Rusak B, McNaughton L, Robertson H A, Hunt S P
Department of Psychology, Dalhousie University, Halifax, N.S., Canada.
Brain Res Mol Brain Res. 1992 Jun;14(1-2):124-30. doi: 10.1016/0169-328x(92)90019-8.
Exposure of rodents to light at daily times at which it can phase-shift circadian rhythms (subjective night) induces an increase in immunoreactivity for the immediate-early gene product Fos in cells of the circadian pacemaker, the suprachiasmatic nuclei (SCN). Light exposure at other phases (subjective day) does not increase Fos immunoreactivity in SCN cells, but it is not known whether this failure reflects the inability of light to induce transcription of appropriate mRNAs, or a post-transcriptional block. We used in situ hybridization studies to examine levels of mRNA in the SCN of rats exposed to light during the subjective day and subjective night. We studied levels of mRNAs for several immediate-early genes: c-fos, NGFI-A, NGFI-B, c-jun, junB and junD, before and after light exposure at these phases. Levels of mRNAs for all of the genes tested were unaffected by light exposure during the subjective day, and all were increased in response to light during the subjective night. With the exception of a weak constitutive label for junD, none of the genes were expressed in the SCN in darkness at either phase. Light-induced increases in the levels of several mRNAs in the SCN occur only during the subjective night; the mechanisms which prevent such responses during the subjective day remain unknown.
在啮齿动物昼夜节律可发生相位转移的时段（主观夜间）使其暴露于光照下，会导致昼夜节律起搏器视交叉上核（SCN）细胞中即早基因产物Fos的免疫反应性增加。在其他时段（主观白天）暴露于光照下并不会增加SCN细胞中的Fos免疫反应性，但尚不清楚这种无反应是反映了光照无法诱导适当mRNA的转录，还是转录后阻断。我们使用原位杂交研究来检测在主观白天和主观夜间暴露于光照下的大鼠SCN中的mRNA水平。我们研究了几个即早基因的mRNA水平：c-fos、NGFI-A、NGFI-B、c-jun、junB和junD，在这些时段光照暴露前后的情况。所有测试基因的mRNA水平在主观白天不受光照暴露的影响，而在主观夜间均对光照有反应而增加。除了junD有微弱的组成性标记外，在两个时段的黑暗中，这些基因在SCN中均未表达。SCN中几种mRNA水平的光照诱导增加仅发生在主观夜间；阻止主观白天出现这种反应的机制仍然未知。
