Sympathetic innervation and endogenous catecholamines in neuromuscular preparations of muscles of different functional profiles

Abstract

Influence of the sympathetic nervous system on the work of skeletal muscles contractile apparatus is now beyond doubt. However, until recently there was no evidence that the endings of sympathetic nerves can be located in close proximity to the neuromuscular synapses, and there is also no reliable data on how much endogenous adrenaline and noradrenaline can be contained near the synaptic contact in skeletal muscles. In this research, using fluorescent analysis, immunohistochemical and enzyme immunoassays the isolated neuromuscular preparations of three skeletal muscles of different functional profiles and containing different types of muscle fibers were examined. Close contact between the sympathetic and motor cholinergic nerve endings and the presence of tyrosine hydroxylase in this area were demonstrated. Concentrations of endogenous adrenaline and noradrenaline in the solution perfusing the neuromuscular preparation were determined under different modes of its functioning. The effects of α and β adrenoreceptor blockers on the processes of acetylcholine quantal secretion from the motor nerve endings were compared. The data obtained provide evidence for the presence of endogenous catecholamines in the neuromuscular junction region and their role in the modulation of the synaptic function.