THE EFFECT OF GENDER ON THE DISTRIBUTION OF UROCORTIN NEURONS IN THE BRAINSTEM

Abstract

Intraventricular (icv) administration of urocortin (ucn), a neuropeptide closely related to the hypothalamic hormone corticotropin-releasing factor, has been shown to elicit transient sympathoexcitatory responses in the male rat. However, the central sites at which ucn exerts these effects and whether gender differences exist in the location and distribution of ucn neurons are not known. In this study, experiments were done in male, and in female ovariectomized (OVX) only and OVX 17β-estradiol (30 pg/ml plasma; OVX+E) treated Wistar rats to investigate the distribution of neurons in the brainstem containing ucn-like immunoreactivity. Six to 9 weeks after OVX or OVX+E, animals were given an icv injection of colchicine 48 hours prior to sacrifice. In all three experimental cases, ucn neurons were identified in the Edinger Westphal nucleus, superior olivary nucleus, and a few scattered neurons were found in the compact formation of the nucleus ambiguus (Ambc). However, in both female groups, ucn neurons were observed within the nucleus tractus solitarius (NTS) and the number of ucn neurons in the Ambc was increased compared to the male. Finally, in the OVX group distinct groups of ucn neurons were also identified in the rostral nucleus paragigantocellularis lateralis, the magnocellular reticular nucleus, and throughout the external formation of Amb. Taken together, these data suggest that the wide distribution of ucn neurons within autonomic brainstem structures in the OVX female may be associated with the greater effects observed on cardiovascular variables during stress. Heart and Stroke Foundation of Ontario