Neuromuscular transmission inElectrophorus electricus (L.)

Résumé Le système neuromusculaire dansElectrophorus electricus est étudié avec des électrodes intracellulaires. La transmission neuromusculaire est supprimée avec D-tubocurarine (5 · 10^–7 p/v) ou avec un excès des ions Mg⁺⁺ (12 mM) dans la solution.     

Magnesium-calcium antagonism in the contraction of arterioles

Zusammenfassung Erhöhung des Mg-Spiegels im Blut hemmt Tonus und Kontraktilität der Widerstandsgefässe im Muskel. Durch Noradrenalin hervorgerufene Verengerung wird gleich stark gehemmt wie die durch Reizung sympathischer Nerven verursachte Kontraktion. Ein Überschuss an Ca⁺⁺ verhindert die blockierende Wirkung des Mg⁺⁺ auf die Kontraktilität, der Tonusverlust der Gefässe wird durch Ca⁺⁺ jedoch nicht rückgängig gemacht. Die antagonistischen Wirkungen von Mg⁺⁺ und Ca⁺⁺ beruhen wahrscheinlich auf deren gegensätzlicher Wirkung auf die elektromechanische Kopplung im Gefässmuskel.

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U.S. Public Health Service International Fellow.     

Neuromuscular spindles in bovine foetuses with hereditary muscle fiber hyperplasia

Summary In cattle with genetic hyperplasia of skeletal muscle fibers, foetuses have an increased number of intrafusal muscle fibers in their neuromuscular spindles.     

Neuromuscular synaptogenesis: clustering of acetylcholine receptors revisited

Clustering of neurotransmitter receptors in the postsynaptic membrane is critical for efficient synaptic transmission. During neuromuscular synaptogenesis, clustering of acetylcholine receptors (AChRs) is an early sign of postsynaptic differentiation. Recent studies have revealed that the earliest AChR clusters can form in the muscle independent of motorneurons. Neurally released agrin, acting through the muscle-specific kinase MuSK and rapsyn, then causes further clustering and localization of clusters underneath the nerve terminal. AChRs themselves are required for agrin-induced clustering of several postsynaptic proteins, most notably rapsyn. Once formed, AChR clusters are stabilized by several tyrosine kinases and by components of the dystrophin/utrophin glycoprotein complex, some of which also direct postnatal synaptic maturation such as formation of postjunctional folds. This review summarizes these recent results about AChR clustering, which indicate that early clustering can occur in the absence of nerves, that AChRs play an active role in the clustering process and that partly different mechanisms direct formation versus stabilization of AChR clusters. Received 10 April 2002; received after revision 4 June 2002; accepted 10 June 2002     

Neuromuscular junction blocking agents: an initial screening bioassay

A simple, rapid and sensitive in vivo bioassay for the initial screening of neuromuscular junction (NMJ) blocking agents has been accomplished. The i.v. retro-orbital plexus (IVROP) mode of injection was utilized, for the first time, in conjunction with the mouse inclined screen bioassay.     

The adrenergic innervation of the efferent arterioles and the vasa recta in the mammalian kidney

Résumé En employant des techniques histochimiques nous avons étudié l'innervation adrénergique du rein des mammifères et démontré que les fibres adrénergiques entourent les artérioles et la partie supérieure des faisceaux des vasa recta.     

Neuromuscular blocking activity of dibekacin,a new semisynthetic aminoglycoside antibiotic

Summary Dibekacin possesses the untoward effect of producing a neuromuscular blockade. Neostigmine is unable to reverse the neuromuscular blockade produced by dibekacin. Calcium has not only the ability to restore the neuromuscular transmission but also to exert protective action against the neuromuscular blocking activity of dibekacin.     

Enhancement of the sensitivity of hamster cheek pouch arterioles to beta-adrenergic stimulus during pregnancy

Summary The adrenergic beta stimulant fenoterol induced a dose-dependent vasodilation of hamster cheek pouch arterioles. The response to fenoterol was significantly larger on day 14 of pregnancy than in metoestrous animals. Since the serum progesterone and 17 beta-oestradiol level were also elevated on day 14, a relationship was suggested between the enhancement of vascular sensitivity and sex-steroid hormone levels.     

Hypertrophy of pulmonary arteries and arterioles with cor pulmonale in rats induced by seneciphylline,a pyrrolizidine alkaloid

Summary Seneciphylline, one of the hepatotoxic pyrolizidine alkaloids, induced, as do also monoclotaline, etc., a marked arterial and arteriolar hypertrophy of the lung of young Wistar rats a month after a single s. c. injection of 50–80 mg/kg. Cor pulmonale with leftward shift of the ventricular septum was also noted.     

Light transmission. II. Instruments for making in-vivo light transmission measurements

Summary 2 instruments for making in vivo light transmission measurements are described. A special device makes it possible to measure the thickness of the tissue as well.Acknowledgments. The author would like to thank Dr Leonard Salzarulo, chairman of the Physics Department of the New Jersey Institute of Technology for the critical reading of the paper. Special thanks are extended to Mr Simon H. Gregory of the Valtec Corp. for supplying the fibreoptics and for his helpful suggestions in how to handle them. Appreciations are also extended to Prof. Giuseppe Battendieri of the Liceo Scientifico Enrico Fermi in Cosenza, Italy, for the schematic reproduction of the instruments.     

Effects of angiotensin II and epinephrine infusion on juxtaglomerular cell granularity and arterioles of the rat kidney

Zusammenfassung In Ratten wurde durch Injektion von Angiotensin II und Epinephrin akuter systemischer Hochdruck erzeugt. Angiotensin II verursachte Kontraktion der kleinen Arterien mit Zylindern in distalen Abschnitten und Sammelröhrchen. Der Juxtaglomeruläre Index (JGI) war leicht erhöht (p < 0.02). Epinephrin verursachte erhebliche Hyperämie und Dilatation der kleinen Arterien; der JGI war etwas erniedrigt (p < 0,1). Die Ergebnisse zeigen, dass, obwohl Angiotensin II und Epinephrin hochaktive Vasokonstriktoren sind und auch erhöhten Blutdruck aufrechtzuerhalten vermögen, sie verschiedene Effekte auf individuelle Gefässbereiche haben.

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This investigation was supported by U.S.P.H.S. Grant No. HE 06975 of the National Heart Institute.     

The active role of astrocytes in synaptic transmission

In the central nervous system, astrocytes form an intimately connected network with neurons, and their processes closely enwrap synapses. The critical role of these cells in metabolic and trophic support to neurons, ion buffering and clearance of neurotransmitters is well established. However, recent accumulating evidence suggests that astrocytes are active partners of neurons in additional and more complex functions. In particular, astrocytes express a repertoire of neurotransmitter receptors mirroring that of neighbouring synapses. Such receptors are stimulated during synaptic activity and start calcium signalling into the astrocyte network. Intracellular oscillations and intercellular calcium waves represent the astrocyte's own form of excitability, as they trigger release of transmitter (i.e. glutamate) via a novel process sensitive to blockers of exocytosis and involving cyclooxygenase eicosanoids. Astrocyte-released glutamate activates receptors on the surrounding neurons and modifies their electrical and intracellular calcium ([Ca2+]i) state. These exciting new findings reveal an active participation of astrocytes in synaptic transmission and the involvement of neuronastrocyte circuits in the processing of information in the brain.