Day-night variation of preprosomatostatin messenger RNA level in the suprachiasmatic nucleus.

Day-night variation of the preprosomatostatin mRNA level in the suprachiasmatic nucleus (SCN), the site of the circadian pacemaker, was determined in rats maintained under light-dark cycles by semiquantitative Northern blot hybridization of micropunched tissues. Preprosomatostatin mRNA abundance in the SCN showed significant variation during a day with a peak level at around light on and a trough at around 4 h after light off. This time course was essentially identical with that previously found in blinded rats, indicating that environmental light did not produce an immediate effect on the preprosomatostatin mRNA level in the SCN. Moreover, this rhythm in the preprosomatostatin mRNA appeared specific to the SCN, since levels in the cortex and anterior hypothalamus did not oscillate even under light-dark conditions.