Toad

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

Aldosterone increases the apical Na+ permeability of toad bladder by two different mechanisms.

Abstract: The aldosterone-induced augmentation of Na+ transport in toad bladder was analyzed by comparing the hormonal actions on the transepithelial short-circuit current and on the amiloride-sensitive 22Na+ uptake in isolated membrane vesicles. Incubating bladders with 0.5 microM aldosterone for 3 hr evoked more than a 2-fold increase of the short-circuit current (because of the activation or insertion of apical amiloride-blockable channels) but had no effect on the amiloride-sensitive Na+ transport in apical vesicles derived from the treated tissue. A longer incubation (e.g., 6 hr) produced an additional augmentation of the short-circuit current, which was accompanied by about a 3-fold increase of the channel activity in isolated membranes. The stimulatory effect of aldosterone sustained in vesicles was inhibited by the antagonist spironolactone (present at 1000-fold excess) and the protein synthesis inhibitor cycloheximide (1 microM). In addition, triiodothyronine and butyrate, previously reported to partly inhibit the aldosterone-induced increase in short-circuit current, blocked the hormonal effect in vesicles. It is suggested that aldosterone elevates the apical Na+ permeability of target epithelia by two different mechanisms: a relatively fast effect (less than or equal to 3 hr), which is insensitive to triiodothyronine or butyrate and is not sustained by the isolated membrane, and a slower or later (greater than 3 hr) response blocked by these reagents, which is preserved by the isolated membrane. The data also indicate that these processes are mediated by different nuclear receptors.

Allometry and selection in a novel predator-prey system : Australian snakes and the invading cane toad

Abstract: Because many organismal traits vary with body size, interactions between species can be affected by the respective body sizes of the participants. We focus on a novel predator–prey system involving an introduced, highly toxic anuran (the cane toad, Bufo marinus) and native Australian snakes. The chance of a snake dying after ingesting a toad depends on the size of the snake and the size of the toad, and ultimately reflects the effect of four allometries: (1) physiological tolerance (the rate that physiological tolerance to toad toxin changes with snake size); (2) swallowing ability (the rate that maximal ingestible toad size (i.e. snake head size) increases with snake body size); (3) prey size (the rate that prey size taken by snakes increases with snake head size) and (4) toad toxicity (the rate that toxicity increases with toad size). We measured these allometries, and combined them to estimate the rate at which a snake's resistance changes with toad toxicity. The parotoid glands (and thus, toxicity) of toads increased disproportionately with toad size (i.e. relative to body size, larger toads were more toxic) but simultaneously, head size relative to body size (and thus, maximal ingestible prey size relative to predator size) declined with increasing body size in snakes. Thus, these two allometries tended to cancel each other out. Physiological tolerance to toxins did not vary with snake body size. The end result was that across snake species, mean adult body size did not affect vulnerability. Within species, however, smaller predators were more vulnerable, because the intraspecific rate of decrease in relative head size of snakes was steeper than the rate of increase in toxicity of toads. Thus, toad invasion may cause disproportionate mortality of juvenile snakes, and adults of the sex with smaller mean adult body sizes.

Color discrimination mechanisms in the retina of the toad ( Bufo bufo )

Abstract: In many class 2 ganglion cells in the toad (Bufo bufo) retina the blue-sensitive green rods contribute only to the “on” responses, while the yellow-sensitive cones contribute to both “on” and “off”. Thus the spectral sensitivities of the on and off responses deviate in the blue and violet parts of the spectrum (Fig. 1). This correlates with Dietz's (1972) finding that toads detect a moving blue prey-dummy irrespective of the intensity of the grey background.