A neuroanatomical correlate of paternal and maternal behavior in the biparental California mouse (Peromyscus californicus).

The medial preoptic area (MPOA) is important in the control of maternal behavior in rodents, and it is sexually dimorphic. This study demonstrates that the MPOA of nonparental virgin male Peromyscus californicus (n = 10) is larger than that of virgin females (n = 9) because of a significantly greater number of neurons in the MPOA of virgin males. However, this sex difference in MPOA volume disappeared when males and females became parents. Soma size increased significantly when females became mothers. These data suggest that maternal behavior may require a structural change in the MPOA, whereas paternal responsivity, which is normally inhibited in virgin males, may require a change in neuronal activity. Furthermore, these results underscore the importance of reproductive status in examination of sexually dimorphic nuclear structures.