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

Purpose of the study: Nerve-muscle physiology is a very basic and vital module in undergraduate physiologycurriculum. The practical sessions on this system are demonstrated on amphibian (frog) nerve-musclepreparation, which becomes a limiting factor in most of the medical colleges of India. In this study, wepropose an alternative approach by using mammalian (rat) model for nerve-muscle physiology undergraduatepractical experiments.Materials and methods: Rat in-situ sciatic nerve-soleus muscle preparation was used to study neuromusculartransmission. Stimulation of nerve and recording of muscle contraction (force) were done by using digitalrecording system. To demonstrate fatigue, repetitive electrical stimulation was applied to nerve-musclepreparation and muscle twitches were recorded. A reduction in amplitude of contraction to 50% of their basalrecording was considered as onset of fatigue. To demonstrate site of fatigue, the muscle was stimulateddirectly after the fatigue was observed with nerve stimulation and muscle twitch recorded. To observe theeffect of neuromuscular blocking drug Pancuronium bromide, on neuromuscular transmission, in a separateset up the drug was injected in muscle belly at multiple sites and nerve was stimulated to elicit muscletwitch. 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 inamplitude of contraction but progressively amplitude went on decreasing. After development of fatigue ondirect muscle stimulation, amplitude recorded was same as the initial twitch amplitude. This demonstratesthat the site of fatigue is not the muscle. Further, as nerve is also non- fatigable, site of fatigue wasneuromuscular 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 remainedsame as initial, confirming the effect of drug on neuromuscular junction.

Effect of Load on In-situ Rat Skeletal Muscle Preparation Under Free Loaded and After Loaded Condition

Purpose of the study: The effect of free loaded and after loaded condition in mammalian skeletal musclecontraction can be studied using an in-situ nerve-muscle preparation in rat. The experimental setup mimicsthe physiological conditions very closely unlike the classical in vitro frog nerve-muscle preparation andhence could be considered as an effective practical module to demonstrate the work done in a skeletalmuscle in both free loaded and after loaded condition.Methodology: A simple, feasible and novel practical is designed in which muscle twitch is recorded in anin-situ nerve-muscle preparation of an anaesthetized rat under free loaded and after loaded condition atdifferent weights using an isotonic transducer. Work done was calculated under free loaded and after loadedcondition and compared.Main finding: Difference was observed with respect to displacement and work done during free loaded andafter loaded condition. Work done was higher in free loaded condition.Conclusion: We propose a simple and novel practical to demonstrate the effect of free loaded and afterloaded condition in muscle twitch for undergraduate teaching in physiology.

Demonstration of Nerve Muscle Preparation in Rats: For Nerve-Muscle Physiology Teaching

Purpose of the study: Physiology practical complement learning of concepts taught in didactic theorylectures. Therefore, they are instrumental to comprehensive learning. Learning of physiology of excitabletissues is supplemented by observing the same phenomena in action in the laboratory. We developed anin-situ rat nerve-muscle model to demonstrate nerve-muscle physiology phenomenon to undergraduate andpostgraduate students. This mimics the physiological conditions unlike the Rana tigrina experiments whichwere done earlier. Further, frequent unavailability of frogs envisaged us to find an alternative for demonstrationof these concepts.Materials and methods: We developed and standardized an in-situ rat soleus muscle-sciatic nerve modelto demonstrate the phenomenon of nerve-muscle properties like simple muscle twitch, effect of strength ofstimulus, effect of two successive stimuli and tetanus to the undergraduate and postgraduate students atour institute.Results: Simple muscle twitch was recorded and effect of increasing strength of stimuli was observed.Thereafter, effect of two successive stimuli and genesis of tetanus was recorded in the same experimentalset up. We successfully standardised this in-situ model for teaching nerve and muscle physiology to our students.Conclusion: We propose an easy and effective experimental rat in-situ model for nerve-muscle physiologyteaching to students

Slower Rise of Exhaled Breath Temperature in Cystic Fibrosis.

Objective: To measure exhaled breath temperature in patients with cystic fibrosis. Methods: 17 patients (6-18 years) with cystic fibrosis and 15 age- and gender-matched healthy controls were recruited in this cross sectional study. Exhaled breath temperature was measured in subjects recruited in both the groups with a device X-halo and analyzed as plateau temperature achieved and rate of temperature rise. Results: Patients with cystic fibrosis showed no significant difference in plateau temperature [34.4(32.3-34.6) versus 33.9 (33.0- 34.4)oC; P=0.35] while mean (SEM.) rate of temperature rise was significantly less in patients [0.09 (0.01) versus 0.14 (0.02) ΔºC/s ; P=0.04] as compared to controls. Conclusion: There was a slower rise of exhaled breath temperature in patients with cystic fibrosis whereas plateau temperature was not significantly different from controls.