Asymmetric neuroplasticity in stellate ganglia: Unveiling side-specific adaptations to aerobic exercise

The stellate ganglia (SG) are a cluster of sympathetic nerve cells situated in the neck, positioned ventrally to the longus colli muscle and play a vital role in regulating cardiovascular function, especially by modulating cardiac sympathetic nerve activity. While the cardiovascular effects of exercise have been extensively studied, little is known about how physical activity influences the three-dimensional structure of SG neurons. Previous research in Wistar rats demonstrated that aerobic exercise training affects cardiovascular physiology, notably by decreasing heart rate without altering arterial pressures. Remarkably, hypertrophy of SG neurons was observed, suggesting a potential overload-induced adaptation. However, whether these structural changes exhibit side-specific patterns remain unclear. To address this gap, we investigated the effects of moderate-intensity aerobic exercise on SG structure with a focus on body-side asymmetry. Using advanced 3D image analysis and stereological methods, we quantified total neuron count, mean neuronal volume, and overall SG volume in four experimental groups: (1) untrained left SG, (2) trained left SG, (3) untrained right SG, and (4) trained right SG. After 10 weeks of treadmill exercise, trained animals displayed a fourfold increase in neuron count in the right SG compared to the left, an asymmetry absent in untrained animals. Additionally, exercise produced divergent effects on neuronal size: right-side neurons underwent atrophy (1.2-fold decrease), whereas left-side neurons exhibited hypertrophy (1.8-fold increase). In trained animals SG volume was reduced by 1.04- (left SG) or 1.4-fold (right SG) depending on the body side considered. These findings reveal a complex, side-specific neuroplastic response of the autonomic nervous system to physical exercise. The observed asymmetric changes in neuron count, size, and ganglia volume challenge traditional views on exercise-induced neuroplasticity, suggesting a more nuanced and functionally relevant adaptation. This study advances our understanding of autonomic nervous system plasticity in response to exercise and encourages further research into side-specific adaptations, with potential implications for targeted interventions in autonomic disorders, including those impacting cardiovascular function.