Cervical Spinal Contusion Injury Alters Membrane Expression of NKCC1 and KCC2 in Phrenic Motor Neurons: Impact of Repetitive Acute Intermittent Hypoxia

Spinal cord injury is associated with respiratory muscle paralysis and spasticity. In normal spinal cords, chloride‐dependent synaptic inhibition plays a key role in sculpting and coordinating breathing; membrane chloride co‐transporters establish chloride gradients necessary for effective chloride‐dependent synaptic inhibition in neurons, including competing influences from NKCC1 and KCC2. Since complete spinal transection disrupts NKCC1/KCC2 balance, we tested the hypothesis that less‐severe cervical spinal contusion injuries would similarly disrupt NKCC1/KCC2 balance in the phrenic motor nucleus, a key region for respiratory motor control. Further, since many kinases regulating NKCC1 and KCC2 membrane expression are necessary for repetitive acute intermittent hypoxia (rAIH) mediated phrenic motor functional recovery, we tested the hypothesis that rAIH normalizes membrane expression of NKCC1 and KCC2 in phrenic motor neurons after cervical contusion injury. Rats with lateral C2 contusions or sham surgeries were exposed to rAIH (5 min hypoxia, 5 min normoxia; 3 days weekly; 4 weeks) or normoxia for an equivalent duration. Preliminary immunofluorescent analyses show: 1) C2 contusions reduce KCC2 membrane expression in phrenic motor neurons; and 2) that rAIH restores these levels towards normal. NKCC1 results were variable, but suggest decreased cytosolic NKCC1 after C2 contusion and restoration by rAIH. A follow‐up study with refined techniques and surgical approach is underway to verify these results. DoD W81XWH‐13‐1‐0410 and NIH HL69064