Modulation of glutamatergic signaling after proximal axotomy: glial response and neuroprotective potential

Abstract

Peripheral nerve injuries are responsible for significant costs to the healthcare system and a considerable decrease in the quality of life of affected individuals. Proximal spinal root injuries are known to be particularly severe, resulting in up to 50% neuronal degeneration in cases of ventral root crush (VRC). Among the retrograde responses within the spinal cord, resident microglia and astrocytes respond through morphofunctional changes. This process triggers changes in glutamatergic signaling, primarily mediated by AMPA-type receptors (AMPAr), which play a critical role in the development and function of glial cells in response to neuronal circuit activity. However, excessive activation of AMPAr can inadvertently induce excitotoxic injury through the excessive concentrations of glutamate, which can trigger pathophysiological responses that threaten all resident cell types and amplify ongoing disease processes. Furthermore, the identification of therapeutic approaches capable of protecting the glial cells functions and viability under excitotoxic conditions represents a critical target for future research. Among the therapeutic possibilities, the use of sulbactam is emerging, as a drug that has shown promising neuroprotective results, mainly related to the control and mediation of glutamate concentration in the nervous system's microenvironment. Therefore, this project aims to chronologically study glutamatergic signaling and reinnervation after VRC, focusing on the role of glial cells in the inflammatory response and excitotoxicity, neuronal survival, motor function, and muscle reinnervation, and to comparatively investigate the neuroprotective role of sulbactam in this context. For this, adult C56BL/6JUnib female mice will be used and the spatiotemporal and morphological dynamics of glial cell activation and its relationship to the process of motoneuron death will be evaluated by immunohistochemical analysis and Nissl staining in the spinal cord on days 1, 3, 7, 14, and 28 after injury. Moreover, neuromuscular analyses will be performed to evaluate the regenerative histological profile of the muscle, nerve, and neuromuscular junctions affected by VRC. These analyses will be complemented by functional gait analysis using the Catwalk system and reinnervation capacity by electrophysiological evaluation. The inflammatory profile of the spinal cord will also be characterized by flow cytometry. This study will contribute to a better understanding of the underlying mechanisms of the glial cell response to glutamatergic signaling after VRC, with potential implications for the development of innovative therapeutic strategies.