摘要:

AbstractIn order to examine the relationship between gephyrin (the peripheral membrane protein associated with glycine receptors) and glycinergic boutons, we have carried out a post‐embedding immunogold study of glycine‐like immunoreactivity on sections of rat lumbar spinal cord which had previously been reacted with monoclonal antibody to gephyrin. In all three areas examined (laminae I and II, lamina III and lamina IX) the majority of profiles which were presynaptic at gephyrin‐immunoreactive synapses were enriched with glycine‐like immunoreactivity. It was estimated that at least 83% of profiles presynaptic to gephyrin‐immunoreactive synapses in the superficial dorsal horn (laminae I and II) were glycine‐immunoreactive, while for lamina III and the ventral horn (lamina IX) the proportions were at least 91% and 98% respectively. This provides strong evidence that glycine is a transmitter at those synapses where gephyrin‐ and glycine‐like immunoreactivities are both present, but suggests that gephyrin may sometimes be expressed at non‐glycinergic synapses and indicates the need for caution in using gephyrin‐immunoreactivity as a marker for glycinergic synapses within the spinal cord. By reacting serial sections of dorsal horn with antisera to glycine and GABA, we have shown that many boutons in laminae I‐III of the dorsal horn show both types of immunoreactivity and are therefore likely to use both amino acids as inhibitory transmitters. Many of the boutons which were presynaptic at axoaxonic synapses in the ventral part of lamina II and in lamina III were glycine‐ and GABA‐immunoreactive and in many cases the postsynaptic element was the central axon of a type II synaptic glomerulus. Taken together with pharmacological evidence, this suggests that inhibitory intemeurons in the dorsal horn which use both GABA and glycine may be important in controlling the flow of information from hair follicle afferent

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb01014.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe effects of morphine on the depolarizing synaptic responses produced in motoneurons by electrical stimulation of primary sensory neurones have been recorded in hemisected spinal cord preparations (8‐ to 12‐day‐old rat pups). Morphine at concentrations of 0.1‐20 μM reduced a slow, long‐lasting (latency greater than 1 s, duration up to 10 s) component of the ventral root potential (VRP) evoked by C‐fibre strength stimulation of the dorsal root. At 2μM the reduction in area of this slow synaptic potential was 71.7 ± 0.9% of control values (n= 15). The earliest components of the C‐fibre strength VRP (the first 100 ms) and the responses to Aβ strength stimuli were unaffected by the opioid even at 10‐20μM. The intermediate, NMDA receptor antagonist (D‐AP5, 40μM)‐sensitive component (which lasts 100‐1000 ms) was reduced by 34 ± 2.2% of control (n= 15), which was significantly less than the reduction of the later NMDA‐independent component (P<0.001). Morphine (0.1‐20 μM) also depressed the cumulative depolarization generated by the temporal summation of synaptic responses evoked by brief trains of C‐fibre strength stimuli (1 or 10 Hz). A significantly greater reduction at the lower frequency of stimulation (56.3 ± 2.0%) than at the higher (20.3 ± 1.69%,n =10, measured at 2 μM morphine) was found (P<0.005). The effects of morphine were reversible upon wash‐out or superfusion with the opioid receptor antagonist naloxone (2 μM). The depression in the C‐fibre‐evoked VRPs produced by the NMDA receptor antagonist D‐AP5 (10‐40 μM) was different from that produced by morphine, as D‐AP5 only reduced a shorter latency component of the VRP (100 ms‐1 s) and was equally effective in decreasing the cumulative depolarizations evoked by 1 and 10 Hz trains. The preferential effect of morphine on the longest latency and longest lasting components of the high‐threshold VRP are discussed in relatio

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb01015.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThis study investigated the pattern of axonal projections of single corticothalamic neurons from the cortical barrel field representing the vibrissae in the rat. Microiontophoretic injections of biocytin were performed in cortical layers V and VI to label small pools of corticothalamic cells and their intrathalamic axonal projections. After a survival period of 48 h, the animals were perfused and the tissue was processed for biocytin histochemistry. On the basis of the intrathalamic distribution of axonal fields and of the types of terminations found in the thalamus, four types of corticothalamic projections were identified, (i) Cells of the upper part of layer VI projected exclusively to the ventral posteromedial (VPm) nucleus, where they arborized in long rostrocaudally oriented bands or‘rods’, (ii) All cells of the lower part of layer VI projected to the medial part of the thalamic posterior group (Pom) but the vast majority of them also collateralized in VPm where they participated in the formation of rods, (iii) A minority of corticothalamic cells in the lower portion of layer VI, possibly located under the interbarrel spaces (septae), arborized exclusively in Pom. (iv) The corticothalamic projection of layer V cells originated from collaterals of corticofugal cells whose main axons ran caudally towards the brainstem. These collaterals arborized exclusively in Pom or in the central lateral nucleus. All corticothalamic cells from layer VI displayed the same type of axonal network, made of long branches decorated by terminal buttons emitteden passantat the tip of fine stalks. Corticothalamic fibres arising from layer V pyramids, however, remained smooth as they ran across the lateral thalamus and they generated in Pom one or two clusters of large boutons. All corticothalamic axons derived from layer VI cells, but not those derived from layer V cells, gave off collaterals as they traversed the thalamic reticular complex. These observations are discussed in the light of previous studies bearing on the topological organization and function of corticothalamic projections to VPm and Pom in rats. The possibility that a similar cellular specificity and a similar organizational plan may characterize corticothalamic relationships in other sensory systems is also conside

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb01016.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThis study describes the axonal projections of single neurons of the thalamic reticular complex within the somatosensory thalamic nuclei in rats. Experiments were performed under urethane anaesthesia and reticular cells were labelled by extracellular microiontophoretic applications of biocytin. The axonal arborization of 25 thalamic reticular cells projecting to the ventrobasal (VB) nucleus and/or to the posterior thalamic (PO) complex were reconstructed from serial horizontal sections. Reticular cells labelled with biocytin display somatodendritic features similar to those reported previously. Their cell body is fusiform and their dendrites bear few spines and show a high degree of streaming along the horizontal curved axis of the nucleus. In most cells, axon‐like beaded processes stem out from dendrites but, contrary to previous descriptions, no intrareticular axonal collateral was observed. The axonal arborization of most thalamic reticular cells is confined within the limits of a single thalamic nucleus; only two neurons were seen projecting to both the VB and the Po nuclei. In VB, termination fields form short rods (diameter ∼ 150 μm, length ∼ 200‐300 μm) densely packed with grape‐like boutons and varicosities; termination fields in Po are larger, much less dense, and they are contained within a horizontal slab of tissue (thickness ∼ 200 μm, mediolateral width ∼ 400 μm, rostrocaudal length ∼ 1 mm. By charting the position of all labelled cells within the thickness of the thalamic reticular complex, a strip‐like arrangement was revealed. Cells projecting to Po occupy the innermost portion of the nucleus whereas those projecting to the ventral‐posteromedial and ventral‐posterolateral nuclei are located respectively in the middle and in the outer tiers of the nucleus. This strip‐like reciprocity was confirmed by separate biocytin injections performed in VB and in Po. These results show that inhibition of reticular origin is distributed within the rat dorsal thalamus in a highly specific manner, most likely according to a principle of reciprocity within the somatotopic

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb01017.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIt has been reported that the indolizinsulphone SR33557, which binds to a site on the α1subunit of the dihydropyridine receptor, blocks both L‐type calcium channel activity and contraction in skeletal muscle. Moreover, we know that charge movement plays a key role in the mechanism of excitation‐contraction coupling and in controlling the opening of L‐type calcium channels. We demonstrate here that SR33557 reduces intramembrane charge movement in skeletal muscle from normal mice with an IC50of ‐10 nM. The drug does not completely inhibit charge movement since ‐20% of total charge movement persists even in the presence of 30 μM SR33557. However, the SR33557‐sensitive charge component is more important than the dihydropyridine‐sensitive one. Surprisingly, SR33557 also reduces intramembrane charge movement in dysgenic myotubes which are characterized by a very strong reduction of the number of dihydropyridine binding sites. In these muscles, 10 μM SR33557 reduces ‐40% of total charge movement. These observations suggest the presence of a new component of charge movement which is sensitive to SR33557 but insensitive to nifedipine. This component is also present in dysgenic myotubes, and it could be produced by the lower molecular weight α1, subunit described by Malouf, N. N., McMahon, D. K., Hainsworth, C. N. and Kay, B. K. (1992)

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb01018.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIn patch‐clamped Purkinje cells (PCs), bath application of the ionotropic glutamate receptor antagonist, 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) prevents induction of long‐term depression (LTD) of parallel fibre (PF)‐mediated EPSPs by a pairing protocol between Ca2+spike firing and PF stimulation whereas bath application of (RS)‐α‐methyl‐4‐carboxyphenylglycine (MCPG), a metabotropic glutamate (mGLU) receptor antagonist, does not. On the other hand, LTD can be also induced by pairing direct depolarization of PCs with activation of mGLU receptors by 1 S,3R‐aminocyclopentyl‐dicarboxylate (1S, 3R‐ACPD), even in the presence of CNQX. In this case, LTD induction is not consistently blocked by bath application of the nitric oxide synthase inhibitor,NG‐methyl‐l‐arginine (l‐NMMA), whereas it is strongly blocked when the protein kinase C inhibitor peptide 19‐36 is dialysed into PCs. These results are at variance with LTD induced by a pairing protocol between Ca2+spikes and PF‐mediated EPSPs which depends to the same extent on both cascades. Finally, thapsigargin, which depletes most intracellular Ca2+pools, does not block induction of LTD by a pairing protocol between Ca2+spikes and PF‐mediated EPSPs whereas it prevents the induction of LTD

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb01019.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe involvement of local and remote associative fibres in the generation of piriform cortex synaptic potentials was investigated in the isolated guinea‐pig brain maintainedin vitroby arterial perfusion by implementing current source density analysis (CSD) on cortical field potential profiles. Previous hypotheses were verified using acute surgical isolation of piriform cortical areas to study different synaptic events separately. Stimulation of the lateral olfactory tract activated associative potentials throughout the piriform cortex. In the anterior piriform cortex, the current sinks responsible for the generation of associative potentials were located in the superficial portion of layer lb and in layer III. In the posterior piriform cortex, two associative events were observed: an early sink located in the superficial part of layer Ib, followed by a sink in the deep part of the same layer. In the anterior piriform cortex, local associative synaptic potentials were separated from the component carried by long projective fibres by surgically isolating a small area of cortex monosynaptically activated by lateral olfactory tract stimulation. In this patch of lateral olfactory tract‐connected anterior piriform cortex, local associative sinks were observed in the superficial lb layer and in layer III. Monosynaptic activation of the isolated patch of anterior piriform cortex induced purely associative potentials throughout the piriform cortex. These potentials were mediated by the synaptic activation of apical dendrites in the superficial lb layer and selectively abolished by severing the long associative fibres. The anterior piriform cortex layer III sink and the posterior piriform cortex deep lb associative component were evoked by the activation of large population spikes in the monosynaptic anterior piriform cortex and the disynaptic posterior piriform cortex response respectively. These two sinks are presumably generated locally through a polysynaptic circuit, whose activation depends on the degree of cortical excitation. Olfactory signal processing in the guinea‐pig piriform cortex during states of normal excitability is supported by the interactions between associative inputs impinging on the synapses located separately on the dendrites of pyramidal neurons. An increase in the synchronization of piriform cortex neuron discharge activates usually silent local circuit syn

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb01020.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIn the CNS of the snailLymnaea stagnalis, Phe‐Met‐Arg‐Phe‐amide (FMRFamide)‐like and additional novel neuropeptides are encoded by a common, multi‐exon gene. This complex locus, comprising at least five exons, is subject to post‐transcriptional regulation at the level of alternative RNA splicing. Our aim was first to analyse the pattern by which exons of this neuropeptide locus combine during splicing of the primary RNA transcript, and second to investigate the functional significance of splicing by mapping the expression and neuronal localization in the CNS of the alternative mRNA transcripts, in the context of defined neuronal networks and single identified neurons. The approach was a combination of comparativein situhybridization and immunocytochemistry, using a battery of exon‐specific oligonucleotides and anti‐peptide antisera. The analysis illustrated that exons III, IV and V were always coexpressed and colocalized whereas the expression of exon II was always differential and mutually exclusive. Both sets of exons were, however, coexpressed with exon I: the total number of exon I‐expressing neurons was equal to the combined number of neurons expressing exon III/IVA/ and neurons expressing exon II. In addition, it was revealed that the extreme 5’of exon II, encoding a potential hydrophobic leader signal, was not expressed in the CNS ofLymnaeabut was apparently spliced out during RNA processing. Both mRNA transcripts of the FMRFamide locus, type I (exons I/II) and type 2 (exons I/III/IV/V), were translated in the CNS and the resulting protein precursors were also expressed in a mutually exclusive fashion, as were their respective transcripts. The expression of alternative transcripts within identified networks or neuronal clusters was heterogeneous, as exemplified by the cardiorespiratory network. On the basis of this work and a previous cDNA analysis, we put forward a revised model of differential splicing and expression of the FMRFamide gene

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb01021.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIn embryonic rat nerves, we recently identified an early cell in the Schwann cell lineage, the Schwann cell precursor. We found that when these cells were removed from contact with axons they underwent rapid apoptotic death, and that in a proportion of the cells this death could be prevented by basic fibroblast growth factor (bFGF, FGF‐2). We now report that 100% of Schwann cell precursors isolated from peripheral nerves of 14‐day‐old‐rat embryos can be rescued by a combination of insulin‐like growth factor (IGF) 1 or 2 in combination with either acidic FGF (aFGF, FGF‐1), bFGF or Kaposi's sarcoma FGF (K‐FGF; FGF‐4). The precursors display an absolute requirement for both an IGF and an FGF to achieve maximal survival. Elevation of intracellular levels of cAMP by forskolin does not result in a significant shift in the IGF/FGF dose‐response curves. In contrast, the percentage of precursors rescued by FGF in the presence of insulin is dramatically increased by elevation of cAMP. These growth factor combinations did not stimulate DNA synthesis significantly in Schwann cell precursors. These findings show that cooperation between growth factors is required to suppress cell death in Schwann cell precursors, and suggest that survival and DNA synthesis are regulated by distinct growth factor combinations in these cells. The observations are consistent with the idea that survival regulation by FGFs and IGFs plays an important role in the development of glial cells in early

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb01022.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe present study extends knowledge of the basic properties of correlated oscillatory activity patterns in the visual cortex of anaesthetized cats. Recordings with multiple electrodes were performed in area 18 and the correlations of multi‐unit activity in the frequency range 35‐80 Hz were determined using the coherence function. Statistical analysis revealed that the multi‐unit correlations depended on the cortical distance between the recording sites, the orientation selectivity of the neurons and their cortical layer. On average, correlations dropped to chance level within several millimetres and were higher in lower than in upper cortical layers. Similar results were found by analysing the correlations of oscillatory patterns in local field potentials recorded from the same electrodes. Correlations of neurons with similar orientation preferences were higher than those of neurons with different orientation preferences. Comparison to a matched sample from area 17 showed that the correlations in areas 18 and 17 depended on similar properties of the neurons. The dependences of correlated oscillations resembled the known pattern and specificity of intra‐areal fibre connections, suggesting that the correlations were intracortically established. Since correlations were specifically and not randomly related to the response properties of cortical neurons and were prominent in a visual area other than area 17, the findings suggest that correlated oscillatory activity provides a potential neural code supporting sensory information pro

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb01023.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY