Achieving synaptically relevant pulses of neurotransmitter using PDMS microfluidics

Abstract

Fast synaptic transmission is mediated by post-synaptic ligand-gated ion channels (LGICs) transiently activated by neurotransmitter released from pre-synaptic vesicles. Although disruption of synaptic transmission has been implicated in numerous neurological and psychiatric disorders, effective and practical methods for studying LGICs in vitro under synaptically relevant conditions are unavailable. Here, we describe a novel microfluidic approach to solution switching that allows for precise temporal control over the neurotransmitter transient while substantially increasing experimental throughput, flexibility, reproducibility, and cost-effectiveness. When this system was used to apply ultra-brief (~400 μs) GABA pulses to recombinant GABAA receptors, members of the cys-loop family of LGICs, the resulting currents resembled hippocampal inhibitory post-synaptic currents (IPSCs) and differed from currents evoked by longer, conventional pulses, illustrating the importance of evaluating LGICs on a synaptic timescale. This methodology should therefore allow the effects of disease-causing mutations and allosteric modulators to be evaluated in vitro under physiologically relevant conditions.

Acute and Chronic Neural Stimulation via Mechano-Sensitive Ion Channels

“…91 Photo-activation of 'caged' neurotransmitters requires expensive reagents and equipment and this technique is limited by the library of photoactivatable compounds. 91 Optogenetics also require exogenous expression of photo-sensitive genes.…”

“…91 Photo-activation of 'caged' neurotransmitters requires expensive reagents and equipment and this technique is limited by the library of photoactivatable compounds. 91 Optogenetics also require exogenous expression of photo-sensitive genes. 92 Microfluidic devices have been employed in solution switching to transiently apply brief (~400 µs) gamma-aminobutyric (GABA) to recombinant GABAA receptors 22 to evoke current resembling hippocampal inhibitory post-synaptic currents.…”

“…92 Microfluidic devices have been employed in solution switching to transiently apply brief (~400 µs) gamma-aminobutyric (GABA) to recombinant GABAA receptors 22 to evoke current resembling hippocampal inhibitory post-synaptic currents. 91 Taylor et al also described a microfluidic local perfusion (µLP) chamber to direct the formation of synapses in >100 parallel rows for high throughput manipulation of pre-and post-synaptic regions. 93 The presence of multiple perfusion channels facilitate high spatiotemporal control of glutamate treatment and monitoring of calcium fluctuations.…”

Microfluidic Platforms for the Investigation of Intercellular Signalling Mechanisms

“…While Botzolakis et al [ 74 ] demonstrated delivery of neurotransmitter pulses on a physiologically-relevant synaptic timescale. Coming from a different angle, Mutch and co-workers [ 75 ] used quantitative microscopy aided by a microfl uidic platform to determine the number of proteins in synaptic vesicles, and the variability of this, information relevant to regulation of synaptic signalling.…”

Environmentally friendly surface modification of PDMS using PEG polymer brush

“…PDMS is one of the most extensively used polymer materials for fabricating low-cost microuidic devices because of its chemical stability, biocompatibility, optical transparency, and ease of fabrication [16,17]. However, the hydrophobic nature of PDMS induces adsorption of proteins, which hampers its application in protein separations [18,19].…”