title: Tyrosine availability modulates potassium-induced striatal catecholamine efflux in vivo.
abstract: The relationship between tyrosine availability and high potassium (K+) induced dopamine (DA) and norepinephrine (NE) efflux was examined in striatum using in vivo microdialysis. High K+ (80 mM) was included in perfusate for two 30 min periods, 2.5 h apart. After the first high-K+ perfusion, a tyrosine- and phenylalanine-free mixture of large neutral amino acids (LNAA(-)) was administered (IP) to lower brain tyrosine. Tyrosine (0, 25, 50 or 100 mg/kg IP) was administered 30 min prior to the second high-K+ perfusion. The ratio of catecholamine efflux during the two perfusions (P2/P1) was compared between groups. LNAA(-) significantly lowered P2/P1 for both DA and NE. Tyrosine 25-50 mg/kg blocked the LNAA(-) effect. We conclude that catecholamine efflux during prolonged depolarization is tyrosine dependent. Analyses of LNAA levels suggest that availability of tyrosine for tyrosine hydroxylation may be modulated by competition between LNAAs within brain extracellular fluid.
authors.affiliation: Psychiatry Service, Louis Stokes Cleveland Veterans Affairs Medical Center, USA. gxj5@case.edu
authors.forename: George E
authors.initials: GE
authors.lastname: Jaskiw
authors.forename: Erica
authors.initials: E
authors.lastname: Newbould
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Bongiovanni
mesh_terms: D000596:Amino Acids / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002395:Catecholamines / Q000096:biosynthesis* / Q000378:metabolism; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism*; D004298:Dopamine / Q000096:biosynthesis / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D045604:Extracellular Fluid / Q000187:drug effects / Q000378:metabolism; D008297:Male; D009638:Norepinephrine / Q000096:biosynthesis / Q000378:metabolism; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism* / Q000494:pharmacology; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
chemical_list: D000596:Amino Acids; D002395:Catecholamines; D014443:Tyrosine; D014446:Tyrosine 3-Monooxygenase; D011188:Potassium; D004298:Dopamine; D009638:Norepinephrine