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H Schröck

Publications and source records attributed to H Schröck.

At least 19 recordsLinked to original sources
PubMed2001

[Late radiation changes after small volume radiosurgery of the rat brain. Measuring local cerebral blood flow and histopathological studies].

BACKGROUND: The goal of this study was to investigate late effects following stereotactic single fraction and small volume irradiation on cerebral blood flow and histologic alterations in the rat brain parenchyma. MATERIAL AND METHODS: 66 Copenhagen rats, separated into eleven groups of six animals each received single doses of 20, 30, 40, 50 and 100 Gy using a 15 MV linear accelerator. Six rats served as controls. Two cylindrical collimators of 2 mm and 3 mm aperture were used. The diameters of the spherical 80% isodose were 3.7 and 4.7 mm, respectively (Table 1). Irradiation was applied to a predefined area in the right frontal lobe. 19 months after irradiation local cerebral blood flow (LCBF) was measured by the autoradiographic method in one animal of each dose group between 20 and 50 Gy. 9 and 19 months after irradiation, half of the animals of each group were sacrificed for brain histology. All animals irradiated with 100 Gy were sacrificed 7 months after irradiation. RESULTS: An increase of local cerebral blood flow was measured in brain structures within the 80% isodose in animals irradiated with 50 Gy (Figure 3) compared to the contralateral hemisphere. Measurements close to necrotic areas showed a strong decrease of local cerebral blood flow (Figure 1). A volume increase of the irradiated hemisphere was seen after 19 months (Figure 2). The histologic examination after 19 months showed necrotic areas in the 30-50 Gy groups (Figure 4b) but not in the 20 Gy groups (Figure 4c). The animals who received 100 Gy demonstrated brain necrosis within 9 months after irradiation (Figure 4a). At both points in time the groups irradiated with the 3-mm collimator showed more pronounced histomorphologic and functional changes compared to the groups irradiated with the 2-mm collimator. CONCLUSION: Alterations of the local cerebral blood flow were measured as a late effect after single dose irradiation. The alterations of the local cerebral blood flow could be explained by the histomorphologic changes of the blood vessels. Using a semi-quantitative classification a dose, time and volume dependence for the endpoint radionecrosis was seen.

Animals↗
PubMed1998

Autoradiographic determination of local cerebral blood flow and local cerebral glucose utilization during chemical stimulation of the nucleus tractus solitarii of anesthetized rats.

This study was conducted to determine whether the decrease in cerebral blood flow (CBF) observed during chemical stimulation of the nucleus tractus solitarius (NTS) can be explained by a decrease in cerebral metabolism. In anesthetized (urethane and chloralose), paralyzed and artificially ventilated rats, neurons in the NTS were chemically stimulated by microinjection of L-glutamate. Local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCGU) were quantified in 43 brain structures by quantitative autoradiographic techniques using [14C]iodoantipyrine and 2-[14C]deoxyglucose, respectively. During chemical stimulation of the NTS (n = 6), LCBF decreased significantly in 32 of the 43 structures investigated when compared to either a control group with artificial cerebrospinal fluid injection (n = 6), or a controlled hemorrhage group (n = 5). In the controlled hemorrhage group, blood pressure was decreased to a degree comparable to that induced by microinjection of L-glutamate into the NTS. Mean blood flow of all structures investigated was significantly (P < 0.01) lower in the stimulation group than that in the control group and in the hemorrhage group. No significant differences in LCGU were observed between the three investigated groups in all structures examined except for an increase in LCGU in the chemically stimulated NTS site. It is concluded that the decrease in LCBF measured in most brain structures during chemical stimulation of the NTS is not caused by a decrease in LCGU in these structures and may therefore be explained by neurogenic influences on brain vessels.

Animals↗
PubMed1996

Parallel changes of blood flow and heterogeneity of capillary plasma perfusion in rat brains during hypocapnia.

Plasma perfusion patterns were investigated in brain capillaries during decreased cerebral blood flow induced by hyperventilation. Anesthetized rats were decapitated 3-4 s after being given an intravenous bolus injection of Evans blue dye. the measured steep increase of the arterial dye concentration at this moment ensures that different capillary plasma transit times are reflected in different intracapillary dye concentrations. The observed heterogeneity of capillary plasma transit time was expressed as the coefficient of variation (means +/- SD) of the intracapillary dye concentrations. For comparison, cerebral blood flow was determined at comparable PCO2 values in a second experimental group. At arterial PCO2 values between 40 and 25 mmHg, the cerebral blood flow and the coefficient of variation of the intracapillary dye concentration decreased with decreasing PCO2, whereas at PCO2 values <25 mmHg cerebral blood flow and coefficient of variation did not correlate with the arterial PCO2. However, it cannot be excluded that the coefficient of variation of the intracapillary dye concentration increases between 25 and 14 mmHg and decreases between 14 and 10 mmHg. It is concluded that the reduction of cerebral blood flow measured during moderate hypocapnia is paralleled by a decreased heterogeneity of the brain capillary perfusion. During severe hypocapnia this relationship is lost, indicating a potential disturbance of the cerebral microcirculation.

Animals↗
PubMed1995

Autoradiographic analysis of the regional distribution of Glut3 glucose transporters in the rat brain.

Glut3 is a glucose transporter protein which facilitates the transport of glucose across the neuronal membranes. The local distribution of Glut3 in the brain is not well known. The present study had the aim to verify the local distribution of Glut3 in the brain and to compare it with the local glucose utilization. A polyclonal antibody directed against the C-terminal peptide sequence of Glut3 was applied to cryosections of rat brains. A secondary antibody was added which had been coupled to 35S. Using autoradiography and radioactive standards, 17 cerebral structures were investigated. The results show moderate differences of Glut3 density in the structures investigated ranging from -23% to +41% of the mean density. The pineal gland was an exception with a density 66% lower than mean. Local cerebral glucose utilization (LCGU) was analyzed in identical brain structures by application of the quantitative autoradiographic 2-deoxyglucose method to conscious rats. The range of LCGU was from -59% to +55% of the mean. No correlation was found between the moderately heterogeneous Glut3 transporter density and the strongly heterogeneous local cerebral glucose utilization. The results show that the local density of Glut3 glucose transporter protein does not reflect the local level of glucose utilization in the brain.

Animals↗
PubMed1995

The importance of baroreceptor afferents for the decrease in brain glucose utilization during stimulation of the rostroventrolateral medulla of the rat.

The rostroventrolateral medulla (RVLM) is the main integration center for the regulation of the sympathetic outflow. The present study had the aim of investigating the effects of stimulation of the RVLM on the glucose utilization of the brain. Local cerebral glucose utilization (LCGU) can be regarded as an indicator of the brain functional activity. In anesthetized (chloralose-urethan), paralyzed (pancuronium) and ventilated rats, the medulla was exposed by a ventral craniotomy. The RVLM was stimulated by microinjection of 100 nl of 0.5 M sodium glutamate (n = 6). The effective stimulation was verified by the increase in arterial blood pressure. In a control group (n = 7), an identical volume of saline was injected into the RVLM. Local cerebral glucose utilization was measured in both groups using the 2-[14C]deoxyglucose method. The results showed a significant decrease in LCGU in the stimulated group in 33 of 39 brain structures examined. In order to investigate whether the decrease in brain glucose utilization is secondary to the stimulation of baroreceptor afferents by the increase in arterial blood pressure the carotid sinus nerves and both vagal nerves were cut. In this denervated group (n = 5) the decrease in LCGU was abolished in all brain structures although blood pressure was increased to a degree comparable to the innervated group. It is concluded that cerebral glucose metabolism is decreased during stimulation of the RVLM and that this decrease is secondary to the activation of baroreceptor afferents by the increase in blood pressure.

Afferent Pathways↗
PubMed1995

Controlled superfusion of the rat spinal cord for studying non-synaptic transmission: an autoradiographic analysis.

Recently, evidence has been raised that long-term changes in the central nervous system are mediated by extrasynaptic spread of neuropeptides ('volume transmission'). To study the effects of volume transmission in the spinal cord we developed the technique of controlled superfusion of the rat cord dorsum. This paper presents quantitative data about the spread, local spinal tissue concentration and redistribution of (2-[125I]iodohistidyl)neurokinin applied for 15, 30 or 60 min to the spinal cord dorsum in concentrations of 0.05 or 50 microM (10 microliters). Analysis of autoradiograms of sagittal and transverse spinal cord sections was done by computer-assisted densitometry. Under all experimental conditions, the spread of radiolabel into the superfused spinal cord segments reached Rexed's laminae V and VI; maximal spread (1.6 +/- 0.3 mm) was measured after superfusion for 30 min. The amount of radiolabel decreased in ventral direction as a function of distance. Highest tissue concentrations of neurokinin A (NKA) were obtained within the superficial spinal cord up to a depth of 0.5 mm and ranged from 700 to 2000 pmol/g following superfusions for 15 or 30 min with 50 microM NKA. Thus, these tissue concentrations were 25-70 times lower than the concentration of NKA in the superfusate. Since pool content was not exchanged, the radioactivity within the spinal cord was lower after superfusion periods of 60 min than after 15 or 30 min. Detection of radiolabel in blood and urine suggests that capillary clearance is relevant and limits the accumulation of the peptide within the spinal cord tissue and the spread into deeper laminae. The controlled superfusion of the rat cord dorsum is a useful method to mimick the spinal release of endogenous neuropeptides such as NKA during intense noxious stimulation, and it can be employed for versatile investigations of the effects of neuroactive molecules on the processing of sensory information in the intact spinal network.

Animals↗
PubMed1994

Intracerebroventricular injection of streptozotocin induces discrete local changes in cerebral glucose utilization in rats.

The purpose of the present study was to investigate whether or not cerebral glucose utilization is changed locally after damage of the neuronal insulin receptor by means of intracerebroventricular (icv) streptozotocin (STZ) administered in a subdiabetogenic dosage (1.5 mg/kg bw.). STZ was administered at the start of the study, and 2 and 21 days later bilaterally into the cerebral ventricles in rats of a mean age of 18 months. The local distribution of cerebral glucose utilization was analyzed in conscious rats on the 42nd day after the first STZ injection using the quantitative (14C)-2-deoxyglucose method. Of the 35 brain structures investigated from autoradiograms of brain sections, 17 showed a reduction in glucose utilization. Decreases in glucose utilization were observed in the frontal, parietal, sensory motor, auditory and entorhinal cortex and in all hippocampal subfields. In contrast, glucose utilization was increased in two white matter structures. The decrease in cerebral glucose utilization observed in cortical and hippocampal areas in the present study may correspond to changes in morphobiological parameters which have been found in patients with Alzheimer's disease. The present data are in accordance with the hypothesis that an impairment in the control of neuronal glucose metabolism at the insulin receptor site may exist in sporadic dementia of Alzheimer type (DAT), and can be studied by the icv STZ animal model.

Animals↗
PubMed1994

Gross persistence of capillary plasma perfusion after middle cerebral artery occlusion in the rat brain.

The densities of perfused and existing capillaries were measured in different cortical regions of rat brains after subtemporal occlusion of the middle cerebral artery (MCA). Capillary perfusion patterns (perfused capillaries versus nonperfused capillaries) were verified immediately after MCA occlusion in one group of rats and 1 h later in a second group using fluorescent double staining of capillary morphology and plasma perfusion in identical brain sections. In addition, local cerebral blood flow (CBF) was measured in another group of rats 1 h after MCA occlusion using the autoradiographic iodo-[14C]-antipyrine method. Although cortical CBF was decreased by up to 75% 1 h after MCA occlusion, plasma perfusion was not completely stopped in most capillaries (circulation time of Evans blue, 10 s). Only small patchy perfusion deficits (< 0.1 mm2 of brain section) were detected in the capillaries immediately and 1 h after MCA occlusion in all brains except for one that exhibited a more extensive lack of capillary perfusion. The data show that a drastic reduction of cortical CBF after MCA occlusion is not accompanied by a corresponding amount of nonperfused capillaries.

Animals↗
PubMed1993

Capillary perfusion during incomplete forebrain ischemia and reperfusion in rat brain.

Previous studies have shown a complete plasma perfusion of all capillaries in the rat brain under normal physiological conditions. This raises the question under which experimental conditions nonperfused capillaries may show up in the brain. Two experimental models were investigated in rats. 1) Reduced cerebral blood flow (CBF) during incomplete forebrain ischemia: hemorrhagic hypotension was maintained for 30 min at a mean arterial blood pressure of 41 mmHg. During the final 5 min of hypotension both carotid arteries were ligated. 2) Reperfusion after incomplete forebrain ischemia: reperfusion lasted for 4 h after either 15 or 30 min of incomplete forebrain ischemia. Under both experimental conditions, the density of the existing as well as the plasma-perfused brain capillary network was quantified using fluorescent double staining. Local CBF was measured during incomplete forebrain ischemia using the quantitative autoradiographic 4-iodo-[N-methyl-14C]antipyrine technique. The results showed a decrease in CBF during incomplete forebrain ischemia, which amounted up to 94%. Whereas normotensive control animals showed a complete staining of all capillaries within 5 s after the intravenous injection of Evans blue, this period of time was increased to 10 s during incomplete forebrain ischemia, indicating a delayed capillary perfusion. Four hours of reperfusion after 15 min of incomplete forebrain ischemia resulted in a complete capillary staining, whereas reperfusion after 30 min of ischemia was followed by intracerebral bleedings and a few nonperfused capillary areas (circulation time of Evans blue: 10 s).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Local cerebral blood flow and glucose utilization after blood exchange with a hemoglobin-based O2 carrier in conscious rats.

The effects of a blood exchange on cerebral blood flow and glucose utilization were studied. A near to total blood exchange (hematocrit < 3%) was achieved in conscious rats by isovolemic hemodilution. Ultrapurified, polymerized, bovine hemoglobin (UPBHB) served as a blood substitute. Local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCGU) were measured in 34 brain structures of conscious rats by means of the ido[14C]antipyrine and the 2-[14C]-deoxy-D-glucose methods. A group of rats without blood exchange served as control. After blood exchange LCBF increased from 36 to 126% in the different brain structures resulting in a nearly doubled mean cerebral blood flow (+82%). LCGU increased only moderately by 0-24%. Significant increases in LCGU were observed in 16 brain structures. Mean cerebral glucose utilization slightly increased (+14%). The relationship between LCGU and LCBF was found to be tight both in the control group (r = 0.95) as well as after blood replacement (r = 0.94), although it was reset to a higher overall LCBF-to-LCGU ratio. The profound increases in LCBF observed after blood exchange, which were not paralleled by comparable increases in LCGU, might be explained by a reduction of blood viscosity after blood exchange. Additional effects of blood exchange observed in the present study were an increase of mean arterial blood pressure and a decline of heart rate. The results indicate that replacement of blood with the hemoglobin-based oxygen carrier UPBHB appears to meet the cerebral circulatory and metabolic demands of the brain tissue.

Animals↗
PubMed1993

Changes in local cerebral glucose utilization in the awake rat during acute and chronic administration of ethanol.

Local cerebral glucose utilization (LCGU) was measured in 51 structures of the rat brain after acute and/or chronic oral administration of ethanol using the quantitative autoradiographic 2-deoxyglucose method. In the acute experiments, ethanol (3.2 g/kg) was administered via a gastric tube 110 min before the 2-deoxy-D-[1-14C]glucose. The chronic pretreatment was performed using increasing concentrations of ethanol in the drinking water for a period of 20-24 days. The most striking effects on LCGU were seen in the inferior colliculus. Acute and acute plus chronic treatment with ethanol significantly decreased LCGU by 33% and 37%, respectively, whereas chronic treatment significantly increased LCGU by 25%. In general, acute administration of ethanol decreased LCGU in 16 brain structures, particularly of the auditory system. Chronic treatment, besides its effect on the inferior colliculus, only decreased LCGU in the internal capsule. Chronic plus acute administration of ethanol decreased LCGU significantly in 22 structures. It is concluded that an acute oral administration of ethanol has distinct and mainly depressive effects on the functional activity of several brain areas. Chronic administration is less effective.

Administration, Oral↗
PubMed1991

Effects of nicotine withdrawal on the local cerebral glucose utilization in conscious rats.

Chronic infusion of nicotine has been shown to result (1) in an increase in nicotine binding sites in the brain and (2) in a distinct pattern of increases in local cerebral metabolic rate for glucose (CMRglc). The present study addresses two questions: (1) whether a one-day withdrawal of nicotine after a two-week exposure is long enough to restore local CMRglc to the preinfusion values and (2) whether an acute nicotine infusion after one day's withdrawal would influence local CMRglc. Chronic infusion of L-nicotine (12.5 micrograms/kg/min) was performed by osmotic minipumps. Local CMRglc was measured using the quantitative 2-deoxyglucose method in conscious rats. The following results were obtained: (1) a one-day withdrawal of nicotine after a two-week chronic infusion restores local CMRglc to a pattern which is close to the control pattern obtained without any nicotine infusion, and (2) an acute infusion of nicotine after a one-day withdrawal of a chronic nicotine infusion induces distinct increases in local CMRglc of several brain structures; these are essentially identical with structures which are activated during an acute nicotine infusion in otherwise untreated rats (no chronic infusion). The data indicate: (1) The main effects of chronic nicotine infusion on local CMRglc have disappeared after one day of nicotine withdrawal. (2) An acute load of nicotine in such nicotine-withdrawal rats has effects on local CMRglc which resemble those found in previously untreated rats during an acute nicotine infusion. (3) In contrast to most binding studies which have shown persisting increases in nicotine binding sites after one day's withdrawal of chronic nicotine, local CMRglc is restored to control values and can be again activated by an acute nicotine infusion.

Animals↗
PubMed1991

The influence of nicotine on local cerebral blood flow in rats.

Local cerebral blood flow (LCBF) was measured in conscious rats during an acute nicotine infusion. LCBF was measured using the autoradiographic iodoantipyrine method. LCBF was unchanged in most brain structures during nicotine infusion compared to controls. Significant (P less than 0.05) increases were found in 3 structures (lateral geniculate body, superior colliculus, anteroventral nucleus of the thalamus). These structures have already shown increases in local glucose utilization in a previous study [2]. The observed increases in LCBF are interpreted to be secondary to metabolic activation by nicotine indicating the lack of a direct action of nicotine on cerebral blood vessels.

Animals↗
PubMed1991

Dynamics of capillary perfusion in the brain.

The present study investigates the question of capillary recruitment and reserve capillaries in the brains of awake rats. Perfused capillaries were marked by intravenous globulin-coupled fluorescein isothiocyanate (FITC) and cerebral blood flow was measured autoradiographically. During hypercapnia, the density of perfused capillaries was unchanged compared to normocapnia, although blood flow was markedly increased. This shows the lack of capillary recruitment in the brain during the high flow that occurs during hypercapnia. In additional studies using fluorescent staining both of morphologically existing and of perfused capillaries, perfusion of all capillaries during normal, normocapnic conditions was found. These experiments show the lack of any capillary reserve in the rat brain.

Animals↗
PubMed1990

Glucose utilization, blood flow and capillary density in the ventrolateral medulla of the rat.

A specific population of neurons in the ventrolateral medulla (VLM) acts as the main integration center for the regulation of the sympathetic outflow to the cardiovascular system. In order to investigate whether this nucleus can be distinguished from its surroundings in the reticular formation of the medulla with respect to functional and morphological variables, the present study investigates several of such variables in this area on a quantitative basis. Local medullary glucose utilization was measured by the 2-[14C]deoxyglucose method; local medullary blood flow was quantified using iodo[14C]-antipyrine, and the local density of perfused capillaries was calculated by counting the number of intravascular fluorescent spots in brain sections after i.v. infusion of a globulin-coupled fluorescent dye. The values obtained from the VLM were compared with the respective values found in a reference area of the same brain section (gigantocellular nucleus). The values for glucose utilization, blood flow and capillary density were significantly (P less than 0.05) higher in the VLM than in the reference area (gigantocellular nucleus). This difference was 44.7% for glucose utilization, 34.1% for blood flow and 19.7% for capillary density. These data support the hypothesis that neurons in the VLM are specifically well supplied for being directly regulated in their activity by the PCO2 and pH in the arterial blood.

Animals↗
PubMed1990

Effect of gamma-hydroxybutyrate on local and global glucose metabolism in the anesthetized cat brain.

This study addresses three topics in the chloralose-anesthetized cat: (a) distribution of local CMRglc: values ranging from 5 to 109 mumols/100 g/min were found in 37 brain structures and the mean CMRglc over all examined structures was 30.6 mumols/100 g/min; (b) effect of gamma-hydroxybutyrate (GHB, 250 mg/kg i.v.) on local CMRglc, which was significantly (p less than 0.05) depressed in 16 of 37 structures, most prominently in the auditory system, and the mean CMRglc over all structures after GHB was 20.4 mumols/100 g/min; and (c) global values of CMRglc, CMRO2, and CBF before and after GHB: in these experiments, a modified Kety-Schmidt technique was employed measuring saturation/desaturation of inhaled H2 and concentrations of glucose and oxygen in aortic and sagittal sinus blood. CBF and CMRO2 were not altered after GHB, whereas CMRglc was significantly decreased from 35.7 to 28.8 mumols/100 g/min. The values of CMRglc obtained with both techniques (autoradiography and the Kety-Schmidt technique) are concordant, especially when considering the different sampling areas of both methods. The main finding of the present study is a reduction in cerebral glucose consumption after GHB, irrespective of the technique of measurement. This reduction occurs at an unchanged CMRO2 and CBF.

Animals↗
PubMed1989

Lack of capillary recruitment in the brains of awake rats during hypercapnia.

The present study investigates the question of whether increases in CBF induced by hypercapnia in awake rats are accompanied by increases in the number of perfused capillaries. For the detection of perfused capillaries, gamma-globulin-coupled fluorescein isothiocyanate was injected intravenously. In 10 brain structures the density of perfused capillaries per square millimeter was determined from coronal sections using a highly sensitive fluorescent microscopical method that, in contrast to others, avoided air drying of the frozen brain sections. The results showed an inhomogeneous local distribution of the density of perfused capillaries during normo- and hypercapnia. The density of perfused capillaries was unchanged during hypercapnia compared with normocapnia, although blood flow was markedly increased. It is concluded that a capillary recruitment does not exist in the brain during the high-flow situation of hypercapnia.

Animals↗