Effects of Suprachiasmatic Transplants on Circadian Rhythms of Neuroendocrine Function in Golden Hamsters

E. L. Meyer-Bernstein
1999 Endocrinology  
Grafts of fetal tissue including the suprachiasmatic nucleus (SCN) of the hypothalamus restore locomotor rhythmicity to behaviorally arrhythmic, SCN-lesioned Syrian hamsters. We sought to determine whether such transplants also reinstate endocrine rhythms in SCNlesioned hamsters. In Exp 1, SCN lesions interrupted estrous cycles in a 14 h light, 10 h dark photoperiod and locomotor rhythms in constant dim red light (DD). SCN grafts that reinstated behavioral circadian rhythms consistently failed
more » ... onsistently failed to reestablish estrous cycles. After ovariectomy, estradiol implants triggered LH surges at approximately circadian time 8 in 10 of 12 brain-intact control females and 0 of 9 SCN-lesioned, grafted females. Daily rhythms of the principal urinary melatonin metabolite, 6␣-sulfatoxymelatonin, were not reestablished by behaviorally functional grafts. In Exp 2, SCN lesions eliminated locomotor rhythmicity in adult male hamsters maintained in DD. Seven to 12 weeks after restoration of locomotor activity rhythms by fetal grafts, hosts and sham-lesioned controls were de-capitated at circadian times 4, 8, 12, 16, 20, or 24. Clear circadian rhythms of both serum corticosterone and cortisol were seen in shamlesioned males, with peaks in late subjective day. No circadian rhythms in either adrenal hormone were evident in serum from lesioned-grafted males. Testicular regression, observed in intact and sham-lesioned males maintained in DD, was absent not only in arrhythmic SCN-lesioned hamsters given grafts of cerebral cortex, but also in animals in which hypothalamic grafts had reinstated locomotor rhythmicity. The pineal melatonin concentration rose sharply during the late subjective night in control hamsters, but not in SCNlesioned animals bearing behaviorally effective transplants. Even though circadian rhythms of locomotor activity are restored by SCN transplants, circadian endocrine rhythms are not reestablished. Endocrine rhythms may require qualitatively different or more extensive SCN outputs than those established by fetal grafts. (Endocrinology 140: 207-218, 1999) Adult Syrian hamsters (LVG strain) were obtained from the Lakeview hamstery (Wilmington, MA) or bred locally from that source. Animals
doi:10.1210/en.140.1.207 pmid:9886827 fatcat:wpjrfrfnqzd7vnd6ndmbt5klv4