Circadian rhythmicity after neural transplant to hamster third ventricle: specificity of suprachiasmatic nuclei.

Neural transplants into the third ventricle utilized to quantitatively assess the effectiveness of fetal tissue from selected brain sites in restoring circadian locomotor rhythmicity of adult hamsters rendered arrhythmic by lesions of the suprachiasmatic nuclei (SCN). Circadian function was continuously monitored in recording wheel cages under controlled environmental conditions. Animals which remained arrhythmic for 3-4 weeks after SCN lesions received transplants of neural tissue from 13-14-day-old fetuses: either SCN tissue or non-SCN tissue (cerebral cortex or hypothalamus excluding SCN). Quantitative evaluation of the data indicated partial restoration of circadian rhythmicity in 37% of 19 animals with SCN transplants, but in 0% of the 9 animals with non-SCN neural transplants. The mean time for reappearance of rhythmicity was 20 days after SCN transplantation. Animals were sacrificed 8-10 weeks after transplantation for histological analysis in order to visualize lesion placement and to characterize transplants. The cytoarchitecture and neuropeptide organization of the transplants were consistent with the brain region. Only SCN transplants were characterized by aggregates of small neurons with codistributed immunoreactivity for SCN-characteristic neuropeptides.