EFFECTS OF ESTROUS CYCLICITY ON THE EXPRESSION OF THE GALANIN RECEPTOR GAL-R1 IN THE RAT PREOPTIC AREA - A COMPARISON WITH THE MALE

Variations in the number of galanin receptor (Gal-R1)-expressing cells and levels of Gal-R1 messenger RNA (mRNA) were determined in the preo ptic area in intact female rats throughout the phases of the estrous c ycle and compared with those in the male. Female and male Wistar rats were fixed by perfusion with 4% paraformaldehyde. Cryostat sections we re hybridized with a S-35-labeled antisense Gal-R1 riboprobe. The numb er of Gal-R1 mRNA-expressing cells was lower in the rostral preoptic a rea than in the medial preoptic area. During the estrous cycle, the hi ghest number of Gal-R1 mRNA-expressing cells in the rostral preoptic r egion was detected at 0800 h on proestrus, whereas in the medial preop tic area, the maximum number was observed at 1800 h on estrus. Gal-R1 mRNA levels in individual cells mere low during diestrus and increased at estrus in both areas. In the male, the number of mRNA-expressing c ells and the hybridization signal were significantly lower than those in females during estrus. The results demonstrate that Gal-R1 gene exp ression in the preoptic area varies during the estrous cycle and is lo w in males. Short term treatment of ovariectomized rats with estradiol plus progesterone caused significantly decreased preoptic Gal-R1 mRNA levels compared with those after treatment with estrogen only. These observations suggest that in the preoptic area, expression of Gal-R1 i s influenced by progesterone. The variation in Gal-R1 expression is li kely to influence the extent to which galanin can influence the preopt ic cells implicated in the control of neighboring GnRH cells.