Visualization of ghrelin-producing neurons in the hypothalamic arcuate nucleus using ghrelin-EGFP transgenic mice.

The gut-brain hormone ghrelin is known to stimulate growth hormone release from the pituitary gland, and to regulate appetite and energy metabolism. Ghrelin-containing neurons have been shown to form neuronal network with several types of appetite-regulating neurons in the hypothalamus. Although ghrelin-containing cell bodies have been reported to localize in the hypothalamic arcuate nucleus, the published results present large discrepancies regarding the localization of ghrelin-positive cell bodies in the brain. In order to address this issue, we have generated a transgenic mouse model by microinjecting a DNA construct in which the transcription regulatory regions of ghrelin drive the enhanced green fluorescent protein (EGFP) gene. These transgenic mice expressed EGFP and ghrelin mRNA in the stomach and hypothalamus. Double immunostaining revealed that GFP-like immunoreactivity was co-localized with ghrelin-like immunoreactivity in the stomach of these animals, while EGFP fluorescence was clearly demonstrated in the hypothalamic arcuate nucleus by confocal laser microscopy. The ghrelin-EGFP transgenic mouse model described in this study therefore provides a powerful tool with which to analyze ghrelin neuronal circuits in the brain and should contribute to our understanding of the functional significance of ghrelin in the central nervous system.