Relationships between taste reactivity and intake in the neurologically intact rat

Abstract

To investigate the differences between short-term intake tests and taste reactivity responses to tastes, rats received 1-min intraoral infusions of a variety of tastants delivered at the rate of 1 ml/min. Oral responses were videotaped and analysed in terms of the sequence and number of ingestive and aversive taste reactivity response components evoked. Intake was also measured. The number of rats displaying ingestive taste reactivity components and the mean number of ingestive components displayed per rat elicited by sucrose and NaCl increased with increasing concentration. Intake was high across all concentrations. HCl infusions elicited alternation between ingestive and aversive response components. The number of rats displaying aversive taste reactivity response components and the mean number of aversive response components displayed per rat, elicited by QHCl, increased with increasing concentration, while both intake and the median latency to reject QHCl decreased (Experiment I). To determine whether other tastes judged bitter by humans would elicit a quinine-like taste reactivity response in the rat, sucrose octa-acetate (SOA), quinine sulfate (QS) and caffeine (CAF) stimuli were examined. Both QS and CAF infusions elicited an increased number of aversive response components with increasing concentration, and intake decreased. SOA infusions elicited alternation between ingestive and aversive response components followed by a display of solely aversive components, and both intake and median latency to reject the infusions decreased significantly with increased concentration (Experiment II). Experiment I demonstrated that hypertonic NaCl infusions elicit ingestive response components, while short-term intake tests show that hypertonic NaCl is rejected and is thus inferred to be aversive. Rats received prolonged infusions of hypertonic NaCl solutions at the rate of 1 ml/min until fluid was seen on the surface of the chamber, indicating rejection. Prolonged infusions of hypertonic NaCl solutions elicited an initial display of solely ingestive response components followed by an abrupt shift to solely aversive response components and active fluid rejection. Higher concentrations elicited this shift sooner than lower ones (Experiment III). The results suggest that patterns of taste reactivity response components are good predictors of intake duration.