Vasopressin-deficient suprachiasmatic nucleus grafts re-instate circadian rhythmicity in suprachiasmatic nucleus-lesioned arrhythmic rats

It was investigated whether grafts of the suprachiasmatic nucleus could re- instate circadian rhythmicity in the absence of its endogenous vasopressin production and whether the restored rhythm would have the long period lengt h of the donor. Grafts of 17-days-old vasopressin-deficient homozygous Brat tleboro rat fetuses, homotopically placed in arrhythmic suprachiasmatic nuc leus-lesioned Wistar rats, re-instated circadian drinking rhythm within 20- 50 days similar as seen for grafts of heterozygous control fetuses. Period length of the recovered rhythm revealed a similar difference (average 24.3 vs 23.8 h) as reported for the rhythm between the adult Brattleboro genotyp es. In all transplants, also those of the two-third non-recovery rats, a su rviving suprachiasmatic nucleus was visible as a vasoactive intestinal poly peptide-positive neuronal cell cluster, whereas heterozygous transplants al so revealed the complementary vasopressinergic cell part. Explanation of th e absence of recovery failed since no undisputable correlation emerged betw een recovery of rhythm and vasoactive intestinal polypeptide, vasopressin a nd/or somatostatin immunocytochemical characteristics of the suprachiasmati c nucleus of the transplant. Special focus on the somatostatinergic neurons revealed their presence only occasionally near or in between the vasoactiv e intestinal polypeptidergic and (in the case of heterozygous grafts) vasop ressinergic cell cluster. However their aberrant cytoarchitectural position appeared not to have affected the possibility to restore drinking rhythm o f the suprachiasmatic nucleus-lesioned arrhythmic rat. It was concluded that grafted Brattleboro fetal suprachiasmatic nucleus dev elop their intrinsic rhythm conform their genotype and that vasopressin is not a crucial component in the maintenance nor in the transfer of circadian activity of the biological clock for drinking activity. Vasopressin of the suprachiasmatic nucleus may instead serve modulation within the circadian system. (C) 1998 IBRO. Published by Elsevier Science Ltd.