Galanin Gene Expression in the Hypothalamopituitary Axis of the Ames Dwarf Mouse

Abstract

The peptide galanin is localized in lactotrophs, somatotrophs, and thyrotrophs of the female rat anterior pituitary gland (AP). These cell types are absent in the AP of the Ames dwarf mouse. Moreover, estrogen increases galanin gene expression in the rat AP, but has little effect on galanin in the hypothalamus. The objectives of this study were to (i) determine whether estrogen increases galanin gene expression in the normal mouse AP or hypothalamus, and (ii) compare the distribution of galanin peptide in the hypothalamopituitary axis of normal and Ames dwarf mice. Adult female mice (normal and Ames dwarf) were treated with estrogen pellets (0.25 mg; sc) for 2 weeks. Estrogen increased galanin peptide levels fivefold in the normal mouse AP, but did not alter peptide levels in the neurointermediate lobe or hypothalamus. Galanin peptide levels were undetectable in the AP of the dwarf mouse. In addition, galanin peptide levels in the hypothalamus of the dwarf mice were 30% lower than in normal mice, regardless of the steroid treatment. Galanin peptide levels in the neurointermediate lobe were similar in dwarf and control mice. Galanin mRNA levels were undetectable in the AP of estrogen-treated dwarf mice by Northern blot analysis and were elevated by estrogen in the AP of normal mice. Galanin mRNA levels were similar in the hypothalamus of normal and dwarf mice and were unchanged by estrogen. The following conclusions were drawn: (i) Estrogen increases galanin gene expression in the normal mouse AP but has no effect in the hypothalamus; (ii) galanin peptide is undetectable in the AP of Ames dwarf mice, lower in the hypothalamus, and unchanged in the neurointermediate lobe compared to normal mice; and (iii) galanin mRNA is present in similar quantities in normal and Ames dwarf mouse hypothalamus, whereas galanin mRNA is undetectable in the dwarf mouse AP.