Running exercise attenuates excitatory synaptic loss in the medial prefrontal cortex of CUS rats: Potential modulation of microglial and astrocytic synaptic contacts.

Reduction of excitatory synapses in the medial prefrontal cortex (mPFC) is closely associated with depression and can be mitigated by running exercise. However, precise quantitative studies focusing on subregion-specific excitatory synaptic changes under depression remain limited, and the potential involvement of microglia and astrocytes in exercise-mediated synaptic protection remains unclear. In this study, Sprague-Dawley (SD) rats were subjected to chronic unpredictable stress (CUS) followed by a 6-week treadmill running program. Behavioral assessments included the sucrose preference test and the elevated plus maze test. Nissl staining, immunogold staining, and stereological methods were employed to evaluate the volume of mPFC subregions and the number of dendritic spines in each subregion. Immunofluorescence combined with three-dimensional confocal imaging was used to evaluate microglial and astrocytic density, morphology, and synaptic contacts. Our results demonstrated that running exercise exerted significant antidepressant effects in CUS rats, as evidenced by improved anhedonia-related behaviors. Concurrently, running exercise increased the volume of the mPFC in CUS model rats, particularly in the anterior cingulate cortex (ACC) subregion, and restored the number of dendritic spines across all mPFC subregions. Additionally, running exercise reversed the CUS-induced alterations in microglial and astrocytic morphology and reduced excitatory synapse contacts on glial cells in a subregion-specific manner in the mPFC. These findings provide novel morphological evidence that running exercise protects excitatory synapses in the mPFC, potentially via modulation of glial-synapse interactions, offering insights into the cellular mechanisms underlying exercise-based antidepressant effects.