Pituitary adenylate cyclase-activating polypeptide neurons of the ventromedial hypothalamus project to the midbrain central gray.

The pituitary adenylate cyclase-activating polypeptide (PACAP) and brain-derived neurotrophic factor (BDNF) neurons have recently been established as markers of the ventromedial hypothalamic nucleus (VMH). However, their neural projections from the VMH remained unknown. We examined whether PACAP and BDNF neurons in the VMH connected to the mesencephalic central gray (MCG), using the combination of in-situ hybridization and immunohistochemical tracing of Fluorogold (FG) injected into the MCG. Approximately 49% of PACAP neurons and 19% of BDNF neurons in the VMH contained the retrograde-transported FG, and 52% of FG-positive cells were PACAP neurons. These results indicate that a large number of PACAP neurons and a small number of BDNF neurons of the VMH project to the MCG.