Expression and sexual dimorphism of galanin messenger ribonucleic acid in growth hormone-releasing hormone neurons of the rat during development
Date
1994-02Author
Delemarre-van de Waal, Henriette A.
Clifton, Donald K.
Burton, Kimberly A.
Steiner, Robert A.
Kabigting, Emilia B.
Metadata
Show full item recordAbstract
In the rat, the secretion of GH is episodic and sexually dimorphic. The
development and regulation of this patterning of GH secretion are governed
by the reciprocal influence of the hypothalamic peptide somatostatin and
GH-releasing hormone (GHRH). Galanin is a neuropeptide that is colocalized
with GHRH in hypothalamic neurons and is thought to be involved in
generating the episodic pattern of GH secretion. We hypothesized that
galanin mRNA expression in GHRH neurons increases over development in both
sexes, and that in the adults, galanin expression in GHRH neurons is
greater in males than in females. To test these hypotheses, we used a
double label in situ hybridization procedure to detect and measure galanin
mRNA expression in GHRH neurons in the rat brain. GHRH mRNA-positive cells
were visualized by an alkaline phosphatase color reaction, and galanin
mRNA levels were measured by counting autoradiographic grains over
individual GHRH mRNA-positive cells. Galanin mRNA coexpression was found
in GHRH mRNA-containing cells of the arcuate nucleus, periarcuate area,
and ventromedial hypothalamus. In both males and females there was a
significant increase in galanin mRNA in GHRH neurons over development.
Galanin mRNA levels in GHRH neurons of 10- and 25-day-old rats were higher
in females than in males [10-day-old: females, 12 +/- 2; males, 6 +/- 1
grains/cell (P < 0.05); 25-day-old: females, 28 +/- 4; males, 15 +/- 3
grains/cell (P < 0.02)]. In adults (70 days), galanin mRNA levels in GHRH
neurons were significantly higher in males than in females (males, 54 +/-
4; females, 32 +/- 3 grains/cell; P < 0.005). In the adult rat, galanin
mRNA levels in the individual hypothalamic areas exhibited a significant
sexual dimorphism in the arcuate nucleus and periarcuate area, with higher
levels in the male, whereas no sexual dimorphism was observed in the
ventromedial hypothalamus. To determine whether galanin gene expression is
influenced by circulating levels of testosterone, we measured galanin mRNA
levels in castrated male rats with and without testosterone replacement.
Castration reduced galanin message levels in GHRH neurons (intact, 73 +/-
6; castrate, 57 +/- 4 grains/cell), and although this reduction was not
statistically significant (P = approximately 0.07), testosterone
replacement significantly increased galanin message content
(castrate/sham, 58 +/- 4 grains/cell; castrate plus testosterone
replacement, 77 +/- 5 grains/cell; P < 0.02) to intact levels (intact, 73
+/- 6 grains/cell). In summary, galanin message expression in GHRH neurons
of both male and female rats increases over development.(ABSTRACT
TRUNCATED AT 400 WORDS)