Sugar Dependence in Low-versus High-Saccharin Consuming Rats
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Intermittent access to glucose can produce opioid-mediated dependence in rats. The current study investigated whether rats selectively bred for high (HiS) and low (LoS) saccharin intake develop dependence to glucose after 14 days of exposure and while on a food deprivation schedule. Dependence was assessed using increased glucose intake, acoustic startle amplitude, and behavioral withdrawal measures.. Naloxone, an opioid receptor antagonist, was used to precipitate withdrawal in half the animals. Not surprisingly, startle habituated over trials. Average glucose consumption was positively correlated with startle in the LoS rats but not in the HiS rats. In striking contrast to earlier studies, saline-treated HiS exhibited elevated startle overall; this effect was reversed by naloxone treatment. Rats treated with naloxone exhibited more tremorless jaw movements and less grooming and scratching behaviors. Perhaps most perplexing is the fact that animals in all groups displayed forepaw tremors. Food deprivation appeared to have an overall effect on the rats, as indicated by withdrawal behaviors in the control condition rats and elevation of startle in the HiS rats. That naloxone affected several behaviors overall and reversed the elevation of startle in HiS rats implicates changes in the endogenous opiate system in these effects. This opiate-focused hypothesis will guide future research.