Rectifying electrical synapses are more interesting than they might seem at first. Our recent study finds that they have the potential to allow a circuit to control how robust the circuit output is to modulation of synaptic strength.

Gap junctions allow neurons to communicate quickly by serving as a direct conduit of electrical signals. Non-rectifying gap junctions probably come to mind first for most neuroscientists when they think about electrical synapses, since they are the idealized textbook variety. The electrical current that passes through the non-rectifying type of gap junction is simply a function of the voltage difference between the coupled neurons. However, this is only the case when the two hemi-channels that form a gap junction pore have the same voltage-dependencies.

Schematic shows that neurons can express diverse gap junction subunits (top left). Rectifying gap junction conductance is a function voltage difference between two neurons (top right). Bottom panel illustrates how coupled neuron output depends on the polarity of the rectifying electrical synapse and the intrinsic properties of the coupled neurons.

We know from past electrophysiology studies that a single neuron can express a diverse set of gap junction hemi-channels, enabling it to form similarly diverse gap junction channels with another neuron. This could result in rectifying electrical synapses in which current flows asymmetrically between neurons so that current flow can either be permitted or restricted depending on whether the current is positive or negative. What we didn’t know were the consequences of electrical synapse rectification for a pattern-generating circuit of competing oscillators. Our recently published study in J. Neuroscience addressed this question and led us to conclude that rectifying electrical synapses can change how a neuronal circuit responds to modulation of its synapses – including its chemical synapses. Although we used a computational model for our study, our results indicate that rectifying electrical synapses in biological networks can be an important component in neuronal circuits that produce rhythmic patterns, such as those found in motor systems.

Gabrielle Gutierrez obtained her PhD in Neuroscience from Brandeis earlier this year, and is currently doing a postdoc with Sophie Deneuve at the Ecole Normale Superieure in Paris

Gutierrez GJ, Marder E. Rectifying electrical synapses can affect the influence of synaptic modulation on output pattern robustness. J Neurosci. 2013;33(32):13238-48.