Effects of hypophysectomies and thyroxine replacement upon the initiation of tail regeneration in the lizard, Anolis carolinensis

A histological evaluation of the effects of hypophysectomy and throxine therapy in young tail regenerates was carried out in the small iguanid lizard, Anolis c. carolinensis. Hypophysectomy caused a delay but did not inhibit blastema formation. The growth of the ependyma into the wound region was delayed in hypophysioprivic regenerates by about a week. Growth and differentiation of hypophysioprivic regenerates after blastema formation was variable, ranging from virtually no growth to the formation of a differentiated but very small protuberance. However, actual tail elongation was inhibited by hypophysectomy. In those hypophysioprivic regenerates that did show signs of differentiation, muscle groups were poorly defined, scanty in appearance and not as well differentiated as the cartilage tube. Thyroxine treatment in the young hypophysioprivic regenerates stimulated normal growth and normal appearance and differentiation of promuscle and procartilage aggregates as well as the growth of the ependymal tube into the blastema.     

Direct effects of retinoic acid on the development of the tail bud in chick embryos

Retinoic acid (RA) has been reported to induce vascular lesions and haematoma formation in the vicinity of the tail bud during the critical period for inducing abnormalities of tail bud development in hamsters (Wiley, '83; Tibbles and Wiley, '88), mice (Tibbles and Wiley, '88) and chicken embryos (Jelinek and Kistler, '81). Experiments were conducted to determine whether or not these vascular lesions were the primary cause of the malformations which they accompanied. Chick embryos were exposed for varying lengths of time to several dosages of RA. Primitive streaks or tail buds from treated embryos were then excised prior to vascularization and transplanted to the coelomic walls of untreated host embryos. The grafts were harvested at 3 or 6 days after grafting and processed for histological examination. Observations of serial sections of controls showed that the primitive streak and early (stage 13-14) tail bud were able to form neural tubes and a variety of other structures including ganglia, nerve fibres, and kidney tubules. Treatment of donor embryos with RA prior to grafting, however, affected the frequency and characteristics of the neural tubes and other tissues developing in the grafts. The effects of RA on development were correlated with both the dosage and length of exposure to the teratogen prior to grafting. Since the grafts were made before the appearance of blood vessels in the tail buds, we have concluded that the effects of RA on the development of tail bud tissues, and especially the secondary neural tube, are direct and are not mediated solely through the disruptive effects of vascular lesions seen in intact embryos.     

Comparative postautotomy tail activity in six Mediterranean lacertid lizard species

Tail autotomy, the self-induced tail separation from the body, is a common and effective antipredator mechanism in lizards. In this study, we examine the muscle energetics of tail shedding in six lacertid lizard species (Podarcis erhardii, Podarcis peloponnesiaca, Podarcis muralis, Podarcis gaigeae, Podarcis milensis, and Lacerta graeca) from the northeast Mediterranean region. Very long periods of postautotomy tail movement were demonstrated for all species (range=6-8 min), and differences among species were not statistically significant. Postautotomy tail movement, powered by anaerobic muscle activity, resulted in a strong increase in lactate concentrations and a concomitant depletion of muscle glycogen of exhausted tails relative to resting tails. No significant differences were found in either lactate or glycogen concentrations among the species examined. Duration of movement was negatively correlated with final lactate concentrations. The lack of differentiation in postautotomy energetic physiology in this group of species that have evolved under very different predation environments indicates that postautotomy muscle metabolism involves an overall conservative suite of characters.     

Energetic costs of tail loss in a montane scincid lizard

Most species of lizards will shed their tails at the point of contact when grasped by a predator. We investigated the energetic consequences of tail loss by measuring lipids in a scincid lizard that stores energy in its tail for reproduction. Most of the lipids were concentrated in the proximal portion of the tail. Thus, partial tail loss may not severely affect energy stores if the distal portion of the tail is shed in predatory encounters. We also found that the width of the tail was a reliable non-invasive index of energy reserves in this species.     

Selection of cryoprotectants based on their toxic effects on oyster gametes and embryos

Cryopreservation is a valuable tool for aquaculture by providing continuous seed production, regardless of the spawning seasons. This study aimed to select the least toxic among the cryoprotectants dimethyl sulfoxide (Me2SO), propylene glycol (PG), and methanol (MET) based on their toxicological effects on Crassostrea rhizophorae gametes and trochophores. They were exposed for 10, 20, and 30 min to a range of concentrations of those cryoprotectants. The endpoint was EC15-24 h (effective concentration which causes abnormalities in 15% of the population exposed to the cryoprotectants for 24 h), recently determined as the chronic value (the concentration at which chronic effects are first observed) for C. rhizophorae embryonic phases. There were no significant differences (p>0.05) among the exposure times in Me2SO toxic effects to either gametes or trochophores. For MET, the increase in exposure time resulted in higher toxicity for gametes, but not for trochophores, while for PG there was a significant (p>0.05) increase in toxicity with the increase of exposure for trochophores and spermatozoa, but not for oocytes. For gametes, MET was the most toxic among the cryoprotectants, while PG was the most toxic for trochophores.     

Some morphological and ultrastructural changes in the ependyma of the amputation stump during early regeneration of the tail in the lizard,Anolis carolinensis

Light and electron microscope studies indicate that the old ependyma just proximal to the plane of amputation in early lizard tail regenerates shows a sequence of morphological changes which suggests that it as well as the new ependyma growing into the regenerate may play an active role in the initiation and maintenance of early tail regeneration. The old ependyma close to the plane of amputation undergoes hypertrophy and/or hyperplasia causing a partial closure of the central canal and pseudostratification. Its nuclei shift from an original apical position to a basal one. The ependymal processes become more prominent and extend to the pia, a condition not found more rostrally. There is also a significant increase in the amount of Golgi substance and a moderate increase in the rough endoplasmic reticulum. These observations lead to the thought that these cellular changes may be an expression of enhanced secretion and other activities in the old and new ependyma just proximal or distal to the plane of amputation.     

Amino acid-permeable anion channels in early mouse embryos and their possible effects on cleavage

Effects of several Cl(-) channel blockers on ionic currents in mouse embryos were studied using whole-cell patch-clamp and microelectrode methods. Microelectrode measurements showed that the resting membrane potential of early embryonic cells (1-cell stage) was -23 mV and that reduction of extracellular Cl(-) concentration depolarized the membrane, suggesting that Cl(-) conductance is a major contributor for establishing the resting membrane potential. Membrane currents recorded by whole-cell voltage clamp showed outward rectification and confirmed that a major component of these embryonic currents are carried by Cl(-) ions. A Cl(-) channel blocker, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), suppressed the outward rectifier current in a voltage- and concentration-dependent manner. Other Cl(-) channel blockers (5-nitro-2-[3-phenylpropyl-amino] benzoic acid and 2-[3-(trifluoromethyl)-anilino] nicotinic acid [niflumic acid]) similarly inhibited this current. Simultaneous application of niflumic acid with DIDS further suppressed the outward rectifier current. Under high osmotic condition, niflumic acid, but not DIDS, inhibited the Cl(-)current, suggesting the presence of two types of Cl(-) channels: a DIDS-sensitive (swelling-activated) channel, and a DIDS-insensitive (niflumic acid-sensitive) Cl(-) channel. Anion permeability of the DIDS-insensitive Cl(-) current differed from that of the compound Cl(-) current: Rank order of anion permeability of the DIDS-sensitive Cl(-) channels was I(-) = Br(-) > Cl(-) > gluconate(-), whereas that of the DIDS-insensitive Cl(-) channel was I(-) = Br(-) > Cl(-) > gluconate(-). These results indicate that early mouse embryos have a Cl(-) channel that is highly permeable to amino acids, which may regulate intracellular amino acid concentration.     

The effects of retinoic acid on mitosis during tail and limb regeneration in the axolotl larva,Ambystoma mexicanum

Summary Regenerating tails and limbs of axolotl larvae (A. mexicanum) were studied for overall growth and for mitosis after the animals received intraperitoneal injections of all-trans retinoic acid. Both processes were depressed to approximately the same extent (60–70%). Some mitosis always survived, even when the treatment was in effect during the entire history of the regenerate. The treatment duration was a major variable in the severity of the effect, whereas the post-amputation age of the regenerate was not. In limb regenerates the epithelial cap and the mesenchymal blastema were affected to roughly the same degree.Supported by PHS Grant 507RR7031H of the BMRG, Indiana University     

Satellite cells in mature,uninjured skeletal muscle of the lizard tail

The uninjured caudal skeletal muscle of two lizards, Lygosoma and Anolis, contains satellite cells. The satellite cell nuclei constitute 7.5% and 4.8% of the combined satellite and muscle nuclei, in Lygosoma and Anolis, respectively.     

Fine observation on nerves colonizing the regenerating tail of the lizard Podarcis sicula

During the regeneration of lizard tail, nerves sprouting from ganglia and the spinal cord invade the blastema as far as the apical epidermis. Electron microscopical observations reveal axons storing dense granules (dg) and dense core vesicles (dcv) which are concentrated in nerve terminals or in axoplasmatic regions. In the regenerating spinal cord (SC) these terminals resemble aminergic-peptidergic endings and grow as far as the distal portion of the SC, which is made up of irregularly arranged ependymal cells. Some axons storing dcv contact blastematic cells and other nerve terminals show a plasma membrane incomplete or broken. Whether this latter aspect is due to fixation artifacts or physiological rupture is unknown. Nerves containing dcv and a few dg also originate from spinal ganglia innervating the regenerating tail. The accumulation of material into these endings is probably slow and a possible trophic influence on the regeneration of lizard tail is discussed.     

Regeneration of the tail bud in Xenopus embryos.

In an attempt to solve some aspect of the long-standing controversy about the regenerative ability of appendages in vertebrate embryos, the tail bud of Xenopus laevis embryos has beenamputated at stage sranging from St. 26 to St. 32 and its ability to regenerate duringa culture period of 2-3 days has been studied. At amputation stages 26-28,the tail bud consisted only undifferentialted mesoderm and ectoderm, but at stage 32 it had afully differentiated neural tube, a vaculotaed notochord and segmented somites. A total of 137amputations at differnt stages gace consistent results: a tail formed in all the operated larvacand it had normal, well-developed axial tissues in most cases. The relatively few cases with abnormal tail struture were stunted, oedematour larvae with defects in the trunk region as well. It is concluded from these experiments that cells near the original tail budare able to differentiate into tialbud tissues and to replace the amputated regoin, even at these late embryoic stages. The implications of these findings for comparative studies on regeneration in vertebrates are discussed.     

Electric currents in Xenopus tadpole tail regeneration

Xenopus laevis tadpoles can regenerate tail, including spinal cord, after partial amputation, but lose this ability during a specific period around stage 45. They regain this ability after stage 45. What happens during this “refractory period” might hold the key to spinal cord regeneration. We hypothesize that electric currents at amputated stumps play significant roles in tail regeneration. We measured electric current at tail stumps following amputation at different developmental stages. Amputation induced large outward currents leaving the stump. In regenerating stumps of stage 40 tadpoles, a remarkable reversal of the current direction occurred around 12-24 h post-amputation, while non-regenerating stumps of stage 45 tadpole maintained outward currents. This reversal of electric current at tail stumps correlates with whether tails regenerate or not (regenerating stage 40—inward current; non-regenerating stage 45—outward current). Reduction of tail stump current using sodium-free solution decreased the rate of regeneration and percentage regeneration. Fin punch wounds healed normally at stages 45 and 48, and in sodium-free solution, suggesting that the absence of tail re-growth at stage 45 is regeneration-specific rather than a general inhibition of wound healing. These data suggest that electric signals might be one of the key players regulating regeneration.     

Lizard and newt tail regeneration: a quantitative study

Almost perfect fits of the Gompertz equation to the growth in length of tail regenerates in the lizard, Lacerta lepida, and the newt, Notophthalmus viridescens, were obtained. Comparison of certain parameters of the equation with published mitotic index data suggests that the Gompertz equation characterizes each system at least from the time that significant mitotic activity is first observed histologically. An objective method for comparing the regeneration periods of the two species is described and applied. A unified hypothesis derived from consideration of properties of the Gompertz equation successfully accounts for the following phenomena reported, but previously unexplained, in the literature: (1) proximal amputations result in longer regenerates than do distal amputations; (2) proximal amputations elicit greater absolute rates of elongation (in mm/day) than do distal amputations; (3) the percent replaced of the length removed is rather constant, regardless of the absolute length regenerated; and (4) one of the parameters of the Gompertz equation appears to be lognormally distributed in a regenerating population. (See text for references.) A computerized interactive graphical system for normalizing growth equations of individual regenerates and integrating the mathematical model with potential candidates for biological control factors is briefly described.