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Characterization of Tritiated Noradrenaline Release from the Rat Preoptic Area with Microdialysis In Vivo
Author(s) -
FernándezGalaz Carmen,
Herbison Allan E.,
Dyer Richard G.
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.tb13407.x
Subject(s) - microdialysis , in vivo , tritiated water , chemistry , preoptic area , endocrinology , central nervous system , biology , tritium , microbiology and biotechnology , physics , nuclear physics
Present techniques are unable to provide a sensitive and accurate index of noradrenergic activity in the rat preoptic area. In this study, we have examined the brainstem A 1 noradrenergic input to the preoptic area using a new technique whereby [ 3 H]noradrenaline is preloaded into the preoptic area and release of radioactivity from this region is measured subsequently using microdialysis in vivo. Electrical stimulation of the ipsilateral A 1 area for 20 min at 5, 10, and 15 Hz evoked significant increases in dialysate radioactivity that were repeatable and frequency‐dependent. After removal of calcium from the perfusion medium, basal release of radioactivity was markedly reduced and the effect of A 1 stimulation abolished. Changing to a 100 m M K + medium evoked an increase in the release of radioactivity that was sixfold greater than that seen after A 1 stimulation. Separation of the dialysate with HPLC showed that 33% of the increase in measured radioactivity after A 1 stimulation was directly attributable to [ 3 H]noradrenaline and the remainder to the metabolites vanillylmandelic acid, 3,4‐dihydroxymandelic acid, and 3,4‐dihydroxyphenylglycol. In contrast, the increase in radioactivity after K + depolarization was due almost completely to [ 3 H]noradrenaline. Addition of 10 μ M clonidine to the perfusion medium markedly reduced basal release of radioactivity, but had no effect on evoked release following A 1 stimulation. Conversely, perfusion with 10 μ M yohimbine had no effect on basal release, but significantly increased evoked release after A 1 stimulation. These results now provide a characterization of noradrenergic activity in the preoptic area and indicate the importance of the A 1 noradrenergic input to this region. The technique of measuring radioactivity with microdialysis after preloading with [ 3 H]noradrenaline provides a relatively simple, sensitive index of noradrenergic activity in vivo with good temporal resolution.