Hydroxyl Radical Production after Intrastriatal Injection of Dopamine and the Effect of Growth Hormone on the Apoptosis of Striatal Neurons Injured by Hypoxia-ischemia in Newborn Rat Brain

Cho, Jae Ju; Yu, Jeesuk; Jee, Youn Hee; Lee, Soon Bum; Oh, Soo Yeun; Kim, Hyung Gun; Chang, Young Pyo

Abstract

PURPOSE
We investigated the production of oxygen hydroxyl radicals in the striatum of neonatal rat brain after intrastriatal injection of dopamine (DA) and the effect of growth hormone (GH) on the apoptosis of striatal neurons injured by hypoxia-ischemia.
METHODS
The extracellular striatal levels of 2,3-dihydroxybenzoic acid (DHBA) and 2,5-DHBA as indicators of hydroxyl radical(OH-) production were measured by in vivo microdialysis in the striatums of 7 day-old newborn rats (n=10) after direct intrastriatal infusion of dopamine hydrochloride (1.0 micromol/microL). The samples of perfused artificial cerebrospinal fluid (CSF) were collected every 10 minutes interval. The levels of DA, 2,3-DHBA and 2,5-DHBA of CSF were analysed by HPLC (high performance liquid chromatography). Also, the brains were removed at 24 hour after hypoxic-ischemic injury by Rice-Vannucci method. The coronal sections (12 micrometer) of paraffin-fixed brains were stained by TUNEL (terminal transferase-mediated dUTP nick-end-labelling) technique, and the neuronal cells undergoing apoptosis in the striatum were observed by fluorescent microscopy and compared between GH-treated (50 mg/kg, Dong-Ah Pharmacy Co.) and saline-treated rats.
RESULTS
The extracellualr striatal levels of 2,3-DHBA and 2,5-DHBA increased abruptly in the first 10 minutes samples after intrastriatal injection of DA. After then, the levels declined slowely. The levels of striatal extracelluar 2.3-DHBA increased up to 621.8+/-508.7% of basal levels (P<0.05), and the levels of 2.5-DHBA increased up to 262.8+/-198.1% of basal levels (P<0.05). GH reduced markedly the number of apoptotic neuronal cells in the striatum after hypoxic-ischemic brain injury.
CONCLUSION
The level of hydroxyl radicals increased abruptly after intrastriatal injection of DA and GH reduced markedly the number of apoptotic neuronal cells in the striatum after hypoxic-ischemic brain injury.