2013 Theses Doctoral

Alcohol alters the expression of Soluble N-Ethylmaleimide-Sensitive Factor Attachment Protein Receptors (SNAREs) and spontaneous γ-Aminobutyric Acid (GABA) release...

Varodayan, Florence Prabha

Many synapses within the central nervous system are highly sensitive and responsive to ethanol. Although the regulation of postsynaptic receptors by alcohol is well studied, the mechanisms underlying the presynaptic effects of alcohol to alter neurotransmitter release remain relatively unexplored. This dissertation addresses whether alcohol-induced changes in transcriptional activity can promote synaptic vesicle fusion and therefore, neurotransmitter release. To identify a transcriptional pathway by which ethanol can regulate neurotransmitter release, we first investigated the effects of acute alcohol on the expression of genes encoding for synaptic vesicle fusion machinery proteins that form the soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) complex. The proteins in this complex reside on the vesicle membrane (synaptotagmin 1 and synaptobrevin/vesicle-associated membrane protein, which is also known as VAMP) and the plasma membrane (syntaxin 1 and synaptosomal associated protein of 25 kDa, which is also known as SNAP-25), and their interactions within the SNARE complex trigger vesicle fusion and neurotransmitter release. We found that ethanol treatment of mouse cortical neurons increased the mRNA and protein expression levels of a subset of SNARE complex proteins, including synaptotagmin 1 (Syt1) and one of the isoforms of synaptobrevin, VAMP2, but not the other isoform, VAMP1. The gene induction of Syt1 and Vamp2 by alcohol occurs via activation of the transcription factor heat shock factor 1 (HSF1), while HSF1 transcriptional activity had no effect on Vamp1 mRNA levels. We then investigated whether ethanol altered neurotransmitter release in cortical neurons, using whole-cell voltage clamp electrophysiology. We found that alcohol increased gamma-aminobutyric acid (GABA) release via HSF1, but had no effect on glutamatergic synaptic vesicle fusion. Collectively, these data indicate that alcohol induction of HSF1 transcriptional activity triggers a specific coordinated adaptation in GABAergic presynaptic terminals that ultimately results in increased GABA release. This molecular mechanism could explain some of the transient changes in synaptic function that occur after alcohol exposure, and may underlie some of the enduring effects of chronic alcohol drinking on local circuitry.