The Neuroprotection of Kappa Opioid Receptor Agonist BRL52537 is Partly Through Enhancing Endogenous GABA Function

Objective: We previously demonstrated that pretreatment with selective κ-opioid agonist BRL52537 hydrochloride [(κ)-1-(3,4-dichlorophenyl) acetyl-2-(1-pyrrolidinyl) methylpiperidine] provides ischemic neuroprotection following transient focal ischemia in rats. The present study was undertaken to determine whether the neuroprotection of BRL52537 attenuates ischemia-evoked efflux of GABA in the striatum in vivo following transient focal ischemia. Materials and Methods: Using the intraluminal filament technique, halothane-anesthetized male Wistar rats (n = 20) were subjected to 2 hours of middle cerebral artery occlusion (MCAO). In a blinded, randomized fashion, rats were treated with saline (vehicle) or 1 mg/kg/hr BRL52537 started 30 minutes before MCAO and continued at 0.5 mL/hr until the 22^nd hour of reperfusion. We also utilized in vivo microdialysis to measure extracellular levels of amino acids including glutamate and GABA in the striatum during the 2 hours of MCAO and 3 hours of reperfusion. Data are presented as mean ± standard error of the mean. Statistical analysis was performed using the unpaired Student's t test. Results: Infarct volume of 26.2 ± 3.6% in the cortex and 42.9 ± 4.2% in the striatum were significantly attenuated in the BRL52537 group when compared with the control subjects (42.8 ± 5.7% in cortex; 74.0 ± 3.7% in striatum). Pretreatment with BRL52537 significantly increased microdialysate levels of GABA in the striatum during MCAO and early reperfusion, when compared with the control subjects. However, other amino acids did not show significant changes. Conclusion: The data demonstrated that BRL52537 provided robust ischemic neuroprotection with altering ischemia-evoked efflux of GABA in the striatum during ischemia and early reperfusion.