Decreased calcium influx into the neonatal rat motor nerve terminals can recruit additional neuromuscular junctions during the synapse elimination period

• Published in: Neuroscience 2002-01, Vol.110 (1), p.147-154
• Main Authors: Santafé, M.M, Garcia, N, Lanuza, M.A, Uchitel, O.D, Salon, I, Tomàs, J
• Format: Article
• Language: English
• Subjects: Animals; Animals, Newborn; Biological and medical sciences; Calcium Channel Blockers - pharmacology; calcium channels; Calcium Channels - drug effects; Calcium Channels - metabolism; Calcium Signaling - drug effects; Calcium Signaling - physiology; Cell Differentiation - drug effects; Cell Differentiation - physiology; Development. Senescence. Regeneration. Transplantation; Excitatory Postsynaptic Potentials - drug effects; Excitatory Postsynaptic Potentials - physiology; Fluorescent Dyes; Fundamental and applied biological sciences. Psychology; Magnesium - pharmacology; Motor Neurons - cytology; Motor Neurons - drug effects; Motor Neurons - metabolism; Muscle, Skeletal - drug effects; Muscle, Skeletal - growth & development; Muscle, Skeletal - innervation; Neuromuscular Junction - drug effects; Neuromuscular Junction - growth & development; Neuromuscular Junction - metabolism; Neuronal Plasticity - drug effects; Neuronal Plasticity - physiology; nitrendipine; polyneuronal innervation; Presynaptic Terminals - drug effects; Presynaptic Terminals - metabolism; Presynaptic Terminals - ultrastructure; Rats; Rats, Sprague-Dawley; silent synapses; Synaptic Transmission - drug effects; Synaptic Transmission - physiology; Vertebrates: nervous system and sense organs; ω-agatoxin-IVA; ω-conotoxin-GVIA
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/S0306-4522(01)00543-7

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; P0.05 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