Molecular signaling during taste aversion learning.

Behavioral and neural assessment tools have been used to identify cellular and molecular events that occur during taste aversion acquisition. Studies described here include an assessment of taste information processing and taste-illness association using fos-like immunoreactivity (FLI) to mark populations of cells that react strongly to the taste conditioned stimulus (CS), the illness unconditioned stimulus (US), or the pairing of CS and US. Exposure to a novel, but not a familiar, CS taste (saccharin) was found to induce robust increases in FLI in some, but not all, brain regions previously implicated in taste processing or taste aversion learning. Striking effects of taste novelty on FLI were found in central amygdala (CNA) and insular cortex (IC) but not in basolateral amygdala (BLA), pontine parabrachial nucleus (PBN), or nucleus of the solitary tract (NTS). Of those regions responding to taste novelty, only CNA showed significant elevations in FLI in response to the US, LiCl. In additional studies, FLI was examined after an effective training experience, novel CS-US pairing, and compared with an ineffective one, familiar CS-US pairing. After CS-US pairing, taste novelty modulated FLI in virtually all the regions previously implicated in conditioned taste aversion (CTA) learning, including PBN, CNA, BLA, IC, as well as NTS. Thus, a distributed and interdependent neural CTA circuit is mapped using this method, and the use of localized lesion and inactivation studies promises to further define the functional role of structures within this circuit.