Coexistence of neuropeptide Y and progesterone receptor in neurons of guinea-pig arcuate nucleus.

Double-label immunocytochemistry has been employed to determine whether progesterone receptor (PR)-containing neurons in the arcuate nucleus (AR) of female guinea pig contain neuropeptide Y (NPY). Animals were ovariectomized, primed by estradiol and microinjected intracerebroventricularly with colchicine to visualize NPY-immunoreactive (IR) neurons. Only a very small population of NPY-IR perikarya (2.5% approximately) were found to be also PR-IR. NPY-IR varicosities appeared in close proximity to neurons with PR-containing nuclei. This restricted coexistence provides morphological evidence that most NPY neurons in the AR are not directly regulated by progesterone.