J Manipulative Physiol Ther. 2007 (Jun); 30 (5): 336–342
Barclay W. Bakkum, DC, Charles N.R. Henderson, DC, PhD, Se-Pyo Hong, DC, PhD, Gregory D. Cramer, DC, PhD
Department of Basic and Health Sciences, Illinois College of Optometry, Chicago, Ill 60616, USA. firstname.lastname@example.org
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.
From the FULL TEXT Article
These data offer the first anatomical evidence that altered spinal mechanics may produce neuroplastic changes in the dorsal horn of the spinal cord. These interesting findings suggest the need for larger definitive studies.
It has been hypothesized that positively curved synapses are more active synapses, whereas negatively curved synapses are thought to be less active or inactive. [7, 21, 22] Therefore, the increased percentage of positively curved synapses, along with the increased number of synapses, in the experimental animals compared with the controls may indicate an increase in synaptic activity in the dorsal horn of animals with hypomobile (fixated) vertebrae.
In addition, previous studies suggest that axospinous synapses are generally excitatory in nature.  Our small sample size precludes a definitive determination, but the decreased proportion of axospinous synapses seen in the experimental animals compared with the controls is consistent with a decreased amount of excitatory synaptic activity in the dorsal horn of animals with hypomobile (fixated) vertebrae.
Relatively few axosomatic synapses were observed in this study because the sampling strategy was not designed to capture cell bodies, the profiles of which occur much less frequently than synapses in tissue sections. Axosomatic synapses, by their proximity to the site where action potentials are generated, may be very important in determining neuronal activity. Specific studies to determine the effect of vertebral hypomobility on axosomatic synapse morphology, using unbiased sampling strategies that include at least 200 axosomatic synapses, should be conducted.
The relative numbers of perforated synapses identified in this study were either similar to or lower than those percentages of this type of synapse identified in other regions of the central nervous system.  Follow-up studies, with more power to capture this type of synapse, which has been linked to neuroplasticity, should be conducted.
These preliminary data suggest that chronic vertebral hypomobility (fixation) at L4 through L6 in the rat affects synaptic density and morphology in the superficial dorsal horn of the L2 spinal cord level. Morphological parameters that appear to be affected include synaptic curvature, type of postsynaptic profile, and perforations of the PSD. Additional more definitive studies are warranted, and the biologic significance of these finding should be investigated.
Henderson CNR. Three neurophysiological theories on the chiropractic subluxation. In: Gatterman MI editors. Foundations of chiropractic: subluxation. 2nd ed. St Louis: Elsevier Mosby; 2005;p. 296–303
Leach RA, Pickar JG. Segmental dysfunction hypothesis: joint and muscle pathology and facilitation. In: Leach RA editors. The chiropractic theories. 4th ed.. Philadelphia: Lippincott Williams & Wilkins; 2005;p. 137–206
Henderson CNR, Cramer GD, Zhang Q, DeVocht JW, Fournier JT. Introducing the external link model for studying spine fixation and misalignment: part 2, biomechanical features.
J Manipulative Physiol Ther. 2007;30:279–294[in press]
Henderson CNR, Cramer GD, Zhang Q, DeVocht JW, Fournier JT. Introducing the external link model for studying spine fixation and misalignment: part 1, need, rationale, and applications.
J Manipulative Physiol Ther. 2007;30:239–245
Wolpaw JR, Tennissen AM. Activity-dependent spinal cord plasticity in health and disease.
Annu Rev Neurosci. 2001;24:807–843
Bertoni-Freddari C, Fattoretti P, Paoloni R, Caselli U, Galeazzi L, Neier-Ruse W. Synaptic structural dynamics and aging.
Marrone DF, Petit TL. The role of synaptic morphology in neural plasticity: structural interactions underlying synaptic power.
Brain Res Rev. 2002;38:291–308
Calverley RKS, Jones DG. Contributions of dendritic spines and perforated synapses to synaptic plasticity.
Brain Res Rev. 1990;15:215–249
Chung K, Langford A, Applebaum A, Coggeshell RE. Primary afferent fibers in the tract of Lissauer in the rat.
J Comp Neurol. 1979;184:587–598
Budgell B, Noda K, Sato A. Innervation of posterior structures in the lumbar spine of the rat.
J Manipulative Physiol Ther. 1997;20:359–368
Suseki K, Takahashi K, Chiba T, Tanaka K, Morinaga T, et al. Innervation of the lumbar facet joints: origins and functions.
Mollander C, Xu Q, Grant G. The cytoarchitectonic organization of the spinal cord in the rat. I. The lower thoracic and lumbosacral cord.
J Comp Neurol. 1984;230:133–141
Kandel ER, Schwartz JH, Jessel TM. The perception of pain. In: Principles of neural science. 4th ed. New York: McGraw-Hill, Health Professions Division; 2000;p. 472–491
Woolf CJ, Salter MW. Plasticity and pain: role of the dorsal horn. In: McMahon SB, Koltzenburg M, Wall PD editor. Wall and Melzack's textbook of pain. 5th ed.. Edinburgh: Elsevier Churchill Livingstone; 2005;p. 91–106
Ygge J, Grant G. The organization of the thoracic spinal nerve projection in the rat dorsal horn demonstrated with transganglionic transport of horseradish peroxidase.
J Comp Neurol. 1983;216:1–9
Geinisman Y. Perforated axospinous synapses with multiple, completely partitioned transmission zones: probable structural intermediates in synaptic plasticity.
Bakkum BW, Benevento LA, Cohen RS. The effects of light- and dark-rearing on the synaptogenesis of the superior colliculus and visual cortex of the rat.
J Neurosci Res. 1991;28:65–80
Colonnier M. Synaptic patterns on different cell types in the different laminae of cat visual cortex. An electron microscope study.
Brain Res. 1968;9:268–287
Peters A, Feldman ML, Saldanha J. The projection of the lateral geniculate nucleus to area 17 of the rat cerebral cortex. II. Termination upon neuronal perikarya and dendritic shafts.
J Neurocytol. 1976;5:85–107
Chung SK, Pfaff DW, Cohen RS. Estrogen-induced alterations in synaptic morphology in the midbrain central gray.
Exp Brain Res. 1988;69:522–530
Dyson SE, Jones DG. Quantitation of terminal parameters and their interrelationships in maturing central synapses: a perspective for experimental studies.
Brain Res. 1980;183:43–59
Wesa JM, Chang F-LF, Greenough WT, West RW. Synaptic contact curvature: effects of differential rearing on occipital cortex.
Dev Brain Res. 1982;4:253–257
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