AGE-RELATED-CHANGES IN LIGHT-INDUCED JUN-B AND JUN-D EXPRESSION - EFFECTS OF TRANSPLANTATION OF FETAL TISSUE CONTAINING THE SUPRACHIASMATICNUCLEUS

Fos and Jun mRNA and peptide exhibit a daily light-induced rhythm in t he suprachiasmatic nucleus (SCN). The authors previously have reported that Fos expression in the SCN is elevated prematurely during the dar k, Light-induced Fos expression is attenuated in middle-aged rats, and transplantation of fetal SCN tissue into the third ventricle of rats of this age restores the daily pattern of Fos expression to that of th e young. Using immunocytochemistry, the authors performed the present study to determine whether Jun-B and Jun-D expression in the SCN is al tered at the same stage during aging and, if so, whether transplantati on of fetal tissue containing the SCN can restore the Light-induced rh ythms of these two immediate early genes. All groups of rats were tran scardially perfused 90 min prior to and after light onset. In young ra ts, Light induced a robust increase in the number of Jun-B positive ce lls in the SCN, whereas very few cells were labeled before light onset . In middle-aged rats, the light-induced increase in the number of Jun -B positive cells was significantly attenuated. Transplantation of fet al SCN tissue into the middle-aged rats successfully restored light-in duced Jun-B expression to the levels of young rats. By contrast, Jun-D exhibited a constitutively high level of expression in the SCN both b efore and after light onset, and light induced only a slight but signi ficant increase. No age-related changes were detected in the expressio n of Jun-D either before or after Light onset. Transplantation of feta l SCN tissue did not alter the daily pattern of Jun-D expression in th e middle-aged rats. These data suggest that (1) Light-induced activati on of SCN neural activity is blunted during aging, (2) fetal SCN tissu e can provide the critical support to allow the host to respond proper ly to light cues, and (3) the age-related change in Jun-B expression i n the middle-aged host SCN can be rescued by fetal SCN transplants.