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At least 847 records · Page 47Linked to original sources
PubMed1977

Cardiac mutant salamanders: evidence for heart induction.

Homozygosity for gene c in Ambystoma mexicanum results in no detectable heartbeat in situ. Alteration of the cardiac environment through organ culture results in rapid initiation of spontaneous heartbeat, indicating that absence of cardiac function in situ is not the result of failure of embryonic induction.

Ambystoma↗
PubMed1979

Allopurinol-induced melanism in the tiger salamander (Ambystoma tigrinum nebulosum).

The enzyme, xanthine dehydrogenase (XDH), has been examined in Ambystoma tigrinum nebulosum with respect to its role in pigmentation. It now seems probable that the melanoid gene (m) either codes directly for XDH or is somehow intimately connected with the normal function of this enzyme. Inhibition of XDH using the drug, allopurinol, results in animals which appear to be phenocopies of melanoid mutants as described for the Mexican axolotl (Ambystoma mexicanum). The effects of allopurinol in terms of specific pigmentary alterations were examined, and a new method for analyzing heterogeneous extracts of skin pigments (e.g., purines and pteridines) is presented. The significance of the link between XDH and melanism is discussed with emphasis on possible mechanisms of pigment induction and general applicability to biological systems.

Allopurinol↗
PubMed1980

Renal excretion of urea in the salamander, Ambystoma tigrinum.

Renal excretion of urea was assessed in adult and larval Ambystoma tigrinum by comparing simultaneous clearances of urea and inulin. The mean adult urea clearance ratio (CU/CIn) was 0.70 +/- 0.08 indicating net urea absorption. Larvae yielded a mean CU/CIn of 0.92 +/- 0.04. Individual larvae were quite variable however as approximately 30% displayed CU/CIn > 1. There was a significant negative correlation between CU/CIn and fractional water reabsorption. Comparisons of larval kidney urea concentration (KU) and plasma urea concentration (PU) revealed a mean KU/PU of 1.43 +/- 0.15. Treatment with 2,4-dinitrophenol decreased larval CU/CIn to 0.80 +/- 0.05 and KU/PU to 0.91 +/- 0.08. Phloridzin also decreased CU/CIn (0.67 +/- 0.06) however para-aminohippuric acid had no effect. Hypophysectomy combined with cautery of the pituitary stalk resulted in CU/CIn of 1.71 +/- 0.33 as compared to 0.84 +/- 0.08 in shams. These results are consistent with the possibility of net urea secretion at some point in the A. tigrinum nephron, followed by passive reabsorption in the distal segments under the influence of antidiuretic hormone.

Animals↗
PubMed1985

Neural fold and neural crest movement in the Mexican salamander Ambystoma mexicanum.

In studies of amphibian neurulation, the terms "neural ridge," "neural fold," and "neural crest" are sometimes used as synonyms. This has occasionally led to the misconception that grafting of the neural crest is equivalent to grafting of the neural fold. The neural fold, however, is composed of three parts: the neural crest, prospective neural tube tissue, and epidermis. In order to investigate how these neural fold components move during neurulation, time-lapse photography, electron microscopy, and grafting were performed. Ambystoma mexicanum embryos were photographed during neurulation at regular intervals. The photographs were analyzed to find the position of those cells at beginning of neurulation that end up on the line of fusion as the neural folds close. Posteriorly, these cells are already on the emerging neural fold. In the anterior neural folds, however, these cells are located in the lateral epidermis. Electron microscopy of the neural folds confirms the presence of epidermis. To follow the movement of the cells differentiating into melanophores (neural crest), neural fold parts were grafted into albino hosts. The crest cells differentiating into melanophores following ectopic grafting are located in the flank of the neural fold that is in contact with the neural plate. In grafts from the outside (distal) flank, no melanophores developed. Semithin sections show that the third part of the neural fold consists of apically constricted cells known to differentiate into neural tissue. Because the neural folds consist of epidermis, neural tissue, and neural crest, neural fold and neural crest cannot be used as synonyms.

Ambystoma↗