Expression of mRNA for galanin, galanin-like peptide and galanin receptors 1-3 in the ovine hypothalamus and pituitary gland: effects of age and gender

The neurotransmitters/neuromodulators galanin (GAL) and galanin-like peptide (GALP) are known to operate through three G protein-coupled receptors, GALR1, GALR2 and GALR3. The aim of this study was to investigate changes in expression of mRNA for galanin, GALP and GALR1-3 in the hypothalamus and pituitary gland, of male and female sheep, to determine how expression changed in association with growth and the attainment of reproductive competence. Tissue samples from the hypothalami and pituitary glands were analysed from late foetal and pre-pubertal lambs and adult sheep. Although mRNA for galanin and GALR1-3 was present in both tissues, at all ages and in both genders, quantification of GALP mRNA was not possible due to its low levels of expression. mRNA expression for both galanin and its receptors was seen to change significantly in both tissues as a function of age. Specifically, hypothalamic galanin mRNA expression increased with age in the male, but decreased with age in the female pituitary gland. mRNA expression for all receptors increased between foetal and pre-pubertal age groups and decreased significantly between pre-pubertal and adult animals. The results indicate that the expression of mRNA for galanin and its receptors changes dynamically with age and those significant differences exist with regard to tissue type and gender. These changes suggest that galaninergic neuroendocrine systems could be involved in the regulation of ovine growth and or the development of reproductive competence. The roles played by these systems in the sheep, however, may differ from other species, in particular the neuroendocrine link between nutrition and reproduction and GALR1's role in pituitary signalling.