PROGESTERONE-RECEPTOR AND NEUROTENSIN ARE COLOCALIZED IN NEURONS OF THE GUINEA-PIG VENTROLATERAL HYPOTHALAMUS

A double-labeling immunofluorescence procedure was used to determine w hether progesterone receptor (PR)-containing neurons in the mediobasal hypothalamus of female guinea pig also contain neurotensin (NT). Anim als were ovariectomized, primed by estradiol to induce PR and injected intracerebroventricularly with colchicine to visualize NT-immunoposit ive neurons. Approximatively 24% of the NT-immunoreactive (IR) neurons in the ventrolateral nucleus (VL) displayed PR immunoreactivity, acco unting for 4% of the total population of cells containing PR in this r egion. The arcuate nucleus (AR) was observed to have both populations, but coexistence was rare. These findings provide neuroanatomical evid ence that a subset of NT neurons is directly regulated by progesterone in the VL, a site that plays a key role in the control of female sexu al behavior.