My latest paper came out from J Neurophys:
by Akira Sakurai and Paul S. Katz
DOI: 10.1152/jn.00150.2016
This paper describes the central oscillatory circuit underlying rhythmic swimming of a nudibranch sea slug, Dendronotus iris.
The circuit is a typical "half-center oscillator" that consists of only two bilateral pairs of neurons. The paired neurons each inhibit their contralateral counterparts. The circuit has a “twisted” organization; that is, a neuron in one pair is excitatory-coupled contralaterally to a neuron in the other pair.
The half-center oscillator is the simplest design of a network oscillator, in which two neuronal elements with no endogenous rhythmicity form reciprocally inhibititory synapses. The half-center theory was first proposed by T. Graham Brown in 1911 after the historical experiment with a walking cat with transected spinal cord.
In addition to the reciprocal inhibition, each functional unit of the half-center oscillator generally contains the excitatory neurons that provide rhythmic excitatory drive onto the mutually-inhibitory neurons (eg., Clione, tadpole, lamprey, zebrafish, and mice). Because of high complexity with so many neurons involved, the role of the excitatory neurons have not been clearly understood. Here, we found that the Dendronotus swim circuit consists of only 4 neurons. By using "Dynamic Clamping" technique, we manipulated the strength of the excitatory synapse and found that they play crucial roles for the circuit to function as the half-center oscillator. To our knowledge, this is probably the simplest half-center oscillator described to date. Because of such simplicity, this circuit is also highly manipulable, and hence may provide a good system to study the fundamental properties of a network oscillator.
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| Dendronotus iris swims by rhythmically flexing its body to left and right. |
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| The Dendronotus brain is a cluster of lobes or "ganglia." The neurons that produce the rhythmic motor output for swimming have their cell bodies in the pedal ganglia. They all project the axons toward the other side of the brain to synapse with their contralateral counterparts. |
The circuit is a typical "half-center oscillator" that consists of only two bilateral pairs of neurons. The paired neurons each inhibit their contralateral counterparts. The circuit has a “twisted” organization; that is, a neuron in one pair is excitatory-coupled contralaterally to a neuron in the other pair.
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The Dendronotus swim CPG is a half-center oscillator. The left illustration shows actual synaptic connections. The left Si3 (L-Si3) neuron forms an excitatory synapse and electrical connection onto the right Si2 (R-Si2), forming a twisted configuration. A modified version is shown on the right. Coupled Si2 and Si3 neurons form a functional unit that works as a half-center to produce rhythmic bursting.
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In addition to the reciprocal inhibition, each functional unit of the half-center oscillator generally contains the excitatory neurons that provide rhythmic excitatory drive onto the mutually-inhibitory neurons (eg., Clione, tadpole, lamprey, zebrafish, and mice). Because of high complexity with so many neurons involved, the role of the excitatory neurons have not been clearly understood. Here, we found that the Dendronotus swim circuit consists of only 4 neurons. By using "Dynamic Clamping" technique, we manipulated the strength of the excitatory synapse and found that they play crucial roles for the circuit to function as the half-center oscillator. To our knowledge, this is probably the simplest half-center oscillator described to date. Because of such simplicity, this circuit is also highly manipulable, and hence may provide a good system to study the fundamental properties of a network oscillator.
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