Toad

About: Toad is a research topic. Over the lifetime, 1624 publications have been published within this topic receiving 28732 citations.

Mast cells in the amphibian brain during development.

Abstract: This is the first descriptive study of ontogenesis and anatomical distribution of mast cells in the developing brain of three different amphibian species. In the toad and the green frog, mast cells are preferentially located in: (i) the meningeal lining (pia mater), (ii) the choroid plexuses, both anterior and posterior, and (iii) the neuropil, in close association with the epithelial cell lining of blood vessels. It is only in the perennially aquatic African clawed frog that mast cells never appear inside brain ventricles and within the neuropil. Mast cells first become identifiable in brain of different species in different stages of development. While there are differences in the number of mast cells in different species at different stages of development, the number nearly doubles in all three species during the transition from pro-metamorphic stage of larval development to the peak of metamorphic climax. Furthermore, the number of mast cells is comparatively higher in the toad and remarkably lower in the fully aquatic Xenopus laevis, in which species the first appearance of identifiable mast cells during larval development occurs much later than in equivalent stages of development of the toad and the green frog. The secretory nature of mast cells can be assumed by the presence of cytoplasmic granules, which may show species-specific texture. Further experimental analyses are required to unveil the usefulness of mast cells in the amphibian brain.

Caffeine effects on heart muscle energetics: species differences.

Abstract: The effects of caffeine (1mM) on energy expenditure and mechanical parameters in rat and toad perfused heart ventricles were examined at various stimulation frequencies. While in rat muscles caffeine significantly depressed developed tension and maximal rates of contraction and relaxation at all frequencies tested, in toad ventricle a slight positive inotropic effect was observed. Even though caffeine did not alter total contraction time in both preparations, in the rat ventricle the last part of relaxation was prolonged. In rat ventricle in the presence of caffeine, the ratios between active heat production per beat and either developed tension or tension time integral increased at all frequencies tested (+303 +/- 47 microJ.mN-1 x g-1 and +1.21 +/- 0.13 mJ.mN-1 x s-1 x g-1 respectively) indicating a decrease in contractile economy. In toad ventricle no changes on these ratios were observed. The fact that only in rat ventricle caffeine decreased muscle economy suggests that caffeine affects a system that is active in rat ventricle but it is not operative in toad ventricle. This gives support to the hypothesis that if in rat ventricle SR-Ca pump (1 ATP hydrolyzed/2 Ca transported) is inhibited by caffeine cytosolic Ca would have to be removed by alternative mechanisms such as Na-Ca exchanger or sarcolemmal Ca pump both with a higher rate of ATP hydrolysis (1 ATP hydrolyzed/Ca transported) with the consequent decrease in muscle economy. Resting heat production was increased by caffeine in both preparations and the magnitude of the increment (+3.0 +/- 0.6 mW.g-1 and +0.75 +/- 0.21 mW.g-1 for rat and toad ventricle respectively) also correlates with the different degree of SR activity in both species.