fMRI of supraspinal areas after morphine and one week pancreatic inflammation in rats.

Abdominal pain is a major reason patients seek medical attention yet relatively little is known about neuronal pathways relaying visceral pain. We have previously characterized pathways transmitting information to the brain about visceral pain. Visceral pain arises from second order neurons in lamina X surrounding the spinal cord central canal. Some of the brain regions of interest receiving axonal terminations directly from lamina X were examined in the present study using enhanced functional magnetic resonance imaging (fMRI) before and one week after induction of a rat pancreatitis model with persistent inflammation and behavioral signs of increased nociception. Analysis of imaging data demonstrates an increase in MRI signal for all the regions of interest selected including the rostral ventromedial medulla, dorsal raphe, periaqueductal grey, medial thalamus, and central amygdala as predicted by the anatomical data, as well as increases in the lateral thalamus, cingulate/retrosplenial and parietal cortex. Occipital cortex was not activated above threshold in any condition and served as a negative control. Morphine attenuated the MRI signal, and the morphine effect was antagonized by naloxone in lower brainstem sites. These data confirm activation of these specific regions of interest known as integration sites for nociceptive information important in behavioral, affective, emotional and autonomic responses to ongoing noxious visceral activation.

A new technique allowing prolonged temporary cerebral artery occlusion.

OBJECT: Clipping of complex cerebral aneurysms often requires temporary vessel occlusion. The risk of stroke, however, increases exponentially with occlusion time. The authors hypothesized that prolonged temporary occlusion might be tolerated if the occluded vessels were perfused with cold physiological saline solution (CPSS). A low-flow perfusion rate would permit surgical manipulation of an aneurysm distal to the occlusion. METHODS: To test this hypothesis, the authors temporarily occluded the middle cerebral artery (MCA) with an endovascular catheter in 6 rats. Three animals, the treatment group, were perfused with 5-ml CPSS/hour through the occluding endovascular catheter into the MCA, and the other 3 served as an ischemic control group. In both groups, the catheter was removed after 90 minutes of occlusion. The brain temperature was monitored with a stereotactically placed probe in the caudate-putamen in 2 separate experimental groups (11 animals). RESULTS: Magnetic resonance imaging perfusion scanning during vessel occlusion confirmed similar reduction of cerebral blood flow during MCA occlusion in both the simple-occlusion and perfusion-occlusion groups. Magnetic resonance imaging diffusion scans performed 24 hours after temporary occlusion revealed infarcts in the ischemic control group of 138.3 +/- 28.0 mm(3) versus 9.9 +/- 9.9 mm(3) in the cold saline group (p < 0.005). A focal cooling effect during perfusion with CPSS was demonstrated (p < 0.05). CONCLUSIONS: Prolonged temporary cerebral vessel occlusion can be tolerated using superselective CPSS perfusion through an occluding endovascular catheter into the ischemic territory. This technique could possibly be applied in neurosurgery practice to the management of complex intracranial aneurysms.

Effects of 2-deoxy-d-glucose on focal cerebral ischemia in hyperglycemic rats.

The authors examined the effects of pretreatment with 2-deoxy-d-glucose (2DG) on the middle cerebral artery occlusion-reperfusion (MCAO/R) model in hyperglycemic rats. Proton magnetic resonance imaging and spectroscopy were used to measure the lesion size, the level of cerebral perfusion deficit, and ratio of lactate to N-acetyl aspartate (NAA) in brain regions. By performing sequential diffusion weighted imaging, gradient echo bolus tracking, steady-state spin echo imaging, and water-suppressed proton magnetic resonance spectroscopy techniques, the time course of the early changes of the lactate/NAA peak ratio and perfusion deficit was examined in hyperglycemic rats undergoing 90-minute MCAO followed by 24-h reperfusion. Compared with the saline-treated hyperglycemic rats, 2DG treatment at 10 minutes before MCAO significantly reduced diffusion weighted imaging hyperintensity by approximately 60% and the lactate/NAA peak ratio by approximately 70% at 4 h after MCAO/R. Both spin echo-measured cerebral blood volume and dynamic gradient echo-relative cerebral blood flow showed that the restoration of blood supply recovered and remained at approximately 80% of baseline during reperfusion in 2DG-treated hyperglycemic rats. These data suggest that inhibition of glucose metabolism by 2DG has a beneficial effect in reducing brain injury and minimizing the production of brain lactate during MCAO/R in hyperglycemic rats.

Reduction of brain injury by antithrombotic agent acutobin after middle cerebral artery ischemia/reperfusion in the hyperglycemic rat.

In vivo magnetic resonance imaging (MRI) was used to observe the effect of acutobin, a purified thrombin-like enzyme (TLE), isolated from the snake venom of Deinagkistrodon acutus, on MRI-detected brain lesion volume and tissue perfusion deficit in a hyperglycemic rat right middle cerebral artery occlusion/reperfusion (MCAO/R) model. Acutobin (0.75 U/ml) was intravenously injected with a dosage of 2.5 U/kg body weight 30 min after MCAO (MCAO duration=60 min) and again 24 h after reperfusion. Multislice diffusion weighted imaging (DWI) and single-slice dynamic bolus tracking gradient echo (GE) imaging were sequentially acquired before and after MCAO/R. DWI-detected lesion volume was significantly (p<0.05) reduced by 24-31% from 350+/-45, 369+/-45 and 374+/-36 mm(3) in the saline-treated group to 239+/-17, 282+/-26 and 259+/-32 mm(3) at 3, 4 and 24 h after reperfusion in the acutobin-treated group, respectively. Residual cerebral blood flow (CBF) in the right hemisphere recovered and remained at approximately 80% of normal perfusion over the measurement period in the acutobin-treated group, compared to approximately 40% in the saline-treated group. Mortality at 1 week after MCAO/R in the acutobin-treated group was significantly lower (25% mortality) than the saline control group (85% mortality). Our results indicate that acutobin improves brain tissue perfusion and reduces infarct volume and mortality in the hyperglycemic rat MCAO/R model.

Aspartoacylase deficiency does not affect N-acetylaspartylglutamate level or glutamate carboxypeptidase II activity in the knockout mouse brain.

Aspartoacylase (ASPA)-deficient patients [Canavan disease (CD)] reportedly have increased urinary excretion of N-acetylaspartylglutamate (NAAG), a neuropeptide abundant in the brain. Whether elevated excretion of urinary NAAG is due to ASPA deficiency, resulting in an abnormal level of brain NAAG, is examined using ASPA-deficient mouse brain. The level of NAAG in the knockout mouse brain was similar to that in the wild type. The NAAG hydrolyzing enzyme, glutamate carboxypeptidase II (GCP II), activity was normal in the knockout mouse brain. These data suggest that ASPA deficiency does not affect the NAAG or GCP II level in the knockout mouse brain, if documented also in patients with CD.

Expression of glutamate transporter, GABRA6, serine proteinase inhibitor 2 and low levels of glutamate and GABA in the brain of knock-out mouse for Canavan disease.

Canavan disease (CD) is an autosomal recessive leukodystrophy characterized by spongy degeneration of the brain. The clinical features of CD are hypotonia, megalencephaly, and mental retardation leading to early death. While aspartoacylase (ASPA) activity increases with age in the wild type mouse brain, there is no ASPA activity in the CD mouse brain. So far ASPA deficiency and elevated NAA have been ascribed with the CD. Other factors affecting the brain that result from ASPA deficiency may lead pathophysiology of CD. The NMR spectra and amino acid analysis showed lower levels of glutamate and gamma-aminobutyric acid in the CD mouse brain compared to the wild type. Microarray gene expression on CD mouse brain showed glutamate transporter-EAAT4 and gamma-aminobutyric acid-A receptor, subunit alpha6 (GABRA6) were lower 9.7- and 119.1-fold, respectively. Serine proteinase inhibitor 2 (Spi2) was 29.9-fold higher in the CD mouse brain compared to the wild type. The decrease of GABRA6 and high expression of Spi2 in CD mouse brain were also confirmed by real-time RT-PCR. This first report showing abnormal expression of EAAT4, GABRA6, Spi2 combined with lower levels of glutamate and GABA are likely to be associated with the pathophysiology of CD.

Magnetic resonance histology: in situ single cell imaging of receptor cells in an invertebrate (Lolliguncula brevis, Cephalopoda) sense organ.

Utilizing contrast-enhanced MR histology, individual cell bodies were identified in situ and compared one-to-one with conventional histology. The squid Lolliguncula brevis served as a model where the receptor cells of the proprioceptive neck receptor organ were labeled with paramagnetic cobalt(II) ions by conventional cobalt iontophoresis. Stimulated echo images were obtained using a 9.4 T magnet and followed by conventional histologic treatment and light microscopy. Images obtained from both these techniques match well and validate MR histology.

Abdominal obesity, insulin resistance, and colon carcinogenesis are increased in mutant mice lacking gastrin gene expression.

BACKGROUND: The authors recently reported that gastrin gene knockout (GAS-KO) mice had an increased risk for colon carcinogenesis in response to azoxymethane (AOM) compared with their wild type (WT) littermates. In the current report, the authors discuss the predisposition of GAS-KO mice to develop obesity and metabolic hormonal changes that may contribute to their increased risk of colon carcinogenesis. METHODS: The weight and deposition of fat was monitored in the mice over a 14 month period, using magnetic resonance imaging and nuclear magnetic resonance techniques. Changes in plasma concentrations of ghrelin, leptin, insulin, and glucose were assessed using radioimmunoassay analysis and enzyme-linked immunosorbent assays. Preneoplastic markers of colon carcinogenesis (aberrant crypt foci [ACFs]), in response to AOM, were measured in a subset of obese versus lean GAS-KO mice and were compared with the markers in WT mice. RESULTS: Increases in visceral adiposity were evident by age 2 months in GAS-KO mice, resulting in macroscopic obesity by age 7 months. Hyperinsulinemia and insulin:glucose ratios were increased significantly in GAS-KO mice as young as 1 month and preceded alterations in nonfasting leptin and ghrelin levels. The number of ACFs per mouse colon were increased significantly in the following order: obese GAS-KO mice > lean GAS-KO mice > WT mice. Fasting plasma insulin levels were 0.88 +/- 0.1 ng/mL, 1.45 +/- 0.3, and 2.76 +/- 0.9 ng/mL in the WT, GAS-KO lean, and GAS-KO obese mice, respectively. CONCLUSIONS: The current results suggest the novel possibility that loss of amidated gastrins may increase adipogenesis, hyperinsulinemia, and colon carcinogenesis in GAS-KO mice. The increase in colon carcinogenesis may be due in part to hyperinsulinemia, increased obesity, and other associated hormone changes that were measured in GAS-KO mice.

Canavan disease: a monogenic trait with complex genomic interaction.

Canavan disease (CD) is an inherited leukodystrophy, caused by aspartoacylase (ASPA) deficiency, and accumulation of N-acetylaspartic acid (NAA) in the brain. The gene for ASPA has been cloned and more than 40 mutations have been described, with two founder mutations among Ashkenazi Jewish patients. Screening of Ashkenazi Jews for these two common mutations revealed a high carrier frequency, approximately 1/40, so that programs for carrier testing are currently in practice. The enzyme deficiency in CD interferes with the normal hydrolysis of NAA, which results in disruption of myelin and spongy degeneration of the white matter of the brain. The clinical features of the disease are macrocephaly, head lag, progressive severe mental retardation, and hypotonia in early life, which later changes to spasticity. A knockout mouse for CD has been generated, and used to study the pathophysiological basis for CD. Findings from the knockout mouse indicate that this monogenic trait leads to a series of genomic interaction in the brain. Changes include low levels of glutamate and GABA. Microarray expression analysis showed low level of expression of GABA-A receptor (GABRA6) and glutamate transporter (EAAT4). The gene Spi2, a gene involved in apoptosis and cell death, showed high level of expression. Such complexity of gene interaction results in the phenotype, the proteome, with spongy degeneration of the brain and neurological impairment of the mouse, similar to the human counterpart. Aspartoacylase gene transfer trial in the mouse brain using adenoassociated virus (AAV) as a vector are encouraging showing improved myelination and decrease in spongy degeneration in the area of the injection and also beyond that site.

A method for measuring cerebral glucose metabolism in vivo by 13C-NMR spectroscopy.

Current methods for estimating the rate of cerebral glucose utilization (CMR(glc)) typically measure metabolic activity for 40 min or longer subsequent to administration of [(13)C]glucose, 2-[(14)C]deoxyglucose, or 2-[(18)F]deoxyglucose. We report preliminary findings on estimating CMR(glc) for a period of 15 min by use of 2-[6-(13)C]deoxyglucose. After a 24-hr fast, rats were anesthetized, infused with [1-(13)C]glucose for 50 min, and injected with 2-[6-(13)C]deoxyglucose (500 mg/kg). During the subsequent 12.95 min the estimated value of CMR(glc) was 0.6 +/- 0.4 micromol/min/g (mean +/- SD, N = 7), in agreement with values reported for anesthetized rats studied with the 2-[(14)C]deoxyglucose method and other (13)C-NMR methods that measure CMR(glc). In rats injected with bicuculline methiodide (a known stimulant of CMR(glc)), CMR(glc) increased by more than 75% during 12.95 min following injection of bicuculline (Wilcoxon signed rank test, P = 0.042, N = 8).

Future role of large neutral amino acids in transport of phenylalanine into the brain.

OBJECTIVE: The treatment of phenylketonuria (PKU) in children and adults has been difficult because of erosion of dietary adherence, leading to poor school performance, impairment of executive functioning, loss of IQ, and deterioration of white matter in the brain. Mutant PKU mice produced by exposure to N-ethyl-N'-nitrosourea (ENU) were used to examine the effect of large neutral amino acid (LNAA) supplementation on brain and blood phenylalanine (Phe). METHODS: Mice with PKU, genotype ENU 2/2 with features of classical PKU, were supplemented with LNAA while on a normal diet. Two dosages of LNAA were given 0.5 g/kg and 1.0 g/kg by gavage. Blood Phe was determined in the experimental, control, and sham-treated mice. Brain Phe was determined by magnetic resonance spectroscopy after perchloric acid extraction. Branched-chain amino acid transferase (BCAT) was determined in brain as a marker for energy metabolism. RESULTS: Blood Phe was reduced in the LNAA-treated mice by an average of 15% (0.5 g/kg) and 50% (1.0 g/kg) in 48 hours. There was a sustained decrease in the blood Phe levels over a 6-week trial. The untreated mice and sham-treated mice maintained high blood Phe throughout the experiments. Brain Phe level determined by magnetic resonance spectroscopy showed a decline of 46% after the LNAA treatment. BCAT levels were lower (33%) in the ENU 2/2 mice compared with wild-type. The BCAT normalized in mice with PKU that were treated with LNAA. CONCLUSION: The results suggest that giving LNAA lowered brain and blood Phe levels in mice with PKU. Energy metabolism generated from BCAT also improved in mice with PKU after treatment with LNAA. Data from the mice suggest that LNAA should be considered among the strategies to treat PKU in humans.

Adeno-associated virus-mediated aspartoacylase gene transfer to the brain of knockout mouse for canavan disease.

Canavan disease (CD) is an autosomal recessive leukodystrophy caused by deficiency of aspartoacylase (ASPA). Deficiency of ASPA leads to elevation of N-acetyl-L-aspartic acid (NAA) in the brain and urine. To explore the feasibility of gene transfer to replace ASPA in CD, we generated a knockout mouse and constructed an AAV vector that encodes human ASPA cDNA (hASPA) followed by green fluorescent protein (GFP) after an intraribosomal entry site. We injected CD mice with rAAV-hASPA-GFP in the striatum and thalamus or injected rAAV-GFP identically into control animals. Three to five months after the injection, we determined the presence of ASPA in the CD mouse brain by ASPA activity assay, GFP expression, and Western blot analysis. While rAAV-GFP-injected animals displayed undetectable levels of ASPA, all detection methods revealed significant ASPA levels in rAAV-hASPA-GFP-injected CD mice. We evaluated the functional effects of rAAV-hASPA-GFP-mediated ASPA expression by standard histological methods, magnetic resonance spectroscopy (MRS) for in vivo NAA levels, and magnetic resonance imaging of CD mice. rAAV-hASPA-injected animals displayed a remarkable lack of spongiform degeneration in the thalamus. However, pathology in sites unrelated to the injected areas showed no improvement in histopathology. The improvement in thalamic neuropathology was also detectable via in vivo MRI. MRS revealed that in vivo NAA levels were also reduced. These data indicate that rAAV-mediated ASPA delivery may be an interesting avenue for the treatment of CD.