bluuebunny/crossref_metadata_2025 huggingface dataset:
Δ9‐tetrahydrocannabinol‐induced MAPK/ERK and Elk‐1 activation in vivo depends on dopaminergic transmission
Authors: Valjent Emmanuel , Pagès Christiane , Rogard Monique , Besson Marie‐Jo , Maldonado Rafael , Caboche Jocelyne
Published: March 2003

It is now well established that central effects of Δ9‐tetrahydrocannabinol (THC), the main psychoactive component of marijuana, are mediated by CB1 cannabinoid receptors. However, intraneuronal signalling pathways activated in vivo by THC remain poorly understood. We show that acute administration of THC induces a progressive and transient activation (i.e. phosphorylation) of the mitogen activated protein kinase/extracellular signal‐regulated kinase (MAPK/ERK) in the dorsal striatum and the nucleus accumbens (NA). This activation, corresponding to both neuronal cell bodies and the surrounding neuropil, is totally inhibited by the selective antagonist of CB1 cannabinoid receptors, SR 141716A. However, blockade of dopaminergic (DA) D1 receptors by administration of SCH 23390, prior to THC, totally prevents ERK activation in the striatum, thus demonstrating a critical involvement of DA systems in THC‐induced ERK activation. DA‐D2 and glutamate receptors of NMDA subtypes also participate, albeit to a lesser extent, to THC‐induced ERK activation in the striatum, as shown after injection of selective antagonists (raclopride and MK801, respectively). Furthermore, THC‐induced phosphorylation of the transcription factor Elk‐1, and up‐regulation of zif268 mRNA expression are blocked by SL327, a specific inhibitor of MAPK/ERK kinase (MEK), the upstream kinase of ERK, as well as SCH 23390. Finally, using the place‐preference paradigm, we show that ERK inhibition blocks THC‐induced rewarding properties. Altogether, our data strongly support that ERK activation in the striatum is critically involved in long‐term neuronal adaptive responses underlying THC‐induced long‐term behaviours.
NAIP protects the nigrostriatal dopamine pathway in an intrastriatal 6‐OHDA rat model of Parkinson's disease
Authors: Crocker Stephen J. , Wigle Nichola , Liston Peter , Thompson Charlie S. , Lee Chris J. , Xu Daigen , Roy Sophie , Nicholson Donald W. , Park David S. , MacKenzie Alex , Korneluk Robert G. , Robertson George S.
Published: March 2003

Parkinson's disease (PD) is a progressive neurodegenerative disorder of the basal ganglia, associated with the inappropriate death of dopaminergic neurons of the substantia nigra pars compacta (SNc). Here, we show that adenovirally mediated expression of neuronal apoptosis inhibitor protein (NAIP) ameliorates the loss of nigrostriatal function following intrastriatal 6‐OHDA administration by attenuating the death of dopamine neurons and dopaminergic fibres in the striatum. In addition, we also addressed the role of the cysteine protease caspase‐3 activity in this adult 6‐OHDA model, because a role for caspases has been implicated in the loss of dopamine neurons in PD, and because NAIP is also a reputed inhibitor of caspase‐3. Although caspase‐3‐like proteolysis was induced in the SNc dopamine neurons of juvenile rats lesioned with 6‐OHDA and in adult rats following axotomy of the medial forebrain bundle, caspase‐3 is not induced in the dopamine neurons of adult 6‐OHDA‐lesioned animals. Taken together, these results suggest that therapeutic strategies based on NAIP may have potential value for the treatment of PD.
Excess target‐derived neurotrophin‐3 alters the segmental innervation of the skin
Authors: Ritter Amy M. , Woodbury C. Jeffery , Davis Brian M. , Albers Kathryn , Koerber H. Richard
Published: March 2003

It is thought that dermatomes are established during development as a result of competition between afferents of neighbouring segments. Mice that overexpress neurotrophins in the skin provide an interesting model to test this hypothesis, as they possess increased numbers of sensory neurons, and display hyperinnervation of the skin. When dermatomal boundaries were mapped in adult mice, it was found that those in nerve growth factor and brain‐derived neurotrophic factor overexpressers were indistinguishable from wild‐type animals but that overlap between adjacent segments was greatly reduced in neurotrophin‐3 (NT‐3) overexpressers. However, dermatomes in heterozygous NT‐3 knockout mice displayed no more overlap than wild‐types. In order to quantify differences across strains, innervation territories of thoracic dorsal cutaneous nerves were mapped and measured in adult mice. Overlap between adjacent dorsal cutaneous nerves was normal in nerve growth factor overexpressing mice, but much reduced in NT‐3 overexpressers. However, this restriction was not reflected in the central projection of the dorsal cutaneous nerve, creating a mismatch between peripheral and central projections. Dorsal cutaneous nerve territories were also mapped in neonatal mice aged postnatal day 7–8. In neonates, nerve territories of NT‐3 overexpressers overlapped less than wild‐types, but in neonates of both strains the amount of overlap was much greater than in the adult. These results indicate that substantial separation of dermatomes occurs postnatally, and that excess NT‐3 enhances this process, resulting in more restricted dermatomes. It may exert its effects either by enhancing competition, or by direct effects on the stability and formation of sensory endings in the skin.
Hypocretin (orexin) in the rat pineal gland: a central transmitter with effects on noradrenaline‐induced release of melatonin
Authors: Mikkelsen Jens D. , Hauser Frank , DeLecea Luis , Sutcliffe J. Gregor , Kilduff Thomas S. , Calgari Chistiane , Pévet Paul , Simonneaux Valérie
Published: March 2003

Hypocretin‐1 (HCRT‐1) and hypocretin 2 (HCRT‐2), also known as orexin‐A and orexin‐B, are two neuropeptides derived from the same precursor. Hypocretinergic neurons have been found exclusively in the hypothalamic dorsolateral area. These neurons are implicated in sleep and feeding through activation of specific G‐protein‐coupled orexin‐1 and orexin‐2 receptor (OR‐R1 and OR‐R2). The purpose of this study was to determine the existence of the HCRT peptides in the central input of the rat pineal gland. Further, OR‐R1 and OR‐R2 expression was determined in the pineal gland and the effect of HCRT‐2 on melatonin synthesis and secretion was analysed in dissociated rat pinealocytes. A large contingent of HCRT‐positive nerve fibres and terminals were observed in the epithalamus, many of which entered into the pineal parenchyma. A significant number of nerve fibres endowed with positive boutons were identified in the pineal stalk, though the number of positive fibres decreased along the extension of the stalk. So far, no positive fibres have been found in the superficial pineal gland. RT‐PCR analysis revealed the expression of OR‐R2 mRNA, whereas OR‐R1‐receptor mRNA was not detected. When tested alone, HCRT‐2 had no effect on secretion of melatonin from cultured rat pinealocytes. However, HCRT‐2 partially inhibited (by a maximum of 30%) the β‐adrenergic‐induced melatonin secretion. The same effect was seen on activation of N‐acetyltransferase activity. The distribution and the large number of HCRT‐positive fibres together with the effect on noradrenaline‐mediated melatonin release through specific receptors suggests that these peptides may be significant central transmitters in pineal function, probably mediating homeostatic signals to the pineal gland.
A role for protein kinase intracellular messengers in substance P‐ and nociceptor afferent‐mediated excitation and expression of the transcription factor Fos in rat dorsal horn neurons in vitro
Authors: Badie‐Mahdavi H. , Worsley M. A. , Ackley M. A. , Asghar A. U. R. , Slack J. R. , King A. E.
Published: March 2003

Expression of the inducible transcription factor Fos in the spinal dorsal horn in vivo is associated with nociceptive afferent activation, but the underlying stimulation‐transcription pathway is less clear. This in vitro spinal cord study concerns the role of protein kinase A and C second messengers in substance P receptor (NK1R)‐mediated or nociceptive afferent‐evoked neuronal excitation and Fos expression. Nociceptive afferent (dorsal root) stimulation of isolated spinal cords (10–14 day old rats) evoked a ‘prolonged’ excitatory polysynaptic potential (DR‐EPSP) that was attenuated (P < 0.05) by: the protein kinase A inhibitor, Rp‐cAMP; the protein kinase C inhibitor, bisindolymaleimide I; and the selective NK1R antagonist, GR82334. Neuronal excitations induced by the NK1R agonist [Sar9,Met(O2)11]‐SP were attenuated by Rp‐cAMP, bisindolymaleimide I and GR82334. Effects of the protein kinase A and C inhibitors on the DR‐EPSP or the [Sar9,Met(O2)11]‐SP‐induced depolarization were nonadditive, suggesting convergence of these intracellular signalling pathways onto a common final target. Nociceptor afferent‐induced Fos, detected by immunohistochemistry in superficial and deep dorsal horn laminae, was attenuated by Rp‐cAMP, bisindolymaleimide I and GR82334. In spinal cords pretreated with TTX to eliminate indirect neuronal activation, [Sar9,Met(O2)11]‐SP (1–20 µm) elicited a dose‐related expression of Fos that was reduced by Rp‐cAMP, bisindolymaleimide I and GR82334. The effects of these inhibitors were most pronounced in the deep laminae. These data support a causal relationship between protein kinase A‐ or C‐dependent signal transduction, nociceptive afferent‐ or NK1R‐induced neuronal excitation and Fos expression in dorsal horn. Implications for short‐ versus long‐term modulation of nociceptive circuitry are discussed.
BDNF increases the early expression of TRH mRNA in fetal TrkB+ hypothalamic neurons in primary culture
Authors: Guerra‐Crespo Magdalena , Ubieta Raimundo , Joseph‐Bravo Patricia , Charli Jean‐Louis , Pérez‐Martínez Leonor
Published: March 2003

Known effects of neurotrophins in the developing central nervous system include induction or regulation of peptide expression. Hypothalamic postmitotic thyrotropin‐releasing hormone (TRH)‐producing neurons may require neurotrophins for survival and/or differentiation. This issue was investigated using primary cell cultures derived from 17‐day‐old fetal rat hypothalamus seeded in serum‐free medium and analysed up to 4 days in vitro culture. Neurotrophin receptor (TrkB and TrkC) mRNA expression was detected by RT–PCR in fetal hypothalamus and throughout the culture period. Western blots confirmed the expression of the full‐length proteins in vitro. Semi‐quantitative RT–PCR showed that the addition of brain‐derived neurotrophic factor (BDNF) increases TRH mRNA levels while the addition of neurotrophin‐3 does not. TRH cell content was not modified. Studies on the effect of cell density or homologous conditioned medium demonstrated that endogenous factors probably contribute to determine TRH mRNA levels. One of these factors was BDNF because basal TRH mRNA levels were reduced by the addition of a Trk inhibitor or anti‐BDNF. TrkB mRNA was expressed in 27% of cells and TRH mRNA in 2% of cells. The number of TRH+ cells was not affected by BDNF treatment. Forty‐eight per cent of TRH neurons contained TrkB mRNA; these neurons had higher amounts of TRH mRNA than TrkB– neurons. Only TrkB+ cells responded to BDNF by increasing their TRH mRNA levels suggesting that BDNF may directly affect TRH biosynthesis. In conclusion, fetal hypothalamic TRH neurons are probably heterogeneous in regard to the neurotrophic factors enhancing peptide and mRNA levels. BDNF enhances TRH mRNA levels in a population of TrkB+ fetal hypothalamic TRHergic neurons in primary culture. However, additional influences may be necessary for the establishment of peptide phenotype in the TrkB+ neurons.
EGF‐responsive neural stem cells are a transient population in the developing mouse spinal cord
Authors: Represa Alfonso , Shimazaki Takuya , Simmonds Matthew , Weiss Samuel
Published: March 2003

The adult mouse forebrain, which exhibits substantial ongoing cell genesis, contains self‐renewing multipotent neural stem cells that respond to epidermal growth factor (EGF), but the adult spinal cord, which exhibits limited cell genesis, does not. Spinal cord development is a process characterized by defined periods of cell histogenesis. Thus, in the present study we asked whether EGF‐responsive neural stem cells are present within the spinal cord during development. At embryonic day (E) 11, subsequent to the onset of neurogenesis, only fibroblast growth factor (FGF) receptors and FGF‐2 (requiring heparan sulphate)‐responsive stem cells are present in the spinal cord. Between E12 and 14, at the peak of spinal cord neurogenesis and the onset of gliogenesis, EGF receptors appear along with clonally derived highly expandable EGF‐responsive neural stem cells. Following the cessation of cell histogenesis, the adult spinal cord is largely devoid of both EGF receptors and EGF‐responsive stem cells. On the other hand, the FGF receptor1c subtype and multipotent FGF‐2‐responsive neural stem cells are present in early development and in the adult. The order of appearance of spinal cord neural stem cells and in vitro lineage analysis suggests that a more primitive FGF‐2‐responsive stem cell produces the EGF‐responsive stem cell. These findings suggest that EGF‐responsive neural stem cells appear transiently in the spinal cord, during the peak period of cell histogenesis, but are no longer present in the relatively quiescent adult structure.
Astrocyte‐released cytokines induce ramification and outward K+ channel expression in microglia via distinct signalling pathways
Authors: Schilling Tom , Nitsch Robert , Heinemann Uwe , Haas Dorit , Eder Claudia
Published: March 2003

Differentiation of microglial cells is characterized by transformation from ameboid into ramified cell shape and up‐regulation of K+ channels. The processes of microglial differentiation are controlled by astrocytic factors. The mechanisms by which astrocytes cause developmental changes in morphological and electrophysiological properties of microglia have remained unclear. We show here that the cytokines transforming growth factor‐β (TGF‐β), macrophage colony‐stimulating factor (M‐CSF) and granulocyte/macrophage colony‐stimulating factor (GM‐CSF) are released by astrocytes at concentrations sufficient to induce ramification and up‐regulation of delayed rectifier (DR) K+ channels in microglia. Transformation from ameboid into ramified morphology induced in microglia by exposure to astrocyte‐conditioned medium (ACM) was inhibited by neutralizing antibodies against TGF‐β, M‐CSF or GM‐CSF, whilst ACM‐induced DR channel expression was exclusively inhibited by antibodies against TGF‐β. Although both ramification and DR channel up‐regulation occurred simultaneously, DR channel blockade by charybdotoxin failed to inhibit microglial ramification. The ACM‐induced ramification of microglia was inhibited by the tyrosine kinase inhibitor genistein, whereas DR channel up‐regulation did not occur in the presence of the serine/threonine kinase inhibitor H7. Our data suggest that astrocytes modulate processes of microglial differentiation in parallel but via distinct signalling pathways.
Cortical projections of the non‐entorhinal hippocampal formation in the cynomolgus monkey (Macaca fascicularis)
Authors: Insausti R. , Muñoz M.
Published: March 2003

Episodic memory consolidation requires the integrity of the anatomical pathways between the cerebral cortex and the hippocampal formation. Whilst the largest cortical output of the hippocampal formation originates in the entorhinal cortex, direct projections from CA1, subiculum and presubiculum to the cortex have been reported. The aim of this study is the assessment of the extent, topography and relative strength of those projections, as a parallel/alternate route of memory processing. A total of 45 injections in 28 Macaca fascicularis monkeys were used. Cortical deposits of fluorescent tracers (20 cases, 3% Fast Blue, 2% Diamidino Yellow) or 1% WGA‐HRP (eight cases) were made in different cortical areas of the frontal, temporal and parietal lobes, as well as cingulate cortex by direct exposure of the cortical surface. After appropriate survival, animals were perfused and the brains serially sectioned at 50 µm and the retrograde labelling charted with an X–Y digitizing system. Retrograde neuronal labelling was observed in CA1, subiculum, presubiculum and parasubiculum; it was absent in the dentate gyrus, CA3 and CA2. Compared to other portions of the hippocampal formation, the CA1–subiculum border had the highest number of labelled neurons (especially after deposits in the rostral perirhinal cortex), followed by medial frontal cortex, temporal pole, orbitofrontal, anterior and posterior cingulate cortices, parietal and inferotemporal cortices, and no labelling after posterior inferotemporal and lateral frontal cortices. Our results indicate that CA1, subiculum, presubiculum and parasubiculum send direct output to cortical areas. This nonentorhinal, hippocampal formation cortical output may be relevant in memory processing.
Effects of steroids on NMDA receptors and excitatory synaptic transmission in neonatal motoneurons in rat spinal cord slices
Authors: Abdrachmanova Galya , Chodounská Hana , Vyklický Ladislav
Published: March 2003

The effect of steroids on NMDA receptors and excitatory postsynaptic transmission was studied in fluorescence‐labelled motoneurons in thin spinal cord slices. In outside‐out patches, NMDA‐induced responses were potentiated by 79% in the presence of 20‐oxopregn‐5‐en‐3β‐yl sulfate (PS), while in the presence of 20‐oxo‐5α‐pregnan‐3α‐yl sulfate (3α5αS) and 20‐oxo‐5β‐pregnan‐3α‐yl sulfate (3α5βS) they were diminished by 57% and 66%, respectively. PS and 3α5βS had no effect on the amplitude of single NMDA receptor channel openings, however, both compounds altered relative distribution of the openings to individual conductance levels. In control cases, the most frequent openings of the NMDA receptor channels were at the 70 pS conductance level, while in the presence of PS or 3α5βS, the most frequent openings were at the 55 pS conductance level. Analysis of the mean current transferred by NMDA receptor channel openings at individual conductance levels indicated that in the presence of PS, the mean current induced by 55 pS conductance openings was significantly increased. In the presence of 3α5βS, the mean currents induced by 55 pS and 70 pS conductance openings were significantly decreased. The amplitude of NMDA receptor‐mediated EPSCs was potentiated by 54% in the presence of PS and the deactivation kinetics slowed. Neither the amplitude nor the kinetics of NMDA receptor‐mediated EPSCs was significantly changed in the presence of 3α5βS. The results of our experiments indicate that neurosteroids affect NMDA receptors in motoneurons. The effect appears to be influenced by the receptor subunit composition.
Requirement of appropriate glutamate concentrations in the synaptic cleft for hippocampal LTP induction
Authors: Katagiri Hiroyuki , Tanaka Kohichi , Manabe Toshiya
Published: March 2003

Although glutamate transporters maintain low extracellular levels of the excitatory neurotransmitter glutamate in the nervous system, little is known about their roles in synaptic plasticity. Here, using knockout mice lacking GLT‐1, that is the most abundant glial subtype of glutamate transporters, we showed that long‐term potentiation (LTP) induced by tetanic stimulation in mutant mice was impaired in the hippocampal CA1 region. When tetanic stimulation was applied in the presence of low concentrations of an N‐methyl‐d‐aspartate (NMDA) receptor antagonist, the impairment was overcome. Consistent with these results, the increased glutamate in the synaptic cleft of mutant mice preferentially activated NMDA receptors. Furthermore, analyses of mutant mice revealed that the magnitude of NMDA receptor‐dependent transient synaptic potentiation during low‐frequency stimulation depended on the concentration of glutamate in the synaptic cleft. These findings suggest that GLT‐1 plays critical roles in LTP induction, as well as in short‐term potentiation, through regulation of extracellular levels of glutamate, which enables appropriate NMDA receptor activation.
Developmental shift of vanilloid receptor 1 (VR1) terminals into deeper regions of the superficial dorsal horn: correlation with a shift from TrkA to Ret expression by dorsal root ganglion neurons
Authors: Guo A. , Simone D. A. , Stone L. S. , Fairbanks C. A. , Wang J. , Elde R.
Published: March 2003

The cloned vanilloid receptor VR1 can be activated by capsaicin and by thermal stimuli. The pattern of nerve terminals that contain VR1 in adult rat spinal cord does not correspond to axons that arise from a single subset of dorsal root ganglion neurons. Thus, we postulated that the basis underlying this complexity might be better understood from a developmental perspective. First, using capsaicin‐induced hyperalgesia as a measure of VR1 function, we found that vanilloid receptors were functional as early as postnatal day 10 (P10), although hyperalgesia was of longer duration in adult. Interestingly, the appearance of VR1 protein in terminals of dorsal root ganglion neurons shifts over this postnatal period. From embryonic day 16 to P20, the majority of VR1 protein in the spinal cord was observed in lamina I. As animals matured, VR1 protein became more abundant in lamina II, particularly in the inner portion. Consistent with these observations, the number of dorsal root ganglion neurons coexpressing VR1 and isolectin B4 binding sites doubled while the number of neurons that had both VR1 and substance P remained relatively constant from P2 to P10. In peripheral processes, the number of VR1‐positive nerve fibres and terminals in cutaneous structures in postnatal day 10 was half of that in adults. We also show that the association of VR1 with Ret is the reciprocal of the association of VR1 with Trk A. These results suggest that neurotrophins may regulate the extent to which populations of dorsal root ganglion neurons express VR1.
Neuroinflammation‐induced acceleration of amyloid deposition in the APPV717F transgenic mouse
Authors: Qiao Xiaoxi , Cummins David J. , Paul Steven M.
Published: March 2003

It has been postulated that neuroinflammation plays a critical role in the pathogenesis of Alzheimer's disease (AD). To directly test whether an inflammatory stimulus can accelerate amyloid deposition in vivo, we chronically administered the bacterial endotoxin, lipopolysaccharide (LPS), intracerebroventricularly (i.c.v.) to 2‐month‐old APPV717F+/+ transgenic (TG) mice, which overexpress a mutant human amyloid precursor protein (APP 717V‐F) with or without apolipoprotein E (apoE) for 2 weeks. Two weeks following central LPS administration a striking global reactive astrocytosis with increased GFAP immunoreactivity was found throughout the brains of all LPS‐treated wild‐type and transgenic mice including the contralateral brain hemisphere. Localized microglial activation was also evident from lectin immunostaining adjacent to the cannula track of LPS‐treated mice. Quantification of thioflavine‐S‐positive Aβ deposits revealed a marked acceleration of amyloid deposition in LPS‐treated APPV717F+/+–apoE+/+ mice compared to nontreated or vehicle‐treated APPV717F+/+–apoE+/+ mice (P = 0.005). By contrast, no amyloid deposits were detected by thioflavine‐S staining in LPS or vehicle‐treated apoE‐deficient APPV717F TG mice. Our data suggest that neuroinflammation can accelerate amyloid deposition in the APPV717F+/+ mouse model of AD and that this process requires the expression of apoE.
ErbB‐4 and neuregulin expression in the adult mouse olfactory bulb after peripheral denervation
Authors: Oberto Michela , Soncin Ilaria , Bovolin Patrizia , Voyron Samuele , De Bortoli Michele , Dati Claudio , Fasolo Aldo , Perroteau Isabelle
Published: March 2003

ErbB‐4 is expressed by the periglomerular and the mitral/tufted cells of the adult mouse olfactory bulb (OB) and in the present work we tested whether this expression is regulated by the olfactory nerve input to the OB. Reversible zinc sulphate lesions of the olfactory mucosa were made in adult mice and the deafferented OB analysed by immunohistochemistry, Western blotting and semiquantitative RT‐PCR. Following deafferentation, the expression of erbB‐4, erbB‐2 and neuregulin‐1 (NRG‐1) mRNAs in the OB was altered. At early stages (7–14 days) after lesion the levels of expression of olfactory marker protein (OMP), tyrosine hydroxylase (TH), erbB‐4 and NRG‐1 mRNAs were decreased, whilst expression of erbB‐2 increased and that of NRG‐2 was not significantly altered. We observed at least two distinct time courses for these expression changes. The lowest amounts of mRNA for erbB‐4 and NRG‐1 were observed at day 7 after lesion, whilst mRNAs for TH and OMP were lowest at day 14. At day 28 after the lesion, when olfactory receptor neuron axons had reinnervated the olfactory bulb, the expression levels of OMP, TH, erbB‐2, erbB‐4 and NRG‐1 were identical to control values. These results indicate that the expression of erbB‐4 mRNA and protein in periglomerular and mitral cells is controlled by peripheral olfactory innervation. The tight correlation in NRG‐1 and erbB‐4 expression levels also suggests a possible functional link that deserves further exploration.
Calcium currents in rat dentate granule cells are altered after adrenalectomy
Authors: Karst Henk , Joëls Marian
Published: March 2003

Adrenal corticosteroid hormones modulate voltage‐gated calcium currents in rat CA1 hippocampal neurons. In the present whole‐cell recording study we examined whether calcium currents in dentate granule cells are also under control of corticosteroids. In a first series of experiments, in which the calcium chelator BAPTA was added to the recording solution, the amplitude of calcium currents induced by a voltage step to −10 mV was found to be enhanced shortly (1 or 2 days) after adrenalectomy compared to sham operation. No enhancement was seen when adrenalectomized animals received a low dose of corticosterone in the drinking water. By contrast, 3 or 7 days after adrenalectomy calcium current amplitude was decreased. Starting 3 days after adrenalectomy, some of the granule cells underwent apoptosis. This caused a bias in the recorded cell population towards relatively apoptosis‐resistant cells, suggesting that restricted calcium influx may be a key feature of cells withstanding the apoptotic route. In accordance, cells from a small percentage (≈ 20%) of animals that resisted apoptosis after adrenalectomy also displayed small calcium currents. In a second series without BAPTA, thus focusing on the endogenous calcium‐buffering capacity, we found that the time constant for the decay of the calcium current was decreased after adrenalectomy, probably due to enhanced calcium‐dependent inactivation of the current. The data indicate that cellular calcium current characteristics of dentate granule cells are altered after adrenalectomy and that the alterations may in part determine the vulnerability to undergo apoptosis.
Involvement of the cerebellar thalamus in human saccade adaptation
Authors: Gaymard B. , Rivaud‐Péchoux S. , Yelnik J. , Pidoux B. , Ploner C. J.
Published: March 2003

Saccade adaptation can be experimentally induced by systematically displacing a visual cue during a targeting saccade. Non‐human primate studies have highlighted the crucial role of the cerebellum for saccade adaptation, but its neural substrates in humans are poorly understood. Recent physiological experiments suggest that, in addition to cerebellar structures, cortical areas may be involved as well. We have therefore hypothesized that saccade adaptation may rely on a cerebello‐cerebral network, in which the cerebellar thalamus may link cerebellar and cerebral structures. To test this hypothesis, we studied saccade adaptation in a group of four patients with a thalamic lesion, with (n = 2) or without (n = 2) involvement of the cerebellar thalamus. Compared to healthy subjects, saccade adaptation was reduced in patients with associated cerebellar syndrome, but normal in patients without cerebellar syndrome. These results are consistent with the hypothesis that cerebello‐thalamic pathways contribute to saccade adaptation in humans and suggest that the thalamus relays adaptation‐related information from the cerebellum to cerebral cortical oculomotor areas.
Contact‐dependent aggregation of functional Ca2+ channels, synaptic vesicles and postsynaptic receptors in active zones of a neuromuscular junction
Authors: DiGregorio David A. , Negrete Oscar , Jeromin Andreas , Peng H. Benjamin , Vergara Julio L.
Published: March 2003

To examine whether Ca2+ channels aggregate in a contact‐dependent manner, we characterized the distribution of synaptic vesicles and postsynaptic receptors, and compared it to the location of Ca2+ entry sites, in a Xenopus laevis nerve‐muscle coculture preparation using a localized Ca2+ detection method. The majority (75%) of Ca2+ entry sites at spontaneously formed nerve–muscle contacts were associated with enhanced immunofluorescence to the synaptic vesicle protein, SV2. In contrast, only 11% of recorded sites without Ca2+ transients exhibited significant SV2 immunofluorescence. When comparing the spatial distribution of synaptic markers with that of Ca2+ entry sites, we found that the majority of Ca2+ entry sites (61%) were associated with both enhanced SV2 immunofluorescence and R‐BTX fluorescence, thereby identifying putative neurotransmitter release sites where Ca2+ channels, synaptic vesicles and postsynaptic receptors are colocalized. Using polystyrene beads coated with a heparin binding protein known to mediate in vitro postsynaptic receptor clustering, we show that the location of Ca2+ domains was associated with enhanced SV2 immunofluorescence at neurite‐to‐bead contacts. We conclude that the localization of functional Ca2+ channels to putative active zones follows a contact‐dependent signalling mechanism similar to that known to mediate vesicle aggregation and AChR clustering.
Double‐pulse transcranial magnetic stimulation over the frontal eye field facilitates triggering of memory‐guided saccades
Authors: Wipfli Marius , Felblinger Jacques , Mosimann Urs P. , Hess Christian W. , Schlaepfer Thomas E. , Müri René M.
Published: March 2003

The study investigated the influence of double‐pulse transcranial magnetic stimulation (dTMS) on memory‐guided saccade triggering. Double pulses with interstimulus intervals (ISIs) of 35, 50, 65 or 80 ms were applied over the right frontal eye field (FEF) and as control over the occipital cortex. A significant dTMS effect was found exclusively for contralateral saccades; latency of memory‐guided saccades was reduced after FEF stimulation with an ISI of 50 ms compared to latency without stimulation. This effect proved to be specific for the ISI of 50 ms over the FEF because control stimulation with the same ISI over the occipital cortex had no significant effect on latency of memory‐guided saccades. The results of our study showed that, by using an appropriate ISI, dTMS is able to facilitate contralateral saccade triggering by stimulating the FEF. This suggests that TMS interferes specifically with saccade triggering mechanisms, probably by acting on presaccadic neurons of the FEF.
Intrahippocampal injections of somatostatin dissociate acquisition from the flexible use of place responses
Authors: Lamirault Laëtitia , Guillou Jean‐Louis , Micheau Jacques , Jaffard Robert
Published: March 2003

Previous studies showed that injections of somatostatin (SS‐14) into the hippocampus facilitate the acquisition of spatial tasks in mice. The present study was aimed at better understanding the learning and memory processes that could be affected by hippocampal SS‐14 stimulation. Balb/c mice were submitted to a two‐stage learning paradigm. In stage 1, they were trained for acquisition of a spatial discrimination task in a radial maze and, in stage 2, were submitted to a probe test aiming at evaluating their ability to use flexibly their previously acquired knowledge. Injections of vehicle or SS‐14 were given during the acquisition phase and/or before the probe test using a 2 × 2 factorial design. Mice receiving SS‐14 during acquisition failed to succeed in the probe test despite showing a trend to faster acquisition of the initial spatial discrimination task. By contrast, when given only prior to probe trials, SS‐14 did not yield any behavioural effects. Thus, SS‐14 interfered with the establishment of a flexible form of memory, not with its expression per se, and therefore dissociated the acquisition of place responses from their flexible use. The theoretical issues raised by the present findings are discussed.
Transplantation of neural precursor cells into the dysmyelinated CNS of mutant mice deficient in the myelin‐associated glycoprotein and Fyn tyrosine kinase
Authors: Ader Marius , Schachner Melitta , Bartsch Udo
Published: March 2003

We have studied in long‐term experiments the fate of intraventricularly transplanted neural precursor cells in a dysmyelinated mouse brain. Precursor cells were isolated from striata or spinal cords of transgenic mouse embryos ubiquitously expressing enhanced green fluorescent protein (EGFP). Cells were expanded in vitro in the presence of mitogens for up to 14 weeks, and injected into the lateral ventricle of young postnatal mouse mutants deficient in the myelin‐associated glycoprotein (MAG) and the nonreceptor‐type tyrosine kinase Fyn. The CNS of these mutants is severely hypomyelinated and most myelin sheaths display ultrastructural abnormalities. Despite this phenotype, MAG/Fyn‐deficient mice have a normal longevity. Analysis of mutant brains 1 to 6 months after transplantation revealed widespread distribution of EGFP‐positive cells in the recipient tissue. Grafted cells preferentially populated white matter tracts and differentiated into a variety of morphologically distinct cell types. A significant fraction of donor cells was identified as oligodendrocytes. Electron microscopic analysis revealed the presence of numerous donor‐derived, ultrastructurally intact, myelin sheaths around host axons. EGFP‐positive oligodendrocytes and myelin survived for up to 6 months after transplantation, the latest time point investigated. Remarkably, the number of donor‐derived oligodendrocytes increased significantly with increasing time intervals after transplantation, resulting in widespread myelination of 6‐month‐old host brains. These long‐term experiments thus demonstrate that extensive myelination of a dysmyelinated brain can be achieved after a single injection of neural precursor cells.
Spatial coding of visual and somatic sensory information in body‐centred coordinates
Authors: Galati Gaspare , Committeri Giorgia , Sanes Jerome N. , Pizzamiglio Luigi
Published: March 2003

Because sensory systems use different spatial coordinate frames, cross‐modal sensory integration and sensory–motor coordinate transformations must occur to build integrated spatial representations. Multimodal neurons using non‐retinal body‐centred reference frames are found in the posterior parietal and frontal cortices of monkeys. We used functional magnetic resonance imaging to reveal regions of the human brain using body‐centred coordinates to code the spatial position of both visual and somatic sensory stimuli. Participants determined whether a visible vertical bar (visual modality) or a location touched by the right index finger (somatic sensory modality) lay to the left or to the right of their body mid‐sagittal plane. This task was compared to a spatial control task having the same stimuli and motor responses and comparable difficulty, but not requiring body‐centred coding of stimulus position. In both sensory modalities, the body‐centred coding task activated a bilateral fronto‐parietal network, though more extensively in the right hemisphere, to include posterior parietal regions around the intraparietal sulcus and frontal regions around the precentral and superior frontal sulci, the inferior frontal gyrus and the superior frontal gyrus on the medial wall. The occipito‐temporal junction and other extrastriate regions exhibited bilateral activation enhancement related to body‐centred coding when driven by visual stimuli. We conclude that posterior parietal and frontal regions of humans, as in monkeys, appear to provide multimodal integrated spatial representations in body‐centred coordinates, and these data furnish the first indication of such processing networks in the human brain.
Neuronal nitric oxide synthase (nNOS) mRNA is down‐regulated, and constitutive NOS enzymatic activity decreased, in thoracic dorsal root ganglia and spinal cord of the rat by a substance P N‐terminal metabolite
Authors: Kovacs Katalin J. , Cai Yongjiu , Larson Alice A.
Published: March 2003

Nitric oxide (NO) in the spinal cord plays a role in sensory and autonomic activity. Pain induced by acetic acid in the abdominal stretch (writhing) assay and hyperalgesia associated with chronic pain are highly sensitive to NO synthase (NOS) inhibitors. Because substance P (SP) is released and up‐regulated in some models of chronic pain, we hypothesized that an accumulation of SP metabolites may influence NOS expression and activity. To test this hypothesis, we examined the effect of intrathecally (i.t.) injected substance P (1‐7) [SP(1‐7)], the major metabolite of SP in the rat, on neuronal NOS (nNOS) mRNA in the thoracic and lumbar spinal cord, dorsal root ganglia (DRG) and on the corresponding constitutive NOS (cNOS) enzyme activity. Detected using quantitative RT‐PCR, nNOS mRNA content in the thoracic spinal cord was decreased 6 h after injection of 5 µmol of SP(1‐7) and returned to control 2 days later. In thoracic DRG, nNOS mRNA was reduced 48 h after SP(1‐7). The cNOS enzymatic activity in thoracic spinal tissue was gradually decreased to a minimum at 72 h. Down‐regulation of NOS by SP(1‐7) in the thoracic area appears to be highly associated with capsaicin‐sensitive primary afferent neurons. No similar changes in either parameter were measured in the lumbar area after SP(1‐7). These data suggest that N‐terminal SP fragments, which are known to cause long‐term antinociception in the writhing assay, may do so by their ability to down‐regulate NO synthesis along nociceptive pathways.
Four different types of protease‐activated receptors are widely expressed in the brain and are up‐regulated in hippocampus by severe ischemia
Authors: Striggow Frank , Riek‐Burchardt Monika , Kiesel Annett , Schmidt Werner , Henrich‐Noack Petra , Breder Jörg , Krug Manfred , Reymann Klaus G. , Reiser Georg
Published: March 2003

A variety of extracellular serine proteases are expressed in the central nervous system or might permeate the blood–brain barrier under pathological conditions. However, their intracerebral targets and physiological functions are largely unknown. Here, we show that four distinct subtypes of protease‐activated receptors (PARs) are abundantly expressed in the adult rat brain and in organotypic hippocampal slice cultures. PAR‐1 expression was significant in the hippocampus, cortex and amygdala. Highest densities of PAR‐2 and PAR‐3 were observed in hippocampus, cortex, amygdala, thalamus, hypothalamus and striatum. Apart from the striatum, a similar localization was found for PAR‐4. Within the hippocampal formation, each PAR subtype was predominantly localized in the pyramidal cell layers. Additionally, we identified PAR‐2 in mossy fibers between dentate gyrus and CA3, PAR‐3 in the subiculum and PAR‐4 in CA3 and in mossy fibres as well as in the stratum lacunosum moleculare. After exposing hippocampal slice cultures to a severe experimental ischemia (oxygen–glucose deprivation), the expression of PARs 1–3 was up‐regulated with subtype‐specific kinetics. The localization of PARs in brain regions particularly vulnerable to ischemic insults as well as distinct alterations in the expression pattern after experimental ischemia support the notion of an important role of extracellular serine proteases and PARs in cerebral ischemia.
Two distinct types of repetitive bursting activity mediated by NMDA in hypothalamic neurons in vitro
Authors: Poulain Pierre
Published: March 2003

Hypothalamic magnocellular dorsal nucleus neurons were recorded from adult guinea pig brain slices with the whole‐cell patch‐clamp technique to determine the effects of N‐methyl‐d‐aspartate (NMDA) applied in the bath or by iontophoresis. In a majority of cells (59 of 77, 76.6%), rhythmic bursting discharges were evoked by specific activation of NMDA receptors when the membrane was more negative than −60 mV. This endogenous rhythmic activity was resistant to tetrodotoxin. It was suppressed by removal of extracellular Mg2+, indicating the involvement of the voltage‐dependent block of the NMDA channel by Mg2+. Application of thapsigargin showed that rhythmic activity did not depend on the release of Ca2+ from reticulum stores. Blockers of Ca2+ conductances Ni2+ and nifedipine had no effects on the bursts. Their repolarization did not involve the activation of a strophantidin‐ or ouabain‐sensitive pump, but partly depended on an apamine‐sensitive Ca2+‐dependent K+current. In a small subset of cells (9 of 69, 13%), specific activation of NMDA receptors induced another type of bursting activity which consisted of repetitive low‐threshold spikes sustaining bursts of action potentials. Rhythmic low‐threshold spikes subsisted in the presence of tetrodotoxin but were suppressed by Ni2+. Increasing the amount of NMDA brought about a switch from the rhythmic low‐threshold spike burst firing to the rhythmic bursting activity observed for the majority of cells. The present data show for the first time that NMDA receptor activation can induce two independent rhythmic bursting behaviours in the same neuron, probably depending on the strength of the glutamatergic drive.
Glutamate receptor stimulation induces a persistent rhythmicity of the GABAergic inputs to rat midbrain dopaminergic neurons
Authors: Berretta Nicola , Paolucci Egle , Bernardi Giorgio , Mercuri Nicola B.
Published: March 2003

The substantia nigra pars compacta and the ventral tegmental area are part of a complex network in the basal ganglia involved in behaviours as diverse as motor planning, generation of pleasure and drug addiction. Here we report that in the dopaminergic neurons of the rat ventral midbrain a brief coactivation of group I metabotropic and NMDA glutamate receptors may transform a temporally dispersed synaptic GABAergic input into a rhythmic pattern (range 4.5–22.5 Hz), probably through a mechanism involving electrotonic couplings. The plastic and long‐lasting modification in the temporal code of the inhibitory synaptic activity induced by glutamate may be a key element in determining the function of midbrain dopaminergic neurons in both normal and pathological behaviour.
Differential induction of LTP and LTD is not determined solely by instantaneous calcium concentration: an essential involvement of a temporal factor
Authors: Mizuno Tomoyuki , Kanazawa Ichiro , Sakurai Masaki
Published: March 2003

Two opposite types of synaptic plasticity in the CA1 hippocampus, long‐term potentiation (LTP) and long‐term depression (LTD), require postsynaptic Ca2+ elevation. To explain these apparently contradictory phenomena, the current view assumes that a moderate postsynaptic increase in Ca2+ leads to LTD, whereas a large increase leads to LTP. No detailed study has so far been attempted to investigate whether the instantaneous Ca2+ elevation level differentially induces LTP or LTD. We therefore used low‐frequency (1 Hz) stimulation of Schaffer collateral/commissural fibers in rat hippocampal slices, during a Mg2+‐free period, as the conditioning stimulus to investigate this. This allowed low‐frequency afferent stimulation to cause a postsynaptic Ca2+ influx because the voltage‐dependent block of N‐methyl‐d‐aspartate (NMDA) receptor‐channels by Mg2+ was removed. When delivered during the Mg2+‐free period, a single pulse, as well as 2–600 pulses, induced LTP that was occluded with tetanus‐induced LTP. To decrease the Ca2+ influx, α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid (AMPA) receptors were completely blocked by the addition of 10 µm 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) to the conditioning medium, in which 1 Hz afferent stimuli (1–600 pulses) induced less LTP and never induced LTD. To further reduce the Ca2+ influx, NMDA receptors were partially blocked with d‐(–)‐2‐amino‐5‐phosphonopentanoic acid (d‐AP5). A small number of 1 Hz stimuli, however, never induced LTD. Only when the conditioning stimuli exceeded 200 pulses was LTD induced. The present findings provide definitive evidence that protracted conditioning is a prerequisite for the induction of LTD. Thus, not only the amplitude but also the duration of postsynaptic Ca2+ elevation could be essential factors for differentially inducing LTP or LTD.
Exogenous nitric oxide causes potentiation of hippocampal synaptic transmission during low‐frequency stimulation via the endogenous nitric oxide–cGMP pathway
Authors: Bon Christelle L. M. , Garthwaite John
Published: March 2003

Nitric oxide (NO) is a putative participant in synaptic plasticity and demonstrations that exogenous NO can elicit the same plastic changes have been taken to support such a role. The experiments, carried out on the CA1 region of rat hippocampal slices, were aimed at testing this interpretation. A major component of tetanus‐induced long‐term potentiation (LTP) was lost in response to l‐nitroarginine, which inhibits NO synthase, and 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ), which inhibits NO‐sensitive soluble guanylyl cyclase (sGC). At 0.2 Hz afferent fibre stimulation, exogenous NO produced, concentration‐dependently, a synaptic depression that reverted on washout to a persistent potentiation that occluded tetanus‐induced LTP. The NO concentrations necessary (estimated in the 100‐nm range), however, were mostly supramaximal for stimulating hippocampal slice sGC activity. Nevertheless the potentiation, but not the preceding depression, was blocked by ODQ. l‐nitroarginine and an NMDA antagonist were similarly effective, indicating mediation by the endogenous NMDA receptor–NO synthase–sGC pathway. At a concentration normally too low to affect synaptic transmission but sufficient to stimulate sGC (estimated to be 50 nm), exogenous NO reversed the effect of l‐nitroarginine and caused a potentiation which was blocked by ODQ. At a concentration inducing the depression/potentiation sequence, NO partially inhibited hippocampal slice oxygen consumption. It is concluded that, at physiological levels, exogenous NO can directly elicit a potentiation of synaptic transmission through sGC, provided that the synapses are suitably primed. At higher concentrations, NO inhibits mitochondrial respiration, which can result in an enduring synaptic potentiation due to secondary activation of the endogenous NO–cGMP pathway.