The connection between muscle and nerve is a biological mechanism severely impaired in many pathological conditions, as aging and Amyotrophic Lateral Sclerosis (ALS). Investigating the functionality of neuron conduction and muscle contraction is crucial in all those diseases where neuromuscular junction (NMJ) is altered. The NMJ fatigue is most often studied on neuromuscular disease animal models as a response to repeated stimulations in isometric conditions, comparing muscle contractile response elicited by two electrical stimulations, one on muscle membrane (direct) and the other through the nerve (indirect). However, the condition that better reflects body movements is the isotonic one. To date, in the literature, the isotonic fatigue test is only performed by repeatedly stimulating the muscle to lift a load equal to one-third of its maximal force (optimal force), a value proposed as the best representative of the force at which the tissue develops its maximum power. In view of this, the aim of this project is to devise a new experimental technique for NMJ functionality characterization during isotonic fatigue. Moreover, a software will be developed in LabVIEW 2019 to provide a real-time measurement of the maximum power the muscle is able to generate, both directly and indirectly, aiming at fatiguing the muscle at its own exact optimal force. Indeed, the experimental value of the optimal force will be applied as a constant load during the isotonic fatigue test. Finally, the isotonic fatigue protocol will be employed to test mouse models of Amyotrophic Lateral Sclerosis (SOD1G93A) at different stages of the disease progression, thus evaluating the impaired communication between muscle and nerve in a condition which better mimics the fatigue occurring in-vivo during muscle dynamic activity.
Investigating the functional path between neuron conduction and muscle contraction is crucial in all those diseases where neuromuscular junction (NMJ) is severely compromised. Despite the heterogeneity of neuromuscular diseases, it is fundamental to determine whether the alterations are due to changes either in muscles functionality or in neuromuscular transmission, in order to develop efficient therapeutic strategies. Coupling alterations between muscle and nerve have been widely investigated on different neuromuscular disease animal models during isometric fatigue. However, the experimental model of muscle fatigue should be extended to isotonic contractions, in order to better mimic body movements. Since in the literature coupling alterations in neurotransmission signalling have never been investigated in isotonic conditions, we will develop a new experimental technique to characterize NMJ functionality during isotonic fatigue.
The proposed research project will be innovative for the following reasons:
- the results of this research will provide new insights on the physiopathologic interplay between muscle and nerve in ALS mouse models (SOD1G93A) in a situation that best mimics the fatigue occurring in-vivo during muscle activity.
- the real-time measurement of muscle maximum power, and therefore the evaluation of the real optimal force, will allow testing the muscle in the exact condition in which it is able to generate the maximum power.
Moreover, it has to be remarked that the testing technique here proposed to study NMJ functionality in SOD1G93A mice will represent a general model which could be therefore applied to all those models in which impairments in the communication between muscle and nerve are expected. In view of this, it is expected that the proposed study will have a direct impact on the field of neuromuscular junction functionality and will contribute to highlight fundamental issues related to the coupling alterations between muscle and nerve in neuromuscular diseases.