EFFECTS OF CHRONIC EPISODIC HYPOXIA ON MONOAMINE METABOLISM AND MOTOR-ACTIVITY

Chronic episodic hypoxia produces a wide array of cardiovascular dysfu nctions in rats, including increases in blood pressure, heart rate, an d sympathetic nerve activity. The action of episodic hypoxia might be related to low oxygen itself (hypoxemia) and/or combined with low CO2 (hypocapnia) resulting from hyperventilation. It is unknown whether or not the cardiovascular abnormalities are related to alterations in th e central nervous system (CNS) that may be manifested as neurotransmit ter and/or behavioral changes. In this study, we investigated effects of episodic eucapnic and hypocapnic hypoxia on monoamine metabolism in both CNS and adrenal glands, and on motor behavioral activity. Thirty -five male rats were divided into 3 groups. Experimental rats were exp osed 8 h daily to varying fractional concentrations of inspired oxygen (FiO(2)) and carbon dioxide (FiCO(2)) for 35 days. These consisted of brief exposures (3-6 s) of episodic (twice every min) eucapnic (3.5% FiO(2) and 10% FiCO(2), n = 6) or hypocapnic (3.5% FiO(2) and 0% FiCO( 2), n = 14) hypoxia, or room air (21% FiO(2) and 0.03% FiCO(2), n = 15 ). Norepinephrine, dopamine, serotonin, and their metabolites in the h ypothalamus, hippocampus, and adrenal glands were measured by high-per formance liquid chromatography (HPLC). spontaneous behavioral activity was assessed for 30 min by automated activity monitors. Episodic hypo capnic hypoxia produced a decrease in dopamine turnover and eucapnic h ypoxia increased norepinephrine levels in the hypothalamus. Animals ex posed to hypocapnic hypoxia also exhibited a consistent increase in ho rizontal (walking) and vertical (rearing) activity, as well as in tota l activity time. From these results, it is concluded that episodic euc apnic and hypocapnic hypoxia may affect metabolism of different neurot ransmitters in the CNS.