Three-dimensional representation and analysis of brain energy metabolism

Bilateral Common Carotid Artery Ligation in Sheep. Could These Animals be Used as Human Models for Vascular and Cerebral Research?

Experimental animals are still used in today’s medicine to understand better physiological or pathological processes, or to develop, for example better vascular prostheses. For that reason, these animals must show some similarities with humans, from the anatomical to the physiological point of view. When developing vascular prostheses, we have to evaluate if the graft will react in the expected way and if during experimental research there will be some factors that might influence the proper functioning of vascular prostheses in the human body. We observed the consequences of bilateral common carotid artery ligation (BCCAL) or Sham operation in seventeen healthy Merinolandschaf / Württemberg sheep, aged between 2 and 4 years, after testing new types of carbon-coated ARTECOR® and ADIPOGRAFT Ra 1vk 7/350 vascular prostheses. After the follow-up period the prostheses were extirpated, so the blood supply was provided from the vertebral arteries. Sheep in both groups were not sacrificed, but were observed for 18 months. After the observation period all sheep showed no physical or neurological changes and all are still alive. Animal responses to BCCAL are different, depending on the animal species, age, and condition. In sheep, bilateral blocking of the blood fl ow in the carotid bed seems to be conceivable since the brain was sufficiently supplied with blood from the vertebral arteries.

Extracting Cross-Sectional Clinical Images Based on Their Principal Axes of Inertia

Cross-sectional imaging is considered the gold standard in diagnosing a range of diseases. However, despite its widespread use in clinical practice and research, no widely accepted method is available to reliably match cross-sectional planes in several consecutive scans. This deficiency can impede comparison between cross-sectional images and ultimately lead to misdiagnosis. Here, we propose and demonstrate a method for finding the same imaging plane in images obtained during separate scanning sessions. Our method is based on the reconstruction of a "virtual organ" from which arbitrary cross-sectional images can be extracted, independent of the axis orientation in the original scan or cut; the key is to establish unique body coordinates of the organ from its principal axes of inertia. To verify our method a series of tests were performed, and the same cross-sectional plane was successfully extracted. This new approach offers clinicians access, after just a single scanning session, to the morphology and structure of a lesion through cross-sectional images reconstructed along arbitrary axes. It also aids comparable detection of morphological and structural changes in the same imaging plane from scans of the same patient taken at different times-thus potentially reducing the misdiagnosis rate when cross-sectional images are interpreted.

Brain maps on the go: functional imaging during motor challenge in animals

Brain mapping in the freely moving animal is useful for studying motor circuits, not only because it avoids the potential confound of sedation or restraints, but because activated brain states may serve to accentuate differences that only manifest partially while a subject is in the resting state. Perfusion or metabolic mapping using autoradiography allows one to examine changes in brain function at the circuit level across the entire brain with a spatial resolution (approximately 100 micro) appropriate for the rat or mouse brain, and a temporal resolution (seconds-minutes) sufficient for capturing acute brain changes. Here we summarize the application of these methods to the functional brain mapping of behaviors involving locomotion of small animals, methods for the three-dimensional reconstruction of the brain from autoradiographic sections, voxel based analysis of the whole brain, and generation of maps of the flattened rat cortex. Application of these methods in animal models promises utility in improving our understanding of motor function in the normal brain, and of the effects of neuropathology and treatment interventions such as exercise have on the reorganization of motor circuits.

Chronic corticosterone injections induce a decrease of ATP levels and sustained activation of AMP-activated protein kinase in hippocampal tissues of male mice

Chronic corticosterone injections induce hippocampus tissue damage and depression-like behavior in rodent animals, the cause of which is not known. Nevertheless, increasing evidence shows that adenylate kinase (AK) and AMP-activated protein kinase (AMPK) play a very important role in intracellular energy metabolism and are especially critical for neurons which are known to have very small energy reserves and narrow margin of safety between the energy that can be generated and the energy required for maximum activity. Abnormalities of AK or AMPK system have detrimental effects on neurons or brain function especially at times of increased activity. In this study, we investigated the effects of chronic corticosterone exposure on energy metabolism, as well as AK and AMPK in hippocampal tissues in male C57BL/6N mice. Our results show that chronic corticosterone injection induced depression-like behavior in male mice, significantly decreased the energy levels and caused a sustained increase of AMP:ATP ratio in hippocampal tissues. Interestingly, chronic corticosterone injections did not produce obvious effects on AK1 protein and mRNA levels, but caused a sustained activation of AMPK. The results indicate that sustained AMPK activation might be a mechanism by which chronic corticosterone treatment causes depression-like behavior in male mice.

Image registration based on neural network and Fourier transform

An image registration technique based on feed forward neural network and Fourier Transform is developed and presented. In the proposed scheme, the spectrums of the acquired images are computed, the Fourier coefficients within a selected central window of each spectrum are extracted and fed as inputs to the neural network. The feed forward neural network is implemented to estimate the transformation, defined in terms of the translation, rotation and magnification parameters, to align the corresponding images. This approach does not estimate the various registration parameters separately. They are estimated simultaneously leading to a better-optimized set of registration parameters. The approach is successful and yields better results than another Fourier based registration technique. The approach is validated on 2D images. However, it can be easily extended to 3-D application.

Pixel-based statistical analysis by a 3D clustering approach: application to autoradiographic images

Statistical analysis of medical images in experimental laboratories plays an important role in confirming scientific findings and in guiding potential clinical applications. In experimental neuroscience studies, autoradiographic images taken under differing physiological or pathological conditions from replicate animals are often compared in order to detect any significant change in glucose utilization or blood flow and to localize these changes. For these comparisons to be valid and informative, proper statistical procedures are in order. Conventional methods include statistic parametric mapping (SPM) analysis, non-parametric analysis and cluster-analysis. Each method of comparison has a specific purpose. This paper describes an approach that combines these conventional methods and presents a non-parametric statistical procedure based on cluster-analysis for localizing significant differences in autoradiographic data sets. By thresholding cluster sizes rather than pixel values to reject false positives, this approach enhances statistical power. By re-shuffling the data sets to produce the null distribution of a cluster size statistic, the test makes few assumptions as to the statistical properties of the SPM, and thus it is valid under a broad range of conditions. The designed method was tested on autoradiographic images of rats subjected to moderate traumatic brain injury (TBI). Different methods were also performed on the same data sets. Comparison among these methods shows that this method is suitable for the statistical analysis of autoradiographic images.

Statistical parametric mapping applied to an autoradiographic study of cerebral activation during treadmill walking in rats

Autoradiographs are conventionally analyzed by a region-of-interest (ROI) analysis. However, definition of ROIs on an image set is labor intensive, is subject to potential inter-rater bias, and is not well suited for anatomically variable structures that may not consistently correspond to specific ROIs. Most importantly, the ROI method is poorly suited for whole-brain analysis, where one wishes to detect all activations resulting from an experimental paradigm. A system developed for analysis of imaging data in humans, Statistical Parametric Mapping (SPM), avoids some of these limitations but has not previously been adapted as a tool for the analysis of autoradiographs. Here, we describe the application of SPM to an autoradiographic data set mapping cerebral activation in rats during treadmill walking. We studied freely moving, non-tethered rats that received injections of the cerebral blood flow tracer [14C]-iodoantipyrine, while they were performing a treadmill task (n = 7) or during a quiescent control condition (n = 6). Results obtained with SPM were compared to those previously reported using a standard ROI-based method of analysis [J. Cereb. Blood Flow Metab. 23(2003) 925]. The SPM method confirmed most areas detected as significant using the ROI approach. However, in the subcortex, SPM detected additional significant regions that, because of their irregular structures, fell short of statistical significance when analyzed by ROI. The SPM approach offers the ability to perform a semi-automated whole-brain analysis, and coupled with autoradiography, provides an effective means to globally localize functional activity in small animals.

Brain glucose metabolism in Rett Syndrome

Rett syndrome is a progressive neurologic disorder affecting girls in early childhood with loss of achieved psychomotor abilities and mental retardation. Six sedated female patients (4 to 15 years of age) with a diagnosis of Rett syndrome were studied with [(18)F]fluorodeoxyglucose (FDG) and underwent positron emission tomography scanning of the brain. Relative tracer concentrations between different areas of the brain were assessed, and results were compared with 18 age-matched control subjects. Patients were divided into two age groups: 3 to 8 years of age and 9 to 15 years of age. A relative decrease in [(18)F]FDG uptake in the lateral occipital areas in relation with the whole brain and a relative increase in the cerebellum was evident in both age groups (P < 0.001, unpaired Student t test). A relative increase in frontal tracer uptake was observed in the younger group. Sensorimotor areas and relations between cortical and subcortical structures were preserved in all patients. Changes in glucose cerebral metabolism resemble the regional distribution of normal children less than 1 year of age, likely reflecting a maturational arrest. Changes in frontal areas parallel those in postmortem N-methyl-D-aspartate receptor densities and could correlate with different clinical stages of the disease. This pattern differs from those described in Down syndrome, autism, and Alzheimer's disease.

CNS energy metabolism as related to function

Large amounts of energy are required to maintain the signaling activities of CNS cells. Because of the fine-grained heterogeneity of brain and the rapid changes in energy demand, it has been difficult to monitor rates of energy generation and consumption at the cellular level and even more difficult at the subcellular level. Mechanisms to facilitate energy transfer within cells include the juxtaposition of sites of generation with sites of consumption and the transfer of approximately P by the creatine kinase/creatine phosphate and the adenylate kinase systems. There is evidence that glycolysis is separated from oxidative metabolism at some sites with lactate becoming an important substrate. Carbonic anhydrase may play a role in buffering activity-induced increases in lactic acid. Relatively little energy is used for 'vegetative' processes. The great majority is used for signaling processes, particularly Na(+) transport. The brain has very small energy reserves, and the margin of safety between the energy that can be generated and the energy required for maximum activity is also small. It seems probable that the supply of energy may impose a limit on the activity of a neuron under normal conditions. A number of mechanisms have evolved to reduce activity when energy levels are diminished.

Glucose transporters and glucose utilization in rat brain after acute ethanol administration

In the normal adult brain, glucose provides 90% of the energy requirements as well as substrate for nucleic acid and lipid synthesis. In the present study, effects of ethanol on glucose transporters (GLUT) and glucose utilization were examined in rat brain. Male Sprague-Dawley rats weighing 250-300 gms were given either ethanol 3 gm/kg BW or saline i.p. 4 hrs prior to the animal sacrifice and removal of the cerebral cortical tissue. The cortical plasma membranes analyzed by cytochalasin B binding assay showed a decrease in GLUT number but not in GLUT affinity in the ethanol treated rats as compared to the control rats. The estimated Ro values were 70 +/- 8.9 Vs 91 +/- 8.9 pmoles/mg protein (p < 0.05 N=4) and the estimated Kd values were 0.37 +/- 0.03 and 0.28 +/- 0.05 microM (p: NS) in ethanol and control experiments respectively. Immunoblots of purified cerebral plasma membranes and low density microsomal fraction showed 17% and 71% decrease for GLUTI and 54% and 21% (p<0.05 or less; n=6) for GLUT3 respectively in ethanol treated rats than in control animals. Immunofluoresence studies also showed reduction of GLUT1 immunoreactively in choroid plexus and cortical microvessels of ethanol treated rats as compared to control rats. The effect of ethanol on regional cerebral metabolic rates for glucose (CMR(Glc)) was studied using [6-(14)C] glucose and showed statistically insignificant decrease in brain glucose utilization. These data suggest that ethanol in-vivo decrease GLUT number and protein content in rat cerebral cortex.

A new method for reliable and efficient reconstruction of 3-dimensional images from autoradiographs of brain sections

Valuable information on metabolism and function of distinct brain regions can be extracted from autoradiographs of 2D brain sections, e.g. after labelling with the non-metabolisable sugar derivate [14C]-2-fluoro-deoxyglucose (2-FDG). For a more complete comprehension of the data and for a comparison with information obtained by modern functional imaging techniques it is essential to have a reliable and efficient method for the 3D reconstruction of autoradiographs of serial sections. This paper describes a new method for the alignment of 2D 2-FDG images, that combines two established algorithms, i.e. principal axes alignment followed by consistent matrix transformation. The power and efficiency of this new 2-step method is compared to those of various previously described procedures.

External marker-based automatic congruencing: a new method of 3D reconstruction from serial sections

BACKGROUND

Computer-based three-dimensional (3D) visualizations reconstructed from sectional images represent a valuable tool in biomedical research and medical diagnosis. Particularly with those imaging techniques that provide virtual sections, such as CT, MRI, and CLSM, 3D reconstructions have become routine. Reconstructions from physical sections, such as those used in histological preparations, have not experienced an equivalent breakthrough, due to inherent shortcomings in sectional preparation that impede automated image-processing and reconstruction. The increased use of molecular techniques in morphological research, however, generates an overwhelming amount of 3D molecular information, stored within series of physical sections. This valuable information can be fully appreciated and interpreted only through an adequate method of 3D visualization.

METHODS AND RESULTS

In this paper we present a new method for a reliable and largely automated 3D reconstruction from physically sectioned material. The 'EMAC' concept (External Marker-based Automatic Congruencing) successfully approaches the three major obstacles to automated 3D reconstruction from serial physical sections: misalignment, distortion, and staining variation. It utilizes the objectivity of external markers for realignment of the sectional images and for geometric correction of distortion. A self-adapting dynamic thresholding technique compensates for artifactual staining variation and automatically selects the desired object contours.

CONCLUSIONS

Implemented on a low-cost hardware platform, EMAC provides a fast and efficient tool that largely facilitates the use of computer-based 3D visualization for the analysis of complex structural, molecular, and genetic information in morphological research. Due to its conceptual versatility, EMAC can be easily adapted for a broad range of tasks, including all modern molecular-staining techniques, such as immunohistochemistry and in situ hybridization.

GABAergic neurons in barrel cortex show strong, whisker-dependent metabolic activation during normal behavior

Electrophysiological data from the rodent whisker/barrel cortex indicate that GABAergic, presumed inhibitory, neurons respond more vigorously to stimulation than glutamatergic, presumed excitatory, cells. However, these data represent very small neuronal samples in restrained, anesthetized, or narcotized animals or in cortical slices. Histochemical data from primate visual cortex, stained for the mitochondrial enzyme cytochrome oxidase (CO) and for GABA, show that GABAergic neurons are more highly reactive for CO than glutamatergic cells, indicating that inhibitory neurons are chronically more active than excitatory neurons but leaving doubt about the short-term stimulus dependence of this activation. Taken together, these results suggest that highly active inhibitory neurons powerfully influence relatively inactive excitatory cells but do not demonstrate directly the relative activities of excitatory and inhibitory neurons in the cortex during normal behavior. We used a novel double-labeling technique to approach the issue of excitatory and inhibitory neuronal activation during behavior. Our technique combines high-resolution 2-deoxyglucose (2DG), immunohistochemical staining for neurotransmitter-specific antibodies, and automated image analysis to collect the data. We find that putative inhibitory neurons in barrel cortex of behaving animals are, on average, much more heavily 2DG-labeled than presumed excitatory cells, a pattern not seen in animals anesthetized at the time of 2DG injection. This metabolic activation is dependent specifically on sensory inputs from the whiskers, because acute trimming of most whiskers greatly reduces 2DG labeling in both cell classes in columns corresponding to trimmed whiskers. Our results provide confirmation of the active GABAergic cell hypothesis suggested by CO and single-unit data. We conclude that strong activation of inhibitory cortical neurons must confer selective advantages that compensate for its inherent energy inefficiency.

Reversal of portacaval shunting normalizes brain energy consumption in most brain structures

The cerebral metabolic rate of glucose consumption (CMRGlc) was measured throughout brains of rats with 1) portacaval shunts created for 2 wk, followed by restoration of normal blood circulation for 2 wk; 2) portacaval shunts created for 2 wk, followed by a sham operation and 2 wk of recovery; 3) two sham operations, each with 2 wk of recovery times. Portacaval-shunted rats had diminished CMRGlc (decreases of 7-23%) throughout the brain in agreement with previous studies. After restoration of normal liver blood flow, the CMRGlc of most structures returned to near-normal values, although a few structures, notably the hippocampus, remained 11-13% lower. These data suggest that the consequences of portacaval shunting to brain energy metabolism can be markedly improved, if not completely reversed, by restoring the normal pattern of blood flow to an otherwise healthy liver. Other metabolic and physical data collected (liver weight, liver-to-body weight, plasma ammonia) returned to normal except plasma glucose concentrations, which remained lower by 11%, suggesting a persistent, albeit mild, defect in glucose homeostasis.

Three-dimensional metabolic and hemodynamic imaging of the normal and ischemic rat brain

Unique insights into the topography of local metabolism/blood flow interrelationships in focal cerebral ischemia have afforded by the recent development of powerful image-processing techniques permitting three-dimensional (3D) autoradiographic image-averaging and analysis of replicate studies by a novel method termed "disparity analysis". This method, based upon a linear affine transformation model, directly estimates scaling, translation and rotation parameters simultaneously. The method was validated in awake Wister rats studied for local cerebral glucose metabolism (lCMRgl) with 14C-2-deoxyglucose. Brains were subserially sectioned, aligned by disparity analysis, and mapped into a common template so as to generate aggregate 3D data sets of the mean and standard deviation of the entire series (n = 9). Internal anatomic architecture was faithfully represented in the average image, and Fourier analysis revealed satisfactory retention of low-frequency information. The method was then applied to study metabolism/blood flow relationships in the acute focal ischemic penumbra of Sprague-Dawley rats subjected to distal photothrombotic middle cerebral artery (MCA) occlusion, coupled with permanent ipsilateral and 1 h contralateral common carotid artery occlusions. Matched series were studied for lCBF at 1.5 h and for lCMRgl at 1.25-2 h post-occlusion. The averaged lCBF image revealed the ischemic penumbra (defined as lCBF 20-40% of control) to form a "shell" around the cortical ischemic core and a confluent aggregate at the anterior and posterior poles of the core-zone. lCMRgl in the penumbra was heterogeneous, ranging from near-normal to markedly increased. An average lCMRgl/lCBF ratio data set revealed marked metabolism-flow uncoupling in penumbral pixels, averaging nearly five-fold above control ratio values. Sustained deflections of the DC potential were recorded in the penumbra, the site of marked uncoupling. This analysis defined for the first time the 3D topography of the ischemic penumbra and substantiated marked metabolism/flow dissociation, which is believed to be a metabolic consequence of the energy demand imposed by repeated peri-infarct depolarizations.

Multiscale detection and analysis of the senile plaques of Alzheimer's disease

Senile plaques (SP) are one of the characteristic neuropathologic lesions of Alzheimer's Disease (AD), and studies of SP cortical distribution, density (number of SP/mm2), and morphology are expected to lead to new information about the mechanism and pathogenesis of AD. We describe a digital image analysis procedure to detect SP, and to measure SP size, shape, and total fractional area in digital micrographs of silver-stained tissue sections. This histology is nonspecific so the program detects all the significant stained objects and a classifier sorts the SP from other tissue elements. SP vary greatly in size and form, and detection is based on multiscale template correlation. Three independent comparisons of computed versus expert-determined SP densities produced correlation coefficients greater than 0.8. The program found 94,000 SP in 2800 digital images of tissue sections from 42 postmortem cases including healthy aged controls and severely demented subjects.

Enhanced displays of medical images: evaluation of the effectiveness of color, motion, and contour for detecting and localizing liver lesions

RATIONALE AND OBJECTIVES

Many perceptual studies have shown that the detection of large, low-contrast targets is better either in color or in contrast-reversing presentations than in standard gray scale. We determined the value of several new display techniques for viewing liver computed tomography (CT) scans.

METHODS

Eight observers (four radiologists and four nonradiologists) viewed sets of 100 liver CT images (50 with lesions and 50 without) under five display conditions on a Macintosh computer: (1) color (equiluminant color contrast); (2) color-luminance (combined luminance and chromatic contrast); (3) flicker (luminance contrast that reversed polarity at 2 Hz); (4) contour (shaded intensity mapping); and (5) control (conventional gray scale). Receiver operating characteristics (ROC) techniques were used for analysis.

RESULTS

The measured ROC curve areas for the different viewing conditions were as follows: control = 0.77 +/- 0.01 (mean +/- standard error of the mean); color = 0.78 +/- 0.01; color-luminance = 0.82 +/- 0.01; flicker = 0.78 +/- 0.01; and contour = 0.76 +/- 0.01. The percentage of lesions correctly located ranged from 0.82 (color-luminance) to 0.75 (flicker). Performance under the color-luminance condition was significantly better than in the control condition (p = .01), whereas the other experimental conditions were not significantly different from the control condition (p > .21).

CONCLUSION

The use of mixed color and luminance displays may have perceptual advantages for radiologists and can improve performance over that of gray-scale viewing.

Three-dimensional quantitative autoradiography by disparity analysis: theory and application to image averaging of local cerebral glucose utilization

Traditional autoradiographic image analysis has been restricted to the two-dimensional assessment of local cerebral glucose utilization (LCMRglc) or blood flow in individual brains. It is advantageous, however, to generate an entire three-dimensional (3D) data set and to develop the ability to map replicate images derived from multiple studies into the same 3D space, so as to generate average and standard deviation images for the entire series. We have developed a novel method, termed "disparity analysis," for the alignment and mapping of autoradiographic images. We present the theory of this method, which is based upon a linear affine model, to analyze point-to-point disparities in two images. The method is a direct one that estimates scaling, translation, and rotation parameters simultaneously. Disparity analysis is general and flexible and deals well with damaged or asymmetric sections. We applied this method to study LCMRglc in nine awake male Wistar rats by the [14C]2-deoxyglucose method. Brains were physically aligned in the anteroposterior axis and were sectioned subserially at 100-microns intervals. For each brain, coronal sections were aligned by disparity analysis. The nine brains were then registered in the z-axis with respect to a common coronal reference level (bregma + 0.7 mm). Eight of the nine brains were mapped into the remaining brain, which was designated the "template," and aggregate 3D data sets were generated of the mean and standard deviation for the entire series. The averaged images retained the major anatomic features apparent in individual brains but with some defocusing. Internal anatomic features of the averaged brain were smooth, continuous, and readily identifiable on sections through the 3D stack. The fidelity of the internal architecture of the averaged brain was compared with that of individual brains by analysis of line scans at four representative levels. Line scan comparisons between corresponding sections and their template showed a high degree of correlation, as did similar comparisons performed on entire sections. Fourier analysis of line scan data showed retention of low-frequency information with the expected attenuation of high-frequency components produced by averaging. Region-of-interest (ROI) analysis of the averaged brain yielded LCMRglc values virtually identical to those derived from measurements and subsequent averaging of data from individual brains.(ABSTRACT TRUNCATED AT 400 WORDS)

Vision-based object registration for real-time image overlay

This paper presents a computer vision-based technique for object registration, real-time tracking, and image overlay. The capability can be used to superimpose registered medical images such as those from CT or MRI on to a video image of a patient's body. Real-time object registration enables an image to be overlaid consistently on to objects even while the objects and cameras viewing it are moving. Object registration is composed of feature tracking, feature correspondence, and pose calculation of objects. This technique is based on geometric models of objects, but it can be extended so that some image overlay is possible without a prior model of the object.

A 3D digital map of rat brain

A three dimensional (3D) computerized map of rat brain anatomy created with digital imaging techniques is described. Six male Sprague-Dawley rats, weighing 270-320 g, were used in the generation of this atlas. Their heads were frozen, and closely spaced cryosectional images were digitally captured. Each serial data set was organized into a digital volume, reoriented into a flat skull position, and brought into register with each other. A volume representative of the group following registration was chosen based on its anatomic correspondence with the other specimens as measured by image correlation coefficients and landmark matching. Mean positions of lambda, bregma, and the interaural plane of the group within the common coordinate system were used to transform the representative volume into a 3D map of rat neuroanatomy. images reconstructed from this 3D map are available to the public via Internet with an anonymous file transfer protocol (FTP) and World Wide Web. A complete description of the digital map is provided in a comprehensive set of sagittal planes (up to 0.031 mm spacing) containing stereotaxic reference grids. Sets of coronal and horizontal planes, resampled at the same increment, also are included. Specific anatomic features are identified in a second collection of images. Stylized anatomic boundaries and structural labels were incorporated into selected orthogonal planes. Electronic sharing and interactive use are benefits afforded by a digital format, but the foremost advantage of this 3D map is its whole brain integrated representation of rat in situ neuroanatomy.

Computed detection and quantitative morphometry of Alzheimer senile plaques

Senile plaques (SP) are the most characteristic neuropathologic lesions of Alzheimer's disease (AD) and studies of plaque cortical distribution, density, and morphology may lead to new information about the origin and pathogenesis of this disease. We have developed an automated computer image analysis program to detect SP (including diffuse and mature forms) and to measure SP size, shape, and fractional area or load in digital micrographs of silver-stained tissue sections. The plaques are detected with adaptive thresholding, requiring no user interaction. Measures of SP size, morphology, and load are readily calculated from the pixel values in the detected SP features. These measurements are achieved accurately and exhaustively, and this method offers an alternative to manual SP counting. We demonstrate its application to 4 cases spanning the full range of the severity of the disease.

Superpositioning of 3-dimensional neuroanatomic data sets

Superpositioning of multiple 3-dimensional digital volumes is essential to extending neuroimaging capabilities from single-subject analysis to group evaluation. In this study, 6 rat heads were cryoplaned and digital images of the specimen blockface were organized into data volumes. The midline plane of each brain guided coronal and horizontal rotations and medial-lateral positioning. Four different methods of determining sagittal rotation, dorsoventral position, and anteroposterior position were tested. The first technique uses lambda and bregma as fiducial points; the second method employs bony sutures in the base of the skull; and the third strategy fits both sets of alignments points. The fourth method differs from the previous landmark-based approaches by employing cross-correlation of image densities. A composite of midsagittal cutplanes through the volumes aligned by the first method revealed significant misalignment. Use of ventral fiducials resulted in improved correlation statistics for orthogonal cutplanes through the volumes and significantly reduced positional variability of anteroposterior landmarks. Combining dorsal and ventral fiducials produced a slight improvement in midsagittal image correlation but had mixed effects on landmark variability. Following the fourth method of registration, correlation statistics and the alignment of reference points were similar to those obtained with the 4-point approach.

Computed three-dimensional reconstruction of median-eminence capillary modules: image alignment and correlation

Image alignment is an absolute requirement for three-dimensional (3-D) reconstruction from serial sections, and Fourier correlation is the most powerful way to compute alignments. The rotational and translational components of misalignment can be corrected by an iterative correlation procedure, but for images having significant differences, alignment can fail with a likelihood proportional to the extent of the differences. We found that translational correction was determined much more reliably when low-pass filters were applied to the product transforms from which the correlations were calculated. Rotational corrections based on polar analyses of the auto-correlations of the images instead of on the images directly contributed to more accurate alignments. These methods were used to generate 3-D reconstructions of brain capillary modules from serial-section mosaics of digitized transmission electron micrographs.

Registration and three-dimensional reconstruction of autoradiographic images by the disparity analysis method

Quantitative autoradiography is a powerful radioisotopic-imaging method for neuroscientists to study local cerebral blood flow and glucose-metabolic rate at rest, in response to physiologic activation of the visual, auditory, somatosensory, and motor systems, and in pathologic conditions. Most autoradiographic studies analyze glucose utilization and blood flow in two-dimensional (2D) coronal sections. With modern digital computer and image-processing techniques, a large number of closely spaced coronal sections can be stacked appropriately to form a three-dimensional (3D) image. 3D autoradiography allows investigators to observe cerebral sections and surfaces from any viewing angle. A fundamental problem in 3D reconstruction is the alignment (registration) of the coronal sections. A new alignment method based on disparity analysis is presented, which can overcome many of the difficulties encountered by previous methods. The disparity analysis method can deal with asymmetric, damaged, or tilted coronal sections under the same general framework, and it can be used to match coronal sections of different sizes and shapes. Experimental results on alignment and 3D reconstruction are presented.

Computer-assisted alignment of standard serial sections without use of artificial landmarks. A practical approach to the utilization of incomplete information in 3-D reconstruction of the hippocampal region

An algorithm for the alignment of stained serial sections without the support of artificial landmarks is described. Four-hundred-thirty serial sections of the rabbit hippocampal region were digitized, and computer-based alignment was performed without use of artificial markers, resulting in a consistent matrix. Following proper filtration, artificial sections were cut through the matrix. In a second experiment every second image was deleted and reconstructed by interpolation with a minor loss of biological information. In a third experiment every second image was deleted and the rest of the images were 'disordered', realigned and the missing planes reconstructed by interpolation. Under these circumstances the matrix was reconstructed with some loss of information. These results may widen the limits of 3-dimensional (3-D) reconstruction, as routine histological preparations normally include only every second or every third section without artificial landmarks.

Infraorbital nerve blockade from birth does not disrupt central trigeminal pattern formation in the rat

We tested the hypothesis that patterned primary afferent impulse activity during early postnatal periods is necessary for central trigeminal pattern formation. Newborn rats had their whiskers trimmed daily and new slices of slow release polymer containing the sodium channel blocker, tetrodotoxin, were placed under the infraorbital nerve every 8 h for up to 9 days. Electrophysiological recordings indicated that trigeminal ganglion cells were unresponsive to peripheral stimuli and chronically silenced. Trigeminal ganglion cell numbers were unaffected by nerve blockade. Cytochrome oxidase staining patterns in the trigeminal brainstem complex, thalamus, and barrel cortex were normal on postnatal day 1, 3, 5, 7, or 9 (n = 4 each). Whisker-related patches were of normal sizes and staining densities. Similar negative results were obtained in 9 rats in which whiskers were trimmed daily and the long-acting local anesthetic bupivacaine was injected into the whisker pad at 2.5- to 4-h intervals from birth to sacrifice on postnatal day 5-9. Cytochrome oxidase staining patterns and patch properties again did not differ from normal. Thus, trigeminal pattern formation occurs even when the entire infraorbital nerve is silenced from birth.

Regional distribution and kinetics of three sites on the GABAA receptor: lack of effect of portacaval shunting

The regional distribution of binding sites on the GABAA receptor and their kinetic parameters were measured by quantitative autoradiography in brains from normal rats and rats with a portacaval shunt, a model of portal systemic encephalopathy in which GABA neurotransmission may be altered. The ligands used were [3H]flunitrazepam (a benzodiazepine-site agonist), [3H]-Ro15-1788 (a benzodiazepine-site antagonist), [3H]muscimol (a GABA-site agonist), and [35S]t-butylbicyclophosphorothionate (35S-TBPS, a convulsant that binds to a site near the chloride channel). Some brains were analyzed by computerized image analysis and three-dimensional reconstruction. The regional distribution of binding of the benzodiazepines was very similar, but the patterns obtained with [3H]muscimol and [35S]TBPS were different in many areas, suggesting a heterogeneous distribution of several subtypes of the GABAA receptor. The kinetic parameters were determined in brain regions for [3H]flunitrazepam, [3H]Ro15-1788, and [3H]muscimol. For each ligand, the Kd showed a significant heterogeneity among brain regions (at least threefold), contrary to conclusions drawn from earlier studies. In portacaval shunted rats, binding of all four ligands was essentially unchanged from that in control rats, indicating that, if there was an abnormality in GABA neurotransmission during portal systemic shunting, it was not reflected by altered binding to the main sites on the GABAA receptor.

Computed alignment of dissimilar images for three-dimensional reconstructions

Three-dimensional reconstructions from serial section images require the accurate registration of those images. Image correlation is the most powerful computed alignment method and its performance on identical images, or parts thereof, has been thoroughly studied. Correlation alignments of complex, dissimilar images can fail, however, with a likelihood proportional to the magnitude of the differences. We report that alignments can be computed more reliably and more accurately (higher-valued correlation coefficients) by the combined use of lowpass-filtered product transforms (from which the correlation functions are formed), autocorrelation correction of rotational misalignment, and covariance correction of translation misalignment. A simple rule is proposed for the lowpass filter cutoff radius depending on measures of the images' differences. These methods are demonstrated with a reconstruction of a capillary loop in the median eminence of the hypothalamus.

Animating the 3D structure and function of brain

Three dimensional (3D) reconstructions of brain anatomy and physiology have greatly improved our understanding of complex spatial and densitometric relationships. The complexity and sophistication of these imaging techniques has steadily improved in the last few years and there are many situations in which the static display of 3D models contains more information than can be easily appreciated. Animating a sequence of these displays adds another dimension to the visualization, understanding and communication of 3D data. This paper describes those situations that warrant animations, the techniques necessary to compute them and the results that can be obtained.

Microcomputer-based three-dimensional reconstruction of in situ hybridization autoradiographs

A number of software routines were written for the public domain Macintosh-based video-densitometry program, Image, to facilitate in situ hybridization analysis. These routines utilize fiducial marks drilled in unused portions of the brain to rotate high-magnification images of individual sections so that they may be placed in register. The regions of interest within the registered sections are outlined and intermediate sections interpolated to produce a data set representing a three-dimensional volume. This shell is then filled with the original density data obtained with one or more in situ hybridization probes. The final object can be viewed in various degrees of translucency and examined from different angles or computationally resectioned to yield new information concerning activity changes within the region and relationships between reactive sites. These static images can be collected and rapidly displayed as a movie. These routines have been used in this paper to display the differential hybridization of three different mRNA probes in the hypothalamic paraventricular nucleus.

Analysis of 2-DG autoradiograms using image-averaging and image-differencing procedures for systems-level description of neurobehavioral function

Computer assisted 2-deoxyglucose (2-DG) autoradiography has been used to provide functional maps of areas of altered neural activity related to changes in an animal's behavior or state. The standard procedure for comparison of autoradiograms between different treatment groups has been to take measurement samples from predefined neuroanatomical regions and to average these across brains to attain statistical sensitivity for detecting treatment effects. Unfortunately, when sampling is restricted to predefined areas, important topographic information is lost along with the ability to reveal an unexpected change in neural activity. To preserve the rich topographical detail of metabolic information and to enhance the capacity to uncover novel areas of altered metabolic activity, we have developed a system for averaging entire images from 2-DG autoradiograms and for comparing the average images from two experimental groups by creating an image of differences. This procedure does not rely on sampling only preselected regions, but still allows statistical comparisons between experimental groups. The procedures we describe can be readily and inexpensively adapted for use in individual laboratories and are based on modifications of preexisting image analysis software. We show that, when average and difference images are created using standardized protocols for sectioning brain tissue and editing section images, they are impressively resolved and realistic and can serve as effective topographic descriptions of group differences in neural activity of functional and behavioral relevance.

Regional brain glucose metabolism is altered during rapid eye movement sleep in the cat: a preliminary study

Glucose utilization was measured in 74 brain regions of the cat during states of wakefulness or rapid eye movement (REM) sleep. These data were obtained from intact, unanesthetized animals which were instrumented for objectively measuring states of consciousness. Through a chronically implanted intravenous catheter, the cats received 250 microCi of magnitude of 6-14C glucose during REM sleep (N = 3) or during wakefulness (N = 3). After spending approximately 8 min in REM sleep or in quiet wakefulness, the cats were administered a lethal dose of barbiturate and the brains were removed and processed for autoradiography. The results revealed site-specific changes in glucose metabolism during REM sleep. Significant alterations in glucose use occurred in the thalamus, the limbic system, and specific regions of the pontine reticular formation. These data demonstrate for the first time that during states comprised entirely of REM sleep there are anatomically specific changes in cerebral glucose metabolism. The majority of brain regions exhibiting REM sleep-dependent changes in glucose metabolism either overlapped with regions known to contain cholinergic cell bodies, or with areas that receive prominent cholinergic input.

Image analyzers for bioscience applications

Image analysis systems are becoming more sophosticated, less costly, and very common in research laboratories. Therefore, the bioscience researcher is faced with a bewildering array of choices in establishing an image analysis facility. Critical components and characteristics of commercial image analyzers are discussed. State-of-the-art systems feature a graphical user interface, a powerful operating system (e.g., Microsoft OS/2), 1000 line image acquisition, processing and display, true color imaging, and very flexible scanner interfaces. Such systems are best suited to technically difficult applications, such as ratio fluorescence, or to automated analysis of anatomical features, particularly in stained material. Less powerful image analyzers offer medium resolution, and typically work with monochrome data acquired from video cameras. Such systems are suitable for many bioscience applications, including quantitative autoradiography and routine morphometry.

Assessment of a superparamagnetic iron oxide (AMI-25) as a brain contrast agent

We have applied a superparamagnetic iron oxide formulation (AMI-25, Advanced Magnetics, Inc., Cambridge, MA) to image the cerebral vasculature. Contrast-enhanced images of normal anesthetized rats demonstrated excellent gray/white matter differentiation, consistent with known differences in blood perfusion, and cerebrospinal fluid spaces were clearly seen. Alterations in normal perfusion patterns due to barbiturate anesthesia and ischemia were clearly visible. We propose the use of this agent as an adjunct to MRI for the imaging of conditions with perfusion abnormalities.

Non-invasive in-vivo autoradiographic method to measure axonal transport in serotoninergic neurons in the rat brain

We studied axonal transport of serotoninergic neurons by autoradiography following intravenous administration of alpha-[14C]methyl-L-tryptophan (alpha-[14C]MTrp). Autoradiograms obtained 24 h after intravenous injection of the tracer demonstrated clearly all raphe nuclei and the major ascending pathway, the medial forebrain bundle (MFB). From these autoradiograms it was clear that radioactivity traveling along the MFB had already reached the substantia nigra and ventrolateral geniculate body nuclei, terminal field. The whole route of the MFB was well visualized from an axial cross-section of a three-dimensional display of data. Autoradiograms obtained at 6 h after injection revealed only the caudal part of the MFB but all raphe nuclei were labelled, indicating that the tracer was in the process of being transported, probably as an alpha-methyl-5-hydroxytryptamine, via the MFB. The axonal transport rate was estimated from the brain autoradiograms of 4 rats killed 6 h after injection of the tracer. The mean distance of the tracer transported via the medial forebrain bundle in 4 rats was 3.8 +/- 0.4 (S.D.) mm, which corresponded to the level of the posterior to mid-hypothalamus. The axonal transport rate calculated from this distance from the medial raphe was 0.63 +/- 0.07 mm/h (14 mm/day). There was no significant difference in the axonal transport rate between the right and left side of the MFB.

Calibration of 125I-polymer standards with 125I-brain paste standards for use in quantitative receptor autoradiography

125I-Polymer standards were calibrated by interpolation of their optical densities in [125I]-brain paste standard curves to obtain dpm/mg protein. There was a linear relationship between the calibrated polymer standards and the dpm/mg polymer, as provided by the manufacturer. One dpm/mg polymer was equivalent to 7.34 +/- 0.22 dpm/mg protein. Receptor quantification in selected rat brain areas with comparison to either brain paste or calibrated polymer standards yielded similar results.

The identification of a novel synaptosomal-associated protein, SNAP-25, differentially expressed by neuronal subpopulations

cDNA clones of a neuronal-specific mRNA encoding a novel 25-kD synaptosomal protein, SNAP-25, that is widely, but differentially expressed by diverse neuronal subpopulations of the mammalian nervous system have been isolated and characterized. The sequence of the SNAP-25 cDNA revealed a single open reading frame that encodes a primary translation product of 206 amino acids. Antisera elicited against a 12-amino acid peptide, corresponding to the carboxy-terminal residues of the predicted polypeptide sequence, recognized a single 25-kD protein that is associated with synaptosomal fractions of hippocampal preparations. The SNAP-25 polypeptide remains associated with synaptosomal membrane components after hypoosmotic lysis and is released by nonionic detergent but not high salt extraction. Although the SNAP-25 polypeptide lacks a hydrophobic stretch of residues compatible with a transmembrane region, the amino terminus may form an amphiphilic helix that may facilitate alignment with membranes. The predicted amino acid sequence also includes a cluster of four closely spaced cysteine residues, similar to the metal binding domains of some metalloproteins, suggesting that the SNAP-25 polypeptide may have the potential to coordinately bind metal ions. Consistent with the protein fractionation, light and electron microscopic immunocytochemistry indicated that SNAP-25 is located within the presynaptic terminals of hippocampal mossy fibers and the inner molecular layer of the dentate gyrus. The mRNA was found to be enriched within neurons of the neocortex, hippocampus, piriform cortex, anterior thalamic nuclei, pontine nuclei, and granule cells of the cerebellum. The distribution of the SNAP-25 mRNA and the association of the protein with presynaptic elements suggest that SNAP-25 may play an important role in the synaptic function of specific neuronal systems.

A method of image registration for three-dimensional reconstruction of microscopic structures using an IBAS 2000 image analysis system

Registration of histological tissue sections is a longstanding problem in three-dimensional reconstruction. Our solution is to insert rigid straight narrow birefringent structures namely cactus spines as artificial registration points (ARPs) into the tissue block before embedding in wax or resin. The microscopic image of the tissue section with ARPs in situ is presented to an IBAS 2000 Image Analyser and digitised. Registration is performed in two stages using the ARP nearest to the area to be reconstructed as the principle reference point for alignment. The automatic stage is then used to align the structure under reconstruction. These reconstructions are more accurate than those produced without the use of ARPs.

Purification and characterization of a benzodiazepine-like substance from mammalian brain

An endogenous brain ligand which competes with [3H]-flunitrazepam for the binding to benzodiazepine receptor has been isolated and purified to homogeneity. The purification procedures involve the extraction of the endogenous ligand by homogenizing the brain tissue in water containing various protease inhibitors followed by filtration through a PM 10 membrane (exclusion limit: 10,000-dalton), column chromatographies on Sephadex G-50, Bio-Rad P2 and a series of C18 reverse phase HPLC columns. The purified endogenous ligand was eluted as a single and symmetrical peak monitored at either 220 or 280 nm. Furthermore, the ligand activity coincided with the absorption peak. The purified endogenous ligand is thermostable, insensitive to various peptidases and proteolytic enzymes, resistant to DNAse, RNAse, and carbohydrate enzyme e.g. neuraminidase (EC 3.2.1.18) and acid treatment. It has a major absorption peak at 220 nm and a minor one at 313 nm. The endogenous ligand appears to be quite specific since it only inhibits the binding of ligand to the central type benzodiazepine receptor but not to other receptors, e.g. peripheral type benzodiazepine receptor, alpha 1-adrenoceptor, alpha 2-adrenoceptor, beta-adrenoceptor and muscarinic cholinergic receptor. Furthermore, the inhibition of the receptor binding by the endogenous ligand is enhanced by GABA suggesting that the endogenous ligand is a benzodiazepine receptor agonist. The structure of the endogenous ligand is unknown.

Patterns of 2-deoxyglucose uptake reflect the neural processing of lordosis-inducing somatosensory stimuli in hamsters

Semi-quantitative [14C]2-deoxyglucose (2DG) autoradiography was used to map the neural responses of female hamsters to lordosis-inducing flank stimuli. Specifically, manual stimulation of one flank was used to maintain estrous females in lordosis for 20 min after an IV injection of 200 muCi/kg of 2DG. Hemispheric differences in 2DG uptake then were sought in brain nuclei implicated in the programming of lordosis, or in the mediation of somatosensory or hormonal influences on this response. The responses to lateralized flank stimulation included reliable contralateral elevations in 2DG uptake in the ventral posterior lateral nucleus of the thalamus (VPL), the dorsal mesencephalic central gray (dCG), and the tectum. Elevated activity on the part of the VPL may not be crucial for lordosis. However, the effects of flank stimulation on 2DG uptake by the dCG and tectum confirm and extend much previous evidence implicating the dorsal midbrain in the mediation of tactile and hormonal effects on sexual responses. For example, these results suggest that somatosensory influences on hamster lordosis are mediated by both the dCG and tectum. In addition, they suggest that these influences are strongly lateralized until at least this stage of sensory processing, leaving for some subsequent element of neural circuitry the task of translating these lateralized inputs into the bilaterally symmetric outputs ultimately required to program the normal, bilaterally symmetric, lordosis response.

Localized metabolic responses to optokinetic stimulation in the brain stem nuclei and the cerebellum investigated with the [14C]2-deoxyglucose method in rats

The localized metabolic effects of monocular optokinetic stimulation to the cerebellar flocculus and brain stem nuclei were measured in pigmented rats. Quantitative [14C]2-deoxyglucose autoradiography was performed on alert rats stimulated with a drum either rotated horizontally in the temporonasal direction (optokinetic group) or kept stationary (control group). The superior colliculus in both groups showed a higher amount of activity on the contralateral side to the stimulated eye than on the ipsilateral side. The dorsal cap of the inferior olive, the nucleus of the optic tract, and the lateral pontine nucleus showed a higher amount of activity on the contralateral side only in the optokinetic group. The nucleus reticularis tegmenti pontis and the ventromedial aspect of the cerebellar paraflocculus showed no lateralized activity in either group. Local glucose utilization rates of both flocculi were significantly enhanced in the optokinetic group. Only in the optokinetic group did the ipsilateral flocculus show a higher local glucose utilization rate than the contralateral flocculus. The most enhanced activity was localized in the middle aspect of the rostrocaudal extent of the ipsilateral flocculus. The activity was greater in the granular layer than in the molecular layer or in the white matter. The pattern of activation in the granular layer was characterized by a patchy appearance in the frontal sections. Serial reconstruction of these sections showed metabolic blobs appearing with intervals of several hundred micrometers.

New high-resolution 2-deoxyglucose method featuring double labeling and automated data collection

A new approach to high-resolution 2-deoxy-D-glucose (2DG) emulsion-autoradiography which combines improved retention of 2DG labeling, staining with immunohistochemical and other specific markers, and automated data collection and analysis of local silver grain and stain densities is described. The Durham et al. (J. Neurosci. 1:519-526, '81) procedure for fixation of 2DG with periodate-lysine-paraformaldehyde (PLP, McLean and Nakane: J. Histochem. Cytochem. 22:1077-1083, '74) was adapted to increase retained label roughly tenfold. Phenobarbital anesthesia is induced 45 minutes after 2DG injection. Barbiturate anesthesia increases brain glycogen (Nelson et al.: J. Neurochem. 15:1271-1279, '68) and presumably increases the incorporation of intracellular 2DG from 2DG-6P into brain glycogen and other molecules (Nelson et al.: J. Neurochem. 43:949-956, '84; Pentreath et al.: Neuroscience 7:759-767, '82). Iodoacetate is added to cold fixative to prevent glycogen breakdown (Cammermeyer and Fenton: Histochemistry 76:339-356, '82). This high-resolution 2DG protocol is directly compatible with many other neuroanatomical techniques. We demonstrate 2DG emulsion autoradiography combined with cytochrome oxidase (CO) histochemistry, markers for axonal pathway tracing, plastic embedding for semithin sections, and immunohistochemical staining for glutamate decarboxylase (GAD). The method should be compatible with antibodies for other antigens and with other neuroanatomical stains. To collect the data directly from microscope slides, a computer-controlled microscope was integrated with image-processing software to eliminate the need for manual counting and scoring of autoradiograms. Regions of interest are scanned automatically at high resolution to map regional labeling and/or stain density. There is excellent correspondence between computer-enhanced two-dimensional maps of the data and the original autoradiograms. Automated counts for five specimens were compared to counts of labeled cells by trained observer. The correlation between the two sets of measurements is high (r = .93). Automated data collection has been generalized to measure regional stain densities on the autoradiographed sections for direct comparison with silver grain density. The method is extremely flexible, especially since new image-processing strategies can be developed in software to extract the desired information from materials labeled by other methods (e.g., HRP).(ABSTRACT TRUNCATED AT 400 WORDS)

Objective image alignment for three-dimensional reconstruction of digital autoradiograms

Autoradiography can generate large quantities of information related to brain metabolism, blood flow, transport across the blood-brain barrier, neurotransmitter-receptor binding and other aspects of brain function. Three-dimensional (3D) reconstruction of digitized autoradiograms provides a mechanism for efficient analysis of function, in detail, over the entire brain. 3D reconstructions of the mean and variance can be obtained by superimposing data from similar experiments, leading ultimately to 3D reconstructions of differences with statistical tests of significance. Image registration is essential for reconstruction, and this article reports two independent algorithms for coronal image alignment that have been successfully implemented in computer programs. The first algorithm superimposes the centroids and principal axes of serial images; the extent and direction of the translation and rotation required for each image is obtained from an analysis of the inertia matrix of that image. The second algorithm matches the edges of structure features in serial-adjacent images, from analyses of the cross-correlation function of each pair of adjacent images. The cross-correlation method requires a great deal more computation than the principal axes method, but it can align damaged sections not reliably treated by the principal axes method. The methods are described in detail, and a quantitative assessment of the registration of non-identical images is considered.

Reduction of cellular energy requirements. Screening for agents that may protect against CNS ischemia

Protection of the brain and spinal cord against ischemia is a goal of vast clinical importance. One approach to this objective is to reduce the tissue's functional activity in order to preserve energy for the metabolic processes that are essential to viability. Experiments to explore ways of reducing function-related energy demands were performed on isolated rabbit retina, a well-characterized model of organized adult mammalian central nervous system (CNS) tissue. The retina was maintained in a nearly physiological state in a miniature "heart-lung" apparatus. Energy metabolism (oxygen consumption and glycolysis) and electrophysiological function (determined by electroretinogram) of the in vitro retina were monitored, and their responses to a series of agents that may reduce energy requirements were determined. Large reversible reductions in O2 consumption, glycolysis, and electrophysiological function were seen in response to mild hypothermia (-3 degrees to -6 degrees C), phenytoin (Dilantin, 100 to 200 mg/kg), chlordiazepoxide (Librium, 200 microM), lithium (1 to 4 mM), Mg++ (6 to 20 mM), strophanthidin (0.15 to 0.25 microM), CO2 (25% to 30%), 2-amino-5-phosphonovaleric acid (APV, 500 microM), amiloride (1 mM), and dantrolene (1 mM). One retina was exposed simultaneously to a combination of six of these agents, which reduced its oxidative and glycolytic metabolism to less than 50% of the control level. The retina recovered metabolic and electrophysiological function after a 2 1/2-hour exposure period. Other agents tested (diphenhydramine, midazolam, nifedipine, nimodipine, and quercetin) had effects on energy metabolism and electrophysiological function that were poorly reversible. Surprisingly little effect was seen in response to general anesthetic agents (thiopental and Althesin) and other CNS depressants (chlorpromazine, ethanol, lidocaine, paraldehyde, valproic acid, and baclofen). The presumed mechanisms through which these agents reduce cellular energy requirements, as well as their potential roles in the treatment of CNS ischemia, are discussed.

Comparison of [14C]glucose and [14C]deoxyglucose as tracers of brain glucose use

Because glucose metabolism and functional activity in brain regions are normally coupled, knowledge of regional brain glucose use can yield insights into regional functional activity. The deoxyglucose (DG) method is widely used for this purpose in experimental animals and humans but questions have arisen regarding its limits and accuracy. Therefore an experiment was designed to compare the DG method on a structure-by-structure basis with another tracer of glucose use, [6-14C]glucose, in normal rats. The cerebral metabolic rates obtained using the two tracers were similar in the telencephalon, but the results using DG were substantially lower in the midbrain and hindbrain (diencephalon, 18%; mesencephalon, 20%; metencephalon, 29%; and myelencephalon, 35%). The primary DG metabolite, DG 6-phosphate (DG-6-P) was found to disappear in a non-uniform manner from the major brain structures: telencephalon less than diencephalon less than mesencephalon = metencephalon less than myelencephalon. Thus a correlation was found between the rate of DG-6-P loss and the extent to which the DG method gave lower values of glucose use. Thus this may explain, at least in part, the discrepancies between the two methods.