title: Tyrosine depletion lowers in vivo DOPA synthesis in ventral hippocampus.
abstract: In vivo dopamine synthesis in the medial prefrontal cortex of the rat is sensitive to the availability of tyrosine. Whether other limbic cortical dopamine terminal regions are similarly tyrosine-dependent is not known. In this study we examined the effects of tyrosine depletion on dopamine synthesis and catecholamine levels in the ventral hippocampus. A tyrosine- and phenylalanine-free neutral amino acid mixture was used to lower brain tyrosine levels in rats undergoing in vivo microdialysis. In one group, NSD-1015 was included in perfusate to permit measurement of DOPA levels. In a second group, NSD-1015 was not included in perfusate so that catecholamine levels could be assayed. Tyrosine depletion significantly lowered DOPA levels in the NSD-1015 treated group and lowered DOPAC but not dopamine or noradrenaline levels in the group not exposed to NSD-1015. We conclude that while catecholamine synthesis in the ventral hippocampus declines when tyrosine availability is lowered, under basal conditions, compensatory mechanisms are able to maintain stable extracellular catecholamine levels.
authors.affiliation: Psychiatry Service, Louis Stokes Cleveland VA Medical Center, 10701 East Blvd., Cleveland, Ohio 44106, USA. rodolfo.bongiovanni@yahoo.com
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Bongiovanni
authors.forename: Abby N
authors.initials: AN
authors.lastname: Kyser
authors.forename: George E
authors.initials: GE
authors.lastname: Jaskiw
mesh_terms: D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D004295:Dihydroxyphenylalanine / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism*; D006834:Hydrazines / Q000494:pharmacology; D008297:Male; D009638:Norepinephrine / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D014443:Tyrosine / Q000172:deficiency*
chemical_list: D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D006834:Hydrazines; D015102:3,4-Dihydroxyphenylacetic Acid; D014443:Tyrosine; D004295:Dihydroxyphenylalanine; C004297:3-hydroxybenzylhydrazine; D004298:Dopamine; D009638:Norepinephrine