Sex-Specific Effects of Experience With Pups on Perineuronal Net Expression in the Biparental California Mouse (Peromyscus californicus).

In biparental species, repeated exposure to infants can induce parental behavior in virgin males and females. Little is known, however, about the mechanisms underlying neuroplasticity resulting from experience with infants. Perineuronal nets (PNNs), extracellular matrix structures, regulate neuroplasticity during development and adulthood. We examined the impact of pup exposure on PNN expression in the medial prefrontal cortex (mPFC), medial amygdala (MeA), and medial preoptic area (MPOA) in male and female California mice (Peromyscus californicus), a biparental rodent. We stained brain sections with the lectin Wisteria floribunda agglutinin (WFA) to examine WFA-positive PNN expression in adult virgins exposed to pups one, two, or three times and new parents. Controls were tested with a pup-sized object. Pup exposure altered WFA+ PNN density in the mPFC and MeA, but not MPOA, of males. Virgin males exposed to pups twice exhibited reduced WFA+ PNN density in the mPFC compared to virgin males exposed to pups only once. Pup-exposed fathers had lower WFA+ PNN density in the MeA than virgin males exposed to pups once. In contrast, pup exposure did not alter WFA+ PNN density in females. Additionally, WFA PNN density in the mPFC was higher in males than females. PNNs preferentially associated with GABAergic cells in the mPFC of males, whereas in the MeA, PNNs associated with a similar percentage of GABAergic and glutamatergic neurons. Our results suggest that dynamic changes in PNN expression occur with repeated exposure to pups in male California mice and might contribute to the onset of paternal behavior.