Brain opioid receptors in the hibernating bat, Myotis lucifugus: Modification by low temperature and comparison with rat, mouse and hamster

Several studies have provided evidence that brain opioid peptides may be involved in the control of the hibernation cycle. We have now examined the influence of hibernation on central opioid receptors. We have characterized the receptor binding properties of [3H]-naloxone in slices of the cerebral cortex and hypothalamus of the bat Myotis lucifugus. These receptors possess those characteristics expected of an opioid site namely high affinity, stereospecificity and saturability. Under normal incubation conditions (30 degrees C) we observed no effect of hibernation on [3H]-naloxone binding. However, when binding assays were performed at temperatures corresponding to the appropriate body temperature (e.g., 4 degrees C for hibernation) we detected a significant low temperature-induced increase in hypothalamic binding. Similar experiments in rat, mouse and hamster revealed that [3H]-naloxone binding was also increased at 4 degrees C when compared to 30 degrees C. This was true in hypothalamus and cortex. Additional studies in the rat demonstrated that the opioid receptor is of higher affinity at low temperatures. The behavioural and neurochemical consequences of this change in the opioid receptor, and whether this might be involved in the regulation of hibernation, remain to be studied.