Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Shiva M. Singh

Abstract

Alcohol is a neuroactive molecule that is able to exert variable and often detrimental effects on the developing brain, resulting in a broad range of physiological, behavioural, and cognitive phenotypes that characterize ‘fetal alcohol spectrum disorders’ (FASD). Factors affecting the manifestation of these phenotypes include alcohol dosage, timing of exposure, and pattern of maternal alcohol consumption; however, the biological processes that are vulnerable to ethanol at any given neurodevelopmental stage are unclear, as is how their disruption results in the emergence of specific pathological phenotypes later in life.

The research included in this thesis utilizes a C57BL/6J (B6) mouse model to examine the changes to gene expression and behaviour following a binge-like exposure to ethanol during synaptogenesis, a period of neurodevelopment characterized by the rapid formation and pruning of synaptic connectivity that correlates to brain development during the human third trimester. B6 pups were treated with a high dose (5 g/kg over 2 hours) of ethanol at postnatal day 4 (P4), P7, or on both days (P4+7). Mice were evaluated using a battery of behavioural tests designed to assess FASD-relevant phenotypes, and showed delayed achievement of neuromuscular coordination, hyperactivity, increased anxiety-related traits, and impaired spatial learning and memory.

Gene expression analysis identified 315 transcripts that were altered acutely (4 hours) following ethanol exposure. Up-regulated transcripts were associated with cellular stress response, including both pro- and anti-apoptotic molecules, as well as maintenance of cell structural integrity. Down-regulated transcripts were associated with energetically costly processes such as ribosome biogenesis and cell cycle progression. Genes critical to synapse formation were also affected, as well as genes important for the appropriate development of the hypothalamic-pituitary-adrenal axis. Additionally, gene expression changes within the adult brain of mice treated with ethanol at P4+7 were examined to evaluate the long-term effects of neurodevelopmental alcohol exposure. Array analysis identified 376 altered mRNA transcripts with roles in synaptic function, plasticity, and stability, as well as epigenetic processes such as folate metabolism and chromatin remodeling. MicroRNA analyses identified changes in the levels of 33 microRNA species, suggesting that that long-term changes to gene expression following may be maintained (at least in part) via epigenetic mechanisms.

Taken together, these analyses illustrate the sensitivity of synaptogenesis to ethanol exposure, leading to a ‘molecular footprint’ of gene expression changes that persists into adulthood and may contribute to the emergence of long-term behavioural and cognitive phenotypes associated with FASD.


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