Catecholamine metabolism in the rat locus coeruleus as studied by in vivo differential pulse voltammetry. II. Pharmacological and behavioral study.

Differential pulse voltammetry used in combination with electrochemically treated carbon fiber electrodes allowed us to detect catechols in the locus coeruleus (LC) of conscious freely moving rats. A micromanipulator cemented on the rat skull was designed in order to implant carbon fiber electrodes without anesthesia. Voltammograms were recorded every 2 min for 5 h. After the in vivo experiments electrodes were tested in 3,4-dihydroxyphenylacetic acid (DOPAC), 3,4-dihydroxyphenylglycol (DOPEG) and noradrenaline (NA) solutions. The catechol peak recorded from LC was suppressed by pargyline treatment and slightly reappeared after inhibition of the NA reuptake by desipramine (DMI). This reappearing signal was attributed to NA and estimated at a concentration 50 nM NA. Various drug treatments (piperoxane, haloperidol, clonidine, DMI and reserpine) allowed us to further support the conclusion of part I of this study: the catechol peak recorded from LC is mainly due to DOPAC synthesized by LC noradrenergic neurons. This DOPAC signal corresponded to a DOPAC concentration which reached 23 microM when the whole active part of the electrode was implanted in the LC. In addition to this pharmacological study, data from stress experiments pointed out a striking parallel between the variations of the DOPAC signal and those of the activity of LC noradrenergic neurons as revealed by reported electrophysiological studies.