bluuebunny/crossref_metadata_2025 huggingface dataset:
Mast Cell Degranulating Peptide Increases the Frequency of Spontaneous Miniature Postsynaptic Currents in CA3 Rat Hippocampal Neurons
Authors: Neuman R. , Ben Ari Y. , Cherubini E.
Published: April 2006

Mast cell degranulating peptide (MCDP) is a neurotoxic agent isolated from bee venom. It produces a long‐term potentiation in the hippocampus. We now report that MCDP, at nanomolar concentrations, induces a reduction of a transient voltage‐dependent potassium current (ID) in CA3 rat pyramidal neurons and a persistent (>30 min) enhancement of the frequency of spontaneous miniature excitatory and inhibitory postsynaptic currents (m.e.p.s.c.s. and m.i.p.s.c.s.). M.e.p.s.c.s. and m.i.p.s.c.s. were recorded in the presence of bicuculline (30 μM) and 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX, 10 μM), respectively. The increased frequency of m.e.p.s.c.s. (408±60%) and m.i.p.s.c.s. (583±553%) was independent of the reduction of ID because 4‐aminopyridine (4‐AP, 30 μM‐2 mM) blocked ID but had no effects on m.e.p.s.c.s. and m.i.p.s.c.s. In the presence of the calcium channel blocker manganese (3 mM), MCDP still enhanced the frequency of m.e.p.s.c.s. (326±162%). It is concluded that MCDP augments the release of excitatory and inhibitory transmitter by an action, which is independent of calcium influx, through voltage‐dependent channels.
Acidic Amino Acids and Self‐stimulation of the Prefrontal Cortex in the Rat: A Pharmacological Study
Authors: Cobo M. , Mora F.
Published: April 2006

The effects of intraventricular and intracortical microinjections of acidic amino acid antagonists on self‐stimulation (SS) of the medial prefrontal cortex (MPC) were investigated. Self‐stimulation was measured by depressing a lever in a standard chamber. Spontaneous motor activity of the animal and SS of the contralateral non‐injected MPC were used as control for non‐specific effects of the drugs. Intraventricular microinjections of γ‐d‐glutamylglycine (DGG), an antagonist of NMDA, kainate and quisqualate receptors, or 2‐amino‐5‐phosphonovalerate (AP‐5), a specific antagonist of NMDA receptors, produced a dose‐related decrease of SS in the MPC. Spontaneous motor activity of the animal was not significantly affected. Unilateral microinjections into the medial prefrontal cortex of DGG or AP‐5 produced a decrease of SS in the ipsilateral side while no effects were found on the contralateral MPC. On the contrary, intraventricular microinjections of γ‐d‐glutamyltaurine (Glu‐tau), an antagonist with more relative affinity for kainate and quisqualate receptors, produced a dose‐related decrease of both self‐stimulation and spontaneous motor activity of the rats. Moreover, intracortical microinjections of Glu‐tau had no effect on self‐stimulation of this cortical area. These results suggest that acidic amino acids through NMDA, but not kainate or quisqualate, receptors could be part of the neurochemical substrate underlying SS of the MPC in the rat.
Reorganization of the Cytoskeleton in Rat Neurons Following Stimulation With Excitatory Amino Acids In Vitro
Authors: Bigot D. , Matus A. , Hunt S. P.
Published: April 2006

The state of neuronal microtubule polymerization is influenced by microtubule‐associated proteins such as MAP2, which is specifically localized within neuronal dendrites and cell bodies. We have demonstrated that stimulation of spinal cord or cortical neurons in vitro with excitatory amino acids results in a dramatic modification of the neuronal cytoskeleton as monitored with antibodies against MAP2 and tubulin. Stimulation of cultures with glutamate receptor agonists induced a reorganization of MAP2 immunoreactivity into a distinctive network of bundles within certain neuronal cell bodies and their proximal neurites. The effect was not abolished by depolymerizing drugs such as nocodazole, or protein synthesis inhibitors. The effect was dependent upon the entry of sodium following depolarization and was not associated with neuronal damage. We suggest that in neurons the state of the neuronal cytoskeleton can be modulated by glutamate receptor activation acting through MAP2.
Excitatory Connections Between CA1 Pyramidal Cells Revealed by Spike Triggered Averaging in Slices of Rat Hippocampus are Partially NMDA Receptor Mediated
Authors: Thomson Alex M. , Radpour Shahrzad
Published: April 2006

Spike triggered averaging was used to record local circuit connections between pairs of CA1 pyramidal neurons in isolated slices of rat hippocampus. Of 795 pairs of neurons tested, six were connected. These epsps were only partially blocked by 2‐amino‐5‐phosphonovalerate (AP‐5), which decreased the amplitude and half width of the epsp, but did not affect the early rising phase. In contrast, 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) blocked all phases of the epsp and combinations of AP‐5 and CNQX blocked the epsp almost entirely. These results indicate that these epsps were mediated by both N‐methyl‐d‐aspartate (NMDA) and non‐NMDA excitatory amino acid receptors. Moreover, they exhibited a voltage relation typical of neuronal responses to NMDA, increasing in amplitude and duration as the postsynaptic cell was depolarized. These epsps were brief (10–90% rise time < 5 ms, width at half amplitude < 20 ms), indicating a proximal location. Increasing presynaptic firing rate (1–4 spikes/s) reduced average epsp amplitude by almost 50%. When epsps were evoked by pairs of spikes (interval 3–25 ms), a large response to the first spike precluded a large response to the second. No evidence for selective enhancement of the NMDA receptor component by paired spike activation was found. It is concluded that a significant NMDA receptor mediated input to CA1 is provided by local circuit CA1–CA1 connectionsx and that these synapses can be demonstrated under control conditions.
Coactivation of Local Circuit NMDA Receptor Mediated epsps Induces Lasting Enhancement of Minimal Schaffer Collateral epsps in Slices of Rat Hippocampus
Authors: Radpour Shahrzad , Thomson Alex M.
Published: April 2006

Lasting enhancement of minimal Schaffer collateral epsps in CA1 pyramidal neurons was induced when these epsps were coactivated with putative local circuit N‐methyl‐d‐aspartate (NMDA) receptor‐mediated epsps. In transverse slices of hippocampus, minimal epsps were evoked by stimulating the Schaffer collateral/commissural pathway within CA3 stratum radiatum and the local circuit axons were stimulated within CA1 stratum oriens or alveus using fine, two barrel glass micropipettes. Minimal Schaffer collateral epsps were insensitive to d‐2‐amino‐5‐phosphonovalerate (AP‐5) and displayed conventional voltage relations. Local epsps were sensitive to AP‐5 and increased in amplitude and duration with membrane depolarization. High frequency tetanic stimulation of the minimal Schaffer collateral epsps induced no lasting enhancement. However, pairing of the Schaffer epsp with a frequency potentiated local epsp resulted in a delayed, but lasting increase in the Schaffer epsp. When the local epsp did not exhibit frequency potentiation during pairing, no enhancement resulted. When either epsp was contaminated with an ipsp, no lasting increase resulted. When transmission through the alveus was blocked by focal application of local anaesthetic, traditional protocols for long‐term potentiation (LTP) induction were relatively ineffective. These results indicate that a significant source of the NMDA receptor activation required for the induction of LTP in the Schaffer collateral input to CA1 derives from local circuit connections between CA1 pyramidal neurons and, moreover, that lasting enhancement can be induced with low frequency activation, at postsynaptic resting potential, in the presence of Mg2+ and with local inhibition intact.
Molecular Association of the Neural Adhesion Molecules L1 and N‐CAM in the Surface Membrane of Neuroblastoma Cells is Shown by Chemical Cross‐linking
Authors: Simon Horst , Klinz Stephan , Fahrig Thomas , Schachner Melitta
Published: April 2006

The two neural cell adhesion molecules L1 and N‐CAM could be shown to be associated in the surface membrane of cultured neuroblastoma cells by chemical cross‐linking with 3,3′‐dithiobis(sulphosuccinimidylpropionate) and subsequent immunopurification and precipitation using antibodies to L1 and N‐CAM. Glycoproteins recognized in neuroblastoma cells by antibodies to mouse liver membranes were not chemically cross‐linked to L1 or N‐CAM. These observations suggest that a molecular association between the two molecules may be the basis for their functional cooperativity (Kadmon et al., 1990a, b, J. Cell Biol., 110, 193–208; 209–218).
Auditory Pontine Grey: Connections and Response Properties in the Horseshoe Bat
Authors: Schuller Gerd , Covey Ellen , Casseday John H.
Published: April 2006

This study investigates the role of the pontine grey as a link between the auditory system and the cerebellum in the bat, Rhinolophus rouxi. We recorded response properties of single neurons in the pontine grey and, in the same preparation, injected wheat germ agglutinin ‐ horseradish peroxidase (WGA‐HRP) in areas responsive to sound. Thus the functional evidence was correlated with retrograde and anterograde transport. The main results are: (i) all auditory neurons in the pontine grey are tuned within one of two harmonically related frequency ranges of the echolocation call. The upper range corresponds to the constant frequency and frequency modulated components of the second harmonic, but the lower range corresponds only to the frequency modulated component of the first harmonic. There is no systematic tonotopic organization; (ii) discharge patterns are extremely variable, latencies cover a wide range, and about half of the neurons are binaurally responsive with excitation from both ears; (iii) most pontine auditory neurons respond preferentially to frequency modulated stimuli; (iv) there is massive input to the pontine grey from the central nucleus of the inferior colliculus; (v) cortical input to the pontine grey does not originate in tonotopically organized auditory cortex. The input is from a dorsal belt area that is specialized for processing combinations of sounds with specific frequency ratios and delays; (vi) projections from the auditory region of the pontine grey are widespread within the cerebellar cortex. The data suggest that the pontine grey transmits to the cerebellum information contained in specific components of the bat's biosonar signal.
Modulation of Human Neurite Outgrowth by Serine Proteases: A Comparison of the Interaction of Thrombin and Prothrombin with Glia‐Derived Nexin
Authors: Grabham P. W. , Monard D. , Gallimore P. H. , Grand R. J. A.
Published: April 2006

Neurite outgrowth from cells of neuroepithelial origin is under the reciprocal control of thrombin and the thrombin inhibitor‐glia‐derived nexin (GDN). The neurite retraction activity of thrombin is blocked when GDN complexes with the enzyme and inhibits its proteolytic activity. However, we have previously shown that enzymically inactive proenzyme is also capable of inducing neurite retraction. We present evidence here to show that GDN does not bind to prothrombin in solution. When a mixture of prothrombin and GDN is subjected to either polyacrylamide gel electrophoresis or immunoprecipitation, a stable complex cannot be detected. This is in direct contrast to thrombin, which exhibits stable complexes with GDN under both conditions. At the cell surface, however, GDN is able to inhibit the biological activity of prothrombin. When a mixture of proenzyme and inhibitor is applied to previously differentiated transformed retinobiasts (Ad12 HER10), the ability of prothrombin to induce neurite retraction is blocked. Furthermore, following 1 h exposure to Ad12 HER10 cells, a solution of prothrombin was found to contain half the potential enzyme activity as detected by chromogenic assay. These results have been interpreted as evidence for the ability of neuronal cells to cleave prothrombin and subsequently release activated enzyme.
Characterization and Regional Distribution of a Class of Synapses with Highly Concentrated cAMP Binding Sites in the Rat Brain
Authors: Caretta Antonio , Cevolani Daniela , Luppino Giuseppe , Matelli Massimo , Tirindelli Roberto
Published: April 2006

A class of putative synaptic terminals with concentrated cAMP binding sites are labelled in unfixed sections of rat brain by means of the ligand 8‐thioacetamido fluorescein cAMP (SAF‐cAMP), a fluorescent analogue of cAMP. The labelled terminals appear as sharply delimited bouton‐like structures in close proximity but external to the cell body of neurons. The SAF‐cAMP binding, measured at equilibrium in competition with other nucleotides, indicates that the binding site recognizes the cAMP moiety of SAF‐cAMP. In the labelled terminals of the frontal cortex the concentration of SAF‐cAMP binding sites is estimated to be in the millimolar range (at least 2.1 ± 1.0 mM). In a brain homogenate, labelled terminals are visualized only in the membrane fraction enriched in synaptosomes. The cAMP binding activity of the synaptosomes is insoluble in high and in low ionic strength solution and is only partially solubilized by detergents, suggesting that the binding sites are intrinsic membrane proteins and/or proteins associated with the cytoskeleton. There is the possibility that SAF‐cAMP labels new cAMP binding sites highly concentrated in a class of synaptic terminals. SAF‐cAMP labelling is prominent in well defined regions of the rat brain: (i) the frontal and entorhinal areas of the cortex; (ii) the field CA1 of the hippocampus; (iii) the olfactory system; (iv) the medial nuclei of the thalamus; (v) the parabrachial nuclei and other less defined regions of the reticular substance; (vi) the substantia gelatinosa of Rolando in the spinal cord; and (vii) the neo‐ and paleocerebellum in the Purkinje cell layer, the archicerebellum in the granular cell layer. SAF‐cAMP labelling is absent in specific motor and sensory structures, with the exception of the olfactory system. It is proposed that SAF‐cAMP binding sites single out a new type of synaptic terminals involved in complex nervous functions.
Cells that Express Brain‐Derived Neurotrophic Factor mRNA in the Developing Postnatal Rat Brain
Authors: Friedman Wilma J. , Olson Lars , Persson Håkan
Published: April 2006

Brain‐derived neurotrophic factor (BDNF) is a member of a family of related neurotrophic proteins which includes nerve growth factor (NGF) and hippocampus‐derived neurotrophic factor/neurotrophin‐3 (NT‐3). To obtain information regarding possible roles for BDNF during postnatal brain development, we have examined the temporal and spatial expression of this trophic factor using in situ hybridization. In specific neocortical regions BDNF mRNA‐expressing cells were seen at 2 weeks of age and thereafter. One particular neuronal cell type strikingly labelled was the inverted pyramidal cell population in the deep layers of parietotemporal cortex. In pyriform and cingulate cortices, BDNF mRNA was detected at postnatal day 1 and 1 week of age, respectively, with increasing levels during ontogeny. Several forebrain regions, including the thalamic anterior paraventricular nucleus, hypothalamic ventromedial nucleus as well as the preoptic area, contained moderate levels of BDNF mRNA throughout development. BDNF mRNA was detected transiently in several brainstem structures, notably in the substantia nigra and interpeduncular nucleus. Expression of this trophic factor in hippocampus was relatively low in the early neonatal brain, but attained high levels in the CA3 and CA4 regions as well as in the dentate gyrus by 2 weeks of age. At this early age, which is still during the period of neurogenesis in the dentate gyrus, labelling was restricted to the outer layer, which contained cells with a more mature appearance. However, by 3 weeks of age labelling was distributed throughout the granule cell layer. Our results show both transient and persistent expression of BDNF mRNA in various regions of the developing rat brain and suggest that there is a caudal to rostral gradient of BDNF expression during postnatal brain development, which may be correlated to neuronal maturation.
Nerve Growth Factor is Required for Induction of c‐Fos Immunoreactivity by Serum, Depolarization, Cyclic AMP or Trauma in Cultured Rat Sympathetic Neurons
Authors: Buckmaster A. , Nobes C. D. , Edwards S. N. , Tolkovsky A. M.
Published: April 2006

Nerve growth factor (NGF) induces transient Fos‐immunoreactivity (Fos‐IR) independently of any other factor, both in newly isolated rat sympathetic neurons and in established cultures after NGF deprivation. The same proportion of neurons that express Fos‐IR in response to NGF also survive. In addition to direct stimulation of Fos‐IR expression, the presence or recent exposure to NGF is required to obtain Fos‐IR expression by other stimuli. In newly isolated neurons no Fos‐IR is detected in response to stimulation by serum alone and a response to depolarization or cyclic AMP is obtained only if neurons are stimulated within a short period after ganglion excision. In established cultures none of these stimuli, nor the trauma of cutting neurites or spiking cell bodies with a microinjection needle induce Fos‐IR unless NGF is present or had been removed for <8–16 h. The lack of response is not due to a general decrease in the rate of protein or RNA synthesis. These findings show that in regenerating sympathetic neurons NGF induces c‐Fos and suggest that NGF may activate a master trigger that is required for c‐Fos expression to be induced by other stimuli.
Mechanisms of AMPA Neurotoxicity in Rat Brain Slices
Authors: Garthwaite Giti , Garthwaite John
Published: April 2006

The mechanisms underlying the neurodegenerative effects of the glutamate receptor agonist, AMPA (α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate), were studied using brain slice preparations of young rat (8–9 days old) cerebellum and hippocampus. Rapid AMPA toxicity (exerted on some cerebellar interneurons) was inhibited by including the appropriate receptor blocker, CNQX (6‐cyano‐7‐nitroquinoxaline‐2,3‐dione, 10 μM), in the exposing solution. The degeneration of other neurons, including Purkinje cells and hippocampal pyramidal neurons, persisted. It could, however, be largely prevented if CNQX was included for 1.5 h during the post‐incubation period, suggesting that an enduring ‘rebound’ AMPA receptor activation was responsible for this delayed type of degeneration, not the exposure itself. In cerebellar slices, independent evidence for the occurrence, postexposure, of persisting AMPA receptor stimulation was obtained electrophysiologically. Omission of Ca2+ during the exposure period (and for 10 min beforehand) markedly reduced rapid AMPA toxicity but was ineffective in protecting most of the Purkinje cells. However, if the slices were previously starved of Ca2+ for 1 h, then most of these neurons survived, even if the ion was reinstated during the recovery period. Slow AMPA toxicity, which takes place during long (2 h) exposures, could be inhibited either by CNQX or by omission of Ca2+ (30 min preincubation). The results indicate that the rapid oedematous necrosis induced by AMPA, like that caused by N‐methyl‐d‐aspartate and kainate, is likely to involve excessive influx of Ca2+. In contrast, the induction of the delayed mechanism, as well as its ‘expression’ during the postincubation period, probably depends on intracellular Ca2+, rather than Ca2+ influx.
Calcitonin Gene‐related Peptide (CGRP)‐like Immunoreactivity and CGRP mRNA in Rat Spinal Cord Motoneurons after Different Types of Lesions
Authors: Piehl Fredrik , Arvidsson Ulf , Johnson Hans , Cullheim Staffan , Villar Marcelo , Dagerlind Åke , Terenius Lars , Hökfelt Tomas , Ulfhake Brun
Published: April 2006

By use of the indirect immunofluorescence (IF) technique, radioimmunoassay (RIA) and in situ hybridization (ISH) histochemistry, the staining pattern, content and expression of calcitonin gene‐related peptide (CGRP) in lumbar motoneurons of normal rats and rats subjected to sciatic nerve transection (SNT), ventral root transection (VRT), low thoracic spinal cord transection (SCT) alone or in combination with a subsequent SNT, as well as rats subjected to chemical lesioning of 5‐hydroxytryptamine (5‐HT) neurons by 5,7‐dihydroxytryptamine (5,7‐DHT), were studied. We here confirm that a large number of the lumbar motoneurons normally contain CGRP‐like immunoreactivity (LI) and CGRP mRNA. SNT induced a transient increase in CGRP‐LI, with a peak at days 2–5 after lesion, and normalized levels again after ∼2–3 weeks. Comparable results were obtained with IF and RIA. This increase is probably a consequence of increased CGRP synthesis, since a parallel up‐regulation of CGRP mRNA levels was seen. A normalization of CGRP mRNA did not occur during the period studied, despite an apparent normalization of peptide levels after 2 weeks, and this may in turn be due to an increased turnover and/or release of CGRP. The up‐regulation of CGRP is probably caused by the axon injury itself, since a similar cellular reaction with respect to CGRP was observed in motoneurons subjected to VRT. However, SNT, which also lesions dorsal root afferents and causes a decline in CGRP‐LI in the dorsal horn, induced an increase in CGRP‐LI in motoneurons on the contralateral side also. Thus, it may be that severance of dorsal root afferents and/or changes in reflex activity may also influence the production of CGRP in motoneurons. SCT, which severs all descending synaptic input to the motor nucleus and causes a paralysis of muscles innervated by motoneurons below the lesion, resulted in a marked decline in both content of CGRP‐LI (IF and RIA) and expression of CGRP mRNA. However, treatment with 5,7‐DHT, which lesions 5‐HT neurons, including those giving rise to the bulbospinal serotoninergic pathway, did not cause any dramatic changes in motor behaviour but induced an increase in both motoneuron content of CGRP‐LI and expression of CGRP mRNA. In rats first subjected to SCT, which depresses CGRP, followed 2 weeks later by SNT, we found a marked increase in both content of CGRP‐LI (IF and RIA) and expression of mRNA coding for CGRP. In summary our results show that the cellular production of the CGRP peptide, normally expressed in motoneurons, is influenced in a complex way by motoneuron injury as well as changes in the afferent input. There also appear to be important differences in the expression of CGRP in small (gamma) and large (alpha) motoneurons as well as between motoneurons of different nuclei, in normal as well as axotomized rats.
Bypassing the Saccadic Pulse Generator: Possible Control of Head Movement Trajectory by Rat Superior Colliculus
Authors: King Sheila M. , Dean Paul , Redgrave Peter
Published: April 2006

Saccades produced by electrical stimulation of the superior colliculus in primates are influenced primarily by the location of the stimulating electrode, with the suprathreshold intensity or frequency of the stimulating pulse train having little effect. Any given collicular site produces a characteristic movement of relatively fixed amplitude and velocity. In accordance with this finding, in models of the saccadic eye movement system the superior colliculus specifies the change of eye position: the velocity of movement components are determined by ‘pulse generators’ located between the superior colliculus and the oculomotor neurons. Previous findings in rodents, however, have suggested that eye and head movements induced by stimulation at some collicular sites may be critically dependent on stimulation parameters, implying that in these animals the superior colliculus has access to a non‐saccadic control system. To investigate this possibility, rats with electrodes implanted into the lateral intermediate layers were stimulated with pulse trains of varying frequency and duration, and the resultant head movements analysed from video tape. At seven of the nine sites studied, amplitude of the horizontal component of the head movement was linearly related to stimulating frequency for fixed‐duration trains, in some cases over a ten‐fold range. Subsequent variation of train duration showed that amplitude was affected not by frequency as such, but by the number of pulses in the train; frequency was related to the mean velocity of the movement. By appropriate setting of these parameters, independent control of head movement amplitude and velocity could be achieved. These results suggest that the rodent superior colliculus may be able to control head movement without recourse to a pulse generator, and thus influence the trajectory of the movement directly. If so, it may prove to be a useful preparation for testing theories of trajectory formation.
Chromatic Discrimination in a Cortically Colour Blind Observer
Authors: Heywood C. A. , Cowey A. , Newcombe F.
Published: April 2006

We tested the ability of a subject with cerebral achromatopsia to discriminate between colours and to detect chromatic borders. He was unable to identify colours or to arrange them in an orderly series or choose the odd colour out of an array or even to pick out a colour embedded in an array of greys. Nevertheless, he could select the odd colour when the colours were contiguous, even when they were isoluminant, and could discriminate an ordered from a disordered chromatic series as long as the colours in each row abutted one other. His verbal replies showed that he did so by detecting an edge between two stimuli that were, to him, perceptually identical. Introducing a narrow isoluminant grey stripe between adjacent colours abolished or greatly impaired this ability. As long as isoluminant colours were contiguous the patient could identify the orientation of the chromatic borders. Photopic spectral sensitivity showed evidence both for activity of three cone channels and for chromatic opponent processing, indicating that postreceptoral chromatic processing is occurring despite the absence of any conscious awareness of colour. The results indicate that both parvocellular colour opponent and magnocellular broad‐band channels are active and that the cortical brain damage has selectively disrupted the appreciation of colour but not the ability to detect even isoluminant chromatic borders, which would be invisible to a retinal achromat. The subject's performance on non‐colour tasks involving the discrimination of shape, texture, greyness and position was excellent. His disorder is therefore not like that of macaque monkeys in which cortical area V4 has been removed, and which are much more severely impaired at discriminating shape than colour.
Genotypic m3‐Muscarinic Receptors Preferentially Inhibit M‐currents in DNA‐transfected NG108‐15 Neuroblastoma × Glioma Hybrid Cells
Authors: Robbins J. , Caulfield M. P. , Higashida H. , Brown D. A.
Published: April 2006

The ability of different genotypic muscarinic acetylcholine receptors (mAChR) to inhibit the neural K+‐current, IM, was assessed in clones of NG108‐15 mouse neuroblastoma × rat glioma cells transfected with DNA for the genomic mAChRs ml –4 using tight‐seal, whole‐cell patch clamp recording. No significant inhibition of IM was seen in native (non‐transfected) cells, or in m2 or m4 DNA‐transfected cells at concentrations of acetylcholine up to 1 mM or muscarine up to 100 μM. Both acetylcholine and muscarine produced complete inhibition of IM in m3 DNA‐transfected cells, but only partial (50–60%) inhibition in m1 DNA‐transfected cells at maximally effective concentrations. This difference could not be explained by differences in mAChR number, as measured by radioligand binding and was not eliminated by adding GTP to the pipette. It is concluded that genotypic m3 receptors couple most effectively to IM and that this may explain previously reported instances of pirenzepine‐resistant IM‐inhibition.
Long‐term Depression of Glutamate Currents in Cultured Cerebellar Purkinje Neurons Does Not Require Nitric Oxide Signalling
Authors: Linden David J. , Connor John A.
Published: April 2006

Cerebellar long‐term depression (LTD) is produced when conjunctive stimulation of parallel fibre (PF) and climbing fibre (CF) inputs to a Purkinje neuron (PN) results in a prolonged decrease in the strength of the PF‐PN synapse. In cultured PNs, LTD may be induced by substituting depolarization of the PN and iontophoretic glutamate pulses for CF and PF stimulation, respectively, allowing an unambiguous analysis of post‐synaptic processes (Linden et al., Neuron, 7, 81–89, 1991). Recent studies have suggested that release of the newly described second messenger, nitric oxide, in the cerebellar molecular layer, is necessary for LTD produced in the slice preparation by PF/CF conjunctive stimulation (Shibuki and Okada, Nature, 349, 326–328, 1991) or PF/depolarization conjunctive stimulation (Crepel and Jaillard, NeuroReport, 1, 133–136, 1990). We report that LTD of glutamate currents produced without synaptic stimulation in cultured PNs is unaffected by reagents that stimulate (sodium nitroprusside) or inhibit (haemoglobin, NG‐nitro‐l‐arginine) nitric oxide signalling.
Synaptic Activation of GABAA Receptors Causes a Depolarizing Potential Under Physiological Conditions in Rat Hippocampal Pyramidal Cells
Authors: Avoli Massimo
Published: April 2006

Intracellular recordings with K‐acetate‐filled microelectrodes were performed in slices of the adult rat hippocampus maintained in vitro at 35–36°C to analyse the potentials associated with the orthodromic inhibitory sequence generated by CA1 pyramidal cells. In 43 of 72 cells, stimuli that were delivered in the stratum radiatum induced (i) an initial excitatory postsynaptic potential (EPSP), (ii) an early, hyperpolarizing inhibitory postsynaptic potential (IPSP) (peak latency from the stimulus artefact 20 ms), (iii) an intermediate depolarizing component (peak latency = 60–120 ms; duration = 60‐150 ms, and (iv) a late, long‐lasting hyperpolarizing IPSP (peak latency = 120–160 ms, duration >400 ms). In the remaining cells the orthodromic inhibitory response lacked the intermediate depolarization. The depolarizing component was selectively blocked by local applications of bicuculline or picrotoxin on the apical dendrites of pyramidal cells. This pharmacological procedure induced an increase in the amplitude of the EPSP that was capable of triggering 2–3 action potentials, but no reduction of the recurrent IPSP which is caused by GABAA receptors located close to the soma. The amplitude and duration of the depolarizing component was enhanced by lowering the temperature in the tissue chamber to 29–31°C or by application of the GABA uptake blocker nipecotic acid, further indicating that the depolarizing component represented an active phenomenon mediated through GABA. Application of the CI‐ pump blocker furosemide reduced and eventually blocked the early IPSP and the depolarizing component. These data demonstrate that under physiological conditions rat hippocampal pyramidal cells generate a depolarization that is presumably caused by an outwardly directed CI‐ movement due to the activation of GABAA receptors located on the apical dendrites. This novel mechanism might modulate hippocampal excitability in both physiological and pathophysiological conditions.
The Critical Period for Experience‐dependent Plasticity in a System of Binocular Visual Connections in Xenopus laevis: Its Temporal Profile and Relation to Normal Developmental Requirements
Authors: Keating M. J. , Grant S.
Published: April 2006

A commissural system of ‘intertectal’ connections in Xenopus mediates the registration of binocular visual maps at the midbrain optic tectum. Following surgical eye rotation in larval animals, the system can completely alter its pattern of connectivity to restore binocular visual registration at the tectum. This experimentally induced plasticity is known to require visual experience and thought to be subject to an age‐related restriction: eye rotation in adult animals is reported to provoke no subsequent intertectal alteration. In this paper we describe the detailed age‐dependence of this plasticity. One eye was rotated in 238 animals of various developmental stages between mid‐larval and adult life. At each age, different animals received rotations of different sizes, ranging from 20 to 180°. The pattern of intertectal connectivity was mapped electrophysiologically 1–2 years postoperatively. A ‘critical’ period was defined around the time of metamorphosis: the vast majority of animals receiving a rotation in larval life (up to ‐2 weeks before metamorphic climax) showed altered intertectal connections, whereas none of the animals operated upon at 3 months or more postmetamorphosis displayed the plasticity. At intervening ages, altered intertectal connections were found only in response to progressively smaller eye rotations. The profile of this critical period was further shown to mirror temporal features of the changes in eye position that occur in Xenopus as natural consequences of head growth, and which themselves impose a normal developmental requirement for intertectal plasticity. We conclude that the capacity of the Xenopus intertectal system for plasticity in response to abnormal experience undergoes a progressive age‐dependent decline, and that the profile of this decline is delimited by normal requirements.
Contrasting Effects of Raclopride and SCH 23390 on the Cellular Content of Preproenkephalin A mRNA in Rat Striatum: A Quantitative Non‐radioactive In Situ Hybridization Study
Authors: Augood Sarah J. , Faull Richard L. M. , Emson Piers C.
Published: April 2006

The effects of acute i. p. administration of selective dopamine (DA) receptor antagonists on the expression of preproenkephalin A (PPE A) mRNA was investigated in the adult rat striatum. Animals were injected with either (a) a selective D1 receptor antagonist SCH 23390 (0.25 mg/kg), (b) a selective D2 receptor antagonist raclopride (5 mg/kg), or (c) SCH 23388 (0.25 mg/kg), the (S)‐enantiomer of SCH 23390. Control naive animals did not receive an injection. At specific time points following drug administration (1, 3 or 9 h), rats were killed and striatal tissue processed for in situ hybridization with an alkaline phosphatase‐labelled oligonucleotide probe complementary to a portion of the rat PPE A cDNA. Treatment of rats with SCH 23388 did not affect the content of PPE A mRNA expressed by striatal cells at any time point. However, 1 h after SCH 23390 administration, a significant decrease in striatal PPE A mRNA was detected, reflected by a decrease in the cellular content of mRNA. No significant changes in PPE A mRNA were detected in raclopride‐treated sections at this time point. In contrast, both 3 and 9 h after an injection of raclopride a significant increase in the cellular content of PPE A mRNA was detected in the striatum. No change in the cellular content of mRNA was detected in SCH 23390‐treated rats at these two latter time points. Throughout the striatum ‐46% of neurons were found to express PPE A mRNA, with the highest percentage of cells (55%) being detected in the mid‐caudal striatum. No significant differences in striatal DA content were detected with any drug treatment using HPLC electrochemical detection methods. These results demonstrate that acute administration of the DA D1 and D2 receptor antagonists has contrasting effects on the cellular content of PPE A mRNA in the adult rat striatum. These effects may reflect changes in the rate of mRNA transcription which may be mediated by cAMP.
Putative Single Quantum and Single Fibre Excitatory Postsynaptic Currents Show Similar Amplitude Range and Variability in Rat Hippocampal Slices
Authors: Raastad Morten , Storm Johan F. , Andersen Per
Published: April 2006

Transmission at excitatory synapses in the mammalian brain is thought to depend on the release of transmitter quanta through exocytosis of presynaptic vesicles (Katz, 1969). The number of vesicles released by a single presynaptic action potential is important for understanding the impact of a single synapse, and the variability in transmission from one impulse to the next. In addition, the number of vesicles released may be an important factor for synaptic regulation and plasticity, such as facilitation, post‐tetanic potentiation and long‐term potentiation (LTP). Three recent studies suggest that an increase in the number of transmitter quanta underlies hippocampal LTP (Malinow and Tsien, 1990; Bekkers and Stevens 1990; Malinow, 1991), whereas other reports suggest a postsynaptic mechanism (Kauer et al 1988; Muller et al, 1988; Foster and McNaughton, 1989). We have used the whole‐cell recording technique to compare putative quantal and single fibre responses at excitatory synapses in rat hippocampal slices, and find (i) a surprisingly large variability in single fibre excitatory postsynaptic currents (sfEPSCs); (ii) an equally large variability of putative quantal (pq) EPSCs elicited by hyperosmolar media or ruthenium red; (iii) the observed amplitude ranges for the sfEPSCs and the pqEPSCs overlap almost completely; and (iv) in neither case can the variability be attributed to a scatter in electrotonic distance from the soma of the engaged synapses. Thus, the data are compatible with the hypothesis that a presynaptic action potential usually releases only a single quantum. Other possibilities are also discussed.
GAP‐43 mRNA in Rat Spinal Cord and Dorsal Root Ganglia Neurons: Developmental Changes and Re‐expression Following Peripheral Nerve Injury
Authors: Chong M. S. , Fitzgerald M. , Winter J. , Hu‐Tsai M. , Emson P. C. , Wiese U. , Woolf C. J.
Published: April 2006

The expression of growth‐associated protein GAP‐43 mRNA in spinal cord and dorsal root ganglion (DRG) neurons has been studied using an enzyme linked in situ hybridization technique in neonatal and adult rats. High levels of GAP‐43 mRNA are present at birth in the majority of spinal cord neurons and in all dorsal root ganglion cells. This persists until postnatal day 7 and then declines progressively to near adult levels (with low levels of mRNA in spinal cord motor neurons and 2000–3000 DRG cells expressing high levels) at postnatal day 21. A re‐expression of GAP‐43 mRNA in adult rats is apparent, both in sciatic motor neurons and the majority of L4 and L5 dorsal root ganglion cells, 1 day after sciatic nerve section. High levels of the GAP‐43 mRNA in the axotomized spinal motor neurons persist for at least 2 weeks but decline 5 weeks after sciatic nerve section, with the mRNA virtually undetectable after 10 weeks. The initial changes after sciatic nerve crush are similar, but by 5 weeks GAP‐43 mRNA in the sciatic motor neurons has declined to control levels. In DRG cells, after both sciatic nerve section or crush, GAP‐43 mRNA re‐expression persists much longer than in motor neurons. There was no re‐expression of GAP‐43 mRNA in the dorsal horn of the spinal cord after peripheral nerve lesions. Our study demonstrates a similar developmental regulation in spinal cord and DRG neurons of GAP‐43 mRNA. We show moreover that failure of re‐innervation does not result in a maintenance of GAP‐43 mRNA in axotomized motor neurons.
Cell Type‐specific Effects of the Neural Adhesion Molecules L1 and N‐CAM on Diverse Second Messenger Systems
Authors: von Bohlen und Halbach Friedrich , Taylor Joanne , Schachner Melitta
Published: April 2006

We have previously shown that the neural adhesion molecules L1 and N‐CAM influence second messenger systems when triggered with specific antibodies at the surface of the phaeochromocytoma PC12 cell line (Schuch et al., Neuron, 3, 13–20, 1989). To determine whether the two molecules are linked to the same intracellular signalling cascades, independent of the cell type expressing them, or whether different neural cell types respond with different signal transduction mechanisms, we have investigated the effects of antibodies to L1 and N‐CAM, and the isolated molecules themselves, on second messenger systems in different neural cell types. We have investigated cultures of cerebellar and dorsal root ganglion neurons and transformed Schwann cells and related these results to those obtained with the PC12 cell line. Here we show that addition of L1 and N‐CAM antibodies and the isolated molecules themselves elicit cell type‐specific responses that can be modulated by the substrate on which the cells are maintained. Depending on the cell type, cells respond to the triggering of L1 and N‐CAM with antibodies, or addition of the purified molecules, by either up‐regulation or down‐regulation of inositol phosphate turnover, by a rise in intracellular Ca2+ levels dependent on or independent of the opening of voltage‐gated Ca2+ channels, or by an increase or decrease in intracellular pH. Moreover, cerebellar neurons expressing N‐CAM respond to addition of N‐CAM, but not to N‐CAM antibodies, in contrast to the other neural cell types studied, which respond to both triggers. Furthermore, cerebellar neurons were the only cells to show a rise in cAMP levels in response to any of the ligands tested. This stimulation of cAMP production by L1 antibodies depended on the cross‐linking of L1 molecules at the cell surface, whereas the other responses did not depend on clustering of L1. Simultaneous addition of L1 and N‐CAM antibodies either elicited an additive or more than additive effect on the intracellular responses which, for cerebellar neurons, depends on the substrate on which the cells are maintained. These observations indicate that L1 and N‐CAM or their antibodies activate cell type‐specific intracellular signalling systems and that the two molecules can act interdependently or independently of each other.
Protein SP40,40‐like Immunoreactivity in the Rat Brain: Progressive Increase With Age
Authors: Senut M. C. , Jazat F. , Choi N. H. , Lamour Y.
Published: April 2006

The pattern of distribution of SP40,40‐like immunoreactive structures has been studied in the rat brain using a well‐characterized polyclonal antibody raised against the SP40,40 protein. Protein SP40,40 is the human counterpart of the rat sulphated glycoprotein 2, whose mRNA shows widespread expression in the developing and mature brain. In young adult rats few immunoreactive structures were observed. Some immunoreactive neurons were found in the cingulate cortex, the arcuate and perifornical hypothalamic nuclei, as well as glial labelling in the hypothalamus. A striking increase in the number of immunoreactive cells was observed as a function of age. In 20–22‐month‐old rats, numerous immunoreactive cells were observed in the cingulate cortex, several thalamic and hypothalamic nuclei, the red nucleus, olivary nuclei, superior colliculus, and many cranial nerve nuclei. Whereas the immunoreactivity was restricted to a diffuse labelling of the cell bodies and processes in young rats, other forms of labelling were observed in aged rats: punctate cytoplasmic labelling and intensely stained granules with no visible cell membrane. A further increase in the density of the immunoreactive material was observed in 30–31‐month‐old rats. Double labelling experiments demonstrated that the SP40,40 immunoreactivity was almost exclusively located in neurons and not in glial cells (with the exception noted above). The distribution of SP40,40 immunoreactivity in aged rats did not coincide with the distribution of the microtubule‐associated tau protein, OX42 or lipofuscin.
Quantitative Autoradiographic Demonstration of Changes in Binding to NMDA‐sensitive [3H]Glutamate and [3H]MK801, but not [3H]AMPA Receptors in Chick Forebrain 30 min After Passive Avoidance Training
Authors: Stewart Michael G. , Bourne Rachel C. , Steele Robert J.
Published: April 2006

Day‐old domestic chicks (Gallus domesticus) were trained on a one‐trial passive avoidance task in which the aversive stimulus was an unpleasant tasting substance, methyl anthranilate. Thirty minutes later, localization of N‐methyl‐d‐aspartic acid (NMDA)‐sensitive [3H]glutamate receptor binding sites, [3H]MK801 and [3H]AMPA binding sites in 17 regions of the forebrain of methylanthranilate‐trained and control (water‐trained) chicks was determined using quantitative receptor autoradiography. Significant differences in binding to both MK801‐ and NMDA‐sensitive glutamate receptors, but not α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptors, were found in three regions of the forebrain of trained compared to control chicks; two of these regions have been implicated from previous lesion, biochemical and morphological studies as playing a key role in the process of memory formation and storage following passive avoidance training. For NMDA‐sensitive [3H]glutamate receptors, significant elevations in binding were observed in two regions, the left intermediate and medial hyperstriatum ventrale (IMHV) (39%) and the lobus parolfactorius (LPO) (34%), at 30 min post‐training, but a decrease (44%) occurred in binding to the lateral neostriatum. Significant increases in binding to MK801 receptors were observed in the left IMHV (19%) and right IMHV (13%), and left LPO (22%) at 30 min post‐training, though there was a decrease in the right LPO (15%). These findings, coupled with those described in a previous paper from our group (Burchuladze and Rose, Eur. J. Neurosci., 4, 533–538, 1992), demonstrate that a glutamate receptor subtype is involved in learning and memory formation in the chick.
Differential Expression of Markers and Activities in a Group of PC12 Nerve Cell Clones
Authors: Clementi Emilio , Racchetti Gabriella , Zacchetti Daniele , Panzeri Maria Carla , Meldolesi Jacopo
Published: April 2006

Sixteen clones, recently isolated from the PC12 nerve cell line, were analysed for a variety of markers and activities. Two endoplasmic reticulum (ER) luminal markers, the chaperone protein BiP and the major Ca2+ storage protein calreticulin, as well as the 40‐kD rough ER membrane marker and the plus‐end‐directed mirotubule motor protein, kinesin, were found to be expressed at similar levels. These results suggest that the size of the ER, the function of microtubules and the capacity of the rapidly exchanging Ca2+ store do not change substantially among the clones. Other proteins expressed at comparable levels were synapsin I and IIa, members of a nerve cell‐specific protein family known to bind synaptic vesicles to the cytoskeleton. In contrast, another ER membrane protein, calnexin, and the markers of secretory organelles were found to vary markedly. One clone (clone 27) completely lacked both chromogranin B and secretogranin II, the proteins contained within dense granules, and synaptophysin, a marker of clear vesicles. Other clones expressed these markers to variable and apparently mutually unrelated levels. Marked variability was observed also in the uptake of exogenous catecholamines, in their release both at rest and after stimulation, and in nerve growth factor‐induced differentiation. These results provide indirect information about the mechanisms that regulate the expression of structures and activities in PC12 cells. Of particular interest is clone 27, which appears globally incompetent for regulated secretion and might therefore be a valuable tool for the study of this activity in a nerve cell.