Evaluation of Neuropathic Pain in a Rat Model
of Total Brachial Plexus Avulsion from Behavior
to Brain Metabolism
Authors: Xu Jian-Guang 
Published: February 2021

Background: Approximately 30% to 80% of patients with brachial plexus avulsion (BPA)
developed neuropathic pain. It is an intolerable neuropathic pain, which brings heavy burden
to family and society. In addition to motor and sensory deficits, neuropathic pain can be
another serious sequela that equally influences the patient. The development of a microsurgical
technique has promoted the treatment and rehabilitation of brachial plexus injury, but pain relief
after BPA is still a difficult problem.
Objectives: The present study aimed to semi-quantify changes in the behavior, spinal cord and
cerebral metabolism in a neuropathic pain model following BPA injury in rats.
Study Design: Controlled animal study.
Setting: Institute of Rehabilitation Medicine, Shanghai, China.
Methods: A total of 15 Sprague-Dawley rats, weighing 200 to 220 g, were randomly divided
into 2 groups: experimental group (n = 10) and control group (n = 5). In the experimental group,
neuropathic pain induced by BPA was established by directly avulsing the C5, C6, C7, C8, and
T1 roots on the right side from the spinal cord. Rats in the control group only received openclose surgery. The autotomic behavior of biting their own digits was recorded and scored at 2
months after the surgery. Small animal positron emission tomography/computed tomography
(PET/CT) images after injection of a 2-[18F]-fluoro-2-deoxy-D-glucose (18F-FDG) tracer were
acquired to evaluate glucose metabolism in pain-related brain regions before and after the
surgery, respectively. Semi-quantitative values of cortical to cerebellum standardized uptake
value (SUV) ratios were calculated. Then, the animals were euthanized and the cervical segments
of the spinal cord were removed for detection of glial fibrillary acidic protein (GFAP) expression
in the astrocytes by immunohistochemical assay.
Results: Nine of the 10 rats (90%) in the experimental group showed autotomic behavior at 2
months after the surgery. Slight autotomic behavior was noted only in one of 5 rats (20%) from
the control group. The autotomic score in the experimental group was significantly higher than
that in the control group (5.4 ± 1.0 vs. 0.2 ± 0.4, P < 0.05). The experimental group showed
significantly higher SUV ratio in both the right and left thalamus, compared to the control group
(P < 0.05). Immunohistochemical assay demonstrated that GFAP positive astrocytes in the dorsal
horn at the injured side significantly increased compared to the control group (P < 0.05).
Limitations: There are differences between small animals and human beings, and the structure
and function of the human brain is more complex than in rodents. Therefore, extrapolation of
the present conclusion should be cautious.
Conclusions: The present study reported a unique model of neuropathic pain following total
BPA in rodents, which was demonstrated by a higher rate and score of autotomic behavior.
More astrocytes were found activated in the spinal cord at the corresponding level of C5 and
C6 spinal cord. In the small animal PET/CT imaging, significantly higher standardized glucose metabolic activity was found in both the right and left thalamus in the experimental group. The present study semi-quantified the
neuropathic pain behavior in rats and explored the plastic changes in the spinal and brain metabolism.
Key words: Brachial plexus avulsion, small animal PET/CT, glucose metabolism, neuropathic pain, astrocyte, 18F-FDG