Intraoral intake and c-Fos induction in rats with conditioned flavor taste preferences.

Abstract

Conditioned flavor taste preferences (CFTP) are a robust form of associative learning in which rats will choose a flavor (e.g. kool-aid) previously mixed with a prefered taste (e.g. 8% fructose) over a flavor previously mixed with a less prefered taste (e.g. 0.2% saccharin). To explore the neural substrates of CFTP, we examined c-Fos induction in response to intraoral infusions of kool-aid/saccharin solutions in rats after acquisition of CFTP. In order to minimize post-ingestive effects, kool-aid was paired with two concentrations of saccharin, 0.2% ( highly preferred) and 0.05% sacccharin (isopreferred to water). To condition a CFTP, adult male rats were given 24-h access to 2 bottles with kool-aid mixed in either 0.2% saccharin (CS+/US+) or 0.05% saccharin (CS-/US-); grape and cherry flavors were counterbalanced as CS+ and CS−. After 8 days, CFTP was confirmed in a 24-h, 2-bottle test of CS+/US- vs. CS-/US-. Rats were implanted with intraoral catheters, and infused with 10 ml over 10 min of one of 4 solutions: CS+/US-, CS-/US-, US+, or US- (n=5–6/group). Intake was measured by weighing rats before and after infusion. One hour after infusion, rats were perfused and the brains processed for c-Fos immunohistochemistry. Intraoral intakes of the 2 kool-aid mixtures, CS+/US- (5.2±1.0 g) and CS-/US- (5.1±1.1 g), and the 2 saccharin solutions, US+ (5.5±1.7 g) and US- (3.2±1.1 g), were not different. Preliminary analysis of c-Fos patterns revealed widespread activation of the rostral olfactory and gustatory pathways, but greater activation within the amygdala after CS+/US- infusion. Support: NIDCD 03198 and 00044.