Melatonin accelerates metamorphosis in Xenopus laevis

Abstract

Delayed metamorphosis associated with large body size has been observed in Woodhousei fowleri tadpoles reared in continuous dark (DD). To evaluate the mechanism by which DD delayed metamorphosis, light-cycle exposure was controlled and thyroxine (T4), melatonin, or drugs that alter prolactin (Prl) concentrations were given to Xenopus laevis tadpoles. It was hypothesized that exogenous melatonin would delay metamorphosis and increase body size, and that elevation of Prl concentrations would have effects similar to melatonin exposure. Xenopus laevis tadpoles were randomized to three light conditions [light/dark (LD, 12 h/12 h), DD, and continuous light (LL)] and subgroups in each light condition were treated with T4, melatonin, bromocriptine (Bro), haloperidol (Hal), or no drug. Each subgroup included 12 tadpoles. Drugs were administered in the water either continuously or daily from 07.00 to 19.00 h (Intermittent). Measurements of total length, leg length, and stage of metamorphosis were obtained at regular intervals. DD resulted in delayed metamorphosis, while LL did not. T4 accelerated metamorphosis as expected, countering the delaying effects of DD. In contrast to the hypothesis, melatonin accelerated metamorphosis and impaired body size compared to controls. Intermittent Hal also accelerated metamorphosis, while Bro delayed it. In DD, both T4 and melatonin led to increased tadpole size in contrast to their counterparts in LD or LL. Delayed metamorphosis in DD is not caused by increased melatonin production. Melatonin and Hal (as given in this study) accelerate metamorphosis. Melatonin acceleration of metamorphosis may occur through alteration of the concentration of prolactin.

New Insights Into the Evolutionary History of Melatonin Receptors in Vertebrates, With Particular Focus on Teleosts

“…As in other vertebrates, melatonin regulates pleiotropic actions in amphibians. It has been shown that photoperiod has an effect on the growth and the development of tadpoles ( 80 ), and administration of melatonin accelerates metamorphosis ( 81 ). Melatonin has been shown to be involved in the direct regulation of body blanching in axolotl and anuran tadpoles, a background adaptation response, resulting from the contraction of dermal melanophores in response to a dark environment.…”

A Note on the Goormaghtigh Equation Concerning Difference Sets

“…Let be the set of all positive integers. One hundred years ago, Ratat [27] and Rose and Goormaghtigh [28] conjectured that the equation has only two solutions and with . Equation (1.1) is usually called the Goormaghtigh equation.…”

Detailed Review Paper on Amphibian Metamorphosis Assay for the Detection of Thyroid Active Substances

“…Both factors inhibit TSH secretion and are capable of retarding metamorphosis (Denver, 1996). Melatonin may also inhibit metamorphosis through the induction of prolactin pathways (Rose and Rose, 1998). On the contrary, gonadotropin-releasing hormone (GnRH) has been found to increase TH levels in axolotls and frogs, thus has the potential of accelerating metamorphosis (Shi, 2000).…”