Consequences of placentophagia by adult virgin male California mice (Peromyscus californicus)

Abstract

Placentophagia increases parental motivation in sexually inexperienced adult female rodents. We hypothesized that placenta ingestion has similar effects in virgin male California mice (Peromyscus californicus), a monogamous rodent in which fathers provide extensive care for their offspring. To test this hypothesis, we administered either a conspecific's placenta in oil or oil alone to adult virgin males via oral gavage. One, 7 or 24 hours later, each male underwent a 1-hour behavior test with either an unfamiliar pup or a novel object marble), immediately after which the mouse was perfused and the brain collected. Neural activation (Fos-immunoreactivity) was quantified in brain regions involved in parental care (bed nucleus of the stria terminalis, medial preoptic area, amygdala). We found few significant effects of placenta treatment, but at 7 h post-gavage, placenta-treated males had decreased latencies to approach both pups and marbles, compared to oil-treated controls (p = 0.05). Placenta-treated males also showed lower Fos-immunoreactivity in the dorsal bed nucleus of the stria terminalis, irrespective of stimulus type, compared to controls, both 1 h (p = 0.04) and 7 h (p = 0.05) post-treatment. These results suggest that placentophagia does not directly affect paternal motivation but might increase willingness to interact with novel stimuli in virgin male California mice.