Interaction between catecholaminergic terminals and urocortinergic neurons in the Edinger-Westphal nucleus in the rat.

Central stress regulatory pathways utilize various neurotransmitters/neuropeptides, such as urocortin (Ucn) and catecholamines. Ucn is most abundantly expressed in the Edinger-Westphal nucleus (E-WN), co-distributed with catecholaminergic terminals. Acute stress recruits E-WN neurons, and ascending catecholaminergic pathways also contribute to the activation of various brain areas in response to stress. We hypothesized that catecholamine and Ucn interactions in the E-WN mediated the recruitment of these neurons in response to stress. Using double-labeling immunohistochemistry, we found close appositions between urocortin-immunoreactive nervous structures and dopaminergic terminals, however, depletion of them had no effect on the activation pattern of E-WN neurons upon acute immune challenge. From these results we conclude that dopaminergic terminals innervating E-WN Ucn neurons do not play a major role in mediating the responses of E-WN neurons upon acute immune challenge.