Pseudopregnancy and reproductive cycle synchronisation cannot be induced using conventional methods in the spiny...

The menstruating spiny mouse is the first rodent identified to exhibit natural spontaneous decidualisation, cyclical endometrial shedding and regeneration. While the spiny mouse shares several primate-like characteristics in its reproductive biology, it has not been established whether pseudopregnancy can be induced or if its cycles can be synchronised as in non-human mammals. Here we describe attempts to induce pseudopregnancy and synchronisation of menstrual cycles (i.e. Whitten effect) in spiny mice. Virgin females (n=3-8 per group) underwent one of the following procedures to induce pseudopregnancy: daily vaginal lavage only (control), progesterone injection, mechanical stimulation of the cervix and sterile mating. A separate cohort was also exposed to male-soiled bedding to assess the Whitten effect. Pseudopregnancy was deemed successful if females presented with extended (>12 consecutive days) leukocytic vaginal cytology. No female from any method of induction met this criterion. In addition, the menstrual cycles of a group of six females could not be synchronised, nor immediate ovulation induced via exposure to male-soiled bedding. These responses indicate that the spiny mouse does not behave as a typical rodent. Like higher-order primates, the spiny mouse exhibits a relatively rare reproductive strategy, of failure to show pseudopregnancy or cyclical synchronisation. This is further endorsement of the use of this species as a versatile animal model for translational studies of menstruation and fertility.