Food intake and the HPT axis in the cichlid fish: The implications of the gut-brain peptide cholecystokinin.

This work aimed to investigate the response of cholecystokinin (CCK) to starvation and its impact on food intake and the reproductive axis of the tilapia Oreochromis mossambicus. The fish subjected to 21 days of starvation showed a significant decrease in CCK immunoreactivity in the hypothalamus, pituitary gland, and intestine. The administration of injections of 0.5 and 5 μg of sulfated CCK-8 (CCK-8S) over 21 days resulted in a significant, dose-dependent decrease in food consumption. Administration of a high dose of CCK-8S (5 μg) resulted in a substantial decrease in the number of various spermatogenic cells, the intensity of androgen receptor immunoreactivity in the testis, and the percentage area of GnRH-immunoreactive fibres in the pars distalis of the pituitary gland (PPD), concurrent with a significant decline in serum levels of luteinizing hormone (LH) and 11-ketotestosterone (11-KT). Moreover, CCK-8S treatment markedly reduced the in vitro testicular 11-KT level. The results indicate for the first time that CCK influences hypothalamic GnRH release into the pituitary gland, resulting in the inhibition of LH release from the pituitary and affecting testicular spermatogenesis, androgen receptor protein expression, and steroidogenesis in teleosts. In addition, CCK may also directly affect testicular steroidogenesis.