Maternal care experienced during postnatal development has enduring effects on neuroendocrine function and behavior. Previous studies in rats have illustrated the effect of maternal licking/grooming (LG) on hormone receptors and maternal behavior of adult female offspring associated with altered DNA methylation. However, the developmental timing of these effects, which provide insight into the cellular and molecular pathways through which early experience alters later behavior, had not been explored. Here, we demonstrate the developmental emergence of these outcomes and use cross-fostering to identify sensitive periods for these effects. Estrogen receptor (ER)α and ERβ mRNA levels within the medial preoptic area (MPOA) of the hypothalamus were increased by postnatal day (PN)21 in female offspring of high LG dams; LG-associated increases in oxytocin receptor mRNA levels were observed beyond the weaning period. Quantification of ERα-immunoreactivity indicated a high degree of neuroanatomical specificity of LG effects within the MPOA that were observed by PN6. Reduced DNA methylation and histone 3 lysine 9 tri-methylation and increased histone 3 lysine 4 tri-methylation at the ERα gene promoter (Esr1) were detected at PN21 in high LG female offspring. Latency to engage in maternal behavior toward donor pups was significantly shorter among high LG females. Cross-fostering revealed that maternal sensitization and MPOA ERα levels are sensitive to maternal care experienced before but not after PN10. Differential windows of plasticity were identified for ERβ and oxytocin receptor mRNA levels. These studies contribute significantly to our understanding of the molecular, neurobiological, and behavioral pathways through which variation in maternal behavior is transmitted from one generation to the next.

Variation within mesolimbic dopamine (DA) pathways has significant implications for behavioral responses to rewards, and previous studies have indicated long-term programming effects of early life stress on these pathways. In the current study, we examined the impact of natural variations in maternal care in Long Evans rats on the development of DA pathways in female offspring and the consequences for reward-directed behaviors. We found that tyrosine hydroxylase (TH) immunoreactivity in the ventral tegmental area was elevated by postnatal day 6 in response to maternal licking/grooming (LG), and that these effects were sustained into adulthood. Increased TH immunoreactivity was not found to be associated with altered epigenetic regulation or transcriptional activation of Th, but probably involved LG-associated changes in the differentiation of postnatal DA neurons through increased expression of Cdkn1c, and enhanced survival of DA projections through LG-associated increases in Lmx1b and brain-derived neurotrophic factor. At weaning, high-LG offspring had elevated DA receptor mRNA levels within the nucleus accumbens and increased conditioned place preference for a high-fat diet. In contrast, high-LG, as compared with low-LG, juvenile offspring had a reduced preference for social interactions with siblings, and haloperidol administration abolished group differences in conditioned place preference through a shift towards increased social preferences in high-LG offspring. The effects of maternal care on developing DA pathways and reward-directed behavior of female offspring that we have observed may play a critical role in the behavioral transmission of maternal LG from mother to daughter, and account for individual differences in the mesolimbic DA system.

Kidney disease is emerging as an arsenic (As)-linked disease outcome, however further evidence of this association is warranted. Our first objective for this paper was to examine the potential renal toxicity of As exposure in Bangladesh. Our second objective relates to examining whether the previously reported positive association between urinary creatinine (uCrn) and As methylation may be explained by renal function. We had hypothesized that these associations relate to supply and demand for s-adenosylmethionine, the methyl donor for both creatine synthesis and As methylation. Alternatively, renal function could influence both As and creatinine excretion, or the As metabolites may influence renal function, which in turn influences uCrn. We conducted a cross-sectional study (N = 478) of adults, composed of a sample recruited in 2001 and a sample recruited in 2003. We assessed renal function using plasma cystatin C, and calculated the estimated glomerular filtration rate (eGFR). Consistent with renal toxicity of As, log-uAs had a marginal inverse association with eGFR in the 2003 sample (b = −5.6, p = 0.07), however this association was not significant in the 2001 sample (b = −1.9, p = 0.24). Adjustment for eGFR did not alter the associations between uCrn and the %uAs metabolites, indicating that GFR does not explain these associations. Increased eGFR was associated with increased odds of having %uInAs >12.2% (2001: OR = 1.01, 95%CI (1.00,1.03); 2003: OR = 1.04, 95%CI (1.01,1.07)). In the 2003 sample only, there was a negative association between eGFR and %uDMA (b = −0.08, p = 0.02). These results may indicate differential effects of renal function on excretion of InAs and DMA. Alternatively, a certain methylation pattern, involving decreased %InAs and increased %DMA, may reduce renal function. Given that these studies were cross-sectional, we cannot distinguish between these two possibilities. Discrepancies between the samples may be due to the higher As exposure, poorer nutrition, and lower As methylation capacity in the 2003 sample.

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