Initiation of development of diapausing embryo by mammary denervation during lactation in a marsupial

Abstract

MOST macropodid marsupials conceive at postpartum oestrus and the 100-cell embryo enters into and remains in embryonic diapause while there is a suckling young in the pouch¹. Removal of the pouch young results in reactivation of the quiescent corpus luteum and of the diapausing blastocyst. Prolactin inhibits corpus luteum development tonically during lactational quiescence in the tammar wallaby, Macropus eugenii². However, it is not known whether the hormonal milieu associated with lactation, or the neural stimulus of suckling itself is the primary signal to the hypothalamus which results in the maintenance of embryonic diapause in M. eugenii. I therefore examined the role of the neural pathway from the mammary gland in tammar wallabies carrying diapausing embryos. I report here that after denervation of the suckled mammary gland, the quiescent corpus luteum and the diapausing blastocyst resumed development, whereas none of a sham-operated group initiated blastocyst development. The pouch young grew at a normal rate and continued to obtain milk from denervated glands, despite the presence of a developing embryo in the uterus.