An ultrastructural study of the synaptic densities,nematosomes, neurotubules,neurofilaments and of a further three-dimensional filamentous network as disclosed by the E-PTA staining procedure

Summary After the staining of nervous tissue with phosphotungstic acid in absolute ethanol (E-PTA), a selective opacification occurs at certain specific sites, while other structures, especially the plasma and intra-cellular membranes, remain electron-lucent. Among those selectively stained sites, our studies have been focussed on: (1) The dense synaptic material consisting of several presynaptic clumps, termed projections, an intrasynaptic dense line and a subsynaptic web from which fine fibrillar wisps extend into the surrounding ground substance; (2) Neurofilaments and neurotubules, the surface of which is bristled by numerous side-arms; (3) A microfilamentous network intertwines the neurotubules, the neurofilaments and the mitochondria in the dendrites and axon, and is also connected to the E-PTA dense undercoating delineating the inner aspect of the plasma membrane and to the fine wisps emanating from the subsynaptic web. A three-dimensional microfilamentous latticework is thus formed in the nerve cell processes; (4) Dense cytoplasmic inclusions, termed nematosomes, which are usually located in the ground substance of the perikaryon among or in the vicinity of clusters of ribosomes. Tiny microfilaments emanate from the peripheral strands of these bodies. The presence of basic residues in the chains of structural proteins of which consist the subsynaptic web and the nematosome is plausible, since the specificity of the E-PTA staining procedure for the detection of basic residues has previously been put forth. The occurrence of a three-dimensional microfilamentous network in the nerve cell processes led us to hypothesize that it plays a role in translocation of materials. It may provide the motive force for the axoplasmic transport, for instance, with the neurotubules, as well as, plausibly, with the neurofilaments, serving as attachment sites and guideways.Supported by grant MA-3448 from The Medical Research Council of Canada.     

Effects of colchicine and vinblastine on neurotubules of the sciatic nerve and cholinesterases in the developing myoneural junction of the rat

Summary Colchicine (0.1 M) or vinblastine (0.01 M) was locally applied on the sciatic nerves of newborn rats. Both colchicine and vinblastine caused reversible disappearance of axonal neurotubules and appearance of increased amounts of neurofilaments at the site of application. Subsequent morphogenesis of myoneural junctions in the tibialis anterior muscle was studied after histochemical demonstration of acetylcholinesterase (AChE; E.C. 3.1.1.7) and non-specific cholinesterase (Ns. ChE; E.C. 3.1.1.8) activity in the myoneural area.Development of the postsynaptic muscle plasma membrane of the myoneural junction was arrested in the ipsilateral, but not in the contralateral control side, for a period of about three weeks following treatment with the test substances. After this delay the myoneural morphogenesis continued normally and neurotubules were seen in the axoplasm.Since disruption of neurotubules is likely to cause blockage of the intratubular axoplasmic transport system, it seems possible that the neurotrophic influence responsible for the development of the postsynaptic muscle membrane is mediated through a secretory product transported along axons intratubularly to the nerve endings.     

Studies on the transport of secretory granules in the magnocellular hypothalamic neurons

Summary The axonal flow of neurosecretory elementary granules has been studied in the paraventricular neurons of the rat (PVN), with the help of three techniques: light microscopy, radioautography after labelling with ³⁵S-L-cysteine, and electron microscopy.Colchicine treatment does not alter the uptake of ³⁵S cysteine in the PVN but the flow of labelled neurosecretory material towards the neurohypophysis is interrupted. Interruption of the axonal flow is also evidenced by the stagnation of neurosecretory granules at the periphery of the neuronal cytoplasm and by the presence of numerous axonal swellings, heavily loaded with neurosecretory granules and often containing abnormal elongated granules, surrounded by a single membrane, oriented more or less parallely to the long axis of the axons. Other cell organelles and neurotubules are not altered. The present experiments bring further evidence of the arrest by colchicine of the axonal flow of secretory granules without apparent changes of the neurotubules.This work was supported by a grant (1970/1971) from the Belgian National Fund for Scientific Research (J. F.-D), and by grant No 1120 from the Belgian National Fund for Medical Research (P. D).The authors wish to thank Mrs. A.-M. Hunninck-Couck for her devoted and skillful technical assistance, and are endebted to Dr. J. C. Heuson for kindly supplying the rats.