DD Motor Neuron

From NeuronBankWiki

The DD Motor Neurons constitute a class of inhibitory GABA-ergic motor neurons in the free living nematode C. elegans. They are involved in the regulation of the Sinusoidal movement of the animal.

DD Motor Neurons are neurons located in the ventral nerve cord of Caenorhabditis elegans.

Basic Information

Flourescence micrograph showing the positions of the DD motor neurons in the body of C. elegans at the first larval stage. This image was taken from http://www.wormatlas.org/neurons/Images/DD'sL1.jpg.

Schematic diagram showing the wiring of the VD and the DD motor neurons. The hollow triangles represent inputs to the neurons and the solid triangles represent the outputs. This image was taken from http://www.wormatlas.org/neurons/Images/VCMNventraldorsalD.jpg

DD motor neurons are inhibitory neurons that receive synaptic input from excitatory motor neurons and body wall muscles, and cause inhibition in the body wall muscles located in the opposite side of the body. Initially, the neurons receive input from dorsal side of the body and inhibit the ventral body wall muscles. However, towards the end of the first larval stage, when the VD motor neurons are born, the DD motor neurons respecify and reverse the flow of information. In other words, after the L1/L2 molt, they receive input from the ventral side and inhibit the dorsal muscles.

Neuronal Type: Motor Neuron

Anatomy

The cell body of the DD motor neuron is located in the Ventral nerve cord. There are six neurons of this type in a typical C. elegans. There is a short process and a long process protruding from opposite sides of the cell body. The short process extends towards the posterior end, whilst the long process is directed in the anterior direction. A branch of the anterior process forms a commissure and runs around the dorsal nerve cord.

Molecular profile

• Neurotransmitter: Gamma Amino-Butyric Acid (GABA) is used for inhibition, and Acetylcholine receptors are used as synaptic input in the postsynaptic processes.

Physiology

Synaptic Connections

Synaptic Inputs

Prior to respecification at the end of L1, the DD motor neurons receive synaptic input from dorsal body wall muscles and other dorsal excitatory motor neurons. However, after respecification, input is received from the ventral body wall muscles and ventral excitatory motor neurons.

Synaptic Outputs

The synaptic outputs of the DD motor neuron are the body wall muscles. Initially, it inhibits the ventral muscles, and after respecification, it inhibits the dorsal muscles.

Behavior

The DD Motor neurons aid in sinusoidal body movement of the nematode. They are most likely active during ventral muscle contractions, whereby they receive input from VA and VB neurons, and coordinately relax the dorsal muscles during ventral muscle contraction . They are also thought to regulate the wave amplitude of the sinusoidal movement since unc-25 and unc-30 mutants that lack functional D neurons generate rhythmic sinusoidal movement with a reduced amplitude.

References

1. White JG, Albertson DG, Anness M (1978) Connectivity changes in a class of motoneurone during the development of a nematode, Nature, 271:764-766. PMID: 625347
2. Walthall WW, Li L, Plunkett JA, Hsu CY (1993) Changing synaptic specifications in the nervous system of Caenorhabditis elegans - Differentiation of the DD motoneurons, Journal of Neurobiology, 24:1589-1599. PMID: 8301267
3. McIntire SL, Jorgensen E, Horvitz HR (1993) Genes required for GABA function in Caenorhabditis elegans, Nature, 364:334-337. PMID: 8332190

Additional information

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