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At least 955 records · Page 53Linked to original sources
PubMed1988

Block of light responses of salamander rods by pertussis toxin and reversal by nicotinamide.

Transducin is the substrate for a pertussis toxin-catalyzed ADP-ribosylation in isolated retinal rod disk membranes [(1984) J. Biol. Chem. 259, 23-26]. The effects of the toxin on the light responses of intact dark-adapted rods were studied. Applied close to a rod outer segment in a retinal slice, pertussis toxin depolarized the rod by a few millivolts and produced a long-lasting depression of light responses, effects which depended on penetration of toxin into rods. Nicotinamide, an inhibitor of ADP-ribosylation, not only blocked the action of the toxin, but also reversed the effects once established. The action of nicotinamide itself on rods indicates the presence of endogenous ADP-ribosyltransferases which may constitute a control system modulating phototransduction. Inhibition of phospholipase C by neomycin had only transient effects indicating that the cGMP, rather than a phosphoinositide, pathway is primary in vertebrate phototransduction. Rapid reversal of pertussis toxin action suggests possible clinical applications of nicotinamide or congeners to the treatment of disease caused by ADP-ribosylating bacterial toxins.

Adenosine Diphosphate Ribose↗
PubMed1983

Effect of parathyroidectomy on plasma calcium levels in the seal salamander, Desmognathus monticola.

The parathyroid glands of Desmognathus monticola are located in the subdermal connective tissue of the neck. Although they are smaller than previously described urodele parathyroid glands, their histological structure is similar. Parathyroidectomy caused a decrease in plasma calcium concentrations within 4 days following the operation. By Days 12 and 21, however, the plasma calcium levels of parathyroidectomized animals were not significantly different from those of sham-operated animals. Thus, the parathyroid gland of this species contains a hypercalcemic principle, but the recovery from hypocalcemia suggests that some hypercalcemic mechanism other than the parathyroid system must be involved in calcium homeostasis.

Age Factors↗
PubMed1985

Seasonal variations in spermatogenesis, testicular weights, vasa deferentia, and androgen levels in neotenic male tiger salamanders, Ambystoma tigrinum.

Significant seasonal changes were observed in spermatogenesis, testicular weights, vasa deferentia, and cloacal development as well as in plasma androgen levels (testosterone and dihydrotestosterone). Androgen levels were highest in the fall and lowest during the period of spermatogenesis. Low levels of androgens were also observed during the breeding season. Diameter of the vasa deferentia corresponded to presence of stored spermatozoa and not to plasma androgen levels. Testicular weights were independent of androgen levels and stage of spermatogenesis. Maximal testicular weight occurred at the onset of spermiation. Hypertrophy of the epithelial lining of the vasa deferentia and the condition of the cloacal gland complex were correlated closely to plasma androgen levels. Comparison of spermatogenetic events, androgen-dependent sex accessory structures, and plasma androgen levels suggests either differential release of pituitary gonadotropins on a seasonal basis or variable testicular responsiveness to gonadotropins.

Ambystoma↗
PubMed1991

Tectectomy in the cyclopean salamander.

In an Ambystoma larva with both natural eyes removed and one eye grafted atop the head (Cyclops preparation), vision-dependent behavior usually recovers from the enucleation inherent in the operation, but the optically activated skin blanching reaction reappears in a very small number of instances. In the present studies, while the latter trend continued for the conventional Cyclops preparation, tectectomy concurrent with the ectopic eye transplantation resulted in a several-fold increase in the recovery of blanching competency. Some 60 percent of the tectectomized Cyclops animals exhibited the same Hogben-Slome pigmentation indices as larvae with one natural eye intact (controls). As measured planimetrically with an image analyzer, the pigment spots (melanosome containing portions of dermal melanocytes) contracted to the same extent in the blanch-competent Cyclops animals as in controls with a single natural eye.

Ambystoma↗