Ascending vocalization pathways in the female ring dove: projections of the nucleus intercollicularis

Nest-coo (courtship) vocalization is an estrogen-dependent component of a sequence of behaviors leading to egg-laying in the ring dove (Streptopelia risoria). Implantation of estrogen in the nucleus intercollicularis of ovariectomized females restores the ability to produce nest-coos. Lesion of n. intercollicularis specifically disrupts nest-cooing and inhibits follicular development. We used anterograde transport of tritiated leucine to identify regions that receive input from n. intercollicularis. As a control, isotope was injected in an auditory nucleus (nucleus mesencephalicus lateralis, pars dorsalis) neighboring the n. intercollicularis. A strong projection to the nucleus was observed, demonstrating a potential interaction between auditory and vocalization systems at the level of the midbrain. Local projections of n. intercollicularis were observed in midbrain and hind brain nuclei including the nucleus tegmenti pedunculo-pontinus, pars compacta and nucleus papillioformis. A conspicuous projection ascended centrally via the mesencephalic central gray. Proceeding rostrally, this pathway was traced to the nucleus periventricularis magnocellularis and tissue surrounding it. At its rostral extent, the pathway was found to project to the nucleus preopticus medialis, the anterior medial hypothalamus, and the lateral hypothalamus. These results are consistent with the possibility of a nucleus intercollicularis projection to regions that regulate reproductive function.