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In situ examination of tyrosine hydroxylase activity in the rat locus coeruleus using (3′,5′)‐[ 3 H 2 ]‐α‐fluoromethyl‐tyrosine as substrate of the enzyme
Author(s) -
Bezin Laurent,
Marcel Dominique,
Garcia Christine,
Blum David,
Lafargue Pierre,
Lellouche JeanPaul,
Pujol JeanFrançois,
Weissmann Dinah
Publication year - 2000
Publication title -
synapse
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.809
H-Index - 106
eISSN - 1098-2396
pISSN - 0887-4476
DOI - 10.1002/(sici)1098-2396(20000301)35:3<201::aid-syn5>3.0.co;2-v
Subject(s) - tyrosine hydroxylase , locus coeruleus , tyrosine , enzyme assay , chemistry , enzyme , aromatic l amino acid decarboxylase , tyrosine 3 monooxygenase , substrate (aquarium) , stereochemistry , biochemistry , endocrinology , biology , central nervous system , ecology
Tyrosine hydroxylase (TH) activity can be modified by changes in the specific activity of the enzyme (SA TH ) or in the levels of active enzyme. We developed a methodology making it possible to measure with excellent anatomical resolution TH enzymatic activity and TH protein quantity by quantitative autoradiography and immunoautoradiography, respectively, from adjacent sections taken at serial intervals along the longitudinal extent of a same brain. SA TH was estimated by the slope of linear regressions established between TH activity and TH quantity measured at each anatomical plane. To evaluate TH activity, we used (3′,5′)‐[ 3 H 2 ]‐(D, L)‐α‐fluoromethyl‐tyrosine [ 3 H 2 ]‐MFMT, which is transformed by TH to [ 3 H]‐MFM‐dopa, a potent and irreversible substrate for aromatic amino acid decarboxylase. We found that the SA TH in the cell body area of the LC (PKA) was 48% lower than that evaluated in the surrounding pericoerulean neuropil (PCN). In the PCN, 22% only of TH level exhibited a level of enzymatic activity above threshold. We also examined how SA TH was distributed in the LC 15 min and 3 days after RU 24722 treatment, a potent phasic and tonic activator of TH enzyme in noradrenergic neurons. Two distinct mechanisms have been observed: the short‐term effect was due to an increase in the SA TH in the PKA only, while the long‐term effect was mainly caused by an increase in the number of active TH proteins in the PCN. These results suggest that the fine regulation of TH activity which occurs in the different compartments of LC neurons may be critical in the functions involving the LC. Synapse 35:201–211, 2000. © 2000 Wiley‐Liss, Inc.