Fast Capillary Electrophoresis for the Study of Dopamine in the Central Nervous System.

Abstract

The study of neurochemical events in the central nervous system (CNS) with temporal resolution ranging from seconds to minutes facilitates the evaluation of intercellular communication on times scales that are relevant to behavior. This dissertation demonstrates the use of capillary electrophoresis (CE) with ≤ 100 s temporal resolution to explore how the anorexigenic, adipose-derived hormone leptin modulates the dopaminergic reward system and to develop a faster method for in vivo calibration of a microdialysis probe. Previous results have shown that leptin promotes dopamine (DA) synthesis in genetic knock-out models of obesity. We show that 4 hr of systemic leptin treatment in normal animals enhances amphetamine-stimulated DA efflux and activates tyrosine hydroxylase and the DA transporter in the nucleus accumbens. Leptin did not alter the basal DA concentration. These data suggested that leptin causes a balanced activation of the mesolimbic DA system. This hypothesis was supported by the observation that leptin enhances cocaine-stimulated DA. That leptin enhances DA exocytosis and uptake while leaving basal extracellular DA unaffected may indicate that leptin preferentially promotes wired phasic DA transmission over volume transmission. Leptin may affect satiety by reducing the length of phasic DA exocytosis and therefore facilitating less reward of feeding. Previously, quantitative microdialysis of neurotransmitters has required some combination of very long experiments, between-animals experimental design, or dilution of dialysate. Rapid no net flux (rNNF) was developed to complete an in vivo calibration of DA in 24-36 min in one animal with no dilution. NNF calibrations using only 6 min of data for each concentration of DA accurately reproduced calibrations generated from longer analysis times and permitted sequential, replicate, within-animal calibrations. Nomifensine caused a decrease in slope of the calibration which was comparable to the published effects of dopamine uptake inhibition during NNF. rNNF permits fast, quantitative measurement of DA and could be paired with other experimental treatments. These experiments show the utility of CE-LIF for neuroscience applications and method development.