ACTIVATION OF 5-HT1A RECEPTORS POTENTIATES THE CLONIDINE INHIBITORY EFFECT IN THE LOCUS-COERULEUS

Using in vivo extracellular recordings, we have examined the effect of the application of the prototypical 5-HT1A receptor agonist 8-hydroxy -2-(di-n-propylamino)-tetralin (8-OH-DPAT), on the firing rate of locu s coeruleus neurons. 8-OH-DPAT(1 mu g/kg, i.v.) did not modify the bas al activity of the locus coeruleus but shifted to the left the dose-re sponse curve for the clonidine induced inhibition of firing rate and r educed the corresponding ED50 by 77%. l]ethyl]-4,4-dimethyl-1,3(2H,4H) -isoquinolinedione (ARC 239; 75 mu g/kg, i.v.), and chlorpromazine (75 mu g/kg, i.v.) also shifted to the left the dose-response curve for c lonidine and reduced by 38 and 46%, respectively, the ED50, while slig htly increasing the basal firing rats. The results indicated that 5-HT 1A receptors may modulate the responses mediated by alpha(2A)-adrenoce ptors in the locus coeruleus. (C) 1997 Elsevier Science B.V.