Effects of corticotropin-releasing factor on neuronal activity in the serotonergic dorsal raphe nucleus

The present study examined the regional localization of: corticotropin-rele asing factor (CRF)- and 5-hydroxytryptamine (5-HT)-immunoreactive (IR) fibe rs within the rat dorsal raphe nucleus (DRN) using immunohistochemistry. Ad ditionally, the effects of CRF, administered intracerebroventricularly (0.2 -3.0 mu g) or intraraphe (0.3-30 ng), on discharge rates of putative 5-HT D RN neurons were quantified using in vivo single unit recording in halothane -anesthetized rats. CRF-IR fibers were present nf all rostrocaudal levels o f the DRN and exhibited a topographical distribution. CRF produced predomin antly inhibitory effects on DRN discharge at lower doses and these effects diminished or became excitatory; at higher doses. Inhibition of DRN dischar ge by CRF was attenuated by the nonselective CRF antagonist, DPheCRF(12-41) and the CRF-R1-selective antagonist, antalarmin, implicating the CRF-R1 re ceptor subtype in these electrophysiological nl effects. The present findin gs provide anatomical and physiological evidence for an impact of CRF on th e DRN-5HT system. Published by Elsevier Science Inc.