Dorsal Motor Neurons

Cross references:   Amphioxus Nervous System     Amphioxus Motor Nerves    
Ventral Motor Neurons    Primary Motor Center        Amphioxus Locomotion  
Amphioxus Muscles   Motor Neuron Evolution   


Dorsal Compartment Locomotory Control System (PubMed) 
http://www.ncbi.nlm.nih.gov/pubmed/11948671   
Only the abstract is available online.  I got the PDF through the library.  Also discussed in
Amphioxus Locomotion


"The larval head and anterior nerve cord of amphioxus. 

A: Lateral view of the head of a 12-day larva with three functional gill slits. The mouth is located on the left side; the gill slits, seen faintly through the body, are on the right. The nerve cord lies directly above the notochord (shaded); a bar (marked *) shows the axial extent of the serial section series on which this account of the DC locomotory control system is based.

B: A dorsal view of the region marked in A showing the anterior nerve cord, some key landmarks, and the adjacent somites (shaded and numbered).  The cerebral vesicle, containing the frontal eye and lamellar body, extends through most of somite 1. The primary motor  center begins immediately behind this region. Cells of interest in the present context include the large paired neurons, of which the third pair (LPN3) are shown, and two pairs (numbered) of dorsal  compartment (DC) motoneurons. The section series through this  region consists of ca. 2,100 sections, as indicated by the small  numerals; 100 sections . 6.8 .m." 
 



The dorsal compartment locomotory control system in amphioxus larvae (Goog) 
http://www3.interscience.wiley.com/journal/92013518/abstract 
or 
The dorsal compartment locomotory control system in amphioxus larvae. 
Abstract only online.  I got the PDF from the library. 
"Amphioxus myotomes consist of separate sets of superficial and deep muscle fibers, each with its own innervation, that are thought to be responsible for slow swimming and escape behavior, respectively. ... An analysis of the pattern of cell contacts also suggests that the LPN3s are probably pacemakers for both slow and fast locomotion... The overall circuitry of the locomotory control system suggests that the PPN2s may be instrumental in sustaining slow swimming, whereas mechanical stimulation, especially of the rostrum, preferentially activates the fast mode.




The cholinergic gene locus in amphioxus ... (PubMed)   
http://www.ncbi.nlm.nih.gov/pubmed/18407548?itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum&ordinalpos=2 
Only abstract available online for free.  I got the PDF through the library.  Also discussed in Ventral Motor Neurons and Amphioxus Neurotransmitters


" ... it is worth pointing out that the photoreceptor cells of the larval ocellus, which also express
cholinergic gene locus (CGL) genes, are known to have DC motoneurons as their principal synaptic targets " 




2002   
Dorsal Compartment Locomotory Control System (PubMed) 
http://www.ncbi.nlm.nih.gov/pubmed/11948671   
Only the abstract is available online.  I got the PDF through the library. 


"Amphioxus myotomes consist of separate sets of superficial and deep muscle fibers, each with its own innervation, that are thought to be responsible for slow swimming and escape behavior, respectively.

Tracings from serial EM sections of the anterior nerve cord in the larva show that the motoneurons and premotor interneurons controlling the superficial fibers (the dorsal compartment, or DC pathway) are linked by specialized junctions of a previously undescribed type, referred to here as juxta-reticular (JR) junctions for the characteristic presence of a cisterna of endoplasmic reticulum on each side.

JR junctions link the DC motoneurons with each other, with the largest of the anterior paired neurons (LPN3s) and with one class of ipsilateral projection neurons (IPNs), but occur nowhere else.

Because of the paucity of synaptic input to the DC system, larval behavior can only be explained if the JR junctions act as functional links between cells. An analysis of the pattern of cell contacts also suggests that the LPN3s are probably pacemakers for both slow and fast locomotion, but act through junctions in the former case and conventional synapses in the latter.

The only major synaptic input to the DC system identified in somites 1 and 2 was from four neurons located in the cerebral vesicle, referred to here as Type 2 preinfundibular projection neurons (PPN2s). They have unusually large varicosities, arranged in series, that make periodic contacts with the DC motoneurons. More caudally, the DC motoneurons receive additional input via similar large varicosities from the receptor cells of the first dorsal ocellus, located in somite 5.

The overall circuitry of the locomotory control system suggests that the PPN2s may be instrumental in sustaining slow swimming, whereas mechanical stimulation, especially of the rostrum, preferentially activates the fast mode.









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