Effects of Bombesin on Behavioral Thermoregulation in the Bullfrog

Abstract

Bombesin is a member of a class of neuroactive chemicals that have potent thermoregulatory effects in ectothermic and endothermic vertebrate species. Bombesin-like peptides are found in the brains of ectothermic and endothermic vertebrates and have been implicated in the central nervous system modulation of behavioral thermoregulation. Amphibians rely on behavioral thermoregulation to maintain their body temperature within developmental stage-dependant critical limits. To investigate the influence of bombesin on behavioral thermoregulation, we examined the effects of central injections of bombesin on thermal habitat selection at different stages of bullfrog development. Tadpoles and adult male and female frogs were allowed to select a preferred temperature, within an aquatic thermal gradient, before and after receiving an intracerebroventricular injection of bombesin. In larval and adult female bullfrogs, bombesin administration caused a decrease in preferred temperature values. This effect was clearly dose-dependent in tadpoles. Bombesin effects were variable in adult males, probably due to an overriding stress response to handling exhibited by males. The bombesin-induced hypothermia was blocked by [D-Phe⁶, Des-Met¹⁴]-bombesin (6–14), ethyl amide, a bombesin/gastrin-releasing peptide receptor antagonist. These data suggest that bombesin/gastrin-releasing peptide receptors are functional in the central nervous system of larval and adult amphibians and that receptor binding can modulate thermoregulation. They raise the question: under what natural conditions is endogenous bombesin/gastrin-releasing peptide released in the brain to activate thermoregulatory behavior?

Conflicts and interactions among reproduction, thermoregulation and feeding in viviparous reptiles: are gravid snakes anorexic?

“…Neuoroactive chemicals presumably also play a role in eliciting thermoregulatory behaviour (e.g. Leger & Mathieson, 1997).…”

Where the Tadpole Meets the World—Observations and Speculations on Biomechanical and Biochemical Factors that Influence Metamorphosis in Anurans

“…In a similar vein, one notes that bombesin injected into anurans alters their thermal preference (Leger and Mathieson, 1997) and that tadpoles change their thermal preference when they metamorphose. Could the up-regulation of bombesin-like compounds in the skin of anurans at metamorphosis play a role in this shift as well?…”