DD1, DD2, DD3, DD4, DD5, DD6

Type: Motor neuron
In MoW: DDn
Male Wiring Project: DD01, DD02, DD03, DD04, DD05, DD06
In Wormbase: DDn, DD1, DD2, DD3, DD4, DD5,
DD6
Lineage: AB plppappap, AB prppappap
AB plppapppa, AB prppapppa
AB plppapppp, AB prppapppp
Location: Body (ventral nerve cord)
Description: GABAergic inhibitory ventral cord motor neurons. DD's receive dyadic synapses from excitatory ventral cord motor neurons along with body wall muscles. The initial pattern of synapses made by DD neurons are presynaptic and inhibitory to ventral body wall muscles while being postsynaptic to neurons that activate dorsal body wall muscles. During late L1, after the birth of VD motor neurons, DD neurons change their

synaptic pattern such that their dorsal branches become presynaptic and inhibitory to dorsal body wall muscles while their ventral branches become postsynaptic to excitatory neurons that synapse on ventral body wall muscles (White et al., 1978; Walthall et al., 1993). Hermaphrodites and males exhibit some differences in DDn connectivity.
Neurotransmitter/ Neuropeptide:
- GABA
(Rand and Nonet, 1997-Appendix 2)
Innexin expression:
- INX-3
- INX-10
- INX-14
- UNC-7
- UNC-9
(Altun et al., 2009)
Receptor expression:
- ACR-14; nicotinic AChR non-alpha subunit
(Fox et al., 2005)
Function:
- Sinusoidal body movement-locomotion. DD's receive input from VA and VB neurons, and hence, are likely to be active during ventral muscle contractions. They form neuromuscular junctions dorsally that coordinately relax the dorsal muscles during ventral muscle contraction (Driscoll and Kaplan, 1997). D-type neurons may also 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 (McIntire et al., 1993).
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Male Wiring Project

Note: In males, the DD6 cell body lies posterior to the male-specific CP9 neuron, which defines the anterior boundary of the male pre-anal ganglion (see Male Tail Cell ID). In males, DD6 is therefore considered part of the pre-anal ganglion rather than the ventral nerve cord.

For Male Wiring Project details see Emmons lab website.

Schematic Diagrams of Ventral Cord motor neurons:

AS Neurons
AS neurons		 DA and DB Neurons
Dosal DA and DB neurons
VA Neurons
VA neurons
 VB Neurons
VB neurons
VC Neurons
VC neurons		 DD and VD Neurons
DD VD neurons

In all diagrams,axon processes with neuromuscular synapses (NMJ) are shown as whereas dendritic processes where synaptic inputs are received are shown as .

Class A axons run forward in both cords (VNC and DC) whereas the class B axons run backwards. The dendritic branches of the dorsal and ventral class A neurons run in opposite directions as do those from class Bneurons. Ventral class D neurons receive their synaptic input on the dorsal side and give NMJ's on the ventral side. The dorsal type D neurons have half the periodicity of their ventral counterparts and receive synapses on the ventral side and give NMJ's on the dorsal side. Class AS neurons only synapse on the dorsal side and have no ventral counterpart, whereas, the class C neurons only synapse on the ventral side. The synapses from class C motor neurons onto body muscles are less dense than for the other classes (White J. et al, 1976.)

Synaptic map and process positioning of the VNC motor neurons (from White J. et al, 1976):

Connections of each motor neuron class

Motor neuron class Chemical synapses to other motor neurons Chemical synapses from Gap junctions
AS DA, DD, VD AVA, AVB, AVD, AVE DA, VA, AVA
DA DB, DD, VD AVA, AVD, AVE, HSNR, PVCL, SABVL AS, VA, AVA
DB AS, DD, VD DVA, PVC, PVR DB, VB, AVB
DD VD RID, VC1-3 DD, VD
VA* DD, VA, VB, VD AVA, AVB, AVD, AVE AS, DA, AVA, SABD
VB* DD, VA, VD PVC VB, DB, AVB
VD VA, VB AVEL, PVNR, VC1-3 DD, VA, VD, PVPR
(Based on the Mind of a Worm and Haspel & Donovan 2011; *VA1,3,5 and VB1,4,7 have slightly different connections than the remainder of the class)
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