Real-Time Monitoring of Changes in Brain Extracellular Sodium and Potassium Concentrations and Intracranial Pressure after Selective Vasopressin-1a Receptor Inhibition following Focal Traumatic Brain Injury in Rats

Brain swelling and increased intracranial pressure (ICP) following traumatic brain injury (TBI) contribute to poor outcome. Vasopressin-1a receptors (V1aR) and aquaporin-4 (AQP4) regulate water transport and brain edema formation, perhaps in part by modulating cation fluxes. After focal TBI, V1aR inhibitors diminish V1aR and AQP4, reduce astrocytic swelling and brain edema. We determined whether V1aR inhibition with SR49059 after lateral controlled-cortical-impact (CCI) injury affects extracellular Na+ and K+ concentrations ([Na+](e); [K+](e)). Ion-selective Na+ and K+ electrodes (ISE) and an ICP probe were implanted in rat parietal cortex, and [Na+](e), [K+](e), and physiological parameters were monitored for 5 h post-CCI. Sham-vehicle-ISE, CCI-vehicle-ISE and CCI-SR49059-ISE groups were studied, and SR49059 was administered 5 min to 5 h post-injury. We found a significant injury-induced decrease in [Na+](e) to 80.1 +/- 15 and 87.9 +/- 7.9 mM and increase in [K+](e) to 20.9 +/- 3.8 and 13.4 +/- 3.4 mM at 5 min post-CCI in CCI-vehicle-ISE and CCI-SR49059-ISE groups, respectively (p < 0.001 vs. baseline; ns between groups). Importantly, [Na+](e) in CCI-SR49059-ISE was reduced 5-20 min post-injury and increased to baseline at 25 min, whereas recovery in CCI-vehicle-ISE required more than 1 hr, suggesting SR49059 accelerated [Na+](e) recovery. In contrast, [K+](e) recovery took 45 min in both groups. Further, ICP was lower in the CCI-SR49059-ISE group. Thus, selective V1aR inhibition allowed faster [Na+](e) recovery and reduced ICP. By augmenting the [Na+](e) recovery rate, SR49059 may reduce trauma-induced ionic imbalance, blunting cellular water influx and edema after TBI. These findings suggest SR49059 and V1aR inhibitors are potential tools for treating cellular edema post-TBI.