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A J Hansen

Publications and source records attributed to A J Hansen.

At least 37 records · Page 2Linked to original sources
PubMed1997

HNF1 alpha activates the rat UDP glucuronosyltransferase UGT2B1 gene promoter.

The rat UDP glucuronosyltransferase UGT2B1 is expressed mainly in the liver where it glucuronidates steroids and environmental toxins and carcinogens. A region between -42 and -55 bp upstream from the UGT2B1 gene transcription start site was previously identified as sharing sequence similarity with the hepatocyte nuclear factor 1 (HNF1) consensus binding site. In this study, the importance of this region in the regulation of the UGT2B1 gene was confirmed by functional and DNA binding assays. A minimal UGT2B1 gene promoter containing the putative HNF1 binding site was fused to the CAT reporter gene and transfected into HepG2 cells. Only low levels of CAT activity were detected. This activity was increased 50-fold when an HNF1 alpha expression vector was co-transfected with the UGT2B1 promoter CAT construct but was not altered when a HNF1 beta expression vector was used. A UGT2B1 promoter construct with the HNF1-like region deleted was not activated by either co-transfected HNF1 expression vector. DNase 1 footprinting and gel-shift analysis demonstrated that nuclear proteins present in both HepG2 cells and rat liver bind to the HNF1-like element. The presence of HNF1 alpha in these nuclear proteins that bind to the HNF1-like element was confirmed by supershift analysis with antisera to HNF1 alpha. Specific binding of nuclear proteins to the HNF1-like element was not seen in extracts from three cell lines derived from nonhepatic tissues. These data strongly suggest that the liver-enriched factor HNF1 alpha binds to, and activates, the UGT2B1 gene promoter

Animals↗
PubMed1996

Membrane stiffness and channel function.

Alterations in the stiffness of lipid bilayers are likely to constitute a general mechanism for modulation of membrane protein function. Gramicidin channels can be used as molecular force transducers to measure such changes in bilayer stiffness. As an application, we show that N-type calcium channel inactivation is shifted reversibly toward negative potentials by synthetic detergents that decrease bilayer stiffness. Cholesterol, which increases bilayer stiffness, shifts channel inactivation toward positive potentials. The voltage activation of the calcium channels is unaffected by the changes in stiffness. Changes in bilayer stiffness can be predicted from the molecular shapes of membrane-active compounds, which suggests a basis for the pharmacological effects of such compounds.

Calcium Channels↗
PubMed1996

Is calcium accumulation post-injury an indicator of cell damage?

It is generally agreed that excessive intracellular calcium accumulation is the main culprit for nerve cell damage following brain injury. Many autoradiographic studies of the post-injury brain have demonstrated an accumulation of 45Ca2+ in regions exhibiting neuronal damage. We have recently observed, after cortical contusion trauma [10], that there was a discrepancy between the extent of cell damage and the extent of 45Ca2+ in autoradiograms; rather the distribution of 45Ca2+ followed that of serum proteins. In addition 45Ca2+ was also observed in white matter, which had no signs of damage. We tested the hypothesis that 45Ca2+ accumulation was coupled to the presence of protein by directly injecting albumin into the brain cortex. There was a highly significant correlation between the content of 45Ca2+ and of albumin as measured by ELISA. A similar pattern was found after a cortical freeze-lesion in the contralateral hemisphere. However, in the ipsilateral hemisphere where cell damage was observed, the relation broke down and calcium accumulated in excess. We conclude that calcium accumulation in the brain is not only the result of cell damage but also the presence of calcium-binding proteins, e.g. albumin.

Animals↗
PubMed1996

Calcium movements in traumatic brain injury: the role of glutamate receptor-operated ion channels.

Ion-selective microelectrodes were used to study acute effects of N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy- 5-methyl-4-isoxazole (AMPA) receptor blockade on posttraumatic calcium disturbances. An autoradiographic technique with 45 Ca2+ was used to study calcium disturbances at 8, 24, and 72 h. Compression contusion trauma of the cerebral cortex was produced by a 21-g weight dropped from a height of 35 cm onto a piston that compressed the brain 2 mm. Pre- and posttrauma interstitial [Ca2+] ([Ca2+]e) concentrations were measured in the perimeter, i.e., the shear stress zone (SSZ) and in the central region (CR) of the trauma site. For the [Ca2+]e studies the animals were divided into controls and groups pretreated with dizocilipine maleate (MK-801) or with 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[F]quinoxaline (NBQX). In all groups, [Ca2+]e decreased from pretrauma values of approximately 1 mM to posttraumatic values of 0.1 mM in both the CR and the SSZ. This was followed by a slow restitution toward pretraumatic levels during the 2-h observation period. There was no significant difference in recovery pattern between controls and pretreated animals. Accumulation of 45Ca2+ and serum proteins was seen in the entire SSZ, while neuronal necrosis was confined to a narrow band within the SSZ. The CR was unaffected apart from occasional eosinophilic neurons and showed no accumulation of 45Ca2+. Posttraumatic treatment with MK-801 or NBQX had no obvious effect on neuronal injury in the SSZ. We conclude that (a) acute [Ca2+]e disturbances in compression contusion brain trauma are not affected by blockade of NMDA or AMPA receptors, (b) 45Ca2+ accumulation in the SSZ reflects mainly protein accumulation due to blood-brain barrier breakdown rather than cell death, and (c) acute cellular Ca2+ over-load per se does not seem to be a major determinant of cell death after cerebral trauma in our model.

Animals↗
PubMed1995

Changes in N-acetyl-aspartate content during focal and global brain ischemia of the rat.

N-Acetyl-aspartate (NAA) is almost exclusively localized in neurons in the mature brain and might be used as a neuronal marker. It has been reported that the NAA content in human brain is decreased in neurodegenerative diseases and in stroke. Since the NAA content can be determined by nuclear magnetic resonance techniques, it has potential as a diagnostic and prognostic marker. The objective of this study was to examine the change of NAA content and related substances following cerebral ischemia and compare the results to the damage of the tissue. We used rats to study the changes of NAA, N-acetyl-aspartyl-glutamate (NAAG), glutamate, and aspartate contents over a time course of 24 h in brain regions affected by either permanent middle cerebral artery occlusion (focal ischemia) or decapitation (global ischemia). The decreases of NAA and NAAG contents following global brain ischemia were linear over time but significant only after 4 and 2 h, respectively. After 24 h, the levels of NAA and NAAG were 24 and 44% of control values, respectively. The concentration of glutamate did not change, whereas the aspartate content increased at a rate comparable with the rate of decrease of NAA content. This is consistent with NAA being preferentially degraded by the enzyme amidohydrolase II in global ischemia. In focal ischemia, there was a rapid decline of NAA within the first 8 h of ischemia followed by a slower rate of reduction. The reductions of NAA and NAAG contents in focal ischemia were significant after 4 and 24 h, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Halothane anesthesia enhances the effect of dopamine uptake inhibition on interstitial levels of striatal dopamine.

The anesthetic, isoflurane, has been shown to potentiate the ability of the dopamine (DA)-uptake inhibitor, nomifensine, to increase the brain interstitial dopamine level ([DA]e). Since the effect of the more commenly used anesthetic, halothane, on this system is unknown, we determined [DA]e by microdialysis in the striatum of rats, conscious or anesthetized with halothane, in the presence of the more selective DA uptake inhibitor, vanoxerine (GBR 12909), or the DA releaser, d-amphetamine. Basal [DA]e was not changed by halothane. However, in halothane-anesthetized rats, the vanoxerine (3 mg/kg i.v.)-induced DA response increased severalfold compared to the response in conscious rats. The initial peak response to d-amphetamine (1 mg/kg i.v.) did not change, but the late response (1-3 h after injection) was augmented in anesthetized rats. Halothane is believed to increase firing of DA neurons in the substantia nigra and, hence, to release striatal DA. We hypothesize that [DA]e is maintained at a normal level during the increased firing by equally increased activity of the DA transporter. However, when the DA transporter is blocked by vanoxerine, the increased DA release is unimpaired and [DA]e rises.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

Cerebrovascular permeability and brain edema after cortical photochemical infarcts in the rat.

The importance of protein extravasation for the development of vasogenic brain edema is still controversial. We, therefore, assessed the cerebrovascular permeability to serum proteins in relation to the development and resolution of brain edema in a photochemical cortical lesion in the rat. Cortical infarction was induced by in situ thrombosis using an argon laser beam aimed at the exposed parietal bone in animals given rose bengal i.v. The histology and the cerebrovascular permeability to serum proteins were scrutinized from 2 h to 3 weeks after the insult. The presence of serum proteins was demonstrated by an immunoperoxidase technique. The cerebral water content was estimated by specific gravity measurements of the cortical tissue in a kerosene-monobromobenzene gradient column from 2 h to 7 days after infarction. The blood-brain barrier was permeable to proteins at 2 h following the insult and proteins spread into the medial and lateral tissue reaching a maximum at 24 h. The specific gravity did not deviate from control values at 2 h. After 8 h the specific gravity of the lesion decreased with smaller decreases in the immediately adjacent tissue. At 24 h the changes in specific gravities reached a maximum in all regions except the immediately lateral area. The edema was generally worse in tissue medial to rather than lateral to the infarct. The degradation of serum proteins and the resolution of the brain edema followed the same time course with partial resolution of 72 h. By 1 week serum proteins and edema were confined to the central necrotic core. The results suggest a relationship between cerebrovascular permeability and cerebral edema in photochemical cortical infarction.

Animals↗
PubMed1993

Regional changes in interstitial K+ and Ca2+ levels following cortical compression contusion trauma in rats.

Brain trauma is associated with acute functional impairment and neuronal injury. At present, it is unclear to what extent disturbances in ion homeostasis are involved in these changes. We used ion-selective microelectrodes to register interstitial potassium ([K+]e) and calcium ([Ca2+]e) concentrations in the brain cortex following cerebral compression contusion in the rat. The trauma was produced by dropping a 21 g weight from a height of 35 cm onto a piston that compressed the cortex 1.5 mm. Ion measurements were made in two different locations of the contused region: in the perimeter, i.e., the shear stress zone (region A), and in the center (region B). The trauma resulted in an immediate increase in [K+]e from a control level of 3 mM to a level > 60 mM in both regions, and a concomitant negative shift in DC potential. In both regions, there was a simultaneous, dramatic decrease in [Ca2+]e from a baseline of 1.1 mM to 0.3-0.1 mM. Interstitial [K+] and the DC potential normalized within 3 min after trauma. In region B, [Ca2+]e recovered to near control levels within 5 min after ictus. In region A, however, recovery of [Ca2+]e was significantly slower, with a return to near baseline values within 50 min after trauma. The prolonged lowering of [Ca2+]e in region A was associated with an inability to propagate cortical spreading depression, suggesting a profound functional disturbance. Histologic evaluation 72 h after trauma revealed that neuronal injury was confined exclusively to region A. The results indicate that compression contusion trauma produces a transient membrane depolarization associated with a pronounced cellular release of K+ and a massive Ca2+ entry into the intracellular compartment. We suggest that the acute functional impairment and the subsequent neuronal injury in region A is caused by the prolonged disturbance of cellular calcium homeostasis mediated by leaky membranes exposed to shear stress.

Animals↗
PubMed1993

Characterization of cortical depolarizations evoked in focal cerebral ischemia.

Cortical tissue surrounding acute ischemic infarcts undergoes repetitive spontaneous depolarizations. It is unknown whether these events are episodes of spreading depression (SD) elicited by the elevated interstitial K+ ([K+]e) in the ischemic core or whether they are evoked by transient decreases of the local blood flow. Electrophysiologically, depolarization caused by SD or by ischemia (ID) can be distinguished by their characteristic patterns of [K+]e rise: During SD, [K+]e rises abruptly, while in ID, this fast rate of increase is preceded by a slow rate lasting minutes. To characterize the depolarizations, we occluded the right middle cerebral artery (MCA) in rats and inserted two K(+)-sensitive microelectrodes into the cortex surrounding the evolving infarct. Repeated increases in [K+]e arose spontaneously following MCA occlusion. [K+]e increased during these transients from a resting level of 3-6 to 60 mM. One-third of these transient increases in [K+]e were biphasic, consisting of a slow initial increase to 10-12 mM, which lasted for minutes, followed by an abrupt increase, a pattern characteristic of ID. The remaining two-thirds exhibited a steep monotonic increase in [K+]e (< 10 s), characteristic of SD. The duration of the transients was a function of the pattern of [K+]e increase: ID-like transients lasted an average 10.7 +/- 5.1 min, whereas the duration of SD-like transients was 5.7 +/- 3.4 min. Both types of K+ transients occurred in an apparently random fashion in individual animals. A K+ transient was never observed solely at one electrode.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Lactate and postischemic recovery of energy metabolism and electrical activity in the isolated perfused rat brain.

The aim of the present study was to evaluate whether lactate can maintain the energy metabolism and electrical activity of isolated perfused rat brain in the absence of glucose. To exhaust cerebral glucose stores and simultaneously raise endogenous lactate, complete ischemia was induced. After ischemia, when a glucose-free perfusate was supplied, restoration of interstitial potassium (Ke+), cortical discontinuous current (DC) potential, electroencephalogram (EEG) activity, and ATP and phosphocreatine (PCr) was not significantly different from postischemic recovery findings when a glucose-containing perfusate was used. In the group receiving glucose-free perfusate, postischemic application of 1 mM iodoacetic acid did not inhibit the recovery of electrical activity, Ke+, or DC potential. After recovery of Ke+ in glucose-free reperfusion, a 20-30-Hz EEG pattern appeared and was maintained for about 20 min followed by disappearance of spontaneous electrical activity. An abrupt increase of Ke+, a steep negative DC shift, and a substantial decrease of ATP and PCr occurred after about 22 min of reperfusion. During the first 5 min of glucose-free reperfusion, consumption of lactate was significantly higher (0.89 mumol/g wet weight/min) than during reperfusion with medium containing glucose (0.41 mumol/g ww/min). Increasing amounts of tissue lactate prolonged maintenance of electrical function in glucose-free reperfusion. This correlation could not be found for free fatty acids. In conclusion, after a few minutes of ischemia, the brain is able to recover cellular ion transport and electrical activity without a supply of glucose, preferentially by combustion of lactate accumulated in brain tissue. This mechanism is only useful during a limited time period until the lactate accumulated during ischemia is combusted.

Animals↗
PubMed1992

The effect of glutamate receptor blockade on anoxic depolarization and cortical spreading depression.

We examined the effect of blockade of N-methyl-D-aspartate (NMDA) and non-NMDA subtype glutamate receptors on anoxic depolarization (AD) and cortical spreading depression (CSD). [K+]e and the direct current (DC) potential were measured with microelectrodes in the cerebral cortex of barbiturate-anesthetized rats. NMDA blockade was achieved by injection of (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate [MK-801; 3 and 10 mg/kg] or amino-7-phosphonoheptanoate (APH; 4.5 and 10 mg/kg). Non-NMDA receptor blockade was achieved by injection of 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)quinoxaline (NBQX; 10 and 20 mg/kg). MK-801 and APH blocked CSD, while NBQX did not. In control rats, the latency from circulatory arrest to AD was 2.1 +/- 0.1 min, while the amplitude of the DC shift was 21 +/- 1 mV, and [K+]e increased to 50 +/- 6 mM. All variables remained unchanged in animals treated with MK-801, APH, or NBQX. Finally, MK-801 (14 mg/kg) and NBQX (40 mg/kg) were given in combination to examine the effect of total glutamate receptor blockade on AD. This combination slightly accelerated the onset of AD, probably owing to circulatory failure. In conclusion, AD was unaffected by glutamate receptor blockade. In contrast, NMDA receptors play a crucial role for CSD.

2-Amino-5-phosphonovalerate↗
PubMed1992

Brain interstitial volume fraction and tortuosity in anoxia. Evaluation of the ion-selective micro-electrode method.

The micro-electrode method for determination of interstitial volume fraction (alpha) (Nicholson & Phillips 1981), was evaluated. The extracellular marker, tetramethylammonium+, is iontophoretically ejected from a micropipette and the change in concentration measured at a distance by an ion-sensitive micro-electrode and fitted to a diffusion equation. We used suspensions of human red blood cells as a model system and found that the values of alpha determined by this method and by haematocrit measurement were linearly correlated (r = 0.94) and not significantly different. The micro-electrode method was used to characterize the interstitial space in rat brain cortex during normal conditions and during arrest of blood flow supply. Transport of solutes in interstitial space is governed by two characteristics, the interstitial volume fraction and the tortuosity factor. During control conditions, the interstitial volume fraction was 0.18 +/- 0.02 (mean +/- SEM), whereas it decreased to 0.07 +/- 0.01 in ischaemia. The tortuosity factor was 1.40 +/- 0.05 in controls and increased to 1.63 +/- 0.09 during ischaemia. Our measurements support the validity of the micro-electrode method (Nicholson & Phillips 1981) and demonstrate that arrest of blood supply changes interstitial diffusional characteristics of brain cortex mainly by diminishing the size of the interstitial diffusional space.

Animals↗
PubMed1991

Transcriptional regulation of the chicken CYP2H1 gene. Localization of a phenobarbital-responsive enhancer domain.

The mechanism by which the drugs phenobarbital and 2-allyl-2-isopropylacetamide induce levels of chicken cytochrome P-450 (CYP) mRNAs has been investigated in primary hepatocyte cultures from 17-day-old chick embryos. It has been demonstrated that three CYP mRNAs of 3.5, 2.5, and 2.2 kilobases (kb) are strongly induced by phenobarbital in primary hepatocytes, as found previously in chick embryo liver in ovo (Hansen, A. J., Elferink, L. A., and May, B. K. (1989) DNA (NY) 8, 179-191), and that, at least for the 3.5-kb mRNA, this is predominantly a result of enhanced transcription of the corresponding gene, CYP2H1. Transient transfection assays were carried out in primary cultures using constructs containing different lengths of CYP2H1 gene 5'-flanking sequence fused to the reporter chloramphenicol acetyl-transferase (CAT) gene. These experiments established that cis-acting elements located in the first 0.5 kb of the CYP2H1 gene 5'-flanking region direct high basal expression of the CAT gene, but do not mediate phenobarbital inducibility. When constructs containing more than 1.1 kb of CYP2H1 gene 5'-flanking sequence were examined, phenobarbital induction of CAT expression was observed, and a drug-responsive domain between positions -5.9 and -1.1 kb was identified. This domain has the properties of an enhancer, since it is able to confer phenobarbital responsiveness to the enhancerless SV40 promoter when tested in either orientation or at different distances from the promoter. The enhancer domain also responds to 2-allyl-2-isopropylacetamide, but whether the action of the two drugs is mediated by a single nuclear receptor interacting with common DNA elements in the domain remains to be established.

Animals↗
PubMed1991

Distribution of single-channel conductances in cultured rat hippocampal neurons.

1. The nonhomogeneous spatial distribution of ionic channels in neurons has been implied from intracellular recordings at somatic and dendritic locations. These reports indicate that Na- and Ca-dependent regenerative currents are distributed differently throughout the neuron. Although a variety of K conductances and a noninactivating Na conductance have been described in intracellular studies, little is known about the spatial distribution of inward and outward currents throughout different regions of the neuron. 2. We recorded from cell-attached patches from cultured hippocampal cells from 1-day-old rats. The cells were cultured for 3-21 days. The spatial distribution of a variety of ionic channels was determined by comparing the conductances from somatic and dendritic membranes. Single-channel currents obtained from cell-attached patches were identified by the time course of ensemble (averaged) responses, voltage dependence, and the effect of channel blocking agents. 3. We consistently observed that only the rapidly inactivating inward current was localized to the soma. The other channel types that we studied, including an inward noninactivating, delayed rectifier and transient A-type currents, were observed in both the somatic and dendritic regions. 4. We suggest that the distribution of ionic conductances that we have observed may be functional in limiting excitability during development of neurons.

Animals↗
PubMed1990

[Risk factors in home accidents among preschool children].

The present investigation is part of an investigation concerning preschool children's accidents at home. A total of 3,011 homes with preschool children were examined with the object of reducing the number of accidents involving preschool children. Selected risk factors were registered (falls, burns, poisoning) responsible for accidents to preschool children in their homes and this information was compared with information about the type of housing, district and the social status. The investigation revealed that 30% of the homes had "dangerous" windows, 30% had taps which could be swung out over free floor space and 42% did not have special electric safety main switches. Articles for cleaning, medicine and poisons were only stored in locked cupboards in 2.5 and 8% of the homes, respectively. These circumstances were more common in flats than in one-family homes. No significant differences were found between the physical risk factors chosen in the present investigation between the individual social status groups. Prevention of children's accidents in the home consists of increased information to families with children, to architects and manufacturers and increased attention to safety in the home by legislation and guidelines.

Accidental Falls↗
PubMed1990

2,3-Dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline: a neuroprotectant for cerebral ischemia.

2,3-Dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX) is an analog of the quinoxalinedione antagonists to the non-N-methyl-D-aspartate (non-NMDA) glutamate receptor. NBQX is a potent and selective inhibitor of binding to the quisqualate subtype of the glutamate receptor, with no activity at the NMDA and glycine sites. NBQX protects against global ischemia, even when administered 2 hours after an ischemic challenge.

Animals↗