Evaluation of brain activation related to resting pain using functional magnetic resonance imaging in cynomolgus macaques undergoing knee surgery.

Purpose: Functional magnetic resonance imaging (fMRI) visualizes hemodynamic responses associated with brain and spinal cord activation. Various types of pain have been objectively assessed using fMRI as considerable brain activations. This study aimed to develop a pain model in cynomolgus macaques undergoing knee surgery and confirm brain activation due to resting pain after knee surgery. Methods: An osteochondral graft surgery on the femoral condyle in the unilateral knee was performed on four cynomolgus macaques (Macaca fascicularis). Resting pain was evaluated as changes in brain fMRI findings with a 3.0-T MRI scanner preoperatively, postoperatively, and after postoperative administration of morphine. In the fMRI analysis, Z-values >1.96 were considered statistically significant. Results: Brain activation without stimulation after surgery in the cingulate cortex (3.09) and insular cortex (3.06) on the opposite side of the surgery was significantly greater than that before surgery (1.05 and 1.03, respectively) according to fMRI. After the administration of morphine, activation due to resting pain decreased in the cingulate cortex (1.38) and insular cortex (1.21). Conclusion: Osteochondral graft surgery on the femoral condyle can lead to postoperative resting pain. fMRI can reveal activation in pain-related brain areas and evaluate resting pain due to knee surgery.

Regenerative effects of platelet-rich plasma releasate injection in rabbit discs degenerated by intradiscal injection of condoliase.

BACKGROUND: Intradiscal condoliase injection is an alternative therapeutic option for lumbar disc herniation (LDH). However, it is often associated with disc degeneration. Several in vivo studies have demonstrated the regenerative potential of platelet-rich plasma (PRP) in disc degeneration. Thus, we hypothesized that the intradiscal injection of PRP releasate (PRPr), a soluble releasate isolated from PRP, has the potential to regenerate degenerated intervertebral discs (IVDs) induced by condoliase. This study examined the regenerative effects of PRPr on rabbit IVDs degenerated following condoliase injection. METHODS: Eleven New Zealand white rabbits were used in this study. Condoliase (12.5 mU/10 µl) was injected into two non-contiguous discs (L2-L3 and L4-L5), and L3-L4 disc was left intact as a non-injection control. Saline (20 µl) or PRPr (20 µl) was randomly injected into L2-L3 and L4-L5 discs 4 weeks after the condoliase injection. Disc height (DH) was radiographically monitored biweekly from the day of condoliase injection to 16 weeks post-injection. Changes in DH were expressed as percentage DH (%DH) normalized to the baseline DH. Sixteen weeks after condoliase injection, all rabbits were euthanized, and subjected to MRI and histological analyses. RESULTS: Intradiscal injection of condoliase induced a significant decrease in %DH (L2-L3 and L4-L5) to 52.0% at week 4. However, the %DH began to return to normal after saline injection and reached 76.3% at week 16. In the PRPr group, %DH began to recover to normal after the PRPr injection and was restored to 95.5% at week 16. The MRI-modified Pfirrmann grade of the PRPr group was significantly lower than that of the saline group (P < 0.01). Histological analyses showed progressive degenerative changes, including reduction of the NP area and condensation of the matrix in the saline and PRPr groups. The histological score of the PRPr group was significantly lower than that of the saline group (P < 0.01). CONCLUSIONS: PRPr has great potential to enhance the regeneration of degenerated rabbit IVDs induced by condoliase. The results of this preclinical study suggest that PRPr injection therapy may be indicated for patients with LDH who have poor recovery from disc degeneration after chemonucleolysis treatment with condoliase.

Potential sex differences in activation of pain-related brain regions in nonhuman primates with a unilateral spinal nerve ligation.

The lack of truly robust analgesics for chronic pain is owed, in part, to the lack of an animal model that reflects the clinical pain state and of a mechanism-based, objective neurological indicator of pain. The present study examined stimulus-evoked brain activation with functional magnetic resonance imaging in male and female cynomolgus macaques following unilateral L7 spinal nerve ligation and the effects of clinical analgesics pregabalin, duloxetine, and morphine on brain activation in these macaques. A modified straight leg raise test was used to assess pain severity in awake animals and to evoke regional brain activation in anesthetized animals. The potential effects of clinical analgesics on both awake pain behavior and regional brain activation were examined. Following spinal nerve ligation, both male and female macaques showed significantly decreased ipsilateral straight leg raise thresholds, suggesting the presence of radicular-like pain. Morphine treatment increased straight leg raise thresholds in both males and females whereas duloxetine and pregabalin did not. In male macaques, the ipsilateral straight leg raise activated contralateral insular and somatosensory cortex (Ins/SII), and thalamus. In female macaques, the ipsilateral leg raise activated cingulate cortex and contralateral insular and somatosensory cortex. Straight leg raises of the contralateral, unligated leg did not evoke brain activation. Morphine reduced activation in all brain regions in both male and female macaques. In males, neither pregabalin nor duloxetine decreased brain activation compared with vehicle treatment. In females, however, pregabalin and duloxetine decreased the activation of cingulate cortex compared with vehicle treatment. The current findings suggest a differential activation of brain areas depending on sex following a peripheral nerve injury. Differential brain activation observed in this study could underlie qualitative sexual dimorphism in clinical chronic pain perception and responses to analgesics. Future pain management approaches for neuropathic pain will need to consider potential sex differences in pain mechanism and treatment efficacy.

In vivo imaging of acute physiological responses after treatment of cancer with near-infrared photoimmunotherapy.

PURPOSE: Near-infrared photoimmunotherapy (NIR-PIT) is a new cancer phototherapy using an antibody-photosensitizer conjugate (Ab-IR700). By NIR light irradiation, Ab-IR700 forms a water-insoluble aggregation on the plasma membrane of cancer cells, leading to lethal membrane damage of cancer cells with high selectivity. However, IR700 produces singlet oxygen, which induces non-selective inflammatory responses such as edema in normal tissues around the tumor. Understanding such treatment-emergent responses is important to minimize side effects and improve clinical outcomes. Thus, in this study, we evaluated physiological responses during NIR-PIT by magnetic resonance imaging (MRI) and positron emission tomography (PET). PROCEDURES: Ab-IR700 was intravenously injected into tumor-bearing mice with two tumors on the right and left sides of the dorsum. At 24 h after injection, a tumor was irradiated with NIR light. Edema formation was examined by T1/T2/diffusion-weighted MRI and inflammation was investigated by PET with 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG). Because inflammation can increase vascular permeability via inflammatory mediators, we evaluated changes in oxygen levels in tumors using a hypoxia imaging probe, [18F]fluoromisonidazole ([18F]FMISO). RESULTS: The uptake of [18F]FDG in the irradiated tumor was significantly decreased compared to the control tumor, indicating the impairment of glucose metabolism induced by NIR-PIT. MRI and [18F]FDG-PET images showed that inflammatory edema with [18F]FDG accumulation was present in the surrounding normal tissues of the irradiated tumor. Furthermore, [18F]FMISO accumulation in the center of the irradiated tumor was relatively low, indicating the enhancement of oxygen supply due to increased vascular permeability. In contrast, high [18F]FMISO accumulation was observed in the peripheral region, indicating enhancement of hypoxia in the region. This could be because inflammatory edema was formed in the surrounding normal tissues, which blocked blood flow to the tumor. CONCLUSIONS: We successfully monitored inflammatory edema and changes in oxygen levels during NIR-PIT. Our findings on the acute physiological responses after light irradiation will help to develop effective measures to minimize the side effects in NIR-PIT.

Regional brain activation during rectal distention and attenuation with alosetron in a nonhuman primate model of irritable bowel syndrome.

Greater understanding of the mechanism that mediates visceral pain and hypersensitivity associated with irritable bowel syndrome (IBS) would facilitate the development of effective therapeutics to manage these symptoms. An objective marker associated with the underlying mechanisms of visceral pain and hypersensitivity could be used to guide therapeutic development. The current study examined brain activation evoked by rectal distention with functional magnetic resonance imaging (fMRI) in a cynomolgus macaque model of visceral hypersensitivity. Male, cynomolgus macaques underwent five four-week treatments of dextran sodium sulfate (DSS)-distilled water (DW), which induced mild-moderate colitis with remission during each treatment cycle. Balloon rectal distention (RD) was performed under anesthesia 14 weeks after the final DSS-DW treatment. Colonoscopy confirmed the absence of colitis prior to the start of RD. In naïve, untreated macaques, 10, 20 and 30 ml RD did not evoke brain activation. However, insular cortex/somatosensory II cortex and cerebellum were significantly activated in DSS-treated macaques at 20 and 30 ml rectal distention. Intra-rectal pressure after DSS treatment was not significantly different from that of naïve, untreated macaques, indicating lack of alteration of rectal functioning following DSS-treatment. Treatment with 5-HT3 receptor antagonist alosetron (p.o.) reduced distension-evoked brain activation and decreased intra-rectal pressure. The current findings demonstrated activation of brain regions to RD following DSS treatments which was not present in naïve macaques, suggesting visceral hypersensitivity. Brain activation in turn was reduced by alosetron, which could underlie the analgesic effect alosetron in IBS patients.

Adenosine A1R/A3R (Adenosine A1 and A3 Receptor) Agonist AST-004 Reduces Brain Infarction in a Nonhuman Primate Model of Stroke.

BACKGROUND AND PURPOSE: Treatment with A1R/A3R (adenosine A1 and A3 receptor) agonists in rodent models of acute ischemic stroke results in significantly reduced lesion volume, indicating activation of adenosine A1R or A3R is cerebroprotective. However, dosing and timing required for cerebroprotection has yet to be established, and whether adenosine A1R/A3R activation will lead to cerebroprotection in a gyrencephalic species has yet to be determined. METHODS: The current study used clinical study intervention timelines in a nonhuman primate model of transient, 4-hour middle cerebral artery occlusion to investigate a potential cerebroprotective effect of the dual adenosine A1R/A3R agonist AST-004. Bolus and then 22 hours intravenous infusion of AST-004 was initiated 2 hours after transient middle cerebral artery occlusion. Primary outcome measures included lesion volume, lesion growth kinetics, penumbra volume as well as initial pharmacokinetic-pharmacodynamic relationships measured up to 5 days after transient middle cerebral artery occlusion. Secondary outcome measures included physiological parameters and neurological function. RESULTS: Administration of AST-004 resulted in rapid and statistically significant decreases in lesion growth rate and total lesion volume. In addition, penumbra volume decline over time was significantly less under AST-004 treatment compared with vehicle treatment. These changes correlated with unbound AST-004 concentrations in the plasma and cerebrospinal fluid as well as estimated brain A1R and A3R occupancy. No relevant changes in physiological parameters were observed during AST-004 treatment. CONCLUSIONS: These findings suggest that administration of AST-004 and combined A1R/A3R agonism in the brain are efficacious pharmacological interventions in acute ischemic stroke and warrant further clinical evaluation.

A longitudinal comparison in cynomolgus macaques of the effect of brimonidine on optic nerve neuropathy using diffusion tensor imaging magnetic resonance imaging and spectral domain optical coherence tomography.

Early detection of optic neuropathy is crucial for initiating treatment that could delay or prevent visual field loss. Preclinical studies have advanced a number of potential neuroprotective strategies to prevent retinal ganglion cell (RGC) degeneration, but none have successfully completed clinical trials. One issue related to the lack of preclinical to clinical translation is the lack of preclinical morphometric assessments that could be used to track neuroprotection, as well as neurodegeneration, over time within the same animal. Thus, to assess whether clinically used morphometric assessments can identify neuroprotection of RGC, the current study compared optic nerve fractional anisotropy (FA) obtained with diffusion tensor imaging (DTI) and retinal nerve fiber layer (RNFL) thickness measured with spectral domain optical coherence tomography (SD-OCT) to observe not only the early progression of RGC axonal degeneration but to also discern which imaging modality identifies signs of neuroprotection during treatment with the alpha-adrenoceptor agonist brimonidine. Elevated and sustained intraocular pressure (IOP) was observed following laser photocoagulation of the trabecular meshwork in one eye of nonhuman primates (NHP). Either brimonidine (0.1%) or control treatment was instilled twice daily for two months. In control-treated eyes, increased IOP, increased vertical cup-to-disc (C/D), reduced rim-to-disc (R/D) ratio, decreased RNFL thickness and decreased FA were observed. While IOP remained elevated during the course of the study, brimonidine tended to delay the progression of RNFL thinning. However, in the same animal, optic nerve FA did not appear to decline. Brimonidine treatment did not affect other measures of RGC axonal degeneration. The current findings demonstrate that early progression of optic neuropathy can be tracked over time in a nonhuman primate model of ocular hypertension using either DTI or SD-OCT. Furthermore, the delayed changes to RNFL thickness and FA appear to be a neuroprotective effect of brimonidine independent of its effect on IOP.

Pharmacological modulation of brain activation to non-noxious stimulation in a cynomolgus macaque model of peripheral nerve injury.

In vivo neuroimaging could be utilized as a noninvasive tool for elaborating the CNS mechanism of chronic pain and for elaborating mechanisms of potential analgesic therapeutics. A model of unilateral peripheral neuropathy was developed in the cynomolgus macaque, a species that is phylogenetically close to humans. Nerve entrapment was induced by placing a 4 mm length of polyvinyl cuff around the left common sciatic nerve. Prior to nerve injury, stimulation of the foot with a range of non-noxious von Frey filaments (1, 4, 8, 15, and 26 g) did not evoke brain activation as observed with functional magnetic resonance imaging (fMRI). Two weeks after injury, stimulation of the ipsilateral foot with non-noxious filaments activated the contralateral insula/secondary somatosensory cortex (Ins/SII) and anterior cingulate cortex (ACC). By contrast, no activation was observed with stimulation of the contralateral foot. Robust bilateral activation of thalamus was observed three to five weeks after nerve injury. Treatment with the clinical analgesic pregabalin reduced evoked activation of Ins/SII, thalamus and ACC whereas treatment with the NK1 receptor antagonist aprepitant reduced activation of the ipsilateral (left) thalamus. Twelve to 13 weeks after nerve injury, treatment with pregabalin reduced evoked activation of all regions of interest (ROI). By contrast, brain activation persisted in most ROI, except the ACC, following aprepitant treatment. Activation of the contralateral Ins/SII and bilateral thalamus was observed six months after nerve injury and pregabalin treatment suppressed activation of these nuclei. The current findings demonstrated persistent changes in CNS neurons following nerve injury as suggested by activation with non-painful mechanical stimulation. Furthermore, it was possible to functionally distinguish between a clinically efficacious analgesic drug, pregabalin, from a drug that has not demonstrated significant clinical analgesic efficacy, aprepitant. In vivo neuroimaging in the current nonhuman model could enhance translatability.

Pharmacologic Modulation of Noxious Stimulus-evoked Brain Activation in Cynomolgus Macaques Observed with Functional Neuroimaging.

Maintaining effective analgesia during invasive procedures performed under general anesthesia is important for minimizing postoperative complications and ensuring satisfactory patient wellbeing and recovery. While patients under deep sedation may demonstrate an apparent lack of response to noxious stimulation, areas of the brain related to pain perception may still be activated. Thus, these patients may still experience pain during invasive procedures. The current study used anesthetized or sedated cynomolgus macaques and functional magnetic resonance imaging (fMRI) to assess the activation of the parts of the brain involved in pain perception during the application of peripheral noxious stimuli. Noxious pressure applied to the foot resulted in the bilateral activation of secondary somatosensory cortex (SII) and insular cortex (Ins), which are both involved in pain perception, in macaques under either propofol or pentobarbital sedation. No activation of SII/Ins was observed in macaques treated with either isoflurane or a combination of medetomidine, midazolam, and butorphanol. No movement or other reflexes were observed in response to noxious pressure during stimulation under anesthesia or sedation. The current findings show that despite the lack of visible behavioral symptoms of pain during anesthesia or sedation, brain activation suggests the presence of pain depending on the anesthetic agent used. These data suggest that fMRI could be used to noninvasively assess pain and to confirm the analgesic efficacy of currently used anesthetics. By assessing analgesic efficacy, researchers may refine their experiments, and design protocols that improve analgesia under anesthesia.

Brain Activation in a Cynomolgus Macaque Model of Chymopapain-Induced Discogenic Low Back Pain: A Preliminary Study.

INTRODUCTION: There is currently a lack of translatable, preclinical models of low back pain (LBP). Chymopapain, a proteolytic enzyme used to treat lumbar intervertebral disc (IVD) herniation, could induce discogenic LBP. The current study developed a behavioral model of discogenic LBP in nonhuman primates. Significant brain activation is observed in clinical LBP. Thus, the current study also sought to define brain activation over time in a macaque with discogenic LBP. METHODS: Responses to pressure applied to the back at L4/L5 were measured in eight adult male Macaca fasciculata using a pressure algometer. The nucleus pulpous of the IVD between L4 and L5 was aspirated and chymopapain (1 mg/mL) was injected under fluoroscopic guidance (n = 2). In two macaques, the nucleus pulpous was only aspirated. Brain activation in response to pressure applied to the lower back was assessed using a 3.0T magnetic resonance imaging scanner in four macaques before and 1, 3, 9, and 14 days after treatment. RESULTS: The mean (±SD) response pressure before treatment was 1.4 ± 0.1 kg. One day after chymopapain treatment, the response pressure decreased to 0.6 ± 0.05 kg (P < 0.01), suggestive of pressure hypersensitivity. Over time, the pressure thresholds following chymopapain treatment gradually returned to normal. Following aspiration only, the response pressure was 1.4 ± 0.05 kg, which was not significantly different from the uninjured controls. There was activation of the secondary somatosensory cortex and insular cortex one and three days after chymopapain treatment; there was no activation following aspiration only. CONCLUSIONS: Enzymatic treatment of the nucleus pulpous leads to acute LBP and pressure-evoked activation in pain-related brain areas. The current model of discogenic LBP parallels clinical LBP and could be used to further elaborate the mechanism of acute LBP.

Distinguishing analgesic drugs from non-analgesic drugs based on brain activation in macaques with oxaliplatin-induced neuropathic pain.

The antineoplastic agent oxaliplatin is a first-line treatment for colorectal cancer. However, neuropathic pain, characterized by hypersensitivity to cold, emerges soon after treatment. In severe instances, dose reduction or curtailing treatment may be necessary. While a number of potential treatments for oxaliplatin-induced neuropathic pain have been proposed based on preclinical findings, few have demonstrated efficacy in randomized, placebo-controlled clinical studies. This failure could be related, in part, to the use of rodents as the primary preclinical species, as there are a number of distinctions in pain-related mechanisms between rodents and humans. Also, an indicator of preclinical pharmacological efficacy less subjective than behavioral endpoints that is translatable to clinical usage is lacking. Three days after oxaliplatin treatment in Macaca fascicularis, a significantly reduced response latency to cold (10 °C) water was observed, indicating cold hypersensitivity. Cold-evoked bilateral activation of the secondary somatosensory (SII) and insular (Ins) cortex was observed with functional magnetic resonance imaging. Duloxetine alleviated cold hypersensitivity and significantly attenuated activation in both SII and Ins. By contrast, neither clinically used analgesics pregabalin nor tramadol affected cold hypersensitivity and cold-evoked activation of SII and Ins. The current findings suggest that suppressing SII and Ins activation leads to antinociception, and, therefore, could be used as a non-behavioral indicator of analgesic efficacy in patients with oxaliplatin-induced neuropathic pain.

Pain-related behavior and brain activation in cynomolgus macaques with naturally occurring endometriosis.

STUDY QUESTION: Can pain be objectively assessed in macaques with naturally occurring endometriosis? SUMMARY ANSWER: Behavioral, pharmacological and in vivo brain imaging findings indicate that pain can be quantified in macaques with endometriosis. WHAT IS KNOWN ALREADY: Endometriosis is characterized by abdominopelvic hypersensitity. The mechanism by which endometriosis evokes pain is largely unknown, as currently available analgesics offer limited pain relief. Thus, there is a need for both greater understanding of the in vivo mechanism of endometriosis-associated pain and better methods of testing novel therapeutics. STUDY DESIGN, SIZE, DURATION: Pain-related behavior and brain activation were assessed in five cynomolgus macaques with endometriosis. Three healthy female macaques served as controls. PARTICIPANTS/MATERIALS, SETTING, METHODS: Abdominopelvic sensitivity to force was assessed with an algometer. Activation of brain areas using block design force stimulation and the effects of a single dose of the analgesic drug morphine and 2-month treatment with the progestin dienogest on brain activation were observed via functional magnetic resonance imaging. MAIN RESULTS AND THE ROLE OF CHANCE: Pain response thresholds in macaques with endometriosis were significantly less than that of healthy macaques (P = 0.0003). In addition, non-noxious force activated the insula and thalamus, which was reduced with morphine and 2-month dienogest treatment. LIMITATIONS, REASONS FOR CAUTION: The specific role of cysts, such as peritoneal cysts, in endometriosis pain was not explored. While non-noxious stimulation activated the insula and thalamus, macaques were sedated during fMRI scans. Current findings need further confirmation in a larger cohort. WIDER IMPLICATIONS OF THE FINDINGS: The current study demonstrated central sensitization and related pain behavior in macaques with naturally occurring endometriosis. Altered functioning of the central nervous system could be the focus of future mechanistic studies and for the development of novel therapeutics. STUDY FUNDING/COMPETING INTEREST(S): Supported by a grant from the Shizuoka Industrial Foundation. All authors are employees of Hamamatsu Pharma Research, Inc.

[Pharmacological profile of a novel nonhuman primate model of knee osteoarthritis].

A number of promising compounds developed in rodent arthritis models lack efficacy in clinical osteoarthritis (OA) pain. To enhance successful translation of preclinical findings, a nonhuman primate (NHP) model of knee OA was developed and characterized using behavioral assessments designed for use in the NHP. A unilateral medial meniscectomy (MMx) was performed and animals underwent an exercise regimen. Decreased ipsilateral knee pressure threshold, pressure "hyperalgesia", and decreased ipsilateral weight bearing, suggestive of pain at rest were observed. The sensitivity of the pain-related behaviors to pharmacological manipulation was evaluated. A single dose of the opioid morphine reduced pain-related behaviors. Likewise, the serotonin-norepinephrine reuptake inhibitor duloxetine reduced pain-related behavior, and efficacy was similar to that of morphine. By contrast, the anticonvulsant pregabalin did not significantly affect pain-related behavior. Repeated dosing with the non-steroidal anti-inflammatory drug (NSAID) diclofenac reduced pain-related behaviors whereas repeated dosing with the NK1 receptor antagonist aprepitant did not. The drug effects observed in the NHP OA model mirror the efficacy observed clinically.

Gaps in Understanding Mechanism and Lack of Treatments: Potential Use of a Nonhuman Primate Model of Oxaliplatin-Induced Neuropathic Pain.

The antineoplastic agent oxaliplatin induces an acute hypersensitivity evoked by cold that has been suggested to be due to sensitized central and peripheral neurons. Rodent-based preclinical studies have suggested numerous treatments for the alleviation of oxaliplatin-induced neuropathic pain, but few have demonstrated robust clinical efficacy. One issue is that current understanding of the pathophysiology of oxaliplatin-induced neuropathic pain is primarily based on rodent models, which might not entirely recapitulate the clinical pathophysiology. In addition, there is currently no objective physiological marker for pain that could be utilized to objectively indicate treatment efficacy. Nonhuman primates are phylogenetically and neuroanatomically similar to humans; thus, disease mechanism in nonhuman primates could reflect that of clinical oxaliplatin-induced neuropathy. Cold-activated pain-related brain areas in oxaliplatin-treated macaques were attenuated with duloxetine, the only drug that has demonstrated clinical efficacy for chemotherapy-induced neuropathic pain. By contrast, drugs that have not demonstrated clinical efficacy in oxaliplatin-induced neuropathic pain did not reduce brain activation. Thus, a nonhuman primate model could greatly enhance understanding of clinical pathophysiology beyond what has been obtained with rodent models and, furthermore, brain activation could serve as an objective marker of pain and therapeutic efficacy.

Pain-Related Behavior and Brain Activation in a Cynomolgus Macaque Model of Postoperative Pain.

BACKGROUND: Inadequate postoperative pain management could lead to persistent pain and this is, in part, due to incomplete understanding of the mechanism of postoperative pain. Currently available rodent models may have limited translatability to clinical postoperative pain. Thus, a preclinical model of postoperative pain was developed in the cynomolgus macaque, a species that is phylogenetically closer to humans than rodents. METHOD: The presence of pressure hypersensitivity was assessed with non-noxious pressure applied proximally and distally (approximately 10 cm) to an abdominal incision in macaques. The effect of the opioid morphine (intramuscular, i.m.), the nonsteroidal anti-inflammatory drug diclofenac (i.m.) and the anticonvulsant pregabalin (i.m.) on pressure hypersensitivity was evaluated one and two days following surgery. Brain activation during non-noxious pressure stimulation was observed with functional magnetic resonance imaging. RESULTS: Hypersensitivity to non-noxious pressure applied proximally and distally (approximately 10 cm) to the incision was observed, lasting for up to seven days and three days, respectively, following surgery. Postoperative pressure hypersensitivity was attenuated with morphine but not with either diclofenac or pregabalin. Bilateral activation of the insular cortex and cingulate cortex was observed during non-noxious pressure stimulation proximal to the incision, which was attenuated with morphine. By contrast, pregabalin reduced only cingulate cortex activation. CONCLUSION: The lack of antinociceptive efficacy of pregabalin on postoperative pain could be due to the incomplete suppression of pressure-evoked brain activation. It is speculated that incomplete postoperative pain relief observed in general could be due to residual or persistent activity of key pain nuclei such as the insular cortex. The current macaque model could be used for further elaborating the mechanism of postoperative pain as well as confirming the efficacy of potential treatments for the management of postoperative pain.

Underestimation of myocardial blood flow by dynamic perfusion CT: Explanations by two-compartment model analysis and limited temporal sampling of dynamic CT.

PURPOSE: Previous studies using dynamic perfusion CT and volume perfusion CT (VPCT) software consistently underestimated the stress myocardial blood flow (MBF) in normal myocardium to be 1.1-1.4 ml/min/g, whilst the O 15-water PET studies demonstrated the normal stress MBF of 3-5 ml/min/g. We hypothesized that the MBF determined by VPCT (MBF-VPCT) is actually presenting the blood-to-myocardium transfer constant, K1. In this study, we determined K1 using Patlak plot (K1-Patlak) and compared the results with MBF-VPCT. MATERIAL AND METHODS: 17 patients (66 ± 9 years, 7 males) with suspected coronary artery disease (CAD) underwent stress dynamic perfusion CT, followed by rest coronary CT angiography (CTA). Arterial input and myocardial output curves were analyzed with Patlak plot to quantify myocardial K1. Significant CAD was defined as >50% stenosis on CTA. A simulation study was also performed to investigate the influence of limited temporal sampling in dynamic CT acquisition on K1 using the undersampling data generated from MRI. RESULTS: There were 3 patients with normal CTA, 7 patients with non-significant CAD, and 7 patients with significant CAD. K1-patlak was 0.98 ± 0.35 (range 0.22-1.67) ml/min/g, whereas MBF-VPCT was 0.83 ± 0.23 (range 0.34-1.40) ml/min/g. There was a linear relationship between them: (MBF-VPCT) = 0.58 x (K1-patlak) + 0.27 (r(2) = 0.65, p < 0.001). The simulation study done on MRI data demonstrated that Patlak plot substantially underestimated true K1 by 41% when true K1 was 2.0 ml/min/g with the temporal sampling of 2RR for arterial input and 4RR for myocardial output functions. CONCLUSIONS: The results of our study are generating hypothesis that MBF-VPCT is likely to be calculating K1-patlak equivalent, not MBF. In addition, these values may be substantially underestimated because of limited temporal sampling rate.

Robot-assisted partial nephrectomy: Superiority over laparoscopic partial nephrectomy.

Nephron-sparing surgery has been proven to positively impact the postoperative quality of life for the treatment of small renal tumors, possibly leading to functional improvements. Laparoscopic partial nephrectomy is still one of the most demanding procedures in urological surgery. Laparoscopic partial nephrectomy sometimes results in extended warm ischemic time and severe complications, such as open conversion, postoperative hemorrhage and urine leakage. Robot-assisted partial nephrectomy exploits the advantages offered by the da Vinci Surgical System to laparoscopic partial nephrectomy, equipped with 3-D vision and a better degree in the freedom of surgical instruments. The introduction of the da Vinci Surgical System made nephron-sparing surgery, specifically robot-assisted partial nephrectomy, safe with promising results, leading to the shortening of warm ischemic time and a reduction in perioperative complications. Even for complex and challenging tumors, robotic assistance is expected to provide the benefit of minimally-invasive surgery with safe and satisfactory renal function. Warm ischemic time is the modifiable factor during robot-assisted partial nephrectomy to affect postoperative kidney function. We analyzed the predictive factors for extended warm ischemic time from our robot-assisted partial nephrectomy series. The surface area of the tumor attached to the kidney parenchyma was shown to significantly affect the extended warm ischemic time during robot-assisted partial nephrectomy. In cases with tumor-attached surface area more than 15 cm(2) , we should consider switching robot-assisted partial nephrectomy to open partial nephrectomy under cold ischemia if it is imperative. In Japan, a nationwide prospective study has been carried out to show the superiority of robot-assisted partial nephrectomy to laparoscopic partial nephrectomy in improving warm ischemic time and complications. By facilitating robotic technology, robot-assisted partial nephrectomy will be more frequently carried out as a safe, effective and minimally-invasive nephron-sparing surgery procedure.

Theoretical considerations in measurement of time discrepancies between input and myocardial time-signal intensity curves in estimates of regional myocardial perfusion with first-pass contrast-enhanced MRI.

The purpose of this study was to develop a method to determine time discrepancies between input and myocardial time-signal intensity (TSI) curves for accurate estimation of myocardial perfusion with first-pass contrast-enhanced MRI. Estimation of myocardial perfusion with contrast-enhanced MRI using kinetic models requires faithful recording of contrast content in the blood and myocardium. Typically, the arterial input function (AIF) is obtained by setting a region of interest in the left ventricular cavity. However, there is a small delay between the AIF and the myocardial curves, and such time discrepancies can lead to errors in flow estimation using Patlak plot analysis. In this study, the time discrepancies between the arterial TSI curve and the myocardial tissue TSI curve were estimated based on the compartment model. In the early phase after the arrival of the contrast agent in the myocardium, the relationship between rate constant K1 and the concentrations of Gd-DTPA contrast agent in the myocardium and arterial blood (LV blood) can be described by the equation K1={dCmyo(tpeak)/dt}/Ca(tpeak), where Cmyo(t) and Ca(t) are the relative concentrations of Gd-DTPA contrast agent in the myocardium and in the LV blood, respectively, and tpeak is the time corresponding to the peak of Ca(t). In the ideal case, the time corresponding to the maximum upslope of Cmyo(t), tmax, is equal to tpeak. In practice, however, there is a small difference in the arrival times of the contrast agent into the LV and into the myocardium. This difference was estimated to correspond to the difference between tpeak and tmax. The magnitudes of such time discrepancies and the effectiveness of the correction for these time discrepancies were measured in 18 subjects who underwent myocardial perfusion MRI under rest and stress conditions. The effects of the time discrepancies could be corrected effectively in the myocardial perfusion estimates.

Successful serial imaging of the mouse cerebral arteries using conventional 3-T magnetic resonance imaging.

Serial imaging studies can be useful in characterizing the pathologic and physiologic remodeling of cerebral arteries in various mouse models. We tested the feasibility of using a readily available, conventional 3-T magnetic resonance imaging (MRI) to serially image cerebrovascular remodeling in mice. We utilized a mouse model of intracranial aneurysm as a mouse model of the dynamic, pathologic remodeling of cerebral arteries. Aneurysms were induced by hypertension and a single elastase injection into the cerebrospinal fluid. For the mouse cerebrovascular imaging, we used a conventional 3-T MRI system and a 40-mm saddle coil. We used non-enhanced magnetic resonance angiography (MRA) to detect intracranial aneurysm formation and T2-weighted imaging to detect aneurysmal subarachnoid hemorrhage. A serial MRI was conducted every 2 to 3 days. MRI detection of aneurysm formation and subarachnoid hemorrhage was compared against the postmortem inspection of the brain that was perfused with dye. The imaging times for the MRA and T2-weighted imaging were 3.7±0.5 minutes and 4.8±0.0 minutes, respectively. All aneurysms and subarachnoid hemorrhages were correctly identified by two masked observers on MRI. This MRI-based serial imaging technique was useful in detecting intracranial aneurysm formation and subarachnoid hemorrhage in mice.

Development of a method for automated and stable myocardial perfusion measurement using coronary X-ray angiography images.

The purpose of this study was to develop a method for automatic and stable determination of the optimal time range for fitting with a Patlak plot model in order to measure myocardial perfusion using coronary X-ray angiography images. A conventional two-compartment model is used to measure perfusion, and the slope of the Patlak plot is calculated to obtain a perfusion image. The model holds for only a few seconds while the contrast agent flows from artery to myocardium. Therefore, a specific time range should be determined for fitting with the model. To determine this time range, automation is needed for routine examinations. The optimal time range was determined to minimize the standard error between data points and their least-squares regression straight line in the Patlak plot. A total of 28 datasets were tested in seven porcine models. The new method successfully detected the time range when contrast agent flowed from artery to myocardium. The mean cross correlation in the linear regression analysis (R(2)) was 0.996 ± 0.004. The mean length of the optimal time range was 3.61 ± 1.29 frames (2.18 ± 1.40 s). This newly developed method can automatically determine the optimal time range for fitting with the model.