Effects of suprachiasmatic nuclear ablation and melatonin on delayed implantation in the spotted skunk.

The suprachiasmatic nuclei (SCN) have been implicated as neural timers of reproductive events and as possible sites of action for melatonin. We tested the hypothesis that ablation of the SCN (SCNx) would counteract the inhibitory effect of exogenous melatonin in blastocyst implantation in the spotted skunk by removing a possible site of action. Thirty-eight pregnant females with unimplanted blastocysts were treated as follows: 4 served as untreated controls, 6 received empty Silastic capsules, 5 received Silastic capsules containing melatonin, 10 received sham lesions in the SCN, 7 received lesions in the SCN and Silastic capsules containing melatonin, and 6 received lesions in the SCN and empty Silastic capsules. All surgical treatments were completed by February 15. The skunks were subjected to a natural photoperiod, and the duration of preimplantation was measured. The lesions destroyed an average of 87 +/- 10% of the SCN and a small amount of the surrounding hypothalamus. SCNx had no significant effect on duration of preimplantation (200 +/- 25.6 days) when compared to sham SCNx (205 +/- 21.5 days). Melatonin significantly (p less than 0.05) lengthened the duration of preimplantation in both intact (277 +/- 59 days) and SCNx (265 +/- 64.7 days) skunks when compared to all other groups. These data are not consistent with the hypothesis that the SCN are required for melatonin to exert its influence on timing of implantation in the spotted skunk.