Urocortin 1 administered into the hypothalamic supraoptic nucleus affects open-field behaviour in rats

The presence of both Urocortin 1 (Ucn1) and corticotropin-releasing factor 2 receptors (CRF(2)R) in the hypothalamic supraoptic nucleus (SON) suggests that endogenous Ucn1 released within this brain area acts as a local signal that might be involved in the regulation of not only endocrine but also behavioural stress responses. To test this hypothesis, we monitored the effects induced by the administration of a range of doses of synthetic Ucn1 (0.001-1.0 microg) bilaterally into the SON of rats in the open field test (OFT). Ucn1 administration produced an inverted U-shaped dose-response curve on OFT behaviour, in particular the dose of 0.01 microg of Ucn1 significantly increased the number of rearing and grooming episodes without affecting locomotion. In addition, this dosage augmented also the latency to visit the centre of the open field. Pre-treatment with the CRF(2)R antagonist, astressin-2B (0.1 microg) normalized Ucn1 treatment-induced effects. These results suggest that Ucn1 released within the SON area interacts with CRF(2)R to control the state of arousal.