Gene expression in the CNS of lactating rats with different patterns of maternal behavior.

For most mammalian species, maternal behavior has an essential role in the development of the offspring. The frequency of licking/grooming (LG) the pups has been used as a parameter to evaluate maternal care, having mothers with high (HL) or low (LL) frequencies of LG. This study aimed to analyze the gene expression of the receptors for dopamine (Drd1a), prolactin (Prlr), serotonin (Htr1a, Htr1b), estrogen (Esr1, Esr2), and of Bdnf in the olfactory bulb (OB), hippocampus (HP), prefrontal cortex (PFC), and striatum (ST) of Wistar rats from three groups: LL (n = 8); HL (n = 8); virgin females in diestrus (D; n = 6). Maternal behavior was studied between the 1st and 7th postpartum days. Brain parts were analyzed by qRT-PCR. LL showed a decrease in the frequency of nursing, and an increase of remaining off the pups. There was an increase in gene expression of Drd1a, Prlr, Htr1a, Htr1b and Esr1 in the OB of HL, compared to LL. In the HP, Drd1a, Prlr and Htr1a were differently expressed when comparing HL, or LL, with D. The main finding is that HL had higher gene expression levels in the OB, which is a crucial structure to promote behavioral differences.

Analysis of transcriptional levels of the oxytocin receptor in different areas of the central nervous system and behaviors in high and low licking rats.

The natural variation in maternal care is an interesting model to analyze the physiological mechanisms that lead to differences in the mother-infant interaction. Several studies have shown differences in the expression of brain receptors such as the dopamine, estrogen and oxytocin receptors in areas classically involved in the onset and/or maintenance of maternal behavior: the medial preoptic area, the nucleus accumbens, the amygdala, the lateral septum, and the bed nucleus of the stria terminalis. The present study examined the responses of HL and LL rats in several behavioral tests and analyzes the transcription of the oxytocin receptor (OXTR) in the olfactory bulb (OB), the prefrontal cortex (FPC), the hippocampus (HP) and the striatum (ST) in different patterns of licking behavior. Our results showed that, in the second week postpartum, HL and LL mothers did not show behavioral differences in the elevated plus maze (EPM), the forced swimming test (FST) or the open field test. In the maternal aggressive behavior test, HL females showed a higher frequency of biting compared to LL females, but no significant differences in other aggressive behaviors were detected. LL mothers had higher levels of transcriptional OXTR in the OB and in the HP when compared to HL mothers. No differences in other areas were detected when compared LL and HL. These findings suggest that variations in maternal behavior may be associated with biting behavior of mothers and that OXTR participates in modulation of maternal behavior in rats, while other emotional behaviors are less related to such behavior.