosum of the lamina terminalis). The results presented suggest that stronger levels of osmotic stimulation recruit additional afferents from the forebrain and brainstem that can act on magnocellular neurons via alternative receptors. A single systemic injection of the peptide cholecystokinin produced robust induction of c‐fos and nur77 mRNAs in afferent neurons of the brainstem nucleus tractus solitarii and in magnocellular neurons. Despite the fact that these two neuronal populations are clearly electrically active, egr1 was not induced by this stimulus, providing examples of cell‐ and stimulus‐specificity of its expression. This study re‐emphasizes that the induction of transcription factors is largely dependent on the nature of the afferent input and does not correlate necessarily to the electrical activity of the neuron.
Effect of Cerebellar Granule Cell Depletion on Learning of the Equilibrium Behaviour: Study in Postnatally X‐irradiated Rats
Authors: Le Marec N. , Stelz T. , Delhaye‐Bouchaud N. , Mariani J. , Caston J.
Published: April 2006

To assess the role of the mossy fibre‐granule cell pathway in learning, the cerebellum of young DA/HAN strain rats was irradiated to make the cortex completely or partially agranular. The X‐rays were delivered according to two different schedules, between 5–14 postnatal days (early group) and between 10–14 postnatal days (late group). Histological controls at 35 days showed a mean loss of granule cells of 96 ± 1% in the early group and of 61 ± 3% in the late group. The irradiated animals were subjected, from day 23 to day 35, to daily sensorimotor training on a rotorod. The scores and the strategy used (walking or hanging) by the rats were noted. The results demonstrate that a partial loss of granule cells due to a late X‐irradiation schedule induced mild motor disabilities but no learning deficit, the only problem being difficulty in elaborating rapidly an efficient strategy to solve a novel problem. A sub‐total loss of the granule cells, due to an early X‐irradiation schedule, induced gross motor disabilities and the animals used hanging >90% of the time. Due to the discrepancy between the learning abilities, which were preserved at least in part, and the gross motor impairments, the animals elaborated a novel strategy (jumping from the beam), allowing them to escape the experimental situation. This avoidance behaviour may be due to a decrease of anxiety, a lack of behavioural inhibition and/or attentional deficits that have been already observed in several other examples of cerebellar abnormalities.
AMPA Receptors are Coupled to the Nitric Oxide/Cyclic GMP Pathway in Cerebellar Astroglial Cells
Authors: Baltrons María Antonia , Garcia Agustina
Published: April 2006

In cultured rat cerebellar astroglia kainate induces cGMP formation with low potency (EC50 310 μM). In the presence of cyclothiazide, a blocker of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionate (AMPA) receptor desensitization, the effect of kainate was potentiated and glutamate and AMPA elicited large increases (>100‐fold) in cGMP levels. The response to all three agonists was abolished by the nitric oxide synthase inhibitor NG‐nitro‐L‐arginine and required extracellular calcium. Uptake of Co2+ was induced by AMPA in a limited population of astroglial cells and this effect was potentiated by cyclothiazide. These results indicate that calcium‐permeable AMPA receptors mediate stimulation of nitric oxide formation in cerebellar astroglia. This effect may be relevant for glutamate‐dependent synaptic plasticity processes in the cerebellum.
Cloning, Chromosomal Localization and Functional Expression of the Gene Encoding the α‐Subunit of the cG‐MP‐Gated Channel in Human Cone Photoreceptors
Authors: Wissinger Bernd , Müller Frank , Weyand Ingo , Schuffenhauer Simone , Thanos Solon , Kaupp U. Benjamin , Zrenner Eberhart
Published: April 2006

Cyclic nucleotide‐gated (CNG) ion channels serve as final targets of signal transduction in vertebrate photoreceptors. While the basic mechanisms of phototransduction are similar in rod and cone photoreceptors, both cell types express distinct sets of components of the transduction pathway. We report here the cloning of the cDNA encoding the α‐subunit of the cGMP‐gated channel of human cone photoreceptors. The open reading frame predicts a polypeptide of 694 amino acid residues with conserved functional parts and amino acid positions typical for the α‐subunit of CNG‐channels. Heterologous expression of the cDNA in Xenopus oocytes gave rise to cGMP‐gated channel activity. Antiserum directed against the C‐terminus of the bovine cone CNG channel α‐subunit crossreacted specifically with the heterologously expressed polypeptide and stained cone photoreceptors and weakly also the outer plexiform layer in human retinal sections. Northern blot analysis detected a prominent mRNA species of ∼3.8 kb in human retina. The entire gene spans ∼30 kb of genomic sequence and is located on the pericentric band q11.2 of human chromosome 2. The gene is composed of seven exons, with introns located at positions which are preserved with respect to the human rod gene, indicating a common ancestral gene structure. RT‐PCR analysis gave no evidence for alternatively spliced transcripts.
Neurotransmitter Modulation of Gap Junctional Communication in the Rat Hippocampus
Authors: Velazquez Jose L. Perez , Han Dan , Carlen Peter L.
Published: April 2006

Increasing experimental evidence indicates that gap junctions can be modulated by neurotransmitters, in particular dopamine. To examine possible modulation of gap junctional communication in the rat hippocampus by neurotransmitters, we studied dye coupling and electrotonic transmission in the CAI area in the presence of carbachol, a cholinergic agonist, and dopamine agonists. Carbachol markedly reduced dye coupling and the frequency of electrotonic potentials (spikelets). Spikelet amplitudes were decreased in the presence of carbachol. These effects were reversed by the cholinergic antagonist atropine, suggesting a muscarinic action of carbachol on gap junctional function. The non‐specific dopamine agonist apomorphine, and the specific D1receptor agonist SKF 38393, reduced dye coupling between pyramidal cells. Spikelet frequency was also decreased in the presence of dopamine agonists, but less than with carbachol. The specific D1receptor antagonist, SCH 23390, reversed the effects of both dopamine agonists. These observations indicate that cholinergic and dopaminergic transmission can affect electrical and chemical (dye coupling) communication through gap junctions, and could therefore alter properties of neuronal assemblies, in addition to their effects on intrinsic membrane properties.
In vivo Amygdala Dopamine Levels Modulate Cocaine Self‐administration Behaviour in the Rat: D1 Dopamine Receptor Involvement
Authors: Hurd Y. L. , McGrego A. , Pontén M.
Published: April 2006

Nucleus accumbens dopamine is often hypothesized as the critical factor for modulating cocaine self‐administration. In the current study we examined the extent to which dopamine in the amygdala could contribute to cocaine intake behaviour and modify nucleus accumbens dopamine levels. Rats were trained to self‐administer intravenous cocaine (1.5 mg/kg/injection) under a fixed‐ratio reinforcement schedule in daily 3 h operant training sessions. In the first in vivo microdialysis experiment, extracellular dopamine levels were found to be increased 200% of baseline in the amygdala and by 400% in the nucleus accumbens. Although cocaine induced similar profiles of dopamine overflow in the two mesolimbic areas, in the nucleus accumbens the latency of the dopaminergic response was shorter (three‐ to four‐fold) during both initiation and termination of the cocaine self‐administration session than in the amygdala. Despite achieving a stable self‐regulated pattern of cocaine intake and high dopamine concentrations in the nucleus accumbens, a unilateral injection of the D1 receptor antagonist SCH 23390 (0.5 or 1.5 μg) into the amygdala was still able to increase the rate of cocaine intake. This behavioural effect was accompanied by a dose‐dependent increase in nucleus accumbens dopamine levels; at the highest SCH 23390 concentration cocaine intake was increased by 400% and dopamine levels were potentiated by an additional 400%. In vivo autoradiography using [3H]SCH 23390 showed that D1 receptor sites contributing to the behavioural and subsequent neurochemical effects were predominantly localized to the amygdala and not the nucleus accumbens. Altogether these results point to a significant contribution of in vivo amygdala D1 dopamine transmission to cocaine self‐administration behaviour.
VEGF mRNA Induction Correlates With Changes in the Vascular Architecture Upon Spinal Cord Damage in the Rat
Authors: Bartholdi Deborah , Rubin Beatrix P. , Schwab Martin E.
Published: April 2006

The multiple cellular and molecular processes induced by injury to the central nervous system (CNS) are still poorly understood. In the present study, we investigated the response of the vasculature and the expression of mRNA for the angiogenic vascular endothelial growth factor (VEGF) following X‐irradiation of the spinal cord in the newborn and following traumatic spinal cord injury in the adult rat. Both lesion models induced changes in the density and the distribution pattern of blood vessels: while X‐irradiation led to a permanent local increase in vascular density in the fibre tracts of the exposed segments, a transient local sprouting of vessels was induced upon traumatic spinal cord injury. In situ hybridization showed that an increase of VEGF mRNA anticipated and overlapped with the vascular responses in both lesion models. In addition to the temporal correlation of VEGF expression and vascular sprouting, there was a clear correlation in the spatial distribution patterns. Following X‐irradiation, the expression of VEGF mRNA was restricted to the fibre tracts, precisely the areas where the changes in the vasculature were observed later on. Upon transection in the adult animal, VEGF was mainly detectable at the border of the lesion area, where the transient increase in vascular density could be observed. Interestingly, according to the type of lesion applied, astrocytes (X‐irradiation) or inflammatory cells (presumably microglial cells or macrophages; traumatic lesion) are the cellular sources of VEGF mRNA. Our results strongly indicate that VEGF is crucially involved in mediating vascular changes following different types of injury in the CNS.
Neurotrophins Stimulate Chemotaxis of Embryonic Cortical Neurons
Authors: Behar T. N. , Dugich‐Djordjevic M. M. , Li Y‐X. , Ma W. , Somogyi R. , Wen X. , Brown E. , Scott C. , McKay R. D. G. , Barker J. L.
Published: April 2006

During mammalian cortical development, neuronal precursors proliferate within ventricular regions then migrate to their target destinations in the cortical plate, where they organize into layers. In the rat, most cortical neuronal migration occurs during the final week of gestation (Bayer et al., 1991; Jacobson, 1991). At this time (E15–E21), reverse transcriptase‐polymerase chain reaction demonstrated that cortical homogenates contain mRNA encoding brain derived neurotrophic factor (BDNF) and the catalytic form of its high‐affinity receptor, TrkB. lmmunocytochemistry and in situ hybridization of sections revealed that the catalytic TrkB receptors predominantly localize to regions containing migratory cells. Many TrkB+ cells exhibited the classic morphology of migrating neurons, suggesting that TrkB ligands play a role in cortical neuronal migration. We analysed whether TrkB ligands influence the motility of embryonic cortical cells (from E15–E21) using a quantitative in vitro chemotaxis assay. High‐affinity TrkB ligands (BDNF and NT4/5) stimulated chemotaxis (directed migration) of embryonic neurons at concentrations ranging from 1 to 100 ng/ml. NT‐3, a low‐affinity TrkB ligand, only stimulated significant migration at high concentrations (±100 ng/ml). Peak migration to BDNF was observed at gestational day 18 (E18). BDNF‐induced chemotaxis was blocked by either tyrosine kinase inhibitor, K252a, or the Ca2+‐chelator, BAPTA‐AM, suggesting that BDNF‐induces motility via autophosphorylation of TrkB receptor proteins and involves Ca2+‐dependent mechanisms. BDNF‐stimulation of increased cytosolic Ca2+ was confirmed with optical recordings of E18 cortical cells loaded with Ca2+ indicator dye. Thus, signal transduction through the TrkB receptor complex directs neuronal migration, suggesting that, in vivo, BDNF exerts chemotropic effects that are critical to morphogenesis of the cortex.
Phenotype Specification of Cortical Neurons During a Period of Molecular Plasticity
Authors: Obst Kirstin , Wahle Petra
Published: April 2006

The transient expression of neuropeptide transmitters is a common feature of the developing cortex. We have now analysed the role of cortical afferents in shaping the neurochemical architecture of rat visual cortex using organotypic cultures. Deafferented cortex monocultures prepared from newborn rats reveal a constant NPY mRNA expression in 6–8% of all cortical neurons up to 90 days in vitro (DIV). In contrast, afferent thalamocortical and corticocortical axonal innervation elicits a progressive reduction in the percentage of NPY mRNA expressing neurons from initially 6–8% in 30DIV cocultures to 2–3% and 3–4% respectively in 60DIV cocultures, which is maintained for up to 90DIV. This phenotype restriction is not observed in only efferently connected corticocollicular cocultures. Further, axonal innervation does not change the percentage of GAD mRNA‐expressing neurons, which remains at 13% in mono‐ and cocultures. When feeding thalamocortical cocultures with monoculture‐conditioned medium between 3–20DIV followed by normal medium up to 60DIV, the phenotype restriction fails to occur in the cocultured cortex. We conclude that cortex‐derived factors secreted into the medium by a monoculture suppress the phenotype‐restricting capacity of the afferents, but only when present within the first 14DIV during the period of formation of axonal connections. To elucidate the nature of the cortex‐derived factors, brain‐derived neurotrophic factor was applied to the medium. When applied for the first 14DIV, it does not prevent the phenotype restriction from occurring. This suggests that epigenetic factors such as axonal innervation and cortex‐derived factors other than brain‐derived neurotrophic factor govern a phenotype decision in neocortical neurons during a period of molecular plasticity.
Learning Deficit in BDNF Mutant Mice
Authors: Linnarsson Sten , Björklund Anders , Ernfors Patrik
Published: April 2006

Brain‐derived neurotrophic factor (BDNF) has been implicated in the regulation of high‐frequency synaptic transmission and long‐term potentiation in the hippocampus, processes that are also thought to be involved in the learning of spatial tasks such as the Morris water maze. In order to determine whether BDNF is required for normal spatial learning, mice carrying a deletion in one copy of the BDNF gene were subjected to the Morris water maze task. Young adult BDNF mutant mice were significantly impaired compared with wild‐type mice, requiring twice the number of days to reach full performance. Aged wild‐type mice performed significantly worse than young wild‐type mice and the effect was even more pronounced in the BDNF mutant mice, which did not learn at all. Although there was no difference in mean swimming speed between BDNF mutant and wild‐type mice, we cannot exclude the possibility that developmental or peripheral deficits also contribute to the learning deficits in these mice. In situ hybridization and RNase protection analysis revealed that BDNF mRNA expression was indeed decreased in BDNF mutant mice. Furthermore, a pronounced effect of age on BDNF mRNA expression was seen, displayed as both a reduced level of mRNA expression and a reduced or entirely absent layer‐specific expression pattern in the cerebral cortex of aged animals. Thus, our data suggest that BDNF expression may be linked to learning.
HERG‐ and IRK‐like Inward Rectifier Currents are Sequentially Expressed During Neuronal Development of Neural Crest Cells and their Derivatives
Authors: Arcangeli Annarosa , Rosati Barbara , Cherubini Alessia , Crociani Olivia , Fontana Lucrezia , Ziller Catherine , Wanke Enzo , Olivotto Massimo
Published: April 2006

Quail neural crest cells were cultured in a differentiative medium to study the inward K+ channel profile in neuronal precursors at various stages of maturation. Between 12 and 24 h of culture, neural crest‐derived neurons displayed, in addition to the previously described outward depolarization‐activated K+ currents, an inward current enhanced in high K+ medium. A biophysical and pharmacological analysis led us to conclude that this inward K+ current is identical to that previously demonstrated in mouse and human neuroblastoma cell lines (IIR). This current (quail IIR or qllR), which is active at membrane potentials positive to ‐35 mV, was blocked by Cs+ and by class Ill antiarrhythmic drugs, thus resembling the K+ current encoded by the human ether‐a‐go‐go‐related gene (HERG). At later stages of incubation (>48 h), neural crest‐derived neurons underwent morphological and biochemical differentiation and expressed fast Na+ currents. At this stage the cells lost qllR, displaying instead a classical inward rectifier K+ (IRK) current (quail IIRK= qIIRK). This substitution was reflected in the resting potential (VREST), which became hyperpolarized by >20 mV compared with the 24 h cells. Neurons were also harvested from peripheral ganglia and other derivatives originating from the migration of neural crest cells, viz. ciliary ganglia, dorsal root ganglia, adrenal medulla and sympathetic chain ganglia. After brief culture following harvesting from young embryos, ganglionic neurons always expressed qilR. On the other hand, when ganglia were explanted from older embryos (7–12 days), briefly cultured neurons displayed the IRK‐like current. Again, in all the above derivatives the qllR substitution by qllRK was accompanied by a 20 mV hyperpolarization of VREST. Together, these data indicate that the VREST of normal neuronal precursors is sequentially regulated by HERG‐ and IRK‐like currents, suggesting that HERG‐like channels mark an immature and transient stage of neuronal differentiation, probably the same stage frozen in neuroblastomas by neoplastic transformation.
Evidence from Confocal Fluorescence Microscopy for a Dense, Reciprocal Innervation Between AVP‐,somatostatin‐, VIP/PHI‐, GRP‐ and VIP/PHI/GRP‐immunoreactive Neurons in the Rat Suprachiasmatic Nucleus
Authors: Romijn H. J. , Sluiter A. A. , Pool C. W. , Wortel J. , Buijs R. M.
Published: April 2006

The rat suprachiasmatic nucleus (SCN) consists of several classes of neurons which can be identified by their transmitter content. Knowledge of putative interaction between these different cell types is essential in order to understand the possibilities of information processing within the SCN. The aim of the present study was therefore to obtain more information about the mutual innervation between the main cell classes in the rat SCN, viz. those containing the neuropeptides arginine vasopressin (AVP), vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI), gastrin‐releasing peptide (GRP) and somatostatin respectively. For this purpose, vibratome sections were double‐immunolabelled for seven different peptide combinations and subsequently analysed by high‐resolution confocal laser scanning fluorescence microscopy. Attention was focused on axosomatic appositions, the occurrence and frequency of which were quantitatively estimated. Our analysis of double‐immunolabelled sections demonstrated that some of the VIP‐ and some of the GRP‐immunoreactive nerve cells and endings showed colocalization. Assuming, on the basis of literature data, that VIP and PHI are always colocalized at the cellular level, the five main cell classes in the SCN appeared to be interconnected, at least axosomatically, in the following reciprocal way: AVP ↔ VIP/PHI, AVP ↔ GRP, AVP ↔ somatostatin, somatostatin ↔ VIP/PHI, somatostatin ↔ GRP, VIP/PHI ↔ GRP, VIP/PHI/GRP ↔ GRP, VIP/PHI/GRP ↔ VIP/ PHI. In addition to this heterologous axosomatic innervation, these cell groups also showed substantial homologous innervation. Supported by electron microscope data from the literature showing the existence of axodendritic synapses for some of these peptide combinations, our findings strongly suggest that the rat SCN comprises a complex synaptic network with strong interactive capabilities, which is probably a requisite for its biological clock function.
Pronase Acutely Modifies High Voltage‐activated Calcium Currents and Cell Properties of Lymnaea Neurons
Authors: Hermann P. M. , Lukowiak K. , Wildering W. C. , Bulloch A. G. M.
Published: April 2006

Pronase E (‘pronase’) is one of the proteolytic enzymes that are used in preparative procedures such as cell isolation and to soften the sheath of invertebrate ganglia. Although several effects of proteolytic enzymes on the physiology of non‐neuronal tissues have been described, the effects of these enzymes on central neurons have received little attention. We examined the effects of bath‐applied pronase on neurons in the Lymnaea central nervous system and in vitro. Pronase caused action potential broadening in neurons that exhibit a shoulder on the repolarization phase of their action potentials. This effect of pronase was accompanied by, although unrelated to, a depolarization and decrease in action potential interval. Some, but not all, effects of pronase in the central nervous system were reversible. For example, the decreases in membrane potential and action potential interval were both reversed after ∼1 h of washing with saline. However, the effect of pronase on the action potential duration was not reversed after a period of 90 min. The modulation of action potential width prompted us to examine Ca2+ currents. Exposure to pronase resulted in an increase in both peak and late high voltage‐activated Ca2+ currents in isolated neurons. Pronase neither changed the inactivation rate nor caused a shift in the current‐voltage relationship of the current. The changes in action potential duration could be prevented by application of 0.1 mM Cd2+, indicating that the action potential broadening caused by pronase depends on Ca2+ influx. This is the first systematic study of the acute and direct actions of pronase on Ca2+ currents and cell properties both in the CNS and in vitro.
The Role of the Mouse Macrophage Scavenger Receptor in Myelin Phagocytosis
Authors: da Costa Cristiane Cabral , van der Laan Luc J. W. , Dijkstra Christine D. , Brück Wolfgang
Published: April 2006

Myelin phagocytosis during Wallerian degeneration and immune‐mediated demyelination depends on the action of mononuclear cells of the monocyte/macrophage system. The present study investigated the role of the macrophage scavenger receptor, a trimeric membrane glycoprotein, in myelin uptake by macrophages. Two in vitro models of myelin phagocytosis were used: an organ culture model of mouse peripheral nerves exposed to cocultured macrophages and a quantitative flow cytometric assay. Different concentrations of the monoclonal rat anti‐mouse scavenger receptor antibody (2F8) were applied to these systems to selectively block the macrophage scavenger receptor. Concentration‐dependent effects on macrophage migration and myelin uptake were seen when the macrophage scavenger receptor was blocked by the antibody 2F8. Low concentrations reduced myelin phagocytosis by the invading macrophages; higher concentrations completely abolished macrophage invasion of the nerves. Using a quantitative flow cytometric assay it was also shown that the 2F8 antibody inhibits phagocytosis of myelin in a dose‐dependent manner. These data indicate that the macrophage scavenger receptor is involved in myelin phagocytosis by macrophages.
Localization of Putative Receptors for Tetanus Toxin and Botulinum Neurotoxin Type A in Rat Central Nervous System
Authors: Herreros J. , Marti E. , Ruiz‐Montasell B. , Casanova A. , Niemann H. , Blasi J.
Published: April 2006

Clostridial neurotoxins (tetanus and botulinum toxins) are potent blockers of neurotransmitter release. These toxins act specifically on the nervous system by interacting with still non‐identified protein receptors together with gangliosides. Whereas many biochemical data are available on their binding properties to neuronal membranes in vitro, there is poor morphological evidence of their binding to mammalian central nervous system. In the present study, the binding of tetanus and botulinum neurotoxin type A to rat brain sections is reported. Both toxins bound to nerve terminals with a broad distribution in brain. Tetanus toxin additionally bound to nerve fibres. The staining patterns were clearly shown to be due to the interaction of the heavy chains, which contain the binding moiety, with the tissue. In an attempt to investigate the nature of the acceptors present in the tissue, some sections were pre‐incubated with periodic acid. This treatment resulted in the additional binding of botulinum neurotoxin type A to nerve fibres. Since the extended staining of nerve terminals was not modified by this pretreatment, it is suggested that protein receptors of clostridial neurotoxins are located at the nerve terminals, which may be common constituents of the synapses.
NMDA Receptor Activation Triggers Voltage Oscillations, Plateau Potentials and Burstinq in Neonatal Rat Lumbar Motoneurons ln Vitro
Authors: MacLean Jason N. , Schmidt Brian J. , Hochman Shawn
Published: April 2006

Whole‐cell recordings of lumbar motoneurons in the intact neonatal rat spinal cord in vitro were undertaken to examine the effects of Kmethyl‐D‐aspartate (NMDA) receptor activation on membrane behaviour. Bath application of NMDA induced rhythmic voltage oscillations of 5.9 ± 2.1 mV (SD) at a frequency of 4.4 ± 1.5 Hz. Amplitude, but not frequency, of the voltage oscillations was membrane potential‐dependent. Voltage oscillations could recruit action potentials and/or plateau potentials with or without superimposed bursting. Blockade of synaptic transmission with tetrodotoxin (TTX) sometimes resulted in a loss of oscillatory activity which could then be restored by increasing the NMDA concentration. After application of TTX, the trajectory of NMDA‐induced oscillations was similar to the trajectory induced in the presence of intact synaptic networks, although the mean oscillation duration was longer and the oscillation frequency was slower (1.8 ± 1.1 Hz). Current ramps delivered after bath application of NMDA demonstrated bistable membrane properties which may underlie the plateau potentials. Injection of intracellular current pulses could initiate, entrain and terminate individual plateau potentials. The results suggest that membrane depolarization produced by oscillations may activate other intrinsic conductances which generate plateau potentials, thereby providing the neuron with enhanced voltage sensitivity, compared to that produced by NMDA receptor activation alone. These oscillatory events may have a role in the regulation of motor output in a variety of rhythmic behaviours including locomotion.
Phosphorylation‐dependent Effects of Synapsin IIa on Actin Polymerization and Network Formation
Authors: Nielander Hendrikus B. , Onofri Franco , Schaeffer Eric , Menegon Andrea , Fesce Riccardo , Valtorta Flavia , Greengard Paul , Benfenati Fabio
Published: April 2006

The synapsins are a family of synaptic vesicle phosphoproteins which play a key role in the regulation of neurotransmitter release and synapse formation. In the case of synapsin I, these biological properties have been attributed to its ability to interact with both synaptic vesicles and the actin‐based cytoskeleton. Although synapsin II shares some of the biological properties of synapsin I, much less is known of its molecular properties. We have investigated the interactions of recombinant rat synapsin Ila with monomeric and filamentous actin and the sensitivity of those interactions to phosphorylation, and found that: i) dephosphotylated synapsin II stimulates actin polymerization by binding to actin monomers and forming actively elongating nuclei and by facilitating the spontaneous nucleation/elongation processes; ii) dephosphorylated synapsin II induces the formation of thick and ordered bundles of actin filaments with greater potency than synapsin I; iii) phosphorylation by protein kinase A markedly inhibits the ability of synapsin II to interact with both actin monomers and filaments. The results indicate that the interactions of synapsin II with actin are similar but not identical to those of synapsin I and suggest that synapsin II may play a major structural role in mature and developing nerve terminals, which is only partially overlapping with the role played by synapsin I.
DeveIopmentalIy ReguIated Alternative SpIicing of mRNAs encoding N‐Terminal Tau Variants in the Rat Hippocampus: Structural and Functional Implications
Authors: Collet Joan , Fehrat Lotfi , Pollard Hélène , de Pouplana Lluis Ribas , Charton Gérard , Bernard Anne , Moreau Jo'lle , Ben‐Ari Yezekiel , Khrestchatisky Michel
Published: April 2006

Tau protein variants are axonal microtubule‐associated phosphoproteins whose expression correlates with developmentally regulated neurite outgrowth. A single gene encodes multiple tau transcripts via complex alternative splicing. We studied the expression of the mRNAs encoding N‐terminal variants of tau, and we showed distinct alternative splicing of exons 2 and 3 in nervous tissues of the adult rat, including the inner ear, hippocampus, cortex, striatum, brainstem, cerebellum, olfactory bulb and retina. Using the reverse transcriptase‐coupled polymerase chain reaction and in situ hybridization, we then focused our developmental study on hippocampal neurons, both in vivo and in vitro, to address the developmental and spatial expression of the alternatively spliced mRNAs encoding N‐terminal variants of tau. Tau mRNAs devoid of exons 2 and 3 were present throughout development, although their levels decreased in adults. Those containing exon 2 but not exon 3 were already present in the hippocampus of newborn rats and their levels increased during the first postnatal week, mainly in the pyramidal cell layer. Tau RNAs containing exons 2 and 3 appeared at the end of this period in the pyramidal cell layer and in the dentate granule cells. Exon 2‐containing mRNAs seemed to be associated with cells undergoing axonal sprouting, while exon 3‐containing RNAs were expressed in mature neurons that had established their connections. The timing and pattern of tau alternative splicing were maintained in cultured hippocampal neurons, suggesting that splicing processes are independent of the organized connectivity and of the environmental cues provided in vivo. Secondary structure predictions of tau variants revealed that the insertion of the exon 3‐encoded domain substantially modifies the secondary structure of the N‐terminal region of tau. This N‐terminal heterogeneity may confer distinct regulatory roles on the tau variants during ontogeny and may contribute to plasticity in the adult rat brain.
Rat Mature Sympathetic Neurones Derive Neurotrophin 3 from Peripheral Effector Tissues
Authors: Zhou Xin‐Fu , Chie Edward T. , Deng Yan‐Shen , Rush Robert A.
Published: April 2006

In a previous study we have demonstrated that endogenous neurotrophin 3 (NT3) is required for the survival of most sympathetic neurones in postnatal rats. However, the mechanisms underlying the action of NT3 on sympathetic neurones is not known. Neither is it understood whether NT3 is retrogradely transported from peripheral tissues or acts locally in an autocrine fashion. In the present study, NT3‐mRNA was quantified in sympathetic effector tissues and NT3 protein was localized in intact and lesioned sympathetic nerves in rats. NT3‐mRNA is expressed and developmentally regulated in many effector tissues including mesenteric arteries, salivary gland, heart and kidney but hardly detectable in the superior cervical ganglia of adult animals. The majority of sympathetic neurones express immunoreactivity for TrkA and TrkC in both neonatal and adult rats. Sympathetic somata are normally immunoreactive for NT3, but the immunoreactivity is abolished by systemic administration of NT3 antibodies or axotomy of postganglionic neurones, suggesting an accumulation of NT3 from extraneuronal sources. Furthermore, the detection of NT3‐immunoreactivity in the internal carotid nerve as early as 3 h following a compression and only on the distal side indicates endogenous NT3 is retrogradely transported by sympathetic neurones. These studies provide evidence indicating that NT3, like nerve growth factor, is an effector tissue‐derived neurotrophic factor for sympathetic neurones both during development and in the adult animal. Thus, we have provided a clear example that one type of neurone derives, through a retrograde transport mechanism, two neurotrophic factors simultaneously from its peripheral effector tissues.
Activation of gp 130 by IL‐6/soluble IL‐6 receptor induces neuronal differentiation
Authors: März Pia , Herget Thomas , Lang Elke , Otter Uwe , Rose‐John Stefan
Published: April 2006

Interleukin‐6 (IL‐6) on target cells binds to the specific IL‐6 receptor (IL‐6R) and subsequently induces homodimerization of the signal‐transducing protein gpl30. Cells which express gpl30 but no IL‐6R and which therefore do not respond to IL‐6 can be stimulated by the complex of IL‐6 and soluble IL‐6R (slL‐6R). Here we show that on rat pheochromocytoma cells (PC12), the combination of IL‐6 and slL‐6R but not IL‐6 alone induces expression of c‐fos, GAP‐43 and neuron‐specific enolase followed by neuron‐specific differentiation and formation of a neuronal network. The differentiation was dose‐and time‐dependent and followed the same kinetics as nerve‐growth factor (NGF)‐induced differentiation. The responses of PC12 cells to IL‐6/slL‐6R and NGF were additive, suggesting independent signaling pathways. We demonstrate that activation of gpl30 generates a neuronal differentiation signal that is equivalent to and independent of trk/NGF receptor tyrosine kinase. Interestingly, the failure of IL‐6 to induce differentiation of PC12 cells is not due to lack of surface expression of IL‐6R as IL‐6 alone triggered expression of GAP‐43 mRNA and protein. We hypothesize that PC12 cells express more gp130 than IL‐6R and that the extent of activated gp130 molecules determines the quality of the response.