FETAL GRAFTS CONTAINING SUPRACHIASMATIC NUCLEI RESTORE THE DIURNAL RHYTHM OF CRH AND POMC MESSENGER-RNA IN AGING RATS

We assessed whether fetal tissue containing the suprachiasmatic nuclei (SCN) can restore age-related changes in the diurnal rhythm of hypoth alamic corticotropin-releasing hormone (CRH) and anterior pituitary pr oopiomelanocortin (POMC) mRNA. Young, middle-aged, and middle-aged SCN -transplanted rats were killed at seven times of day. In young rats, C RH mRNA exhibited a diurnal rhythm in the dorsomedial paraventricular nuclei but not in other subdivisions of the nuclei. No rhythm was dete cted in aging rats. SCN transplants restored a rhythm in CRH mRNA, but tile timing was not precisely the same as in young animals. POMC mRNA exhibited a daily rhythm in young rats. Aging abolished the rhythm an d decreased the average mRNA level; fetal transplants restored the rhy thm, but the amplitude remained attenuated. These data are the first d emonstration that fetal tissue can restore the diurnal rhythm of a neu roendocrine axis that is driven by the SCN. We conclude that the neuro endocrine substrate from the aging host remains capable of responding to diurnal cues to express diurnal rhythmicity in CRH/POMC mRNA when f etal SCN transplants confer the appropriate signals.