Aromatase inhibition during adolescence reduces adult sexual and paternal behavior in the biparental dwarf hamster Phodopus campbelli

Previous studies have failed to identify an activational role for estradiol in the paternal behavior of Phodopus campbelli fathers. However, none of these studies addressed a developmental role that estradiol might play in establishing paternal behavior in this species. Males were orally administered the aromatase inhibitor letrozole (1 mg/kg/day) for three days at 18, 34, or 90 days of age. As adults, males were tested for paternal and sexual behavior. Letrozole treatment at 18 days resulted in males that spent less time huddling over pups during the birth, and had higher pup losses and male-biased pup survival for the first litter. Letrozole treatment at 34 days resulted in males that had altered sexual behavior; males had a longer interval between mounts and between intromissions, and took longer to achieve ejaculations over the first three ejaculatory series. Furthermore, these males sired smaller first litters and produced second litters with a male-biased sex ratio. Males treated with letrozole as adults showed a modest increase in paternal care during the birth, but pup development and survival were not altered. There was no effect of treatment on attack or retrieval behavior either as sexually naive adults or as new fathers. Thus, the results of the present study suggest that estradiol acts during adolescence to establish the normal expression of midwifery behavior and sexual behavior during adulthood.