C-FOS EXPRESSION IN THE PUTATIVE AVIAN SUPRACHIASMATIC NUCLEUS

c-fos induction was investigated as a potential component in the avian photic entrainment pathway and as a possible means of locating the ce ntral pacemaker in birds. In both quail (Coturnix coturnix japonica) a nd starlings (Sturnus vulgaris) exposure to 1 h of light induced Fos-l ir in the visual suprachiasmatic nucleus but not in the medial suprach iasmatic nucleus. However, the degree of c-fos induction in the visual suprachiasmatic nucleus was similar at different circadian times desp ite the fact that the light pulses caused differential phase shifts in the locomotor rhythm. For golden hamsters the same experiment resulte d in significantly different levels of Fos-lir in the suprachiasmatic nucleus, as well as different phase shifts. Starlings and hamsters wer e also entrained to T-cycles that caused a large daily phase shift (T = 21.5 h in starlings, T = 22.67 hours in hamsters), or no daily phase shift (T free running period). No difference in the induced levels of Fos-lir in the visual suprachiasmatic nucleus region was observed bet ween the two groups of starlings, but in hamsters there were significa ntly different levels of Fos-lir in the suprachiasmatic nucleus betwee n the two groups.