Urocortin 1 distribution in mouse brain is strain-dependent.

Urocortin 1 has been implicated in a number of specific behaviors, which include energy balance, stress reactivity and ethanol consumption. To elucidate genetically influenced differences in the mouse urocortin 1 system, we performed immunohistochemical characterization of urocortin 1 distribution in C57BL/6J and DBA/2J mouse brain. Urocortin 1 analysis reveals strain-dependent differences in distribution of urocortin 1 immunoreactive neurons and neuronal fibers. In both strains, the highest number of urocortin 1-positive neurons was observed in the Edinger-Westphal nucleus and lateral superior olive. Urocortin 1-positive neurons were detected in the dorsal nucleus of the lateral lemniscus of DBA/2J mice, but were absent in the C57BL/6J strain. Differences in urocortin 1 fibers were detected in many areas throughout the brain, and were most apparent in the septal areas, thalamic areas, several midbrain regions, and medulla. Strain-dependent distribution of urocortin 1-containing cells and fibers suggests that differences in this neuropeptide system may underlie differences in behavior and physiological responses between these strains. Further, we found that in both mouse strains, urocortin 1 in the Edinger-Westphal nucleus and choline acetyltransferase are not coexpressed. We show that the urocortin 1-positive neurons of this brain area form a separate population of cells that we propose to be called the non-preganglionic Edinger-Westphal nucleus.