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A case of spinal myoclonus that complicated spasticity management is presented. A 37-year-old man with a C6 American Spinal Injury Association class B spinal cord injury was referred for treatment of spasticity. He had failed previous treatments with baclofen and dantrolene but was partly relieved by diazepam, although with unacceptable side effects. Further evaluation, including simultaneous electroencephalogram, videotaping, and electromyography of the quadriceps, anterior tibialis, posterior tibialis, and medial hamstring suggested myoclonic jerks of spinal origin that initiated episodes of unsustained clonus. During the worst episodes, myoclonic jerks came once every 16 to 22 seconds and persisted for 4 to 5 hours. Each episode of clonus lasted approximately 4 to 6 seconds. Treatment with valproic acid greatly diminished the frequency of myoclonic jerks with minimal side effects. Functionally, the patient was much less fatigued and better able to maintain his full time employment.

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The mammalian superior cervical sympathetic ganglion has been extensively used to study the kinetics of ACh metabolism and release. The present investigation examined the time course of changes in the number of synaptic vesicles and abundance of plasma membrane at preganglionic nerve terminals using stimulation protocols similar to those used in previous biochemical and electrophysiological studies. Continuous stimulation of the preganglionic trunk to the cat superior cervical ganglion in vivo produced an initially rapid fall in the number of clear synaptic vesicles followed by a subsequent plateau. Reciprocal changes in plasma membrane occurred with a similar time course. The plateau phase is interpreted as a steady-state where vesicle exocytosis is balanced by the rate of vesicle reformation from plasma membrane. During quiescent recovery, restoration of normal resting ultrastructure is initially rapid but slows with time as vesicle number and plasma membrane abundance approach pre-stimulation values, indicating that the rate of vesicle reformation at the end of stimulation is high and proportional to the number of vesicles incorporated into the plasma membrane. These results are interpreted as consistent with the 'vesicle hypothesis' of neurotransmitter release.

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Apposed plasma membranes of mitral cells and granule cell gemmules of mouse olfactory bulb are internalized in a conjugate fashion into mitral cell perikarya during postnatal development. Such conjugate internalization of plasma membranes occurs by way of double-walled coated vesicles (DWCVs) and becomes accelerated between 16 and 37 days of postnatal age. The formation of DWCVs appears to be a mechanism for the internalization of intercellularly adhered plasma membranes.

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The employment of rapid freezing of fresh tissue for electron microscopic studies of nervous tissue is receiving increasing attention. We report here on the design of a specimen carrier for use with freezing machines. This apparatus permits electrical stimulation and recording of responses closely comparable to those obtained in ordinary in vitro conditions. The essential features of this apparatus are that it employs miniature suction electrodes for stimulation and recording, a detachable well for mounting the specimen in Ringer's solution and a detachable cap for maintaining the specimen in a physiologic state suitable for freezing. This specimen carrier was designed for sympathetic ganglia but could be used with other types of neural tissue for correlative electrophysiological and morphological or biochemical studies.

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Mice allowed to exercise during the late postnatal period had Purkinje cells with larger dendritic trees and greater numbers of spines than littermates whose physical activity was severly restricted. These changes in Purkinje cells were accompanied by a selective reduction in the thickness of the cerebellar molecular layer. The data provide evidence for cerebellar plasticity during late development and demonstrate that physical activity can modify the development of Purkinje cell dendrites.

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A massive and transient increase in the formation of double-walled coated vesicles (DWCVs) from surface membranes during late cerebellar development is reported here. These structures are characterized by an outer vesicle (65 nm in diameter), bearing a 15 nm thick spiny coat, containing an inner vesicle (30 nm in diameter). DWCVs occur free in the cytoplasm or attached to the plasma membranes. In the latter case, the membrane of the outer vesicle can be seen to be an invagination of the plasmalemma of the parent cell process while the membrane of the inner vesicle is an evagination of the plasmalemma of the adjacent cell process. DWCVs were observed in a variety of cellular elements in the granular and molecular layers of immature mouse cerebellum, including axons, dendrites, glia and cell bodies. Morphometric analysis revealed that the number of DWCVs in cerebellar mossy terminals became elevated between 16 and 37 days of age and reached a peak 45--50 times higher at 20 days than at either 10 or 70 days of age. The data suggest that a massive conjugate internalization of apposed plasma membranes occurs during late postnatal development which may serve to remodel neural membranes.

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The late postnatal development of the Purkinje cell dendritic tree in mouse cerebellar vermis was investigated in Golgi preparations by morphometric techniques in order to determine at what age adult characteristics of the Purkinje cell are achieved in the rodent brain which grows continuously throughout adult life. B6D2F1 hybrid mice were sacrificed at 9, 15, 20, 35 and 250 days of age. "Hind-brain" weights (by direct weighing) and vermis volume (determined histometrically from Golgi sections), both increased rapidly from 9 to 20 days of age and continued to increase steadily with advancing age. The growth of Purkinje dendritic field areas, determined by planimetric measurements from Golgi sections paralleled the growth curves for vermis cross-sectional area, vermis volume and "hindbrain" weight. However, stereological determinations revealed an unexpected disparity between the growth of the Purkinje dendritic field areas and changes in the total length of dendrites of Purkinje cells. The total dendritic branch length per Purkinje cell increased sharply up to 20 days of age but thereafter declined with advancing age. Dendritic spine counts on Purkinje cells revealed no change in the number of dendritic spines per unit length of dendrites between 20 and 250 days of age, however, since the Purkinje cell total branch length declined-calculations suggest that the total number of spines per cell declined after 20 days of age. Thus, the size of the cerebellum and the Purkinje cell dendritic tree continued to enlarge during late postnatal development; however, the total dendritic surface area and the total number of dendritic spines on each Purkinje cell, after reaching a peak at 20 days of age, declined with advancing age. The data suggest that the late postnatal development of the Purkinje cell dendritic tree is characterized by resorption as well as dendritic growth. The functional significance of such developmental remodelling is unknown.

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This study examined the ultrastructure of presynaptic terminals after short periods of vigorous acetylcholine (ACh) secretion in the cat superior cervical ganglion in vivo. Experimental trunks of cats anesthetized with chloralose-urethane were stimulated supra-maximally for periods of 15-30 min and at several frequencies including the upper physiological range (5-10 Hz). Stimulated and contralateral control ganglia from each animal were fixed by intra-arterial aldehyde perfusion, processed simultaneously, and compared by electron microscopy. Stimulation produced an absolute decrease in the number of synaptic vesicles, an enlargement of axonal surface membrane, and distinct alterations in the shape of presynaptic terminals. Virtually complete recovery occurred within 1 h after stimulation at 10 Hz for 30 min. These results support the hypothesis that ACh release at mammalian axodendritic synapses occurs by exocytosis of synaptic vesicles resulting in the incorporation of vesicle membrane into the presynaptic membrane and that synaptic vesicles subsequently are reformed from plasma membrane.

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Prolonged preganglionic stimulation produces marked ultrastructural changes in presynaptic endings, which develop larger zones of contact with post-synaptic dendrites. Profiles of such endings, compared to controls, have fewer synaptic vesicles, similar areas, and greater circumferences. These results are compatible with the hypothesis that synaptic vesicles become incorporated into the plasma membrane during stimulation.

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