Regional brain volumes, diffusivity, and metabolite changes after electroconvulsive therapy for severe depression.

OBJECTIVE: To investigate the role of hippocampal plasticity in the antidepressant effect of electroconvulsive therapy (ECT). METHOD: We used magnetic resonance (MR) imaging including diffusion tensor imaging (DTI) and proton MR spectroscopy (1 H-MRS) to investigate hippocampal volume, diffusivity, and metabolite changes in 19 patients receiving ECT for severe depression. Other regions of interest included the amygdala, dorsolateral prefrontal cortex (DLPFC), orbitofrontal cortex, and hypothalamus. Patients received a 3T MR scan before ECT (TP1), 1 week (TP2), and 4 weeks (TP3) after ECT. RESULTS: Hippocampal and amygdala volume increased significantly at TP2 and continued to be increased at TP3. DLPFC exhibited a transient volume reduction at TP2. DTI revealed a reduced anisotropy and diffusivity of the hippocampus at TP2. We found no significant post-ECT changes in brain metabolite concentrations, and we were unable to identify a spectral signature at ≈1.30 ppm previously suggested to reflect neurogenesis induced by ECT. None of the brain imaging measures correlated to the clinical response. CONCLUSION: Our findings show that ECT causes a remodeling of brain structures involved in affective regulation, but due to their lack of correlation with the antidepressant effect, this remodeling does not appear to be directly underlying the antidepressant action of ECT.

Nervous system defects of AnkyrinB (-/-) mice suggest functional overlap between the cell adhesion molecule L1 and 440-kD AnkyrinB in premyelinated axons.

The L1 CAM family of cell adhesion molecules and the ankyrin family of spectrin-binding proteins are candidates to collaborate in transcellular complexes used in diverse contexts in nervous systems of vertebrates and invertebrates. This report presents evidence for functional coupling between L1 and 440-kD ankyrinB in premyelinated axons in the mouse nervous system. L1 and 440-kD ankyrinB are colocalized in premyelinated axon tracts in the developing nervous system and are both down-regulated after myelination. AnkyrinB (-/-) mice exhibit a phenotype similar to, but more severe, than L1 (-/-) mice and share features of human patients with L1 mutations. AnkyrinB (-/-) mice exhibit hypoplasia of the corpus callosum and pyramidal tracts, dilated ventricles, and extensive degeneration of the optic nerve, and they die by postnatal day 21. AnkyrinB (-/-) mice have reduced L1 in premyelinated axons of long fiber tracts, including the corpus callosum, fimbria, and internal capsule in the brain, and pyramidal tracts and lateral columns of the spinal cord. L1 was evident in the optic nerve at postnatal day 1 but disappeared by postnatal day 7 in mutant mice while NCAM was unchanged. Optic nerve axons of ankyrinB (-/-) mice become dilated with diameters up to eightfold greater than normal, and they degenerated by day 20. These findings provide the first evidence for a role of ankyrinB in the nervous system and support an interaction between 440-kD ankyrinB and L1 that is essential for maintenance of premyelinated axons in vivo.

A three-dimensional digital atlas database of the adult C57BL/6J mouse brain by magnetic resonance microscopy.

A comprehensive three-dimensional digital atlas database of the C57BL/6J mouse brain was developed based on magnetic resonance microscopy images acquired on a 17.6-T superconducting magnet. By using both manual tracing and an atlas-based semi-automatic segmentation approach, T2-weighted magnetic resonance microscopy images of 10 adult male formalin-fixed, excised C57BL/6J mouse brains were segmented into 20 anatomical structures. These structures included the neocortex, hippocampus, amygdala, olfactory bulbs, basal forebrain and septum, caudate-putamen, globus pallidus, thalamus, hypothalamus, central gray, superior colliculi, inferior colliculi, the rest of midbrain, cerebellum, brainstem, corpus callosum/external capsule, internal capsule, anterior commissure, fimbria, and ventricles. The segmentation data were formatted and stored into a database containing three different atlas types: 10 single-specimen brain atlases, an average brain atlas and a probabilistic atlas. Additionally, quantitative group information, such as variations in structural volume, surface area, magnetic resonance microscopy image intensity and local geometry, were computed and stored as an integral part of the database. The database augments ongoing efforts with other high priority strains as defined by the Mouse Phenome Database focused on providing a quantitative framework for accurate mapping of functional, genetic and protein expression patterns acquired by a myriad of technologies and imaging modalities.

Early postischemic 45Ca accumulation in rat dentate hilus.

Several studies have found postischemic regional accumulation of calcium to be time-dependent and coincident with the progression of ischemic cell change. In the most vulnerable cells in the hippocampus one would therefore expect to find a primary and specific early uptake of calcium after ischemia. Autoradiograms of 45Ca and 3H-inulin distribution were investigated before and 1 h after 20 min ischemia in the rat hippocampus. Two different methodological approaches were used for administration of 45Ca: (a) administration via microdialysis probes, (b) intraventricular injection. During control conditions the 45Ca autoradiograms showed variations in distribution volume in accordance with 3H-inulin determination of extracellular space size. One hour after ischemia a massive accumulation of 45Ca was found in the dentate hilus. No change in the distribution pattern of 3H-inulin could be demonstrated 1 h after ischemia. We suggest that 45Ca accumulation in dentate hilus 1 h after ischemia is a result of increased Ca2+ uptake before irreversible cell damage occurs and is not due to passive influx of calcium across a leaky plasma membrane.

Hydrogen peroxide production by monoamine oxidase during ischemia-reperfusion in the rat brain.

Monoamine oxidase (MAO) as a source of hydrogen peroxide (H2O2) was evaluated during ischemia-reperfusion in vivo in the rat brain. H2O2 production was assessed with and without inhibition of MAO during and after 15 min of ischemia. Metabolism of H2O2 by catalase during ischemia and reperfusion was measured in forebrain homogenates using aminotriazole (ATZ), an irreversible H2O2-dependent inhibitor of catalase. Catecholamine and glutathione concentrations in forebrain were measured with and without MAO inhibitors. During ischemia, forebrain blood flow was reduced to 8% of baseline and H2O2 production decreased as measured at the microperoxisome. During reperfusion, a rapid increase in H2O2 generation occurred within 5 min as measured by a threefold increase in oxidized glutathione (GSSG). The H2O2-dependent rates of ATZ inactivation of catalase between control and ischemia-reperfusion were similar, indicating that H2O2 was more available to glutathione peroxidase than to catalase in this model. MAO inhibitors eliminated the biochemical indications of increased H2O2 production and increased the catecholamine concentrations. Mortality was 67% at 48 h after ischemia-reperfusion, and there was no improvement in survival after inhibition of MAO. We conclude that MAO is an important source of H2O2 generation early in brain reperfusion, but inhibition of the enzyme does not improve survival in this model despite ablating H2O2 production.

Ischemic damage in hippocampal CA1 is dependent on glutamate release and intact innervation from CA3.

The removal of glutamatergic afferents to CA1 by destruction of the CA3 region is known to protect CA1 pyramidal cells against 10 min of transient global ischemia. To investigate further the pathogenetic significance of glutamate, we measured the release of glutamate in intact and CA3-lesioned CA1 hippocampal tissue. In intact CA1 hippocampal tissue, glutamate increased sixfold during ischemia; in the CA3-lesioned CA1 region, however, glutamate only increased 1.4-fold during ischemia. To assess the neurotoxic potential of the ischemia-induced release of glutamate, we injected the same concentration of glutamate into the CA1 region as is released during ischemia in normal, CA3-lesioned, and ischemic CA1 tissue. We found that this particular concentration of glutamate was sufficient to destroy CA1 pyramids in the vicinity of the injection site in intact and CA3-lesioned CA1 tissue when administered during control (non-ischemic) conditions. In contrast, the same amount injected during ischemia in the CA3-lesioned CA1 region destroyed pyramidal cells in a widely distributed zone around the injection site in the CA1 region. It is concluded that the ischemia-induced damage of pyramidal cells in CA1 is dependent on glutamate release and intact innervation from CA3.

Extracellular glutamate and dopamine measured by microdialysis in the rat striatum during blockade of synaptic transmission in anesthetized and awake rats.

We investigated the effect of high dose tetrodotoxin (TTX) on microdialysis measurements of extracellular striatal glutamate and dopamine in normal female rats. Both halothane-anesthetized rats with acutely implanted microdialysis probes and awake rats with microdialysis probes implanted for 24 h were tested. Glutamate levels in awake rats were 45% higher than those of anesthetized rats. Extracellular glutamate remained TTX-insensitive regardless of TTX concentration, anesthesia, or time lapsed after probe implantation. In contrast, TTX reduced dialysate dopamine in all TTX concentrations tested. We speculate that the lower glutamate levels in anesthetized rats reflect the effect of anesthesia. Because glutamate is involved, either as a reactant or a product in a variety of reactions critical to intermediary metabolism in the brain, basal dialysate glutamate levels might indirectly reflect brain metabolism. Further, we conclude that extracellular glutamate collected during non-stimulated conditions is TTX-insensitive. The fact that glutamate levels are TTX-independent does not rule out that glutamate is synaptic in origin but rather demonstrates that it is not nerve impulse-dependent. However, the brain interstitial glutamate pool accessible to the microdialysis probe during control conditions is most likely isolated from the synapse, and therefore does not impose a neurotoxic potential.

Inhibition of nitric oxide synthase increases extracellular cerebral glutamate concentration after global ischemia.

The effects of nitric oxide synthase (NOS) inhibition on extracellular glutamate release were investigated in rats during global brain ischemia and reperfusion (IR) using cerebral microdialysis. A dialysis probe was inserted into the hippocampus of anesthetized rats. Forebrain ischemia was produced by hypotension and occlusion of both carotid arteries. After 15 min, brain flow was restored for 60 min. Time-dependent changes in the dialysate glutamate concentration were analyzed with HPLC in both control rats and those treated with N omega-nitro-L-arginine methyl ester 30 min prior to ischemia. The data show that the NOS inhibitor did not prevent glutamate release from hippocampus during ischemia. Inhibition of NOS also enhanced glutamate release during reperfusion resulting in dialysate concentrations up to 10 times higher than control values.

Direct digitization of optical images using a photostimulable phosphor system.

The authors describe a method for directly digitizing optical images with a photostimulable phosphor (PSP) system. A PSP plate is initially charged with an exposure to a uniform x-ray field, and is then exposed to an optical image which discharges the plate in relation to the amount of incident light. Two applications were investigated: a contact-print technique for digitizing film radiographs, and a projection technique for digitizing transparent objects such as histology slides. Spatial uniformity was found to be adequate, and linearity of optical density response was excellent from 0.0-2.9 o.d. after look-up table correction. Spatial frequency response was degraded with the optical technique relative to the x-ray imaging properties of the plates, but was restorable by Fourier filtering. Image noise following spatial enhancement was satisfactory at intermediate to high optical densities using a high-resolution PSP plate, but was somewhat degraded at low densities.

Cerebral hemorrhage and edema following brain biopsy in rats: significance of mean arterial blood pressure.

OBJECT: It is taken for granted that patients with hypertension are at greater risk for intracerebral hemorrhage during neurosurgical procedures than patients with normal blood pressure. The anesthesiologist, therefore, maintains mean arterial blood pressure (MABP) near the lower end of the autoregulation curve, which in patients with preexisting hypertension can be as high as 110 to 130 mm Hg. Whether patients with long-standing hypertension experience more hemorrhage than normotensive patients after brain surgery if their blood pressure is maintained at the presurgical hypertensive level is currently unknown. The authors tested this hypothesis experimentally in a rodent model. METHODS: Hemorrhage and edema in the brain after needle biopsy was measured in vivo by using three-dimensional magnetic resonance (MR) microscopy in the following groups: WKY rats, acutely hypertensive WKY rats, spontaneously hypertensive rats (SHR strain), and SHR rats treated with either sodium nitroprusside or nicardipine. Group differences were compared using Tukey's studentized range test followed by individual pairwise comparisons of groups and adjusted for multiple comparisons. There were no differences in PaCO2, pH, and body temperature among the groups. The findings in this study indicated that only acutely hypertensive WKY rats had larger volumes of hemorrhage. Chronically hypertensive SHR rats with MABPs of 130 mm Hg did not have larger hemorrhages than normotensive rats. There were no differences in edema volumes among groups. CONCLUSIONS: The brains of SHR rats with elevated systemic MABPs are probably protected against excessive hemorrhage during surgery because of greater resistance in the larger cerebral arteries and, thus, reduced cerebral intravascular pressures.

Anxiety, vocalization, and agitation following peripheral nerve block with ropivacaine.

BACKGROUND AND OBJECTIVES: Central nervous system (CNS) and cardiovascular toxicity are potential side effects of local anesthetics. However, ropivacaine has been reported to be less CNS toxic than bupivacaine in human volunteers. METHODS: We describe three cases of peripheral nerve blockade with ropivacaine that resulted in unusual symptoms of CNS toxicity. RESULTS: In three patients, unexpected behavioral changes occurred during administration of ropivacaine. The patients became extremely agitated, anxious, and screamed, and they did not respond to verbal commands. CONCLUSION: This case report shows that ropivacaine may cause CNS toxicity that differs from classical signs of local anesthetic-induced toxicity. This effect might be related to the unique structure of ropivacaine, which is formulated in an S-enantiomer preparation. It has been shown that S-enantiomers bind differently to receptors in both the CNS and cardiovascular systems. This property may account for the disinhibition of select neural pathways that are specifically involved in mediation of anxiety and aggression.

Spinal cord neural anatomy in rats examined by in vivo magnetic resonance microscopy.

BACKGROUND AND OBJECTIVES: Magnetic resonance microscopy (MRM) is a technique that is worthwhile for anesthesiologists because it allows spinal cord and plexus anatomy to be visualized three dimensionally and followed over time in the same animal. For example, the long-term effect of indwelling intrathecal or plexus catheters can be studied in situ, and convective and diffusive forces within intrathecal, epidural, or nerve sheath spaces can be investigated. Further, diffusion-weighted MRM, which measures an "apparent diffusion coefficient" (ADC), can be used to track the presence of ischemia, hypoperfusion, or cytotoxic edema. This study investigates problems associated with the use of in vivo MRM for spinal cord and peripheral nerve studies in the rat. METHODS: Twenty-one anesthetized female Fisher CDF rats were used. Group 1 (n=7) was used for anatomic three-dimensional studies. Groups 2 (n=4), 3 (n=4), and 4 (n=6) were used for measurements of the ADC. Group 2 served as controls, group 3 received lumbar intrathecal catheters, and group 4 received cervical intrathecal catheters. RESULTS: Cervical spine, lumbar spine, and spinal nerves and ganglia were accurately visualized with MRM. As a rule, spinal cord gray and white matter were better demonstrated using diffusion-weighted proton stains. By contrast, T2-weighted proton staining superiorly demonstrated structures surrounding the spinal cord. In groups 3 and 4, indwelling intrathecal catheters did not affect the spinal cord ADC, indicating normal blood flow and no cytotoxic edema. Contrast studies revealed nonhomogeneous distribution of contrast predominately in the lateral and ventral intrathecal space. CONCLUSION: Three-dimensional diffusion-weighted MRM displays cervical and lumbar spine anatomy accurately in vivo. Apparent diffusion coefficients measurements are feasible in rat cervical spinal cord with intrathecal catheters. Spinal cord ADCs are unaffected by intrathecal catheters, indicating normal spinal cord perfusion.

In vivo diffusion-weighted magnetic resonance microscopy of rat spinal cord: effect of ischemia and intrathecal hyperbaric 5% lidocaine.

BACKGROUND AND OBJECTIVES: Pathophysiologic mechanisms underlying persistent neurologic deficits after continuous spinal anesthesia using hyperbaric 5% lidocaine are still not well understood. It has been suggested that high-dose intrathecal lidocaine induces irreversible conduction block and even ischemia in white matter tracts by breakdown of the blood-nerve barrier. In this study, we use diffusion-weighted magnetic resonance microscopy to characterize the effect of intrathecal hyperbaric 5% lidocaine in rat spinal cord. The parameter measured with DWM, is an "apparent diffusion coefficient," (ADC), which can be used to exclude the presence of ischemia. METHODS: Female Fischer CDF rats were used. Group 1 (n = 5) was exposed to ischemia, group 2 (n = 7) was exposed to intrathecal 5% hyperbaric lidocaine, and group 3 (n = 5) was exposed to intrathecal 7.5% glucose. Diffusion-weighted MR images in group 1 were acquired before and after ischemia induced by cardiac arrest and in groups 2 and 3 rats prior to and during perfusion of the spinal catheter with either 5% hyperbaric lidocaine or 7.5% glucose. RESULTS: Ischemia decreased the ADC by 40% in gray matter and by 30% in white matter of spinal cord. Continuous intrathecal anesthesia with hyperbaric 5% lidocaine did not affect the spinal cord ADC. Further, 7.5% intrathecal glucose had no effect on ADCs in gray or white matter of spinal cord. CONCLUSIONS: Ischemia reduced the ADC in both spinal cord white and gray matter. Hyperbaric 5% lidocaine did not affect the spinal cord ADC during the first 1.5 hours. We suggest that 5% hyperbaric lidocaine does not induce irreversible neurologic deficits by causing spinal cord ischemia.

Ventricular dilation and elevated aqueductal pulsations in a new experimental model of communicating hydrocephalus.

In communicating hydrocephalus (CH), explanations for the symptoms and clear-cut effective treatments remain elusive. Pulsatile flow through the cerebral aqueduct is often significantly elevated, but a clear link between abnormal pulsations and ventriculomegaly has yet to be identified. We sought to demonstrate measurement of pulsatile aqueductal flow of CSF in the rat, and to characterize the temporal changes in CSF pulsations in a new model of CH. Hydrocephalus was induced by injection of kaolin into the basal cisterns of adult rats (n = 18). Ventricular volume and aqueductal pulsations were measured on a 9.4 T MRI over a one month period. Half of the animals developed ventricular dilation, with increased ventricular volume and pulsations as early as one day post-induction, and marked chronic elevations compared to intact controls (volume: 130.15 +/- 83.21 microl vs. 15.52 +/- 2.00 microl; pulsations: 114.51 nl +/- 106.29 vs. 0.72 +/- 0.13 nl). Similar to the clinical presentation, the relationship between ventricular size and pulsations was quite variable. However, the pulsation time-course revealed two distinct sub-types of hydrocephalic animals: those with markedly elevated pulsations which persisted over time, and those with mildly elevated pulsations which returned to near normal levels after one week. These groups were associated with severe and mild ventriculomegaly respectively. Thus, aqueductal flow can be measured in the rat using high-field MRI and basal cistern-induced CH is associated with an immediate change in CSF pulsatility. At the same time, our results highlight the complex nature of aqueductal pulsation and its relationship to ventricular dilation.

Metabolomics of neural progenitor cells: a novel approach to biomarker discovery.

Finding biomarkers of human neurological diseases is one of the most pressing goals of modern medicine. Most neurological disorders are recognized too late because of the lack of biomarkers that can identify early pathological processes in the living brain. Late diagnosis leads to late therapy and poor prognosis. Therefore, during the past decade, a major endeavor of clinical investigations in neurology has been the search for diagnostic and prognostic biomarkers of brain disease. Recently, a new field of metabolomics has emerged, aiming to investigate metabolites within the cell/tissue/ organism as possible biomarkers. Similarly to other "omics" fields, metabolomics offers substantial information about the status of the organism at a given time point. However, metabolomics also provides functional insight into the biochemical status of a tissue, which results from the environmental effects on its genome background. Recently, we have adopted metabolomics techniques to develop an approach that combines both in vitro analysis of cellular samples and in vivo analysis of the mammalian brain. Using proton magnetic resonance spectroscopy, we have discovered a metabolic biomarker of neural stem/progenitor cells (NPCs) that allows the analysis of these cells in the live human brain. We have developed signal-processing algorithms that can detect metabolites present at very low concentration in the live human brain and can indicate possible pathways impaired in specific diseases. Herein, we present our strategy for both cellular and systems metabolomics, based on an integrative processing of the spectroscopy data that uses analytical tools from both metabolomic and spectroscopy fields. As an example of biomarker discovery using our approach, we present new data and discuss our previous findings on the NPC biomarker. Our studies link systems and cellular neuroscience through the functions of specific metabolites. Therefore, they provide a functional insight into the brain, which might eventually lead to discoveries of clinically useful biomarkers of the disease.

Evolution of a focal brain lesion produced by interlaced microplanar X-rays.

Stereotactic radiosurgery has led to advances in the treatment of central nervous system disease. It relies upon the principle of delivering relatively high dose irradiation to a precise target, while exposing surrounding tissues to extremely low doses. We describe a novel radiosurgical approach using interlaced microplanar X-rays which we have termed "microradiosurgery." The use of microbeams allows for 1,000-times greater precision than current clinically employed techniques. As a demonstration of this new method, we produced a approximately 3.8 mm (3) lesion in the rat brain. The lesion was followed over a period of 216 days using 9.4 Tesla magnetic resonance imaging. Our results show a gradually developing lesion at the site of the interlaced beams. The lesion began as a high T2 signal only, but advanced to include a central area of low T1 and mixed T2 signal within 2 months. No lesion was observed in the other side of the brain which was exposed to non-interlaced microbeams only. Interlaced microbeams is an effective method to create focal brain microlesions. This technique may allow the future treatment of pathology not accessible by surgical or more traditional radiosurgical means.