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

The present study examined the regional localization of: corticotropin-releasing factor (CRF)- and 5-hydroxytryptamine (5-HT)-immunoreactive (IR) fibers within the rat dorsal raphe nucleus (DRN) using immunohistochemistry. Additionally, 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 DRN neurons were quantified using in vivo single unit recording in halothane-anesthetized rats. CRF-IR fibers were present nf all rostrocaudal levels of the DRN and exhibited a topographical distribution. CRF produced predominantly inhibitory effects on DRN discharge at lower doses and these effects diminished or became excitatory; at higher doses. Inhibition of DRN discharge by CRF was attenuated by the nonselective CRF antagonist, DPheCRF(12-41) and the CRF-R1-selective antagonist, antalarmin, implicating the CRF-R1 receptor subtype in these electrophysiological nl effects. The present findings provide anatomical and physiological evidence for an impact of CRF on the DRN-5HT system. Published by Elsevier Science Inc.