Postmortem stability of melatonin receptor binding and clock-relevant mRNAs in mouse suprachiasmatic nucleus.

The stability of receptor proteins and mRNAs in brain tissue is variable after death. As a prelude to quantitative studies of melatonin receptor density and clock gene expression in the human brain, the stability of these macromolecules was examined in the mouse brain under simulated postmortem conditions using the model of Spokes and Koch. In the mouse suprachiasmatic nucleus (SCN), melatonin receptor binding was significantly reduced after 18 to 24 h under postmortem conditions. Two mRNAs that are rhythmically expressed in the SCN, mPer1 and prepropressophysin (AVP), also decreased significantly over the interval studied, and mPer1 declined more rapidly than AVP. Both mPer1 and AVP mRNA levels in the SCN declined more rapidly in vivo than under postmortem conditions, suggesting that the degradation of these mRNAs is an active process. The results indicate that quantitative studies of melatonin receptor density on human postmortem material are feasible and that detection of rhythmic gene expression in the human SCN will likely require collection of specimens with a rather short (< 8 h) interval from death to tissue collection. The relative stability of melatonin receptor binding in the SCN also suggests that receptor binding may be a reliable marker for the location of the SCN in studies assessing clock gene expression in postmortem material.