Reliability and Reproducibility of Neuromelanin-Sensitive Imaging of the Substantia Nigra: A Comparison of Three Different Sequences.

BACKGROUND: Neuromelanin-sensitive MRI (NM-MRI) of the substantia nigra provides a noninvasive way to acquire an indirect measure of dopamine functioning. Despite the potential of NM-MRI as a candidate biomarker for dopaminergic pathology, studies about its reproducibility are sparse. PURPOSE: To assess the test-retest reproducibility of three commonly used NM-MRI sequences and evaluate three analysis methods. STUDY TYPE: Prospective study. POPULATION: A total of 11 healthy participants age between 20-27 years. FIELD STRENGTH/SEQUENCE: 3.0T; NM-MRI gradient recalled echo (GRE) with magnetization transfer (MT) pulse; NM-MRI turbo spin echo (TSE) with MT pulse; NM-MRI TSE without MT pulse. ASSESSMENT: Participants were scanned twice with a 3-week interval. Manual analysis, threshold analysis, and voxelwise analysis were performed for volume and contrast ratio (CR) measurements. STATISTICAL TESTS: Intraclass correlation coefficients (ICCs) were calculated for test-retest and inter- and intrarater variability. RESULTS: The GRE sequence achieved the highest contrast and lowest variability (4.9-5.7%) and showed substantial to almost perfect test-retest ICC (0.72-0.90) for CR measurements. For volume measurements, the manual analysis showed a higher variability (10.7-17.9%) and scored lower test-retest ICCs (-0.13-0.73) than the other analysis methods. The threshold analysis showed higher test-retest ICC (0.77) than the manual analysis for the volume measurements. DATA CONCLUSION: NM-MRI is a highly reproducible measure, especially when using the GRE sequence and CR measurements. Volume measurements appear to be more sensitive to inter/intrarater variability and variability in placement and orientation of the NM-MRI slab. The threshold analysis appears to be the best alternative for volume analysis. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY STAGE: 1.

Pharmacodynamics and Pharmacokinetics of Lidocaine in a Rodent Model of Diabetic Neuropathy.

BACKGROUND: Clinical and experimental data show that peripheral nerve blocks last longer in the presence of diabetic neuropathy. This may occur because diabetic nerve fibers are more sensitive to local anesthetics or because the local anesthetic concentration decreases more slowly in the diabetic nerve. The aim of this study was to investigate both hypotheses in a rodent model of neuropathy secondary to type 2 diabetes. METHODS: We performed a series of sciatic nerve block experiments in 25 Zucker Diabetic Fatty rats aged 20 weeks with a neuropathy component confirmed by neurophysiology and control rats. We determined in vivo the minimum local anesthetic dose of lidocaine for sciatic nerve block. To investigate the pharmacokinetic hypothesis, we determined concentrations of radiolabeled (C) lidocaine up to 90 min after administration. Last, dorsal root ganglia were excised for patch clamp measurements of sodium channel activity. RESULTS: First, in vivo minimum local anesthetic dose of lidocaine for sciatic nerve motor block was significantly lower in diabetic (0.9%) as compared to control rats (1.4%). Second, at 60 min after nerve block, intraneural lidocaine was higher in the diabetic animals. Third, single cell measurements showed a lower inhibitory concentration of lidocaine for blocking sodium currents in neuropathic as compared to control neurons. CONCLUSIONS: We demonstrate increased sensitivity of the diabetic neuropathic nerve toward local anesthetics, and prolonged residence time of local anesthetics in the diabetic neuropathic nerve. In this rodent model of neuropathy, both pharmacodynamic and pharmacokinetic mechanisms contribute to prolonged nerve block duration.

Efficacy of liver graft washout as a function of the perfusate, pressure, and temperature.

Donor graft washout can be impaired by colloids in organ preservation solutions that increase the viscosity and agglutinative propensity of red blood cells (RBCs) and potentially decrease organ function. The colloid-induced agglutinative effects on RBCs and RBC retention after liver washout with Ringer's lactate (RL), histidine tryptophan ketoglutarate solution, University of Wisconsin solution, and Polysol were determined as a function of the washout pressure (15 or 100 mm Hg) and temperature (4 or 37°C) in a rat liver washout model with (99m) Tc-pertechnetate-labeled RBCs. Colloids (polyethylene glycol in Polysol and hydroxyethyl starch in University of Wisconsin) induced RBC agglutination, regardless of the solution's composition. RL was associated with the lowest degree of (99m) Tc-pertechnetate-labeled RBC retention after simultaneous arterial and portal washout at 37°C and 100 mm Hg. RL washout was also associated with the shortest washout time. A single portal washout with any of the solutions did not result in differences in the degree of RBC retention, regardless of the temperature or pressure. In conclusion, no differences were found in portal washout efficacy between colloidal solutions, histidine tryptophan ketoglutarate, and RL. Simultaneous arterial and portal washout with RL at 37°C and 100 mm Hg resulted in the least RBC retention and the shortest washout time.

Cannabinoid-1 receptor antagonist rimonabant (SR141716) increases striatal dopamine D2 receptor availability.

The cannabinoid 1 receptor antagonist rimonabant (SR141716) alters rewarding properties and intake of food and drugs. Additionally, striatal dopamine D2 receptor (DRD2) availability has been implicated in reward function. This study shows that chronic treatment of rats with rimonabant (1.0 and 3.0 mg/kg/day) dose-dependently increased DRD2 availability in the dorsal striatum (14 and 23%) compared with vehicle. High-dose rimonabant also increased DRD2 availability in the ventral striatum (12%) and reduced weight gain. Thus, up-regulation of striatal DRD2 by chronic rimonabant administration may be an underlying mechanism of action and confirms the interactions of the endocannabinoid and dopaminergic systems.

Quantitative assessment of liver function after ischemia-reperfusion injury and partial hepatectomy in rats.

BACKGROUND: Liver function after hepatic ischemia-reperfusion (I/R) injury and partial liver resection (PHx) is influenced by the extent of PHx, hepatocellular damage, and liver regeneration. This study investigates the effect of minor PHx with increasing degrees of I/R-induced damage on postoperative liver function parameters and compares the indocyanine green (ICG) clearance test with (99m)Tc-mebrofenin hepatobiliary scintigraphy (HBS) for quantitative measurement of hepatic function in a standardized rat model. METHODS: Rats were subjected to 70% partial liver I/R combined with resection of the nonischemic lobes. Various degrees of hepatic damage were induced by 0, 15, 30, 45, and 60 min ischemia. Prothrombin time and bilirubin were used as indirect parameters of liver function. (99m)Tc-mebrofenin HBS and ICG clearance were used as dynamic quantitative liver function tests. RESULTS: After 24 h reperfusion hepatocellular damage increased with prolonged ischemia times. Hepatocellular damage and liver regeneration were closely interrelated. Moderate I/R-induced damage enhanced regeneration, while extensive damage debilitates the regenerative capacity. PHx alone resulted in no significant decrease in liver uptake function measured by HBS or ICG. Increasing severity of hepatic I/R injury had a differential effect on ICG clearance and (99m)Tc-mebrofenin uptake and excretion. CONCLUSIONS: The specific impact of 30% PHx combined with progressive ischemia times is different for each liver function test. Albeit (99m)Tc-mebrofenin HBS and the ICG clearance test provide complementary quantitative information to biochemical parameters, they only quantify one or two components of liver function. ICG and (99m)Tc-mebrofenin uptake profiles differed significantly, suggesting that the specific hepatic transporters may be distinct.

Serial noninvasive assessment of apoptosis during right ventricular disease progression in rats.

UNLABELLED: Right ventricular (RV) function is the major determinant of survival in patients with pulmonary hypertension. Yet, the pathophysiologic basis of RV disease is unresolved. We aimed to study the role of apoptosis in RV disease by monitoring it serially during disease progression using in vivo (99m)Tc-annexin-V ((99m)Tc-annexin) scintigraphy and study whether the reduction in apoptosis resulting from chronic treatment with valsartan can be detected by (99m)Tc-annexin scintigraphy. METHODS: RV disease after pulmonary hypertension was induced by monocrotaline injection in rats. The following 3 groups were studied: rats treated with monocrotaline (monocrotaline rats), rats treated with monocrotaline plus valsartan (valsartan rats), and age-matched controls (control rats). Serial echocardiography and in vivo (99m)Tc-annexin scintigraphy were performed. Apoptosis was confirmed by (99m)Tc-annexin autoradiography and terminal deoxynucleotidyl-transferase-mediated dUTP nick-end labeling. Fibrosis was assessed by picrosirius red staining. RESULTS: In monocrotaline rats, in vivo (99m)Tc-annexin uptake peaked early and declined thereafter but remained elevated, compared with baseline. These stage-dependent changes of in vivo (99m)Tc-annexin uptake were paralleled by changes in autoradiography and terminal deoxynucleotidyl-transferase-mediated dUTP nick-end labeling. Valsartan rats had longer RV failure-free survival than did monocrotaline rats and had reduced apoptosis. These changes were accompanied by commensurate delays in RV hypertrophy and RV dilation. Valsartan rats also had less fibrosis than monocrotaline rats at all disease stages. CONCLUSION: RV disease progression is associated with an early increase in RV apoptosis, as monitored using serial in vivo (99m)Tc-annexin scintigraphy. Delay in RV disease progression by valsartan is accompanied by reduction in RV apoptosis. Apoptosis plays a role in RV disease progression and may be assessed by serial in vivo (99m)Tc-annexin scintigraphy.

In vivo [(123)I]CNS-1261 binding to D-serine-activated and MK801-blocked NMDA receptors: A storage phosphor imaging study in rats.

Disturbances of activity of the glutamatergic neurotransmitter system in the brain are present in many neuropsychiatric disorders. The N-methyl-D-aspartate (NMDA) receptor is the most abundant receptor of the glutamatergic system. In the neurodegenerative events of Alzheimer's disease, excessive activation of NMDA receptors may contribute to neuronal death. Inhibition of NMDA receptor activation may have neuroprotective effects and (semi)quantitative imaging of the activated system may help in the selection of patients for such inhibition therapies. In this study we evaluated [(123)I]CNS-1261 binding in the rat brain. This radiotracer binds in vivo to the MK801 binding site of activated NMDA receptors. To determine the optimal time point for ex vivo assessments after bolus injection [(123)I]CNS-1261 binding in rats, we performed a time course biodistribution study using dissection techniques. [(123)I]CNS-1261 binding was also studied in the rat brain using autoradiography by means of storage phosphor imaging, with prior facilitation of NMDA receptor activation by injection of the potent coagonist D-serine and after blocking of the NMDA receptor binding site by MK801 injection in D-serine pretreated rats. Measurements of [(123)I]CNS-1261 uptake matched the distribution of similar tracers for the MK801 binding site of the NMDA receptor and revealed an optimal time point of 2 h post injection for the assessment of tracer distribution in the rat brain. The blocking experiments indicated specific binding of [(123)I]CNS-1261 to NMDA receptors but also a considerable amount of nonspecific binding. Facilitation of NMDA receptor activation by D-serine did not result in an enhancement of binding of the radiotracer in the NMDA receptor-rich rat hippocampus compared to the untreated group, as measured by autoradiography. In conclusion, our study has shown that [(123)I]CNS-1261 binding is influenced by NMDA receptor availability. However, high nonspecific binding limits quantification and small changes in receptor availability are unlikely to be detected.

Varenicline increases striatal dopamine D(2/3) receptor binding in rats.

Increasing dopamine D(2/3) receptor availability is postulated to be a treatment for drug addiction. Varenicline, an alpha4beta2-nicotinic partial agonist, is effective for nicotine dependence. We hypothesize that varenicline increases dopamine D(2/3) receptor availability. Twenty male drug-naïve rats were randomized to varenicline (2 mg/kg) or placebo for 14 days, and then injected with the dopamine D(2/3) radiotracer 123I-IBZM. We found significantly higher striatum-to-cerebellum binding ratios in both dorsal and ventral striatum for the varenicline group compared with placebo. Varenicline increases dopamine D(2/3) receptor availability in drug-naïve rats. Therefore, varenicline may be an effective treatment for addictions other than smoking.

99mTc-GSA scintigraphy with SPECT for assessment of hepatic function and functional volume during liver regeneration in a rat model of partial hepatectomy.

UNLABELLED: Small-animal models are crucial to gain insights in the complex recovery mechanisms of liver function during liver regeneration. (99m)Tc-Mebrofenin hepatobiliary scintigraphy (HBS) has been introduced for noninvasive assessment of liver function in the clinical setting as well as in experimental research. However, HBS is restricted to planar modalities in small animals because hepatic kinetics are generally too fast for SPECT acquisition. (99m)Tc-DTPA-galactosyl serum albumin (where DTPA is diethylenetriaminepentaacetic acid) ((99m)Tc-GSA) scintigraphy is an alternative, receptor-mediated, noninvasive liver function test. After hepatic uptake, (99m)Tc-GSA remains trapped in the liver, which readily enables additional SPECT for the assessment of both liver function and liver functional volume within one test. In this study we evaluated the use of (99m)Tc-GSA scintigraphy combined with SPECT for the assessment of liver function and liver functional volume in normal and regenerating rat livers. METHODS: The reproducibility of (99m)Tc-GSA scintigraphy and SPECT was investigated by repeated measurements within the same rat. For the assessment in a regenerating liver, (99m)Tc-GSA scintigraphy with SPECT was performed on 1, 3, 5, and 7 d (n = 6 rats per time point) after 70% partial hepatectomy (PH). RESULTS: The correlation between repeated (99m)Tc-GSA measurements was strong (r = 0.75, P = 0.019). In normal rat livers, there was a strong, significant correlation between liver functional volume and conventional liver volume (r = 0.93; < 0.0001). The correlation between (99m)Tc-GSA uptake and liver volume was moderate (r = 0.62, P = 0.043). During the regeneration process, (99m)Tc-GSA uptake was significantly lower compared with both liver volume (P < 0.001) and liver functional volume (P < 0.001), when expressed as a percentage of baseline levels. There was a strong correlation between liver functional volume and conventional liver volume in the regenerating liver (r = 0.92, P < 0.0001). CONCLUSION: (99m)Tc-GSA scintigraphy combined with SPECT is a feasible, noninvasive method to assess hepatic functional volume in normal rat liver as well as in the regenerating rat liver. However, the hepatic (99m)Tc-GSA uptake as a liver function test seems to underestimate hepatic regeneration in comparison to liver volume.

In vitro and ex vivo storage phosphor imaging of short-living radioisotopes.

Storage phosphor imaging may be of value for biodistribution studies of short-living radiotracers in small animals. Efficiency, sensitivity and resolution of imaging plates for short-living radioisotopes vary considerably but linear response to many radioisotopes was shown previously. However, these properties have not been compared directly for larger series of short-living radioisotopes, and only few studies have directly compared data obtained from phosphor images of tissue slices with results from dissection biodistribution studies. Therefore, we evaluated the properties of imaging plates for 11 short-living radioisotopes (18F, 32P, 67Ga, 89Sr, (99m)Tc, 90Y, 111In, 123I, 125I, 131I and 201Tl). We also evaluated the biodistribution of [123I]FP-CIT in rat brain using both the phosphor technique and conventional dissection methods. The imaging system showed a linear response for all tested radioisotopes over a wide range of radioactive concentrations and the efficiency, sensitivity and resolution varied greatly for the tested radioisotopes. Shielding experiments revealed the contribution of the various emission products of radioisotopes to these properties. However, quantitative biodistribution studies with radiotracers that are labeled with all tested radioisotopes, even 123I, are feasible. The results from the ex vivo biodistribution study, using [123I]FP-CIT as a radiotracer were similar for the phosphor imaging technique as compared to the dissection technique. Advantages of phosphor imaging in radiotracer distribution studies in rat brain as compared to dissection experiments may be more precise measurements, possibility to reanalyze imaging data and 3D-reconstruction. In conclusion, phosphor imaging is an attractive alternative for biodistribution studies of short-living radiotracers in small animals.

Clinical evaluation of [123I]FP-CIT SPECT scans on the novel brain-dedicated InSPira HD SPECT system: a head-to-head comparison.

The InSPira HD system, a novel brain-dedicated SPECT scanner, allows for imaging with a high spatial resolution. Here, we tested whether this scanner can be used to image the dopamine transporter adequately. Therefore, striatal phantom and patient data acquired on the InSPira were compared head-to-head with the well-validated brain-dedicated NeuroFocus system. A striatal phantom filled with [123I] and 14 subjects (after [123I]FP-CIT injection) were scanned on both systems. [123I]FP-CIT SPECT scans were visually assessed. Striatal binding ratios were calculated automatically using the software package BRASS. Striatal phantom and patient data showed strong correlations with respect to striatal ratios (R = 0.99 and R = 0.92; p < 0.05 and p < 0.01, respectively). Slightly higher ratios were found for the NeuroFocus patient data, probably due to differences in system performance. Visual assessment of [123I]FP-CIT scans showed agreement between systems in 13 of the 14 cases. We conclude that [123I]FP-CIT SPECT imaging can be performed adequately on the new InSPira system.

Quantification of striatal dopamine transporters with 123I-FP-CIT SPECT is influenced by the selective serotonin reuptake inhibitor paroxetine: a double-blind, placebo-controlled, crossover study in healthy control subjects.

UNLABELLED: Dopamine transporter (DAT) imaging with (123)I-FP-CIT ((123)I-N-omega-fluoropropyl-2beta-carbomethoxy-3beta-(4-iodophenyl)nortropane) SPECT is frequently used to detect loss of nigrostriatal cells in parkinsonism. Recent (123)I-beta-CIT ((123)I-2beta-carbomethoxy-3beta-(4-iodophenyl)tropane) studies have shown a significant increase in striatal-to-nonspecific beta-CIT binding ratios after treatment with selective serotonin reuptake inhibitors (SSRIs). Due to similarities between (123)I-beta-CIT and (123)I-FP-CIT (both are derived from cocaine and show relatively high affinity for the DAT and the serotonin transporter [SERT]), we hypothesized that quantification of striatal (123)I-FP-CIT binding may be influenced by SSRIs. Moreover, we hypothesized that (123)I-FP-CIT in humans binds not only to DATs but also to central and peripheral SERTs. METHODS: To study the influence of the SSRI paroxetine on (123)I-FP-CIT binding to DATs in the striatum, we conducted a double-blind, placebo-controlled, crossover study with paroxetine in 8 healthy young male control subjects. In addition, we studied whether paroxetine was able to block (123)I-FP-CIT binding in SERT-rich brain areas and in lung tissue, as lung tissue contains a considerable amount of SERTs. Participants were pretreated for 2 d with paroxetine (20 mg/d) or placebo at 2 sessions (crossover design), and brain SPECT was performed 1 and 3 h after (123)I-FP-CIT injection, whereas lung uptake was measured 2 h after injection. RESULTS: Compared with placebo pretreatment, we found after paroxetine pretreatment a statistically significant increase (approximately 10%) in specific striatal-to-nonspecific (123)I-FP-CIT binding ratios at 3 h after injection, a time point at which striatal (123)I-FP-CIT binding ratios are stable. In addition, after paroxetine treatment, statistically significantly lower binding ratios were found in SERT-rich brain areas (e.g., at 1 h after injection, midbrain-to-cerebellar ratios were approximately 90% lower) as well as significantly lower uptake in lung tissue was found (approximately 40% lower after paroxetine). CONCLUSION: In this study we show that the quantification of striatal (123)I-FP-CIT binding to DAT is significantly increased by the SSRI paroxetine in humans. To our knowledge, this is the first study which shows that (123)I-FP-CIT binds in vivo in humans not only to DATs but also to central SERTs and SERTs in lung tissue.

Hepatic parenchymal transection increases liver volume but not function after portal vein embolization in rabbits.

BACKGROUND: Associating liver partition with portal vein ligation for staged hepatectomy induces more extensive liver hypertrophy than ligation alone; however, the mechanisms underlying the accelerated liver regrowth and the functional quality of the hypertrophic liver are presently elusive. This study, therefore, investigated the effect of parenchymal transection on liver volume and function after portal vein embolization in a standardized rabbit model. METHODS: Twelve rabbits were subjected to portal vein embolization of the cranial liver lobes and randomized between parenchymal transection of the left lateral liver lobe versus no transection (portal vein embolization only). Liver volume of the nonembolized liver lobe was assessed using computed tomography-volumetry, and liver uptake function was determined by 99mTc-mebrofenin hepatobiliary scintigraphy before and 3 and 7 days after portal vein embolization. RESULTS: The increase in nonembolized liver volume 3 days after portal vein embolization was 2.7-fold greater in the transected group compared with the portal vein embolization only group (56 ± 16% vs 21 ± 12%, respectively, P < .01) and 1.7-fold greater 7 days after portal vein embolization (113 ± 34% vs 68 ± 24%, P < .01). Liver uptake function did not differ between groups before portal vein embolization (8.4 ± 3.7%/min in the transection group vs 8.9 ± 1.6%/min) on day 3 (33.2 ± 4.7% after transection vs 30.3 ± 4.6%/min, respectively) and day 7 after portal vein embolization (42.6 ± 8.4% vs 39.1 ± 5.3%/min, respectively). CONCLUSION: Parenchymal transection after portal vein embolization increases liver growth in terms of volume but not function. These results indicate that the rapid volume increase observed after associating liver partition with portal vein ligation for staged hepatectomy does not coincide with the clinically more relevant functional increase. Quantitative liver function tests might be essential in associating liver partition with portal vein ligation for staged hepatectomy to better assess the hypertrophy response and improve clinical decision-making.

Comparable liver function and volume increase after portal vein embolization in rabbits and humans.

BACKGROUND: Portal vein embolization is the gold standard approach to preoperatively enhance the future liver remnant before liver resection. Portal vein embolization is studied in several experimental animal models; however, clinical translation of results is often difficult. We aimed to examine the translational value of the portal vein embolization response in a standardized rabbit model by comparing the volume and function increase with the response seen in patients. METHODS: Six rabbits were subjected to embolization of the cranial liver lobes, and the hypertrophy response of the caudal liver lobe was studied using computed tomography volumetry and Technetium-99m-labeled-mebrofenin hepatobiliary scintigraphy. Results were compared to those from patients who underwent portal vein embolization between 2005 and 2014. All patients were subjected to computed tomography volumetry and hepatobiliary scintigraphy before and after portal vein embolization. RESULTS: The increase in liver function of the caudal liver lobe in rabbits was faster compared to the increase in liver volume. There was no decrease in total liver function after portal vein embolization. Results in patients were similar to rabbits, with a faster increase in liver function compared to patients and no decrease in total liver function after portal vein embolization. CONCLUSION: The portal vein embolization response in terms of liver volume and function is similar between rabbits and humans. Accordingly, the rabbit model is a suitable tool to study portal vein embolization-related parameters that cannot be investigated in patients.

Novel molecular imaging ligands targeting matrix metalloproteinases 2 and 9 for imaging of unstable atherosclerotic plaques.

Molecular imaging of matrix metalloproteinases (MMPs) may allow detection of atherosclerotic lesions vulnerable to rupture. In this study, we develop a novel radiolabelled compound that can target gelatinase MMP subtypes (MMP2/9) with high selectivity and inhibitory potency. Inhibitory potencies of several halogenated analogues of MMP subtype-selective inhibitors (N-benzenesulfonyliminodiacetyl monohydroxamates and N-halophenoxy-benzenesulfonyl iminodiacetyl monohydroxamates) were in the nanomolar range for MMP2/9. The analogue with highest inhibitory potency and selectivity was radiolabelled with [123I], resulting in moderate radiochemical yield, and high radiochemical purity. Biodistribution studies in mice, revealed stabilization in blood 1 hour after intravenous bolus injection. Intravenous infusion of the radioligand and subsequent autoradiography of excised aortas showed tracer uptake in atheroprone mice. Distribution of the radioligand showed co-localization with MMP2/9 immunohistochemical staining. In conclusion, we have developed a novel selective radiolabeled MMP2/9 inhibitor, suitable for single photon emission computed tomography (SPECT) imaging that effectively targets atherosclerotic lesions in mice.

Repeated dexamphetamine treatment alters the dopaminergic system and increases the phMRI response to methylphenidate.

Dexamphetamine (AMPH) is a psychostimulant drug that is used both recreationally and as medication for attention deficit hyperactivity disorder. Preclinical studies have demonstrated that repeated exposure to AMPH can induce damage to nerve terminals of dopamine (DA) neurons. We here assessed the underlying neurobiological changes in the DA system following repeated AMPH exposure and pre-treated rats with AMPH or saline (4 times 5 mg/kg s.c., 2 hours apart), followed by a 1-week washout period. We then used pharmacological MRI (phMRI) with a methylphenidate (MPH) challenge, as a sensitive and non-invasive in-vivo measure of DAergic function. We subsequently validated the DA-ergic changes post-mortem, using a.o. high-performance liquid chromatography (HPLC) and autoradiography. In the AMPH pre-treated group, we observed a significantly larger BOLD response to the MPH challenge, particularly in DA-ergic brain areas and their downstream projections. Subsequent autoradiography studies showed that AMPH pre-treatment significantly reduced DA transporter (DAT) density in the caudate-putamen (CPu) and nucleus accumbens, whereas HPLC analysis revealed increases in the DA metabolite homovanillic acid in the CPu. Our results suggest that AMPH pre-treatment alters DAergic responsivity, a change that can be detected with phMRI in rats. These phMRI changes likely reflect increased DA release together with reduced DAT binding. The ability to assess subtle synaptic changes using phMRI is promising for both preclinical studies of drug discovery, and for clinical studies where phMRI can be a useful tool to non-invasively investigate DA abnormalities, e.g. in neuropsychiatric disorders.

Repeated administration of D-amphetamine induces loss of [123I]FP-CIT binding to striatal dopamine transporters in rat brain: a validation study.

UNLABELLED: In recent years, several PET and SPECT studies have shown loss of striatal dopamine transporter (DAT) binding in amphetamine (AMPH) users. However, the use of DAT SPECT tracers to detect AMPH-induced changes in DAT binding has not been validated. We therefore examined if repeated administration of D-AMPH or methamphetamine (METH) may induce loss of binding to striatal DATs in rats by using an experimental biodistribution study design and a SPECT tracer for the DAT ([123I]FP-CIT). METHODS: Groups of male rats (n = 10 per group) were treated with D-AMPH (10 mg/kg body weight), METH (10 mg/kg body weight), or saline, twice a day for 5 consecutive days. Five days later, [123I]FP-CIT was injected intravenously, and 2 h later, the rats were sacrificed and radioactivity was assayed. RESULTS: In d-AMPH but not METH-treated rats, striatal [123I]FP-CIT uptake was significantly lower (approximately 17%) than in the control group. CONCLUSION: These data show that [123I]FP-CIT can be used to detect AMPH-induced changes in DAT binding and may validate the use of DAT radiotracers to study AMPH-induced changes in striatal DAT binding in vivo.

Dedicated pinhole SPECT of intestinal neutrophil recruitment in a mouse model of dextran sulfate sodium-induced colitis.

UNLABELLED: Evaluating the efficacy of therapy in experimental inflammatory bowel disease (IBD) requires information about inflammatory activity in bowel segments or leukocyte recruitment and about kinetics in the follow-up of treatment. This study evaluated a noninvasive scintigraphic technique able to assess neutrophil trafficking in a mouse model of dextran sulfate sodium (DSS)-induced colitis. METHODS: Groups of 4 BALB/c mice were assessed at baseline and after 1, 3, 5, and 8 d of treatment with DSS. Donor neutrophils were harvested by rinsing of the peritoneal cavity with phosphate-buffered saline 5 h after intraperitoneal injection of proteose peptone contained in phosphate-buffered saline and labeled with freshly prepared (99m)Tc-hexamethylpropylene amine oxime (HMPAO). Pinhole SPECT of the abdomen was performed 1 h after reinjection of 50 MBq of labeled neutrophils. In addition, the severity of inflammation was determined by histologic examination. The possibilities of the technique were illustrated by scintigraphic assessment of neutrophil trafficking with and without blocking of neutrophil migration by a CD97 monoclonal antibody in mice with DSS-induced colitis. RESULTS: Colonic uptake of (99m)Tc-HMPAO neutrophils was determined with dedicated animal pinhole SPECT in mice with DSS-induced colitis and correlated well with histologic findings (R = 0.81) and wet colon weight (R = 0.87) and moderately with clinical weight loss (R = 0.62). The neutrophil uptake ratio was reduced significantly (P < 0.01) by blocking of neutrophil migration capacity with the CD97 antibody. CONCLUSION: Animal pinhole SPECT can be used to study inflammatory activity and neutrophil recruitment in vivo in experimental colitis.

Imaging of liver function with dedicated animal dynamic pinhole scintigraphy in rats.

BACKGROUND: Non-invasive evaluation of liver function in small animal models remains a challenge. Hepatobiliary scintigraphy (HBS) enables the assessment of total and regional liver function for both uptake and excretion in larger species. AIM: To validate quantitative liver function assessment with dedicated pinhole HBS in rats. To illustrate an application of this technique, liver function was assessed in two surgical models of liver regeneration. METHODS: HBS was performed in 12 rats with 99mTc-mebrofenin on a dedicated animal pinhole gamma camera. The hepatic uptake rate was calculated twice by different observers to establish a normal range and the reproducibility of processing. The degree of hepatocellular injury and synthesis function were assessed by serum liver tests. Liver function was compared with liver weight. Subsequently, three groups of three rats were scanned on three separate days to assess the reproducibility of HBS. Finally, to illustrate an application of this technique, liver function was assessed in two surgical models of liver regeneration. RESULTS: HBS in rats was feasible without mortality. The mean liver uptake rate was 77.29+/-1.29% . min(-1). Calculation of the liver uptake (% . min(-1)) was highly reproducible (r=0.95, P<0.001). There was a good correlation between liver weight and function measured by HBS at baseline and after partial resection (r=0.94, P<0.001). CONCLUSION: HBS offers a unique combination of functional liver uptake and excretion assessment with the ability to determine the liver function reserve before and after an intervention in rats.

Subchronic administration of short-acting naltrexone has no effect on striatal dopamine transporter availability, food intake or body weight gain in rats.

The opioid receptor antagonist naltrexone is successfully used in the treatment of opioid and alcohol dependence. However, questions have been raised about possible anhedonic side effects, because the opioid system is directly involved in hedonic responses to natural rewarding activities, possibly due to its indirect effects on the striatal dopamine transporter (DAT). In order to test this hypothesis, 30 rats were randomized to either a 10-day treatment with 3 mg/kg short-acting naltrexone or vehicle. No significant differences between the groups were found in striatal DAT availability, cumulative food intake (for 48 or 72 h), body weight gain and abdominal fatpad weight. Thus, the results of this study suggest that (sub)chronic treatment with short-acting naltrexone does not induce possible anhedonic effects. However, it cannot be ruled out the anhedonic effect of naltrexone is only short-lived and thus not detected in the current study. Therefore, future studies are needed to study possible acute anhedonic effects at several time points shortly after short-acting naltrexone administration and to directly compare the possible anhedonic effects of long-acting with those of short-acting opioid antagonists.