bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Neonatal Axoplasmic Transport Attenuation in the Infraorbital Nerve on Vibrissae‐related Patterns in the Rat's Brainstem, Thalamus and Cortex
Authors: Chiaia Nicolas L. , Bennett‐Clarke Carol A. , Crissman Robert S. , Zheng Li , Chen Min , Rhoades Robert W.
Published: April 2006

This study evaluated the effects of neonatal attenuation of axoplasmic transport in the infraorbital nerve (ION) on the organization of vibrissae‐related patterns in the rat's CNS. Application of colchicine‐ or vinblastine impregnated implants to the ION from birth until postnatal day (P)6 to P10 resulted in a 92.4% reduction in the number of trigeminal (V) ganglion cells labelled by application of horseradish peroxidase to the vibrissa pad and a 44.8% decrease in the number of Nissl‐stained ganglion cells in the ophthalamic‐maxillary portion of the V ganglion. These implants also decreased the number of myelinated fibres in the ION. In normal rats killed on P6‐10, there was an average of 10 273±1259 myelinated axons in the nerve. In the animals with colchicine‐ or vinblastine‐treated implants, this value was 3891±1965. The highest axon count in an experimental animal was 9859. In all animals, axoplasmic transport attenuation resulted in the disappearance of normal vibrissae‐related cytochrome oxidase patterns in the brainstem, thalamus and primary somatosensory cortex. Axoplasmic transport attenuation did not result in the disappearance of vibrissae‐related ordering of V primary afferent terminal arbors, as demonstrated by anterograde labelling with neurobiotin. These results suggest that some factor conveyed from the periphery of the V ganglion and perhaps on to the brainstem is necessary for the maintenance of vibrissae‐related patterns in the thalamus and cortex.
Structural Features of a Close Homologue of L1 (CHL1)in the Mouse: A New Member of the L1 Family of Neural Recognition Molecules
Authors: Holm Jürgen , Hillenbrand Rainer , Steuber Volker , Bartsch Udo , Moos Marion , Lübbert Hermann , Montag Dirk , Schachner Melitta
Published: April 2006

We have identified a close homologue of L1 (CHL1) in the mouse. CHL1 comprises an N‐terminal signal sequence, six immunoglobulin (Ig)‐like domains, 4.5 fibronectin type III (FN)‐like repeats, a transmembrane domain and a C‐terminal, most likely intracellular domain of ˜100 amino acids. CHL1 is most similar in its extracellular domain to chicken Ng‐CAM (˜40% amino acid identity), followed by mouse L1, chicken neurofascin, chicken Nr‐CAM, Drosophila neuroglian and zebrafish L1.l (37‐28% amino acid identity), and mouse F3, rat TAG‐1 and rat BIG‐1 (˜27% amino acid identity). The similarity with other members of the Ig superfamily [e.g. neural cell adhesion molecule (N‐CAM), DCC, HLAR, rse] is 16‐11%. The intracellular domain is most similar to mouse and chicken Nr‐CAM, mouse and rat neurofascin (˜60% amino acid identity) followed by chicken neurofascin and Ng‐CAM, Drosophila neuroglian and zebrafish L1.l and L1.2 (˜40% amino acid identity). Besides the high overall homology and conserved modular structure among previously recognized members of the L1 family (mouse/human L1/rat NILE; chicken Ng‐CAM; chicken/mouse Nr‐CAM; Drosphila neuroglian; zebrafish L1.l and L1.2; chicken/mouse neurofascin/rat ankyrin‐binding glycoprotein), criteria characteristic of L1 were identified with regard to the number of amino acids between positions of conserved amino acid residues defining distances within and between two adjacent Ig‐like domains and FN‐like repeats. These show a collinearity in the six Ig‐like domains and four adjacent FN‐like repeats that is remarkably conserved between L1 and molecules containing these modules (designated the L1 family cassette), including the GPI‐linked forms of the F3 subgroup (mouse F3/chicken F1l/human CNTN1; rat BIG‐l/mouse PANG; rat TAG‐l/mouse TAX‐l/chicken axonin‐1). The colorectal cancer molecule (DCC), previously introduced as an N‐CAM‐like molecule, conforms to the L1 family cassette. Other structural features of CHL l shared between members of the L1 family are a high degree of N‐glycosidically linked carbohydrates (˜20% of its molecular mass), which include the HNK‐1 carbohydrate structure, and a pattern of protein fragments comprising a major 185 kDa band and smaller fragments of 165 and 125 kDa. As for the other L1 family members, predominant expression of CHL l is observed in the nervous system and at later developmental stages. In the central nervous system CHL l is expressed by neurons, but, in contrast to L1, also by glial cells. Our findings suggest a common ancestral L1‐like molecule which evolved via gene duplication to generate a diversity of structurally and functionally distinct yet similar molecules.
Development of Trigeminal Nucleus Principalis in the Rat: Effects of Target Removal at Birth
Authors: Jacquin Mark F. , Rana Jamil Z. , Miller Michael W. , Chiaia Nicolas L. , Rhoades Robert W.
Published: April 2006

Little is known about how neurons develop in the trigeminal nucleus principalis (PrV) despite their acknowledged role in establishing whisker‐related patterns in the thalamus and cortex. Golgi‐impregnated PrV cells were studied in newborn, 4‐day‐old and adult rats. Adult neurons typically had short dendrites that were confined to a hemisphere around the soma. In contrast, at birth PrV neurons had radial trees and more primary dendrites than did adults, but adult‐like numbers of dendritic spines. By day 4, most neurons had eccentric dendritic trees and the numbers of primary dendrites per neuron were adult‐like, yet spines were more prevalent than in adults and newborns. Thus, it appears that there is a pruning of the dendritic tree during the first postnatal week. To assess the role of retrograde signals from the thalamus on PrV development, the right thalamus was destroyed at birth. By postnatal day 6, the number of neurons in the left PrV was 59% of that in the right PrV, PrV transverse area was reduced by 21%, cell density was reduced by 48%, and somatic diameter was increased by 36%, relative to the intact right PrV. By contrast, in the left V subnucleus interpolaris, which has only a weak thalamic projection, these measures were unaffected. Thus, neonatal thalamic lesions selectively depopulated the PrV. The morphology of PrV neurons was affected by the thalamic lesions: e.g. the total dendritic length, the number of dendritic branch points and the total number of spines were increased. The number of primary dendrites and the tree's eccentricity, area, and volume of influence were unaffected by the lesion. The structure of neurons in subnucleus interpolaris was unaffected by the lesion. Thus, normal afferent patterning is insufficient for normal development of PrV cells. Interactions among dendrites and retrograde signals from a target are also important.
Serotonin Regulates Gap Junction Coupling in the Developing Rat Somatosensory Cortex
Authors: Rörig Birgit , Sutor Bernd
Published: April 2006

To further elucidate the role of the neuromodulatory transmitter serotonin (5‐HT) during early postnatal development of the neocortex, we investigated the effects of 5‐HT on gap junction coupling in the somatosensory cortex of rats aged between postnatal days 7 and 10. The gap junction‐permeable tracer neurobiotin was injected into single neurons via microelectrodes or patch pipettes. Under control conditions, clusters of about 25 tracer‐coupled neurons were observed. Serotonin reduced dye‐coupling between lamina II/III pyramidal cells in a concentration‐dependent and reversible manner. The 1,4,5‐inositol triphosphate (IP3) receptor antagonist heparin as well as the protein kinase C inhibitor NPC 15437 suppressed the uncoupling action of 5‐HT, suggesting that the serotonergic effect involved IP3 receptor‐mediated release of calcium ions from intracellular stores. In contrast, the 5‐HT‐induced reduction in gap junction coupling was not antagonized by Rp‐adenosine3′,5′‐cyclic monophosphothionate, an inhibitor of CAMP dependent protein kinase. The uncoupling effect of 5‐HT was mimicked by 5‐HT2 receptor agonists and antagonized by the 5‐HT2 receptor antagonist ritanserin, indicating that 5‐HT suppressed gap junction coupling via activation of 5‐HT2 class receptors. Our results suggest that the developmental functions of 5‐HT not only involve the modulation of chemical synaptic transmission but also include the regulation of the gap junctional communication system during differentiation of the neocortex.
Spontaneous Behaviours of Rats are Differentially Affected by Substantia Nigra Infusions of Brain‐derived Neurotrophic Factor and Neurotrophin‐3
Authors: Martin‐Iverson Mathew T. , Altar C. Anthony
Published: April 2006

The effects on spontaneous behaviour after 7 and 14 days of continuous unilateral infusion of brain‐derived neurotrophic factor (BDNF, 12 μg/day) and neurotrophin‐3 (NT‐3, 12 μg/day) into the rat substantia nigra were investigated during the day and night. Animals subjected to these treatments were compared to untreated controls and vehicle‐infused controls that were weight‐matched for the decreases in body weight produced by BDNF and NT‐3. BDNF increased feeding and food retrieval, indicating that BDNF did not decrease appetite. BDNF but not NT‐3 markedly decreased drinking, suggesting that weight loss in BDNF‐treated rats may be secondary to hypodypsia, whereas in NT‐3‐treated rats weight loss was more likely a direct consequence of decreased feeding. Exploratory behaviours, limb flicks and contralateral postural bias were increased by BDNF. The behavioural profile of BDNF‐treated rats is consistent with an increase in dopaminergic activity. In addition, BDNF increased backwards walking, a behaviour that requires the activation of both dopamine and serotonin systems. In contrast, NT‐3 selectively increased behaviours that are mediated primarily by serotonin, such as wet‐dog shakes. NT‐3 increased limb flicks and mouth movements, but had a smaller effect than BDNF on exploratory behaviour. Vehicle infusions produced behavioural effects consistent with cannula‐ or infusioninduced damage to the nigrostriatal dopamine system, and some of these effects were reversed by BDNF. Most of the behavioural effects of the neurotrophins are consistent with the view that BDNF increases activity of both dopaminergic and serotonergic systems within the nigrostriatal system, and that NT‐3 increases serotonin activity. Effects of BDNF and NT‐3 on grooming behaviours, possibly indicative of actions on nigral neuropeptides, provide further evidence of consistencies between reported neurochemical and behavioural effects of neurotrophins.
Bilateral 6‐Hydroxydopamine‐induced Lesion of the Nigrostriatal Dopamine Pathway Reproduces the Effects of Unilateral Lesion on Substance P but not on Enkephalin Expression in Rat Basal Ganglia
Authors: Salin* Pascal , Hajji Moulay Driss , Goff Lydia Kerkerian‐le
Published: April 2006

This study compared the effects of unilateral and bilateral 6‐hydroxydopamine‐induced lesions of the nigrostriatal dopaminergic neurons on substance P and enkephalin expression in the rat striatum and its main target structures by means of quantitative in situ hybridization and immunocytochemistry. In animals with bilateral lesion, substance P mRNA levels were decreased in the striatum, and this was matched by parallel reductions in substance P immunoreactivity in the striatum and in the striatonigral terminals at substantia nigra level in both hemispheres. These changes were similar to those observed ipsilaterally to unilateral lesion. In contrast, whereas increased striatal enkephalin immunoreactivity and mRNA levels and decreased immunoreactivity in the globus pallidus were observed on the lesioned side after unilateral lesion, no significant change in these enkephalin markers occurred in animals with bilateral lesion. These data suggest that the effects of dopamine deafferentation on substance P expression in the striatonigral system may be due primarily to removal of direct dopamine influence, whereas the effects on enkephalin expression in the striatopallidal system may involve complex interhemispheric adaptive mechanisms. The present finding that bilateral dopamine lesion does not simply reproduce the effects of unilateral lesion but creates a new functional state may have a critical bearing on the understanding and treatment of Parkinson's disease.
Functional Characterization and Modulation of Feedback Inhibitory Circuits in Area CA3 of Rat Hippocampal Slice Cultures
Authors: Fortunato Christian , Debanne Dominique , Scanziani Massimo , Gähwiler Beat H. , Thompson Scott M.
Published: April 2006

Feedback inhibitory circuits were characterized electrophysiologically in the CA3 region of organotypic rat hippocampal cultures. Pyramidal cells were impaled with sharp microelectrodes and brief depolarizing current pulses were injected intracellularly to elicit single action potentials. An inhibitory postsynaptic potential (I PSP) was observed at fixed latency after the action potential in 27% of impaled cells (n= 131). These IPSPs were fully blocked by bicuculline, indicating that they were mediated solely by γ‐aminobutyric acid type A (GABAA) receptors. They were also blocked by 6‐cyano‐7‐nitro‐quinoxaline‐2, 3‐dione but not d‐2‐amino‐5‐ phosphonovalerate, indicating that non‐N‐methyl‐d‐asparttate receptors were necessary and sufficient for activating interposed GABAergic interneurons. Adenosine (0.1‐5 μM) increased the percentage of action potentials that were not followed by IPSPs by reducing the probability of glutamatergic activation of the interneurons. In 18 of 21 experiments adenosine also decreased the mean amplitude of successfully elicited IPSPs, indicating that more than one interneuron participated in the feedback inhibition of those pyramidal cells. In three experiments the non‐failure IPSP amplitude was not affected by adenosine, suggesting that only one interneuron participated. Repetitive stimulation at 2‐4 Hz decreased the amplitude of non‐failure feedback IPSPs and usually increased the number of failures of transmission. These effects were transient and insensitive to the GABAB antagonist CGP 35 348. We conclude that both the excitation of interneurons and the release of GABA from interneurons are modulated by repetitive stimulation.
Characterization of a Barium‐sensitive Outward Current following Glutamate Application on Rat Midbrain Dopaminergic Cells
Authors: Mercuri Nicola B. , Bonci Antonello , Calabresi Paolo , Bernardi Giorgio
Published: April 2006

Using intracellular electrophysiological recordings in dopaminergic (principal) neurons of the rat mesencephalon maintained in vitro, we studied a postexcitatory amino acid response (PEAAR). Under current‐clamp mode, bath application of glutamate produced a depolarization that was followed by a hyperpolarization when the perfusion of the excitatory amino acid was discontinued. Under single‐microelectrode voltage‐clamp mode, an outward current followed the glutamate‐induced inward current. The PEAAR was associated with an increase in membrane conductance and reversed polarity at about ‐85 mV (2.5 mM extracellular K+). The null potential for the PEAAR was independent of the intracellular loading of chloride ions and was shifted towards less negative values (˜23 mV) by increasing extracellular K+ from 2.5 to 8.5 mM. The PEAAR was present in neurons treated with tetraethylammonium (5–10 mM), apamin (1 μM) or glibenclamide (1–300 μM). However, it was strongly depressed or blocked by extracellular barium (300 μM to 1 mM), by low‐calcium (0.5 mM) plus cadmium (100 μM) or magnesium (10 mM), and by low‐sodium solutions. An outward response was also generated after an inward current induced by the perfusion of the specific agonists for the ionotropic excitatory amino acid receptors NMDA, a‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole (AMPA) and kainate. The PEAAR was not affected by tetrodotoxin (1 μM), saclofen (100–300 μM), bicuculline (30 μM), sulpiride (1 μM) or strychnine (1 μM). In addition, the inhibition of the ATP‐dependent Na+‐K+ pump by ouabain and strophanthidin (1–10 μM) prolonged the glutamate‐induced membrane depolarization/inward current while the subsequent PEAAR was reduced or not observed. Our data indicate that the PEAAR mainly results from the activation of a barium‐sensitive potassium current. This response might limit the excitatory and eventually neurotoxic effects of glutamate.
Contrast‐dependent Dissociation of Visual Recognition and Detection Fields
Authors: Strasburger Hans , Rentschler Ingo
Published: April 2006

Seeing an object‘as something’is different from simply seeing it (see Watanabe, S., 1985, Pattern Recognition: Human and Mechanical, John Wiley). This distinction between recognition and detection often goes unnoticed in physiology and clinical practice, where visual performance is characterized in terms of acuity, visual field and contrast sensitivity. The corresponding functions of stimulus detection are consistent with the neural projection properties from the retina to the striate cortex, i.e. the‘cortical magnification theory’. Yet recognition performance for characters (Strasburger, H. et al., 1994, Eur. J. Neurosci., 6, 1583‐1588) and grey‐level patterns (Jüttner, M. and Reutschler, I., 1996, Vision Res., 36, 1007–1022) does not fit into this scheme. Here we show that this discrepancy results in the dissociation of visual recognition and detection fields, which is dramatic at low pattern contrast. Form proper can be appreciated exclusively within the much narrower field of recognition, the window of visual intelligence. Its function is, at low contrast, probably mediated by the magnocellular pathway and at all contrasts is determined by the processing characteristics of higher stages of the ventral visual pathway.
Recombinant Human Adenovirus with Rat MIP‐2 Gene Insertion Causes Prolonged PMN Recruitment to the Murine Brain
Authors: Bell M. D. , Taub D. D. , Kunkel S. J. , Strieter R. M. , Foley R. , Gauldie J. , Perry V. H.
Published: April 2006

Single injections of recombinant cytokines/chemokines into tissue have provided insights into their possible roles during the inflammatory response. Adenoviral technology may allow us to mimic the in vivo situation more closely, with protein generated in a continuous but transient fashion. Replication‐deficient human type 5 adenovirus containing a rat macrophage inflammatory protein‐2 (MIP‐2) gene insertion and cytomegalovirus promoter was injected into the mouse brain to investigate the inflammatory response to continuous overproduction of MIP‐2. Adenovirus with a LacZ gene insertion expressing β‐galactosidase was used as a control. At doses of 104 to 107 plaque‐forming units, a minimal inflammatory response was detected to the LacZ virus, with leukocyte recruitment that was restricted to the injection site. A dose of 107 plaque‐forming units of both the LacZ and the MIP‐2 vector produced extensive transgene product expression that persisted for at least 7 days. Astrocytes, recognized by their morphology, were the predominant cell type expressing MIP‐2 and β‐galactosidase. A dose of 107 plaque‐forming units of MIP‐2 vector caused dramatic polymorphonuclear leukocyte (PMN) recruitment to the brain parenchyma after 2 days. PMN recruitment was still observed after 4 and 7 days, but had become more localized to the injection site and was associated with numerous foam‐like macrophages. At both 2 and 7 days the blood‐brain barrier was breached in the region of leukocyte recruitment. Despite the extent of leukocyte recruitment there were no overt signs of neuronal degeneration or demyelination. Our findings demonstrate that continuous production of MIP‐2 in the CNS results in persistent PMN recruitment to the brain parenchyma with no evidence of tachyphylaxis. The lack of PMN recruitment to the brain parenchyma following CNS injury may be a result of deficient production of PMN chemoattractants.
Involvement of p53 in DNA Strand Break‐induced Apoptosis in Postmitotic CNS Neurons
Authors: Enokido Yasushi , Araki Toshiyuki , Tanaka Kiyoji , Aizawa Shinichi , Hatanaka Hiroshi
Published: April 2006

The tumour suppressor p53 gene serves as a critical regulator of the cell cycle and of apoptosis following the exposure of normal cells to DNA damage. To examine the role of p53 in postmitotic CNS neurons, we cultured cerebellar neurons from normal wild‐type mice and mutant p53‐null mice under various conditions inducing neuronal death. When cerebellar neurons from 15‐ to 16‐day postnatal wild‐type mice were treated with ionizing radiation or DNA‐damaging agents, massive neuron death occurred after 24‐72 h. In contrast, neurons from p53+ mice evidently resisted γ‐irradiation and some DNA‐damaging agents, such as etoposide and bleomycin. On the other hand, low‐K+ medium‐induced apoptosis of cerebellar neurons was not affected by p53 status. Neither cell cycle progression nor DNA synthesis occurred during cell death induced by γ‐irradiation and low‐K+ medium, as well as in normal cultures of p53+/+ and p53‐/‐ neurons. These results suggest that p53 is required for the apoptotic death of postmitotic cerebellar neurons induced by DNA strand breaks.
Effect of Feedback from Peripheral Movements on Neuron Activity in the Aplysia Abdominal Ganglion
Authors: Höpp H. P. , Falk C. X. , Cohen L. B. , Wu J. Y. , Cohen A. I.
Published: April 2006

We have made reasonably comprehensive measurements of action potential activity in the Aplysia californica abdominal ganglion to determine the amount of feedback the central nervous system (CNS) receives from a movement which it initiates. Voltage‐sensitive dye measurements of action potential activity of cells in the ganglion were made during the gill‐withdrawal reflex elicited by siphon stimulation. We compared recordings in two situations which differed dramatically in the amount the gill moved. In the control sea water, the gill withdrawal was normal; in low‐Ca2+, high‐Mg2+ sea water, the gill movement was blocked. Both the timing and the number of spikes of the individual neurons were similar in the two situations. Histograms of the summed spike activity versus time and histograms of the number of active neurons versus time in the two conditions were also similar. Finally, two numerical measures of trial‐to‐trial differences, a paired t‐test and a measure we named fractional similarity, did not indicate larger differences between two trials in the different sea waters than two trials in the same sea water. Feedback from sensory neurons activated by the gill movement itself does not make a large contribution to the spike activity in the abdominal ganglion. Apparently the Aplysia CNS issues the command for the withdrawal and does not make adjustments for the magnitude of the actual withdrawal. It may not even receive the information necessary for such adjustments to be made. A second motivation for these experiments was to test whether removing the feedback might simplify the neuronal activity that occurs during the gill‐withdrawal reflex. This did not occur.
Morphological and Biochemical Changes in Neurons: Apoptosis versus Mitosis
Authors: Philpott Karen L. , McCarthy Mary Jane , Becker David , Gatchalian Christine , Rubin Lee L.
Published: April 2006

Apoptosis and mitosis are often thought to share certain morphological similarities and therefore to be regulated by similar sets of enzymes. In this study, the Golgi apparatus and nuclear lamina were examined in PC12 cells and rat superior cervical ganglion neurons undergoing apoptosis in response to withdrawal of nerve growth factor or addition of staurosporine. We found that the Golgi apparatus disperses during apoptosis, without obvious degradation, in a manner similar to that occurring in mitosis. In contrast, the nuclear lamina did not become completely solubilized during apoptosis, as occurs in mitosis, but remained as a distinct structure around the nucleus, although some degradation of nuclear lamins was seen. To assess the integrity of the nuclear envelope, fluorescent probes were introduced into the cytoplasm of live and dying cells. High molecular weight tracers were still excluded from the nuclei of apoptotic cells, demonstrating the continued existence of a functional nuclear barrier. These data suggest, therefore, that cell death is unlikely to occur simply as a result of inappropriate activation of cell cycle enzymes.
Activity‐dependent Decay of Early LTP Revealed by Dual EPSP Recording in Hippocampal Slices from Young Rats
Authors: Xiao Min‐Yi , Niu Yin‐Ping , Wigström Holger
Published: April 2006

The early maintenance of long‐term potentiation (LTP) was studied in the CA1 region of hippocampal slices from 12‐ to 18‐day‐old rats in a low‐magnesium solution (0.1 mM). The α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA) and N‐methyl‐D‐aspartate (NMDA) receptor‐mediated components of the field excitatory postsynaptic potential were estimated in parallel using early and late measurements of the composite potential. At the normal test stimulus frequency of 0.1 Hz, LTP was seen initially as a predominant increase in the AMPA component, but converted, via a substantial decay of this component and a gradual growth of the NMDA component, into nearly equal changes of the two components. Interrupting the test stimulation for 10 min, changing the test stimulus frequency to 1/60 Hz after LTP induction, or using a test stimulus frequency of 1/60 Hz during the entire experiment significantly reduced the decay of the potentiation of the AMPA component while enhancing the potentiation of the NMDA one. The ratio between the magnitudes of the two excitatory postsynaptic potential (EPSP) components showed a decaying time course that was independent of the manipulations used. Application of the NMDA antagonist D(‐)‐2‐amino‐5‐phosphonopentanoic acid (50μM) after LTP induction stabilized the LTP of the AMPA component until washout was started. On the other hand, the phosphatase inhibitor okadaic acid (1 μM) resulted in decay of the potentiation of both EPSP components back to around baseline and altered the time course of the ratio between the components. Our results show that the early maintenance of LTP is controlled in an activity‐dependent and NMDA‐dependent manner. This process accelerates the decay of LTP of both AMPA and NMDA components in parallel, suggesting that it is similar to homosynaptic long‐term depression, although it operates at the normal test stimulus frequency. The data support a scenario in which LTP ensues as a selective AMPA receptor modification and subsequently converts to another modification, possibly a presynaptic one.
Inhibition of N‐type Calcium Channels: The Only Mechanism by which Presynaptic α2‐Autoreceptors Control Sympathetic Transmitter Release
Authors: Boehm Stefan , Huck Sigismund
Published: April 2006

α2‐Adrenoceptors are known to inhibit voltage‐dependent Ca2+ channels located at neuronal cell bodies; the present study investigated whether this or alternative mechanisms, possibly downstream of Ca2+ entry, underlie the presynaptic α2‐adrenergic modulation of transmitter release from chick sympathetic neurons. Using chick sympathetic neurons, overflow of previously incorporated [3H]noradrenaline was elicited in the presence of extracellular Ca2+ by electrical pulses, 25 mM K+ or 10μM nicotine, or by adding Ca2+ to otherwise Ca2+‐free medium when cells had been made permeable by the calcium ionophore A23187 or by α‐latrotoxin. Pretreatment of neurons with the N‐type Ca2+ channel blocker ω‐conotoxin GVIA and application of the α2‐adrenergic agonist UK 14304 reduced the overflow elicited by electrical pulses, K+ or nicotine, but not the overflow caused by Ca2+ after permeabilization with α‐latrotoxin or A23187. In contrast, the L‐type Ca2+ channel blocker nitrendipine reduced the overflow due to K+ and nicotine, but not the overflow following electrical stimulation or α‐latrotoxin‐ and A23187‐permeabilization. The inhibition of electrically evoked overflow by UK 14304 persisted in the presence of nitrendipine and the L‐type Ca2+ channel agonist BayK 8644, which per se enhanced overflow. In ω‐conotoxin GVIA‐treated cultures, electrically evoked overflow was also enhanced by BayK 8644 and almost reached the value obtained in untreated neurons. However, UK 14304 lost its effect under these conditions. Whole‐cell recordings of voltage‐activated Ca2+ currents corroborated these results: UK 14304 inhibited Ca2+ currents by 33%, nitrendipine caused a 7% reduction, and BayK 8644 increased the currents by 30%. Moreover, the dihydropyridines failed to abolish the inhibition by UK 14304, but pretreatment with ω‐conotoxin GVIA, which reduced mean amplitude from 0.95 to 0.23 nA, entirely prevented α2‐adrenergic effects. Our results indicate that the α2‐autoreceptor‐mediated modulation of noradrenaline release from chick sympathetic neurons relies exclusively on the inhibition of ω‐conotoxin GVIA‐sensitive N‐type Ca2+ channels. Mechanisms downstream of these channels and voltage‐sensitive Ca2+ channels other than N‐type appear not to be important.
Transient Brain Ischaemia Provokes Ca2+, PIP2 and Calpain Responses Prior to Delayed Neuronal Death in Monkeys
Authors: Yamashima Tetsumori , Saido Takaomi C. , Takita Masatoshi , Miyazawa Atsuo , Yamano Jun , Miyakawa Atsuo , Nishijyo Hisashi , Yamashita Junkoh , Kawashima Seiichi , Ono Taketoshi , Yoshioka Tohru
Published: April 2006

To clarify the mechanism of postischaemic delayed cornu Ammonis (CA)‐1 neuronal death, we studied correlations among calpain activation and its subcellular localization, the immunoreactivity of phosphatidylinositol 4,5‐bisphosphate (PIP2) and Ca2+ mobilization in the monkey hippocampus by two independent experimental approaches: in vivo transient brain ischaemia and in vitro hypoxia‐hypoglycaemia of hippocampal acute slices. The CA‐1 sector undergoing 20 min of ischaemia in vivo showed microscopically a small number of neuronal deaths on day 1 and almost global neuronal loss on day 5 after ischaemia. Immediately after ischaemia, CA‐1 neurons ultrastructurally showed vacuolation and/or disruption of the lysosomes. Western blotting using antibodies against inactivated or activated μ‐calpain demonstrated μ‐calpain activation specifically in the CA‐1 sector immediately after ischaemia. This finding was confirmed in the perikarya of CA‐1 neurons by immunohistochemistry. CA‐1 neurons on day 1 showed sustained activation of μ‐calpain, and increased immunostaining for inactivated and activated forms of μ‐ and m‐calpains and for PIP2. Activated μ‐calpain and PIP2 were found to be localized at the vacuolated lysosomal membrane or endoplasmic reticulum and mitochondrial membrane respectively, by immunoelectron microscopy. Calcium imaging data using hippocampal acute slices showed that hypoxia‐hypoglycaemia in vitro provoked intense Ca2+ mobilization with increased PIP2 immunostaining specifically in CA‐1 neurons. These data suggest that transient brain ischaemia increases intracellular Ca2+ and PIP2 breakdown, which will activate calpain proteolytic activity. Therefore, we suggest that activated calpain at the lysosomal membrane, with the possible release of biodegrading enzyme, will cause postischaemic CA‐1 neuronal death.
Localization and Axotomy‐induced Regulation of the Peptide Secretoneurin in the Rat Superior Cervical Ganglion
Authors: Klimaschewski Lars , Kroesen Stephan , Eder Ursula , Leitner Bernd , Fischer‐Colbrie Reiner
Published: April 2006

This study demonstrates the localization and regulation of a novel neuropeptide of 33 amino acids, secretoneurin (SN), in the rat superior cervical ganglion. Gel filtration chromatography of ganglion proteins followed by a specific radioimmunoassay revealed that SN is the predominant cleavage product of secretogranin II, a member of the chromogranin/secretogranin protein family, in adult ganglia. SN was detected within the majority of nerve endings surrounding postganglionic neurons that were identified by the presence of synaptophysin and, in part, colocalized leu‐encephalin. Applying immuno‐electronmicroscopy, SN was localized to large dense core vesicles of neuronal and small intensely fluorescent (SIF) cells. In situ hybridization revealed the presence of secretogranin II mRNA in postganglionic neurons and, to a lesser extent, in SIF cells. One week after transection of the postganglionic branches SN levels were not significantly altered; however, a decrease of secretogranin II mRNA was observed in postganglionic neurons but not in SIF cells. After decentralization of the ganglion, SN‐immunoreactive nerve terminals disappeared and intraganglionic SN levels were reduced by 70%, indicating the preganglionic origin of SN‐positive nerve fibres and varicosities. Secretogranin II mRNA was slightly reduced under this condition. Combined axotomy and decentralization further diminished intraganglionic secretogranin II mRNA, although peptide levels increased significantly above control values under these conditions. Double‐labelling immunofluorescence with antibodies against the somatodendritic marker microtubule‐associated protein 2 (MAP2) revealed that the increase in SN immunoreactivity was due to an accumulation of SN in axonal processes of postganglionic neurons. SN immunoreactivity was also detected in dissociated neonatal superior cervical ganglion cultures and increased significantly upon treatment with nerve growth factor, the survival and differentiation factor of sympathetic neurons during perinatal development. Co‐culture with non‐neuronal cells or addition of leukaemia inhibitory factor, a cytokine known to stimulate synthesis of various peptides after nerve transection, did not influence SN immunoreactivity. Therefore, since no fixed relationship between SN and any of the known neuropeptides or neurotransmitters expressed in sympathetic neurons was observed, the expression of this novel peptide appears to be independently regulated.
Activation of Multi‐modal Cortical Areas Underlies Short‐term Memory
Authors: Klingberg Torkel , Kawashima Ryuta , Roland Per E.
Published: April 2006

We wanted to examine whether there are cortical fields active in short‐term retention of sensory information, independent of the sensory modality. To control for selective attention, response selection and motor output, the cortical activity during short‐term memory (STM) tasks was compared with that during detection (DT) tasks. Using positron emission tomography and [15O]‐butanol as a tracer, we measured the regional cerebral blood flow in ten subjects during three STM tasks in which the subjects had to keep in mind: (i) the pitch of tones; (ii) frequencies of a vibrating stylus; and (iii) luminance levels of a monochrome light. Another group of ten subjects undertook three tasks in which subjects detected changes in similar stimuli. Six cortical fields were significantly more activated during STM than during DT. These fields were activated irrespective of sensory modality, and were located in the left inferior frontal gyrus, right superior frontal gyrus, right inferior parietal cortex, anterior cingulate, left frontal operculum and right ventromedial prefrontal cortex. Since the DT tasks and the STM tasks differed only with respect to the STM component, we conclude that the neuronal activity specifically related to retention of the stimuli during the delays was located in these six multi‐modal cortical areas. Since no differences were observed in the sensory‐specific association cortices, the results indicate further that the activity in the sensory‐specific association cortices due to selective attention is not different from the activity underlying short‐term retention of sensory information.
Evidence for Functional Differences between Entopeduncular Nucleus and Substantia Nigra: Effects of APV (DL‐2‐amino‐5‐phosphonovaleric acid) Microinfusion on Reaction Time Performance in the Rat
Authors: Baunez Christelle , Amalric Marianne
Published: April 2006

Overactivity of the excitatory amino acid outputs of the subthalamic nucleus (STN) has recently been found to be one of the cascade of subsequent disruptions caused by nigrostriatal dopaminergic degeneration in Parkinson's disease. The respective contribution of the excitatory glutamatergic output structures of the STN [i.e. the globus pallidus (GP), entopeduncular nucleus (EP) and substantia nigra pars reticulata (SNr)] to the control of movement is not known, however. To investigate further the function of glutamatergic transmission through NMDA receptor subtypes in these three structures, the effects of discrete local infusion of a competitive receptor antagonist, DL‐2‐amino‐5‐phosphonovaleric acid (APV), into the EP, GP and SNr were tested in rats performing a reaction time task. Bilateral infusion of APV into the different output structures of the STN differentially impaired the performance of rats trained to release a lever after the onset of a visual stimulus within a time limit to obtain a food reward. Infusion of APV (0.25 and 0.5 μg/0.5 μl) into the SNr was found to induce behavioural deficits characterized by a dramatic increase in the number of premature lever releases and decreased mean reaction time. In contrast, the infusion of APV at a dose of 0.25 μg into the GP or EP was found to induce a motor initiation deficit characterized by an increased number of delayed responses (lever release after the time limit) and increased mean reaction time. At a dose of 0.5 μg, a premature responding deficit was added to the previous motor impairment. Interestingly, when APV was infused simultaneously into the GP and SNr in the same animals, the behavioural effects tended to be similar to those observed after a single infusion into the SNr. Altogether, these results reveal that the different functional weight of the three main output pathways originating at the STN level is t.o. The behavioural deficits induced by NMDA receptor blockade in the SNr were similar to those observed previously after a neurotoxic lesion of the STN, suggesting that NMDA receptors in this structure play a major role as a functional output of the STN. Furthermore, regarding the differential effects produced by the same dose of APV in the SNr and the EP, these two structures, which are classically believed to be functionally linked should not be considered as the same functional entity in the organization of basal ganglia outflow.
Thiocyanate Ions Inhibit AMPA‐activated Currents in Recombinant non‐NMDA Receptors Expressed in Xenopus laevis Oocytes: the Role of the GluR2 Subunit
Authors: Eugène D. , Moss S. J. , Smart T. G.
Published: April 2006

The functional interaction of thiocyanate (SCN‐) ions with recombinant non‐N‐methyl‐D‐aspartate receptors was examined by studying α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA)‐ and kainic acid (KA)‐activated currents in Xenopus laevis oocytes. Recombinant receptors were expressed after microinjection of oocytes with combinations of cDNAs or cRNAs encoding for GluR1, GluR2, GluR2(R586Q), GluR3 or GluR6 subunits. When the GluR2 subunit was expressed with GluR1, SCN‐ (2 mM) inhibited the responses to 50 μM AMPA, whereas responses to 100 μM KA were slightly increased and responses to 200 μM L‐glutamate were unaffected. Equilibrium concentration‐response curves for AMPA were antagonized in a non‐competitive manner by SCN‐ with a reduction in the EC50. The inhibitory effects of SCN‐ were unaffected by prior reduction of receptor desensitization with either 10 μM Concanavalin‐A or 0.5 mM diazoxide. AMPA‐activated currents recorded from homomeric GluR1 or GluR3 receptors were not affected by SCN‐, and GluR6 homomeric receptors, which are sensitive to KA but not to AMPA, were also unaffected. In contrast, AMPA activation of homomeric GluR2(R586Q) subunit receptors, or combinations of GluR1 or GluR3 + GluR2(R586Q) subunits, were markedly inhibited by SCN‐. In addition, the inhibitory effect of AMPA on KA‐activated responses on these heteromeric receptors, was enhanced by SCN‐. These results indicate that SCN‐ exert an inhibitory effect on ‘AMPA receptors’but only when the recombinant non‐NMDA receptor is a GluR2 homomer, or when GluR2 subunits are present as part of a heteromeric combination. Moreover, this inhibitory effect was unaffected by the ‘Q/R’site in the presumed second transmembrane domain, since currents mediated by the GluR2(R586Q) subunit were also susceptible to inhibition by SCN‐. Thus the inhibition was not related to the rectification properties or calcium permeability of the non‐NMDA receptors. It is suggested that the GluR2 subunit may have a specific binding site for anions which could modulate the function of non‐NMDA receptors and that SCN‐ may be a useful probe for the detection of these subunits in native neurons.
Maturation‐dependent Modulation of Apoptosis in Cultured Cerebellar Granule Neurons by Cytokines and Neurotrophins
Authors: de Luca Ariane , Weller Michael , Frei Karl , Fontana Adriano
Published: April 2006

Immature cerebellar granule neurons die by apoptosis within 1 week in vitro unless maintained in depolarizing (high) concentrations of potassium (25 mM K+). Neurons allowed to survive and differentiate in high K+ medium for several days in vitro are still induced to undergo apoptosis when switched back to physiological (low) concentrations of K+ (5 mM). Here we have investigated the effects of various cytokines and growth factors in these two well‐defined paradigms of neuronal apoptosis. Tumour necrosis factor‐α, leukaemia inhibitory factor, ciliary neurotrophic factor, interleukin‐10 and interleukin‐13 delayed apoptosis and prolonged survival of cerebellar granule neurons maintained in low K+ medium. The effect observed required continuous exposure of the cultures to the cytokines and appeared not to involve modulation of Bcl‐2 protein expression. Brain‐derived neurotrophic factor accelerated neuronal death in low K+ medium. In contrast, when apoptosis of the neurons was precipitated by switching mature high K+ neurons to low K+ medium, neither tumour necrosis factor‐α, leukaemia inhibitory factor, ciliary neurotrophic factor, interleukin‐10 nor interleukin‐13 prevented apoptosis. When testing the cytokines and growth factors for their capacity to alter N‐methyl‐D‐aspartate receptor‐mediated excitotoxicity of differentiated cerebellar granule neurons, no significant effect was observed. These data appear to define a maturation‐dependent modulation of cerebellar granule cell survival by cytokines and neurotrophic factors that are expressed in a developmental pattern in the mammalian brain.
Long‐term Treatment with some Methylxanthines Decreases the Susceptibility to Bicuculline‐ and Pentylenetetrazol‐induced Seizures in Mice. Relationship to c‐ios Expression and Receptor Binding
Authors: Johansson Björn , Georgiev Vasil , Kuosmanen Tarja , Fredholm Bertil B.
Published: April 2006

The effects of long‐term oral administration of low doses of caffeine (0.3 g/l) and its metabolites theophylline, theobromine and paraxanthine (each at 0.5 g/l in drinking water) on bicuculline‐ and pentylenetetrazol (PTZ) ‐induced seizures and c‐fos expression were studied in mice. In addition, adenosine and benzodiazepine receptor density was examined. The plasma levels of the methylxanthines were much higher during the active period at night than during the day. The maximal level of caffeine was 14 μM. Brain theophylline levels (8‐13 nmol/g) tended to be higher and more constant than brain caffeine levels in caffeine‐consuming mice. Clonic seizures induced by bicuculline (4 mg/kg i.p.) were significantly reduced in severity by 14 day caffeine treatment and mortality was also reduced. Long‐term treatment with caffeine metabolites was less effective. The seizures induced by PTZ (60 mg/kg i.p.) were also significantly reduced by long‐term caffeine treatment. After bicuculline or PTZ treatment, c‐fos mRNA expression was weaker in the cerebral cortex in animals receiving caffeine, irrespective of whether the animals had seizures or not. No significant changes in the binding of adenosine receptor ligands or benzodiazepines were seen after long‐term caffeine treatment. These results show that long‐term treatment with caffeine in a dose that is commonly seen in humans decreases the seizures induced by bicuculline, and to a lesser extent, those induced by PTZ. This may be related to a decreased neuronal excitability. The effect is due to the combined effects of theophylline, to which caffeine is metabolized in brain, and of caffeine itself, but could not be ascribed to changes in A1 and A2A adenosine or benzodiazepine receptors.
GABA and Glycine in Synaptic Glomeruli of the Rat Spinal Dorsal Horn
Authors: Todd A. J.
Published: April 2006

The superficial dorsal horn of rat spinal cord contains two types of synaptic glomerulus, which are centred around the terminals of unmyelinated and myelinated primary afferents respectively. Both types of glomerulus contain GABAergic axons and dendrites, which are thought to originate from local inhibitory interneurons. Some of the dendrites contain synaptic vesicles, and may be presynaptic to the central axon at dendroaxonic synapses. In order to determine whether GABAergic structures in the two types of glomerulus are derived from different populations of interneurons, a quantitative post‐embedding immunogold study of GABA‐ and glycine‐immunoreactivity in rat dorsal horn was performed. In type I glomeruli, all of the peripheral axons and most vesicle‐containing dendrites were GABA‐immunoreactive, but only one of 32 axons and none of the vesicle‐containing dendrites was glycine‐immunoreactive. In contrast, most of the peripheral axons and some of the vesicle‐containing dendrites in type II glomeruli possessed both GABA‐ and glycine‐immunoreactivity. This strongly suggests that different types of inhibitory interneuron in the dorsal horn are associated with the two types of glomerulus. It is therefore likely that different populations of interneurons mediate presynaptic inhibition of unmyelinated and myelinated primary afferents.
DA Uptake Sites, D1, and D2 Receptors, D2 and Preproenkephalin mRNAs and Fos Immunoreactivity in Rat Striatal Subregions after Partial Dopaminergic Degeneration
Authors: Chritin M. , Blanchard V. , Raisman‐Vozari R. , Feuerstein C. , Agid Y. , Javoy‐Agid F. , Savasta M.
Published: April 2006

Stereotaxic injection of a limited amount of 6‐ hydroxydopamine in the lateral part of the rat substantia nigra induces a partial degeneration of the nigrostriatal dopaminergic system. This animal model in which the destruction of the dopaminergic nigral cell population reaches ‐50% could be considered as a preclinical Parkinson's model. Autoradiography of dopaminergic uptake sites performed with a specific marker ([3H]GBR 12935) allowed the precise determination of dopaminergic denervated and non‐denervated areas in the striatum 1 month after partial lesion of the substantia nigra pars compacta. In both striatal areas, dopaminergic D1 and D2receptor densities and dopaminergic D2 and preproenkephalin mRNAs levels were measured by autoradiography and in situ hybridization coupled to an image analysis system. Our results show that in the denervated striatal subregion, none of the dopaminergic targets were modified, contrary to the observations made after complete lesion of the nigrostriatal DA system at the same post‐lesion delay. However, striatal Fos activation induced by amphetamine (5 mg/kg i.p., 2 h before killing) revealed that the number of Fos‐positive cells detected in the denervated striatal subregion was lower than that observed in the non‐denervated one. These data argue in favour of the existence of compensatory mechanisms different from the up‐regulation of DA receptor densities, thereby allowing the maintenance of striatal dopaminergic transmission. Such mechanisms could contribute to the delay of the appearance of neurological symptoms (which are reported to be clinically apparent only when depletion of striatal dopamine levels reaches near 80%) in Parkinsonian patients.