Endogenous Rhythm ofcFos Immunoreactivity

c-Fos immunoreactivity was determined with a highly sensitive antiserum generated against the amino acids 2-17 of the N-terminal peptide of c-Fos and characterized elsewhere (43); the antiserum was kindly provided by J.D. Mikkelsen, H. Lundbeck, Copenhagen. The spontaneously c-Fos immunopositive cells were present mostly in the DM-SCN (Figure 6) (35).

In rats maintained in LD 12:12 and released to darkness, c-Fos immunoreactivity in the DM-SCN peaked in the early subjective day and then slowly declined; the decrease to low nighttime levels occurred after the expected dark onset (Figure 7). Before the expected light onset, c-Fos started spontaneously to increase.

Figure 5. Adjustment of the SCN rhythm in the light-induced c-Fos immunoreactivity and of the pineal N-acetyltransferase rhythm to a change from a long to a short photoperiod and vice versa. A and B: Rats maintained in LD 16:8 (circles) were transferred to LD 8:16 and the SCN (A) and the pineal (B) rhythm were followed after 3 (squares), 6 (up-triangles) and 13 (down-triangles) days, respectively. C: Rats maintained in LD 8:16 (circles) were transferred to LD 16:8 and c-Fos photoinduction under unmashed conditions, i.e. under a 4-h advance of the dark onset and a 4-h delay of the light onset, respectively, was measured after 3 days (squares). Full bars indicate dark periods. Data from Sumova et al., 1996 (34) (A,C) and Illnerova et al.. 1986 (11) (B).

Figure 5. Adjustment of the SCN rhythm in the light-induced c-Fos immunoreactivity and of the pineal N-acetyltransferase rhythm to a change from a long to a short photoperiod and vice versa. A and B: Rats maintained in LD 16:8 (circles) were transferred to LD 8:16 and the SCN (A) and the pineal (B) rhythm were followed after 3 (squares), 6 (up-triangles) and 13 (down-triangles) days, respectively. C: Rats maintained in LD 8:16 (circles) were transferred to LD 16:8 and c-Fos photoinduction under unmashed conditions, i.e. under a 4-h advance of the dark onset and a 4-h delay of the light onset, respectively, was measured after 3 days (squares). Full bars indicate dark periods. Data from Sumova et al., 1996 (34) (A,C) and Illnerova et al.. 1986 (11) (B).

Figure 6. Example of the spontaneous induction of the immunoreactive c-Fos protein in the suprachiasmatic nucleus. A rat was manitained in LD 12:12. In the morning, light was not turned on at 06h as usual and the rat was sacrificed in darkness at 10 h. Note, that the spontaneous c-Fos induction occurred mostly in the DM-SCN. Adapted from Sumova et al., 1998 (35).

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