BRAIN AMINES--REGULATION AND FUNCTION

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The main objectives of this project are to: (1) examine formation, release, metabolism and disposition of brain biogenic amines and their alterations after administration of drugs or toxin-induced models of human disease; (2) determine the physiologic role of biogenic amines in mediating responses to stress; and (3) develop methods that can be adapted to study of brain biogenic amine metabolism in humans. In vivo microdialysis has been used to monitor levels of monoamines and their metabolites in extracellular fluid in various regions of the hypothalamus and in the basal ganglia. Receptors and transporters have been examined in vitro using cells from different regions of brain: in cell lines cultured from the hypothalamus; and in the gastrointestinal tract before and after immobilization (IMO) stress. During IMO, release of NE into th extracellular fluid (ECF) in regions of the hypothalamus and the amygdala is increased markedly. After repeated intervals of IMO, indices of NE synthesis and turnover that were not correlated with basal transmitter release in several areas. Yohimbine, an alpha2-adrenoceptor antagonist, enhances release of NE, presumably by blocking presynaptic inhibition of release. This effect appears to be augmented in juvenile spontaneously hypertensive rats and to be attenuated after chronic cortisol treatment. Inhibition of MAO-B, but not MAO-A, gradually elevates ECF level of NE over a time interval of days, consistent with the gradual appearance of clinical efficacy of MAO inhibitors. Inhibition of MAO-A enhances the L-dopa-induced elevation of levels of dopamine in the ECF of the striatum. Using a new method for introducing agents directly into the region of the tip of a microdialysis probe, glycine was shown to stimulate release of dopamine from the striatum in a dose-dependent, strychnine-sensitive manner. In hypothalamic neurons, in culture and in vivo, there appears to be a novel desipramine-sensitive NE transporter which may be responsible for inactivation of the catecholamine. Microdialysis studies will be expanded to include amino acid and peptide neurotransmitters, additional stressors and hormones will be examined and molecular biology techniques will be applied to pursue the role of altered central catecholaminergic function in stress, during the development of hypertension in the SHR rat, and to characterize novel NE transporters.