Voltage-Dependent Medium-Term Synaptic Plasticity in Biomolecular Synapses

Biomolecular assemblies of phospholipids and the pore forming species monazomycin were constructed using the droplet interface bilayer technique to mimic synaptic properties. Electrical characterization of the interface confirms the existence of multiple forms of short-term synaptic plasticity in response to constant stimuli. Memory of prior stimulation can last up to 20 minutes suggesting an unaccounted mechanism of longer term memory retention, termed “medium-term synaptic plasticity.” Monazomycin doped biomembranes were stimulated by a series of step voltage inputs with varying off-times ranging from one to twenty minutes. Percentage of peak current obtained inactivation percentage, and change in inactivation percentage were compared. Peak current is reduced in subsequent stimulations and gradually restores back to 100% after 20 minutes. Inactivation percentage is also reduced but recovers at 20 minutes. Initial current right after application increases and remains elevated up to 20 minutes. Multiple sinusoidal voltage inputs were performed with −80 mV step inputs in between. I-V hysteresis for these inputs were compared. The peak negative current of the hysteresis decreased while the positive peak increased after each cycle. Medium term synaptic plasticity is believed to be the result of lingering concentration differences at the interfaces and lingering presence of nonconducting monazomycin in the bilayer.