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Effect of Calcium Ionophores on Acetylcholine Output from Rat Brain Slices
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Regeneration of Rat Neuromuscular Synapses S. MANOLOV
Regeneration Research Laboratory, Bulgarian Academy of Sciences, 1431 Sofia (Bulgaria) The regeneration of neuromuscular synapses was studied in the rat plantaris muscle over a period of 1 t o 280 days after a crush lesion of the sciatic nerve, The initial signs of regeneration of the neuromuscular synapses were observed within 3 weeks of the operation. Thin axonal sprouts accompanied by large Schwann processes rich in organelles invaded some synaptic grooves. A considerable number of them were completely enveloped by Schwann cell processes and were situated at some distance from the postsynaptic membrane. Other terminals which penetrated deeper into the synaptic groove lost the Schwann processes from their surface and so established contact with the postsynaptic membrane. These terminals did not cover all the foldings of the subneural apparatus, and possessed a few synaptic vesicles, a single mitochondrion and a clear matrix. Single coated vesicles were rarely observed between the synaptic vesicles. The Schwann cell processes accompanying the nerve terminals were filled with filaments and a larger than normal number of free ribosomes and vesicles were situated round the hypertrophied Golgi zones, At the same time the subsynaptic sarcoplasm was rich in vesicles located mainly round the distal parts of the subneural foldings. The free ribosomes, mitochondria and filaments beneath the subneural apparatus were augmented. The axonal terminals began t o grow in the second postoperative month and gradually filled the synaptic groove almost completely. The synaptic vesices increased in number and thickenings, with vesicular aggregations, appeared along the presynaptic membrane, The Schwann cell processes became thinner but were still rich in organelles. After the third postoperative month all neuromuscular synapses were reinnervated and appeared completely normal. -_____
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Effect of Calcium Ionophores on Acetylcholine Output from Rat Brain Slices P. MANTOVANI and G. PEPEU Department of Pharmacology, University of Florence, Florence (Italy) Acetylcholine (ACh) output from cortical slices incubated in Krebs solution was quantified by bioassay. The calcium ionophores BrX-537A and A23187 enhanced ACh o u t p u t ; BrX-S37A exerted its maximal effect, a 6-fold increase, a t a concentration of 1.8 p M ; A23 187 caused a 3-fold increase at 58 pM. Raising Mg2+ to 9.3 mM doubled the peak effect of both ionophores. In Mg-free media the effect of both ionophores was reduced but the spontaneous ACh output was larger. In Ca-free media the effect of A23187 was abolished, and that of BrX-S37A strongly reduced even in the presence of 9.3 mM Mg2+. BrX-537A exerted some effect also when EDTA was added to the Ca-free medium. Raising Ca2+ to 5 mM increased the spontaneous ACh output but decreased the ionophore effect. Hyoscine (0.26 pM), but not the ionophores, further enhanced ACh output stimulated by KCI (25 mM). Hyoscine did not enhance ACh output stimulated by the ionophores The addition of hemicholinium-3 (0.01 mM) did not abolish the effect of the ionophores but suppressed the enhancing action of Mg2*. It is concluded that A23187 stimulates ACh output by transporting extracellular Ca2+ into cholinergic nerve endings. The effect of BrX-537A does not depend only o n Ca2*. The magnitude of the effect of both ionophores is modulated by ions and drugs affecting the synthesis and spontaneous output of ACh. t
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Regeneration of Rat Neuromuscular Synapses S. MANOLOV
Regeneration Research Laboratory, Bulgarian Academy of Sciences, 1431 Sofia (Bulgaria) The regeneration of neuromuscular synapses was studied in the rat plantaris muscle over a period of 1 t o 280 days after a crush lesion of the sciatic nerve, The initial signs of regeneration of the neuromuscular synapses were observed within 3 weeks of the operation. Thin axonal sprouts accompanied by large Schwann processes rich in organelles invaded some synaptic grooves. A considerable number of them were completely enveloped by Schwann cell processes and were situated at some distance from the postsynaptic membrane. Other terminals which penetrated deeper into the synaptic groove lost the Schwann processes from their surface and so established contact with the postsynaptic membrane. These terminals did not cover all the foldings of the subneural apparatus, and possessed a few synaptic vesicles, a single mitochondrion and a clear matrix. Single coated vesicles were rarely observed between the synaptic vesicles. The Schwann cell processes accompanying the nerve terminals were filled with filaments and a larger than normal number of free ribosomes and vesicles were situated round the hypertrophied Golgi zones, At the same time the subsynaptic sarcoplasm was rich in vesicles located mainly round the distal parts of the subneural foldings. The free ribosomes, mitochondria and filaments beneath the subneural apparatus were augmented. The axonal terminals began t o grow in the second postoperative month and gradually filled the synaptic groove almost completely. The synaptic vesices increased in number and thickenings, with vesicular aggregations, appeared along the presynaptic membrane, The Schwann cell processes became thinner but were still rich in organelles. After the third postoperative month all neuromuscular synapses were reinnervated and appeared completely normal. -_____
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_
_
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Effect of Calcium Ionophores on Acetylcholine Output from Rat Brain Slices P. MANTOVANI and G. PEPEU Department of Pharmacology, University of Florence, Florence (Italy) Acetylcholine (ACh) output from cortical slices incubated in Krebs solution was quantified by bioassay. The calcium ionophores BrX-537A and A23187 enhanced ACh o u t p u t ; BrX-S37A exerted its maximal effect, a 6-fold increase, a t a concentration of 1.8 p M ; A23 187 caused a 3-fold increase at 58 pM. Raising Mg2+ to 9.3 mM doubled the peak effect of both ionophores. In Mg-free media the effect of both ionophores was reduced but the spontaneous ACh output was larger. In Ca-free media the effect of A23187 was abolished, and that of BrX-S37A strongly reduced even in the presence of 9.3 mM Mg2+. BrX-537A exerted some effect also when EDTA was added to the Ca-free medium. Raising Ca2+ to 5 mM increased the spontaneous ACh output but decreased the ionophore effect. Hyoscine (0.26 pM), but not the ionophores, further enhanced ACh output stimulated by KCI (25 mM). Hyoscine did not enhance ACh output stimulated by the ionophores The addition of hemicholinium-3 (0.01 mM) did not abolish the effect of the ionophores but suppressed the enhancing action of Mg2*. It is concluded that A23187 stimulates ACh output by transporting extracellular Ca2+ into cholinergic nerve endings. The effect of BrX-537A does not depend only o n Ca2*. The magnitude of the effect of both ionophores is modulated by ions and drugs affecting the synthesis and spontaneous output of ACh. t
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