In Vivo Microdialysis Study of the Extracellular 3,4‐Dihydroxyphenylacetic Acid in the Rat Locus Ceruleus: Topographical and Pharmacological Aspects

Abstract

In vivo microdialysis coupled with HPLC and electrochemical detection was used to monitor extracellular levels of 3, 4‐dihydroxyphenylacetic acid (DOPAC) of the locus ceruleus (LC) in halothane‐anesthetized rats. The identity of DOPAC was confirmed by experiments showing that the chromatographic peak was totally suppressed after inhibition of monoamine oxidase by pargyline. Histological examinations allowed to relate the quantity of DOPAC measured in the dialysates with the localization of the probe implantation site. We found that the DOPAC concentration was inversely proportional to the distance between the probe and the lateral border of the LC. Regardless of the caudorostral level of the nucleus, concentrations were maximal when the axis of the probe was 100 μM from the lateral border of the LC and decreased by 53% when this distance reached 300 μM. Activation of LC noradrenergic neurons by systemic administration of the α2‐antagonist piperoxane increased by 100% DOPAC concentrations in LC dialysates. These results suggest that the DOPAC measured by microdialysis could be considered an indicator of the functional state of LC noradrenergic neurons.

Food-Induced Increase of Acetylcholine in Mouse Hypothalamus

“…Histology. In a representative proportion of animals (typically one per group), probes were perfused with fast green (50 μM) stain to allow histological verification of the probe placement 35 (Figure S6, Supporting Information). For this purpose, mice were anesthetized with isoflurane and decapitated.…”

Rapid and precise method to locate microdialysis probe implantation in the rodent brain

“…Several methods based on post-mortem standard histological staining (i.e., cresyl violet, formalin fixation) have been described. For a precise location of the dialysis probe, the in vivo perfusion of a dye (fast green or pontamine sky blue) (Ortemann et al, 1993;Ungerstedt, 1991), before brain removal, is necessary. However, these methodologies are time consuming, and thus not compatible with a histological validation prior to analysis of microdialysis samples.…”