Elevated levels of either endogenous or exogenous melatonin modulate physiology and behavior in many vertebrates. However, there are no data that address the hormonal action of melatonin on the behavioral transport response in rat pups though there is much evidence suggesting that serotonin, the anabolic precursor to melatonin, modulates this behavior. We conducted two experiments that demonstrate melatonin’s effect on the behavioral transport response in the laboratory rat (Rattus norvegicus). In our first experiment, we found a significant effect of age. We then controlled for age as a variable in our second experiment to investigate possible dose effects of melatonin. We found all doses of melatonin to significantly suppress the transport response, and briefly discuss the neurochemistry and ontogeny for the effects of melatonin on the transport response in rats. This study is the first to document the suppression of the transport response in rats by melatonin and could serve as a new experimental model for investigating the influence of melatonin on the behavioral physiology of vertebrate systems. More importantly, the evolutionary significance of melatonin’s role in physiologically modulating activity and the behavioral transport response may be of interest to future investigators.
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