The spinal cord connections of the myofascial trigger spots.
BACKGROUND
Recent electrophysiological studies revealed that endplate noise (EPN) could be specifically recorded from a myofascial trigger point (MTrP) region. EPN has been considered as the focal graded potentials due to excessive acetylcholine release in neuromuscular junction. A recent histological study has demonstrated a free nerve ending at the vicinity of the site, from where EPN could be recorded in an MTrP region. However, the sensory (afferent) and the motor (efferent) connections between an MTrP and the spinal cord still has never been fully studied.


OBJECTIVE
The aim of this study was to delineate both motor and sensory connections between an MTrP and the spinal cord by applying the stain with horseradish peroxidase (HRP).


METHODS
Nine Wistar rats were studied. When the rat was anesthetized, its biceps femoris muscles were exposed for localizing the myofascial trigger spot (MTrS, equivalent to MTrP in human). In one side, a monopolar Teflon-coated, hollow-needle electrode was used for searching EPN in an MTrS region, and then HRP was injected via this hollow-needle electrode into the site where EPN was recorded. HRP was also injected into a normal (non-taut band, non-MTrS) site in the contralateral side to obtain the control data. Two days after HRP injection, the rats were sacrificed and their spinal cords and dorsal root ganglia (DRG) were sectioned for the identification of the sites where neurons were labeled with HRP.


RESULTS
The HRP-labeled neurons were found in the ventral horn of the spinal cord and in the DRG over L3, L4, and L5, while most were found in the L5 level. The mean numbers of HRP-labeled neurons in the EPN side looked smaller than that in the control side, but the difference did not reach statistically significant level (P>0.05). The mean values of the diameters of the HRP-labeled neurons in the DRG were not significantly different between the EPN side and the control side (P>0.05). However, HRP-neurons in the ventral horn of the spinal cord in the EPN side showed mild tendency to be smaller than that in the control side.


CONCLUSIONS
The spinal cord connections of an MTrS are basically similar to that for a normal tissue region. The motor neurons related to MTrS tended to be smaller in their diameters. The findings in this study further supported the previously proposed hypotheses for the pathogenesis of an MTrP.
Kuan
Ta-Shen
TS
Department of Physical Medicine and Rehabilitation, College of Medicine, National Cheng Kung University, Tainan, Taiwan, ROC.
Hong
Chang-Zern
CZ
Chen
Jo-Tong
JT
Chen
Shu-Min
SM
Chien
Chi-Hsien
CH
D000344:Afferent Pathways / Q000166:cytology / Q000502:physiology*; D000818:Animals; D002452:Cell Count; D048429:Cell Size; D002772:Cholera Toxin; D004525:Efferent Pathways / Q000166:cytology / Q000502:physiology*; D004576:Electromyography; D007839:Functional Laterality / Q000502:physiology; D005727:Ganglia, Spinal / Q000166:cytology / Q000502:physiology; D006735:Horseradish Peroxidase; D009046:Motor Neurons / Q000166:cytology; D018657:Muscle Fibers, Slow-Twitch; D018482:Muscle, Skeletal / Q000294:innervation*; D009209:Myofascial Pain Syndromes; D009469:Neuromuscular Junction / Q000502:physiology*; D009475:Neurons, Afferent / Q000166:cytology; D009619:Nociceptors / Q000166:cytology / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology*; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate
D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D002772:Cholera Toxin; D006735:Horseradish Peroxidase