bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of the aggregation properties, secondary structure and apoptotic effects of wild‐type, Flemish and Dutch N‐terminally truncated amyloid β peptides
Authors: Demeester N. , Mertens C. , Caster H. , Goethals M. , Vandekerckhove J. , Rosseneu M. , Labeur C.
Published: March 2003

The Dutch (E22Q) and Flemish (A21G) mutations in the βAPP region of the amyloid precursor protein (APP) are associated with familial forms of Alzheimer dementia. However, patients with these mutations express substantially different clinical phenotypes. Therefore, secondary structure and cytotoxic effects of the three Aβ(12–42) variants [wild‐type (WT), Dutch and Flemish] were tested. At a concentration of 5 µm the aggregation of these peptides followed the order: Aβ(1–42) WT > Aβ(12–42) WT > Aβ(12–42) Flemish > Aβ(12–42) Dutch. The stability of the secondary structure of these peptides upon decreasing the trifluoroethanol (TFE) concentration in the buffer was followed by circular dichroism measurements. WT peptides progressively lost their α‐helical structure; this change occurred faster for both the Flemish and Dutch peptides, and at higher percentages of TFE in the buffer, and was accompanied by an increase in β‐sheet and random coil content. Apoptosis was induced in neuronal cells by the Aβ(12–42) WT and Flemish peptides at concentrations as low as 1–5 µm, as evidenced by propidium iodide (PI) staining, DNA laddering and caspase‐3 activity measurements. Even when longer incubation times and higher peptide concentrations were applied the N‐truncated Dutch peptide did not induce apoptosis. Apoptosis induced by the full length Aβ(1–42) peptide was weaker than that induced by its N‐truncated variant. These data suggest that N‐truncation enhanced the cytotoxic effects of Aβ WT and Flemish peptides, which may play a role in the accelerated progression of dementia.
NMDA receptor subunits GluRε1, GluRε3 and GluRζ1 are enriched at the mossy fibre–granule cell synapse in the adult mouse cerebellum
Authors: Yamada Kazuyuki , Fukaya Masahiro , Shimizu Hidemi , Sakimura Kenji , Watanabe Masahiko
Published: March 2003

Cerebellar N‐methyl‐d‐aspartate (NMDA) receptors are concentrated in the granular layer and are involved in motor coordination and the induction of long‐term potentiation at mossy fibre–granule cell synapses. In the present study, we used immunohistochemistry to examine the distribution of NMDA receptor subunits in the adult mouse cerebellum. We found that appropriate pepsin pretreatment of sections greatly enhanced the sensitivity and specificity of immunohistochemical detection. As a result, intense immunolabelling for GluRε1 (NR2A), GluRε3 (NR2C), and GluRζ1 (NR1) all appeared in synaptic glomeruli of the granular layer. Double immunofluorescence showed that these subunits were colocalized in individual synaptic glomeruli. Within the glomerulus, NMDA receptor subunits were located between centrally‐located huge mossy fibre terminals and peripherally‐located tiny Golgi axon terminals. By immunoelectron microscopy, all three subunits were detected at the postsynaptic junction in granule cell dendrites, forming synapses with mossy fibre terminals. Consistent with the known functional localization, GluRε1, GluRε3, and GluRζ1 are, thus, anatomically concentrated at the mossy fibre–granule cell synapse. By contrast, immunohistochemical signals were very low in Purkinje cell somata and dendrites in the molecular layer. The lack of GluRζ1 immunolabelling in Purkinje cells was unexpected because the cells express GluRζ1 mRNA at high levels and high levels of GluRζ1 protein in the molecular layer were revealed by immunoblot. As Purkinje cells are exceptionally lacking GluRε expression, the discrepant result may provide in vivo evidence suggesting the importance of accompanying GluRε subunits in synaptic localization of GluRζ1.
Ceramide‐induced apoptosis in cortical neurons is mediated by an increase in p38 phosphorylation and not by the decrease in ERK phosphorylation
Authors: Willaime Sandrine , Vanhoutte Peter , Caboche Jocelyne , Lemaigre‐Dubreuil Yolande , Mariani Jean , Brugg Bernard
Published: March 2003

Ceramide, the central molecule of the sphingomyelin pathway, serves as a second messenger for cellular functions ranging from proliferation and differentiation to growth arrest and apoptosis. In this study we show that c2‐ceramide induces apoptosis in primary cortical neuron cultures and that this effect correlates with differential modulation of mitogen‐activated protein kinase (MAPK) cascades. Phosphorylation of extracellular signal‐regulated kinases (ERKs) and their upstream activators MAPK kinases (MEKs), as measured by immunoblotting is rapidly decreased by c2‐ceramide. However, the MEK inhibitor PD98059 alone does not induce apoptosis and in combination with c2‐ceramide it does not modify c2‐ceramide‐induced apoptosis. Treatment with c2‐ceramide increases p38 and c‐Jun N‐terminal kinase (JNK) phosphorylation before and during caspase‐3 activation. The p38 inhibitor SB203580 partially protects cortical neurons against c2‐ceramide‐induced apoptosis, implicating the p38 pathway in this process. The c2‐ceramide treatment also increases levels of c‐jun, c‐fos and p53 mRNA in primary cortical neuron cultures, but this is independent of p38 activation. Our study further elucidates the time‐courses of MAPK cascade modulation, and of c‐jun, c‐fos and p53 activation during c2‐ceramide‐induced neuronal apoptosis. It reveals that one of the activated kinases, p38, is necessary for this apoptosis.
ATP but not adenosine inhibits nonquantal acetylcholine release at the mouse neuromuscular junction
Authors: Galkin A. V. , Giniatullin R. A. , Mukhtarov M. R. , Švandová I. , Grishin S. N. , Vyskočil F.
Published: March 2003

The postsynaptic membrane of the neuromuscular synapse treated with antiacetylcholinesterase is depolarized due to nonquantal release of acetylcholine (ACh) from the motor nerve ending. This can be demonstrated by the hyperpolarization produced by the application of curare (H‐effect). ATP (1 × 10−5 m) decreased the magnitude of the H‐effect from 5 to 1.5 mV. The membrane input resistance and the ACh sensitivity were unchanged, and so changes in these cannot explain the ATP effect. Adenosine alone was without effect on the nonquantal release. On the other hand, both ATP and adenosine depressed the frequency of spontaneous miniature endplate potentials, to 56% and 43% respectively. The protein kinase A inhibitor Rp‐cAMP or the guanylyl cyclase inhibitor 1H‐[1,2,4]oxidiazolo[4,3‐a]quinoxalin‐1‐one did not affect the inhibitory influence of ATP on the H‐effect, whereas staurosporine, an inhibitor of protein kinase C, completely abolished the action of ATP. Suramin, an ATP antagonist, enhanced the H‐effect to 8.6 mV and, like staurosporine, prevented the inhibitory effect of ATP. ATP thus suppresses the nonquantal release via a direct action on presynaptic metabotropic P2 receptors coupled to protein kinase C, whilst adenosine exerts its action mainly by affecting the mechanisms underlying quantal release. These data, together with earlier evidence, show that nonquantal release of ACh can be modulated by several distinct regulatory pathways, in particular by endogenous substances which may or may not be present in the synaptic cleft at rest or during activity.
Effect of the selective noradrenergic reuptake inhibitor reboxetine on the firing activity of noradrenaline and serotonin neurons
Authors: Szabo Steven T. , Blier Pierre
Published: March 2003

Reboxetine is a non‐tricyclic antidepressant with selective noradrenergic (NA) reuptake‐blocking effects. The effects of acute and sustained administration of reboxetine, on the firing activity of locus coeruleus NA neurons and dorsal raphe 5‐HT neurons, were assessed using in vivo extracellular unitary recording in rats anaesthetized with chloral hydrate. Reboxetine (0.1–1.25 mg/kg, i.v.) dose‐dependently decreased the firing activity of NA neurons (ED50 = 480 ± 14 µg/kg). A 2‐day treatment with reboxetine at 1.25, 2.5, 5, or 10 mg/kg per day (using osmotic minipumps implanted subcutaneously) produced significant decreases of 52%, 68%, 81%, and 83%, respectively, of NA firing activity. When the reboxetine treatment (2.5 mg/kg per day) duration was prolonged to 7 days, a 66% decrease in NA firing activity was observed which further decreased to 80% after 21 days of treatment. In contrast, 5‐HT neuron firing rate remained unaltered following short‐ and long‐term reboxetine treatments. The suppressant effect of the α2‐adrenoceptor agonist clonidine on the firing activity of NA neurons was unchanged in long‐term reboxetine‐treated rats, but its effect on the firing activity of 5‐HT neurons was blunted. The enhancement of NA firing activity by the 5‐HT1A agonist 8‐OH‐DPAT was abolished in long‐term reboxetine‐treated rats, whereas, the inhibitory effect of the 5‐HT2 agonist DOI was attenuated by about three‐fold. In conclusion, sustained NA reuptake blockade by reboxetine lead to profound alterations in the function of NA neurons and of 5‐HT receptors modulating their firing activity.
The group I metabotropic glutamate receptor antagonist S‐4‐CPG modulates the locomotor response produced by the activation of D1‐like, but not D2‐like, dopamine receptors in the rat nucleus accumbens
Authors: David Hélène N. , Abraini Jacques H.
Published: March 2003

Functional interactions between dopamine (DA) and glutamate neurotransmissions in both the dorsal and the ventral striatum have been described for long time. However, there is much controversy as to whether glutamate transmission stimulates or attenuates DA release and locomotor activity. We investigated the functional interactions on locomotor activity between group I metabotropic glutamatergic receptors (mGlu receptors) and both D1‐like and D2‐like DA receptors in the rat nucleus accumbens. Intra‐accumbens administration of the selective group I mGlu receptor antagonist S‐4‐CPG (0.2 or 2 µg per side), which had no effect when injected alone, prevented the increase in locomotor activity produced by the selective D1‐like receptor agonist SKF 38393 (1 µg per side). Co‐administration with S‐4‐CPG of the group I mGlu receptor agonist DHPG, but not of the group II mGlu receptor agonist APDC or the group III mGlu receptor agonist AP4, reversed the antagonistic effect of S‐4‐CPG on the SKF 38393‐induced increase in locomotor activity. This indicates that the antagonistic effect of S‐4‐CPG could result from an action at the group I mGlu receptors. In contrast, administration of S‐4‐CPG showed no effect on the locomotor responses produced by either the selective D2‐like receptor agonist LY 171555 (1 µg per side) or a mixed solution of SKF 38393 + LY 171555 (1 µg per side each). Altogether, these results confirm that glutamate transmission may control locomotor function through mGlu receptors in a DA‐dependent manner, and further indicate that group I mGlu receptors would interact with D1‐like receptors, but not D2‐like receptors, to modulate DA transmission and locomotor activity.
Sphingosine‐1‐phosphate induces proliferation of astrocytes: regulation by intracellular signalling cascades
Authors: Pébay Alice , Toutant Madeleine , Prémont Joël , Calvo Charles‐Félix , Venance Laurent , Cordier Jocelyne , Glowinski Jacques , Tencé Martine
Published: March 2003

Sphingosine‐1‐phosphate (S1P) is a potent lysophospholipid mediator mostly released by activated platelets. It is involved in several functions in peripheral tissues, but its effects in the central nervous system are poorly documented. Therefore, we have examined the effects of S1P on the proliferation of striatal astrocytes from the mouse embryo. These cells have been found to express mRNAs for the S1P receptors, Edg‐1 and Edg‐3. S1P stimulated thymidine incorporation and induced activation of extracellular signal‐regulated kinases (Erks). Both effects were prevented by U0126, an Erk kinase inhibitor. The S1P‐evoked activation of Erk1 was totally blocked in astrocytes pretreated with a combination of either phorbol ester (24 h) and LY294002, or phorbol ester (24 h) and pertussis toxin (PTX). Each individual treatment only partially inhibited Erk1 activation. This suggests that several separate mechanisms mediate this process, one involving protein kinase C and another involving Gi/Go proteins and phosphatidylinositol 3‐kinase. In contrast, the stimulatory effect of S1P on astrocyte proliferation was totally blocked by either PTX or LY294002, but not by a downregulation of protein kinase C. S1P dramatically inhibited the evoked production of cyclic AMP, a response that was impaired by PTX. Finally, S1P stimulated the production of inositol phosphates and increased intracellular calcium by mobilization from thapsigargin‐sensitive stores. These latter effects were mainly insensitive to PTX. Probably, Gi/Go protein activation and phosphoinositide hydrolysis are early events that regulate the activation of Erks by S1P. Altogether, these observations show that astrocytes are targets for S1P. Their proliferation in response to S1P could have physiopathological consequences at sites of brain lesions and alterations of the blood–brain barrier.
Colocalization of CGRP with 5‐HT1B/1D receptors and substance P in trigeminal ganglion neurons in rats
Authors: Ma Qing‐Ping , Hill Ray , Sirinathsinghji Dalip
Published: March 2003

Vasodilatation in the dura mater has been implicated in migraine pathogenesis. Anti‐migraine triptan drugs block vasodilatation by binding to 5‐HT1B/1D receptors localized on the peripheral sensory terminals and dural blood vessel smooth muscles. Previous studies suggest that calcitonin gene‐related peptide (CGRP) released from Aδ‐fibres plays a more important role than substance P (SP) released from C‐fibres in inducing dural vasodilatation and that one of the antimigraine mechanisms of triptan drugs is inhibiting CGRP release. In the present study, the relationship between CGRP and 5‐HT1B/1D receptors, and between CGRP and SP in the trigeminal ganglion neurons in rats was examined by double immunohistochemical staining. CGRP, 5‐HT1B, 5‐HT1D and SP‐positive trigeminal ganglion neurons were all predominantly small and medium‐sized. In the trigeminal ganglia, ≈ 50% of CGRP‐positive neurons were 5‐HT1B positive. Similarly, ≈ 55% of CGRP‐positive neurons were 5‐HT1D immunoreactive. Approximately 50% of CGRP‐positive neurons were SP‐positive, while 93% of SP‐positive neurons were CGRP‐positive, suggesting that nearly all SP‐positive neurons also contain CGRP. The fibre types of the 5‐HT1B‐ and 5‐HT1D‐positive neurons were further investigated with an antibody against the A‐fibre marker 200‐kDa neurofilaments (NF200). Approximately 46% of the 5‐HT1B‐positive and 43% of the 5‐HT1D‐positive trigeminal ganglion neurons were also NF200 positive, indicating that many A‐fibre trigeminal neurons express 5‐HT1B or 5‐HT1D receptors. These results support the hypothesis that one important action of antimigraine drugs is the inhibition of CGRP release and that Aδ‐fibres may play an important role in migraine pathogenesis.
Slow IPSC kinetics, low levels of α1 subunit expression and paired‐pulse depression are distinct properties of neonatal inhibitory GABAergic synaptic connections in the mouse superior colliculus
Authors: Jüttner René , Meier Jochen , Grantyn Rosemarie
Published: March 2003

Remodelling of visual maps in the superior colliculus (SC) depends on neuronal activity. Synaptic inhibition could contribute to this process because spontaneous spike discharge in the SC was modulated by GABAA receptor activation at postnatal days (P) 1–3. To investigate the functional capacity of GABAergic synaptic transmission at this early stage of development, whole‐cell patch‐clamp recordings were made from wide field neurons (WFNs) in horizontal slices comprising the superficial grey layer of the SC. Focal stimulation in the vicinity of WFNs evoked tetrodotoxin‐sensitive stimulus‐locked inhibitory postsynaptic currents (eIPSCs). The failure rate of eIPSCs was low (≈ 0.2), and the maximal amplitude of evoked unitary eIPSCs exceeded the amplitude of average miniature IPSCs (mIPSCs) by a factor of 4–5, suggesting that action potential‐mediated GABA release was more effective than spontaneous release. Some of the properties of GABAergic synaptic transmission in the neonatal SC were age‐specific. In contrast with eIPSCs in the more mature SC at P20–22, neonatal eIPSCs decayed more slowly, preferentially fluctuated in duration, not amplitude, and mostly lacked temporal summation, due to depression at shorter intervals. The paired‐pulse ratio (eIPSC2 : eIPSC1) was inversely related to the duration of eIPSCs. PCR analysis showed, in addition, that the ratio of α1 : α3 subunit expression was lower in the neonatal SC. Together, these results suggest that, at a young age, efficacy of GABAergic synaptic transmission is primarily constrained by the slow kinetics and the saturation of postsynaptic GABAA receptors.
Localized immediate early gene expression related to the strength of song learning in socially reared zebra finches
Authors: Bolhuis Johan J. , Hetebrij Elske , Den Boer‐Visser Ardie M. , De Groot Jurriaan H. , Zijlstra Guus G. O.
Published: March 2003

Recent evidence showed that exposure of tape‐tutored zebra finch (Taeniopygia guttata castanotis) males to the tutor song involves neuronal activation in brain regions outside the conventional ‘song control pathways’, particularly the caudal part of the neostriatum (NCM) and of the hyperstriatum ventrale (CMHV). Zebra finch males were reared with a live tutor during the sensitive period for song learning. When, as adults, they were re‐exposed to the tutor song, the males showed increased expression of Fos, the protein product of the immediate early gene c‐fos, in the NCM and CMHV, compared with expression in two conventional ‘song control nuclei’, high vocal centre (HVC) and Area X. The strength of the Fos response (which is a reflection of neuronal activation) in the NCM (but not in the other three regions) correlated significantly and positively with the number of song elements that the birds had copied from the tutor song. Thus, socially tutored zebra finch males show localized neural activation in response to tutor song exposure, which correlates with the strength of song learning.
Conscious recollection and illusory recognition: an event‐related fMRI study
Authors: Von Zerssen G. Clemens , Mecklinger Axel , Opitz Bertram , Von Cramon D. Yves
Published: March 2003

In this event‐related functional magnetic resonance imaging (fMRI) study we examined the neuronal correlates of the subprocesses underlying recognition memory. In an explicit memory task, participants had to discriminate studied (‘old’) words from semantically related and unrelated ‘new’ (unstudied) words. We examined whether the correct rejection of semantically related words which were similar to old words, which had elicited correct responses, was based on conscious recollection of study phase information. In this task, false‐positive responses to semantically related new words can be assumed to result from the assessment of the semantic similarity between test words and studied words with minimal recollection. For correct identification of old words and correct rejection of new related words we found common activation in a variety of brain areas that have been shown to be involved in conscious recollection, among them the left middle frontal gyrus, the precuneus, the retrosplenial cortex, the left parahippocampal gyrus and the thalamus. For correct responses to old words, the frontomedian wall, the posterior cingulate cortex and the nucleus accumbens were additionally activated, suggesting an emotional contribution to these judgements. Correct rejections of related new words were associated with additional activation of the right middle frontal gyrus, suggesting higher monitoring demands for these more difficult recognition judgements. False‐positive responses to semantically related new words were associated with enhanced activation in the frontomedian wall. The results point to an important role of the prefrontal cortex as well as medial temporal and medial parietal regions of the brain in successful memory retrieval and conscious recollection.
Enhanced inactivation and acceleration of activation of the sodium channel associated with epilepsy in man
Authors: Alekov Alexi K. , Rahman MD. Masmudur , Mitrovic Nenad , Lehmann‐Horn Frank , Lerche Holger
Published: March 2003

Generalized epilepsy with febrile seizures‐plus (GEFS+) is a benign Mendelian syndrome characterized by childhood‐onset febrile and afebrile seizures. Three point mutations within two voltage‐gated sodium channel genes have been identified so far: in GEFS+ type 1 a mutation in the β1‐subunit gene SCN1B, and in GEFS+ type 2 two mutations within the neuronal α‐subunit gene SCN1A. Functional expression of the SCN1B and one of the SCN1A mutations revealed defects in fast channel inactivation which are in line with previous findings on myotonia causing mutations in SCN4A, the skeletal muscle sodium channel α‐subunit gene, all showing an impaired fast inactivation. We now studied the second GEFS+ mutation (T875M in SCN1A), using the highly homologous SCN4A gene (mutation T685M). Unexpectedly, the experiments revealed a pronounced enhancement of both fast and slow inactivation and a defect of channel activation for T685M compared to wild‐type channels. Steady‐state fast and slow inactivation curves were shifted in the hyperpolarizing direction, entry into slow inactivation was threefold accelerated, recovery from slow inactivation was slowed by threefold and the time course of activation was slightly but significantly accelerated. In contrast to other disease‐causing mutations in SCN1A, SCN1B and SCN4A, the only mechanism that could explain hyperexcitability of the cell membrane would be the acceleration of activation. Because the enhancement of slow inactivation was the most obvious alteration in gating found for T685M, this might be the disease‐causing mechanism for that mutation. In this case, the occurrence of epileptic seizures could be explained by a decrease of excitability of inhibitory neurons.
VR1 protein expression increases in undamaged DRG neurons after partial nerve injury
Authors: Hudson L. J. , Bevan S. , Wotherspoon G. , Gentry C. , Fox A. , Winter J.
Published: March 2003

Changes in phenotype or connectivity of primary afferent neurons following peripheral nerve injury may contribute to the hyperalgesia and allodynia associated with neuropathic pain conditions. Although earlier studies using partial nerve injury models have focused on the role of damaged fibres in the generation of ectopic discharges and pain, it is now thought that remaining undamaged fibres may be equally important. We have examined the expression of the sensory neuron‐specific cation channel Vanilloid Receptor 1 (VR1), an important transducer of noxious stimuli, in three models of nerve injury in the rat, using anatomical separation or fluorescent retrograde tracers to identify damaged or undamaged sensory neurons. After total or partial sciatic nerve transection, or spinal nerve ligation, VR1‐immunoreactivity (IR) was significantly reduced in the somata of all damaged dorsal root ganglion (DRG) neuronal profiles, compared to controls. However, after partial transection or spinal nerve ligation, VR1 expression was greater in the undamaged DRG somata than in controls. Unexpectedly, after L5 spinal nerve ligation, VR1‐IR of the A‐fibre somata increased ≈ 3‐fold in the uninjured L4 DRG compared to controls; a much greater increase than seen in the somata with C‐fibres. Furthermore, we found that VR1‐IR persisted in the transected sciatic nerve proximal to the lesion, despite its down‐regulation in the damaged neuronal somata. This persistence in the nerve proximal to the lesion after nerve section, together with increased VR1 in DRG neurons left undamaged after partial nerve injury, may be crucial to the development or maintenance of neuropathic pain.
Presynaptic kynurenate‐sensitive receptors inhibit glutamate release
Authors: Carpenedo R. , Pittaluga A. , Cozzi A. , Attucci S. , Galli A. , Raiteri M. , Moroni F.
Published: March 2003

Kynurenic acid is a tryptophan metabolite provided with antagonist activity on ionotropic glutamate and α7 nicotinic acetylcholine receptors. We noticed that in rats with a dialysis probe placed in the head of their caudate nuclei, local administration of kynurenic acid (30–100 nm) significantly reduced glutamate output. Qualitatively and quantitatively similar effects were observed after systemic administration of kynurenine hydroxylase inhibitors, a procedure able to increase brain kynurenate concentrations. Interestingly, in microdialysis studies, methyllycaconitine (0.3–10 nm), a selective α7 nicotinic receptor antagonist, also reduced glutamate output. In isolated superfused striatal synaptosomes, kynurenic acid (100 nm), but not methyllycaconitine, inhibited the depolarization (KCl 12.5 mm)‐induced release of transmitter or previously taken‐up [3H]‐D‐aspartate. This inhibition was not modified by glycine, N‐methyl‐d‐aspartate or subtype‐selective kainate receptor agents, while CNQX or DNQX (10 µm), two AMPA and kainate receptor antagonists, reduced kynurenic acid effects. Low concentrations of kynurenic acid, however, did not modify [3H]‐kainate (high and low affinity) or [3H]‐AMPA binding to rat brain membranes. Finally, because metabotropic glutamate (mGlu) receptors modulate transmitter release in striatal preparations, we evaluated, with negative results, kynurenic acid (1–100 nm) effects in cells transfected with mGlu1, mGlu2, mGlu4 or mGlu5 receptors. In conclusion, our data show that kynurenate‐induced inhibition of glutamate release is not mediated by glutamate receptors. Nicotinic acetylcholine receptors, however, may contribute to the inhibitory effects of kynurenate found in microdialysis studies, but not in those found in isolated synaptosomes.
Distribution of mossy fibre rosettes in the cerebellum of cat and mice: evidence for a parasagittal organization at the single fibre level
Authors: Sultan Fahad
Published: March 2003

Mossy fibres are the main afferent input to the granular layer of the cerebellar cortex. In this study, the spatial distribution of the mossy fibres' presynaptic enlargements – the so‐called rosettes – were analysed on the single fibre level. Data obtained from the cerebella of cat and mice were compared to look for species differences, and the cerebella of the adult and young mice were also compared to look for developmental changes. The results show that there is a spatial anisotropy in all mossy fibres studied, with neighbouring rosettes being about three times further away from each other along the parasagittal axis and closer to each other in the mediolateral direction. Furthermore, these results suggest that this anisotropy is established at an early developmental stage. The anisotropic orientation of mossy fibres at the single fibre level supports the hypothesis of a timing mechanism in cerebellar function.
Potentiation of 3‐hydroxyglutarate neurotoxicity following induction of astrocytic iNOS in neonatal rat hippocampal cultures
Authors: Kölker Stefan , Ahlemeyer Barbara , Hühne Ricarda , Mayatepek Ertan , Krieglstein Josef , Hoffmann Georg F.
Published: March 2003

Neuronal damage in glutaryl‐CoA dehydrogenase deficiency (GDD) has previously been addressed to N‐methyl‐d‐aspartate (NMDA) receptor‐mediated neurotoxicity of the accumulating neurotoxic metabolite 3‐hydroxyglutarate. However, acute encephalopathic crises in GDD patients are typically precipitated by febrile illness or even routine vaccinations, suggesting a potentiating role of inflammatory cytokines. In the present study we investigated the effect of interleukin‐1β and interferon‐γ on 3‐hydroxyglutarate toxicity in rat cortical astrocyte cultures and neonatal rat hippocampal cultures. A cotreatment of both culture systems with interleukin‐1β and interferon‐γ induced the protein expression of astrocytic inducible nitric oxide synthase (iNOS), resulting in increased nitric oxide (NO) production. Cytokine pretreatment alone had no effect on cell viability but potentiated 3‐hydroxyglutarate neurotoxicity. NOS inhibition by aminoguanidine and L‐NAME prevented an iNOS‐mediated potentiation of 3‐hydroxyglutarate neurotoxicity but failed to protect neurons against 3‐hydroxyglutarate alone. In contrast, superoxide dismutase/catalase as well as MK‐801 prevented toxicity of 3‐hydroxyglutarate alone as well as its potentiation by iNOS, supporting a central role of NMDA receptor stimulation with subsequently increased superoxide anion production. It is concluded that the potentiation of 3‐hydroxyglutarate neurotoxicity is most probably due to an induction of astrocytic iNOS and concomitantly increased NO production, enabling enhanced peroxynitrite formation. Thus, we provide evidence for a neuroimmunological approach to the precipitation of acute encephalopathic crises in GDD by inflammatory cytokines.
GFRalpha3 is expressed predominantly in nociceptive sensory neurons
Authors: Orozco Olivia E. , Walus Lee , Sah Dinah W. Y. , Pepinsky R. Blake , Sanicola Michele
Published: March 2003

Activation of the RET receptor tyrosine kinase by glial‐derived neurotrophic factor family members is dependent on a family of coreceptors, GFRα1–4. GFRα3 preferentially binds the newest member of the glial‐derived neurotrophic factor family of ligands, artemin. The major site of GFRα3 expression is in the dorsal root ganglion; however, the class of sensory neurons that expresses GFRα3 has not been reported previously. Using immunohistochemical methods, we show that the majority of dorsal root ganglion cells that express GFRα3 also express vanilloid receptor type 1, peripherin, RET, trkA and calcitonin gene‐related peptide. In addition, a significant subpopulation of GFRα3‐expressing cells also binds the lectin IB4. We demonstrate that GFRα3 artemin neurons are immunopositive for markers expected of nociceptors and include a subset of neurons distinct from the GDNF‐responsive population. Our results indicate artemin may exert selective effects on pain sensation.
Oligodendroglial tau filament formation in transgenic mice expressing G272V tau
Authors: Götz Jürgen , Tolnay Markus , Barmettler Robi , Chen Feng , Probst Alphonse , Nitsch Roger M.
Published: March 2003

Genetic evidence indicates that several mutations in tau, including G272V, are linked to frontotemporal dementia with parkinsonism. We expressed this mutation in mouse brains by combining a prion protein promoter‐driven expression system with an autoregulatory transactivator loop that resulted in high expression of human G272V tau in neurons and in oligodendrocytes. We show that G272V tau can form filaments in murine oligodendrocytes. Electron microscopy established that the filaments were either straight or had a twisted structure; these were 17–20 nm wide and had a periodicity of ≈ 75 nm. Filament formation was associated with tau phosphorylation at distinct sites, including the AT8 epitope 202/205 in vivo. Immunogold electron microscopy of sarcosyl‐extracted spinal cords from G272V transgenic mice using phosphorylation‐dependent antibodies AT8 or AT100 identified several sparsely gold‐labelled 6‐nm filaments. In the spinal cord, fibrillary inclusions were also identified by thioflavin‐S fluorescent microscopy in oligodendrocytes and motor neurons. These results establish that expression of the G272V mutation in mice causes oligodendroglial fibrillary lesions that are similar to those seen in human tauopathies.
Calcium‐activated potassium current clamps the dark potential of vertebrate rods
Authors: Moriondo Andrea , Pelucchi Bruna , Rispoli Giorgio
Published: March 2003

Vertebrate photoreceptors respond to light with a graded hyperpolarization from a membrane potential in the dark of ≈ −35 mV. The present work investigates the physiological role of the Ca2+‐activated K+ current in the photovoltage generation in mechanically isolated rods from salamander retina. Membrane current or voltage in isolated rods was recorded from light‐ and dark‐adapted rods under voltage‐ or current‐clamp conditions, respectively. In light‐adapted rods of the salamander, selective blockade of Ca2+‐activated K+ channels by means of charybdotoxin depolarized the plasma membrane of current‐clamped rods by ≈ 30 mV, from a resting potential of ≈ −35 mV. A similar depolarization was observed if external Ca2+ (1 mm) was substituted with Ba2+ or Sr2+. Under control conditions, the injection of currents of increasing amplitude (up to −100 pA, to mimic the current entering the rod outer segment) could not depolarize the membrane potential beyond a saturating value of ≈ −20 mV. However, in the presence of charybdotoxin, rods depolarized up to +20 mV. In experiments with dark‐adapted current‐clamped rods, charybdotoxin perfusion lead to transient depolarizations up to 0 mV and steady‐state depolarizations of ≈ 5 mV above the dark resting potential. Finally, the recovery phase of the voltage response to a flash of light in the presence of charybdotoxin showed a transient overshoot of the membrane potential. It was concluded that Ca2+‐activated K+ current is necessary for clamping the rod photovoltage to values close to the dark potential, thus allowing faithful single photon detection and correct synaptic transmission.
Effects of selective thalamic and prelimbic cortex lesions on two types of visual discrimination and reversal learning
Authors: Chudasama Yogita , Bussey Timothy J. , Muir Janice L.
Published: March 2003

The effects of excitotoxic lesions of the mediodorsal nucleus of the thalamus, the anterior thalamic nuclei and of the prelimbic cortex were examined on two tests of discrimination and reversal learning. In experiment 1A (visual discrimination and reversal), rats were required to discriminate two stimuli, and respond to the stimulus associated with reward (the S+ stimulus). There was no effect of lesion on acquisition of this task. However, when stimulus–reward contingencies were reversed, animals with lesions of the mediodorsal nucleus of the thalamus made significantly more errors than control animals or animals of other lesion groups. In experiment 1B (conditional discrimination), animals were required to learn a rule of the type ‘If stimulus A then go left, if stimulus B then go right’. No main effect of lesion on acquisition was observed in this experiment. To test the generality of the reversal effect obtained in experiment 1A, a second cohort of animals with the same lesions was tested on acquisition of the visuospatial conditional task immediately postsurgery, followed by the reversal of the conditional rule (experiment 2). As in experiment 1B, no main effect of lesion group was observed during acquisition of the task. However, lesions of the mediodorsal nucleus of the thalamus resulted in a mild impairment according to number of sessions required to attain criterion performance of the task when the response rule was reversed. The results of the present study provide evidence for a role for the mediodorsal nucleus of the thalamus in new learning, particularly when stimulus–reward contingencies are reversed. Furthermore, they show that the functions of this thalamic nucleus can be dissociated from those of the anterior thalamus and the prelimbic cortex.
Antisense oligodeoxynucleotide‐induced suppression of basal forebrain NMDA‐NR1 subunits selectively impairs visual attentional performance in rats
Authors: Turchi Janita , Sarter Martin
Published: March 2003

It is generally agreed that basal forebrain neuronal circuits contribute to the mediation of the ability to detect, select and discriminate signals, to suppress the processing of irrelevant information, and to allocate processing resources to competing tasks. Rats were trained in a task designed to assess sustained attention, or in a cued discrimination task that did not tax attentional processes. Animals were equipped with guide cannula to infuse bilaterally antisense oligodeoxynucleotides (ODNs) against the N‐methyl‐d‐aspartate (NMDA) NR1 subunits, or missense ODNs, into the substantia innominata of the basal forebrain. Infusions of antisense or missense ODNs did not affect cued visual discrimination performance. Infusions of antisense ODNs dose‐dependently impaired sustained attention performance by selectively decreasing the animals' ability to detect signals while their ability to reject nonsignal trials remained unchanged. The detrimental attentional effects of antisense infusions were maximal 24 h after the third and final infusion, and performance returned to baseline 24 h later. Missense infusions did not affect attentional performance. Separate experiments demonstrated extensive suppression of NR1 subunit immunoreactivity in the substantia innominata. Furthermore, infusions of antisense did not produce neurotoxic effects in that region as demonstrated by the Fluoro‐Jade method. The present data support the hypothesis that NMDA receptor (NMDAR) stimulation in the basal forebrain, largely via glutamatergic inputs originating in the prefrontal cortex, represents a necessary mechanism to activate the basal forebrain corticopetal system for mediation of attentional performance.
N‐methyl‐d‐aspartate receptor‐mediated increase of neurogenesis in adult rat dentate gyrus following stroke
Authors: Arvidsson Andreas , Kokaia Zaal , Lindvall Olle
Published: March 2003

Neurogenesis in the adult rat dentate gyrus was studied following focal ischemic insults produced by middle cerebral artery occlusion (MCAO). Animals were subjected to either 30 min of MCAO, which causes damage confined to the striatum, or 2 h of MCAO, which leads to both striatal and cortical infarction. When compared to sham‐operated rats, MCAO‐rats showed a marked increase of the number of cells double‐labelled for 5‐bromo‐2′‐deoxyuridine‐5′‐monophosphate (BrdU; injected during 4–6 days postischemia) and neuronal‐specific antigen (NeuN; a marker of postmitotic neurons) in the ipsilateral dentate granule cell layer and subgranular zone at 5 weeks following the 2 h insult. Only a modest and variable increase of BrdU‐labelled cells was found after 30 min of MCAO. The enhanced neurogenesis was not dependent on cell death in the hippocampus, and its magnitude was not correlated to the degree of cortical damage. Systemic administration of the N‐methyl‐d‐aspartate (NMDA) receptor blocker dizocilpine maleate (MK‐801) completely suppressed the elevated neurogenesis following 2 h of MCAO. Our findings indicate that stroke leads to increased neurogenesis in the adult rat dentate gyrus through glutamatergic mechanisms acting on NMDA receptors. This modulatory effect may be mediated through changes in the levels of several growth factors, which occur after stroke, and could influence various regulatory steps of neurogenesis.
Effects of cannabinoids on prefrontal neuronal responses to ventral tegmental area stimulation
Authors: Pistis Marco , Porcu Giuseppe , Melis Miriam , Diana Marco , Luigi Gessa Gian
Published: March 2003

Cannabinoids activate the firing of mesoprefrontocortical dopamine neurons and release dopamine in the prefrontal cortex. This study was undertaken with the aim of clarifying the interaction between cannabinoids and mesocortical system in the prefrontal cortex. The effect of Δ9‐tetrahydrocannabinol (Δ9‐THC) and the synthetic CB1 agonist WIN55,212–2 (WIN) was studied by extracellular single unit recordings, in chloral hydrate anaesthetised rats, on the spontaneous activity of pyramidal neurons and on the inhibition produced on these neurons by the electrical stimulation of the ventral tegmental area (VTA). Intravenously administered Δ9‐THC and WIN (1.0 and 0.5 mg/kg, respectively), increased the firing rate of pyramidal neurons projecting to the VTA. VTA stimulation produced a phasic inhibition (167 ± 6 ms) in 79% of prefrontal cortex pyramidal neurons. Δ9‐THC and WIN reverted this inhibition in 73% and 100% of the neurons tested, respectively. The subsequent administration of the selective CB1 antagonist SR141716A (1 mg/kg) readily suppressed the effects of both cannabinoids and restored the inhibitory response to VTA stimulation. Moreover, when administered alone, SR141716A prolonged the inhibition in 55.6% of the neurons tested. The results indicate that stimulation of CB1 receptors by cannabinoids results in an enhanced excitability of prefrontal cortex pyramidal neurons as indexed by the suppression of the inhibitory effect of VTA stimulation and by the increase in firing rate of antidromically identified neurons projecting to the VTA. Furthermore, our results support the view that endogenous cannabinoids exert a negative control on dopamine activity in the prefrontal cortex. This study may be relevant in helping to understand the influence of cannabinoids on cognitive processes mediated by the prefrontal cortex.
Chronic levodopa therapy does not improve skilled reach accuracy or reach range on a pasta matrix reaching task in 6‐OHDA dopamine‐depleted (hemi‐Parkinson analogue) rats
Authors: Metz Gerlinde A. S. , Farr Tracy , Ballermann Mark , Whishaw Ian Q.
Published: March 2003

l‐dopa therapy reverses some but not all of the motor deficits in human Parkinson patients. Although a number rat analogues of human Parkinson's disease have been developed for evaluating the efficacy of drug therapies, it is not known whether l‐dopa has a similar selective action on the motor symptoms in the rat models. To examine the effectiveness of l‐dopa in reversing the motor deficits in rats, we administered 6‐OHDA unilaterally to produce hemi‐Parkinson rats, which were then trained to reach for food using either their impaired (contralateral to the lesion) limb or their good (ipsilateral to the lesion) limb. To assess the skill, accuracy and range of limb movement, rats reached for pasta from a horizontal array of 260 vertically orientated pieces of pasta. The number and location of pasta pieces taken from this matrix was calculated and the qualitative aspects of the reaching movements were rated. The quantitative data on pasta sticks retrieved indicated that forelimb extension and movement radius around the shoulder joint was reduced by 6‐OHDA treatment and did not improve after chronic l‐dopa treatment. The qualitative analysis showed that grasping patterns, paw movements and body movements impaired by the lesion were also not improved by l‐dopa treatment. These findings are the first in the rat to suggest that whereas l‐dopa has a general activating effect on the rat's whole‐body movements, as displayed in contralateral rotation, its effectiveness does not extend to skilled forelimb movements. The results are discussed in relationship to the idea that the restoration of some skilled movements may require normal synaptic function.
D2‐like dopamine receptor activation excites rat dorsal raphe 5‐HT neurons in vitro
Authors: Haj‐Dahmane Samir
Published: March 2003

The aim of the present study was to investigate the effect of dopamine (DA) on the excitability of dorsal raphe nucleus (DRN) 5‐hydroxytryptamine (5‐HT) neurons using the patch‐clamp technique in brain slices. Bath application of DA (1–300 µm) produced a concentration‐dependent membrane depolarization in all 5‐HT neurons examined. This effect persisted in the presence of tetrodotoxin (TTX; 1 µm) and low extracellular calcium. Moreover, blockade of ionotropic glutamate receptors with 6,7‐dinitroquinoxaline‐2,3‐dione (DNQX) and 2‐amino‐5‐phosphonopentanoic acid (AP5) did not prevent DA‐induced depolarization, indicating that it was mediated by a direct effect of DA on 5‐HT neurons. The DA‐induced depolarization was not antagonized by selective α1‐adrenergic receptor antagonists, prazosin and WB 4101, but by a nonselective DA receptor antagonist, haloperidol. In addition, the selective D2‐like receptor agonist quinpirole and antagonist sulpiride mimicked and blocked DA‐induced depolarization, respectively. These results indicate that DA‐induced membrane depolarization in DRN 5‐HT neurons is mediated by the activation of D2‐like DA receptors. The DA‐induced membrane depolarization and inward current were associated with an increase in membrane conductance. Examination of the current–voltage (I–V) relationship for the DA‐induced inward current revealed that the amplitude of the current increased with membrane hyperpolarization and reversed polarity at a potential near −15 mV. These data suggest that DA‐induced depolarization in DRN 5‐HT neurons is not mediated by a decrease in potassium conductance, but most likely by the activation of a nonselective cation current.
Inhibition of synaptically evoked cortical acetylcholine release by intracortical glutamate: involvement of GABAergic neurons
Authors: Materi Leticia M. , Semba Kazue
Published: March 2003

Cortical acetylcholine (ACh) has been shown to regulate diverse cognitive processes and its release can be regulated by neuromodulators that act presynaptically at cholinergic terminals. The neocortex receives dense glutamatergic input from thalamocortical and other fibres. The present study usedin vivomicrodialysis to examine, and pharmacologically characterize, the effect of glutamate on cortical ACh release evoked by electrical stimulation of the pedunculopontine tegmental nucleus in urethane‐anaesthetized rats. All drugs were administered locally within the cortex by reverse dialysis. Application of glutamate had no detectable effect on spontaneous ACh release but reduced evoked cortical ACh efflux in a concentration‐dependent manner. This effect was mimicked by the glutamate transporter blockerl‐trans‐pyrrolidine‐2,4‐dicarboxylic acid, as well as by the ionotropic glutamate receptor agonists N‐methyl‐d‐aspartic acid and α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid, and was blocked by the ionotropic glutamate receptor antagonists 6,7‐dinitroquinoxaline‐2,3‐dione and (+/–)‐3‐(2‐carboxypiperazin‐4yl)‐propyl‐1‐phosphonic acid. Glutamate application also increased extracellular adenosine levels but the simultaneous delivery of the broad‐spectrum adenosine receptor antagonist caffeine failed to affect the inhibitory action of glutamate on evoked ACh release. However, the effect of glutamate was fully blocked by simultaneous delivery of the GABAAreceptor antagonist bicuculline and partially blocked by the GABABreceptor antagonist phaclofen. These results suggest that ionotropic glutamate receptor activation by glutamate inhibits evoked cortical ACh release via an indirect pathway involving GABAergic neurons in the cortex.
Roles of the glutamate receptor ε2 and δ2 subunits in the potentiation and prepulse inhibition of the acoustic startle reflex
Authors: Takeuchi Tomonori , Kiyama Yuji , Nakamura Kazuhiro , Tsujita Mika , Matsuda Ikuo , Mori Hisashi , Munemoto Yumi , Kuriyama Hiromichi , Natsume Rie , Sakimura Kenji , Mishina Masayoshi
Published: March 2003

We examined the regulation of the acoustic startle response in mutant mice of the N‐methyl‐d‐aspartate (NMDA)‐ and δ‐subtypes of the glutamate receptor (GluR) channel, which play important roles in neural plasticity in the forebrain and the cerebellum, respectively. Heterozygous mutant mice with reduced GluRε2 subunits of the NMDA receptor showed strongly enhanced startle responses to acoustic stimuli. On the other hand, heterozygous and homozygous mutation of the other NMDA receptor GluRε subunits exerted no, or only small effects on acoustic startle responses. The threshold of the auditory brainstem response of the GluRε2‐mutant mice was comparable to that of the wild‐type littermates. The primary circuit of the acoustic startle response is a relatively simple oligosynaptic pathway located in the lower brainstem, whilst the expression of GluRε2 is restricted to the forebrain. We thus suggest that the NMDA receptor GluRε2 subunit plays a role in the regulation of the startle reflex. Ablation of the cerebellar Purkinje cell‐specific δ2 subunit of the GluR channel exerted little effect on the acoustic startle response but resulted in the enhancement of prepulse inhibition of the reflex. Because inhibition of the acoustic startle response by a weak prepulse is a measure of sensorimotor gating, the process by which an organism filters sensory information, these observations indicate the involvement of the cerebellum in the modulation of sensorimotor gating.