Distribution and developmental changes in ghrelin-immunopositive cells in the gastrointestinal tract of African ostrich chicks

Ghrelin, the endogenous ligand for the growth hormone secretagogue receptor (GHS-R), has been found in the gastrointestinal tract of many vertebrates, but little is known about its distribution in the gastrointestinal tract of African ostrich chicks. In the present study, the distribution, morphological characteristics, and developmental changes of ghrelin-producing cells in the gastrointestinal tract of African ostrich chicks were investigated using immunohistochemistry. Ghrelin-immunopositive (ghrelin-ip) cells were found to be localized in the mucous membrane of the entire gastrointestinal tract, but not in the myenteric plexus. The greatest number of ghrelin-ip cells was found in the proventriculus, and the ghrelin-ip cell density gradually decreased from the proventriculus to the rectum. Interestingly, from postnatal day 1 to day 45 in the proventriculus, and from postnatal day 1 to day 90 in the gizzard and small intestine, there was a steady increase in the number of ghrelin-ip cells. By day 45 in the proventriculus and day 90 in the gizzard and small intestine, the number of cells reached a plateau and remained steady. These results clearly demonstrate that ghrelin-ip cells exist and the number of ghrelin-ip cells increases with age in the African ostrich gastrointestinal tract from postnatal day 1 to day 90; ghrelin may be involved in gastrointestinal tract development.