Novel tastes elevate c-fos expression in the central amygdala and insular cortex: implication for taste aversion learning.

Taste novelty strongly modulates the speed and strength of taste aversion conditioning. To identify molecular signals responsive to novel tastes, immunostaining for c-fos protein (Fos-like immunoreactivity [FLI]) was used to mark neurons that responded differentially to taste novelty. Novel saccharin induced larger increases in FLI than familiar saccharin. This pattern was seen in central amygdala and insular cortex, but not in basolateral amygdala, parabrachial nucleus, or nucleus of the solitary tract. Other parameters known to influence aversion learning were tested for effects on FLI. Manipulations known to reduce the strength of learning blunted the FLI response, supporting the idea that FLI marks neural pathways critical to taste processing during acquisition, and that c-fos expression is a key transcriptional event underlying this plasticity.