Dr. James Muir
My PhD versed on γ-aminobutyric acid type A receptors (GABAARs), the major mediators of inhibitory neurotransmission in the mammalian Central Nervous System.
These receptors play a critical role in regulating the excitatory/inhibitory balance required for correct brain function. Inhibitory synaptic strength depends on the number of GABAARs at the synapse, which can be regulated by traﬃcking mechanisms controlled by protein-protein interactions and post-translational modiﬁcations.
Recently, it has become clear that neurotransmitter receptors can undergo lateral exchange between synaptic and extrasynaptic regions. My thesis centred on the study of GABAAR surface traﬃcking with live-cell imaging techniques in cultured hippocampal neurons. GABAAR clustering at inhibitorysynapses was monitored via super-ecliptic pHluorin tagging, and single particle tracking with quantum dot labelling was used to image GABAAR lateral mobility.
I described computational tools developed for single particle tracking of GABAARs. Characterisation of GABAAR clustering and lateral mobility under baseline conditions reveals that GABAAR clusters are stable, but thatsingle GABAARs can move rapidly into and out of synapses. GABAAR surface traﬃcking is found to be activity-dependent. Ca2+ inﬂux through NMDA receptors drives the rapid dispersal of GABAAR clusters from synapses and increases GABAAR lateral mobility. This requires activation of calcineurin and dephosphorylation of serine 327 on the GABAAR γ 2 subunit. Finally, GABAAR clustering and lateral mobility in the axon initial segment (AIS) is analysed. A chronic depolarisation stimulus which shifts the AIS away from the cell body was then used. GABAAR cluster positions remain ﬁxed along the axon, but GABAAR lateral mobility in the AIS and proximal axon is increased. These eﬀects require activation of voltage-gated Ca2+ channels.
In summary, this work revealed that GABAAR surface traﬃcking can be modulated by multiple molecular mechanisms, which may have importantfunctional consequences for information processing in the brain.
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