Evidence for pineal involvement in timing implantation in the western spotted skunk.

Experiments were designed to test the hypothesis that the pineal gland mediates the effects of changing day length and thereby synchronizes implantation within the population of spotted skunks. Intact, sham-superior cervical ganglionectomized (SCGx), SCGx, and SCGx/bilateral orbitally enucleated (B1) pregnant skunks were subjected to a natural photoperiod, and the duration of the preimplantation period was monitored. In a second set of experiments, melatonin was administered to pregnant skunks via two methods to determine whether or not this pineal hormone would mimic the effects of short day photoperiods or B1 on duration of the preimplantation period. Bilateral SCGx, which presumably denervated the pineal, had no effect on the average duration of the preimplantation period (232 +/- 57 vs. 199 +/- 6 days). However, SCGx reversed the inhibitory effect of B1 on implantation as SCGx/B1 animals had an average duration of the preimplantation period that was not significantly different from intact controls (262 +/- 46 vs. 214 +/- 11 days) but was significantly shortened in comparison to enucleated animals (262 +/- 46 vs. 316 +/- 45 days). Melatonin significantly lengthened the duration of the preimplantation period in animals receiving either daily afternoon injections of melatonin or those receiving melatonin Silastic capsule implants. These results are consistent with the hypothesis that the pineal gland synchronizes photoperiod-induced blastocyst implantation in the western spotted skunk.