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Microdialysis Monitoring of 3,4‐Dihydroxyphenylalanine Accumulation After Decarboxylase Inhibition: A Means to Estimate In Vivo Changes in Tyrosine Hydroxylase Activity of the Rat Locus Ceruleus
Author(s) -
Robert Frédéric,
LambásSeñas Laura,
Ortemann Catherine,
Pujol JeanFrançois,
Renaud Bernard
Publication year - 1993
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1993.tb03207.x
Subject(s) - locus ceruleus , aromatic l amino acid decarboxylase , tyrosine hydroxylase , dihydroxyphenylalanine , microdialysis , chemistry , tyrosine , locus coeruleus , in vivo , decarboxylase inhibitor , amino acid , perfusion , medicine , endocrinology , tyrosine 3 monooxygenase , enzyme , glutamate decarboxylase , biochemistry , dopamine , extracellular , biology , levodopa , parkinson's disease , central nervous system , substantia nigra , microbiology and biotechnology , dopaminergic , disease
An on‐line microdialysis approach was developed to estimate changes in tyrosine hydroxylase activity in the locus ceruleus noradrenergic neurons of anesthetized rats by measuring the 3,4‐dihydroxyphenylalanine (DOPA) acumulation in the extracellular fluid during perfusion of an aromatic amino acid decarboxylase inhibitor through a dialysis probe. The aromatic amino acid decarboxylase inhibitor used was difluoromethyl‐DOPA, which was shown to be more stable than NSD 1015 or Ro 4‐4602 in the perfusion fluid. A 1‐h perfusion of a 10 −4 mol/L of difluoromethyl‐DOPA solution induced a linear increase in DOPA concentration in the locus ceruleus dialysates that achieved a steady state within 1 h. The identity of DOPA accumulated in dialysates during aromatic amino acid decarboxylase inhibition was confirmed by the disappearance of the chromatographic peak when DOPA formation was blocked by the administration of α‐methyl‐ p ‐tyrosine. Systemic administration of the α 2 ‐antagonist piperoxane before difluoromethyl‐DOPA perfusion markedly increased the DOPA concentration during both the accumulation and the steady‐state periods, showing that the present technique is a suitable in vivo approach to monitor changes in tyrosine hydroxylase activity occurring in the locus ceruleus neurons.