Circadian rhythmicity of vasopressin levels in the cerebrospinal fluid of suprachiasmatic nucleus-lesioned and -grafted rats

Transplantation of the fetal suprachiasmatic nucleus (SCN) in arrhythmic SC N-lesioned rats can reinstate circadian drinking rhythms in 40% to 50% of t he cases. In the current article, it was investigated whether the failure i n the other rats could be due to the absence of a circadian rhythm in the g rafted SCN, using a circadian vasopressin (VP) rhythm in the cerebrospinal fluid (CSF) as the indicator for a rhythmic SCN. CSF was sampled in continu ous darkness from intact control rats and SCN-lesioned and -grafted rats. V P could be detected in all samples, with concentrations of 15 to 30 pg/ml i n the control rats and 5 to 15 pg/ml in the grafted rats. A circadian VP rh ythm with a two- to threefold difference between peak and nadir values was found in all 7 control rats but in only 4 of 13 experimental rats, despite the presence of a VP-positive SCN in all grafts. A circadian VP rhythm was present in 2 drinking rhythm-recovered rats (6 of 13) and in 2 nonrecovery rats. Apparently, in these latter rats, the failure of the grafted SCN to r estore a circadian drinking rhythm cannot be attributed to a lack of rhythm icity in the SCN itself. Thus, the presence of a rhythmic grafted SCN, as i s deduced from a circadian CSF VP rhythm, appears not to be sufficient for restoration of a circadian drinking rhythm in SCN-lesioned arrhythmic rats.