A 5-HYDROXYTRYPTAMINE LESION MARKEDLY REDUCES THE INCIDENCE OF BURST-FIRING DORSAL RAPHE NEURONS IN THE RAT

Recently, we described neurones in the rat dorsal raphe nucleus (DRN) with electrophysiological characteristics typical of 5-hydroxytryptami ne (5-HT) neurones except that the neurones fired brief bursts. Here w e report the effect of 5-HT lesions on the incidence of these burst-fi ring neurones. In vivo extracellular recordings revealed that in rats pretreated with the selective 5-HT neurotoxin, 5,7-dihydroxytryptamine , the occurrence of typical 5-HT neurones was significantly decreased (80%) compared to controls. In these 5-HT lesioned animals, the number of the burst-firing DRN neurones was also significantly reduced (91%) . Neurones previously characterised as not containing 5-HT, were not a ltered by the lesion. These data are further evidence to support our h ypothesis that burst-firing neurones in the DRN contain 5-HT.