Phase relations between host and grafted SCN depend on graft location in rats

Fetal SCN grafts into intact rats were used as a model to study coupling am ong circadian oscillators. The phase relation in metabolic activity was ana lyzed between host SCN and fetal SCN grafted into the third (n = 24) or lat eral (n = 18) ventricles. Host and third ventricle SCN grafts showed metabo lic activity rhythms with peak values at CT 6, as extrapolated from drinkin g rhythmicity. In lateral ventricle grafted animals only the host SCN showe d rhythmicity, although peak values occurred as indicated by the drinking r hythms at CT 9. The present data suggest asymmetrical communication between host and grafted SCN depending on graft location, which may be related to different types of signal transmission.