The neurokinin 3 receptor (NK3R) is a G protein-coupled receptor that is expressed in brain and is highly expressed by magnocellular vasopressinergic neurons in both the paraventricular (PVN) and supraoptic nuclei (SON) of the hypothalamus. Hyperosmolarity causes a ligand-mediated internalization of NK3Rs to the cytoplasm and to the nuclei of vasopressinergic PVN neurons. This receptor activation-dependent pathway is presumed to be a means to directly transmit synaptic signals from the cell membrane to the nucleus. The present study evaluated in vivo the subnuclear domains that associate with NK3R. Rats were administered 2 M NaCl (intragastric) or no intragastric load, and 40 min later, the PVN was dissected and nuclei were isolated. Using double-immuno-transmission electron microscopy (TEM), we show that, compared with controls, hyperosmolarity causes a significant increase in NK3R Immunogold beads in the nucleus of PVN neurons. Furthermore, NK3R spatially colocalized with histone H4 and with highly acetylated H4 in nuclei isolated from the PVN of rats administered 2 M NaCl, but not in nuclei from control rats. Next, coimmunoprecipitation experiments showed that acetylated H4, as well as acetylated H3, were pulled down with NK3R in the PVN nuclear enriched fraction from rats treated with 2 M NaCl, but not from control rats. In response to hyperosmolarity, NK3R is transported to the nucleus of PVN neurons and associates with transcriptionally active chromatin, where it may influence the transcription of genes.