Abstract: By using c-fos protein production as a marker of neuronal activation, the present work attempts to localize the various subdivisions within the amygdala that may participate in the neural mechanism of conditioned immunosuppression (CIS) in a conditioned taste aversion (CTA) paradigm. CTA and CIS were established by intake of saccharin as the conditioned stimulus (CS) with an injection of cyclophosphamide as an unconditioned stimulus (UCS). After animals were re-exposed to CS alone at intervals of 5 or 30 days after two trials of CS-UCS pairing, both CTA and CIS were assessed and the expression of c-fos protein in the amygdala nucleus was also observed correspondingly. The results showed that CTA occurred on both day 5 and day 30 after conditioning but CIS occurred only on day 5 after conditioning. Furthermore, it was found that intensive c-fos expression in the amygdaloid central (CeA) in the CS group was observed at the 5 days interval and a few c-fos immunoreactive inductions at the 30 days interval after re-exposure to CS. In the UCS group, only few c-fos immunoreactive productions in the CeA were detected at either interval testing. By comparing the results of the 5th day with the 30th day, it suggests that the CeA is an important nucleus related to the modulation of CIS. The role of other sub-nuclei of the amygdala in CTA and CIS are also discussed.

Key words: Conditioned immunosuppression, Amygdala, c-fos, Rats