bluuebunny/crossref_metadata_2025 huggingface dataset:
Neuronal and vascular localization of histamine N‐methyltransferase in the bovine central nervous system
Authors: Nishibori Masahiro , Tahara Akihito , Sawada Ken , Sakiyama Junko , Nakaya Naoki , Saeki Kiyomi
Published: March 2003

Histamine N‐methyltransferase (HMT) (EC 2.1.1.8) plays a crucial role in the inactivation of the neurotransmitter histamine in the CNS. However, the localization of HMT remains to be determined. In the present study, we investigated immunohistochemical localization of HMT in the bovine CNS using a polyclonal antibody against bovine HMT. The HMT‐like immunoreactivity was observed mainly in neurons. Strongly immunoreactive neurons were present in the oculomotor nucleus and ruber nucleus in the midbrain, the facial nucleus in the pons, the dorsal vagal nucleus and hypoglossal nucleus in the medulla oblongata and in the anterior horn as well as intermediolateral zone of the spinal cord. Intermediately immunoreactive neurons were present in the piriform cortex and the inferior olivary nucleus. The grey matter of the forebrain regions was diffusely and faintly stained. In the cerebellum and the striatum, the nerve fibres in the white matter were positive. The tuberomammillary nucleus, where histaminergic neurons are present, were weakly positive. The other immunoreactive structures in the CNS were blood vessels. Almost all of the blood vessel walls, irrespective of whether they were arterial or venous, were variably stained. The glial fibrillary acidic protein‐ (GFAP‐) immunoreactive astrocytes were not stained. These findings indicated that histamine released from histaminergic nerve terminals or varicose fibres is methylated mainly in postsynaptic or extrasynaptic neurons rather than in astrocytes. The localization of HMT in the blood vessel wall may mean that blood‐borne histamine and histamine released from mast cells associated with the blood vessels are catabolized in this structure.
Differential sensitivity to Zolpidem of IPSPs activated by morphologically identified CA1 interneurons in slices of rat hippocampus
Authors: Thomson Alex M. , Bannister A. Peter , Hughes David I. , Pawelzik Hannelore
Published: March 2003

Hippocampal pyramidal cells express several α‐subunits, which determine the affinity of GABAA (γ‐aminobutyric acid) receptors for benzodiazepine site ligands. This study asked whether inhibitory postsynaptic potentials (IPSPs) elicited by specific interneuronal subclasses were differentially sensitive to the α1‐preferring agonist Zolpidem, i.e. whether different receptors mediate different inhibitory connections. Paired intracellular recordings in which the presynaptic cell was an interneuron and the postsynaptic cell a CA1 pyramid were performed in slices of adult rat hippocampus. Resultant IPSPs were challenged with Zolpidem, cells filled with biocytin and identified morphologically. IPSPs elicited by fast spiking (FS) basket cells (n = 9) were enhanced more than IPSPs elicited by regular spiking (RS) basket cells (n = 10). At FS basket cell synapses the efficacy of Zolpidem was equivalent to that of Diazepam, while RS basket cell IPSPs are enhanced 50% less by Zolpidem than by Diazepam. Thus, while α1 subunits may dominate at synapses supplied by FS basket cells, RS basket cell synapses also involve α2/3 subunits. Two bistratified cell IPSPs tested with Zolpidem did not increase in amplitude, despite powerful enhancements of bistratified cell IPSPs by Diazepam, consistent with previous indications that these synapses utilize α5‐containing receptors. Enhancements of basket cell IPSPs by Zolpidem and Diazepam were bi‐ or triphasic with steep amplitude increases separated by plateaux, occurring 10–15, 25–30 and 45–55 min after adding the drug to the bath. The entire enhancement was, however, blocked by the antagonist Flumazenil (n = 7). Flumazenil, either alone (n = 3), or after Zolpidem, reduced IPSP amplitude to ∼ 90% of control, suggesting that α4‐containing receptors were not involved.
Cerebral oligaemia episode triggers free radical formation and late cognitive deficiencies
Authors: Heim Christine , Zhang Jianjun , Lan Jing , Sieklucka Maria , Kurz Tino , Riederer Peter , Gerlach Manfred , Sontag Karl‐Heinz
Published: March 2003

Sixty minutes of cerebral oligaemic hypoxia, induced by bilateral clamping of the carotid arteries (BCCA) in pentobarbital‐anaesthetized normotensive rats, induces a late progressive cognitive decline when compared with sham‐operated controls. Analysis at BCCA of hippocampal metabolism using microdialysis showed increased release of glutamate, aspartate and γ‐aminobutyric acid, followed by a progressive rise in the formation of hydroxyl free radicals measured as 2,3‐dihydroxybenzoic acid (2,3‐DHBA), their reaction product with salicylate, though only in the re‐perfusion phase. In the striatum increased dopamine release occurred during BCCA, whereas glutamate and aspartate showed an increase only during the late re‐perfusion phase. γ‐Aminobutyric acid (GABA) concentration increased during BCCA and early re‐perfusion. An increase in 2,3‐DHBA was seen during BCCA, and persisted over 2 h of re‐perfusion. Six and 13 months after surgery, though not as early as 3 months, BCCA‐treated rats perform worse than sham‐operated controls in a water‐maze, where decreased swimming speed reveals striatal dysfunction, while hippocampal dysfunction manifested as diminished spatial bias. These results show that cerebral oligaemia, similarly to cerebral ischaemia, leads to increased extracellular dopamine, aspartate and glutamate, and the production of hydroxyl radicals in structures associated with learning and memory processes. Unlike cerebral ischaemia, in cerebral oligaemia the appearance of spatial memory deficits is delayed.
Selective suppression of horizontal propagation in rat visual cortex by norepinephrine
Authors: Kobayashi Masayuki , Imamura Kazuyuki , Sugai Tokio , Onoda Norihiko , Yamamoto Masao , Komai Shoji , Watanabe Yasuyoshi
Published: March 2003

The release of norepinephrine in the cerebral cortex from axon terminals of locus coeruleus neurons was suggested to be involved in the control of attention. Accumulating data indicate that the responses of cortical neurons are varied when norepinephrine is applied iontophoretically in the vicinity of the cells being recorded. However, it is not known how the pattern of excitatory propagation is modified when norepinephrine is applied over a wide area in the visual cortex. By applying optical imaging to rat visuocortical slices, we found a new mode of norepinephrine action; a prominent suppression of the horizontal propagation in layers II/III. This action of norepinephrine was confirmed by the simultaneous recording of field potentials from multiple sites by use of a multi‐electrode dish. Furthermore, our electrophysiological recordings showed that this norepinephrine action is exerted through suppression of excitatory neural transmission and enhancement of inhibitory transmission to the pyramidal neurons in these layers. Because the release of norepinephrine in the visual cortex is regulated by the level of attention, the neural basis of visual attention may relate partially to the suppression of the integration of visual information by norepinephrine resulting in a state‐dependent restructuring of the receptive field.
Light‐adaptive effects of retinoic acid on receptive field properties of retinal horizontal cells
Authors: Pottek Mark , Weiler Reto
Published: March 2003

Besides its role in ocular development, retinoic acid (RA), which is a light‐correlated byproduct of the phototransduction cycle, was recently shown to affect light‐driven synaptic plasticity in the outer plexiform layer of the adult fish retina. Tuning by ambient light conditions of the retinal network properties is very prominent in outer plexiform layer circuits, and we therefore examined whether RA could affect cone horizontal cell physiology similar to ambient light. Performing intracellular recordings and dye injections in the dark‐adapted inverted eyecup preparation of the carp, we found that RA reduced the receptive fields of horizontal cell somata and impaired gap junctional communication. This action was not observed among coupled axon terminals of horizontal cells and appeared to be stereospecific because it could only be attributed to all‐trans and 13‐cis RA but not to the 9‐cis isomer and photoisomerized all‐trans RA. Modulation of receptive field size occurred independently of the dopaminergic system. Furthermore, RA affected the light responsiveness of cone horizontal cells. Compared to the dark‐adapted condition, responsiveness to intense light stimulation was enhanced but decreased when low intensities were used. Moreover, following RA treatment H2‐type horizontal cells of dark‐adapted retinae which do not give rise to colour‐opponent light properties became colour‐opponent and performed depolarizing responses to long‐wavelength stimulation. In all these cases RA perfectly matched the effects of light adaptation, supporting the notion that RA acts as an endogenous neuromodulator.
The novel brain neuropeptide, orexin‐A, modulates the sleep–wake cycle of rats
Authors: Piper David C. , Upton Neil , Smith Martin I. , Hunter A. Jackie
Published: March 2003

Orexin‐A is a novel neuropeptide initially isolated from hypothalamic extracts but now known to be present in fibres distributed throughout the rat CNS including many regions associated with sleep–wake regulation. The recognition of a particularly dense innervation of orexinergic nerves in the locus coeruleus, together with the observed increase in firing rate of locus coeruleus neurons following application of orexin‐A in vitro, further highlighted a potential involvement of the peptide in modulating the arousal state. The present study was undertaken to determine the effects of intracerebroventricularly (ICV) administered orexin‐A on the sleep–wake cycle of conscious rats using electroencephalographic and electromyographic recordings. When administered at the onset of the normal sleep period, orexin‐A (1, 10 or 30 μg/rat ICV) produced a dose‐dependent increase in the time rats spent awake during the second and third hours after dosing. The enhancement of arousal was accompanied by a marked reduction in paradoxical sleep and deep slow wave sleep at the highest dose. The latency to the first occurrence of paradoxical sleep was also prolonged. This overall profile of increased arousal and decreased paradoxical sleep is consistent with a high rate of firing of locus coeruleus neurons as would be expected to occur following ICV administration of orexin‐A. It is concluded that orexin‐A may play an important physiological role in regulating the sleep–wake state, a hypothesis considerably strengthened by the recently reported narcoleptic phenotype of prepro‐orexin (the precursor for orexin‐A) knockout mice.
Localization of the fragile X mental retardation 2 (FMR2) protein in mammalian brain
Authors: Miller William J. , Skinner Judith A. , Foss Grethe S. , Davies Kay E.
Published: March 2003

The transcriptional silencing of the FMR2 gene has been implicated in FRAXE mental retardation. FRAXE individuals have been shown to exhibit learning deficits, including speech delay, reading and writing problems. FMR2 encodes a large protein of 1311 amino acids and is a member of a gene family encoding proline–serine‐rich proteins that have properties of nuclear transcription factors. To characterize the expression of the fragile X mental retardation 2 (FMR2) protein, polyclonal antibodies were raised against two regions of the human FMR2 protein and used in immunofluorescence experiments on mouse brain cryosections. Our results demonstrate for the first time that the FMR2 protein is localized in neurons of the neocortex, Purkinje cells of the cerebellum and the granule cell layer of the hippocampus. FMR2 staining is shown to colocalize with the nuclear stain 4,6‐diamidino‐2‐phenylindole (DAPI) confirming that FMR2 is a nuclear protein. The localization of FMR2 protein to the mammalian hippocampus and other brain structures involved with cognitive function is consistent with the learning deficits seen in FRAXE individuals.
Leukaemia inhibitory factor is required for normal inflammatory responses to injury in the peripheral and central nervous systems in vivo and is chemotactic for macrophages in vitro
Authors: Sugiura Shigeki , Lahav Ronit , Han Jing , Kou Shi‐Ying , Banner Lisa R. , De Pablo Flora , Patterson Paul H.
Published: March 2003

The cytokine leukaemia inhibitory factor (LIF) is up‐regulated in glial cells after injury to the peripheral and central nervous systems. In addition, LIF is required for the changes in neuropeptide expression that normally occur when the axons of sympathetic and sensory neurons are transected. We investigated whether LIF is also necessary for the initial inflammatory response that follows mechanical injury to the sciatic nerve and cerebral cortex of adult mice. We find that inflammatory cell infiltration into crushed sciatic nerve is significantly slower in LIF knock‐out (KO) mice compared with wild‐type (WT) mice. Similarly, the microglial and astroglial responses to surgical injury of the cortex are significantly slower in LIF KO mice compared with WT mice. Consistent with these in vivo results, LIF is chemotactic for peritoneal macrophages in a microchamber culture assay. Thus, LIF is a key regulator of neural injury in vivo, where it is produced by glia and can act directly on neurons, glia and inflammatory cells. We also find that the initial inflammatory response to cortical injury is diminished in interleukin (IL)‐6 KO mice. Surprisingly, however, the inflammatory response in LIF‐IL‐6 double KO mice is very similar to that of the single KO mice, suggesting that these cytokines may act in series rather than in parallel in this response.
Acetylcholine receptors are required for postsynaptic aggregation driven by the agrin signalling pathway
Authors: Grow Wade A. , Gordon Herman
Published: March 2003

To investigate the role of acetylcholine receptors (AChRs) in the aggregation of postsynaptic molecules on muscle cells, we utilized the 1R– genetic variant of C2 muscle cells which has very little expression of AChRs in its cell membrane. On C2 myotubes, AChRs cluster spontaneously, with the frequency of clustering greatly enhanced by motor neuron‐derived agrin. Signal transduction events driven by agrin, including the tyrosine phosphorylation of muscle‐specific kinase (MuSK) and the AChR β subunit, have been implicated as requirements of postsynaptic scaffold assembly. We show here that some molecules of the postsynaptic scaffold spontaneously aggregate and colocalize on 1R– myotubes at very low frequency, including an as yet unidentified agrin binding molecule, β‐dystroglycan and MuSK. Agrin is unable to increase the frequency of these aggregations, but does cause tyrosine phosphorylation of MuSK. We conclude that free molecules can associate into aggregates independently of AChRs, but AChRs are required for high‐frequency molecular aggregation driven by the agrin signalling pathway. MuSK tyrosine phosphorylation appears to precede a requisite event involving AChRs that aggregates postsynaptic molecules.
A dynamic regulation of GDNF‐family receptors correlates with a specific trophic dependency of cranial motor neuron subpopulations during development
Authors: Mikaels Åsa , Livet Jean , Westphal Heiner , De Lapeyrière Odile , Ernfors Patrik
Published: March 2003

Glial cell line‐derived neurotrophic factor (GDNF) family ligands promote the survival of developing motor neurons in vivo and in vitro. However, not all neurons survive with any single ligand in culture and GDNF null mutant mice display only a partial motor neuron loss. An interesting possibility is that subpopulations of motor neurons based on their function and/or their myotopic organization require distinct members of GDNF family ligands. Because responsiveness to the different ligands depends on the expression of their cognate ligand‐binding receptor we have herein addressed this issue by examining the expression of GDNF‐family receptors (gfr) during development and in the adult in cranial motor nuclei subpopulations. We have furthermore examined the in vivo role of GDNF for cranial motor neuron subpopulations. The shared ret receptor was expressed in all somatic, branchial and visceral cranial embryonic motor nuclei examined, showing that they are all competent to respond to GDNF family ligands during development. At early stages of development both the GDNF receptor, gfrα1, and the neurturin (NTN) receptor, gfrα2, were expressed in the oculomotor, facial and spinal accessory, and only gfrα1 in the trochlear, superior salivatory, trigeminal, hypoglossal and weakly in the dorsal motor nucleus of the vagus and the ambiguus nucleus. The abducens nucleus was negative for both gfrα1 and gfrα2. The artemin (ART) receptor, gfrα3, was expressed only in the superior salivatory nucleus. A motor neuron subnuclei‐specific expression of gfrα1 and gfrα2 was seen in the facial and trigeminal nuclei which corresponded to their dependence on GDNF in null mutant mice. We found that the expression was dynamic in these nuclei, which may reflect developmental changes in their trophic factor dependency. Analysis of GDNF null mutant mice revealed that the dynamic receptor expression is regulated by the ligand in vivo, indicating that the acquirement of changes in dependency could be ligand induced. Our results indicate that specific GDNF family ligands support selective muscle–motor neuron circuits during development.
NOS inhibition during postnatal development leads to increased ipsilateral retinocollicular and retinogeniculate projections in rats
Authors: Vercelli A. , Garbossa D. , Biasiol S. , Repici M. , Jhaveri S.
Published: March 2003

Synthesis of nitric oxide (NO) occurs downstream from activation of N‐methyl‐ d‐aspartate (NMDA) receptors; NO reportedly acts as a retrograde messenger, influencing the refinement and stabilization of coactive afferent terminals. Cells and neuropil in the rat superior colliculus (SC) and lateral geniculate body (LGB) show intense, developmentally regulated activity for NO synthase (NOS). To study the role of NO in the development of retinogeniculate and retinotectal axon arbors, we examined primary visual projections of rats that had received intraperitoneal injections of Nω‐nitro‐l‐arginine (L‐NoArg, an NOS inhibitor) on postnatal day 0, and daily thereafter for 4–6 weeks. Treated rats showed significant alterations in ipsilateral retinotectal projections, in the mediolateral and anteroposterior axes; there was an increase in the density of fibres entering the SC, in branch length, and in the numbers of boutons on retinotectal arbors in the treated group. Ipsilaterally projecting retinal axons also showed an increase in density and distribution in the dorsal nucleus of the LGB. If animals were allowed to survive for several months after stopping treatment, similar changes were also noted, but these were much less striking. Our results support the hypothesis that, in the mammalian visual system, NO released from target neurons in the SC and LGB serves as a retrograde signal which feeds back on retinal afferents, influencing their growth. The effects of NOS inhibition are partially reversed after treatment is stopped, indicating that lack of NO synthesis delays the maturation of retinofugal connections, and also that NO plays a constitutive role in their development.
Abnormal axonal physiology is associated with altered expression and distribution of Kv1.1 and Kv1.2 K+ channels after chronic spinal cord injury
Authors: Nashmi Raad , Jones Owen T. , Fehlings Michael G.
Published: March 2003

Dysfunction of surviving axons which traverse the site of spinal cord injury (SCI) has been linked to altered sensitivity to the K+ channel blocker 4‐aminopyridine (4‐AP) and appears to contribute to post‐traumatic neurological deficits although the underlying mechanisms remain unclear. In this study, sucrose gap electrophysiology in isolated dorsal column strips, Western blotting and confocal immunofluorescence microscopy were used to identify the K+ channels associated with axonal dysfunction after chronic (6–8 weeks postinjury) clip compresssion SCI of the thoracic cord at T7 in rats. The K+ channel blockers 4‐AP (200 μm, 1 mm and 10 mm) and α‐dendrotoxin (α‐DTX, 500 nm) resulted in a significant relative increase in the amplitude and area of compound action potentials (CAP) recorded from chronically injured dorsal column axons in comparison with control noninjured preparations. In contrast, TEA (10 mm) and CsCl (2 mm) had similar effects on injured and control spinal cord axons. Western blotting and quantitative immunofluorescence microscopy showed increased expression of Kv1.1 and Kv1.2 K+ channel proteins on spinal cord axons following injury. In addition, Kv1.1 and Kv1.2 showed a dispersed staining pattern along injured axons in contrast to a paired juxtaparanodal localization in uninjured spinal cord axons. Furthermore, labelled α‐DTX colocalized with Kv1.1 and Kv1.2 along axons. These findings suggest a novel mechanism of axonal dysfunction after SCI whereby an increased 4‐AP‐ and α‐DTX‐sensitive K+ conductance, mediated in part by increased Kv1.1 and Kv1.2 K+ channel expression, contributes to abnormal axonal physiology in surviving axons.
NO‐mediated cGMP synthesis in cholinergic neurons in the rat forebrain: effects of lesioning dopaminergic or serotonergic pathways on nNOS and cGMP synthesis
Authors: De Vente J. , Van Ittersum M. Markerink‐. , Van Abeelen J. , Emson P. C. , Axer H. , Steinbusch H. W. M.
Published: March 2003

Nitric oxide synthase (NOS) activity and NO‐mediated cGMP synthesis were studied in the rat forebrain of control animals and animals which had received a unilateral lesioning of dopaminergic or serotonergic pathways. Lesioning of the dopaminergic innervation using 6‐hydroxydopamine resulted in a 50% decrease in NOS activity in the lesioned frontal cortex and caudate putamen. Lesioning of the serotonergic innervation using 5,7‐dihydroxytryptamine had no effect on NOS activity. NO‐mediated cGMP accumulation in rat forebrain slices was not affected by 6‐hydroxydopamine or 5,7,‐dihydroxytryptamine lesioning. Using cGMP immunocytochemistry, it was demonstrated that NO‐mediated cGMP synthesis was absent from dopaminergic, serotonergic, GABA‐ergic and neuronal NOS‐containing nerve fibres. A minor colocalization of cGMP immunoreactivity was found in parvalbumin‐containing fibres in the cortex. Extensive colocalization between cGMP immunoreactivity and the acetylcholine transporter was found in all cortical areas and in the caudate putamen. There was no effect of the lesions on this colocalization. These results demonstrate NO‐mediated cGMP accumulation in cholinergic fibres in the forebrain of the rat and suggest an anterograde signalling function of NO in cholinergic neuronal systems in the cortex and caudate putamen of the rat.
Hyperpolarization‐activated current, Ih, in inspiratory brainstem neurons and its inhibition by hypoxia
Authors: Mironov S. L. , Langohr K. , Richter D. W.
Published: March 2003

A hyperpolarization‐activated current, Ih, is often implied in pacemaker‐like depolarizations during rhythmic oscillatory activity. We describe Ih in the isolated respiratory centre of immature mice (P6–P11). Ih was recorded in 15% (22/146) of all inspiratory neurons examined. The mean half‐maximal Ih activation occurred at −78 mV and the reversal potential was −40 mV. Ih was inhibited by Cs+ (1–5 mm) and by organic blockers N‐ethyl‐1,6‐dihydro‐1,2‐dimethyl‐6‐(methylimino)‐N‐phenyl‐4‐pyrimidinamine (ZD 7288; 0.3–3 μm) and N,N′‐bis‐(3,4‐dimethylphenylethyl)‐N‐methylamine (YS 035, 3–30 μm), but not by Ba2+ (0.5 mm). The organic Ih blockers did not change the inspiratory bursts recorded from the XIIth nerve and synaptic drives in inspiratory neurons. Hypoxia reversibly inhibited Ih but, in the presence of organic blockers, the hypoxic reaction remained unchanged. We conclude that although Ih channels are functional in a minority of inspiratory neurons, Ih does not contribute to respiratory rhythm generation or its modulation by hypoxia.
Reduction of stress‐induced analgesia but not of exogenous opioid effects in mice lacking CB1 receptors
Authors: Valverde Olga , Ledent Catherine , Beslot Francoise , Parmentier Marc , Roques Bernard P.
Published: March 2003

CB1 cannabinoid receptors are widely distributed in the central nervous system where they mediate most of the cannabinoid‐induced responses. Here we have evaluated the interactions between the CB1 cannabinoid receptors and the endogenous opioid system by assaying a number of well‐characterized opioid responses, e.g. antinociception and stress‐mediated effects, on mutant mice in which the CB1 receptor gene was invalidated. The spontaneous responses to various nociceptive stimuli (thermal, mechanical and visceral pain) were not changed in mutant CB1 mice. Furthermore, the absence of the CB1 cannabinoid receptor did not modify the antinociceptive effects induced by different opioid agonists: morphine (preferential mu opioid agonist), d‐Pen2‐d‐Pen5‐enkephalin (DPDPE) and deltorphin II (selective delta opioid agonists), and U‐50,488H (selective kappa opioid agonist) in the hot‐plate and tail‐immersion tests. In contrast, the stress‐induced opioid mediated responses were modified in CB1 mutants. Indeed, these mutants did not exhibit antinociception following a forced swim in water at 34 °C and presented a decrease in the immobility induced by the previous exposure to electric footshock. However, the antinociception induced by a forced swim in water at 10 °C was preserved in CB1 mutants. These results indicate that CB1 receptors are not involved in the antinociceptive responses to exogenous opioids, but that a physiological interaction between the opioid and cannabinoid systems is necessary to allow the development of opioid‐mediated responses to stress.
Connective tissue growth factor: a novel player in tissue reorganization after brain injury?
Authors: Hertel Moritz , Tretter Yvonne , Alzheimer Christian , Werner Sabine
Published: March 2003

Recent studies have suggested a role of connective tissue growth factor (CTGF) in repair processes of the skin as well as in various types of fibrotic disease. However, a function of this molecule in central nervous system (CNS) repair has not been demonstrated yet. In this study we analysed the temporal and spatial expression pattern of CTGF after unilateral kainic acid lesions of the hippocampal CA3 region in mice. We found a strong induction of CTGF mRNA and protein expression in neurons and glial cells of the lesioned hippocampus. Interestingly, increased expression of this mitogen was accompanied by elevated levels of the extracellular matrix molecule fibronectin, which is a known target of CTGF action. Therefore, our data indicate a novel function of CTGF in postlesional restructuring of the hippocampus, where it possibly participates in glial scar formation.
Dynamics of munc18‐1 phosphorylation/dephosphorylation in rat brain nerve terminals
Authors: De Vries Klaas Jan , Geijtenbeek Arwin , Brian Elisabeth C. , De Graan Pierre N. E. , Ghijsen Wim E. J. M. , Verhage Matthijs
Published: March 2003

Munc18‐1 is a mammalian member of the SEC1 protein family implicated in neuronal secretion. Its sequence contains several consensus sites for phosphorylation by protein kinase C (PKC), a kinase known to enhance secretion. We have characterized the phosphorylation of the synaptic munc18‐1 pool by endogenous, presynaptic PKC‐isoforms. In isolated rat brain nerve terminals, munc18‐1 was almost completely nonphosphorylated. Its phosphorylation state increased by 250% on inhibition of endogenous phosphatases and by 1500% on additional, direct PKC activation using phorbol esters. K+‐evoked depolarization also increased munc18‐1 phosphorylation, by 50% within 5 s in a Ca2+‐dependent manner. Munc18‐1 phosphorylation in nerve terminals was blocked by PKC inhibitors. Activation of endogenous PKC in nerve terminals inhibited the interaction of synaptic munc18‐1 with its binding partner syntaxin‐1A by 50%. Munc18‐1 antisera precipitated 80% of native, brain‐derived munc18‐1 from salt solutions, but only 12% from synaptosomal lysates, together with 6% synaptic syntaxin‐1A/B; these amounts were not changed by PKC activation. In this 12%, the phosphate incorporation per mole of munc18 was four‐fold lower than the total pool. We conclude that the synaptic munc18‐1 pool can be readily and rapidly phosphorylated by endogenous presynaptic PKC isoforms. A high constitutive phosphatase activity keeps its basal phosphorylation state low so that PKC activation can increase the phosphorylation state dramatically. These phosphorylation dynamics and the effects on the interaction with syntaxin‐1A make munc18‐1 a prominent candidate to account for PKC‐dependent enhancement of secretion.
Serotonin may stimulate granule cell proliferation in the adult hippocampus, as observed in rats grafted with foetal raphe neurons
Authors: Brezun Jean Michel , Daszuta Annie
Published: March 2003

The long‐term effects of hippocampal serotonergic denervation and reinnervation by foetal raphe tissue were examined in the dentate gyrus where neurons are continously born in the adult. Complete lesion of serotonin neurons following injections of 5,7‐dihydroxytryptamine in the dorsal and medial raphe nuclei produced long‐term decreases in the number of newly generated granule cells identified with 5‐Bromo‐2′‐deoxyuridine (BrdU) and the polysialylated form of neural cell adhesion molecule (PSA‐NCAM) immunostaining, as observed in 2‐month‐survival rats. The raphe grafts, but not the control grafts of embryonic spinal tissue, reversed the postlesion‐induced decreases in the density of BrdU‐ and PSA‐NCAM‐labelled cells detected in the granule layer. Inhibition of serotonin synthesis in animals with raphe grafts reversed back to lesion‐induced changes in granule cell proliferation. Furthermore, extensive serotonergic reinnervation of the dentate gyrus in the area proximal to the raphe graft could be associated with supranormal density of BrdU‐labelled cells. These results indicate that serotonin may be considered a positive regulatory factor of adult granule cell proliferation. Finally, the lack of effect of embryonic nonserotonergic tissue grafted to serotonin‐deprived rats suggests that neurotrophic factors may not be involved in the effects of serotonin on adult neurogenesis.
Anisomycin uses multiple mechanisms to stimulate mitogen‐activated protein kinases and gene expression and to inhibit neuronal differentiation in PC12 phaeochromocytoma cells
Authors: Töro"csik Beáta , Szeberényi József
Published: March 2003

Treatment of PC12 cells with nerve growth factor (NGF) stimulates extracellular signal‐regulated kinases (ERKs), as well as stress‐activated c‐Jun N‐terminal kinases (JNKs) and p38 kinase, and induces neuronal differentiation. While the pivotal role of ERKs in NGF‐induced morphological differentiation is well established, the contribution of JNK‐ and p38‐pathways is less clear. The role of the JNK‐ and p38‐pathway in PC12 cells was analysed by using anisomycin, a protein synthesis inhibitor that activates JNKs and p38. Non‐toxic concentrations of anisomycin were found to stimulate these enzyme activities as well as the expression of the early response genes c‐jun, c‐fos and zif268, and to inhibit NGF‐induced neurite formation. These effects of anisomycin appear to be mediated by the generation of reactive oxygen species (ROS), which in turn act through both TrkA/Ras‐dependent and ‐independent signalling pathways. In addition, cross‐talk between the p38‐ and ERK‐pathways appears to play a role in the action of anisomycin.
Is right hemisphere specialization for face discrimination specific to humans?
Authors: Broad Kevin D. , Mimmack Michael L. , Kendrick Keith M.
Published: March 2003

Patterns of neural activation during face recognition were investigated in sheep by quantifying altered c‐fos mRNA expression in situations where faces (sheep vs. human) can (faces upright) and cannot (faces inverted) be discriminated. Exposure to upright faces selectively increased expression significantly more in the right inferior temporal cortex than in the left, and active choice between upright faces additionally increased expression bilaterally in basal amygdala and hippocampus (CA1–4). Exposure to inverted faces did not lead to enhanced activation in the right inferior temporal cortex, amygdala or hippocampus but instead increased expression levels in the diagonal band of Broca, parietal and cingulate cortices. These results show that discrimination of upright faces in sheep preferentially engages the right temporal cortex, as it does in humans, and that performance of active choices between such faces may additionally involve the basal amygdala and hippocampus.
Responses to linear and logarithmic frequency‐modulated sweeps in ferret primary auditory cortex
Authors: Nelken Israel , Versnel Huib
Published: March 2003

Multi‐unit responses to frequency‐modulated (FM) sweeps were studied in the primary auditory cortex of ferrets using six different stimulation paradigms. In particular, the differences between the responses to linear FM sweeps (where frequency changes linearly with time) and logarithmic FM sweeps (where frequency changes exponentially with time) were emphasized. Some general features of the responses to FM sweeps are independent of the exact details of the frequency trajectory. Both for linear and for logarithmic FM sweeps, a short burst of spikes occurred when the sweep reached a triggering frequency close to the best frequency of the cluster. The neuronal preference for FM velocity was also independent of frequency trajectory. Thus, clusters that responded best to slow logarithmic FM also preferred slow linear FM and vice versa. Consequently, topographic distributions of velocity preference were roughly independent of the stimulation paradigm. Other characteristics of the responses, however, depended on the exact details of the frequency trajectory. A significant number of clusters showed large differences in directional sensitivity between linear and logarithmic FM sweeps; these differences depended on the velocity preference of the clusters in some paradigms but not in others. Consequently, topographic distributions of directional sensitivity differed between linear and logarithmic paradigms. In conclusion, some characteristics of cluster responses to FM sweeps depend on the exact details of the stimulation paradigm and are not ‘invariants’ of the cluster.
Specific activation of the μ opioid receptor (MOR) by endomorphin 1 and endomorphin 2
Authors: Monory Krisztina , Bourin Marie‐Claude , Spetea Mariana , Tömböly Csaba , Tóth Géza , Matthes Hans W. , Kieffer Brigitte L. , Hanoune Jacques , Borsodi Anna
Published: March 2003

The recently discovered endomorphin 1 (Tyr‐Pro‐Trp‐Phe‐NH2) and endomorphin 2 (Tyr‐Pro‐Phe‐Phe‐NH2) were investigated with respect to their direct receptor‐binding properties, and to their ability to activate G proteins and to inhibit adenylyl cyclase in both cellular and animal models. Both tetrapeptides activated G proteins and inhibited adenylyl cyclase activity in membrane preparations from cells stably expressing the μ opioid receptor, an effect reversed by the μ receptor antagonist CTAP (d‐Phe‐Cys‐Tyr‐d‐Trp‐Arg‐Thr‐Pen‐Thr‐NH2), but they had no influence on cells stably expressing the δ opioid receptor. To further establish the selectivity of these peptides for the μ opioid receptor, brain preparations of mice lacking the μ opioid receptor gene were used to study their binding and signalling properties. Endomorphin 2, tritiated by a dehalotritiation method resulting in a specific radioactivity of 1.98 TBq/mmol (53.4 Ci/mmol), labelled the brain membranes of wild‐type mice with a Kd value of 1.77 nm and a Bmax of 63.33 fmol/mg protein. In membranes of mice lacking the μreceptor gene, no binding was observed, and both endomorphins failed to stimulate [35S]guanosine‐5′‐O‐(3‐thio)triphosphate ([35S]GTPγS) binding and to inhibit adenylyl cyclase. These data show that endomorphins are capable of activating G proteins and inhibiting adenylyl cyclase activity, and all these effects are mediated by the μ opioid receptors.
Hippocampal participation in navigational map learning in young homing pigeons is dependent on training experience
Authors: Ioalè Paolo , Gagliardo Anna , Bingman Verner P.
Published: March 2003

The homing pigeon navigational map is perhaps one of the most striking examples of a naturally occurring spatial representation of the environment used to guide navigation. In a previous study, it was found that hippocampal lesions thoroughly disrupt the ability of young homing pigeons held in an outdoor aviary to learn a navigational map. However, since that study an accumulation of anecdotal data has hinted that hippocampal‐lesioned young pigeons allowed to fly during their first summer could learn a navigational map. In the present study, young control and hippocampal‐lesioned homing pigeons were either held in an outdoor aviary or allowed to fly during the time of navigational map learning. At the end of their first summer, the birds were experimentally released to test for navigational map learning. Independent of training experience, control pigeons oriented homeward during the experimental releases demonstrating that they learned a navigational map. Surprisingly, while the aviary‐held hippocampal‐lesioned pigeons failed to learn a navigational map as reported previously, hippocampal‐lesioned birds allowed flight experience learned a navigational map indistinguishable from the two control groups. A subsequent experiment revealed that the navigational map learned by the three groups was based on atmospheric odours. The results demonstrate that hippocampal participation in navigational map learning depends on the type of experience a young bird pigeon has, and presumably, the type of navigational map learned.
Clustering of δ glutamate receptors is regulated by the actin cytoskeleton in the dendritic spines of cultured rat Purkinje cells
Authors: Hirai Hirokazu
Published: March 2003

The interaction of neurotransmitter receptors with the cytoskeleton is an important mechanism for the targeting of receptors to the postsynaptic membrane. Using cytoskeleton‐perturbing agents, it was demonstrated that δ glutamate receptors, predominantly expressed on the dendritic spines of cerebellar Purkinje cells, are anchored to the actin cytoskeleton. The number of δ glutamate receptor‐immunoreactive clusters was dramatically decreased following treatment of the Purkinje cells with the actin‐disrupting agents, cytochalasin D or latrunculin A, without any significant effect on the number of presynaptic contacts of the granule cell axons. The clusters disrupted by latrunculin A were re‐established 24 h after removal of the drug. These results suggest that morphological changes in the actin cytoskeleton regulate the δ glutamate receptor clustering on the dendritic spines, and may affect synaptic efficacy and plasticity.
Circadian modulation of calcium levels in cells in the suprachiasmatic nucleus
Authors: Colwell Christopher S.
Published: March 2003

There is reason to believe that resting free calcium concentration [Ca2+]i in neurons in the suprachiasmatic nucleus (SCN) may vary with the circadian cycle. In order to start to examine this hypothesis, optical techniques were utilized to estimate resting Ca2+ levels in SCN cells in a rat brain slice preparation. [Ca2+]i measured from the soma was significantly higher in the day than in the night. Animals from a reversed light–dark cycle were used to confirm that the phase of the rhythm was determined by the prior light–dark cycle. The rhythm in Ca2+ levels continued to be expressed in tissue collected from animals maintained in constant darkness, thus confirming the endogenous nature of this variation. Interestingly, the rhythm in Ca2+ levels was not observed when animals were housed in constant light. Finally, the rhythm in Ca2+ levels was prevented when slices were exposed to tetrodotoxin (TTX), a blocker of voltage‐sensitive sodium channels. Similar results were obtained with the voltage‐sensitive Ca2+ channel blocker methoxyverapamil. These observations suggest a critical role for membrane events in driving the observed rhythm in Ca2+. Conceptually, this rhythm can be thought of as an output of the circadian oscillator. Because [Ca2+]i is known to play a critical role in many cellular processes, the presence of this rhythm is likely to have many implications for the cell biology of SCN neurons.
Overexpression of spermidine/spermine N1‐acetyltransferase in transgenic mice protects the animals from kainate‐induced toxicity
Authors: Kaasinen Kyllikki , Koistinaho Jari , Alhonen Leena , Jänne Juhani
Published: March 2003

We recently generated a transgenic mouse line with activated polyamine catabolism through overexpression of spermidine/spermine N1‐acetyltransferase (SSAT). A detailed analysis of brain polyamine concentrations indicated that all brain regions of these animals showed distinct signs of activated polyamine catabolism, e.g. overaccumulation of putrescine (three‐ to 17‐fold), appearance of N1‐acetylspermidine and decreases in spermidine concentrations. In situ hybridization analyses revealed a marked overexpression of SSAT‐specific mRNA all over the brain tissue of the transgenic animals. The transgenic animals appeared to tolerate subcutaneous injections of high‐dose kainate substantially better as their overall mortality was less than 50% of that of their syngenic littermates. We used the expression of glial fibrillary acidic protein (GFAP) as a marker of brain injury in response to kainate. In situ hybridization analysis with GFAP oligonucleotide up to 7 days after the administration of sublethal kainate doses showed reduced GFAP expression in transgenic animals in comparison with their non‐transgenic littermates. This difference was especially striking in the cerebral cortex of the transgenic mice where the exposure to kainate hardly induced GFAP expression. The treatment with kainate likewise resulted in loss of the hippocampal (CA3) neurons in non‐transgenic but not transgenic animals. These results support our earlier findings indicating that elevated concentrations of brain putrescine, irrespective whether derived from an overexpression of ornithine decarboxylase, or as shown here, from an overexpression of SSAT, play in all likelihood a neuroprotective role in brain injury.
Overexpression of neuropeptide Y induced by brain‐derived neurotrophic factor in the rat hippocampus is long lasting
Authors: Reibel Sophie , Vivien‐Roels Berthe , Lê Bich‐Thuy , Larmet Yves , Carnahan Josette , Marescaux Christian , Depaulis Antoine
Published: March 2003

Brain‐derived neurotrophic factor (BDNF) plays an important role in hippocampal neuroplasticity. In particular, BDNF upregulation in the hippocampus by epileptic seizures suggests its involvement in the neuronal rearrangements accompanying epileptogenesis. We have shown previously that chronic infusion of BDNF in the hippocampus induces a long‐term delay in hippocampal kindling progression. Although BDNF has been shown to enhance the excitability of this structure upon acute application, long‐term transcriptional regulations leading to increased inhibition within the hippocampus may account for its suppressive effects on epileptogenesis. Therefore, the long‐term consequences of a 7‐day chronic intrahippocampal infusion of BDNF (12 μg/day) were investigated up to 2 weeks after the end of the infusion, on the expression of neurotransmitters contained in inhibitory hippocampal interneurons and which display anti‐epileptic properties. Our results show that BDNF does not modify levels of immunostaining for glutamic acid decarboxylase, the rate‐limiting enzyme for γ‐aminobutyric acid (GABA) synthesis, and somatostatin. Conversely, BDNF induces a long‐lasting increase of neuropeptide Y (NPY) in the hippocampus, measured by immunohistochemistry and radioimmunoassay, outlasting the end of the infusion by at least 7 days. The distribution of BDNF‐induced neuropeptide Y immunoreactivity is similar to the pattern observed in animals submitted to hippocampal kindling, with the exception of mossy fibres which only become immunoreactive following seizure activity. The enduring increase of neuropeptide Y expression induced by BDNF in the hippocampus suggests that this neurotrophin can trigger long‐term genomic effects, which may contribute to the neuroplasticity of this structure, in particular during epileptogenesis.
Facilitation of cholinergic transmission by substance P methyl ester in the mouse hippocampal slice preparation
Authors: Kouznetsova Maria , Nistri Andrea
Published: March 2003

Using sharp microelectrode recording from CA1 pyramidal neurons of the adult mouse hippocampal slice preparation, we studied the modulatory action of the selective neurokinin 1 (NK1) receptor agonist substance P methyl ester (SPME), a peptidase‐resistant analogue of the peptide substance P (SP), on cholinergic responses. While SPME (0.1–1 μm) had only slight effects on membrane potential and input resistance of CA1 neurons, it largely and reversibly enhanced the membrane depolarization and oscillatory activity induced by the cholinergic agonist carbachol (CCh; 0.1–100 μm). This effect of SPME was prevented by the selective NK1 receptor antagonist SR 140333 (4 μm). In about half of the tested neurons the action of SPME was preserved in tetrodotoxin (TTX) solution, suggesting that it partly occurred at the level of pyramidal cells. Cholinergic slow excitatory postsynaptic potentials (sEPSPs) were reversibly enhanced by SPME which increased their amplitude and prolonged any associated bursting activity. This action was also blocked by SR 140333. The present results suggest that SPME largely enhances cholinergic activity in the mouse hippocampus, an effect which can help to explain, in this brain area, the recently reported facilitation of seizures by SP.
Eye position‐sensitive units in hippocampal formation and in inferotemporal cortex of the Macaque monkey
Authors: Nowicka Anna , Ringo James L.
Published: March 2003

The activity of 330 hippocampal and inferotemporal cells was recorded while seated monkeys with fixed heads worked in a visual discrimination task. Monkeys had to move their eyes to one of five different positions to maintain gaze on an image. The image was then extinguished and the monkeys maintained a fixed gaze on the target position in darkness to obtain a reward. The five positions of image presentation were on a horizontal line, consisting of a centre position and lateral positions which were 10 and 20 degrees right and left of it.

Twenty‐two per cent of single units recorded from the hippocampus showed statistically significant sensitivity to target position in complete darkness. A similar fraction (23%) was significantly affected by target position in the light. Position sensitivity was also found among cells recorded from the inferotemporal cortex. Eye position significantly influenced the activity of 19% of inferotemporal units in darkness and 28% of inferotemporal units in the light. Interestingly, the populations of cells showing position effect in the light and in darkness were independent.