Melatonin attenuates neuronal apoptosis through up‐regulation of K + – C l − cotransporter KCC 2 expression following traumatic brain injury in rats

Traumatic brain injury ( TBI ) initiates a complex cascade of neurochemical and signaling changes that leads to neuronal apoptosis, which contributes to poor outcomes for patients with TBI . The neuron‐specific K + – C l − cotransporter‐2 ( KCC 2), the principal C l − extruder in adult neurons, plays an important role in C l − homeostasis and neuronal function. This present study was designed to investigate the expression pattern of KCC 2 following TBI and to evaluate whether or not melatonin is able to prevent neuronal apoptosis by modulating KCC 2 expression in a S prague D awley rat controlled cortical impact model of TBI . The time course study showed decreased m RNA and protein expression of KCC 2 in the ipsilateral peri‐core parietal cortex after TBI . Double immunofluorescence staining demonstrated that KCC 2 is located in the plasma membrane of neurons. In addition, melatonin (10 mg/kg) was injected intraperitoneally at 5 minutes and repeated at 1, 2, 3, and 4 hours after brain trauma, and brain samples were extracted 24 hours after TBI . Compared to the vehicle group, melatonin treatment altered the down‐regulation of KCC 2 expression in both m RNA and protein levels after TBI . Also, melatonin treatment increased the protein levels of brain‐derived neurotrophic factor ( BDNF ) and phosphorylated extracellular signal‐regulated kinase (p‐ ERK ). Simultaneously, melatonin administration ameliorated cortical neuronal apoptosis, reduced brain edema, and attenuated neurological deficits after TBI . In conclusion, our findings suggested that melatonin restores KCC 2 expression, inhibits neuronal apoptosis and attenuates secondary brain injury after TBI , partially through activation of BDNF / ERK pathway.