Preliminary morphological evidence that vertebral hypomobility induces synaptic plasticity in the spinal cord.
OBJECTIVE
A widely accepted theoretical model suggests that vertebral hypomobility can cause pain and abnormal spinal mechanics because of changes in sensory input from spinal and paraspinal tissues. The purpose of this pilot study was 3-fold: (1) to make a preliminary determination if chronic vertebral hypomobility at L4 through L6 in the rat would affect synaptic density and/or morphology in the superficial dorsal horn of the L2 spinal cord level, (2) to identify relevant outcome variables for future studies, and (3) to obtain preliminary data that would permit estimating an appropriate sample size for future studies.


METHODS
Using an established rat model, we fixed 3 contiguous lumbar segments (L4-L6) for 8 weeks with a specially engineered vertebral fixation device. Electron micrographs were obtained from 2 animals from the experimental (fixed) group and each of 3 control groups (no surgery, surgery but no devices implanted, and devices implanted but not fixed). Synapses were randomly selected using a stereological approach and were analyzed for symmetry, curvature, type of postsynaptic profile, and perforations. The synaptic density was also estimated.


RESULTS
There was increased synaptic density and percentage of positively curved synapses in the dorsal horn of experimental animals as compared with controls. Experimental animals had a lower percentage of axospinous synapses, with a concomitant increase in the percentage of synapses on dendritic shafts.


CONCLUSIONS
These preliminary data suggest for the first time that chronic vertebral hypomobility at L4 through L6 in the rat affects synaptic density and morphology in the superficial dorsal horn of the L2 spinal cord level. More definitive studies are warranted, and the biologic significance of these finding should be investigated.
Bakkum
Barclay W
BW
Department of Basic and Health Sciences, Illinois College of Optometry, Chicago, Ill 60616, USA. bbakkum@ico.edu
Henderson
Charles N R
CN
Hong
Se-Pyo
SP
Cramer
Gregory D
GD
D000818:Animals; D049229:Dendritic Spines / Q000000981:diagnostic imaging / Q000378:metabolism; D008159:Lumbar Vertebrae / Q000294:innervation / Q000601:surgery; D008297:Male; D008854:Microscopy, Electron; D023421:Models, Animal; D009473:Neuronal Plasticity / Q000502:physiology*; D009984:Orthopedic Fixation Devices; D010865:Pilot Projects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000503:physiopathology* / Q000601:surgery; D013569:Synapses / Q000378:metabolism / Q000648:ultrastructure*; D014463:Ultrasonography