Study of Neuromuscular Transmission Under (i) Phenomenon of Fatigue, (ii) Site of Fatigue, (iii) Neuromuscular Blocking in an in-situ Rat Nerve Muscle Preparation: A Novel Approach to Nerve Muscle Physiology Experiment Teaching

摘要

Purpose of the study: Nerve-muscle physiology is a very basic and vital module in undergraduate physiology curriculum. The practical sessions on this system are demonstrated on amphibian (frog) nerve-muscle preparation, which becomes a limiting factor in most of the medical colleges of India. In this study, we propose an alternative approach by using mammalian (rat) model for nerve-muscle physiology undergraduate practical experiments. Materials and methods: Rat in-situ sciatic nerve-soleus muscle preparation was used to study neuromuscular transmission. Stimulation of nerve and recording of muscle contraction (force) were done by using digital recording system. To demonstrate fatigue, repetitive electrical stimulation was applied to nerve-muscle preparation and muscle twitches were recorded. A reduction in amplitude of contraction to 50% of their basal recording was considered as onset of fatigue. To demonstrate site of fatigue, the muscle was stimulated directly after the fatigue was observed with nerve stimulation and muscle twitch recorded. To observe the effect of neuromuscular blocking drug Pancuronium bromide, on neuromuscular transmission, in a separate set up the drug was injected in muscle belly at multiple sites and nerve was stimulated to elicit muscle twitch. The response (amplitude of muscle twitch) was compared with control (injection of 0.9% saline). Main findings: On repeated stimulation of nerve muscle preparation, initially there was an increase in amplitude of contraction but progressively amplitude went on decreasing. After development of fatigue on direct muscle stimulation, amplitude recorded was same as the initial twitch amplitude. This demonstrates that the site of fatigue is not the muscle. Further, as nerve is also non- fatigable, site of fatigue was neuromuscular junction. Injection of Pancuronium bromide showed that the twitch amplitude decreased substantially than the control (saline injection) on stimulation of nerve, but on direct muscle stimulation amplitude of contraction remained same as initial, confirming the effect of drug on neuromuscular junction. Conclusion: In-situ rat nerve-muscle preparation can be used as an alternative approach to amphibian experiments for effective demonstration of neuromuscular transmission.