Effects of age on training‐induced adaptations of the neuromuscular junction

Abstract

Unlike skeletal muscle, the effect of aging on training induced adaptations of the neuromuscular junction (NMJ) has received scant attention. This study aimed to determine whether this important synapse exhibits age‐specific adaptations to endurance training. Twenty young adult (8 mo) and 20 aged (24 mo) male Fischer 344 rats were assigned to either exercise trained or sedentary control groups (4 groups, N=10/group). All trained rats participated in the same 10 week program of treadmill running (5days/wk). Following the 10 week intervention, all rats were euthanized and soleus muscles were removed and quickly frozen at resting length. Muscles were sectioned and stained with cytofluorescent procedures to visualize pre‐synaptic nerve terminal branches, and post‐synaptic acetylcholine receptors. Pre‐ and post‐synaptic images were collected with confocal microscopy and used to quantify various parameters of NMJ morphology. Results showed that young, but not aged rats demonstrated significant (P<0.05) training‐induced increases in pre‐synaptic nerve terminal branch number, total branch length, and branching complexity. Similarly, only the NMJs of young rats displayed significant training‐induced increments in perimeter length around endplate regions, and expanded areas occupied by acetylcholine receptors. Our data show that aging blunts the ability of the NMJ to adapt to endurance exercise training.Supported by the National Institute on Aging, and The Foundation for Aging Studies and Exercise Science Research.