Microinjection of urocortin 2 into the dorsal raphe nucleus activates serotonergic neurons and increases extracellular serotonin in the basolateral amygdala

Abstract

The intra dorsal raphe nucleus (DRN) administration of corticotropin releasing hormone (CRF) inhibits serotonergic (5-HT) activity in this structure, an effect blocked by antagonists selective for the type 1 CRF receptor (CRF 1). The DRN has a high density of the type 2 receptor (CRF 2), and so the present experiments explored the impact of CRF 2 activation within the DRN on 5-HT function. The intra-DRN administration of the selective CRF 2 agonist urocortin 2 (Ucn 2) dose dependently increased 5-HT efflux in the basolateral amygdala, a projection region of the DRN. Intra-DRN Ucn 2 also increased c-fos expression in labeled 5-HT neurons. Both of these effects of Ucn 2 were completely blocked by intra-DRN antisauvagine-30 (ASV-30), a relatively selective CRF 2 antagonist. These data suggest that CRF 1 and CRF 2 activation within the DRN affect 5-HT neurons in opponent fashion. Implications of these results for understanding the behavioral effects of CRF and other CRF-like ligands are discussed.