bluuebunny/crossref_metadata_2025 huggingface dataset:
Adenosine inhibits L‐type Ca2+ current and catecholamine release in the rabbit carotid body chemoreceptor cells
Authors: Rocher A. , Gonzalez C. , Almaraz L.
Published: March 2003

In an in vitro preparation of the intact carotid body (CB) of the rabbit, adenosine (100 μm) inhibited hypoxia‐induced catecholamine release by 25%. The specific A1 antagonist, 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX; 1 μm) prevented the inhibition and increased the response to hypoxia further. In isolated chemoreceptor cells from the same species, adenosine inhibited voltage‐dependent Ca2+ currents by 29% at 1 μm (concentration producing half‐maximal inhibition, IC50 = 50 nM). This inhibition was mimicked by R(–)N6‐(2‐phenylisopropyl)‐adenosine and 2‐chloroadenosine (1 μm), two purinergic agonists poorly active at the intracellular (‘P′) site, and persisted in the presence of dipyridamole (a blocker of adenosine uptake; 1 μm) and was fully inhibited by 8‐phenyltheophylline (10 μm). The A1 antagonists DPCPX (10 μm) and 8‐cyclopentyl‐1,3‐dimethylxantine (0.1 μm) inhibited the effect of adenosine by 93% (IC50 = 0.14 μm) and 59%, respectively. The inhibition of the Ca2+ current (ICa) was reduced by nisoldipine (an L‐type Ca2+ channel antagonist) by nearly 50%, and was unaltered by omega‐conotoxin GVIA, a blocker of N‐type Ca2+ channels. Adenosine did not affect the voltage‐dependent Na+ current (INa) or K+ current (IK.). We conclude that adenosine A1 receptors are located in chemoreceptor cells and mediate the inhibition of L‐type Ca2+ channels and thereby the release of catecholamines produced by hypoxia. The data also indicate that endogenous adenosine acts as a physiological negative modulator of the chemoreceptor cell function. The previously reported excitatory action of adenosine on the activity of the sensory nerve of the CB is discussed in terms of a balance between the inhibition mediated by A1 receptors and the excitation mediated by A2 receptors.
Support stability influences postural responses to muscle vibration in humans
Authors: Ivanenko Yuri P. , Talis Vera L. , Kazennikov Oleg V.
Published: March 2003

We studied the effect of support stability on postural responses to the vibration of Achilles tendons and of neck dorsal muscles in healthy humans. For this purpose we compared postural responses on a rigid floor and on 6 cm high rocking supports (see‐saws) of different curvatures (different radii: 30, 60 and 120 cm). The subject stood with eyes closed, the centre of the feet coincided with the centre of the see‐saw. We recorded platform tilt, horizontal displacements of the upper body, ankle joint angle and activity of ankle joint muscles. On the rocking platform subjects maintained balance in a sagittal direction by making see‐saw rotations placing the support under the body's centre of gravity. Equilibrium maintenance requires that the torque in the ankle joint increases during forward body displacements, as on the rigid floor, and be accompanied by a plantar flexion (not by a dorsiflexion) in the ankle joint. The directional dependence of vibration‐induced reactions on the see‐saw was the same (relative to space) as on the rigid floor: backward body displacement during Achilles tendon vibration and forward body displacement during neck muscle vibration. A decrease of support stability (with a decrease of the radius from 120 to 30 cm) diminished significantly the effect of Achilles tendon vibration and to a lesser extent the effect of neck muscle vibration. In contrast, the increase of platform stability by hand contact with a stable external object gave rise to prominent body sway in response to Achilles tendon vibration. Neck muscle vibration on the movable support provoked a quick initial forward body sway. This initial quick response was absent during vibration of the Achilles tendons. We conclude that postural responses to muscle vibration reflect the participation of different muscles in posture control and depend on the support properties. Support instability changes the role of proprioceptive information and the state of the system of equilibrium maintenance.
Small cardioactive peptide gene: structure, expression and mass spectrometric analysis reveals a complex pattern of co‐transmitters in a snail feeding neuron
Authors: Dobbins Stephen J. Perry andrew C. , Schofield Michael G. , Piper Marian R. , Benjamin Paul R.
Published: March 2003

The small cardioactive peptides (SCPs) are an important group of neural cotransmitters in molluscs where they are known to play both central and peripheral modulatory roles in the control of feeding behaviour. Here we show that in the snail Lymnaea the SCP gene exists in one interrupted copy that produces a single species of transcript which encodes a prepropeptide containing two structurally related SCPs SGYLAFPRMamide (SCPA) and pQNYLAFPRMamide (SCPB). In situ hybridization was used to localize expression specifically to the soma of several types of motoneurons in the feeding system of Lymnaea, including the giant B2 foregut motoneurons. The peptide content of individual B2 cell bodies was analysed by matrix‐assisted laser desorption/ionization mass spectrometry and the structures of the SCPs predicted from the cloned gene were confirmed in these cells by post‐source decay fragmentation analysis. Identical stimulatory activity for the two SCP peptides was demonstrated by their application to the isolated foregut, suggesting that their co‐release from the B2 cells may play an important part in the co‐modulation of gut motility, together with acetylcholine and the myomodulin family of peptides.
Presynaptic GABAergic control of the locomotor drive in the isolated spinal cord of neonatal rats
Authors: Bertrand Sandrine , Cazalets Jean‐René
Published: March 2003

The in vitro newborn rat isolated brain stem/spinal cord preparation was used to study the involvement of presynaptic inhibition in the control of the synaptic locomotor drive. The recording chamber was partitioned with Vaseline walls to separate the L1–L2 locomotor network from the motoneurons in the lower segments. When locomotor like activity was induced by bath applying a mixture of N‐methyl‐d‐l‐aspartate and serotonin to the L1–L2 segments, intracellular recordings of L3–L5 motoneurons show an alternating pattern of monosynaptic excitatory glutamatergic and inhibitory glycinergic inputs known as the locomotor drive. Gamma‐aminobutyric acid (GABA), baclofen and muscimol (respectively GABAB and GABAA agonists) superfused on the L3–L5 segments depressed the synaptic locomotor drive of motoneurons during the ongoing activity. On the contrary, the GABAB receptor antagonist CGP35348 enhanced the locomotor drive, which suggests that an endogenous release of GABA occurs during locomotor‐like activity. Baclofen, unlike muscimol and GABA, did not affect the passive membrane properties and the firing discharge of synaptically isolated motoneurons. Baclofen and muscimol acted on the two phases (inhibitory and excitatory) of the synaptic drive. The effects of GABAergic agonists on the whole locomotor activity were tested. When superfused on the L3–L5 part of the cord, they affected only the L5 burst amplitude. When bath‐applied to the L1–L2 network, GABA and muscimol decreased the amplitude of the L2 and L5 bursts and increased the locomotor period while baclofen had significant effects only on the period. It was concluded that GABA modulates the information conveyed by the L1–L2 network to its target motoneurons presynaptically via GABAB and possibly GABAA receptors and postsynaptically, via GABAA receptors.
Differential brain expression of a new β‐actin gene from zebrafish (Danio rerio)
Authors: Barrallo Alejandro , González‐Sarmiento Rogelio , García‐Isidoro María , Cidad Pilar , Porteros Angel , Rodríguez Raquel E.
Published: March 2003

It has been shown that actin genes exhibit distinct tissue and stage‐specific patterns of expression. We have cloned a new β‐actin gene from the teleost zebrafish (Danio rerio), a well‐established model for developmental studies, and analysed its expression by Northern blot and in situ hybridization studies. Our results suggest that in adult brain zebrafish, this new gene is expressed during neuronal cell proliferation.
mGluR7‐like metabotropic glutamate receptors inhibit NMDA‐mediated excitotoxicity in cultured mouse cerebellar granule neurons
Authors: Lafon‐Cazal Mireille , Fagni Laurent , Guiraud Marie‐Jeanne , Mary Sophie , Lerner‐Natoli Mireille , Pin Jean‐Philippe , Shigemoto Ryuichi , Bockaert Joël
Published: March 2003

Glutamate‐induced glutamate release may be involved in the delayed neuronal death induced by N‐methyl‐d‐aspartate (NMDA). In order to examine a possible modulatory effect of the presynaptic group III mGluRs on glutamate excitotoxicity, the effect of l‐2‐amino‐4‐phosphonobutyrate (L‐AP4) was examined on NMDA‐induced delayed death of mouse cerebellar granule neurons in culture. We found that L‐AP4, at high concentration (in the millimolar range), inhibited in a non‐competitive manner the NMDA‐induced toxicity. This effect was mimicked by high concentration of l‐serine‐o‐phosphate (L‐SOP), and was inhibited by pertussis toxin (PTX) indicating the involvement of a Gi/o protein. This suggests the involvement of mGluR7 in the L‐AP4 effect, and this was consistent with the detection of both mGluR7 protein and mRNA in these cultured neurons. To examine the mechanism of the L‐AP4‐induced protection from excitotoxic damage, the effect of L‐AP4 on glutamate release was examined. L‐AP4 (≥ 1 mm) non‐competitively inhibited by more than 60% the glutamate release induced by NMDA during the insult. We also observed that the 10‐min NMDA receptor stimulation resulted in a dramatic increase in the extracellular glutamate concentration reaching 6000% of the control value 24 h after the insult. This large increase was also inhibited when NMDA was applied in the presence of ≥ 1 mm L‐AP4. Part of the L‐AP4‐induced protection from excitotoxic damage of granule neurons may therefore result from the inhibition of the vicious cycle: dying cells release glutamate, glutamate induced cell death. The present results add to the hypothesis that presynaptic mGluRs, probably mGluR7, may be the targets of drugs decreasing glutamate release and then neuronal death observed in some pathological situations.
Proliferation in the vomeronasal organ of the rat during postnatal development
Authors: Weiler Elke , McCulloch Mary A. , Farbman Albert I.
Published: March 2003

We investigated proliferation of sensory cell precursors in the rat vomeronasal organ (VNO) at various postnatal ages from birth (P1) to P666. In the rat, which continues to grow during most of its adult life, proliferation might be related to growth and/or replacement. Proliferating cells were labelled by BrdU injection, and histological sections of the VNO were evaluated after immunohistochemical detection of BrdU. Proliferation density (number of proliferating cells/section) decreased dramatically from 115 at P1 to 27.2 at P21, although the area increased. Adult values were reached at P66–P333 (10.3 cells/section); at P400–P666 the value was 8.6 cells/section. Distribution of labelled cells changed considerably with age: in neonates the cells were nearly equally distributed throughout the sensory epithelium, whereas from P21 onwards most proliferating cells were concentrated in clusters near the boundaries with non‐sensory epithelium. Labelled cells in the sensory neuronal layer were adjacent to the undulating basement membrane‐bordering capillaries that intrude into the sensory epithelium, indicating that they were true basal cells. The volume of the sensory epithelium increased between P1 and P66, and remained constant thereafter, although the length still increased. Length and volume of the sensory epithelium were related to body size, not to sex; males and females of the same body size had the same VNO size. The complex changes in proliferation pattern during postnatal development indicate differential growth and replacement. We suggest that in adults the labelled cell clusters near the boundaries are a pool for growth, whereas proliferation in the central parts represents a replacement pool.
Spatiotemporal distribution of dying neurons during early mouse development
Authors: Van Den Eijnde S. M. , Lips J. , Boshart L. , Vermeij‐Keers C. , Marani E. , Reutelingsperger C. P. M. , De Zeeuw C. I.
Published: March 2003

Apoptosis is a critical cellular event during several stages of neuronal development. Recently, we have shown that biotinylated annexin V detects apoptosis in vivo in various cell lineages of a wide range of species by binding to phosphatidylserines that are exposed at the outer leaflet of the plasma membrane. In the present study, we tested the specificity by which annexin V binds apoptotic neurons, and subsequently investigated developmental cell death in the central and peripheral nervous system of early mouse embryos at both the cellular and histological level, and compared the phagocytic clearance of apoptotic neurons with that of apoptotic mesodermal cells. Our data indicate: (i) that biotinylated annexin V can be used as a sensitive marker that detects apoptotic neurons, including their extensions at an early stage during development; (ii) that apoptosis plays an important part during early morphogenesis of the central nervous system, and during early quantitative matching of brain‐derived neurotrophic factor and neurotrophic factor 3 responsive postmitotic large clear neurons in the peripheral ganglia with their projection areas; and (iii) that apoptotic neurons are removed by a process that differs from classical phagocytosis of non‐neuronal tissues.
Ca2+ regulation of a large conductance K+ channel in cultured rat cerebellar Purkinje neurons
Authors: Jacquin T. D. , Gruol D. L.
Published: March 2003

The calcium sensitivity of a large conductance voltage‐sensitive potassium channel found in cultured rat cerebellar Purkinje neurons was studied in membrane patches from the somatic region of the cultured Purkinje neurons using single‐channel recording techniques. The potassium channel had a conductance of ≈ 94 picosiemens (pS) under physiologic ionic conditions and was active at depolarized membrane potentials. Activity due to this channel type was not observed when the saline at the internal surface of the membrane was calcium free. Low intracellular calcium concentration (10 nm) triggered channel activity at depolarized membrane potentials. Channel activity increased further with increasing intracellular calcium concentrations and was evident at more negative membrane potentials. The high sensitivity of this potassium channel type to intracellular calcium and its abundance in the Purkinje neuron membrane may reflect a prominent role in the control of action potential duration and interspike interval when the neurons are firing in a rapid, repetitive mode.
Q/R editing of the rat GluR5 and GluR6 kainate receptors in vivo and in vitro: evidence for independent developmental, pathological and cellular regulation
Authors: Bernard Anne , Ferhat Lotfi , Dessi Frédéric , Charton Gérard , Represa Alfonso , Ben‐Ari Yezekiel , Khrestchatisky Michel
Published: March 2003

Kainate (KA) is a potent neuroexcitatory agent in several areas of the adult brain, with convulsant and excitotoxic properties that increase as ontogeny proceeds. Besides its depolarizing actions, KA may enhance intracellular accumulation of Ca 2+ to promote selective neuronal damage. The effects of KA are mediated by specific receptors recently considered to be involved in fast neurotransmission and that can be activated synaptically. KA receptors, e.g. GluR5 and GluR6 have been characterized by molecular cloning. Structure–function relationships indicate that in the MII domain of these KA receptors, a glutamine (Q) or arginine (R) residue determines ion selectivity. The arginine stems from post‐transcriptional editing of the GluR5 and GluR6 pre‐RNAs, and the unedited and edited versions of GluR6 elicit distinct Ca2+ permeability. Using a PCR‐based approach, we show that in vivo, Q/R editing in the GluR5 and GluR6 mRNAs is modulated during ontogeny and differs substantially in a variety of nervous tissues. GluR5 editing is highest in peripheral nervous tissue, e.g. the dorsal root ganglia, where GluR6 expression is barely detectable. In contrast, GluR6 editing is maximal in forebrain and cerebellar structures where GluR5 editing is lower. Intra‐amygdaloid injections of KA provide a model of temporal lobe epilepsy, and we show that following seizures, the extent of GluR5 and GluR6 editing is altered in the hippocampus. However, in vitro, high levels of glutamate and potassium‐induced depolarizations have no effect on GluR5 and GluR6 Q/R editing. GluR6 editing is rapidly enhanced to maximal levels in primary cultures of cerebellar granule neurons but not in cultured hippocampal pyramidal neurons. Finally, we show that cultured glial cells express partially edited GluR6 mRNAs. Our results indicate that Q/R editing of GluR5 and GluR6 mRNAs is structure‐, cell type‐ and time‐dependent, and suggest that editing of these mRNAs is not co‐regulated.
Anandamide and WIN 55212‐2 inhibit cyclic AMP formation through G‐protein‐coupled receptors distinct from CB1 cannabinoid receptors in cultured astrocytes
Authors: Sagan Sandrine , Venance Laurent , Torrens Yvette , Cordier Jocelyne , Glowinski Jacques , Giaume Christian
Published: March 2003

The effects of anandamide and the cannabinoid receptor agonists WIN 55212‐2 and CP 55940 on the evoked formation of cyclic AMP were compared in cultured neurons and astrocytes from the cerebral cortex and striatum of mouse embryos. The three compounds inhibited the isoproterenol‐induced accumulation of cyclic AMP in neuronal cells, and these responses were blocked by the selective CB1 receptor antagonist SR 141716A. The three agonists were more potent in cortical than striatal neurons. Interestingly, WIN 55212‐2, CP 55940 and anandamide also inhibited the isoproterenol‐evoked accumulation of cyclic AMP in astrocytes but, in contrast to WIN 55212‐2 and CP 55940, anandamide was much more potent in striatal than cortical astrocytes. Inhibition was prevented by pertussis toxin pretreatment, but not blocked by SR 141716A. Therefore, G‐protein‐coupled receptors, distinct from CB1 receptors, are involved in these astrocytic responses. Moreover, specific binding sites for [3H]‐SR 141716A were found in neurons but not astrocytes. Furthermore, using a polyclonal CB1 receptor antibody, staining was observed in striatal and cortical neurons, but not in striatal and cortical astrocytes. Taken together, these results suggest that glial cells possess G‐protein‐coupled receptors activated by cannabinoids distinct from the neuronal CB1 receptor, and that glial cells responses must be taken into account when assessing central effects of cannabinoids.
GABAB‐receptor splice variants GB1a and GB1b in rat brain: developmental regulation, cellular distribution and extrasynaptic localization
Authors: Fritschy Jean‐Marc , Meskenaite Virginia , Weinmann Oliver , Honer Michael , Benke Dietmar , Mohler Hanns
Published: March 2003

GABAB (γ‐aminobutyric acid)‐receptors have been implicated in central nervous system (CNS) functions, e.g. cognition and pain perception, and dysfunctions including spasticity and absence epilepsy. To permit an analysis of the two known GABAB‐receptor splice variants GABAB‐R1a (GB1a) and GABAB‐R1b (GB1b), their distribution pattern has been differentiated in the rat brain, using Western blotting and immunohistochemistry with isoform‐specific antisera. During postnatal maturation, the expression of the two splice variants was differentially regulated with GB1a being preponderant at birth. In adult brain, GB1b‐immunoreactivity (‐IR) was predominant, and the two isoforms largely accounted for the pattern of GABAB‐receptor binding sites in the brain. Receptor heterogeneity was pronounced in the hippocampus, where both isoforms occurred in CA1, but only GB1b in CA3. Similarly, in the cerebellum, GB1b was exclusively found in Purkinje cells in a zebrin‐like pattern. The staining was most pronounced in Purkinje cell dendrites and spines. Using electron microscopy, over 80% of the spine profiles in which a synaptic contact with a parallel fibre was visible contained GB1b‐IR at extrasynaptic sites. This subcellular localization is unrelated to GABAergic inputs, indicating that the role of GABAB‐receptors in vivo extends beyond synaptic GABAergic neurotransmission and may, in the cerebellum, involve taurine as a ligand.
Electrophysiological evidence for a reciprocal interaction between amphetamine and cocaine‐related drugs on rat midbrain dopaminergic neurons
Authors: Scarponi Mariangela , Bernardi Giorgio , Mercuri Nicola B.
Published: March 2003

To determine the functional interactions occurring between amphetamine and cocaine‐like drugs on a single neuron, we used intracellular single‐electrode voltage‐clamp recordings from dopaminergic cells of the rat midbrain maintained in vitro. In the presence of cocaine (3–30 μm), the outward current caused by amphetamine (100 μm) on cells held at about – 60 mV was attenuated. The degree of attenuation of the amphetamine‐induced response was almost the same for 3 and 30 μm cocaine (44 and 51% of control, respectively). This effect of cocaine was reversible. We also tested other DA‐uptake inhibitors (nomifensine and 4‐phenyltetrahydroisoquinoline) against the amphetamine‐induced outward current. Both drugs enhanced the effects of dopamine (DA) while reducing the outward response caused by amphetamine. Pretreatment of the animals with reserpine (12 mg/kg/i.p.), which irreversibly depletes the vesicular DA stores, neither affected the amplitude of the current caused by amphetamine nor changed the cocaine‐induced attenuation of the membrane responses to amphetamine. Interestingly, when amphetamine (3 μm) was superfused on the dopaminergic neurons prior and during the application of cocaine, the DA‐uptake blocker was no longer able to potentiate the outward response caused by the superfusion of DA. Taken together, these data suggest that: (i) amphetamine and cocaine interact with the DA transporter to produce distinct actions which under certain circumstances can compete with each other; (ii) the amphetamine‐induced release of DA from the somata and dendrites of the dopaminergic cells is, at least in part, related to the reverse operation of the DA transporter and is not dependent on the integrity of the vesicular content of the catecholamine.
Neuregulin is a mitogen and survival factor for olfactory bulb ensheathing cells and an isoform is produced by astrocytes
Authors: Pollock Graeme S. , Franceschini Isabelle A. , Graham Gerry , Marchionni Mark A. , Barnett Susan C.
Published: March 2003

The rat olfactory bulb is an exceptional CNS tissue. Unlike other areas of the brain, growing axons are able to enter the olfactory bulb and extend within this CNS environment throughout adult life. It appears that the glial cells of the olfactory system, known as olfactory bulb ensheathing cells (OBECs), may have an important role in this remarkable process of CNS neural regeneration. OBECs are unusual glial cells, possessing properties of both astrocytes and Schwann cells. In this study we show that astrocytes (in the form of astrocyte‐conditioned medium; ACM) produce two critical regulatory functions for OBECs: mitogenic activity and a survival factor. Interestingly, the ACM‐derived activity for OBECs appears to reside in a signalling protein(s) belonging to the neuregulin (NRG) family of growth factors, and specifically appears to coincide with one or more products of the nrg‐1 gene. Our observations provide evidence for the following: recombinant human neu differentiation factors (NDFβ1, ‐2 and ‐3) are mitogenic to OBECs; the activity in ACM can be neutralized by NDF antibodies; these same antibodies detect a 50‐kDa, non‐heparin binding protein in concentrated ACM; astrocytes express detectable nrg‐1 transcripts; and OBECs express functional NRG receptors erbB2 and erbB4.
ZFM1/SF1 mRNA in rat and gerbil brain after global ischaemia
Authors: Covini N. , Tamburin M. , Consalez G. , Salvati P. , Benatti L.
Published: March 2003

Cerebral ischaemia results in significant brain damage, but the molecular mechanisms associated with ischaemia‐induced brain injury are not well defined. We have adopted an improved differential‐display method to search for new ischaemia‐related genes. Among the different cDNAs isolated following transient forebrain ischaemia in rat, PH3.3 was selected for further studies. The search for homologies revealed that it is the rat homologue to human zinc finger motif 1 (ZFM1), also called mammalian splicing factor 1 (SF1). With Northern blot, PH3.3 hybridized with three mRNA species of 2.3, 2.9 and 3.6 kb, significantly increased at 6 h and 5 days after the ischaemic insult. These findings were extended also to another animal model. In situ hybridization in ischaemic gerbils showed that PH3.3 mRNA was induced in the dentate gyrus as early as 4 h post‐ischaemia. Expression peaked at 2 days in the whole hippocampus and cortex, and then progressively decreased towards sham levels. By day 4, expression had disappeared almost entirely from the cells in the CA1 region of the hippocampus, concomitant with the degeneration of pyramidal neurons. Interestingly, ZFM1/SF1 has been recently identified as activated following p53‐induced apoptosis. Several lines of evidence suggest that p53 may play two roles in the post‐ischaemic brain. The primary role of p53 is to activate DNA repair processes, but if repair fails, apoptosis will be initiated. Thus, ZFM1/SF1 may represent a relevant link between p53 and the neuroprotective/neurodegenerative processes which follow cerebral ischaemia.
Activity‐dependent regulation of alternative splicing patterns in the rat brain
Authors: Daoud Rosette , Da Penha Berzaghi Maria , Siedler Frank , Hübener Mark , Stamm Stefan
Published: March 2003

Alternative splicing plays an important role in the expression of genetic information. Among the best understood alternative splicing factors are transformer and transformer‐2, which regulate sexual differentiation in Drosophila. Like the Drosophila genes, the recently identified mammalian homologues are subject to alternative splicing. Using an antibody directed against the major human transformer‐2 beta isoform, we show that it has a widespread expression in the rat brain. Pilocarpine‐induced neuronal activity changes the alternative splicing pattern of the human transformer‐2‐beta gene in the brain. After neuronal stimulation, a variant bearing high similarity to a male‐specific Drosophila tra‐2179 isoform is switched off in the hippocampus and is detectable in the cortex. In addition, the ratio of another short RNA isoform (htra2‐beta2) to htra2‐beta1 is changed. Htra2‐beta2 is not translated into protein, and probably helps to regulate the relative amounts of htra2‐beta1 to beta3. We also observe activity‐dependent changes in alternative splicing of the clathrin light chain B, c‐src and NMDAR1 genes, indicating that the coordinated change of alternative splicing patterns might contribute to molecular plasticity in the brain.
SNARE complex at the ribbon synapses of cochlear hair cells: analysis of synaptic vesicle‐ and synaptic membrane‐associated proteins
Authors: Safieddine Saaid , Wenthold Robert J.
Published: March 2003

Neurotransmitters are released via exocytosis of synaptic vesicles involving a fusion complex consisting of a set of highly conserved proteins, which form a multiprotein complex resulting in the docking of synaptic vesicles at the site of release. There are three major differences between cochlear hair cell synapses and CNS synapses: (i) hair cells have a specialized structure, the synaptic ribbon, to which synaptic vesicles are attached; (ii) hair cells can maintain high and sustained release of neurotransmitter; and (iii) hair cells lack synaptophysin and synapsin. These differences suggest that an unconventional mechanism of neurotransmitter release may be involved at ribbon synapses. In this study we used different and complementary approaches to determine whether or not ribbon‐containing hair cells of the cochlea express any component of the core fusion complex found in conventional synapses. Syntaxin 1, the synaptic membrane synaptosome‐associated protein (SNAP)‐25 and vesicle‐associated membrane protein (VAMP or synaptobrevin) were found to be present in the organ of Corti of both rat and guinea‐pig, as shown by reverse transcription polymerase chain reaction and Western blotting. In situ hybridization and immunocytochemistry showed mRNA and protein expression, respectively, in both inner and outer hair cells. Synaptotagmins I and II, generally considered to play major roles in neurotransmitter release at central synapses, were not detected in the organ of Corti.
Lasting reduction in mesolimbic dopamine neuronal activity after morphine withdrawal
Authors: Diana Marco , Muntoni Anna Lisa , Pistis Marco , Melis Miriam , Gessa Gian Luigi
Published: March 2003

The activity of mesolimbic dopaminergic neurons was investigated in rats at various times after a chronic regimen of morphine, which produced, upon suspension, a marked somatic withdrawal syndrome. Single‐cell extracellular recording techniques, coupled with antidromic identification from the nucleus accumbens, were used to monitor neuronal activity while behavioural observations allowed quantification of the somatic signs of morphine withdrawal. Temporal correlation of electrophysiological indices, such as firing rate and burst firing, with scores obtained through behavioural assessments proved negative, in that somatic signs were pronounced at 24 h after suspension of treatment and then subsided to control values at 72 h after the last morphine injection. In contrast, the firing rate and burst firing of mesolimbic dopaminergic neurons were found to be reduced at 1, 3 and 7 days after morphine withdrawal. After 14 drug‐free days, electrophysiological analysis revealed an apparent normalization of various parameters. However, at this time, intravenous administration of morphine produced an increment of electrical activity which was significantly higher than that obtained in control (saline treated) rats. Further, administration of the opiate antagonist naltrexone, administered without prior morphine, at 3, 7 and 14 days after the last morphine administration, failed to alter dopaminergic neuronal activity. The results indicate: (i) that the activity of mesolimbic dopaminergic neurons remains reduced well after somatic signs of withdrawal have disappeared; (ii) after 14 days of withdrawal, the augmented magnitude of the electrophysiological response to exogenous morphine suggests an increased sensitivity of opiate receptors; and (iii) the lack of relationship between dopaminergic activity and somatic signs of withdrawal corroborates the notion that dopaminergic activity in the mesolimbic system does not participate in the neurobiological mechanisms responsible for somatic withdrawal. The present results may be relevant to the phenomenon of drug addiction in humans and consequent relapse after drug‐free periods.
Properties of NMDA receptors in rat spinal cord motoneurons
Authors: Paleček Jir í , Abdrachmanova Galya , Vlachová Viktorie , Vyklický Ladislav
Published: March 2003

Postnatal development and properties of N‐methyl‐d‐aspartate (NMDA) receptors were studied with whole‐cell and outside‐out patch‐clamp techniques in interneurons and fluorescence‐labelled motoneurons in rat spinal cord slices. Both the absolute amplitude of NMDA‐induced currents and currents normalized with respect to the motoneuron capacitance increased significantly at postnatal days 10–13 when compared to the responses evoked at postnatal days 2–3. The mean amplitude of the responses to kainate also increased in motoneurons of postnatal days 10–13. Single‐channel currents induced by low concentrations of glutamate, exhibited four distinct amplitude levels corresponding to 19.2 ± 2.4 pS, 38.4 ± 3.5 pS, 56.3 ± 2.4 pS and 69.6 ± 3.7 pS. In contrast, the conductance of single channels, recorded under identical conditions, in rat spinal cord interneurons was less, 15.3 ± 3.2 pS, 29.9 ± 5.4 pS, 46.7 ± 4.8 pS and 62.4 ± 3.9 pS. The high (56/70 pS) conductance single‐channel openings in motoneuron patches were sensitive to NMDA receptor inhibitors d‐2‐amino‐5‐phosphonovalerate, 7‐chlorokynurenic acid and ifenprodil. Whole‐cell NMDA‐evoked currents were blocked in a voltage‐dependent manner by extracellular Mg2+ with an apparent dissociation constant for Mg2+ binding at 0 mV of 1.8 ± 0.5 mm. The conductance and relative distribution of NMDA receptor channel openings induced by 1 μm glutamate in patches isolated from the motoneurons were independent of age from postnatal day 4 to 14.

 The results suggest that the properties of NMDA receptor channels in motoneurons differ from those in spinal cord interneurons and cells transfected with NR1/NR2 subunits.
Myelin‐associated oligodendrocytic basic protein is essential for normal arrangement of the radial component in central nervous system myelin
Authors: Yamamoto Yoichi , Yoshikawa Hiroo , Nagano Seiichi , Kondoh Gen , Sadahiro Shigeki , Gotow Takahiro , Yanagihara Takehiko , Sakoda Saburo
Published: March 2003

We previously reported that myelin‐associated oligodendrocytic basic protein (MOBP) was abundantly expressed in the central nervous system (CNS) myelin, and shared several characteristics with myelin basic protein (MBP). In particular, a cluster of positively charged amino acids was considered to facilitate compaction of the cytoplasmic face of the myelin sheath, as in the case of MBP. However, the contribution of MOBP in forming and maintaining the myelin sheath still remains unclear. Recent investigations showed that one isoform of MOBP was expressed in the embryo prior to myelination, and MOBP isoforms were colocalized with the microtubular network and nucleus in vitro. To explore the role of MOBP in vivo, we generated MOBP‐deficient mice and analysed the CNS myelin. Surprisingly, the compact myelin was formed, however, the myelin from MOBP‐deficient mice exposed to hexachlorophene, a known dysmyelinating agent, showed widening of the major dense lines. These results suggest that MOBP is not essential for myelin formation, but reinforces the apposition of the cytoplasmic faces of the myelin sheath. A striking phenotype of MOBP‐deficient mice was the presence of the straight ‘condensed’ radial component. This component has been described as a tight junction‐like complex running radially and zig‐zag through the CNS myelin sheath between inner and outer mesaxons. These results suggest that MOBP is essential for normal arrangement of the radial component.
Adrenergic innervation of rat sensory ganglia following proximal or distal painful sciatic neuropathy: distinct mechanisms revealed by anti‐NGF treatment
Authors: Ramer Matt S. , Bisby Mark A.
Published: March 2003

Sympathetic axons invade dorsal root ganglia (DRG) following nerve injury, and activity in the resulting pericellular axonal ‘baskets’ may underlie painful sympathetic–sensory coupling. Sympathetic sprouting into the DRG may be stimulated by nerve growth factor (NGF). To test this hypothesis, we investigated the effect of daily anti‐NGF administration on pain and on sprouting in the DRG induced by chronic sciatic constriction injury (CCI) or L5 spinal nerve ligation (SNL). These models have been shown to differ subtly in the onset of pain behaviours and adrenergic sprouting, and we now demonstrate a fundamental difference in the way sympathetic axons invade the DRG: after CCI, perivascular noradrenergic collaterals sprouted into the DRG in a manner dependent upon peripherally derived NGF. In contrast, after SNL, regenerating sympathetic axons were diverted towards the DRG from the spinal nerve by the obstructing ligature, and this effect was only moderately impeded by anti‐NGF. The differential dependence on anti‐NGF suggests that adrenergic innervation of the DRG after SNL and CCI may reflect regenerative and collateral sprouting, respectively. Pain behaviour was similarly affected: anti‐NGF completely prevented CCI‐induced thermal hyperalgesia and mechanoallodynia, but the same treatment only partly relieved these symptoms following SNL. These differences emphasize that although CCI and SNL may result in similar behavioural abnormalities, the underlying mechanisms may be governed by distinct processes, differentially dependent on peripheral NGF. These mechanistic differences will have to be considered in the development of appropriate treatment strategies for neuropathic pain produced by different types of pathology.
Callosal connections of the parabelt auditory cortex in macaque monkeys
Authors: Hackett T. A. , Stepniewska I. , Kaas J. H.
Published: March 2003

Auditory cortex of macaque monkeys is located on the lower bank of the lateral sulcus and the adjoining superior temporal gyrus. This region of cortex contains a core of primary‐like areas surrounded by a narrow belt of associated fields. Adjacent to the lateral belt on the superior temporal gyrus is a parabelt region which contains at least two subdivisions (rostral and caudal). In previous studies we defined the parabelt region as cortex with topographic cortical connections with the belt areas surrounding the core, and connections with the dorsal and magnocellular divisions of the medial geniculate complex, but minimal connections with the core region and ventral division of the medial geniculate complex. The callosal connections of the parabelt auditory cortex were determined by placing injections, of up to six distinguishable tracers, into different locations of the parabelt region in each of four macaque monkeys. The results indicated that the strongest callosal projections arise from homotopic areas in parabelt cortex, and they roughly matched the rostrocaudal levels of the medial and lateral belt cortex. Weaker callosal inputs to the parabelt originate from the corresponding levels of the superior temporal gyrus and superior temporal sulcus. The core region does not contribute significant callosal projections to the parabelt region. The results provide further support for the conclusion that the parabelt region represents a third level of auditory cortical processing beyond direct activation by primary subcortical and cortical auditory structures.
Functional role of the slow activation property of ERG K+ channels
Authors: Schönherr Roland , Rosati Barbara , Hehl Solveig , Rao Valesvara G. , Arcangeli Annarosa , Olivotto Massimo , Heinemann Stefan H. , Wanke Enzo
Published: March 2003

ERG (ether‐à‐go‐go‐related gene) K+ channels are crucial in human heart physiology (h‐ERG), but are also found in neuronal cells and are impaired in Drosophila‘seizure’ mutants. Their biophysical properties include the relatively fast kinetics of the inactivation gate and much slower kinetics of the activation gate. In order to elucidate how the complex time‐ and voltage‐dependent activation properties of ERG channels underlies distinct roles in excitability, we investigated different types of ERG channels intrinsically present in cells or heterologously expressed in mammalian cells or Xenopus oocytes. Voltage‐dependent activation curves were highly dependent on the features of the eliciting protocols. Only very long preconditioning times produced true steady‐state relationships, a fact that has been largely neglected in the past, hampering the comparison of published data on ERG channels. Beyond this technical aspect, the slow activation property of ERG can be responsible for unsuspected physiological roles. We found that around the midpoint of the activation curve, the time constant of ERG open–close kinetics is of the order of 10–15 s. During sustained trains of depolarizations, e.g. those produced in neuronal firing, this leads to the use‐dependent accumulation of open‐state ERG channels. Accumulation is not observed in a mutant with a fast activation gate. In conclusion, it is well established that other K+ channels (i.e. Ca2+‐activated and M) control the spike‐frequency adaptation, but our results support the notion that the purely voltage‐dependent activation property of ERG channels would allow a slow inhibitory physiological role in rapid neuronal signalling.
CNS pattern of metabolic activity during tonic pain: evidence for modulation by β‐endorphin
Authors: Porro Carlo A. , Cavazzuti Milena , Baraldi Patrizia , Giuliani Daniela , Panerai Alberto E. , Corazza Ruggero
Published: March 2003

CNS correlates of acute prolonged pain, and the effects of partial blockade of the central β‐endorphin system, were investigated by the quantitative 2‐deoxyglucose technique in unanaesthetized, freely moving rats. Experiments were performed during the second, tonic phase of the behavioural response to a prolonged chemical noxious stimulus (s.c. injection of dilute formalin into a forepaw), or after minor tissue injury (s.c. saline injection). During formalin‐induced pain, local glucose utilization rates in the CNS were bilaterally increased in the grey matter of the cervical spinal cord, in spinal white matter tracts and in several supraspinal structures, including portions of the medullary reticular formation, locus coeruleus, lateral parabrachial region, anterior pretectal nucleus, the medial, lateral and posterior thalamic regions, basal ganglia, and the parietal, cingulate, frontal, insular and orbital cortical areas. Pretreatment with anti‐β‐endorphin antibodies, injected i.c.v., led to increased metabolism in the tegmental nuclei, locus coeruleus, hypothalamic and thalamic structures, putamen, nucleus accumbens, diagonal band nuclei and dentate gyrus, and in portions of the parietal, cingulate, insular, frontal and orbital cortex. In formalin‐injected rats, pretreated with anti‐β‐endorphin, behavioural changes indicative of hyperalgesia (increased licking response) were found, which were paralleled by a significant enhancement of functional activity in the anterior pretectal nucleus and in thalamo‐cortical systems. A positive correlation was found between the duration of the licking response and metabolic activity of several forebrain regions. These results provide a map of the CNS pattern of metabolic activity during tonic somatic pain, and demonstrate a modulatory role for β‐endorphin in central networks that process somatosensory inputs.
Episodic corticosterone treatment accelerates kindling epileptogenesis and triggers long‐term changes in hippocampal CA1 cells, in the fully kindled state
Authors: Karst Henk , De Kloet E. Ronald , Joëls Marian
Published: March 2003

We tested the effect of episodic (≈ 10 days) corticosterone treatment on: (i) behavioural symptoms during kindling epileptogenesis; and (ii) electrical activity in the CA1 hippocampal area during epileptogenesis, and later on, in the fully kindled state. Male rats received a corticosterone‐releasing pellet (100 mg/day) shortly before kindling was started, resulting in elevated hormone levels during the early and middle stages of epileptogenesis. The appearance of moderate behavioural signs of epilepsy and severe tonic–clonic seizures was significantly accelerated in corticosterone‐treated animals compared to placebo controls. During epileptogenesis, corticosterone treatment did not affect the amplitude and paired‐pulse characteristics of in vivo‐recorded CA1 field responses, or the duration of the afterdischarge following tetanic stimulation of the Schaffer collaterals. However, other properties of CA1 cells studied in vitro, in the fully kindled state, were altered by the earlier episodic corticosterone treatment. Thus, in kindled rats, the amplitude of the population spike in the CA1 area was significantly enhanced after prior exposure to high corticosterone levels. Prior episodic steroid treatment resulted furthermore in a significantly increased amplitude of voltage‐gated Ca currents, in kindled rats. At that time, corticosterone levels of animals which had received a corticosterone‐releasing pellet earlier were no longer elevated compared to the placebo controls; the corticosteroid‐treated rats did also not differ from the controls with respect to the mRNA expression levels for the two corticosteroid receptor subtypes in the hippocampus. The data suggest that exposure of animals to a period of stressful experiences during a critical phase in epileptogenesis could impose lasting deleterious effects on the course of epilepsy, even when CORT levels have been normalized again.
The close homologue of the neural adhesion molecule L1 (CHL1): patterns of expression and promotion of neurite outgrowth by heterophilic interactions
Authors: Hillenbrand Rainer , Molthagen Martin , Montag Dirk , Schachner Melitta
Published: March 2003

The close homologue of L1 (CHL1), a member of the L1 family of neural adhesion molecules, is first expressed at times of neurite outgrowth during brain development, and is detectable in subpopulations of neurons, astrocytes, oligodendrocyte precursors and Schwann cells of the mouse and rat. Aggregation assays with CHL1‐transfected cells show that CHL1 does not promote homophilic adhesion or does it mediate heterophilic adhesion with L1. CHL1 promotes neurite outgrowth by hippocampal and small cerebellar neurons in substrate‐bound and soluble form. The observation that CHL1 and L1 show overlapping, but also distinct patterns of synthesis in neurons and glia, suggests differential effects of L1‐like molecules on neurite outgrowth.
Organization of visual cortex in the northern quoll, Dasyurus hallucatus: evidence for a homologue of the second visual area in marsupials
Authors: Rosa Marcello G. P. , Krubitzer Leah A. , Molnár Zoltán , Nelson John E.
Published: March 2003

Two visual areas, V1 and V2 (first and second visual areas), appear to be present in the posterior neocortex of all eutherian mammals investigated so far. However, previous studies have not established whether an area homologous to V2 also exists in metatherian mammals (marsupials). Using electrophysiological techniques, we mapped the visual receptive fields of neurons in the striate and peristriate cortices of the northern quoll, an Australian marsupial. We found that neurons in a 2‐mm‐wide strip of cortex rostrolateral to V1 form a single, relatively simple representation of the complete contralateral hemifield. This area resembles V2 of eutherians in several respects: (i) neurons in the medial half of the peristriate area represent the lower visual quadrant, whereas those in the lateral half represent the upper visual quadrant; (ii) the vertical meridian of the visual field is represented adjacent to V1, while the visual field periphery is represented along the lateral and rostrolateral borders of the peristriate area; (iii) there is a marked anisotropy in the representation, with a larger magnification factor parallel to the V1 border than perpendicular to this border; and (iv) receptive fields of multiunit clusters in the peristriate cortex are much larger than those of cells in V1 at comparable eccentricities. The cortex immediately rostral and lateral to V2 did not respond to visual stimulation under our recording conditions. These results suggest that V1 and V2 together form a ‘core’ of homologous visual areas, likely to exist in all therian mammals.