Comprehensive exercise reduces traumatic brain injury deficits via improving the neural network function of hippocampal CA1 and medial entorhinal cortex.

Abstract

The present study aimed to investigate the alterations in functional interaction between hippocampal CA1 and medial entorhinal cortex (MEC) after moderate traumatic brain injury (TBI) in C57BL/6J mice, and the possible beneficial effects of comprehensive exercise (CE). Following TBI, two microelectrodes were implanted into CA1 and MEC for extracellular recording. We found a clear synchronization of neuronal firing in CA1 and MEC, particularly within 100 Hz and peaked at 20-30 Hz range. TBI induced a significant reduction (P < 0.001) of the coherences of firing between 20-40 Hz frequency band. The mean power spectral densities (PSD) of all group mice in MEC were steadily larger than the values in CA1 in both 20-40 Hz and 56-100 Hz ranges. TBI induced significant and consistent increases of averaged 20-40 Hz or 56-100 Hz PSD (P < 0.001 or P < 0.01) in both CA1 and MEC. Injured mice displayed more varied firing patterns, and showed increased burst frequency (BF), burst duration (BD), inter-spike intervals (ISI) and inter-burst interval (IBI). Injured mice also showed worsened neurological function, sleep, gait performance, and working memory. CE facilitated the restoration of aforementioned electrophysiological characteristics and functional deficits in TBI mice. These results suggest that the beneficial effects of CE on TBI functional deficits may be partly attributed to improved neuronal network interaction between CA1 and MEC.