Short-term effects of prednisolone on neuromuscular transmission in the isolated Mdx mouse diaphragm

To determine the mechanism of the beneficial effects of prednisolone on Duc henne muscular dystrophy (DMD), we examined the short-term effects of predn isolone on neuromuscular transmission by using conventional microelectrode methods in the mdx mice. High (56 mu mol/liter) and low (2.8 mu mol/liter) concentrations of prednisolone were applied to a bath containing phrenic ne rve-diaphragm preparations from mdx mice, and several parameters related to neuromuscular transmission were recorded. The high dose of prednisolone si gnificantly decreased parameter n on quantal release by nerve impulse and d ecay time-constant of end-plate potentials, which showed adverse effect on neuromuscular transmission. The low dose of prednisolone did not significan tly increase quantal content, but could assist the compensatory reaction to maintain the safety margin of neuromuscular transmission in the mdx mice. Our results suggest that the latter effect represents one of the possible m echanisms of the therapeutic effects of prednisolone on DMD.