Ingestional responses to metabolic challenges in rats selectively bred for high and low saccharin intake

Rats selectively bred on the basis of saccharin intake also differ on some measures of emotional reactivity. The present studies were designed to contribute to our understanding of this association. Rats selectively bred for relatively high (HiS) versus low (LoS) saccharin intake were tested in two paradigms useful in assessing the ability to respond adaptively to internal perturbations of metabolic regulation or to external events that may produce metabolic challenges. The first study concerned slow-onset (regular insulin) and rapid-onset (2-deoxy-D-glucose [2-DG], fast-acting insulin) glucoprivation and resultant feeding behavior. LoS and HiS lines did not differ in response to saline or slow-onset challenges, but LoS rats ate less in the first half hour after rapid-onset challenges; the line differences were eliminated by pretreatment with caffeine. The second study revealed significantly higher plasma corticosterone (CORT) among LoS rats relative to HiS rats, both in the light and in the dark. Preliminary assessments after a single stressor and a single dose of dexamethasone showed, respectively, CORT elevation and suppression that was comparable in the two lines. These results add further support to the ideas that voluntary consumption of saccharin is related to the expression of classically defined emotional behaviors, and that responsiveness to diverse metabolic challenges may share a common basis, such as genetic pleiotropism.