Abstract: The Medial Hyperstriatum Ventrale (MHV) and Lobus Parolfactorius (LPO) have been known to be the crucial part in the memory formation process in chick, the former is more important in the stability of memory, the latter is necessary for the store of long-term memory in the chick. The Jun protein derived -from c-fos proto-oncogene has been known to form a heterodimer with Fos protein, which functions as a third messenger to induce the expression of target gene. Immunohistochemical technique was used in the present study to detect and compare Jun expressed in HV and LPO of monovisual deprived chick following one-trial passive avoidance task. It was shown that the expression of Jun was scatty in the normal chick: monovisual deprived 2.5 hours, 4 hours or 24 hours induced Jun expression definitely increased in HV and LPO; monovisual deprived hours and 24 hours following one-trail passive avoidance task and memory retention test at 10 minutes and 70 minutes after learning . induced Jun expression continue to increase in HV and LPO; Jun expression in LPO was higher than that in HV.

Key words: chick, Jun-like protein, Immunohistochenical, HV, LPO, one-trail passive avoidance task