Endocrine control of molting in the parasitic nematodes Dirofilaria immitis and Onchocerca lienalis: The effect of juvenile hormone-I, two juvenile hormone analogs, precocene II, 20-hydroxyecdysone, and noradrenaline
Abstract
The potential regulation of larval filarial molting by insect juvenile hormones/analogs (JH/JH-analogs) has not been intensively investigated. JH-I, JH-analogs, the JH antagonist precocene-II, and insect molting hormone 20-hydroxyecdysone, were incorporated into media to generate dose response curves. Precocene-II and JH/JH-analogs inhibit L3-L4 molting in Onchocerca lienalis and Dirofilaria immitis in dose dependent fashion. Ability of JH/JH-analogs, 20-hydroxyecdysone, or noradrenalin to overcome L3-L4 molt inhibition by precocene-II, medium depletion, and low temperature was ascertained. Physiologic and pharmacologic concentrations of precocene II significantly decrease molting. Physiologic concentrations of JH-I, methoprene, and farnesol also inhibit molting. Precocene-II treated L3s fail to overcome molt inhibition when treated with JH/JH-analogs. Molt suppression in D. immitis by methoprene is restored to levels of controls by addition of 20-hydroxyecdysone to the medium. Ecdysterone partially restores molting in farnesol but not precocene-II inhibited L3s. Noradrenalin is implicated in the neuroendocrine cascade postulated in other nematodes. However, it fails to overcome molt inhibition by methoprene or farnesol. Supplementation with farnesol increases molting by O. lienalis L3s in serum-depleted culture medium. Similarly, logarithmic additions of methoprene or farnesol promote molting of D. immitis at the nonpermissive temperature of 26$\sp\circ$C. Hydroxyecdysone fails to promote molting at 26$\sp\circ$C in D. immitis. A 90 min preincubation in iodine, suspected of blocking JH/JH-analog sensitive receptors, fails to prevent molt promotion at 26$\sp\circ$C and molt inhibition at 37$\sp\circ$C by JH-analogs. Examination by Nomarski microscopy of the anterior end of normal D. immitis L3s, L4s, and worms treated with precocene-II or JH-analog, detected changes in amphidial nerve cell bodies only in normal L3s. Failure of JH/JH-analogs to restore molting in precocene-II inhibited L3s suggests that precocene-II may have direct toxic effects on L3s and argues against interference with an endogenous JH-like mechanism. Promotion of molting in nonpermissive culture conditions indicates JH-analogs can induce the molt cycle, presumably by stimulation of a non-I$\sb2$-sensitive receptor. Stimulation of molting at 26$\sp\circ$C by JH-analogs suggests the possible role of a normally temperature dependent cycle, necessary to induce a complex cascade prior to the presumed action of 20-hydroxyecdysone.
Subject Area
Zoology|Veterinary services
Recommended Citation
Bodri, Michael Steven, "Endocrine control of molting in the parasitic nematodes Dirofilaria immitis and Onchocerca lienalis: The effect of juvenile hormone-I, two juvenile hormone analogs, precocene II, 20-hydroxyecdysone, and noradrenaline" (1992). Dissertations available from ProQuest. AAI9235111.
https://repository.upenn.edu/dissertations/AAI9235111