Time course analyses of the thermoregulatory responses to melatonin and chlorpromazine in bull snakes (Pituophis melanoleucus)

Intraperitoneal injections of either melatonin (MEL) or chlorpromazine (CPZ) significantly lowered preferred body temperature (Tb) Of bullsnakes, Pituophis melanoleucus. Multiple comparison procedures showed that Tb for both MEL and CPZ treatments differed significantly from both the injected and non-injected control groups. However, Tb for MEL treatments did not differ from those of CPZ treatments (t = 0.471; df = 12; P = 0.646), indicating that each drug has a similar effect on thermal selection. Our results obtained from time-course experiments support earlier experiments where a repeated measures design was used to test treatment effects of MEL and CPZ on thermal selection. However, we further show that injected controls (saline and ethanol injection) do not differ from noninjected controls (no injection) for both MEL and CPZ experiments. Although there are no differences between Tb Of snakes receiving MEL or CPZ, time-course analyses indicate that the duration of thermoregulatory responses differ between MEL and CPZ treatments. This indicates that CPZ treatments may be more effective in increasing the amount of time required for individuals to return to normal preferred T-b or set temperature (T-set). The initial duration of thermoregulatory responses to the first injection of MEL differed significantly from the second injection. There were no differences in the duration of thermoregulatory responses between the first and second injections of CPZ. There are no data for the metabolic half-life of MEL in ectothermic vertebrates. Our study provides some information regarding the time-course of thermoregulatory responses to elevated levels of MEL via intraperitoneal injections of either MEL or CPZ, a metabolic antagonist of MEL. (C) 1998 Elsevier Science Ltd. All rights reserved.