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.

Proton nuclear magnetic resonance spectroscopy unambiguously identifies different neural cell types

Proton nuclear magnetic resonance (1H NMR) spectroscopy is a noninvasive technique that can provide information on a wide range of metabolites. Marked abnormalities of 1H NMR brain spectra have been reported in patients with neurological disorders, but their neurochemical implications may be difficult to appreciate because NMR data are obtained from heterogeneous tissue regions composed of several cell populations. The purpose of this study was to examine the 1H NMR profile of major neural cell types. This information may be helpful in understanding the metabolic abnormalities detected by 1H NMR spectroscopy. Extracts of cultured cerebellar granule neurons, cortical astrocytes, oligodendrocyte-type 2 astrocyte (O-2A) progenitor cells, oligodendrocytes, and meningeal cells were analyzed. The purity of the cultured cells was > 95% with all the cell lineages, except for neurons (approximately 90%). Although several constituents (creatine, choline-containing compounds, lactate, acetate, succinate, alanine, glutamate) were ubiquitously detectable with 1H NMR, each cell type had distinctive qualitative and/or quantitative features. Our most unexpected finding was a large amount of N-acetyl-aspartate (NAA) in O-2A progenitors. This compound, consistently detected by 1H NMR in vivo, was previously thought to ne present only in neurons. The finding that meningeal cells have an alanine:creatine ratio three to four times higher than astrocytes, neurons, or oligodendrocytes is in agreement with observations that meningiomas express a higher alanine:creatine ratio than gliomas. The data suggest that each individual cell type has a characteristic metabolic pattern that can be discriminated by 1H NMR, even by looking at only a few metabolites (e.g., NAA, glycine, beta-hydroxybutyrate).(ABSTRACT TRUNCATED AT 250 WORDS)

Applications of magnetic resonance spectroscopy and diffusion-weighted imaging to the study of brain biochemistry and pathology

The first practical demonstration that nuclear magnetic resonance (NMR) spectroscopy could be applied to the study of brain biochemistry in vivo came in 1980, with the studies of the rat brain using a surface coil. Since then the technique has been rapidly and extensively developed into a versatile, non-invasive tool for the investigation of various aspects of brain biochemistry, physiology and disease. NMR is non-destructive and can be used to examine a wide variety of samples, ranging from localized regions within the whole brain in humans or animals, through tissue preparations (perfused organ, tissue slices and homogenates), to isolated cells and aqueous solutions, such as tissue extracts. 31P and 1H NMR spectra deriving from endogenous compounds of the brain in situ allow assessment of tissue metabolites and provide information about high-energy phosphates, lactate, certain amino acids, intracellular pH and ionic concentrations. Exogenous substrates or probes labelled with stable isotopes can also be introduced into the brain and used to monitor metabolism. Animal models of brain diseases have given some impetus to rapid progress in clinical NMR spectroscopy and also magnetic imaging techniques. The purpose of this article is to highlight the type of information available from these NMR techniques, and to present this in a neuroscience context, emphasizing the biochemical, physiological and pathological information that can be obtained using these methods.

NMR spectroscopy: current status and future possibilities

Nuclear magnetic resonance (NMR) spectroscopy is now established as a non-invasive method of studying metabolism in living systems, ranging from cellular suspensions to man. With respect to clinical applications, recent developments include the successful implementation of new techniques for spatial localisation, and in particular the acquisition of excellent 1H spectra from selected regions of the human brain. Localised 1H spectroscopy opens the way to monitoring a wide range of compounds that are inaccessible to 31P NMR, and should add considerably to the information that is available from 31P studies. NMR spectroscopy does, however, have its limitations, which arise primarily from the fact that it is an insensitive technique. This lack of sensitivity limits the spatial resolution for metabolic studies, and means that metabolites must be present at fairly high concentrations in order to produce detectable signals. In this article, we illustrate the scope and limitations of NMR spectroscopy by describing a few examples of studies undertaken on animals and humans.

Lugol's iodine dye-enhanced endoscopy in patients with cancer of the oesophagus and head and neck

Lugol's iodine dye indicates the presence of unsuspected early oesophageal cancers during endoscopy at which such cancers fail to show the characteristic black colour change. We evaluated Lugol's iodine dye-enhanced endoscopy in 17 patients with oesophageal cancer. In a further 37 patients with head and neck cancer we examined the use of Lugol's iodine since these patients have a 29% risk of synchronous oesophageal cancer. The oesophagus was sprayed with Lugol's iodine (1.5%) during endoscopy. Any areas not turning black were biopsied. In 13 patients with oesophageal cancer discrete areas beyond the macroscopically obvious primary tumour showed no change in colour. Biopsy revealed cancer in all cases. Six synchronous cancers were found in the head and neck group, one of which was identified only by the use of Lugol's iodine. Lugol's iodine augmented the information gained about the oesophageal mucosa during endoscopy. It revealed unsuspected cancer which altered the management of patients with primary oesophageal cancer as well as those with head and neck cancer. We recommend the routine use of Lugol's iodine-enhanced endoscopy for surveillance of all 'at risk' oesophageal cases.

Orbital infection secondary to sinusitis in children: diagnosis and management

A series of 18 children with orbital infection secondary to sinusitis is described. The presenting symptoms were headache and periorbital swelling but it was found to be impossible to determine the stage of the orbital infection on clinical grounds. CT scanning can accurately identify the presence of a sub-periosteal abscess but both axial and coronal sections may be needed to diagnose abscesses in the superomedial portion of the orbit. Cellulitis may be managed by antibiotic treatment alone, but if an abscess is present it should be drained immediately with a formal ethmoidectomy to decompress the orbit if there is any evidence of reduced visual acuity.

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.

Endoplasmic reticulum: the major contributor to the PDE peak in hepatic 31P-NMR spectra at low magnetic field strengths

31P-NMR spectra of liver in vivo, subcellular fractions and model systems were acquired in order to characterise further the hepatic phosphodiester peak seen at low magnetic field strengths previously shown to be predominantly due to phospholipid bilayers. The data obtained in this study in vitro suggested that the phospholipid membranes of the endoplasmic reticulum provide the dominant contribution to this phosphodiester peak. Support for this hypothesis was provided by experiments on rats. Phenobarbitone, which is known to induce proliferation of the endoplasmic reticulum produced a considerable increase in intensity of the phosphodiester peak in liver spectra in vivo.

Multiple primary cancers in Hong Kong Chinese patients with squamous cell cancer of the head or neck

BACKGROUND

The risk of multiple primary tumors in the head and neck area is higher than that in other areas of the body.

METHODS

A total of 573 patients with squamous cell carcinoma of the head or neck were studied prospectively during a 4.5-year period to determine the incidence of associated synchronous and metachronous second primary carcinoma.

RESULTS

Multiple primary carcinoma was found in 2.4% of these patients (69% with synchronous primary tumors). Sixty-three percent of all second primary tumors occurred in the esophagus.

CONCLUSIONS

This report emphasizes the importance of esophagoscopy in the initial assessment of patients with squamous cell carcinoma of the head or neck.

Necrotizing fasciitis of the face without significant trauma

Necrotizing fasciitis is a rare but well recognized clinical entity which most often occurs on the trunk, perineum or legs following surgery or trauma. The condition is much less common in the head and neck and it is particularly uncommon in the midface/periorbital region. In almost all the cases occurring in the neck the condition follows obvious dental or oropharyngeal sepsis and in all the cases of the scalp there is a history of previous surgery or trauma. However, necrotizing fasciitis of the midface/periorbital region may lack any obvious traumatic aetiology or may follow relatively minor trauma. The diagnosis in these cases may not be suspected and treatment may be delayed with fatal consequences. Treatment by wide excision of all affected skin can lead to disastrous cosmetic consequences in facial disease and it is suggested that disease control can be achieved by raising wide based skin flaps with excision of the underlying necrotic tissue. The flaps are then returned onto normal muscle with much improved cosmetic results. This paper discusses the diagnosis and treatment of patients with necrotizing fasciitis of the face which has arisen without significant trauma.

Regulated expression of monocyte chemoattractant protein-1 in normal human osteoblastic cells

An influx of monocytes is observed in many different physiological and pathophysiological states, including bone remodeling and injury. These cells appear at early stages of bone formation and repair and persist throughout the later stages. In experiments described here, unstimulated normal human osteoblastic cells did not produce detectable levels of monocyte chemotactic activity. However, interleukin-1 (IL-1)-stimulated normal human osteoblastic cells produced a chemoattractant that is similar to monocyte chemoattractant protein-1 (MCP-1) at the levels of mRNA expression, protein production, and chemotactic activity. Northern blot analysis indicates that IL-1 elicits a dose-dependent increase in MCP-1 mRNA in normal human osteoblastic cells. Two proteins of M(r) 9,000 and M(r) 13,000 were specifically immunoprecipitated with MCP-1 antiserum from IL-1-stimulated normal human osteoblastic cells. Monocyte chemotactic activity from IL-1-treated cells was blocked by MCP-1 antiserum. These studies establish that normal human osteoblastic cells can be induced to produce monocyte chemoattractants and that this is accounted for by the induced expression of MCP-1.

Specific expression of N-acetylaspartate in neurons, oligodendrocyte-type-2 astrocyte progenitors, and immature oligodendrocytes in vitro

To test the specificity of N-acetylaspartate (NAA) as a neuronal marker for proton nuclear magnetic resonance (1H NMR) spectroscopy, purified and characterized cultured cells were analyzed for their NAA content using both 1H NMR and HPLC. Cell types studied included cerebellar granule neurons, type-1 astrocytes, meningeal cells, oligodendrocyte-type-2 astrocyte (O-2A) progenitor cells, and oligodendrocytes. A high concentration of NAA was found in extracts of cerebellar granule neurons (approximately 12 nmol/mg of protein), whereas NAA remained undetectable in purified type-1 astrocytes, meningeal cells, and mature oligodendrocytes. However, twice the neuronal level of NAA was found in O-2A progenitors grown in vitro. In addition significant levels of NAA were also detected in cultures of immature oligodendrocytes. Our data partly support previous suggestions that NAA may be a useful neuronal marker for 1H NMR spectroscopic examination of the adult brain. However, they also raise the further possibility that alterations of NAA associated with some specific brain disorders, particularly disorders seen in newborn and young children, may reflect abnormalities in the development of oligodendroglia or their precursors.

Random PCR mutagenesis screening of secreted proteins by direct expression in mammalian cells

We have developed a general method for screening randomly mutagenized expression libraries in mammalian cells by using fluorescence-activated cell sorting (FACS). The cDNA sequence of a secreted protein is randomly mutagenized by PCR under conditions of reduced Taq polymerase fidelity. The mutated DNA is inserted into an expression vector encoding the membrane glycophospholipid anchor sequence of decay-accelerating factor (DAF) fused to the C terminus of the secreted protein. This results in expression of the protein on the cell surface in transiently transfected mammalian cells, which can then be screened by FACS. This method was used to isolate mutants in the kringle 1 (K1) domain of tissue plasminogen activator (t-PA) that would no longer be recognized by a specific monoclonal antibody (mAb387) that inhibits binding of t-PA to its clearance receptor. DNA sequence analysis of the mutants and localization of the mutated residues on a three-dimensional model of the K1 domain identified three key discontinuous amino acid residues that are essential for mAb387 binding. Mutants with changes in any of these three residues were found to have reduced binding to the t-PA receptor on human hepatoma HepG2 cells but to retain full clot lysis activity.

Detection of thymosin beta 4 in situ in a guinea pig cerebral cortex preparation using 1H NMR spectroscopy

In the present work we have investigated the macromolecules that contribute to the brain 1H NMR spectrum. The cerebral cortex showed distinct resonances at the uncrowded methyl- and methylene chemical shift scale of the spin-echo 1H NMR spectrum. The peaks at 1.22 and 1.40 ppm (relative to the methyl protons of N-acetyl aspartate at 2.02 ppm) arise from cerebral macromolecules without evidence for co-resonances from low molecular weight metabolites as shown by the spin-spin relaxation decays of these resonances. In addition to these NMR signals, peaks at 0.9 and 1.7 ppm from macromolecules were detected. These resonances are from proteins, and we have identified the polypeptides that contributed to the 1H NMR peaks. Two proteins that were present at concentrations of 250 and 350 micrograms/g of dryed tissue showed 1H NMR spectra that resembled the macromolecular pattern in the cerebral 1H NMR spectrum. They were identified as thymosin beta 4 and histone H1, respectively. Thymosin beta 4 was present in soluble high speed cytoplasmic fraction and in P2 pellet, whereas histone H1 was detected in nuclear enriched fraction. A chemical shift-correlated two-dimensional 1H NMR spectrum of thymosin beta 4 in vitro revealed a coupling pattern that matched the macromolecule in the cerebral cortex which we have previously noted (Kauppinen R. A., Kokko, H., and Williams, S. R. (1992) J. Neurochem. 58, 967-974). On the basis of both one- and two-dimensional NMR evidence, subcellular distribution and high concentration, we assign the 1H NMR signals at 0.9, 1.22, 1.40, and 1.7 ppm in the cerebral cortex to thymosin beta 4.

T2- and diffusion-weighted magnetic resonance imaging of a focal ischemic lesion in rat brain

We sought to evaluate the application of T2-weighted and diffusion-weighted magnetic resonance imaging techniques in the study of a focal ischemic lesion in the rat brain.

Unilateral cortical infarcts were induced using the photosensitive dye rose bengal and 560 nm light irradiation. Magnetic resonance images were recorded from a total of 11 rats at selected intervals from 1.5 hours to several days after induction of the lesion. Parallel experiments were performed in which Evans blue dye was injected into the lesioned animals either immediately after lesion induction (n = 11) or 1 hour before the animals were killed (n = 11). The second procedure was designed to show regions of blood-brain barrier permeability to plasma proteins at the time of sacrifice, whereas the first procedure showed the accumulation and subsequent dispersion of plasma protein following disruption of the blood-brain barrier.

Regions of the cortex highlighted by the T2-weighted images corresponded well to the pattern of dye staining seen from the first procedure while the diffusion-weighted images showed visual correspondence with the staining pattern obtained using the second procedure.

These results illustrate the complementary use of T2-weighted and diffusion-weighted magnetic resonance imaging in discerning the pathophysiology of developing lesions.

Perfusion and diffusion MR imaging

Diffusion-weighted images of the rat brain were obtained using the pulsed-gradient spin-echo method. An attempt was made to extract perfusion-related parameters from signal intensity data taken from the caudate-putamen region of the images, by using a nonlinear least-squares calculation to fit the Le Bihan biexponential expression (Le Bihan et al., Radiology, 168, 497 (1988)) to the data. The perfusion-related parameters could not be obtained with sufficient accuracy to be useful, although the perfusion-weighted images appear to contain meaningful qualitative information. An analysis of the perfusion model is presented and shows why the Le Bihan pseudo-diffusion coefficient is particularly difficult to measure with reasonable accuracy.

Detection of mobile proteins by proton nuclear magnetic resonance spectroscopy in the guinea pig brain ex vivo and their partial purification

Proton nuclear magnetic resonance (1H NMR) spectroscopy was used to study metabolites of the brain cortex ex vivo. The superfused brain cortex preparation was judged to be metabolically viable on the basis of the 31P NMR spectrum (intracellular pH of 7.23 +/- 0.03 and phosphocreatine/ATP ratio of 1.21 +/- 0.09). Using 1H NMR a group of previously unidentified signals was detectable at 0.94, 1.22, and 1.40 ppm with a water-suppressed spin-echo sequence. These signals had shorter spin-spin relaxation times (51-54 ms) than N-acetylaspartate and lactate (84-93 ms) and also smaller saturation factors, an indication of shorter spin-lattice relaxation times than the latter two low-molecular-weight metabolites. The unidentified signals also displayed homonuclear coupling to other spins in the methine region of the spectrum. Acid extraction of the brain slices or cortex from animals that were killed yielded a mixture of proteins that exhibited NMR properties matching the 1H NMR signals in the brain cortex. The molecular mass of these thermoresistant, "mobile" proteins, which contained proline plus hydroxyproline (9-16% of all amino acids), ranged between 8 and 40 kDa. These "new" assignments of 1H NMR-detectable compounds may influence interpretation of NMR data of some metabolites, as their signals are in the vicinity of the -CH3 1H NMR peaks of lactate and alanine.

Cell and tissue responses of a murine tumour to phthalocyanine-mediated photodynamic therapy

Mice bearing a subcutaneously growing tumour (Colo 26) were injected intravenously with the photosensitiser chloroaluminum sulphonated phthalocyanine (5 mg/kg) 24 h prior to irradiating the tumour with laser light (675 nm; 50mW, 100 J/tumour). Energy status of the tumour, as assessed by the loss of high energy phosphates in the 31P-nuclear magnetic resonance spectra, was altered dramatically following treatment, such that the ATP fell to undetectable levels within 1 h of light irradiation. However, assessment of the clonogenic capacity of neoplastic cells isolated from dissociated tumours showed that these rapid changes in cellular metabolism were not reflected in similar rapid changes in cell viability. Reductions in clonogenic capacity, which fell to less than 0.1% of control values at 24h postirradiation, closely mirrored those resulting from the cessation of vascular perfusion. Evaluation of tumour blood flow, using the technique of hydrogen washout, showed that the treatment protocol evoked a gradual and selective reduction in flow within the tumour resulting in complete vascular stasis by approximately 5 h after treatment. The results indicate that while chloroaluminum sulphonated phthalocyanine-mediated photodynamic therapy caused early metabolic damage in neoplastic cells, loss of viability paralleled the induction of complete inhibition of vascular flow in the tumour.

The extracellular domain of the human interferon gamma receptor interacts with a species-specific signal transducer

At least two species-specific gene products are required for signal transduction by interferon gamma (IFN-gamma). The first is the IFN-gamma receptor, which binds ligand with high affinity in a species-specific manner. The second is an undetermined species-specific signal transducer(s). To determine whether the human IFN-gamma receptor (hIFN-gamma R) interacts directly with this signal transducer(s) and, if so, with what functional domain(s), we constructed expression vectors for the hIFN-gamma R and three hybrid human-murine IFN-gamma receptors. The hybrid receptors contained the extracellular, human IFN-gamma (hIFN-gamma) binding domain of the hIFN-gamma R, either the human or murine transmembrane domain, and either the human or murine intracellular domain. The vectors encoding these receptors were stably transfected into two mouse cell lines, one of which (SCC-16-5) contains a single copy of human chromosome 21. The resulting cell lines were treated with hIFN-gamma, and murine major histocompatibility complex class I antigen expression was analyzed by immunofluorescence flow cytometry. All transfected cell lines lacking human chromosome 21 remained insensitive to hIFN-gamma. However, all four of the IFN-gamma receptors were able to signal when expressed in the cell line containing human chromosome 21. We conclude that the extracellular domain of the IFN-gamma receptor is involved not only in the species specificity of IFN-gamma binding but also in signalling through interaction with an as yet unidentified species-specific factor(s) encoded by a gene(s) on human chromosome 21.

High-affinity binding of PDGF-AA and PDGF-BB to normal human osteoblastic cells and modulation by interleukin-1

Bone has the capacity for repair and regeneration. The repair process is thought to be locally regulated by growth factors. One of the growth factors that potentially plays a significant role in these processes is platelet-derived growth factor (PDGF). Two different PDGF genes have been identified, PDGF-A and PDGF-B, whose gene products give rise to biologically active dimers. We now report that PDGF-AA and PDGF-BB exhibit saturable binding to normal human osteoblastic cells. By Scatchard analysis we estimate that there are approximately 43,000 PDGF-AA binding sites per cell, with a dissociation constant (Kd) of 2.2 x 10(-10)M, and 55,000 high-affinity PDGF-BB binding sites per cell, with a Kd of 1.2 x 10(-10)M. The functional consequence of PDGF binding was also assessed. PDGF-AA and PDGF-BB both stimulated migration of normal human osteoblastic cells and stimulated thymidine incorporation. To gain insight into potential transmodulation of the PDGF response, we investigated the capacity of interleukin-1 beta (IL-1 beta), a cytokine that induces bone resorption, to modulate PDGF binding and PDGF-induced biological activity. IL-1 beta significantly reduced PDGF-AA binding and significantly decreased both PDGF-AA-mediated cell migration and thymidine incorporation. In contrast, IL-1 beta had only a small effect of PDGF-BB binding and PDGF-BB-induced biological activity in normal human osteoblastic cells.

Nondestructive detection of glutamate by 1H nuclear magnetic resonance spectroscopy in cortical brain slices from the guinea pig: evidence for changes in detectability during severe anoxic insults

31P and 1H nuclear magnetic resonance spectroscopy (NMR) was used to study the metabolism of intact superfused cortical brain slices during normoxia and anoxia. Attention was focused on quantification of 1H NMR-detected glutamate by a water-suppressed spin-echo method, using N-acetyl aspartate as an internal concentration reference. To quantify the 1H NMR signals, the spin-spin relaxation times and saturation effects were estimated for given metabolites. In addition, absolute concentrations of metabolites were determined by biochemical methods from acid extracts of the preparations after NMR experiments. Under aerobic conditions, 1H NMR detected 79% of the glutamate determined biochemically from the brain slice extracts. During anoxia in the absence of glucose when a severe energetic failure was evident, both 1H NMR and biochemical assays gave closely matching levels for glutamate. We conclude that in the brain cortex 21% of glutamate is located in an intracellular compartment in which this amino acid does not contribute to the 1H NMR signal. However, during severe anoxia an intracellular reorganisation occurs increasing the detectability of this amino acid neurotransmitter by NMR.

Sequence and functional characterization of the human purine nucleoside phosphorylase promoter

Purine nucleoside phosphorylase (PNP) is a ubiquitously expressed enzyme which contributes to the catabolism and recycling of nucleotides. To characterize the promoter region of the human PNP gene, the nucleotide sequence from a BamHI site located in the 5' untranslated region extending 2237 bp upstream to an XbaI site was determined. The transcriptional start site as determined by primer extension was 119 bp upstream of the coding sequence and consisted of a 5'-CA-3' dimer with A at +1. A TATA box was identified -24 to -29 bp upstream of the transcriptional start site. A CCAAT pentamer sequence in the inverted orientation was present at -51 to -55 bp and two GC rich regions were identified at -68 to -81 bp and -168 to -187 bp. Progressive 5' deletions of the 5' flanking region were fused to the chloramphenicol acetyltransferase (CAT) reporter gene and transient expression measured after transfection of murine NIH/3T3 fibroblasts. A 91 bp promoter (the shortest tested) provided CAT activity at 60% the level of a 216 bp promoter, possibly due to removal of the GC rich region between -168 and -187 bp. Longer promoters resulted in CAT expression at similar or lower levels than the 216 bp promoter indicating that this region contained all of the 5' flanking sequences affecting transcription from the PNP promoter.

Diffusion-weighted imaging of kainic acid lesions in the rat brain

We present T2-weighted and diffusion-weighted images of kainic acid lesions in the rat brain. Our observations show improved image contrast between edematous lesions and unaffected tissue using diffusion-weighted imaging. Furthermore, we show that the anisotropic intensity changes associated with this sequence can be used to highlight white matter tracts and to provide information concerning their orientation in the rat brain.

Measurement of transient cDNA expression in mammalian cells using flow cytometric cell analysis and sorting

Generalized methods for quantitative and sensitive measurement of transient cDNA expression in mammalian cells using flow cytometry (FCM) are described. The techniques are applicable to a wide variety of cDNAs encoding intracellular or cell surface protein products through the use of immunofluorescence- or nonimmunofluorescence-based detection methods. The methods illustrated have been optimized for sensitive detection of transfectants and efficient recovery of the encoding plasmids from the sorted cells. Expression levels and heterogeneities were compared using four methods of DNA transfer in addition to description of a novel method to optimize single copy transfer probabilities by multiparameter analysis. The overall sensitivities are compared by reconstruction and molecular cloning experiments to other methods of selection, such as immunoselection by panning. Through the measurement of multiple heterologous products per cell, or the measurement of multiple epitopes or binding sites per heterologous protein, expression levels on a single cell basis can be measured and correlated with other endpoints for various purposes. The ability to detect and recover rare clones based on a number of single and multiparameter selection criteria should significantly extend the use of transient mammalian cDNA expression methods for applications involving novel FCM-based reporter cDNA assays and for cloning certain rare surface-bound or secreted proteins using FCM.