Abstract
This two part study on the afferent connectivity of lumbar spinal motor neurons in normal ageing mice investigates; Study 1: time course analysis of age-related changes in the synaptic coverage of lumbar spinal cords of male C57BL/BJ mice at 4,15,18 and 24 months of age and Study 2: the effect of long term 8-month resistance wheel exercise (RWE) on lumbar spinal cords of male C57BL/6J mice exercised from 15 to 23 months of age. Uniquely, each study used spinal cords obtained from the same mice that had previously been analysed for changes in skeletal muscles and sciatic nerves in a parallel series of time course and exercise studies. Input to presumed alpha motor neurons was investigated by quantifying VGLUT1 immunoreactive synaptic contacts known to be derived from proprioceptive muscle afferents. Here we found no significant changes in the percentage of synaptic VGLUT1 coverage of motor neurons from 4 to 24 months. Importantly, this differs from our previous results (Krishnan et al., Biogerontology 19:385-399, 2018) where there was about 50% decrease in VGLUT1 innervation of motor neurons in older mice aged 27 months, indicating a rapid deterioration in proprioceptive feedback in late ageing. In the exercise study, 8 months of voluntary wheel running (beginning at 15 months), had no impact on VGLUT1 synaptic connectivity in spinal cords, consistent with our previous report of no effect on peripheral nerves obtained from this same ageing and exercised cohort of mice. Nonetheless there was a significant amount of sarcopenia in these animals. Overall, these studies highlight the variable impact of ageing on different motor-related tissues.
