Cervical spinal contusion alters Na⁺-K⁺-2Cl- and K⁺-Cl- cation-chloride cotransporter expression in phrenic motor neurons.

Spinal chloride-dependent synaptic inhibition is critical in regulating breathing and requires neuronal chloride gradients established by cation-chloride cotransporters Na⁺-K⁺-2Cl^- (NKCC1) and K⁺-Cl^- (KCC2). Spinal transection disrupts NKCC1/KCC2 balance, diminishing chloride gradients in neurons below injury, contributing to spasticity and chronic pain. It is not known if similar disruptions in NKCC1/KCC2 balance occur in respiratory motor neurons after incomplete cervical contusion (C2SC). We hypothesized that C2SC disrupts NKCC1/KCC2 balance in phrenic motor neurons. NKCC1 and KCC2 immunoreactivity was assessed in CtB-positive phrenic motor neurons. Five weeks post-C2SC: 1) neither membrane-bound nor cytosolic NKCC1 expression were significantly changed, although the membrane/cytosolic ratio increased, consistent with net chloride influx; and 2) both membrane and cytosolic KCC2 expression increased, although the membrane/cytosolic ratio decreased, consistent with net chloride efflux. Thus, contrary to our original hypothesis, complex shifts in NKCC1/KCC2 balance occur post-C2SC. The functional significance of these changes remains unclear. Copyright © 2018 Elsevier B.V. All rights reserved.

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