Effects of shaking on the sensitivity of neuromuscular transmission in vitro to d-tubocurarine and neomycin in mice.

The effects of continuous shaking after birth were examined on the sensitivity of neuromuscular transmission to d-tubocurarine (dTc) and neomycin (NMC) in various nerve-muscle preparations from male mice of the ddY strain. Newborn mice were subjected to continuous reciprocal shaking with an amplitude of 2.5 cm at a frequency of 2 cycles per second until they reached 13 weeks of age. Some of them were returned to conventional breeding conditions for 4 weeks at 13 weeks of age. Nerve-muscle preparations were made from the left phrenic nerve and the diaphragm muscle (DPH), the sciatic nerve and the soleus muscle (SOL), and the sciatic nerve and the extensor digitorum lungus muscle (EDL) of 13- or 17-week-old male mice. The results revealed that the shaking augmented the sensitivity of SOL and DPH to dTc, it reduced the sensitivity of all the preparations to NMC, it reduced the rate of spontaneous release of transmitter in SOL and it increased the rate of evoked release of transmitter in DPH. Furthermore, these alterations disappeared upon cessation of shaking. These results suggest diversity in the plasticity of neuromuscular transmission and, moreover, that some changes might be reversible.