The interaction of epsin and Eps15 with the clathrin adaptor AP-2 is inhibited by mitotic phosphorylation and enhanced by stimulation-dependent dephosphorylation in nerve terminals

Clathrin-mediated endocytosis was shown to be arrested in mitosis due to a block in the invagination of clathrin-coated pits. A Xenopus mitotic phosphoprotein, MP90, is very similar to an abundant mammalian nerve terminal protein, epsin, which binds the Eps15 homology (EH) domain of Eps15 and the alpha-adaptin subunit of the clathrin adaptor AP-2. We show here that both rat epsin and Eps15 are mitotic phosphoproteins and that their mitotic phosphorylation inhibits binding to the appendage domain of alpha-adaptin. Both epsin and Eps15, like other cytosolic components of the synaptic vesicle endocytic machinery, undergo constitutive phosphorylation and depolarization-dependent dephosphorylation in nerve terminals. Furthermore, their binding to AP-2 in brain extracts is enhanced by dephosphorylation. Epsin together with Eps15 was proposed to assist the clathrin coat in its dynamic rearrangements during the invagination/fission reactions. Their mitotic phosphorylation may be one of the mechanisms by which the invagination of clathrin-coated pits is blocked in mitosis and their stimulation-dependent dephosphorylation at synapses may contribute to the compensatory burst of endocytosis after a secretory stimulus.     

A novel brain-specific isoform of beta spectrin: isolation and its interaction with Munc13

Munc13 is a component of the neurotransmitter release machinery which is specifically expressed in brain. Munc13 interacts with Doc2 and syntaxin which are also implicated in the neurotransmitter release process. Here we isolated another Munc13-interacting molecule from a rat brain cDNA library by use of the yeast two-hybrid system, identified it to be a novel type of beta spectrin, and named it beta SpIII sigma 1. beta SpIII sigma 1 was specifically expressed in brain, where it was enriched in the synaptic vesicle and plasma membrane fractions. Because spectrin has been shown to interact with the actin cytoskeleton which is involved in the exocytotic process, the present results suggest that the Munc13-beta SpIII sigma 1 interactions play a role in neurotransmitter release.     

Synaptic vesicular localization and exocytosis of L-aspartate in excitatory nerve terminals: a quantitative immunogold analysis in rat hippocampus

To elucidate the role of aspartate as a signal molecule in the brain, its localization and those of related amino acids were examined by light and electron microscopic quantitative immunocytochemistry using antibodies specifically recognizing the aldehyde-fixed amino acids. Rat hippocampal slices were incubated at physiological and depolarizing [K+] before glutaraldehyde fixation. At normal [K+], aspartate-like and glutamate-like immunoreactivities were colocalized in nerve terminals forming asymmetrical synapses on spines in stratum radiatum of CA1 and the inner molecular layer of fascia dentata (i.e., excitatory afferents from CA3 and hilus, respectively). During K+ depolarization there was a loss of aspartate and glutamate from these terminals. Simultaneously the immunoreactivities strongly increased in glial cells. These changes were Ca2+-dependent and tetanus toxin-sensitive and did not comprise taurine-like immunoreactivity. Adding glutamine at CSF concentration prevented the loss of aspartate and glutamate and revealed an enhancement of aspartate in the terminals at moderate depolarization. In hippocampi from animals perfused with glutaraldehyde during insulin-induced hypoglycemia (to combine a strong aspartate signal with good ultrastructure) aspartate was colocalized with glutamate in excitatory terminals in stratum radiatum of CA1. The synaptic vesicle-to-cytoplasmic matrix ratios of immunogold particle density were similar for aspartate and glutamate, significantly higher than those observed for glutamine or taurine. Similar results were obtained in normoglycemic animals, although the nerve terminal contents of aspartate were lower. The results indicate that aspartate can be concentrated in synaptic vesicles and subject to sustained exocytotic release from the same nerve endings that contain and release glutamate.     

Mutual activation of two restriction endonucleases: interaction of EcoP1 and EcoP15

Type III restriction endonucleases recognize nonsymmetric nucleotide sequences. A necessary condition for DNA cleavage is the presence of two unmethylated recognition sites which are inversely ('head-to-head') oriented in the DNA double strand. A DNA substrate possessing one EcoP1 and one EcoP15 site in the head-to-head configuration could not be cleaved by the individual enzymes, however, it was specifically digested in the simultaneous presence of both enzymes. In agreement with the tracking-collision model for the DNA interaction of type III enzymes cleavage could be abolished by Lac repressor bound between the two sites. We conclude that two different type III enzymes can functionally cooperate in the cleavage of DNA.     

Effect of nitroprusside on smooth muscle and adrenergic nerve terminals in isolated blood vessels

Experiments were designed to assess the mode of action of nitroprusside on isolated blood vessels and its relative potency on venous and arterial smooth muscle. Strips from dog blood vessels were mounted in an organ bath for isometric tension recording. Sodium nitroprusside (10(-5) M) depressed the contraction of saphenous vein strips caused by electric stimulation, tyramine, K+, Ba++, norepinephrine and acetylcholine. The depression of the norepinephrine-induced contractions also occurred in a Ca++- free medium and when Ca++ influx was inhibited by verapamil. Nitroprusside reduced the frequency of the spontaneous contractions of strips of portal-mesenteric veins. It depressed the contraction caused by norepinephrine in tibial artery strips more than in saphenous vein strips. Saphenous vein strips were incubated with (3H)norepinephrine and mounted for superfusion and isometric tension recording. Sodium nitroprusside (10(-5) M) had no effect on the basal efflux of 3H compounds. During electric stimulation, it did not change the output of (3H)norepinephrine but increased the outflow of deaminated and O-methylated metabolites. Thus sodium nitroprusside 1) has a direct effect on the smooth muscle cells which is independent of Ca++ influx, 2) depresses contractions of different types of vascular smooth muscle and 3) does not inhibit the release of norepinephrine from the nerve endings.     

Semi-quantitative ultrastructural analysis of the localization and neuropeptide content of gonadotropin releasing hormone nerve terminals in the median eminence throughout the estrous cycle of the rat

The ultrastructural appearance of gonadotropin releasing hormone-immunoreactive elements was studied in the external zone of the median eminence of adult female Wistar rats. On the one hand, the purpose of the study was to determine the distribution of gonadotropin releasing hormone terminals towards the parenchymatous basal lamina at the level of hypothalamo-hypophyseal portal vessels, throughout the estrous cycle. On the other hand, we have semi-quantified the gonadotropin releasing hormone content in nerve terminals or preterminals during this physiological condition. A morphometric study was coupled to a colloidal 15 mn gold postembedding immunocytochemistry procedure. Animals were killed at 09.00 on diestrus II, 0.900, 10.00, 13.00, 17.00 and 18.00 on proestrus and 09.00 on estrus (n = 4-8 rats/group). A preliminary light microscopic study was carried out to identify an antero-posterior part of median eminence strongly immunostained by anti-gonadotropin releasing hormone antibodies but which was, in addition, easily spotted. This last condition was necessary to make a good comparison between each animal. Contacts between gonadotropin releasing hormone nerve terminals and the basal lamina were observed only the day of proestrus. Such contacts, however, were rare and in the great majority of cases, gonadotropin releasing hormone terminals are separated from basal lamina by tanycytic end feet. The morphometric analysis showed no significant variation in average distance between gonadotropin releasing hormone terminals and capillaries throughout the estrous cycle. Consequently, it did not appear that a large neuroglial plasticity exists during the estrous cycle. However, the observation of contacts only on proestrus together with some ultrastructural images evoke the possibility of a slight plasticity. The semi-quantitative results show that the content of gonadotropin releasing hormone in the nerve endings presented two peaks on proestrus: one at 09.00 (23 +/- 5 particles/micrograms2, P < 0.03) before the onset of luteinizing hormone surge, and the second at 18.00 (16 +/- 2 particles/micrograms2, P < 0.01) concomitantly with the luteinizing hormone surge, when compared to baseline values on proestrus 10.00 (8 +/- particles/micrograms2).     

Identification and localization of endothelin-1 and its receptors in human fetal jaws

In the mouse, disruption of the endothelin-1 (ET-1) gene causes severe craniofacial deformities, including mandibular hypoplasia. Since the phenotype of ET-1-deficient mice shows features in common with inherited human mandibulofacial dysostosis, we investigated the presence of ET-1 and its receptors in human fetal craniofacial tissues of 9- to 12-week-old fetuses. We found that ET-1 is immunolocalized in the epithelial cells of the oral cavity. Radioligand binding studies indicate the presence of elevated concentrations of both ETA and ETB receptors in membranes derived from fetal jaws. Using autoradiography, 125I-ET-1 binding sites were shown to be localized within the embryonic mandibular process of the oral cavity, where they were confined to the mesenchymal-derived osteogenic cells. Our data suggest a role for ET-1 in the development of the human mandible.     

Exocytotic release from neuronal cell bodies, dendrites and nerve terminals in sympathetic ganglia of the rat, and its differential regulation

Stimulant-induced exocytosis has been demonstrated in sympathetic ganglia of the rat by in vitro incubation of excised ganglia in the presence of tannic acid, which stabilizes vesicle cores after their exocytotic release. Sites of exocytosis were observed along non-synaptic regions of the surfaces of neuron somata and dendrites, including regions of dendrosomatic and dendrodendritic apposition, as well as along the surfaces of nerve terminals About half the exocytoses associated with nerve terminals were parasynaptic or synaptic, and these appeared mostly to arise from the presynaptic terminal, but occasionally from the postsynaptic element. The results demonstrated that the neurons of sympathetic ganglia release materials intraganglionically in response to stimulation, that release from different parts of the neuron is subject to independent regulation, at least via cholinergic receptors, and that release is partly diffuse, potentially mediating autocrine or paracrine effects, and partly targeted toward other neurons, but that the latter mode is not necessarily, and not evidently, synaptic. Specifically, exocytosis from all locations increased significantly during incubation in modified Krebs' solution containing 56 nm potassium. Observation of the effects of cholinergic agonists (nicotine, carbachol, oxotremorine) and antagonists (atropine, AF-DX 116) showed that nicotinic and muscarinic excitation each, independently, increased the incidence of exocytosis from somata and dendrites. Exocytosis from nerve endings was not altered by nicotine, but was enhanced or, at high initial rates of exocytosis, decreased, by muscarinic stimulation. Evidence was obtained for muscarinic auto-inhibition of exocytosis from nerve terminals, occurring under basal incubation conditions, and for a muscarinic excitatory component of somatic exocytosis, elicitable by endogenous acetylcholine. The M2-selective muscarinic antagonist AF-DX 116 was found to modify the exocytotic response of the dendrites to oxotremorine, widening the range of its variation; this effect is consistent with recent evidence for the presence of M2-like muscarinic binding sites, in addition to M1-like binding, upon these dendrites [Ramcharan E. J. and Matthews M. R. (1996) Neuroscience 71, 797-832]. Over all conditions, disproportionately more sites of somatic and dendritic exocytosis were found to be located in regions of dendrosomatic and dendrodendritic apposition than would be expected from the relative extent of the neuronal surface occupied by these relationships. Such mechanisms of intraganglionic release may be expected to contribute to the regulation and integration of the behaviour of the various functionally distinctive populations of neurons in these ganglia, by autocrine, paracrine, and focal, neuroneuronal, routes of action. Similar phenomena of exocytotic soma-dendritic release might prove to subserve integrative neuroneuronal interactions more widely throughout the nervous system.     

Uncrossed disynaptic inhibition of second-order vestibular neurons and its interaction with monosynaptic excitation from vestibular nerve afferent fibers in the frog

1. Eighth nerve evoked responses in central vestibular neurons (n = 146) were studied in the isolated brain stem of frogs. Ninety percent of these neurons responded with a monosynaptic excitatory postsynaptic potential (EPSP) after electrical stimulation of the ipsilateral VIIIth nerve. In 5% of these neurons, the EPSP was truncated by a disynaptic inhibitory postsynaptic potential (IPSP), and in 5% of these neurons a pure disynaptic IPSP was evoked. 2. Disynaptic IPSPs superimposed upon apparently pure EPSPs were revealed by bath application of the glycine receptor antagonist strychnine (0.5-5 microM) or of the gamma-aminobutyric acid-A (GABAA) receptor antagonist bicuculline (0.5-2 microM). The evoked EPSP increased in most central vestibular neurons (strychnine: 15 out of 16 neurons; bicuculline 26 out of 29 neurons). At higher stimulus intensities, the evoked spike discharge increased from 2 to 3 spikes before up to 8-10 spikes per electrical pulse during the application of blocking agents. The unmasked disynaptic inhibitory component increased with stimulus intensity to a different extent in different neurons. 3. Lesion studies demonstrated that these inhibitory components were generated ipsilaterally with respect to the recording side. The disynaptic strychnine-sensitive inhibition was mediated by neurons located either in the ventral vestibular nuclear complex (VNC) or in the adjacent reticular formation. The spatial distribution of the disynaptic inhibition was investigated by simultaneous recordings of VIIIth nerve-evoked field potentials at different rostrocaudal locations of the VNC. A significant strychnine-sensitive component was detected in the middle and caudal parts but not in the rostral part of the VNC. A bicuculline-sensitive component was detected in the rostral and in the caudal parts but not in the middle part of the VNC. In view of a similar rostrocaudal distribution of glycineor GABA-immunoreactive neurons in the VNC of frogs, our results suggest that part of the disynaptic inhibition is mediated by local interneurons with a spatially restricted projection area. 4. The monosynaptic EPSP of second-order vestibular neurons was mediated in part by N-methyl-D-aspartate (NMDA) and in part by non-NMDA receptors. The relative contribution of the NMDA receptor-mediated component of the EPSP decreased with stronger stimuli. This negative correlation could have resulted from a preferential activation of NMDA receptors via thick vestibular nerve afferent fibers. Alternatively, the activation of NMDA receptors became disfacilitated at higher stimulus intensities due to the recruitment of disynaptic inhibitory inputs. Comparison of data obtained in the presence and in the absence of these glycine and GABAA receptor blockers indicates a preferential activation of NMDA receptors via larger-diameter vestibular nerve afferent fibers. 5. The kinetics of NMDA receptors (delay, rise time) activated by afferent nerve inputs were relatively fast. These fast kinetics were independent of superimposed IPSPs. The association of these receptors with large-diameter vestibular nerve afferent fibers suggests that fast NMDA receptor kinetics might be matched to the more phasic response dynamics of the large diameter vestibular afferent neurons to natural head accelerations.     

Glutamine 170 to tyrosine substitution in yeast mitochondrial F1 beta-subunit increases catalytic site interaction with GDP and IDP and produces negative cooperativity of GTP and ITP hydrolysis

Glutamine 170 to tyrosine mutation in the beta-subunit from Schizosaccharomyces pombe mitochondrial F1 was found to increase both affinity for ADP, apparent negative cooperativity of ATPase activity, and sensitivity to azide inhibition (Falson, P., Di Pietro, A., Jault, J.-M., Gautheron, D.C., and Boutry, M. (1989) Biochim. Biophys. Acta 975, 119-126). The mutation is shown here to increase the affinity for GDP, IDP, and guanosine 5'-(beta,gamma-imidotriphosphate), which are competitive inhibitors of GTPase and ITPase activities. Various fluorescence approaches also reveal an increased affinity of the catalytic site in mutant as compared with wild-type enzyme for GDP, IDP, and 2'(3')-N-methylanthraniloyl GDP. The mutation alters the maximal rates and pH dependence of GTPase and ITPase activities, whereas wild-type F1 exhibits single optima at pH 7.5-8.0. The pH activity profiles of the mutant enzyme for these substrates are biphasic, with optima at pH 8.5-9.0 and below 6.5. The mutation increases the sensitivity of GTPase and ITPase activities to azide inhibition, which increases with decreasing pH. At pH 6.0-7.0, an apparent negative cooperativity is observed when mutant F1 hydrolyzes GTP or ITP, whereas the wild-type enzyme shows Michaelian kinetics. Addition of bicarbonate at pH 7.0 substantially stimulates GTP or ITP hydrolysis and abolishes the apparent negative cooperativity by the mutant enzyme; on the contrary, the anion produces a slight inhibition of these activities catalyzed by wild-type F1. The overall results suggest that apparent negative cooperativity can be observed with GTP or ITP hydrolysis provided that the release of the respective diphosphate is a rate-limiting step.     

Effect of bafilomycin A1 and nocodazole on endocytic transport in HeLa cells: implications for viral uncoating and infection

Bafilomycin A1 (baf), a specific inhibitor of vacuolar proton ATPases, is commonly employed to demonstrate the requirement of low endosomal pH for viral uncoating. However, in certain cell types baf also affects the transport of endocytosed material from early to late endocytic compartments. To characterize the endocytic route in HeLa cells that are frequently used to study early events in viral infection, we used 35S-labeled human rhinovirus serotype 2 (HRV2) together with various fluid-phase markers. These virions are taken up via receptor-mediated endocytosis and undergo a conformational change to C-antigenic particles at a pH of <5.6, resulting in release of the genomic RNA and ultimately in infection (E. Prchla, E. Kuechler, D. Blaas, and R. Fuchs, J. Virol. 68:3713-3723, 1994). As revealed by fluorescence microscopy and subcellular fractionation of microsomes by free-flow electrophoresis (FFE), baf arrests the transport of all markers in early endosomes. In contrast, the microtubule-disrupting agent nocodazole was found to inhibit transport by accumulating marker in endosomal carrier vesicles (ECV), a compartment intermediate between early and late endosomes. Accordingly, lysosomal degradation of HRV2 was suppressed, whereas its conformational change and infectivity remained unaffected by this drug. Analysis of the subcellular distribution of HRV2 and fluid-phase markers in the presence of nocodazole by FFE revealed no difference from the control incubation in the absence of nocodazole. ECV and late endosomes thus have identical electrophoretic mobilities, and intraluminal pHs of <5.6 and allow uncoating of HRV2. As bafilomycin not only dissipates the low endosomal pH but also blocks transport from early to late endosomes in HeLa cells, its inhibitory effect on viral infection could in part also be attributed to trapping of virus in early endosomes which might lack components essential for uncoating. Consequently, inhibition of viral uncoating by bafilomycin cannot be taken to indicate a low pH requirement only.     

碳质金矿中碳质物的物质组成及其与金的相互作用

本文利用广西风山县金牙金矿对碳质金矿中的碳质物进行了研究。探索出从矿石中有效分离各种碳质组分的方法。在碳质物中发现如下的三种物质：（１）活性炭类物质（２）腐殖酸（３）长链酯或长链酯与长链烷烃的混合物。进一步的实验结果表明：产生“劫金”作用的碳质物主要为活性炭类物质,腐殖酸次之,酯或烃类似乎与劫金效应无关。但总的来讲,金牙金矿中碳质物的劫金作用较弱,金滩浸的主要原因不是碳质物对金的吸附,而强能是金的     

Mutations in murine Mx1: effects on localization and antiviral activity

Murine Mx1 is a nuclear localized protein of 631 amino acids with antiviral activity against influenza virus. Fourteen mutations in murine Mx1 were constructed in vitro, expressed in chicken embryo fibroblasts via replication-competent retroviruses, and the effects of the mutations on Mx localization and antiviral activity were assayed. The results suggest that a nuclear location is not sufficient for antiviral activity, that there are intricate structural constrains on the Mx protein for antiviral activity and that multiple domains of the Mx protein are required for the characteristic punctate nuclear Mx distribution. These conclusions are based on the findings showing that: (i) none of the mutants retained antiviral activity; (ii) only a mutant with a Leu to Lys substitution at residue 612 within the nuclear targeting signal retained the characteristic punctate nuclear localization of wildtype Mx1; (iii) diffuse nuclear localization was observed for mutants with substitutions of Pro for Leu at residue 619, 626, or both 619 and 626, and deletions of residues 23 to 95, 159 to 185, 369 to 409, 387 to 440, 522 to 560, or 541 to 596; and (iv) cytoplasmic localization was observed for mutants with carboxy-terminal truncations of 15, 30, or 61 amino acids, or a deletion of residues 610 to 624.     

Immunoreactivity of PMP-22, P0, and other 19 to 28 kDa glycoproteins in peripheral nerve myelin of mammals and fish with HNK1 and related antibodies

Mammalian peripheral nervous system (PNS) myelin contains several glycoproteins with molecular weights of 19 to 28 kDa, including the major 28 kDa P0 glycoprotein and a recently cloned protein called PMP-22. Some glycoproteins in this M(r) range in humans, cats and some other mammals react with HNK1, a mouse monoclonal antibody that identifies a carbohydrate epitope shared between the immune system and a number of adhesion proteins in the nervous system. A variety of antibodies to P0, PMP-22, and the carbohydrate determinants reacting with HNK1 were used to characterize immunochemically these 19 to 28 kDa glycoproteins of cat PNS myelin. The HNK1-reactive components include P0 and two slightly smaller 23 to 26 kDa proteins that are immunologically related to P0. However, HNK1 reacts most strongly with a lower molecular weight glycoprotein that does not react with the antibodies to P0 and was identified as PMP-22. Since the carbohydrate structure reacting with HNK1 is generally expressed on adhesion molecules, this result suggests that PMP-22 may function in cell-cell or membrane-membrane interactions. Furthermore, the related human anti-MAG monoclonal IgM antibodies from patients with neuropathy also react strongly with PMP-22, suggesting that it may be a target antigen in the pathogenesis of this disease. Purified PNS and CNS myelin from bony fish (toadfish and trout) were also shown to contain major glycoproteins, in the same 19 to 28 kDa M(r) range, that react very strongly with HNK1. It is shown that fish myelin has major proteins of this size that are immunologically and structurally related to mammalian P0, and it is demonstrated here that one of the strongly HNK1-positive proteins reacted well with an antiserum raised to bovine P0. The presence of high levels of the adhesion-related HNK1 epitope on these major myelin proteins of fish suggests that this carbohydrate structure may have played a role in the molecular evolution of myelin.     

Characterization of the recombinant extracellular domain of the neurotrophin receptor TrkA and its interaction with nerve growth factor (NGF)

Nerve growth factor (NGF) is the prototype of a family of neurotrophins that support important neuronal programs such as differentiation and survival of a subset of sympathetic, sensory, and brain neurons. NGF binds to two classes of cell surface receptors: p75LANR and p140TrkA. NGF binding to p140TrkA initiates the neuronal signaling pathway through activation of the tyrosine kinase activity, which subsequently results in a rapid signal transduction through a phosphorylation cascade. To examine this crucial signaling step in more detail, the TrkA extracellular domain polypeptide (TrkA-RED) was overexpressed in Sf21 insect cells and purified to homogeneity. The recombinant TrkA-RED is a 70 kDa acidic glycoprotein with a pI of 5.1, and mimics the intact TrkA receptor for NGF binding with a dissociation constant, Kd, of 2.9 nM. Thus, the recombinant TrkA-RED is functionally competent and can be used to elucidate the interaction of NGF and TrkA receptor. Circular dichroism difference spectra indicated that, upon association of NGF with TrkA-RED, a minor conformational change occurred to form a complex with decreased ordered secondary structure. Interaction between NGF and TrkA-RED was also demonstrated by size exclusion chromatography, light scattering, and chemical crosslinking with evidence for formation of a higher molecular weight complex consistent with a (TrkA-RED)2-(NGF dimer) complex. Association and dissociation rates of 5.6 x 10(5) M(-1) s(-1) and 1.6 x 10(-3) s(-1), respectively, were determined by biosensor technology. Thus, initiation of signaling may stem from NGF-induced receptor dimerization concomitant with a small conformational change.     

Expression of merosin in the thymus and its interaction with thymocytes

Merosin is a 700 kDa multichain protein that has several properties in common with laminin, one of the major extracellular matrix proteins present in basement membranes. Both contain B1 and B2 light chains, but merosin has a distinct M-chain compared with the laminin A-chain. Merosin is present in the basement membrane of placenta, striated muscle, and peripheral nerve. Using the RT-PCR assay, we demonstrate that merosin, but not laminin, is also expressed in the thymus. A partial cDNA sequence of the mouse merosin M-chain was 88% identical to the human M-chain, and the deduced amino acid sequences were 95% identical. 18-24% of adult mouse thymocytes bound to human merosin in vitro. Mg2+, but not Ca2+, was essential for binding. Binding was inhibited by antibodies recognizing VLA alpha 6 or beta 1, suggesting that the VLA-6 integrin is a merosin receptor. An anti-beta 4 integrin subunit mAb failed to inhibit binding, suggesting that the alpha 6 beta 4 integrin was not involved. Thymocytes were fractionated into immature and mature populations based on their expression of the heat stable antigen, recognized by the J11d mAb. Virtually all thymocytes expressed VLA-6, but only immature thymocytes (J11d+) bound to meroson. PMA treatment did not significantly increase the binding of J11d+ thymocytes nor did induce binding in the mature J11d- population. In constrast, both splenic T cells and unseparated lymph node cells showed enhanced binding to merosin after PMA stimulation. The expression of merosin in the thymus and its selective interaction with immature thymocytes suggest that thymocyte-merosin interactions may play a role in T cell development.     

Qualitative and quantitative analysis of glycine- and GABA-immunoreactive nerve terminals on motoneuron cell bodies in the cat spinal cord: a postembedding electron microscopic study

The distribution of glycine- and gamma-aminobutyric acid (GABA)-like immunoreactivity (LI) in nerve terminals on the cell soma of motoneurons in the aldehyde-fixed cat L7 spinal cord was examined using postembedding immunogold histochemistry in serial ultrathin sections. Quantitative examination of 405 terminals on eight neurons of alpha-motoneuron size in the L7 motor nuclei from one animal was performed. A majority of the terminals (69%) were immunoreactive to glycine and/or GABA. These terminals contained flat or oval synaptic vesicles, thus classifying them as F type or as C type in one case. In no case was a type-F terminal unlabeled for both glycine and GABA. Most of the immunolabeled terminals were immunoreactive to glycine only (62.5%), whereas 35.4% contained both glycine- and GABA-LI. A very small number of immunolabeled terminals (2%) were immunoreactive to GABA only. In those terminals, where glycine- and GABA-LI coexisted, the gold particle density for each amino acid was only half of that seen in boutons containing only one of the two amino acids. The involvement of glycine and GABA in postsynaptic inhibition of spinal alpha-motoneurons is discussed, with particular reference to the possibility that these two inhibitory amino acids may be coreleased from a significant proportion of the nerve terminals impinging on the cell bodies.