Quantification of prefrontal cortical neuronal ensembles following conditioned fear learning in a Fos-LacZ transgenic rat with photoacoustic imaging in Vivo

Understanding the neurobiology of complex behaviors requires measurement of activity in the discrete population of active neurons, neuronal ensembles, which control the behavior. Conventional neuroimaging techniques ineffectively measure neuronal ensemble activity in the brain in vivo because they assess the average regional neuronal activity instead of the specific activity of the neuronal ensemble that mediates the behavior. Our functional molecular photoacoustic tomography (FM-PAT) system allows direct imaging of Fos-dependent neuronal ensemble activation in Fos-LacZ transgenic rats in vivo. We tested four experimental conditions and found increased FM-PAT signal in prefrontal cortical areas in rats undergoing conditioned fear or novel context exposure. A parallel immunofluorescence ex vivo study of Fos expression found similar findings. These findings demonstrate the ability of FM-PAT to measure Fos-expressing neuronal ensembles directly in vivo and support a mechanistic role for the prefrontal cortex in higher-order processing of response to specific stimuli or environmental cues.

Spatial and temporal dynamics of HDACs class IIa following mild traumatic brain injury in adult rats

The fundamental role of epigenetic regulatory mechanisms involved in neuroplasticity and adaptive responses to traumatic brain injury (TBI) is gaining increased recognition. TBI-induced neurodegeneration is associated with several changes in the expression-activity of various epigenetic regulatory enzymes, including histone deacetylases (HDACs). In this study, PET/CT with 6-([¹⁸F]trifluoroacetamido)-1- hexanoicanilide ([¹⁸F]TFAHA) to image spatial and temporal dynamics of HDACs class IIa expression-activity in brains of adult rats subjected to a weight drop model of diffuse, non-penetrating, mild traumatic brain injury (mTBI). The mTBI model was validated by histopathological and immunohistochemical analyses of brain tissue sections for localization and magnitude of expression of heat-shock protein-70 kDa (HSP70), amyloid precursor protein (APP), cannabinoid receptor-2 (CB2), ionized calcium-binding adapter protein-1 (IBA1), histone deacetylase-4 and -5 (HDAC4 and HDAC5). In comparison to baseline, the expression-activities of HDAC4 and HDAC5 were downregulated in the hippocampus, nucleus accumbens, peri-3rd ventricular part of the thalamus, and substantia nigra at 1-3 days post mTBI, and remained low at 7-8 days post mTBI. Reduced levels of HDAC4 and HDAC5 expression observed in neurons of these brain regions post mTBI were associated with the reduced nuclear and neuropil levels of HDAC4 and HDAC5 with the shift to perinuclear localization of these enzymes. These results support the rationale for the development of therapeutic strategies to upregulate expression-activity of HDACs class IIa post-TBI. PET/CT (MRI) with [¹⁸F]TFAHA can facilitate the development and clinical translation of unique therapeutic approaches to upregulate the expression and activity of HDACs class IIa enzymes in the brain after TBI.

Effects of fentanyl on acute locomotor activity, behavioral sensitization, and contextual reward in female and male rats

BACKGROUND

Although fentanyl has gained widespread prominence, there remains a lack of knowledge on this opioid synthetic agonist, particularly related to sex effects. Therefore, we conducted behavioral tests in female and male rats to measure drug abuse-related responses to fentanyl hypothesizing sex-specific responses.

METHODS

Using female and male rats, we measured the effects of acute or repeated administration of fentanyl (20 μg/kg) on locomotor activity (LMA) and behavioral sensitization in an open field test. We further measured contextual-reward and associated locomotor activity during training in a conditioned place preference (CPP) paradigm using a low (4 μg/kg) or high (16 μg/kg) dose of fentanyl. Vaginal lavage samples were collected from female rats in the CPP study, and the estrous phase was determined based on the cytological characterization.

RESULTS

Female, but not male, rats showed elevated LMA in response to acute fentanyl and behavioral sensitization to repeated administration of fentanyl. Fentanyl produced significant CPP in both sexes, but it was more potent in males. Finally, our secondary investigation of the estrous cycle on fentanyl-CPP suggests that non-estrus phases, likely reflecting high estradiol, may predict the degree of fentanyl preference in females.

CONCLUSIONS

Fentanyl was more potent and/or effective to produce LMA and LMA sensitization in females but more potent to produce CPP in males. Furthermore, the role of sex in fentanyl responses varied across endpoints, and sex differences in LMA were not predictive of sex differences in CPP.

Time course of blast-induced injury in the rat auditory cortex

Blast exposure is an increasingly significant health hazard and can have a range of debilitating effects, including auditory dysfunction and traumatic brain injury. To assist in the development of effective treatments, a greater understanding of the mechanisms of blast-induced auditory damage and dysfunction, especially in the central nervous system, is critical. To elucidate this area, we subjected rats to a unilateral blast exposure at 22 psi, measured their auditory brainstem responses (ABRs), and histologically processed their brains at 1 day, 1 month, and 3-month survival time points. The left and right auditory cortices was assessed for astrocytic reactivity and axonal degenerative changes using glial fibrillary acidic protein immunoreactivity and a silver impregnation technique, respectively. Although only unilateral hearing loss was induced, astrocytosis was bilaterally elevated at 1 month post-blast exposure compared to shams, and showed a positive trend of elevation at 3 months post-blast. Axonal degeneration, on the other hand, appeared to be more robust at 1 day and 3 months post-blast. Interestingly, while ABR threshold shifts recovered by the 1 and 3-month time-points, a positive correlation was observed between rats’ astrocyte counts at 1 month post-blast and their threshold shifts at 1 day post-blast. Taken together, our findings suggest that central auditory damage may have occurred due to biomechanical forces from the blast shockwave, and that different indicators/types of damage may manifest over different timelines.

Factors associated with impaired color vision without retinopathy amongst people with type 2 diabetes mellitus: a cross-sectional study

BACKGROUND

Patients with type 2 diabetes mellitus (T2DM) may develop color vision impairment. This study aimed to determine the prevalence and factors associated with impaired color vision in patients with T2DM but without diabetic retinopathy.

METHODS

Enrolment criteria included multi-ethnic Asian participants, age 21 to 80 years, with known T2DM for a minimum of 2 years. Their diagnoses were affirmed from oral glucose tolerance test results and they were screened for impaired color vision using the Farnsworth D-15 instrument. Demographic characteristics were described and clinical data for the preceding 2 years were analyzed using logistic regression.

RESULTS

Twenty-two percent of 849 eligible participants had impaired color vision with higher involvement of the right eye. Impaired blue-yellow color-vision(Tritanomaly) was the commonest impaired color vision. Participants with impaired color vision were significantly associated with age and lower education; longer duration of T2DM (median 6 years vs 4 years); higher HbA1c level and HDL-Cholesterol in 2nd year; lower mean total cholesterol, mean LDL-Cholesterol and mean triglyceride in 2nd year. They also have poorer vision beyond 6/12 in the affected eye. Logistic regression showed that impaired color vision was associated with older patients (OR=1.04), increased duration of T2DM (OR=1.07); prescription of Tolbutamide (OR=3.79) and lower mean systolic blood pressure (OR=0.98).

CONCLUSION

Almost one in four participants with T2DM had impaired color vision, largely with tritanomaly. Color vision screening may be considered for participants who develop T2DM for 6 years or longer, but this requires further cost-effectiveness evaluation.

Evaluation of an anti-stigma campaign related to common mental disorders in rural India: a mixed methods approach

BACKGROUND

Stigma related to mental health is a major barrier to help-seeking resulting in a large treatment gap in low- and middle-income countries (LMIC). This study assessed changes in knowledge, attitude and behaviour, and stigma related to help-seeking among participants exposed to an anti-stigma campaign.

METHOD

The campaign, using multi-media interventions, was part of the SMART Mental Health Project, conducted for 3 months, across 42 villages in rural Andhra Pradesh, in South India. Mixed-methods evaluation was conducted in two villages using a pre-post design.

RESULTS

A total of 1576 and 2100 participants were interviewed, at pre- and post-intervention phases of the campaign. Knowledge was not increased. Attitudes and behaviours improved significantly (p < 0.01). Stigma related to help-seeking reduced significantly (p < 0.05). Social contact and drama were the most beneficial interventions identified during qualitative interviews.

CONCLUSION

The results showed that the campaign was beneficial and led to improvement of attitude and behaviours related to mental health and reduction in stigma related to help-seeking. Social contact was the most effective intervention. The study had implications for future research in LMIC.

Neuronal Injury and Glial Changes Are Hallmarks of Open Field Blast Exposure in Swine Frontal Lobe

With the rapid increase in the number of blast induced traumatic brain injuries and associated neuropsychological consequences in veterans returning from the operations in Iraq and Afghanistan, the need to better understand the neuropathological sequelae following exposure to an open field blast exposure is still critical. Although a large body of experimental studies have attempted to address these pathological changes using shock tube models of blast injury, studies directed at understanding changes in a gyrencephalic brain exposed to a true open field blast are limited and thus forms the focus of this study. Anesthetized, male Yucatan swine were subjected to forward facing medium blast overpressure (peak side on overpressure 224-332 kPa; n = 7) or high blast overpressure (peak side on overpressure 350-403 kPa; n = 5) by detonating 3.6 kg of composition-4 charge. Sham animals (n = 5) were subjected to all the conditions without blast exposure. After a 3-day survival period, the brain was harvested and sections from the frontal lobes were processed for histological assessment of neuronal injury and glial reactivity changes. Significant neuronal injury in the form of beta amyloid precursor protein immunoreactive zones in the gray and white matter was observed in the frontal lobe sections from both the blast exposure groups. A significant increase in the number of astrocytes and microglia was also observed in the blast exposed sections compared to sham sections. We postulate that the observed acute injury changes may progress to chronic periods after blast and may contribute to short and long-term neuronal degeneration and glial mediated inflammation.

Quantitative electroencephalography in a swine model of blast-induced brain injury

OBJECTIVE

Electroencephalography (EEG) was used to examine brain activity abnormalities earlier after blast exposure using a swine model to develop a qEEG data analysis protocol.

METHODS

Anaesthetized swine were exposed to 420-450 Kpa blast overpressure and survived for 3 days after blast. EEG recordings were performed at 15 minutes before the blast and 15 minutes, 30 minutes, 2 hours and 1, 2 and 3 days post-blast using surface recording electrodes and a Biopac 4-channel data acquisition system. Off-line quantitative EEG (qEEG) data analysis was performed to determine qEEG changes.

RESULTS

Blast induced qEEG changes earlier after blast exposure, including a decrease of mean amplitude (MAMP), an increase of delta band power, a decrease of alpha band root mean square (RMS) and a decrease of 90% spectral edge frequency (SEF90).

CONCLUSIONS

This study demonstrated that qEEG is sensitive for cerebral injury. The changes of qEEG earlier after the blast indicate the potential of utilization of multiple parameters of qEEG for diagnosis of blast-induced brain injury. Early detection of blast induced brain injury will allow early screening and assessment of brain abnormalities in soldiers to enable timely therapeutic intervention.

Biomechanical Responses of the Brain in Swine Subject to Free-Field Blasts

Blast-induced traumatic brain injury (bTBI) is a signature wound of modern warfare. The current incomplete understanding of its injury mechanism impedes the development of strategies for effective protection of bTBI. Despite a considerable amount of experimental animal studies focused on the evaluation of brain neurotrauma caused by blast exposure, there is very limited knowledge on the biomechanical responses of the gyrenecephalic brain subjected to primary free-field blast waves imposed in vivo. This study aims to evaluate the external and internal mechanical responses of the brain against different levels of blast loading with Yucatan swine in free field. The incident overpressure (IOP) was generated using 3.6 kg of C4 charge placed at three standoff distances from the swine. Five swine were exposed to a total of 19 blasts. The three average peak IOP pressure levels in this study were 148.8, 278.9, and 409.2 kPa as measured by a pencil probe. The duration of the first positive wave was in the range of 2.1–3 ms. Pressure changes in the brain and head kinematics were recorded with intracranial pressure (ICP) sensors, linear accelerometers, and angular rate sensors. The corresponding average peak ICPs were in the range of 79–143, 210–281, and 311–414 kPa designated as low, medium, and high blast level, respectively. Peak head linear accelerations were in the range of 120–412 g. A positive correlation between IOP and its corresponding biomechanical responses of the brain was also observed. These experimental data can be used to validate computer models of bTBI.

Abstract 3976: Molecular imaging of epigenetic regulation mediated by HDACs 4, 5 using PET/CT/MRI with 18F-TFAHA in a rat model of human glioma

Histone deacetylases (HDACs) are involved in the pathogenesis of cancer through modulation of the expression of various genes involved in cellular proliferation, migration, angiogenesis and apoptosis. HDAC class IIa enzymes interact with tumor suppressor proteins including HIF-1a, GATA-1, and PLZF-RARa. Given the importance of HDACs class IIa in epigenetic regulation of cancer development, progression, and maintenance, there is a pressing need for non-invasive imaging approaches for monitoring the expression-activity of HDACs in vivo. To address this need, our laboratory has developed 6-(tri-fluoroacetamido)-1-hexanoicanilide (18F-TFAHA) for imaging HDAC class IIa enzymes. Previous studies show that 18F-TFAHA is enzymatically cleaved specifically by HDAC class IIa, predominantly by HDACs 4 and 5. To quantitatively visualize the expression-activity of HDACs 4 and 5 in brain gliomas, immunocompromised rats (NTac:NIH-Foxn1rnu, Taconic Biosciences, NY) were implanted intracerebrally (i.c.) with U87-tdRluc cells (4×105 cells in 20 uL), that have been lentivirally-transfected to express GFP-luciferase and tdTomato fluorescent protein fusion reporter genes. Bioluminescence images (BLI) of GBMs were obtained after administration of luciferin (10 μl/g i.p.) using an InVivo Xtreme system (Carestream, Toronto, Canada) at 7 and 14 days post U87-tdRluc cell implantation. Gross tumor morphology and progression was evaluated with T2 MRI on day 14 after tumor implantation using a CliniScan 7T MRI system (Bruker, UK). Following 15-20 days, the rats were administered with 18F-TFAHA (500 μCi/animal, i.v.) and imaged using microPET R4 and Inveon CT (Siemens, TN). After PET/CT imaging, the animals were sacrificed and their brains extracted for immunohistochemical (IHC) and quantitative autoradiographic (QAR) studies (Typhoon 7000, General Electric, CT). The 18F-TFAHA accumulation in regions of interest (ROI) at 20-30 minutes post i.v. administration and was quantified using Logan graphical analysis, which demonstrated a significant increase in 18F-TFAHA accumulation in tumors versus surrounding normal cortex and white matter (p &lt;0.05), outside the structures with normally-increased HDAC IIa activity (e.g., hippocampus, amygdala, periaqueductal gray, n. accumbens). PET/CT/MR imaging results were validated by IHC of brain tissue sections that demonstrated a significant hypoacetylation of histones H2A, H2B, and H4 in tumor tissue with increased 18F-TFAHA accumulation. The ongoing studies in brain tumor-bearing rats undergoing treatment with HDAC inhibitor vorinostat are aimed to assess the feasibility of PET/CT/MRI with 18F-TFAHA for pharmacodynamic monitoring therapies with HDAC class IIa inhibitors. Ultimately, we aim to translate 18F-TFAHA PET/CT/MR imaging into the clinic.

Support: NIH RO1 DA030333-06, NCI CCGS Core Grant CA 016672, NIH RC2 DA028912-01, NIH P30 CA022453

Citation Format: Maxwell T. Laws, Robin E. Bonomi, Swatabdi Kamal, David Gelovani, Jeremy Llanguez, Vadim Popov, Xin Lu, Srinivasu Kallakuri, Thomas Mangner, Juri G. Gelovani. Molecular imaging of epigenetic regulation mediated by HDACs 4, 5 using PET/CT/MRI with 18F-TFAHA in a rat model of human glioma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3976.

Blast overpressure induced axonal injury changes in rat brainstem and spinal cord

Introduction:

Blast induced neurotrauma has been the signature wound in returning soldiers from the ongoing wars in Iraq and Afghanistan. Of importance is understanding the pathomechansim(s) of blast overpressure (OP) induced axonal injury. Although several recent animal models of blast injury indicate the neuronal and axonal injury in various brain regions, animal studies related to axonal injury in the white matter (WM) tracts of cervical spinal cord are limited.

Objective:

The purpose of this study was to assess the extent of axonal injury in WM tracts of cervical spinal cord in male Sprague Dawley rats subjected to a single insult of blast OP.

Materials and Methods:

Sagittal brainstem sections and horizontal cervical spinal cord sections from blast and sham animals were stained by neurofilament light (NF-L) chain and beta amyloid precursor protein immunocytochemistry and observed for axonal injury changes.

Results:

Observations from this preliminary study demonstrate axonal injury changes in the form of prominent swellings, retraction bulbs, and putative signs of membrane disruptions in the brainstem and cervical spinal cord WM tracts of rats subjected to blast OP.

Conclusions:

Prominent axonal injury changes following the blast OP exposure in brainstem and cervical spinal WM tracts underscores the need for careful evaluation of blast induced injury changes and associated symptoms. NF-L immunocytochemistry can be considered as an additional tool to assess the blast OP induced axonal injury.

Traumatic Brain Injury by a Closed Head Injury Device Induces Cerebral Blood Flow Changes and Microhemorrhages

OBJECTIVES

Traumatic brain injury is a poly-pathology characterized by changes in the cerebral blood flow, inflammation, diffuse axonal, cellular, and vascular injuries. However, studies related to understanding the temporal changes in the cerebral blood flow following traumatic brain injury extending to sub-acute periods are limited. In addition, knowledge related to microhemorrhages, such as their detection, localization, and temporal progression, is important in the evaluation of traumatic brain injury.

MATERIALS AND METHODS

Cerebral blood flow changes and microhemorrhages in male Sprague Dawley rats at 4 h, 24 h, 3 days, and 7 days were assessed following a closed head injury induced by the Marmarou impact acceleration device (2 m height, 450 g brass weight). Cerebral blood flow was measured by arterial spin labeling. Microhemorrhages were assessed by susceptibility-weighted imaging and Prussian blue histology.

RESULTS

Traumatic brain injury rats showed reduced regional and global cerebral blood flow at 4 h and 7 days post-injury. Injured rats showed hemorrhagic lesions in the cortex, corpus callosum, hippocampus, and brainstem in susceptibility-weighted imaging. Injured rats also showed Prussian blue reaction products in both the white and gray matter regions up to 7 days after the injury. These lesions were observed in various areas of the cortex, corpus callosum, hippocampus, thalamus, and midbrain.

CONCLUSIONS

These results suggest that changes in cerebral blood flow and hemorrhagic lesions can persist for sub-acute periods after the initial traumatic insult in an animal model. In addition, microhemorrhages otherwise not seen by susceptibility-weighted imaging are present in diverse regions of the brain. The combination of altered cerebral blood flow and microhemorrhages can potentially be a source of secondary injury changes following traumatic brain injury and may need to be taken into consideration in the long-term care of these cases.

Correlation of mechanical impact responses and biomarker levels: A new model for biomarker evaluation in TBI

A modified Marmarou impact acceleration model was used to help screen biomarkers to assess brain injury severity. Anesthetized male Sprague-Dawley rats were subjected to a closed head injury from 1.25, 1.75 and 2.25 m drop heights. Linear and angular responses of the head were measured in vivo. 24h after impact, cerebrospinal fluid (CSF) and serum were collected. CSF and serum levels of phosphorylated neurofilament heavy (pNF-H), glial fibrillary acidic protein (GFAP), interleukin 6 (IL-6), and amyloid beta (Aβ) 1-42 were assessed by enzyme-linked immunosorbent assay (ELISA). Compared to controls, significantly higher CSF and serum pNF-H levels were observed in all impact groups, except between 1.25 m and control in serum. Furthermore, CSF and serum pNF-H levels were significantly different between the impact groups. For GFAP, both CSF and serum levels were significantly higher at 2.25 m compared to 1.75 m, 1.25 m and controls. There was no significant difference in CSF and serum GFAP levels between 1.75 m and 1.25 m, although both groups were significantly higher than control. TBI rats also showed significantly higher levels of IL-6 versus control in both CSF and serum, but no significant difference was observed between each impact group. Levels of Aβ were not significantly different between groups. Pearson's correlation analysis showed pNF-H and GFAP levels in CSF and serum had positive correlation with power (rate of impact energy), followed by average linear acceleration and surface righting (p<0.01), which were good predictors for traumatic axonal injury according to histologic assessment in our previous study, suggesting that they are directly related to the injury mechanism. The model used in this study showed a unique ability in elucidating the relationship between biomarker levels and severity of the mechanical trauma to the brain.

Acute and subacute effects of the ultrasonic blade and electrosurgery on nerve physiology

Ultrasonic blades have been shown to cause less acute electrophysiological damage when applied near nerves than monopolar electrosurgery (ES). This study was performed to determine whether the acute nerve damage observed for ES, as well as the relative lack of damage observed for ultrasonic dissection, extends through a subacute timeframe. Muscle incisions were made in rat with the Harmonic^® Blade (HB) and ES at a distance of 2 mm from the sciatic nerve. Sham surgery was also performed which consisted of similar exposure of the sciatic nerve without use of an energized device. Electrophysiological function was assessed acutely over a 3-h period, and subacutely after a 7-day survival, by monitoring the sciatic nerve compound action potential (CAP), conduction velocity (CV), von Frey hair (VFH) stimulation force, leukocyte infiltration, and impaired axonal transport via β-amyloid precursor protein (β-APP) immunocytochemistry.

During the acute period, ES produced significantly lower CAP and CV, and higher levels of leukocytes and β-APP than sham, whereas the ultrasonic blade was not significantly different from sham, and had significantly lower VFH force than ES. After the subacute survival, ES continued to display significantly lower CAP and CV, and higher levels of leukocytes and β-APP than sham, whereas ultrasonic blade had higher CAP and CV than sham, and lower VFH than ES. This study confirms that incisions made with an ultrasonic blade cause less acute nerve damage than monopolar ES, and are comparable to sham surgery at a distance of 2 mm from the sciatic nerve. The negative effects of electrosurgery extend through at least a 7-day survival period, whereas subacute recovery after application of the ultrasonic blade was comparable to that of sham surgery. For surgical procedures in the vicinity of vital nerves, use of the ultrasonic blade represents a lower risk than ES for both acute and subacute neural trauma.

Spatial alterations in endothelin receptor expression are temporally associated with the altered microcirculation after brain trauma

OBJECTIVES

To study the cellular distribution of endothelin receptors A and B (ETrA and ETrB) in the post-traumatic sensorimotor cortex and hippocampus.

MATERIALS AND METHODS

We inflicted closed head trauma to male Sprague-Dawley rats and visualized ETrA and ETrB immunoreactivity with 3,3'-diaminobenzidine.

RESULTS

ETrA immunolabeling was the most prominent in pyramidal neurons 24 and 48 hours post-trauma, while it reached its peak in the microvasculature at hour 4. ETrB immunolabeling was observed in endothelial cells, perivascular neurons, smooth muscle cells (SM) and pericytes, the expression being the most pronounced 24 hours post-trauma.

DISCUSSION

The results suggest that the vasoconstrictor effect of endothelin-1 (ET-1) is mediated primarily by ETrA. The dual effects of ETrB are reflected in its vasoconstrictor role at the vascular bed and conversely, in the attenuation of ET-1 availability and synthesis. We conclude that both receptors play a role in the disturbed microvascular autoregulation and in the sustained reduction of blood flow following trauma to the brain.

The effects of ultrasonic and electrosurgery devices on nerve physiology

BACKGROUND

While the risks associated with the use of electrosurgery near nerves are well known, few studies have examined the neurophysiologic effects of application of the Harmonic Blade, an ultrasonic scalpel, in the vicinity of nerve fibres. This study sought to compare the sub-acute neurophysiologic effects of the Harmonic Blade and electrosurgery after incisions close to the sciatic nerve.

METHODS

Incisions were made in rats with the Harmonic Blade and electrosurgery at distances of 1, 2, 3 and 4 mm from the sciatic nerve. Sham surgery was also performed. The compound action potential, conduction velocity and calibrated nylon filament (von Frey hair, VFH) stimulating force were monitored for up to 3 hours after surgery. The sciatic nerve was assessed for inflammation via H&E staining and impaired axonal transport by β-APP immunohistochemistry.

RESULTS

Electrosurgery incisions produced a significantly greater decrease in compound action potential and conduction velocity, and increase in the VFH force than the Harmonic Blade over all time points and distances from the sciatic nerve. The Harmonic Blade was similar to sham surgery for the compound action potential and VFH force. Electrosurgery yielded significantly greater leukocyte infiltration than the Harmonic Blade and produced the highest levels of β-APP immunoreactive swellings.

CONCLUSIONS

Incisions with electrosurgery in the range of 1-4 mm of the sciatic nerve caused substantial changes in neurophysiologic functioning and inflammation. In contrast, the Harmonic Blade was similar to sham surgery in the vicinity of the nerve, producing little observable acute trauma.

Endothelin receptor A antagonism reduces the extent of diffuse axonal injury in a rodent model of traumatic brain injury

OBJECTIVES

While endothelin-1 and its receptors have traditionally been associated with mediating vasoreactivity, we have recently shown that the vast majority of endothelin receptor A expression following traumatic brain injury is localized within the neuron. While it has been suggested that endothelin receptor A plays a role in influencing neuronal integrity, the significance of neuronally expressed endothelin receptor A remains unclear. One report suggests that endothelin-1 signaling mediates diffuse axonal injury. Therefore, this work sought to determine whether treatment with BQ-123, a selective endothelin receptor A antagonist, diminishes the extent of diffuse axonal injury following trauma.

METHODS

A total of 12 male Sprague-Dawley rats (350-400 g) were used in this study. Two groups (n = 6 per group) were generated as follows: sham operation and traumatic brain injury+1·0 mg/kg BQ-123 delivered intravenously 30 minutes prior to the injury. Trauma was induced using a weight acceleration impact device. Animals were terminated 24 or 48 hours after trauma, and a series of six coronal sections through the entire anterior-posterior extent of the corpus callosum were selected from each brain for quantification of diffuse axonal injury by beta-amyloid precursor protein immunostaining.

RESULTS

Our data indicated that animals treated with BQ-123 30 minutes prior to trauma showed a significant reduction in diffuse axonal injury in corpus callosum at both 24 and 48 hours post-injury.

CONCLUSION

The results show that endothelin receptor A antagonism reduced the extent of diffuse axonal injury, demonstrating a potential influence of the endothelin system on the intra-axonal cascade of molecular events underlying diffuse axonal injury.

Impaired axoplasmic transport is the dominant injury induced by an impact acceleration injury device: an analysis of traumatic axonal injury in pyramidal tract and corpus callosum of rats

Traumatic axonal injury (TAI) involves neurofilament compaction (NFC) and impaired axoplasmic transport (IAT) in distinct populations of axons. Previous quantification studies of TAI focused on limited areas of pyramidal tract (Py) but not its entire length. Quantification of TAI in corpus callosum (CC) and its comparison to that in Py is also lacking. This study assessed and compared the extent of TAI in the entire Py and CC of rats following TBI. TBI was induced by a modified Marmarou impact acceleration device in 31 adult male Sprague Dawley rats by dropping a 450 gram impactor from either 1.25 m or 2.25 m. Twenty-four hours after TBI, TAI was assessed by beta amyloid precursor protein (β-APP-IAT) and RMO14 (NFC) immunocytochemistry. TAI density (β-APP and RMO14 axonal swellings, retraction balls and axonal profiles) was counted from panoramic images of CC and Py. Significantly high TAI was observed in 2.25 m impacted rats. β-APP immunoreactive axons were significantly higher in number than RMO14 immunoreactive axons in both the structures. TAI density in Py was significantly higher than in CC. Based on our parallel biomechanical studies, it is inferred that TAI in CC may be related to compressive strains and that in Py may be related to tensile strains. Overall, IAT appears to be the dominant injury type induced by this model and injury in Py predominates that in CC.

Innervation of cervical ventral facet joint capsule: Histological evidence

AIM: To assess the presence of nerves in ventral facet joint capsules as facet capsules are generally implicated in neck pain.

METHODS: Twenty-four ventral cervical facet joint capsules were harvested from 3 unembalmed cadavers. Paraffin sections from these capsules were processed to identify neurofilament and substance P immunoreactive fibers. Nerve fiber presence was also verified by a silver impregnation method.

RESULTS: Neurofilament reactive fibers were observed in sections from 9 capsules. They were observed in areas with collagen fibers and areas with irregular connective tissue. Substance P reactive nerve fibers were found in sections from 7 capsules in similar areas. Silver impregnation also revealed the presence of nerve fibers. The nerve fibers were also found as bundles in the lateral margins of the capsule. A Pacinian corpuscle-like ending was also observed in one specimen.

CONCLUSION: Nerve fibers revealed by neurofilament immunoreactivity and silver staining support innervation of the ventral aspect of the facet joint capsule. The presence of substance P reactive fibers supports the potential role of these elements in mediating pain. The presence of a Pacinian-like ending implicates a potential role in joint movement.

Injury predictors for traumatic axonal injury in a rodent head impact acceleration model

A modified Marmarou impact acceleration injury model was developed to study the kinematics of the rat head to quantify traumatic axonal injury (TAI) in the corpus callosum (CC) and brainstem pyramidal tract (Py), to determine injury predictors and to establish injury thresholds for severe TAI. Thirty-one anesthetized male Sprague-Dawley rats (392±13 grams) were impacted using a modified impact acceleration injury device from 2.25 m and 1.25 m heights. Beta-amyloid precursor protein (β-APP) immunocytochemistry was used to assess and quantify axonal changes in CC and Py. Over 600 injury maps in CC and Py were constructed in the 31 impacted rats. TAI distribution along the rostro-caudal direction in CC and Py was determined. Linear and angular responses of the rat head were monitored and measured in vivo with an attached accelerometer and angular rate sensor, and were correlated to TAI data. Logistic regression analysis suggested that the occurrence of severe TAI in CC was best predicted by average linear acceleration, followed by power and time to surface righting. The combination of average linear acceleration and time to surface righting showed an improved predictive result. In Py, severe TAI was best predicted by time to surface righting, followed by peak and average angular velocity. When both CC and Py were combined, power was the best predictor, and the combined average linear acceleration and average angular velocity was also found to have good injury predictive ability. Receiver operator characteristic curves were used to assess the predictive power of individual and paired injury predictors. TAI tolerance curves were also proposed in this study.

Muscular response to physiologic tensile stretch of the caprine c5/6 facet joint capsule: dynamic recruitment thresholds and latencies

This study examined the cervical muscle response to physiologic, high-rate (100 mm/s) tensile facet joint capsule (FJC) stretch. Six in-vivo caprine C5/6 FJC preparations were subjected to an incremental tensile loading paradigm. EMG activity was recorded from the right trapezius (TR) and multifidus (MF) muscle groups at the C5 and C6 levels; and from the sternomastoid (SM) and longus colli (LC) muscle groups bilaterally at the C5/6 level; during FJC stretch. Capsule load during the displacement applications was recorded via a miniature load cell, and 3D capsule strains (based on stereoimaging of an array of markers on the capsule surface) were reconstructed using finite element methods. EMG traces from each muscle were examined for onset of muscular activity. Capsule strains and loads at the time of EMG onset were recorded for each muscle, as was the time from the onset of FJC stretch to the onset of muscle activity. All muscles were responsive to physiologic high-rate FJC stretch. The deep muscles (MF and LC) were recruited at significantly smaller capsule loads and onset latencies than the superficial muscles (TR and SM). MF activation strain was significantly smaller than LC and TR activation strains. These data were also compared to previously published low-rate data. MF was the first muscle group to be recruited regardless of the activation criterion under consideration (i.e. strain, load, or latency) or the rate of FJC stretch. LC recruitment occurred significantly sooner under high-rate vs. low-rate FJC stretch. The results of this study provide further evidence of extensive ligamento-muscular reflex pathways between the FJC and the cervical musculature, which are responsive to both low-rate and high-rate FJC stretch. These data add to our knowledge of the dynamic response of paraspinal muscles relative to facet joint motion and provide a unique contribution to enhance the precision of computer-simulated impacts.

Quantitative relationship between axonal injury and mechanical response in a rodent head impact acceleration model

A modified Marmarou impact acceleration model was developed to study the mechanical responses induced by this model and their correlation to traumatic axonal injury (TAI). Traumatic brain injury (TBI) was induced in 31 anesthetized male Sprague-Dawley rats (392±13 g) by a custom-made 450-g impactor from heights of 1.25 m or 2.25 m. An accelerometer and angular rate sensor measured the linear and angular responses of the head, while the impact event was captured by a high-speed video camera. TAI distribution along the rostro-caudal direction, as well as across the left and right hemispheres, was determined using β-amyloid precursor protein (β-APP) immunocytochemistry, and detailed TAI injury maps were constructed for the entire corpus callosum. Peak linear acceleration 1.25 m and 2.25 m impacts were 666±165 g and 907±501 g, respectively. Peak angular velocities were 95±24 rad/sec and 124±48 rad/sec, respectively. Compared to the 2.25-m group, the observed TAI counts in the 1.25-m impact group were significantly lower. Average linear acceleration, peak angular velocity, average angular acceleration, and surface righting time were also significantly different between the two groups. A positive correlation was observed between normalized total TAI counts and average linear acceleration (R(2)=0.612, p<0.05), and time to surface right (R(2)=0.545, p<0.05). Our study suggested that a 2.25-m drop in the Marmarou model may not always result in a severe injury, and TAI level is related to the linear and angular acceleration response of the rat head during impact, not necessarily the drop height.

Strain and load thresholds for cervical muscle recruitment in response to quasi-static tensile stretch of the caprine C5-C6 facet joint capsule

The aim of this study was to investigate the response of cervical muscles to physiologic tensile stretch of cervical facet joint capsule (FJC) at a quasi-static displacement rate of 0.5mm/s. In vivo caprine left C5-C6 FJC preparations were subjected to an incremental tensile displacement paradigm. EMG activity was recorded during FJC stretch from the right trapezius (TR) and multifidus (MF) muscle groups at the C5 and C6 levels and bilaterally from the sternomastoid (SM) and longus colli (LC) muscle groups at the C5-C6 level. Onset of muscular activity was later analyzed using visual and computer-based methods. Capsule load and strain at the time of onset were recorded and compared between the muscle groups. Results indicated capsule load was a better indicator of the tensile stretch thresholds for muscular recruitment than capsule strain. MF responded at significantly smaller capsule loads than TR and LC, while TR and LC activation loads were not significantly different. SM did not respond to physiologic FJC stretch. Muscle group recruitment order reflected the muscles' fiber type compositions and functional roles in the spine. This study provides the first evidence that the cervical ligamento-muscular reflex pathways are activated via tensile FJC stretch and extend to superficial and deep musculature on the anterior and posterior aspects of the neck, ipsilateral and contralateral to the side of FJC stretch.

Tensile stretching of cervical facet joint capsule and related axonal changes

This study examines axonal changes in goat cervical facet joint capsules (FJC) subjected to low rate loading. Left C5-C6 FJC was subjected to a series of tensile tests from 2 mm to failure using a computer-controlled actuator. The FJC strain on the dorsal aspect was monitored by a stereo-imaging system. Stretched (n = 10) and unstretched (n = 7) capsules were harvested and serial sections were processed by a silver impregnation method. The mean peak actuator displacement was 21.3 mm (range: 12-30 mm). The average peak strain encompassing various regions of the capsule was 72.9 +/- 7.1%. Complete failure of the capsule was observed in 70% of the stretched capsules. Silver impregnation of the sections revealed nerve fibers and bundles in all the regions of the capsule. A blinded analysis of digital photomicrographs of axons revealed a statistically significant number of swollen axons with non-uniform caliber in stretched FJCs. Axons with terminal retraction balls, with occasional beaded appearance or with vacuolations were also observed. Stretching the FJC beyond physiological range could result in altered axonal morphology that may be related to secondary or delayed axotomy changes similar to those seen in central nervous system injuries where axons are subjected to stretching and shearing. These may contribute to neuropathic pain and are potentially related to neck pain after whiplash events.

A new model of traumatic axonal injury to determine the effects of strain and displacement rates

Traumatic brain injury (TBI) continues to be a major health problem, with over 500,000 cases per year with a societal cost of approximately $85 billion in the US. Motor vehicle accidents are the leading cause of such injuries. In many cases of TBI widespread disruption of the axons occurs through a process known as diffuse axonal injury (DAI) or traumatic axonal injury (TAI). In the current study, an in vivo TAI model was developed using spinal nerve roots of adult rats. This model was used to determine functional and structural responses of axons to various strains and displacement rates. Fifty-six L5 dorsal nerve roots were each subjected to a predetermined strain range (<10%, 10-20% and >20%) at a specified displacement rate (0.01 mm/sec and 15 mm/sec) only once. Image analysis was used to determine actual strains on the roots during the pull. Neurophysiologic recordings were performed on the nerve root before and after stretch to determine functional changes in response to stretch, including conduction velocity (CV) and area of the evoked compound action potential (CAP). Structural changes including vascular injury, axotomy, and impaired axoplasmic transport (IAT) were evaluated using hematoxylin and eosin, Palmgren silver impregnation and beta-APP staining techniques, respectively. Results showed that CV and the area of the CAP decreased as strain and displacement rate increased. Also, threshold strains for complete nerve conduction loss were 16% and 9% at 0.01 mm/sec and 15 mm/sec rate, respectively. These threshold values indicate the rate dependency of functional injury and indicate that axons tolerate slow loading rates better than higher loading rates. Histological studies revealed increased spacing, tearing of axons, IAT and occurrence of hemorrhage to be strain and displacement rate dependent. Linear relationships existed between the increasing strain and the occurrence rate of axonal injury as evidenced by multiple indicators (IAT, hemorrhage, torn fibers or primary axotomy) at both rates. In conclusion, the results from this study indicate that the severity of both functional and structural injury increased with increases in strain and displacement rate.

Distribution of A-delta and C-fiber receptors in the cervical facet joint capsule and their response to stretch

BACKGROUND

It has been proposed that cervical facet joint capsules are a major source of whiplash pain. However, there is a paucity of neurophysiologic data to support this hypothesis. The purposes of this study were to determine the distribution of A-delta and C-fiber sensory receptors in the facet joint capsule and to test their patterns of response to stretch and related sensory function.

METHODS

Laminectomy from C4 to C7 was performed in seventeen goats, while they were under general anesthesia, to expose the C6 nerve roots. Customized dual bipolar electrodes were used to record neural activity from one of the C6 branches. An 8 or 15-V electrical stimulus was used to provoke receptor activity in nine designated areas on the dorsal part of the C5-C6 facet joint capsule. Receptors were classified on the basis of conduction velocities. The waveform of an identified receptor was set up as a template to determine its neural activity in response to capsular stretch. The characteristics of each single receptor's response to capsular stretch were analyzed to determine its sensory function as a mechanoreceptor or nociceptor.

RESULTS

Two hundred and forty-eight receptors on the dorsal part of the C5-C6 facet joint capsule were evoked by electrical stimulation in the seventeen goats. More C-fiber receptors were found on the dorsolateral aspect of the facet joint capsule, where tendons and muscles were attached. The response to stretch of 120 receptors, from twelve goats, were analyzed to classify them into one of four categories (high-threshold mechanoreceptors, non-saturated low-threshold mechanoreceptors, saturated low-threshold mechanoreceptors, and silent receptors) or as unclassified receptors.

CONCLUSIONS

The existence of receptors in the facet joint capsule indicates that the capsule has pain and proprioceptive sensory functions.

Sympathetic afferent units from lumbar intervertebral discs

To clarify the pathomechanisms of discogenic low back pain, the sympathetic afferent discharge originating from the L5-L6 disc via the L2 root were investigated neurophysiologically in 31 Lewis rats. Sympathetic afferent units were recorded from the L2 root connected to the lumbar sympathetic trunk by rami communicantes. The L5-L6 discs were mechanically probed, stimulated electrically to evoke action potentials and, finally, treated with chemicals to produce an inflammatory reaction. We could not obtain a response from any units in the L5-L6 discs using mechanical stimulation, but with electrical stimulation we identified 42 units consisting mostly of A-delta fibres. In some experiments a response to mechanical probing of the L5-L6 disc was recognised after producing an inflammatory reaction. This study suggests that mechanical stimulation of the lumbar discs may not always produce pain, whereas inflammatory changes may cause the disc to become sensitive to mechanical stimuli, resulting in nociceptive information being transmitted as discogenic low back pain to the spinal cord through the lumbar sympathetic trunk. This may partly explain the variation in human symptoms of degenerate discs.

Pain generation in lumbar and cervical facet joints

Facet joints are implicated as a major source of neck and low-back pain. Both cervical and lumbar facet syndromes have been described in the medical literature. Biomechanical studies have shown that lumbar and cervical facet-joint capsules can undergo high strains during spine-loading. Neuroanatomic studies have demonstrated free and encapsulated nerve endings in facet joints as well as nerves containing substance P and calcitonin gene-related peptide. Neurophysiologic studies have shown that facet-joint capsules contain low-threshold mechanoreceptors, mechanically sensitive nociceptors, and silent nociceptors. Inflammation leads to decreased thresholds of nerve endings in facet capsules as well as elevated baseline discharge rates. Recent biomechanical studies suggest that rear-end motor-vehicle impacts give rise to excessive deformation of the capsules of lower cervical facet joints. Still unresolved is whether this stretch is sufficient to activate nociceptors in the joint capsule. To answer this question, recent studies indicate that low stretch levels activate proprioceptors in the facet-joint capsule. Excessive capsule stretch activates nociceptors, leads to prolonged neural afterdischarges, and can cause damage to the capsule and to axons in the capsule. In instances in which a whiplash event is severe enough to injure the joint capsule, facet capsule overstretch is a possible cause of persistent neck pain.

Effects of interleukin-1 beta, interleukin-6, and tumor necrosis factor on sensitivity of dorsal root ganglion and peripheral receptive fields in rats

This study was designed to characterize the effects of low doses (0.5-5 ng) of pro-inflammatory cytokines, interleukin-1 beta (IL-1beta), interleukin-6 (IL-6), and tumor necrosis factor (TNF), on the neural activity of dorsal root ganglion (DRG) in rats. The purpose of this study was to examine the effects of cytokines (IL-1beta, IL-6, and TNF) on the somatosensory neural response of DRG. The release of inflammatory cytokines by an injured disc may play a critical role in pain production at nerve endings, axons, and nerve cell bodies. Herniated disc tissue has been shown to release IL-1beta, IL-6, TNF, and other algesic chemicals. Their effects on nerve endings in disc and adjacent tissue may lead to low back pain and their effects on dorsal root axons and ganglia may lead to sciatica. Exposed lumbar DRGs were investigated by electrophysiologic techniques. Sham (mineral oil), control (carrier solution), or IL-1beta, IL-6, or TNF at doses of 0.5, 1, and 5 ng were applied over the DRG. Baseline discharge rates as well as mechanosensitivity of the DRG and peripheral receptive fields were evaluated over 30 min. Applications of IL-1beta at 1 ng resulted in an increase in the discharge rate, 5 ng resulted in an increased mechanosensitivity of the DRG in group II units. Similarly, after 1 ng TNF applications, group II units also showed an increase in mechanosensitivity of DRG and peripheral receptive fields. At low doses IL-1beta and TNF sensitization of receptive fields were observed. The responses observed in the group II units indicate that a sub-population of afferent units might have long-term effects modifying the sensory input to the central nervous system. This study provides added evidence to the role of cytokines in modulating afferent activity following inflammation.

Neural response of cervical facet joint capsule to stretch: a study of whiplash pain mechanism

Cervical facet joints are implicated as a major source of pain after whiplash injury. The purpose of this study was to investigate the proposed capsule strain injury mechanism of whiplash pain using neurophysiologic methods. Strain thresholds, threshold distribution, saturation strains and afterdischarge responses of capsule neural receptors were characterized in vivo. Goat C5-C6 facet joint capsules were used to identify and characterize capsule receptors in response to controlled uniaxial stretch by recording C6 dorsal rootlet nerve discharge. The joints were stretched at 0.5 mm/sec in a series of tests with 2 mm increments until the capsule ruptured. Ninety-two identified units were responsive to physiologic or noxious stretch while 28 were silent receptors. Among the 50 characterized responsive units, 42 showed low strain thresholds at 10.2+/-4.6% while 8 had high strain thresholds at 47.2+/-9.6%. Further, 35 of the 42 low-threshold units displayed discharge saturation at various strains (44.2+/-16.7%). A significant finding was that twelve low-threshold units exhibited afterdischarge for greater than 30 sec after stretch release at 36.6+/-12.5% strains, and displayed longer-lasting afterdischarge (greater than 4 min) at higher strains (39.0+/-14.4%) with significant difference (p = 0.019) in strains. Two high-threshold units had afterdischarges for greater than 30 sec or 4 min at 50.3+/-5.9% and 57.7+/-10.6% strains, respectively. In addition, the spatial distribution of the 42 low-threshold receptors demonstrated that the receptors on the joint gap were more strain-sensitive, with significantly lower strain thresholds compared to the rostral and caudal regions. No significant difference in strain threshold was observed in the medial-lateral direction. When compared to the reported strains that facet joint capsules experienced in whiplash (35-60%) and the reported capsule subfailure strains (35-67%), the low strain thresholds are substantially lower whereas the high thresholds and afterdischarge strains are within that range. Thus, low threshold units appear to signal proprioception within the physiologic range. High threshold units likely signal nociception (pain sensation) while afterdischarge may signal capsule strain injury and contribute to persistent pain.

Neurophysiological and biomechanical characterization of goat cervical facet joint capsules

Cervical facet joints have been implicated as a major source of pain after whiplash injury. We sought to identify facet joint capsule receptors in the cervical spine and quantify their responses to capsular deformation. The response of mechanosensitive afferents in C5-C6 facet joint capsules to craniocaudal stretch (0.5 mm/s) was examined in anaesthetized adult goats. Capsular afferents were characterized into Group III and IV based on their conduction velocity. Two-dimensional strains across the capsules during stretch were obtained by a stereoimaging technique and finite element modeling. 17 (53%) Group III and 14 (56%) Group IV afferents were identified with low strain thresholds of 0.107+/-0.033 and 0.100+/-0.046. A subpopulation of low-strain-threshold afferents had discharge rate saturation at the strains of 0.388+/-0.121 (n=9, Group III) and 0.341+/-0.159 (n=9, Group IV). Two (8%) Group IV units responded only to high strains (0.460+/-0.170). 15 (47%) Group III and 9 (36%) Group IV units could not be excited even by noxious capsular stretch. Simple linear regressions were conducted with capsular load and principal strain as independent variables and neural response of low-strain-threshold afferents as the dependent variable. Correlation coefficients (R2) were 0.73+/-0.11 with load, and 0.82+/-0.12 with principal strain. The stiffness of the C5-C6 capsules was 16.8+/-11.4 N/mm. Our results indicate that sensory receptors in cervical facet joint capsules are not only capable of signaling a graded physiological mechanical stimulus, but may also elicit pain sensation under excessive deformation.

Recording of neural activity from goat cervical facet joint capsule using custom-designed miniature electrodes

STUDY DESIGN

To establish a methodology for the neurophysiologic study of mechanoreceptors in the cervical facet joint capsule.

OBJECTIVES

To test a custom designed miniature dual bipolar electrode for recording the neural activity in cervical dorsal roots. To determine if the neural activity from different receptors in the capsule can be differentiated using this methodology.

SUMMARY OF BACKGROUND DATA

Injury to cervical facet joint capsules has been regarded as an important source of whiplash pain, but no neurophysiologic study has been performed to demonstrate or characterize sensory nerve function in the capsule.

METHODS

Nineteen goats weighing 34 to 55 kg were used under general anesthesia. A C4-C6 laminectomy was performed to expose the C6 nerve root. Custom designed miniature dual bipolar electrodes were used to record neural activity in the left C6 branches. Electrical and mechanical stimuli were used to evoke receptor activity in the dorsal aspect of the C5/6 capsule. Conduction velocities (CVs) of evoked units were determined by electrical stimulation and dual-bipolar-electrode recording methods. The units were classified based on their CVs. The waveform of each classified unit was saved as a template for later single unit discharge search among multiunit discharges during the stretch of the capsule. The C5/6 facet joint with capsule was pulled by a computer-controlled actuator instrumented with a load cell at a rate of 0.5 mm per second. The evoked neural activity and load were recorded, digitized, and analyzed to determine CV, discharge rate, and response to the stretch.

RESULTS

Miniature bipolar electrodes recorded the neural activity in both channels, with single unit CVs being measured. There was no discernible motion between the electrode and dorsal root when the capsule was pulled. Both local compression and stretch on capsule evoked multiunit discharges. A-beta, A-delta, and C-fiber units were found among these multiunit discharges. The rate of single unit and multiunit discharges increased during capsule stretch in the physiologic range and afterdischarges occurred beyond the physiologic range.

CONCLUSIONS

The novel miniature electrodes not requiring a micromanipulator made it feasible and reliable to record neural activity from short cervical spinal roots. Waveforms of different units could be identified, making it possible to study sensory functions of the facet joint capsule. A-beta, A-delta, and C-fiber units were found responding to mechanical stimuli, indicating that facet joint capsule has functional proprioceptors and nociceptors.

Development of an in vivo method to investigate biomechanical and neurophysiological properties of spine facet joint capsules

Facet joint capsules (FJC) may experience large mechanical deformation under spine motion. There has been no previous quantitative study of the relationship between capsular strain and sensory nerve activation in spine FJC in vivo. Space limitation in the cervical spine makes such a study difficult, as the facet joint must be loaded while simultaneously monitoring nerve discharge from nerve roots immediately adjacent to the loaded tissue. A new methodology was developed to investigate biomechanical and neurophysiological properties of spine facet joint capsules in vivo. The method incorporated a custom-fabricated testing frame for facet joint loading, a stereoimaging system, and a template-matching technique to obtain single afferent response. It was tested by loading goat C5-C6 FJC in vivo with simultaneous nerve root recordings and 3D strain tracking of the capsules. Preliminary data showed that 18 of 23 afferents (78.3%) were found to be mechanosensitive to tensile stretch, and five were not responsive, even under tensile load as high as 27.5 N. Mechanosensitive afferents in goat capsules had tensile strain thresholds of 0.119+/-0.080. Neural responses of all mechanosensitive units showed statistically significant correlations (all P<<0.05) with both capsular load (r(2)=0.744+/-0.109) and local strain (r(2)=0.868+/-0.088). This method enables the investigation of the correlation between tissue load, deformation and neural responses of mechanoreceptors in spine facet joint capsules, and can be adapted to investigate tissue loading and neural response of other soft tissues.

The role of the endovascular surgeon for lower extremity ischemia

Since the data investigating endovascular therapy performed by surgeons is scarce, we retrospectively reviewed our experience of endovascular procedures performed by vascular surgeons in the operating room for lower extremity ischemia due to stenotic lesions.

METHODS

A total of 14,424 procedures were performed by our division between January 1990--October 2003. Of these, 500 involved a balloon angioplasty. These made up 3.5% of the total caseload. The median age of the patients who underwent these 500 balloon angioplasty was 72+/-0.5 years old; 65% were male; 50% had a history of diabetes mellitus, and 6% had ESRD. Indications for the procedures included acute ischemia (47 cases), critical ischemia (rest pain, gangrene, or ischemic ulcers in 254 cases), failing bypass (64 cases), severe claudication (134 cases), and preoperative for a popliteal artery aneurysm repair.

RESULTS

244 of the procedures were percutaneous, and the remaining 256 were combined with some type of open procedure. Those performed as an open technique were in combination with a bypass (135 cases) and in combination with a patch angioplasty (31cases). Balloon angioplasties were performed of the aorta (5 cases), iliac arteries (281 cases), the superficial femoral artery (SFA) (101 cases), the popliteal artery (44 cases), the tibial vessels (77 cases), the subclavian/axillary artery (5 cases) and failing grafts (26 cases). Balloon angioplasty was attempted in eight cases and failed due to inability to cross the lesion with a guidewire. Intraoperative complications included 4 dissections, inability to dilate the lesion adequately (2 cases), and rupture of two iliac lesions that underwent open repair (1 case) or repair with a stent graft (1 case). Stents were initially used highly selectively but recently are now being deployed more liberally in the iliac arteries (total 251 cases with stents).

CONCLUSIONS

Based on these data, we suggest that balloon angioplasty is a useful tool that can be performed by vascular surgeons safely. The advantages to the patients include one combined procedure to treat lower extremity ischemia.

Carotid endarterectomy in octogenarians and nonagenarians : is it worth the effort?

PURPOSE

The safety, effectiveness and cost issues of carotid endarterectomy (CEA) in the elderly patient have been debated due to the limited life expectancy and presumably increased rate of complications. This is despite multiple reports in the literature of excellent results in this population. To further examine this issue, we compared characteristics of three populations who underwent CEA at our institution: 53-79 year old patients (youngest group), 80-89 years old patients (middle group), and 90-98 year old patients (oldest group).

METHODS

Medical and financial data were obtained by retrospective review of hospital charts and billing records. We analyzed 266 random CEAs performed in 251 patients in the youngest group, 280 CEAs performed in 247 patients in the middle group and 19 CEA in 16 patients in the oldest group performed between 2/1/90 and 2/5/01.

RESULTS

Comparing each CEA group, there were no differences in gender (males: 56% vs. 51% vs. 53%), incidence of preoperative symptoms (43% vs. 43% vs. 42%), hypertension (68% vs. 60% vs. 42%), combined perioperative death and stroke rate (1.8% vs. 2.1% vs. 10%) or other complications (11% vs. 10% vs. 10%). Significant differences (p<0.05) were noted between the groups in incidence of diabetes (33% vs. 51% vs. 5% in each group), and heart disease (28% vs. 38% vs. 21%). Length of stay for admissions for CEA only were also similar in all three groups (2.37 days vs. 2.67 days vs. 2.36 days). A cost analysis of the earliest 230 patients in the entire series examining hospital cost per case revealed similar data for the < 80 years old and > 80 year old patients ($7,842 vs. $9,400).

CONCLUSIONS

Carotid endarterectomy can be performed in the elderly as safely and cost effectively as in the younger population.

The effects of epidural application of allografted nucleus pulposus in rats on cytokine expression, limb withdrawal and nerve root discharge

This study investigated cytokine expression, behavioral and neurophysiologic changes in Lewis rats whose lumbar nerve roots were exposed to nucleus pulposus (NP). Allografted NP or fat was implanted over the left L5 nerve root. Sham rats had no NP or fat implantation. Control rats had no surgery. Rats were allowed to survive for 7 days and were tested daily for hind-paw mechanical and thermal withdrawal response (TWR). Granulation tissue was processed by immunohistochemistry for cytokines--interleukin 1 beta (IL-1beta), interleukin 6 (IL-6) and tumor necrosis factor (TNF). Neurophysiological response from the L5 nerve roots was also characterized after 7 days. Significant staining density for IL-1beta, IL-6 and TNF was observed in NP granulation tissue compared with fat and sham (p<0.05). However, there were no significant thermal and mechanical behavioral changes. TWR data computed as percentage-difference scores indicated no significant changes in withdrawal response between the four groups, although NP-treated group showed a trend of decreasing withdrawal latency. Comparison of combined percentage-difference scores revealed increased sensitivity in the NP group on days 4, 5 and 6, 7 when compared with control rats only, with no significant changes in the percentage-difference scores of fat and sham rats when compared to control. Neurophysiologically, the percentage increase in discharge rate in NP-treated rats was higher than control (p<0.05) but not higher than fat and sham rats. These results support the inflammatory nature of NP but offer limited support to NP-mediated thermal behavioral changes.

Demonstration of substance P, calcitonin gene-related peptide, and protein gene product 9.5 containing nerve fibers in human cervical facet joint capsules

STUDY DESIGN

Human cervical facet joint capsules were evaluated by immunohistochemistry.

OBJECTIVES

To study the neuropeptide innervation of the cadaveric cervical facet joint capsules.

SUMMARY OF BACKGROUND DATA

Various clinical and biomechanical studies indicate a role for cervical facet joint capsules in the etiology of neck pain. However, studies on innervation of these capsules are very limited. There is also a dearth of studies on the neuropeptide nature of this innervation.

METHODS

Facet joint capsules harvested from unembalmed cadavers were studied by the avidin biotin peroxidase method for the presence of nerve fibers. Neuropeptide innervation was investigated by using antisera to substance P and calcitonin gene-related peptide. Antisera to protein gene product 9.5 (PGP 9.5), a general neuronal marker, were also used.

RESULTS

In a study of 12 human cervical facet joint capsules, short segments of substance P were observed in 6 capsules, while fibers reactive to calcitonin gene-related peptide were demonstrated in 7 capsules. Nerve fibers immunoreactive to protein gene product 9.5 were also observed in 9 of the 14 capsules studied. Protein gene product 9.5 reactive fibers were the most extensively distributed fibers, observed as bundles and also as single fibers.

CONCLUSIONS

An abundance of protein gene product 9.5 reactive nerve fibers indicates an extensive innervation of the cervical facet joint capsules. The presence of substance P and calcitonin gene-related peptide reactive nerve fibers in a population of these lends credence to cervical facet joint capsules as a key source of neck pain.

Effects of nucleus pulposus on nerve root neural activity, mechanosensitivity, axonal morphology, and sodium channel expression

STUDY DESIGN

This study analyzed the effects of autografted nucleus pulposus on nerve root axon morphology, neurophysiologic function, and sodium channel expression.

OBJECTIVES

To investigate the chronic effects of the epidural implantation of nucleus pulposus on nerve root morphology, neural activity, ectopic discharge, mechanosensitivity, and sodium channel expression.

SUMMARY OF BACKGROUND DATA

It has been reported that ectopic discharges were recorded antidromically from sural nerve on compressing nucleus pulposus exposed spinal nerves. However, it is not clear what the effects of nucleus pulposus are on ectopic discharges recorded directly from the spinal nerve roots. It is also not clear what the effects of nucleus pulposus are on the threshold pressure to provoke ectopic discharges in the spinal nerves. Sodium channel content increases in remodeling axons after nerve injury, but it is not clear what the effects of nucleus pulposus are on sodium channel expression in spinal nerve.

METHODS

Forty-six male Sprague-Dawley rats were used, 20 in a nucleus pulposus-implanted group, 18 in a fat-implanted group, and 8 in a normal group. Fresh autografted nucleus pulposus or fat tissue was implanted into the dorsal epidural space at the L4-L5 disc level. On the 7th, 21st, or 42nd day, neurophysiologic recordings were made to determine nerve root response to compression. Nerve roots were then harvested to determine sodium channel protein concentration and histologic changes in the nerve root. The correlations between sodium channel density and neural activity and mechanosensitivity of dorsal root were analyzed statistically.

RESULTS

Ectopic discharge rate was higher in nucleus pulposus 7-day group. Threshold pressure to evoke ectopic discharges was lower in the nucleus pulposus 7-day group, and higher in the nucleus pulposus 42-day group compared to the normal group. Sodium channel protein density increased in the nucleus pulposus 7-day and nucleus pulposus 21-day group compared to normal nerve. Sodium channel density changes were not correlated to threshold pressure. Ectopic discharge rate increased with increase of sodium channel density in the nerve roots. The number of axons with neuropathy increased in the nucleus pulposus 7-day and 21-day groups.

CONCLUSIONS

Acute exposure of nerve root to nucleus pulposus resulted in increased number of axons with neuropathy, higher intensity of ectopic discharges on compression, and nerve mechanosensitization. Chronic exposure resulted in mechanical desensitization. Changes of sodium channel density were correlated to ectopic discharge rate.

Carotid surgery without external carotid endarterectomy: a 6-year clinical experience with 1027 cases

PURPOSE

previously we routinely performed endarterectomy of the external carotid artery (ECA) during carotid surgery. However, discouraging experience and lack of supportive data in the literature made us question its necessity. The present report describes our experience with a modified carotid endarterectomy (CEA) technique where the ECA is left undisturbed regardless of its degree of stenosis.

METHODS

from January 1996 to June 2001, 1027 CEAs were performed in 905 patients with this technique at our institution. All operations were performed for at least 60% internal carotid artery (ICA) stenosis. A preoperative carotid duplex scan was available for review in 990 cases (96%). Follow-up duplex scans were recovered from 0 to 1 months in 851 cases (83%) and from >1 month in 655 cases (64%). Seventy percent of these cases were performed for asymptomatic lesions.

RESULTS

the perioperative (30-day) mortality rate for the entire group of patients was 0.5% and the stroke rate was 0.7%. Mean follow-up was 18 months (range: 2-66 months). Only two ECAs occluded in the first postoperative month. During the follow-up period, 37 additional ECAs (5.6%) were found to progress from mild to severe (>75%) stenosis postoperatively. In addition, 7% of the cases were found to have worsened the degree of stenosis, 8% improved and 85% remained unchanged.

CONCLUSION

these data support sparing of the ECA during CEA.

Hemodynamics of infrapopliteal PTFE bypasses and adjunctive arteriovenous fistulas

PURPOSE

Blood flow, pressure and peripheral resistance in patients with established polytetrafluoroethylene (PTFE) grafts and adjunctive arteriovenous fistulas (AVF) have rarely been investigated. To better elucidate the effects of this AVF, we obtained noninvasive measurements of hemodynamic variables in patients with infrapopliteal PTFE grafts and an AVF.

METHODS

. Systolic, mean and diastolic arm and toe pressures were measured with an oscillometric technique employed in automatic blood pressure monitors. Peak-systolic velocity, end-diastolic velocity and flow rates at the graft and recipient distal artery were measured with duplex ultrasound. Resistance for the leg and foot in peripheral resistance units ( PRU ) was estimated as mean arm pressure divided by graft flow rate and as mean toe pressure divided by distal artery flow rate respectively. We analyzed data from 21 patients. Toe pressures were measurable in 13 patients. Bypass graft inflow was at the external iliac artery in 11 patients, common femoral in six, common iliac in two and superficial femoral in two. The distal anastomosis was at the anterior tibial artery in 10 patients, peroneal in seven and posterior tibial in four patients.

RESULTS

. Graft systolic and diastolic velocities were 91+/-46 (mean+/-sd) and 38+/-31 (mean+/-sd) cm/s respectively. Toe systolic pressure averaged 81+/-28 (mean+/-SD) mmHg with a corresponding toe/brachial index (TBI) of 0.53+/-0.18 (mean+/-SD). The ratio between arm mean pressure, 104+/-20 (mean+/-SD) mmHg, and graft flow rate, 413+/-290 (mean+/-sd) ml/min, yielded an estimated leg resistance of 0.32+/-0.20 peripheral resistance units (PRU) (mean+/-sd). The ratio between mean toe pressure, 51+/-21 (mean+/-SD) mmHg, and distal artery flow rate, 37+/-26 (mean+/-SD) ml/min, produced an estimated foot resistance averaging 1.66+/-1.18 PRU (mean+/-sd).

CONCLUSIONS

Average graft flow rate was five times greater than flow reported for standard tibial bypasses. Although distal artery flow rate and graft peak systolic velocity were within reported normal ranges, mean toe pressure and toe-brachial index were below normal. Leg and foot resistances were decreased. These data suggest that bypasses with arteriovenous fistulas have increased flow, desirable for graft patency, but may affect distal perfusion pressure.

The effect of varying impact energy on diffuse axonal injury in the rat brain: a preliminary study

Diffuse axonal injury (DAI) is seen as widespread damage in the white matter of brain characterized by morphological changes to axons throughout the brain and brain stem. The current study attempted to investigate the effect of increasing impact energy on the presence and severity of DAI in corpus callosum (CC). DAI was induced in adult male Sprague-Dawley rats using an injury model adapted from Marmarou et al. in 1994. A 450-g cylindrical brass weight was dropped from three different heights (2.0 m, 1.5 m and 1.0 m) on to a metal helmet affixed to the skull of the rats. In the sham group, rats underwent a surgical procedure with no impact. After a 24-h survival period the animals were transcardially perfused. The brain was removed and the cerebral hemispheres were sectioned with a vibrotome and stained by silver impregnation technique. The CC of all the impacted rats showed DAI in the form of beaded axons, retraction balls and vacuole-like enlargements. The axonal injury was most severe in the 2-m group, while mildest in the 1-m group. In the sham group, axons appeared to be normal. This study demonstrates evidence of graded DAI depending on the impact energy. Such data is useful for mathematical modeling of axonal injury in rat brain using the same impact parameters and potential determination of injury thresholds for neural trauma.

Comparison of Magnetic Resonance Angiography (MRA) and Duplex Ultrasound Arterial Mapping (DUAM) prior to infrainguinal arterial reconstruction

OBJECTIVE

the purpose of this study is to compare Magnetic Resonance Angiography (MRA) to Duplex Ultrasound Arterial Mapping (DUAM) and intraoperative findings to determine the clinical, accuracy of MRA for planning lower extremity revascularization procedures.

METHODS

forty-two patients who underwent lower extremity revascularization procedures had both MRA and DUAM evaluations. These data were analyzed retrospectively and two distinct endpoints were considered. First, we compared the MRA and DUAM findings for aorto-iliac, femoral-popliteal and infra-popliteal segments to intraoperative findings and evaluated the degree to which they agreed. Second, if there was a disagreement between imaging modalities, it was established whether a change in operative procedure would have resulted.

RESULTS

MRA and DUAM findings agreed in 26 of 31 cases (83%) of aorto-iliac segments, in 25 of 31 cases (81%) of femoral-popliteal segments, and in 16 of 21 cases (76%) of infra-popliteal segments. In total, DUAM agreed with intraoperative findings in 98% of cases while MRA agreed in 82% (p<.001). Disagreement between intraoperative findings and DUAM lead to an alternate surgical procedure in only one case (2%) while disagreement with MRA lead to a different procedure in 38% of cases (p<.001).

CONCLUSIONS

these data show that MRA is not yet adequate to replace conventional angiography and is less accurate that DUAM. Further improvements are necessary before MRA can be used as the sole modality for formulation of a pre-operative plan for lower extremity revascularization.

Causes of early post carotid endartectomy stroke in a recent series: the increasing importance of hyperperfusion syndrome

OBJECTIVE

Early stroke occurs in 0.9% to 7% of patients undergoing carotid endarterectomy (CEA). These have been thought to be mostly due to embolization. However, in our recent clinical experience, we noted hyperperfusion syndrome to be a significant cause of postoperative strokes. Therefore, we reviewed our experience and investigated the distribution of causes of early postoperative strokes.

MATERIALS AND METHODS

A retrospective chart review of 444 consecutive patients who underwent CEA at our institution between June 1997 and October 1999 (500 operations) was performed to evaluate the incidence and etiology of early postoperative strokes. Indications for operation included history of stroke correlating with the side of ICA stenosis (50 patients or 10%), symptoms of transient ischemic attacks (84 patients or 16.8%), amaurosis fugax (18 patients or 3.6%), or asymptomatic stenosis (348 patients or 69.6%). All patients were evaluated with duplex scan preoperatively and postoperatively. Diagnosis of early postoperative strokes within one month after CEA was made based on clinical examination. Postoperative CT scan of the brain was available in 100% of patients with suspected diagnosis of CVA.

RESULTS

Five patients (3 male and 2 female) were diagnosed with strokes postoperatively (1%). These five were symptomatic patients with ICA stenosis > or = 80% and moderate contralateral ICA stenosis. In two of those patients (40%), the reason for the stroke was considered embolization to the cerebral arteries; one patient suffered a shunt injury as a cause of stroke; two patients (40%) were diagnosed with hyperperfusion syndrome. In both patients diagnosis was made clinically, and in only one of those patients the clinical picture correlated with CT scan. Two patients (0.4%) had asymptomatic ICA occlusion at 2 weeks and 18 days postoperatively.

CONCLUSION

Embolization to the cerebral arteries remains the leading cause of early postoperative strokes. However, hyperperfusion syndrome also accounts for a significant portion of these postoperative strokes. The percentage of patients with this syndrome might be even higher, once clinical picture is clearly defined. These data warrant further investigation of hyperperfusion syndrome.

Impact of reintervention for failing upper-extremity arteriovenous autogenous access for hemodialysis

PURPOSE

Although large published series have described their experience with the management of failed or failing prosthetic arteriovenous grafts for hemodialysis, there are scant data regarding failing arteriovenous fistulae (AVFs). To analyze the management of nonfunctioning or nonmaturing AVFs, we reviewed our experience with salvage procedures for these AVFs.

MATERIALS AND METHODS

Of the 474 AVFs placed at our institution in 380 patients between June 1997 and March 2001, 75 revisions were performed in 46 patients (49 AVFs). Ages of these patients ranged from 29 to 94 years (mean, 68 +/- 1.4 years). Diabetic patients comprised 51%, and hypertensive patients comprised 75%. Twenty patients underwent 26 vein patch angioplasties, and 17 patients underwent 24 balloon angioplasties. Four patients required four vein interpositions, and 12 patients underwent 12 revisions of the fistula to a more proximal level. Extended salvage procedures consisted of four turn-downs to the basilic vein for proximal cephalic vein thrombosis or stenosis and five extension bypasses to the axillary or jugular vein for subclavian vein thrombosis.

RESULTS

Follow-up ranged from 1 to 31 months (mean, 10 months). The patients who underwent open revisions tended to need fewer subsequent procedures. However, primary patency of the vein patch angioplasty was not significantly better as compared with balloon angioplasty (P = .8) by life table analysis. Patency after revision of a radial cephalic fistula and brachial cephalic fistula were not statistically different. One interposition failed during the follow-up, and one revision to a more proximal level thrombosed during the follow-up. Two of the turn-down procedures had thrombosed at 2 and 11 months. The remaining two turn-down procedures have remained functional at 1 and 24 months. One of the extensions thrombosed at 8 months whereas the other four have remained functional at 1, 6, and 8 months.

CONCLUSIONS

Despite the limited follow-up data, this review suggests that simple and extended salvage procedures may allow maturation and add to the life span of AVFs for hemodialysis. In addition, these data suggest an advantage for open techniques as compared with percutaneous techniques but only in terms of requiring fewer subsequent procedures.

Initial steps in the unifying theory of the pathogenesis of artery aneurysms

OBJECTIVES

The objective of this study was to investigate the changes in histology and proteolysis and the role of apoptosis in the development of peripheral artery aneurysms.

METHODS

Eighteen popliteal, 6 abdominal aortic, 10 iliac, 2 carotid, and 6 femoral artery aneurysm specimens were obtained from patients undergoing elective surgical repair. All were males with ages 48 to 93 (mean 71 years). Normal controls were obtained from patients matched for age, sex, and major risk factors. Vascular smooth muscle cells (VSMC), macrophages, T lymphocytes, and apoptosis-regulating molecules were detected immunohistochemically. Detection of apoptosis was by TUNEL assay. Proteolytic activity was determined by 10% gelatin gel zymography.

RESULTS

Paucity of VSMCs, increased amount of inflammatory infiltrate, and fragmentation of elastic lamellae were observed in aneurysmal tissues as compared to normal arteries (P < 0.02). There is increased gelatinolytic activity at 92, 84, 72, and 67 kDa in the aneurysmal tissues. There are fewer CD68+ macrophages and T cells in the media of controls than in the aneurysms (P = 0.01). Apoptosis is significantly high in aneurysm tissues (P < 0.01) and the degree of apoptosis was in the order AAA>FAA>PAA>IAA>CAA. There is increased expression of Bax, CPP-32, Fas, and p53 in PAA specimens as compared to normal popliteal arteries (P < 0.05).

CONCLUSIONS

These data confirm the apparent architectural disruption and loss of VSMCs that are hallmarks of aneurysm development, in peripheral artery aneurysms. Apoptosis and signaling molecules capable of initiating cell death may play a significant role in the pathogenesis of all aneurysms. Our data suggest a common etiology between the various types of aneurysms.

Thiamine reverses hyperglycemia-induced dysfunction in cultured endothelial cells

BACKGROUND

High levels of glucose have previously been shown to inhibit endothelial cell migration and increase secretion of the von Willebrand factor (vWF), a marker of endothelial cell damage. This study investigates whether thiamine, an important coenzyme in intracellular glucose metabolism, improves endothelial cell migration and decreases von Willebrand factor secretion under hyperglycemic conditions.

METHODS

Bovine aortic endothelial cells (BAECs) were grown under physiological glucose (5.5 mmol/L) and hyperglycemic (13.8 mmol/L and 27.7 mmol/L) conditions with or without thiamine (200 micromol/L) supplementation. Endothelial cell migration was investigated in monolayers of BAECs that were wounded by scraping. The distance of migration, the number of migrating cells, and the surface area covered by the migrating cells were measured. Secretion of vWF by BAECs under physiological glucose and high glucose conditions with or without thiamine (200 micromol/L) supplementation was studied with enzyme-linked immunosorbent assay.

RESULTS

Under hyperglycemic conditions, there was a significant decrease in the number of endothelial cells and an increase in the secretion of vWF (P <.001). Thiamine treatment limited this inhibitory effect of elevated glucose levels on BAECs. Glucose (27.7 mmol/L) significantly decreased the migration distance of BAECs into the wounded area to 4.0 +/- 1.4 cm, as compared with 6.2 +/- 0.3 cm in the control. Thiamine supplementation restored the migration distance by BAECs (6.94 +/- 0.7 cm) and the wound surface area covered (47.7 +/- 5.6 cm(2)) (P <.001).

CONCLUSIONS

Hyperglycemia activates BAECs and promotes secretion of vWF, a marker of endothelial cell damage. Thiamine inhibits this endothelial cell activation and the effects of hyperglycemia on endothelial cell migration. This beneficial effect of thiamine limiting endothelial cell dysfunction is possibly through the diversion of glucose flux from anaerobic to aerobic pathways. The data from this study lead to the speculation that thiamine intake may mitigate or delay vascular complications of diabetes.