AGING IMPAIRS GALANIN EXPRESSION IN LUTEINIZING-HORMONE-RELEASING HORMONE NEURONS - EFFECT OF OVARIECTOMY AND OR ESTRADIOL TREATMENT/

In the medial preoptic area and the diagonal band of Broca, a subset o f LHRH neurons coexpresses galanin at a 4- to B-fold higher rate in fe male than male rats, suggesting that estradiol (E(2)) plays a key role in galanin gene expression within LHRH neurons. In the present studie s we investigated the incidence of colocalization of these peptides in different age groups, i.e. 2-, 10-, 18-, and 24-month-old intact fema le Fisher rats; 24-month-old El-treated rats; 24-month-old ovariectomi zed (OVX) rats; and 24-month-old OVX E(2)-treated rats with single or double labeling immunocytochemistry. For cell counting, we took advant age of the typical fusiform morphology of galanin-immunoreactive neuro ns that colocalize LHRH. The presence of both peptides in the same per ikaryon was substantiated by double staining representative sections f rom each brain. Our observations indicate that the number of galanin/L HRH-coexpressing perikarya dramatically decreased with age. Although i n 18-month-old rats a moderate decline was observed, in 24-month-old f emale rats no, or only a few, faintly stained, fusiform galanin-immuno positive perikarya were present. Although galanin was absent from LHRH neurons of aged rats, their LHRH content was not altered. E(2) treatm ent of intact 24-month-old rats had no effect on the low incidence of colocalization. However, when OVX 24-month-old rats were E(2) treated, the incidence of colocalization increased to the level seen in 2- or 10-month-old estrous animals. Our observations on the presence of colo calizing perikarya in intact and E(2)-treated aged animals provide fur ther evidence for the key role of E(2) in galanin gene expression with in LHRH neurons and emphasize that some ovarian factor(s) may blunt th is effect.