The Effect of Long-Term Exercise on Neurotransmission

Abstract

Aerobic exercise is recognized for its many benefits to the cardiorespiratory system, as well as the brain. For this reason, aerobic exercise has been extensively investigated over the last decade to understand the mechanisms involved in its beneficial effects. However, the model of fitness-related neural plasticity remains incomplete. Purpose: The primary goal of this thesis was to investigate the effect of long-term aerobic exercise, in the form of cardiorespiratory fitness, on neurotransmission. In order to achieve this goal, methodological validation was required. The secondary goal was to investigate commonly assessed structural changes associated with exercise, to compare with previous literature. Materials and Methods: The first experiment involved phantom and human validation of measures of the neurotransmitter g-aminobutyric acid (GABA) using magnetic resonance spectroscopy (MRS). Following this objective, the second experiments recruited a total of thirty-five healthy post-menopausal women to investigate the effect of fitness on neurophysiological and structural measures. Transcranial magnetic stimulation (TMS) and MRS were used to evaluate GABA and glutamate (Glu) concentrations and receptor function in the primary motor cortex (M1). Magnetic resonance imaging (MRI) was used to assess cortical thickness (CT) and the microstructure of white matter (WM) tracts. Results: Regression analysis found that fitness improved the microstructure in pre-motor and sensory tracts, as well as the hippocampal cingulum in post-menopausal women. There was no effect of fitness on CT nor neurotransmission. This suggests cardiorespiratory fitness may preserve motor control and tactile acuity, as well as memory in post-menopausal women via improvements in WM microstructure. Conclusion: The results provided in this thesis can improve our understanding of how aerobic exercise and cardiorespiratory fitness achieve their benefits in order to create efficient training programs to prevent agerelated decline and improve prognosis of age-related disease.