Summary: Researchers have validated a new PET tracer that measures synapse loss after spinal cord injury (SCI), revealing molecular changes at the injury site and in distant brain regions. In rat models, the tracer detected substantial reductions in synaptic density both within the spinal cord and in areas such as the amygdala and cerebellum, demonstrating that SCI effects extend beyond the spinal lesion.
Unlike conventional structural imaging, this molecular PET approach provides sensitive, quantitative information about synaptic integrity. That capability makes it a promising tool for objectively monitoring recovery, assessing treatment responses, and guiding personalized therapeutic strategies for people with spinal cord injury.
Key Facts
- Tracer Innovation: The fluorine-18 labeled SV2A tracer [18F]SynVesT-1 detects synapse loss after spinal cord injury.
- Quantitative Findings: Tracer uptake at the injury epicenter decreased markedly—measures showed roughly 52–58% reductions in uptake, with complementary DVR statistics indicating 61% and 53% decreases in some analyses; secondary losses were also observed in multiple brain regions.
- Clinical Potential: SV2A PET provides a non-invasive, objective biomarker to monitor neural network changes, evaluate therapeutic effects, and improve prognostic assessment in SCI.
Source: SNMMI
A newly developed PET tracer generates detailed molecular insight into how spinal cord injuries affect both the spinal cord and the brain, researchers report in The Journal of Nuclear Medicine.
By imaging synaptic vesicle glycoprotein 2A (SV2A), this PET technique supplies information that complements traditional anatomic imaging (x-ray, CT, MRI) by directly quantifying synaptic density and detecting remote neural effects of spinal trauma. Such molecular-level readouts could become essential for evaluating novel therapies and tracking recovery over time.
Traumatic spinal cord injury affects thousands of people and can lead to permanent sensory and motor deficits depending on lesion level and severity. The National Spinal Cord Injury Statistical Center estimates an incidence of about 54 cases per million people per year in the U.S., with roughly 308,600 individuals living with SCI. Current clinical imaging focuses on anatomic damage and spinal stability but provides limited information about underlying synaptic and network-level pathology.
“There is an urgent need for a quantitative, non-invasive imaging method to measure neural network changes after spinal cord injury,” said Jason Cai, PhD, associate professor of radiology and biomedical imaging and of pharmacology at Yale School of Medicine. He and colleagues propose that SV2A PET can visualize and quantify synapse loss across the central nervous system, supporting better assessment and prediction of recovery.
In the study, investigators used the newly developed [18F]SynVesT-1, an 18F-labeled SV2A radiotracer, in a rat model of moderate T7 contusion injury. Nine injured rats and seven sham controls underwent PET imaging on day 1 and again on days 9–11 post-injury. PET findings were compared with ex vivo diffusion tensor imaging (DTI) of the spinal cord and with molecular assays including immunohistochemistry and Western blotting to confirm synaptic loss.
The tracer reliably detected synapse loss at the contusion epicenter. PET uptake measurements indicated reductions of approximately 58% on day 1 and 52% on days 9–11 versus sham controls. When using distribution volume ratio (DVR) analyses, the injury epicenter showed DVR decreases of about 61% on day 1 and 53% on days 9–11. These consistent results across outcome measures support the robustness of [18F]SynVesT-1 PET for quantifying synaptic density.
Beyond the spinal cord, PET revealed reduced [18F]SynVesT-1 uptake in brain regions including the amygdala, limbic insular cortex, and cerebellum early after injury. Ex vivo DTI further identified fiber injury in the internal capsule and somatosensory cortex, linking structural axonal damage with reductions in SV2A signal. Immunohistochemistry and Western blotting confirmed loss of SV2A protein at the lesion site.
Taken together, these multimodal findings indicate that contusive spinal cord injury produces measurable synaptic loss both locally and in remote brain regions, and that [18F]SynVesT-1 PET offers a quantitative, whole-central-nervous-system biomarker to monitor these changes.
“SV2A PET could transform the assessment of spinal cord injury in clinical settings,” Cai added. “It provides an objective metric to evaluate new treatments and could guide more precise, personalized therapeutic decisions.”
COI Statement
Fahmeed Hyder is the founder of Innovacyclics, LLC. Zhengxin Cai is a cofounder of Synvest Imaging Inc. Richard Carson, Yiyun Huang, and Zhengxin Cai are inventors on PCT/US2018/018388, which covers the SV2A PET tracer used in this study.
About this neuroimaging and SCI research news
Author: Susan Martonik
Source: SNMMI
Contact: Susan Martonik – SNMMI
Image: The image is credited to Neuroscience News
Original Research: Open access.
“[18F]SynVesT-1 PET Detects SV2A Changes in the Spinal Cord and Brain of Rats with Spinal Cord Injury” by Jason Cai et al. Journal of Nuclear Medicine
Abstract
[18F]SynVesT-1 PET Detects SV2A Changes in the Spinal Cord and Brain of Rats with Spinal Cord Injury
Traumatic spinal cord injury (SCI) is a severe neurologic condition for which better prognostic and therapeutic evaluation tools are needed. PET imaging of synaptic vesicle glycoprotein 2A (SV2A) enables in vivo measurement of synaptic changes. This study tests whether [18F]SynVesT-1 PET can detect synaptic alterations in a rat model of SCI.
Methods: PET scans with [18F]SynVesT-1 were obtained from rats with a moderate T7 contusion injury (n = 9) and from sham controls (n = 7) on day 1 and on days 9–11 post-injury. The simplified reference region method 2 was applied to calculate distribution volume ratios (DVRs) for spinal cord and brain, using the cervical cord and brainstem as reference regions, respectively. The averaged standardized uptake value (SUV) ratio from 30–60 minutes post-injection was also computed as an alternative outcome measure. Post-mortem diffusion tensor imaging (DTI) assessed axonal injury, while Western blotting and immunostaining validated imaging results at the molecular level.
Results: [18F]SynVesT-1 showed the highest uptake in the cervical spinal cord in controls. At the injury epicenter, DVRs decreased by approximately 61% on day 1 and 53% on days 9–11 compared with sham controls; SUV ratio measures showed parallel reductions (about 58% and 52% in uptake). DTI identified fiber damage at the lesion site, and loss of SV2A protein was confirmed by immunohistochemistry and Western blotting. Early PET assessments also indicated significant involvement of the amygdala, limbic insular cortex, and cerebellum, while DTI detected fiber injury in the internal capsule and somatosensory cortex.
Conclusion: [18F]SynVesT-1 PET reliably detects synapse loss in a contusion SCI rat model. Quantifying synaptic density with SV2A PET provides a promising, objective biomarker to evaluate new therapies and monitor progression in spinal cord injury research and, potentially, clinical care.