Robert B. Page

Regional cerebral and neural lobe blood flow during insulin-induced hypoglycemia in unanesthetized rats

The effects of hypoglycemia on regional cerebral blood flow (rCBF) were studied in awake restrained rats. The rats were divided into three groups consisting of (1) a normoglycemic control group that received only saline, (2) a hypoglycemic group A, which was given insulin 30 min before flow was measured, and (3) a hypoglycemic group B, which was given insulin 90 and 30 min before flow was measured. Regional CBF was measured using 14C-iodoantipyrine. Mean plasma glucose was 8.76 μmol/ml in the control group, 2.63 μmol/ml in hypoglycemic group A, and 1.51 μmol/ml in hypoglycemic group B. Plasma epinephrine and norepinephrine concentrations increased to approximately 375% and 160%, respectively, of control values in hypoglycemic groups A and B. In the hypoglycemic group A, rCBF significantly increased in three brain regions. In the hypoglycemic group B, rCBF increased significantly in all brain regions measured, with the exception of the neural lobe, in which it decreased. The increase in rCBF ranged from 38% in the hypothalamus to 138% in the thalamus. Neural lobe blood flow significantly decreased by 31%. The neural lobe was the only brain region studied that is not protected by a blood-brain barrier. It may be sensitive to changes in the concentration of vasoactive agents in blood, such as epinephrine and norepinephrine.

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.

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.

Three-dimensional reconstruction of median eminence microvascular modules

To test the hypothesis that the median eminence microvasculature has a direct regulatory role in the hormonal communication between the brain and the pituitary gland, it is necessary to determine whether the physical means for such control (e.g. smooth muscle sphincters strategically located in the capillary plexus) actually exists. Our approach is to search for such structures in transmission electron micrographs of thin serial sections of the median eminence. The complexity of these images and the anticipated need to include large numbers of them in the study led us to consider computer reconstruction for this problem. We report here the successful three-dimensional reconstruction of capillary modules using digital image processing techniques for capillary feature detection/extraction, for construction of montages (mosaics) of overlapping images of the same section, and for automatic image registration by two independent methods without the use of fiducial marks. These tasks have been performed manually in nearly all the published neurobiological reconstructions; here they are performed by programs using only the mathematical properties of the images. Methods like those described here provide the only practical means for executing large scale reconstructions and gaining significant new information about the regulation of blood flow in this region of the brain.

Ependymal Alterations in Hydrocephalus

The brain is a hollow organ. Its cavities, the cerebral ventricles, are filled with cerebrospinal fluid (CSF), which resembles brain extracellular fluid.18, 60a Ventricular CSF has two sources. The primary site of ventricular fluid formation is the choroid plexus.12 At this site, CSF is actively secreted by choroid plexus cells into the ventricular cavities.12, 18, 94, 98 A second source of ventricular CSF is the brain extracellular space. Extracellular fluid reaches the ependymal lining by diffusion and by bulk flow, and it passes between adjacent ependymal cells to enter the ventricular cavities.11, 30 Ventricular CSF is actively pumped by arterial pulsations within the choroid plexus4 and moves by bulk flow from the lateral ventricles to the third ventricle (where more CSF may be added), through the aqueduct of Sylvius, to the fourth ventricle, and thence into the subarachnoid space 14, 23 CSF is then carried over the cerebral hemispheres and resorbed through arachnoid villi lying in the convexity dura.14 As is the case with any hollow viscus (for example, the intestine or bladder), obstruction of the flow of its contents is accompanied by proximal dilatation of its lumen.15 In the brain, this condition is termed hydrocephalus.

Aerobic Glycolysis by the Pituitary Gland In Vivo

Abstract: Arteriovenous differences of glucose, lactate, and pyruvate were measured across the pituitary glands of overnight‐fasted female pigs to determine whether net uptake of glucose occurred, and if so, whether it was oxidized or converted to lactate. Arteriovenous differences were also measured across a portion of the cerebral cortex as a control. Cerebral cortex oxidized 84% of the glucose taken up, but this was not true in the pituitary gland, where glucose was almost completely converted to lactate. The arteriovenous difference across the pituitary gland was 0.61 μmol/ml for glucose while the veno‐arterial differences of lactate and pyruvate were 1.0 and 0.07 μmol/ml, respectively. The results indicated that little net oxidation of glucose either by the Krebs cycle or the pentose phosphate pathway occurs in the pituitary gland in vivo. Estimates of the amount of energy released from aerobic glycolysis indicate that, unless the requirements of the neurohypophysis are very different from those in the rest of brain, very little energy could be derived from the metabolism of glucose.

Handbook of Innovation and Standards

Innovation and standardization might seem polar opposites, but over many years various scholars have noted close connections between the two. This Handbook assembles a broad range of thinking on this subject, with contributions from several disciplinary perspectives by over 30 leading scholars and experienced practitioners. Collectively, they summarize and synthesize the existing body of knowledge – theory and evidence – pertaining to standards and innovation, and provide insights into how this knowledge can be useful to scholars, industrial strategists, policy-makers and standards practitioners.

Radionuclide blood flow studies before and after gelfoam embolization of intracranial meningiomas.

Radionuclide blood flow studies were employed to evaluate the success or failure of preoperative Gelfoam embolization in two patients with intracranial meningiomas. In both cases, the initial radionuclide blood flow study showed tumor visualization during the arterial phase. Immediately following the embolization procedure, the radionuclide blood flow study showed no visualization of the meningioma during the arterial phase, indicating a successful embolization procedure in preparation for removal of the tumor in a relatively bloodless field.