Effects of amputation and subsequent regeneration of a leg on the duration of the intermoult period and the level of circulation ecdysteroids in Helleria brevicornis Ebner (ground isopod)

Humoral factors reduce gap junction sensitivity to cytoplasmic pH. I. Organ ablation studies

The sensitivity of gap junctions connecting crayfish lateral axons to uncoupling by axoplasmic acidification was studied after altering the hormonal balance of animals by 1) ablation of eyestalks or sinus glands or 2) inducing long-lasting defensive posturing behavior (stress). Internal pH (pHi) was measured with microelectrodes, and junctional resistance (Rj) was calculated from input and transfer resistances. In isolated nerve cords from intact animals, the maximal Rj (Rjmax) reached after acidification varied diurnally (Rjmax approximately 10 and 0.6 M omega at 0900 and 1800 h, respectively). Basal Rj (20-30 k omega) did not change during the 24-h period. Organ ablation (eyestalks or sinus glands) or stress rendered gap junctions less sensitive to uncoupling by low pHi within 1 h or 2 days; recovery toward control values had different time courses. The reduced pH sensitivity of crayfish junctions seen after eyestalk ablation is attributable to stress in its early phase (lasting 1-2 days) and to ablation of the endocrine organs in its late phase (2-7 days). No striking structural differences accompanied these changes, indicating that the altered properties are not due to major changes in gap junction expression.

Hemolymph ecdysteroids and molt cycle in males and females of Siriella armata M-Edw. (Crustacea: Mysidacea): possible control by the MI-ME X-organ of the eyestalk

Hemolymph ecdysteroids were quantified by radioimmunoassay (RIA) at successive stages of the molt cycle in the mysid Siriella armata. Profiles showed a single peak during premolt, at stage D1 for males, and D2 for reproducing females who displayed ecdysteroid levels 10 times higher than males. Titers were also measured for individuals which had been molt inhibited by early electrocauterization of the eyestalk MI-ME X-organ. In the case of total inhibition of molt preparation, the ecdysteroid peak was suppressed. It was displaced toward the end of the cycle when only ecdysis was inhibited. Ecdysone and 20-hydroxyecdysone were characterized in the hemolymph of both sexes using high-pressure liquid chromatography followed by RIA. High-polarity products, abundant in the female hemolymph, were resolved into 20-hydroxyecdysone and ecdysone by enzymatic hydrolysis and thin-layer chromatography. The quantitative and qualitative variations of ecdysteroid in the different situations (male or female, normal or inhibited cycles) are presented in relation to apolysis, epidermic activity, ecdysis, and secondary vitellogenesis in females, emphasizing the importance not only of ecdysteroids, but also of the MI-ME X-organ in monitoring molt and blood preparation in mysids.

Role of ecdysone and eyestalk factors in regulating regeneration in larval crustaceans

Megalopae of the mud crab Rhithropanopeus harrisii can regenerate autotomized limbs. Regeneration during the megalopal stage required a significant delay in ecdysis to the first crab. Megalopae that failed to initiate regeneration complete ecdysis significantly faster than do controls. Exposure of intermolt- and premolt-stage megalopae to exogenous ecdysone significantly reduced (greater than or equal to 30%) the number of animals completing regeneration. The regeneration-induced delay in ecdysis was not significantly different in animals exposed to ecdysone. The molt cycle of nonregenerating megalopae exposed to ecdysone was further accelerated. Eyestalk ablation did not significantly reduce the molt cycle duration of regenerating animals. Eyestalkless nonregenerating animals did not display accelerated ecdysis. It is hypothesized that two additional hormonal factors are involved in "fine tuning" the molt cycle of regenerating animals. One located outside the eyestalks extends the molt cycle to accommodate regeneration. The second factor accelerates ecdysis in nonregenerating animals and appears to be produced in the eyestalks.