MULTIPLE PEPTIDES INFREQUENTLY COEXIST IN PROGESTERONE RECEPTOR-CONTAINING NEURONS IN THE VENTROLATERAL HYPOTHALAMIC NUCLEUS OF THE GUINEA-PIG - AN IMMUNOCYTOCHEMICAL TRIPLE-LABEL ANALYSIS OF SOMATOSTATIN, NEUROTENSIN AND SUBSTANCE-P

Progesterone plays an important role in regulating reproductive behavi our in guinea-pigs through actions exerted at the ventrolateral nucleu s (VL), an area of the brain that contains progesterone receptors (PR) and neuroactive peptides, somatostatin (SOM), neurotensin (NT) and su bstance P (SP). Previous double-label analyses provided evidence that a substantial proportion of these neuropeptidergic cells contain PR. B y means of triple-label immunofluorescence histochemistry, we examined whether PR are colocalized with two neuropeptides (SOM + NT or SP + S OM or SP + NT) within the same neurons in the VL. Ovariectomized guine a-pigs were primed with estradiol to induce PR immunoreactivity, and t reated with colchicine to visualize immunoreactive (IR) neuropeptiderg ic cells. Both monoclonal mouse PR and polyclonal rabbit neuropeptide antibodies were used in double staining and in elution-restaining expe riments. In the whole VL, the proportion of each coexisting peptide wi th PR obtained after double immunofluorescence appeared in decreasing order as: SOM (34%)>NT(25%)>SP(20%). Occasional colocalization was see n between PR and two neuropeptides throughout the rostrocaudal extent of the VL. Combining our Various quantitative observations, we found t hat, of the total population of PR-IR neurons containing any combinati on of SOM, NT and SP, only about 1.5% contained SOM and NT, 2% contain ed SP and SOM and 1.6% contained SP and NT. These results indicate tha t while many PR-IR neurons also contain SOM or NT or SP in the guinea- pig VL, there may be very few PR-IR neurons that express more than one of these three peptides.