ESTROGEN REGULATES GALANIN BUT NOT TYROSINE-HYDROXYLASE GENE-EXPRESSION IN THE RAT LOCUS-CERULEUS

The neuropeptide galanin (GAL) is coexpressed by the majority of norad renergic neurons in the rat locus ceruleus (LC) and may function as an inhibitory modulator of noradrenergic transmission. Because estrogen has been shown to induce GAL expression in other brain regions and mod ulate noradrenergic transmission, we used in situ hybridization histoc hemistry to assess the effects of chronic estrogen treatment on GAL an d tyrosine hydroxylase (TW) gene expression in the LC of ovariectomize d female rats. We found that GAL mRNA levels were significantly elevat ed in rats implanted with a Silastic capsule containing estradiol comp ared to sham-implanted controls. Both the average optical density (P l ess than or equal to 0.05) and the labelling area (P less than or equa l to 0.007) differed significantly between the groups. In contrast, TH gene expression measured in alternate brain sections did not differ b etween the groups. If GAL functions as an inhibitory modulator of nora drenergic transmission as postulated, these findings suggest that chro nic estrogen treatment could reduce the noradrenergic tone of the brai n in the absence of significant alterations in TH expression by enhanc ing the level of cosecreted GAL. (C) 1997 Elsevier Science B.V.