Histamine H2 receptor agonist dimaprit dihydrochloride stimulates the hypothalamo-hypophysial-testicular axis in the cichlid fish Oreochromis mossambicus

Abstract

Histamine is a naturally occurring biogenic monoamine that acts at both central and peripheral levels, serving a crucial role in regulating a range of physiological processes in vertebrates, including immune function and reproduction. This research aims to understand whether the histamine H2 receptor agonist dimaprit dihydrochloride (DIMP) affects the hypothalamo-hypophysial-testis (HPT) axis of the Mozambique tilapia. Treatment with 5 μg DIMP did not alter the numbers of spermatogonia-B and secondary spermatocytes, but caused a significant increase in the numbers of other germ cells. However, treatment with 20 μg DIMP resulted in significantly higher numbers of all germ cells, including spermatogonia-A and B, primary and secondary spermatocytes, and early and late spermatids, compared to those of controls or 5 μg DIMP-treated fish. There was a dose-dependent increase in the diameters of seminiferous lobules and lumens, but the diameter of the interstitium was significantly decreased in DIMP-treated fish. Furthermore, there was also a dose-dependent, significant increase in the density of gonadotropin-releasing hormone-immunoreactive fibres and intensity of androgen receptor immunoreactivity in 5 and 20 μg DIMP-treated fish, concomitant with a significant increase in serum levels of luteinizing hormone in 5 or 20 μg DIMP-treated fish compared to those of controls. Collectively, these results, for the first time, suggest that treatment with DIMP exerts a stimulatory effect on the HPT axis in the teleosts.