Fos and Egr1 expression in the rat brain in response to olfactory cue after taste-potentiated odor aversion retrieval

When an odor is paired with a delayed illness, rats acquire a relatively weak odor aversion. In contrast, rats develop a strong aversion to an olfactory cue paired with delayed illness if it is presented simultaneously with a gustatory cue. Such a conditioning effect has been referred to as taste-potentiated odor aversion learning (TPOA). TPOA is an interesting model for studying neural mechanisms of plasticity because of its robustness and rapid acquisition. However, the neural substrate involved in TPOA retrieval has not been well characterized. To address this question, we used immunocytochemical detection of inducible transcription factors encoded b the immediate-early genes Fos and Egrl. Thirsty male rats conditioned to TPOA learning, and they were submitted to retrieval in the presence of the learned odor 3 d later. Significant increases in both Fos and Egrl expressions were observed in basolateral amygdala, insular cortex, and hippocampus in aversive rats in comparison with the all the control groups. The pattern of neuronal activity seemed unlikely to be related to the sole LiCI injection. Lastly, opposite patterns of Fos and Egri were noted in the entorhinal cortex and the central nucleus of amygdala, suggesting a differential involvement of these markers in retrieval of TPOA