Robust range of auditory periphery development, eye opening, and brain gene expression in Wistar rat pups that experience variation in maternal backgrounds

ABSTRACTThe experience of variation in maternal licking and grooming (LG) is considered a critical influence in neurodevelopment related to stress and cognition, but little is known about its relationship to early sensory development. In this study, we used a maternal selection approach to test the hypothesis that differences in LG during the first week of life influence the timing of hearing onset in Wistar rat pups. We performed a range of tests, including auditory brainstem responses (ABR), tracking of eye opening (EO), micro-CT X-ray tomography, and qRT-PCR to monitor neurodevelopmental changes in the female and male progeny of low-LG and high-LG dams. Our results show that variation in maternal LG is not overtly associated with different timing of ABR onset and EO in the progeny. However, the data provide insight on the delay between hearing onset and EO, on key functional and structural properties that define hearing onset at the auditory periphery, and on changes in brain gene expression that include the first evidence that: a) the hypoxia-sensitive pathway is regulated in subcortical and cortical auditory brain regions before hearing onset, and b) implicates maternal LG in regulation of Bdnf signaling in auditory cortex after hearing onset. Altogether, these findings provide a baseline to evaluate how factors that severely disrupt the early maternal environment may affect the expression of robust developmental sensory programs.SIGNIFICANCE STATEMENTEarly life experience during sensitive developmental periods can induce long-term effects on the neurobiological development of the offspring. In the present work we tested the hypothesis that variation in maternal licking and grooming (LG) affects the timing of hearing onset in Wistar rat pups. To our surprise the results did not support the hypothesis. Instead, we found a robust range of early and late auditory development that was independent of maternal LG. Nevertheless, the study provides new findings on the delay between hearing onset and eye opening, on key functional and structural properties that define hearing onset at the auditory periphery, and the first evidence that a) the hypoxia-sensitive pathway is regulated in the central auditory system during the sensitive period before hearing onset, and b) maternal LG is implicated in regulation of Bdnf signaling during the sensitive period after hearing onset. These findings provide a baseline to evaluate how factors that severely disrupt the early maternal environment may affect the expression of robust developmental sensory programs.

Epigenetics: rat mum to my Mum?

This chapter explores the epigenetic thought-style in depth, by analysing some of the seminal work on animals. We highlight in particular the work of Michael Meaney and colleagues which has been particularly persuasive in the domain of welfare policy and practice. This work appears to show that rodent mothers who nurture intensively (copious “licking and grooming”) beget more resilient offspring, and that these effects of parenting are mediated by epigenetic mechanisms. Although the meme is potent, we draw attention to some of the flaws in the primary research, and more generally question the degree to which laboratory studies on animals can (ever) be generalized to human parenting. The idea that epigenetic mechanisms transmit permanent changes is inherently contradictory.