Effect of the Organochlorine Pesticide Endosulfan on GnRH and Gonadotrope Cell Populations in Fish Larvae

Endocrine-disrupting chemicals can influence the hypothalamus-pituitary-gonad axis and possibly affect reproduction in vertebrates. We analyzed the effect of 30-day endosulfan (ES) exposure in sexually undifferentiated larvae of the cichlid fish Cichlasoma dimerus. The number, area, mean cytoplasmic and nuclear diameter, and mean cytoplasmic optical density of gonadotropin-releasing hormone (GnRH) I, II, and III immunoreactive (ir-) neurons and beta follicle-stimulating hormone (beta FSH) ir-cells were measured. Animals exposed to the highest ES concentration (0.1 mu g/l) showed a decrease in GnRH I nucleus/cytoplasm area ratio upon exposure. Nuclear area and mean nuclear diameter of beta FSH ir-cells was higher in ES treated fish. beta FSH nucleus/cytoplasm area ratio was high in exposed animals, and animals exposed to 0.1 mu g/l ES showed smaller mean cytoplasmic optical density. These findings suggest that ES affects GnRH I and beta FSH protein synthesis/release. However, these responses seem to be insufficient to affect gonadal differentiation at this stage of development.