Spiny behaviour revealed by voltage imaging
Using an electrochemical voltage-sensitive dye, researchers from the United States, Serbia and Hungary have directly monitored the electrical properties of individual spines on basal dendrites.
Their research shows that – against many hypotheses (based on theoretical models) – synapses on basal dendritic spines are not isolated by the spinal neck and behave as if they are located directly on the dendrite.
Previous studies have been unable to elucidate this information due to technical limitations that have constrained the ability to record inputs to the spines with enough sensitivity and spatiotemporal resolution.
To overcome these restrictions, the team used an electrochromic voltage-sensitive dye and two-photon glutamate uncaging together to measure subthreshold excitatory postsynaptic potentials (EPSPs) from individual spines and thereby quantify the electrical resistance of the spine’s neck. EPSPs were generated in specific synapses in layer five cortical pyramidal neurons of mice by focal glutamate release using a pulsed 720 nm laser.
Dendritic spines in the cells targeted here had similar electrical behaviours even though they were morphologically different.
The method described in this paper, published in Nature Communications, provides a new way of studying the electrical behaviour of dendritic spines. This will help with further studies to elucidate the properties of spines on other areas of the dendritic arbour and in different cell types.
The results of these studies will help answer the question of how specific transmitter receptors and voltage-sensitive ion channels work together on spine heads to integrate the output signals of dendrites.
For glutamate uncaging, the spine head was positioned close to the stationary stimulation site in the centre of the field of view by a Motorised Movable Top Plate.
Paper reference:
Popovic R.A., Carnevale N., Rozsa B., Zecevic D. Electrical behaviour of dendritic spines as revealed by voltage imaging Nature Communications (2015) doi: 10.1038/ncomms9436
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