Identification of ethanolamine in rat and gerbil brain tissue extracts by NMR spectroscopy

Some NMR resonances which have previously been observed but not identified in mammalian brain tissue extracts have been shown to arise from ethanolamine. This conclusion is drawn from a systematic study of the perchloric acid extracts of rodent brain tissue in which several NMR experiments were used to assign the peaks unambiguously. The extraction procedure used in this work gave samples with highly reproducible spectra, and ethanolamine was observed in all our extract samples. A localized increase in the concentration of ethanolamine was seen in the spectra of extracts produced from a cerebral infarct induced by occlusion of the middle cerebral artery in the rat.

Early changes in cerebral sodium distribution following ischaemia monitored by 23Na magnetic resonance imaging

23Na magnetic resonance imaging has been used in this preliminary study to investigate early changes in brain sodium signal intensity during and after cerebral ischaemia in a gerbil model. The total sodium signal in selected brain regions decreased between 15 and 30% within 4 min of the onset of ischaemia, and then remained constant throughout the ischaemic period. The same pattern was observed in the eyes. On reperfusion, there was no significant change in the sodium signal over the first 4 min, but by 8 min the signal intensity had returned to or passed through control levels in all regions measured, with the exception of the eyes. These observations are consistent with the loss and resynthesis of ATP as seen in this model, and may be reflecting the redistribution of tissue sodium resulting from energy failure and recovery.

A sodium magnetic resonance imaging study of acute cerebral ischaemia in the gerbil

23Na magnetic resonance imaging has been used to investigate sodium changes during and after cerebral ischaemia in a gerbil model. The sodium signal decreased within 4 minutes of the onset of ischaemia, and subsequently increased between 4 and 8 minutes after the onset of reperfusion. These observations may be reflecting the redistribution of tissue sodium resulting from energy failure and recovery.

Controllable graded cerebral ischaemia in the gerbil: studies of cerebral blood flow and energy metabolism by hydrogen clearance and 31P NMR spectroscopy

A technique for remotely controlling the degree of carotid artery occlusion in the gerbil model of cerebral ischaemia has been developed. The technique relies on manually adjustable nylon snares around the carotid arteries, in conjunction with a computer-based monitoring system, to control the degree of occlusion. This has allowed us to determine the dependence of energy metabolism (as assessed by 31P NMR spectroscopy) on blood flow in greater detail than was possible in our previous studies. Data obtained show that energy changes first appear at flows of 25-30 mL/100 g/min, while at flows below 20 mL/100 g/min there is a major derangement of energy metabolism. The model was used to determine the sensitivity of cerebral energy metabolism to reduced cerebral blood flow under normothermic conditions and in mild hypothermia (30 degrees C). Hypothermia had a protective effect in that energy metabolites were maintained at flows significantly below the normothermic threshold.

Diffusion-weighted imaging studies of cerebral ischemia in gerbils. Potential relevance to energy failure

BACKGROUND AND PURPOSE

Diffusion-weighted magnetic resonance imaging has been shown to be particularly suited to the study of the acute phase of cerebral ischemia in animal models. The studies reported in this paper were undertaken to determine whether this technique is sensitive to the known ischemic thresholds for cerebral tissue energy failure and disturbance of membrane ion gradients.

METHODS

Diffusion-weighted images of the gerbil brain were acquired under two sets of experimental conditions: as a function of cerebral blood flow after controlled graded occlusion of the common carotid arteries (partial ischemia), as a function of time following complete bilateral carotid artery occlusion (severe global ischemia), and on deocclusion after 60 minutes of ischemia.

RESULTS

During partial cerebral ischemia, the diffusion-weighted images remained unchanged until the cerebral blood flow was reduced to 15-20 ml.100 g-1.min-1 and below, when image intensity increased as the cerebral blood flow was lowered further. This is similar to the critical flow threshold for maintenance of tissue high-energy metabolites and ion homeostasis. After the onset of severe global cerebral ischemia, diffusion-weighted image intensity increased gradually after a delay of approximately 2.5 minutes, consistent with complete loss of tissue adenosine triphosphate and with the time course of increase in extracellular potassium. This hyperintensity decreased on deocclusion following 60 minutes of ischemia.

CONCLUSIONS

The data suggest that diffusion-weighted imaging is sensitive to the disruption of tissue energy metabolism or a consequence of this disruption. This raises the possibility of imaging energy failure noninvasively. In humans, this could have potential in visualizing brain regions where energy metabolism is impaired, particularly during the acute phase following stroke.

A survey of the antibacterial activity of some New Zealand honeys

To assess the variation in antibacterial activity of honey a survey was carried out on 345 samples of unpasteurized honey obtained from commercial apiarists throughout New Zealand. Most of the honeys were considered to be monofloral, from 26 different floral sources. The honeys were tested against Staphylococcus aureus in an agar well diffusion assay, with reference to phenol as a standard. Antibacterial activity was found to range from the equivalent of less than 2% (w/v) phenol to 58% (w/v) phenol, with a median of 13.6 and a standard deviation of 12.5. Neither the age of the honey samples nor whether they had been processed by the apiarist was associated with lower activity. However, the difference between floral sources in the antibacterial activity was very highly significant. Kanuka (Kunzea ericoides (A. Rich.) J. Thompson. Family: Myrtaceae), manuka (Leptospermum scoparium J. R. et G. Forst. Family: Myrtaceae), ling heather (Calluna vulgaris (L.) Hull. Family: Ericaceae) and kamahi (Weinmannia racemosa Linn. f. Family: Cunoniaceae) were shown to be sources likely to give honey with high antibacterial activity. When antibacterial activity was assayed with catalase added to remove hydrogen peroxide, most of the honeys showed no detectable antibacterial activity. Only manuka and vipers bugloss (Echium vulgare L. Family: Boraginaceae) honeys showed this type of activity in a significant proportion of the samples. The high antibacterial activity of manuka honey was in many cases due entirely to this non-peroxide component.

Residues flanking the COOH-terminal C-region of a model eukaryotic signal peptide influence the site of its cleavage by signal peptidase and the extent of coupling of its co-translational translocation and proteolytic processing in vitro

The polar, COOH-terminal c-region of signal peptides has been considered to be most important for influencing the efficiency and fidelity of signal peptidase cleavage while the hydrophobic core or h-region appears indispensable for initiating translocation. To identify structural features of residues flanking the c-region that influence the fidelity and efficiency of signal peptidase cleavage as well as co-translational translocation, we introduced six amino acid substitutions into the COOH terminus of the hydrophobic core and seven substitutions at the NH2 terminus of the mature region (the +1 position) of a model eukaryotic preprotein-human pre(delta pro)apoA-II. This preprotein contains several potential sites for signal peptidase cleavage. The functional consequences of these mutations were assayed using an in vitro co-translational translocation/processing system and by post-translational cleavage with purified, detergent-solubilized, hen oviduct signal peptidase. The efficiency of translocation could be correlated with the hydrophobic character of the residue introduced at the COOH terminus of the h-region. Some h/c boundary mutants underwent co-translational translocation across the microsomal membrane with only minimal cleavage yet they were cleaved post-translationally by hen oviduct signal peptidase more efficiently than other mutants which exhibited a high degree of coupling of co-translational translocation and cleavage. These data suggest that features at the COOH terminus of the h-domain can influence "presentation" of the cleavage site to signal peptidase. The +1 residue substitutions had minor effects on the extent of co-translational translocation and processing. However, these +1, as well as h/c boundary mutations, had dramatic effects on the site of cleavage chosen by signal peptidase, indicating that residues flanking the c-region of this prototypic eukaryotic signal peptide can affect the fidelity of its proteolytic processing. The site(s) selected by canine microsomal and purified hen oviduct signal peptidase were very similar, suggesting that "intrinsic" structural features of this prepeptide can influence the selectivity of eukaryotic signal peptidase cleavage, independent of the microsomal membrane and associated translocation apparatus.

Restoration of energy metabolism and resolution of oedema following profound ischaemia

Cerebral ischaemia was produced in 2 groups of gerbils by occlusion of the common carotid arteries for 30 minutes, resulting in cerebral oedema. In group 1 cerebral oedema was measured by specific gravity microgravimetry, and in group 2 brain metabolism and blood flow were measured by 31P and 1H NMR spectroscopy and hydrogen clearance respectively. In group 1 the brain water content did not return to control levels by 180 minutes of reperfusion. Energy metabolism, determined by 31P NMR spectroscopy returned to control by 12 minutes, intracellular pH (pHi) by 20 minutes, and lactate, determined by 1H NMR spectroscopy, by 50 minutes. There was a lag of about 10 minutes before lactate began to be cleared from the brain. We suggest that while pHi is low, Na+/H+ exchange will negate the Na+ extrusion driven by the Na+/K+ ATPase. When pHi approaches normal there will be a net extrusion of Na+, taking osmotic water with it, and presumably with passive washout of lactate. This may be the cause of the initial delay in lactate clearance.

Parallel effects of signal peptide hydrophobic core modifications on co-translational translocation and post-translational cleavage by purified signal peptidase

The length of the hydrophobic core of the bovine parathyroid hormone signal peptide was modified by in vitro mutagenesis. Extension of the hydrophobic core by three amino acids at the NH2-terminal end had little effect on the proteolytic processing of the signal peptide by microsomal membranes. Deletion of 6 of the 12 amino acids in the core eliminated translocation and processing of the modified protein. Deletion of pairs of amino acids across the core resulted in position-dependent inhibition of signal activity unrelated to hydrophobicity but inversely related to the hydrophobic moments of the modified cores. Deletions in the NH2-terminal region of the core were strongly inhibitory for proteolytic processing whereas deletions in the COOH-terminal region had no effect or increased processing when assessed either co-translationally with microsomal membranes or post-translationally with purified hen oviduct signal peptidase. Deletion of cysteine 18 and alanine 19 increased processing, but deletion of cysteine alone or substitution of leucine for cysteine did not increase processing more than deletion of both residues at 18 and 19. Translations of the translocation-defective mutants with pairs of amino acids deleted in a wheat germ system were inhibited by addition of exogenous signal recognition particle suggesting that interactions of the modified signal peptides with signal recognition particle were normal. The position-dependent effects of the hydrophobic core modifications indicate that structural properties of the core in addition to hydrophobicity are important for signal activity. The parallel effects of the modifications on co-translational translocation and post-translational processing by purified signal peptidase suggest that proteins in the signal peptidase complex might be part of, or intimately associated with, membrane proteins involved in the translocation. A model is proposed in which the NH2-terminal region of the hydrophobic core binds to one subunit of the signal peptidase while the other subunit catalyzes the cleavage.

Stable dicentric chromosomes induced by chemical mutagens in L5178Y mouse lymphoma cells

Stable, tandem dicentric chromosomes were discovered in two mutant cell colonies resulting from exposure of L5178Y mouse lymphoma cells to chemical mutagens. These unusual dicentrics were present in all metaphase cells examined from these colonies, even after approximately 65 cell generations in culture. Observation of cells in metaphase and anaphase suggests that the interstitial centromere in these dicentrics is non-functional, and that the terminal centromere is solely responsible for their orderly anaphase segregation.

Chromosome analysis of trifluorothymidine-resistant L5178Y mouse lymphoma cell colonies

Cells from small (sigma) and large (lambda) trifluorothymidine-resistant (TFTr) colonies induced by chemical mutagen treatment of TK+/-L5178Y mouse lymphoma cells were examined for chromosomal abnormalities. Analysis of G-banded metaphase chromosomes from 34 sigma-TFTr colonies revealed that cells from 20 (59%) possessed one or more chromosomal abnormalities. The most frequent (16/20 colonies) abnormality observed in cells from sigma-TFTr colonies involved the addition of extra chromatin to the distal region of one chromosome number 11. In 13 of these 16 colonies, the origin of the chromatin translocated to chromosome number 11 could not be identified; the chromatin was not missing elsewhere in the genome. The remaining three sigma-TFTr colonies with an abnormal chromosome number 11 had apparently whole chromosomes translocated, in tandem, to the distal region of chromosome number 11. Chromosomal abnormalities observed in cells from sigma-TFTr colonies with normal number 11 chromosomes included 2N/4N and 2N/4N/8N mosaicism (two colonies), a Robertsonian translocation involving chromosome 10 and a marker chromosome (one colony), and trisomy 7 (one colony). In most (14/16) sigma-TFTr colonies with structural damage to chromosome number 11, the cells within a colony were heterogeneous in that some possessed chromosomal damage whereas others were apparently normal. Analysis of chromosomes in cells from eight lambda-TFTr colonies revealed one colony in which all cells had a Robertsonian translocation involving chromosomes 1 and 16 plus other structural abnormalities. The chromosomes of cells from the remaining lambda-TFTr colonies were apparently normal.

Effective bone palliation as related to various treatment regimens

Various dose-time treatment plans have been used to obtain long duration pain relief in patients with metastatic bone disease. Very little has appeared in the literature evaluating the relationship of dose and fractionation to initial, delayed and permanent bone pain relief. At the Swedish Hospital Tumor Institute, 152 treatment fields in 110 patients were evaluated, with a clinical follow-up in many of over five years. Those treated at lower total doses with less fractionation achieved the same quality and duration of pain relief as higher doses. Treatment plans also were compared using the Ellis method of nominal standard dose.

Brain-stem abscess in childhood. Case report

✓ A rare case is reported of a solitary abscess of the brain-stem which was suspected clinically, confirmed surgically, and successfully removed. The few reports of similar cases in the literature are reviewed.