The effects of light and sympathetic innervation to the head on nidation in mink

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Abstract
Ninety primaparae female mink were bred on two consecutive days between March 11–15. Six days after first mating mink were subjected to one of the nine treatments, control (n = 21); sham superior cervical ganglionectomy (Sham SCGX) (n = 5); bilateral orbital enucleation (n = 10); bilateral orbital enucleation and constant light (n = 16); constant light (n = 19); an accelerated photoperiod of 15L, 9D + 5 min of light per day (cumulative) (n = 10); an accelerated photoperiod and SCGX (n = 6); SCGX and environmental light (n = 5); bilateral orbital enucleation and SCGX (n = 5). The interval between first mating and calculated date of nidation [copulation to implantation (CI) interval] was compared among groups. CI interval was significantly abbreviated in accelerated photoperiod treated animals, and significantly lengthened by constant light; blindness regardless of light regime; and SCGX with accelerated photoperiod. Nonsignificant variation in the CI interval was observed in the blinded or environmental light treated SCGX animals that underwent implantation. Reproductive failure, defined as either absence of embryos in necropsied animals or failure to whelp by females alive on June 1, occurred less frequently in accelerated photoperiod animals and with considerably greater frequency in blind, SCGX, or constant light treated intact animals. Observations in blinded animals suggest that this treatment and presumably SCGX and constant light extend the period of embryonic diapause to the point of blastocyst degeneration resulting in reproductive failure. The occurrence of nidation in some blinded, and constant light animals indicates that this event can occur independent of either retinal receptor or photoperiod. The effects of SCGX suggest that the pineal body is either not involved in nidation or has a facilitatory rather than inhibitory role.