Variations in 3,4-dihydroxyphenylacetic acid concentration are correlated to single cell firing changes in the rat locus coeruleus.

The purpose of this study is to see whether variations in the catechol oxidation peak in the locus coeruleus would be closely related with variations in single cell firing, and would be independent of the mechanism triggering the variation of neuronal activity. Single unit and electrochemical (differential pulse voltammetry) recordings were performed, respectively on the left and right locus coeruleus of anaesthetized rats. The variations in single unit activity were induced using well known stimulatory mechanisms (yohimbine, hypovolemia, indirect activation using a 5-hydroxytryptamine central agonist RU 24969, RU 24722 known to activate noradrenergic metabolism), or inhibitory (clonidine, morphine) models. This was done in addition to successive activation or inhibition (reversal of oxotremorine with scopolamine, antagonism of clonidine by piperoxane). In all the experimental conditions, variations in the catechol oxidation current followed variations in single cell activity. Furthermore, the catechol oxidation current variations correlated significantly to changes in the firing rate. Such a close correlation between a catechol oxidation peak, and the electrical activity of the locus coeruleus cell bodies supports the use of catechol oxidation current variations as a good indirect index of functional activity in noradrenergic locus coeruleus perikarya. This suggests a close relationship between dopamine metabolism and electrical activity in locus coeruleus cell bodies.