DAY-NIGHT VARIATION OF PREPROSOMATOSTATIN MESSENGER-RNA LEVEL IN THE SUPRACHIASMATIC NUCLEUS

Day-night variation of the preprosomatostatin mRNA level in the suprac hiasmatic nucleus (SCN), the site of the circadian pacemaker, was dete rmined in rats maintained under light-dark cycles by semiquantitative Northern blot hybridization of micropunched tissues. Preprosomatostati n 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 previo usly found in blinded rats, indicating that environmental light did no t 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 hypothal amus did not oscillate even under light-dark conditions. (C) 1994 Acad emic Press, Inc.