The effects of Bumetanide treatment on the function of bidirectional relay pathways after SCI

Spinal cord injuries (SCI) impair neurons within the spinal cord, disrupting the bidirectional communication and resulting in functional loss for patients with SCI. Research has indicated that the activation of surviving spinal interneurons can restore connections and enable voluntary functional recovery1–3, including SCI patients4–8. However, current strategies for manipulating spinal interneurons, such as epidural stimulation9,10, axon regenerations11,12 and stem cell transplantations13, are intricate and challenging to implement for a broad group of SCI patients. As such, there is an urgent need for financially accessible that are also technically straightforward to administer to a larger patient demographic. In this context, pharmacological treatment emerges as an attractive option. In our prior work, we discovered that the K-Cl Cotransporter 2 (KCC2) agonist, a compound CLP290, significantly promoted locomotor recovery in mice with double lateral hemisection SCI14. Mechanistically, CLP290 treatment is proposed to mitigate the pathological effects of SCI-induced KCC2 downregulation, reducing maladaptive Cl-accumulation in neurons. This facilitates the reactivation of spinal interneurons and spinal relay circuits, thereby enhancing the cortical descending inputs to lumbar spinal cord segments below the injury. These pivotal discoveries suggested that a single compound treatment could substantially improve voluntary functional recovery in severe SCI conditions, presenting a potential therapeutic avenue for SCI patients. Nonetheless, as a relatively new developed compound, CLP290’s recovery scope remains restricted15. While the therapeutic potential of KCC2’s activator is still being explored, the Na+ K+ Cl- Cotransporter 1 (NKCC1) inhibitor, bumetanide is already an FDA-approved diuretic. Both KCC2 and NKCC1 are part of the Cation Chloride Cotransporters (CCCs) family but perform opposite functions: KCC2 extrudes Cl- ions from neurons, while NKCC1 imports them16. Consequently, both bumetanide and CLP290 act to decrease intracellular Cl- concentration in neurons and share therapeutic mechanism to treat SCI. Our preliminary results suggest thatdirect intrathecal delivery of bumetanide to the spinal cord can replicate the therapeutic effects of CLP290 in SCI mice. By exploiting the well-established bidirectional correlation between the activity of neurons in the pontine micturition center (PMC) and bladder contractions17,18, we aim to investigate whether the functional recovery induced by bumetanide is due to improved bidirectional relay pathways in a contusive SCI mouse model.