Colocalization of MR with VP-NP or OT-NP immunoreactivity in coronal section of the rat SON. A and D: MR immunoreactivity labeled with DyLight 488-conjugated secondary antibody. Prominent MR immunoreactivity is observed in somata of MNCs within the PVN. Most of these MR-immunoreactive MNCs are located in a cluster of cells in the posterior magnocellular region (pm). Considerable MR immunoreactivity was also observed in the parvocellular cells in dp, vlp, and posterior parvocellular regions. B: VP-NP immunoreactivity labeled with DyLight 594-conjugated secondary antibody in same section and image plane as in A. Note that the VP-NP immunoreactive cells form a cluster in the lateral portion of the PVN. E: OT-NP immunoreactivity labeled with DyLight 594-conjugated secondary antibody in same section and image plane as in D. C and F: the merged images revealed that MR immunoreactivity is colocalized (yellow) with both VP-NP and OT-NP immunoreactivities within MNCs in the PVN. Note that the lateral cluster of the cells is composed mostly of VP MNCs that are immunoreactive to MR as well as some sparsely located OT MNCs around these VP neurons. However, the parvocellular cells immunoreactive to MR within dp, vlp, and posterior parvocellular regions are not immunoreactive to VP or OT.