title: Kinetic analysis of striatal clearance of exogenous dopamine recorded by chronoamperometry in freely-moving rats.
abstract: Previously, we developed technology that coupled high-speed chronoamperometry with microejections of dopamine (DA) to measure DA clearance in the brains of freely-behaving rats. Here, by varying the ejection volumes of DA across a 200-fold difference, the kinetics of striatal clearance were analyzed as a function of time and DA volume from 289 chronoamperometric signals (n=20 rats). Each DA clearance trace was fitted to a first-order exponential decay function to determine the rate constant for DA clearance (k). Additionally, the apparent Michaelis-Menten V(max) and K(m) kinetic constants were determined in freely-moving rats, enabling quantitative comparison of our values with other models of reuptake. The first-order rate constant for DA clearance, which reflects the V(max)/K(m) ratio or clearance efficiency, did not vary significantly when small volumes of DA were ejected resulting in peak DA signal amplitudes (A(max)) of <5 microM. However, following nomifensine-induced DAT inhibition, A(max) was increased and k was attenuated simultaneously with behavioral activation; and A(max) and behavior remained elevated beyond the initial period. Our results indicate that the analysis of kinetic parameters from chronoamperometric DA signals may be useful for investigating drug-induced regulation of DAT kinetics in relation to the behavior of freely-moving rats.
authors.affiliation: Department of Pharmacology, Neuroscience Program, University of Colorado Health Sciences Center, Box C-236, 4200 East Ninth Avenue, Denver, CO 80262, USA. jilla.sabeti@uchsc.edu
authors.forename: Jilla
authors.initials: J
authors.lastname: Sabeti
authors.forename: Cathy E
authors.initials: CE
authors.lastname: Adams
authors.forename: Jason
authors.initials: J
authors.lastname: Burmeister
authors.forename: Greg A
authors.initials: GA
authors.lastname: Gerhardt
authors.forename: Nancy R
authors.initials: NR
authors.lastname: Zahniser
mesh_terms: D000818:Animals; D003342:Corpus Striatum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004298:Dopamine / Q000032:analysis / Q000493:pharmacokinetics*; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004563:Electrochemistry / Q000379:methods*; D007700:Kinetics; D008297:Male; D008657:Metabolic Clearance Rate; D008845:Microinjections / Q000379:methods; D009043:Motor Activity / Q000187:drug effects; D009627:Nomifensine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D018765:Dopamine Uptake Inhibitors; D009627:Nomifensine; D004298:Dopamine