Regulation of Galanin and Gonadotropin-Releasing Hormone Gene Expression in the Hypothalamus and Basal Forebrain of the Rat

Abstract

Galanin is a cotransmitter in GnRH neurons and is thought to play a role in the control of gonadotropin secretion. The aim of our research has been to learn how galanin mRNA is regulated in GnRH neurons with the goal of understanding galanin's physiological significance. We have used double-label in situ hybridization and computerized image analysis to identify GnRH neurons coexpressing galanin mRNA and to estimate cellular levels of galanin message in these cells under different physiological conditions in the rat. In adult females, levels of galanin mRNA in GnRH neurons increase two- to fourfold with the onset of the proestrous and steroid-induced LH surges. Pharmacological blockade of synaptic transmission with either a general anesthetic (pentobarbital) or an alpha-adrenergic receptor antagonist (phenoxybenzamine) inhibits both the steroid-induced LH surge and the associated induction of galanin expression in GnRH neurons. Compared with the day of diestrus of the estrous cycle, during lactation cellular levels of galanin mRNA in GnRH neurons are profoundly reduced. In contrast to galanin mRNA in GnRH neurons, we could adduce no evidence for changes in cellular levels of GnRH mRNA under any physiological conditions or with any pharmacological manipulations. We conclude that alterations in galanin gene expression play a fundamental role in governing the functional activity of GnRH neurons, possibly by acting presynaptically to shape GnRH pulses, thereby determining the biological efficacy of GnRH action at its target cells in the pituitary.

Galanin Receptor-Mediated Inhibition of Glutamate Release in the Arcuate Nucleus of the Hypothalamus

“…Galanin acts in the hypothalamus to stimulate feeding behavior (Crawley et al, 1990;Kyrkouli et al, 1990;Leibowitz and Kim, 1992;Corwin et al, 1993) and to regulate hormone secretion (Bauer et al, 1986;Bjorkstrand et al, 1993;Kondo et al, 1993;Landry et al, 1995) and the reproductive cycle (Grafstein-Dunn et al, 1994;Sahu et al, 1994;Rossmanith et al, 1996). In addition, galanin has been shown to exert numerous effects elsewhere in the brain, including effects on learning and memory (Sundström et al, 1988;Ö gren and Pramanik, 1991;Crawley et al, 1993).…”

The regulative effect of galanin family members on link of energy metabolism and reproduction

“…On the other hand, the proestrous-and steroid-induced LH surges strongly enhanced the galanin mRNA levels up to two-to fourfold in the GnRH cells in adult female rats [48,60,111]. During the steroid-induce LH surge the number of GnRH cells with galanin immunoreactivity in ovariectomy mice was not proportionately increased [136].…”

Co‐Localisation of Kisspeptin with Galanin or Neurokinin B in Afferents to Mouse GnRH Neurones

“…It is co‐expressed and co‐packaged with GnRH (31–33). Furthermore, its expression within GnRH neurones, as well as in other preoptic and hypothalamic regions, is regulated across the oestrous cycle and, specifically, by oestrogen (34–38). In the presence of high levels of oestradiol, galanin enhances GnRH‐stimulated luteinising hormone (LH) secretion (39).…”