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Abstract:

Individual skeletal muscle fibers in newborn vertebrates are innervated at a single endplate by several motor axons. During the first postnatal weeks, the polyneuronal innervation decreases in an activity-dependent process of synaptic elimination by axonal competition. Because synaptic activity depends strongly on the influx of calcium from the external media via presynaptic voltage-dependent calcium channels, we investigate the relationship between calcium channels, synaptic activity and developmental axonal elimination. We studied how several calcium channel blockers affect (after 1 h of incubation) the total number of functional axons per muscle fiber (poly-innervation index) of the Levator auris longus muscle of 6-day-old rats. We determined the poly-innervation index by gradually raising the stimulus amplitude and recorded the recruitment of one or more axons that produced a stepwise increment of the endplate potential. The L-type channel blocker nitrendipine (1 μM) increased the mean poly-innervation index (35.79%±3.91; P<0.05). This effect was not washed out with normal Ringer, although the poly-innervation index returned to the control value when high-calcium Ringer (5 mM) was used. The P-type channel blocker ω-agatoxin-IVA (100 nM) also increased the number of recruitable endplate potentials (27.49%±1.78; P<0.05), whereas N-type channel blocker ω-conotoxin-GVIA (1 μM) was ineffective (P>0.05). However, neither nitrendipine nor ω-agatoxin-IVA modified the poly-innervation index on high-calcium Ringer (P>0.05 in both cases). A more intense inhibition of calcium influx (by the sequential use of two calcium channel blockers) did not recruit any additional silent synapses. Moderately increasing the magnesium ions (by 500 μM) in the physiological solution produces a synaptic recruitment (36.78%±2.1; P<0.05) similar to that with L- and P-type calcium channel blockers incubation. This magnesium effect was not washed with normal Ringer but a Ringer that is high in calcium can reverse it. The recruited endings were identified by selective activity-dependent loading with styryl dyes. Rhodaminated α-bungarotoxin-labeled acetylcholine receptors were present in the postsynaptic counterpart. Based on these findings we suggest that, before their complete retraction, functionally silent nerve terminals can be manifested or recovered if calcium influx is reduced by a calcium channel blocker or if external magnesium is increased. The normal activation of this calcium-dependent silencing mechanism during development may be related to the final loss of the supernumerary axons. © 2002 IBRO. Published by Elsevier Science Ltd. All rights reserved.

Registro:

Documento: Artículo
Título:Decreased calcium influx into the neonatal rat motor nerve terminals can recruit additional neuromuscular junctions during the synapse elimination period
Autor:Santafé, M.M; Garcia, N.; Lanuza, M.A; Uchitel, O.D; Salon, I.; Tomàs, J.
Filiación:Unitat d'Histologia i Neurobiologia (UHN), Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, carrer St Llorenç, num 21, 43201 Reus, Spain
Laboratorio de Fisiologia y Biologia Molecular : Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II-2do piso, 1428 Buenos Aires, Argentina
Palabras clave:ω-agatoxin-IVA; ω-conotoxin-GVIA; Calcium channels; Nitrendipine; Polyneuronal innervation; Silent synapses; alpha bungarotoxin; calcium; calcium channel; calcium channel blocking agent; calcium channel L type; calcium channel N type; calcium channel P type; cholinergic receptor; dye; magnesium ion; nitrendipine; omega agatoxin IVA; omega conotoxin GVIA; rhodamine; Ringer solution; amplitude modulation; animal tissue; article; association; calcium transport; controlled study; drug effect; electric potential; endplate potential; incubation time; motor nerve; motor unit; muscle cell; nerve conduction; nerve ending; nerve function; neuromuscular synapse; newborn; nonhuman; priority journal; rat; skeletal muscle; Animals; Animals, Newborn; Calcium Channel Blockers; Calcium Channels; Calcium Signaling; Cell Differentiation; Excitatory Postsynaptic Potentials; Fluorescent Dyes; Magnesium; Motor Neurons; Muscle, Skeletal; Neuromuscular Junction; Neuronal Plasticity; Presynaptic Terminals; Rats; Rats, Sprague-Dawley; Synaptic Transmission
Año:2002
Volumen:110
Número:1
Página de inicio:147
Página de fin:154
DOI: http://dx.doi.org/10.1016/S0306-4522(01)00543-7
Título revista:Neuroscience
Título revista abreviado:Neuroscience
ISSN:03064522
CODEN:NRSCD
CAS:Calcium Channel Blockers; Calcium Channels; Fluorescent Dyes; Magnesium, 7439-95-4
Registro:https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_03064522_v110_n1_p147_Santafe

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Citas:

---------- APA ----------
Santafé, M.M, Garcia, N., Lanuza, M.A, Uchitel, O.D, Salon, I. & Tomàs, J. (2002) . Decreased calcium influx into the neonatal rat motor nerve terminals can recruit additional neuromuscular junctions during the synapse elimination period. Neuroscience, 110(1), 147-154.
http://dx.doi.org/10.1016/S0306-4522(01)00543-7
---------- CHICAGO ----------
Santafé, M.M, Garcia, N., Lanuza, M.A, Uchitel, O.D, Salon, I., Tomàs, J.. "Decreased calcium influx into the neonatal rat motor nerve terminals can recruit additional neuromuscular junctions during the synapse elimination period" . Neuroscience 110, no. 1 (2002) : 147-154.
http://dx.doi.org/10.1016/S0306-4522(01)00543-7
---------- MLA ----------
Santafé, M.M, Garcia, N., Lanuza, M.A, Uchitel, O.D, Salon, I., Tomàs, J.. "Decreased calcium influx into the neonatal rat motor nerve terminals can recruit additional neuromuscular junctions during the synapse elimination period" . Neuroscience, vol. 110, no. 1, 2002, pp. 147-154.
http://dx.doi.org/10.1016/S0306-4522(01)00543-7
---------- VANCOUVER ----------
Santafé, M.M, Garcia, N., Lanuza, M.A, Uchitel, O.D, Salon, I., Tomàs, J.. Decreased calcium influx into the neonatal rat motor nerve terminals can recruit additional neuromuscular junctions during the synapse elimination period. Neuroscience. 2002;110(1):147-154.
http://dx.doi.org/10.1016/S0306-4522(01)00543-7