INVIVO STIMULATION OF OVARIAN DEVELOPMENT IN THE RED SWAMP CRAYFISH, PROCAMBARUS-CLARKII (GIRARD), BY 5-HYDROXYTRYPTAMINE

The possibility that biogenic amines affect ovarian development in the red swamp crayfish, Procambarus clarkii, was investigated. Females were administered 15 mug/g body weight (bw) of norepinephrine, dopamine, 5-hydroxytryptamine (5-HT) or octopamine on days 1, 5 and 10 and were sacrificed on day 15. Crayfish given 5-HT showed significant increases in ovarian index (30.5%) and oocyte size (34.0%) over the concurrent controls, while norepinephrine, dopamine and octopamine did not significantly affect either the ovarian index or oocyte size. Significantly more labeling by C-14-leucine of ovarian proteins was found in ovaries of crayfish that were injected with 5-HT in vivo, but when ovarian lobes from crayfish that had not been injected with 5-HT were incubated in vitro with 5-HT added to the incubation medium, no significant change in the level of incorporation of C-14-leucine into ovarian proteins occurred. The 5-HT receptor blocker LY53857 (25 mug/g bw) retarded ovarian development. The 5-HT releaser fenfluramine and the 5-HT potentiator fluoxetine (both 15 mug/g bw) were also used. Crayfish given fenfluramine, fluoxetine, fenfluramine plus 5-HT or fluoxetine plus 5-HT showed significant increases of ovarian index (24.0-102.8%), oocyte size (20.0-87.4%) and in vitro C-14-leucine labeling of ovarian proteins (30.6-123.6%) over the concurrent controls. The ovaries of crayfish that received the 5-hydroxytryptaminergic neurotoxin 5,6-dihydroxytryptamine (10 mug/g bw) did not show any significant change as compared with the initial control. These findings are consistent with the hypothesis that 5-HT, which is present in the central nervous system of Procambarus clarkii, exerts its stimulatory effect on the ovary of this crayfish indirectly by triggering release of the ovary-stimulating hormone.