Paul Kleihues

Sequential morphological changes in the dog brain after interstitial iodine- 125 irradiation

Iodine- 125 seeds (3.55 mCi) were stereotactically implanted into the subcortical white matter of the left coronal gyrus in six beagle dogs. Morphological changes were studied at intervals ranging from 25 to 368 days after implantation. In all of the animals, there was a calcifying necrosis 3 to 6 mm in diameter with an adjacent small zone of demyelination. There were no signs of delayed radiation damage outside the demyelinated perifocal zone. The central tissue necrosis was sharply delineated and did not increase in size after 70 days, i.e., an accumulated dose of 18,000 cGy. In addition, widespread vasogenic edema was present in the homolateral hemisphere. The morphological changes observed differed in many aspects from those found with other radioactive sources, such as gold-198, yttrium-90, or iridium-192. The low energy gamma radiation, the absence of beta radiation, and the half-life of 60.2 days makes iodine-125 a favorable radioactive source to produce a well-defined necrosis without delayed radiation damage in the surrounding brain.

Regionally selective inhibition of cerebral protein synthesis in the rat during hypoglycemia and recovery.

Regional cerebral protein synthesis was investigated in anesthetized, mechanically ventilated rats during progressive insulin‐induced hypoglycemia and the recovery period following glucose infusion. Polysome profiles from precomatose animals with slow wave/polyspike EEG revealed a slight reduction of polyribosomes and a concurrent increase in monoribosomes, but autoradiographs showed a pattern of l‐[3‐3H]tyrosine incorporation indistinguishable from that of control rats. During the initial 30 min of insulin‐induced isoelectric EEG (“coma”), autoradiographs showed a selective inhibition of protein synthesis in neurons and glial cells of the hippocampus and cerebral cortex, i.e., regions with high susceptibility for the development of hypoglycemic brain damage. Basal ganglia were less affected and areas with low vulnerability (hypothalamus, brainstem, and cerebellum) exhibited a normal pattern of amino acid incorporation. Using a flooding dose of l‐[1‐14C]valine (7.5 mmol/kg; 15 μCi/mmol), the rate of incorporation in cerebral cortex and cerebellum was found to be reduced to 2% and 80% of control values, respectively. Inhibition of protein synthesis was paralleled by a breakdown of polyribosomes and a concomitant increase in ribosomal subunits, indicating a block in peptide chain initiation. After 90 min of isoelectric EEG all brain structures with the exception of hypothalamus and area postrema showed an almost complete lack of amino acid incorporation. Glucose infusion after a 30‐min period of hypoglycemic coma led to a partial restoration of cortical and hippocampal protein synthesis. Within 70–90 min of recovery, l‐[1‐14C]valine incorporation into neocortical and cerebellar proteins amounted to 47% and 125% of fasted controls. The very specialized patterns of regional impairment of cerebral protein synthesis during progressive hypoglycemia may reflect a selective vulnerability of some neuronal cell populations to hypoglycemic cell injury. Alternatively, the striking resistance of hypothalamus, brainstem, and cerebellum may be due to a more efficient glucose uptake at very low blood glucose levels.

Excision of O6-methylguanine from DNA of various mouse tissues following a single injection of N-methyl-N-nitrosourea

The persistence of O6-methylguanine produced by a single dose of N-methyl-N-nitrosourea (MNU) was determined in DNA of various murine tissues and compared with the location of tumours induced by MNU and related alkylating carcinogens in this species. A/J and C3HeB/FeJ mice received a single intravenous injection of MNU (10 mg/kg) and were killed at different time intervals ranging from 4 h to 7 days. The rate rate of loss of O6-methylguanine from brain DNA was considerably slower than from liver DNA; tumours have been found in both organs after administration of MNU and other alkylnitrosoureas. There was no difference in the rate of excision from cerebral DNA of A/J and C3HeB/FeJ mice, although these strains differ significantly in their susceptibility to the neurooncogenic effect of MNU and related carcinogens. Excision of O6-methylguanine from hepatic DNA was significantly slower in A/J than in C3HeB/FeJ mice; both strains habe been found to develop hepatic carcinomas following MNU administration. Seven days after the injection of 3H-MNU, O6-methylguanine concentrations were highest in brain and lung DNA, lowest in the liver, and intermediate in kidney, spleen, small intestine and stomach. The lung is a principal target organ for tumour induction by MNU and other carcinogens in mice; however, neural tumours are usually induced at a low incidence. The results obtained do not contradict the hypothesis that O6-alkylation of guanine in DNA is a critical event in the initiation of tumour induction by alkylating agents. However, the location of tumours produced in mice does not seem to depend solely on the formation and persistence of O6-alkylguanine in DNA.

Time Course and Spatial Distribution of Neodymium: Yttrium-Aluminum-Garnet (Nd:YAG) Laser-induced Lesions in the Rat Brain

Cerebral lesions made by focal neodymium:yttrium-aluminum-garnet (Nd:YAG) laser irradiation of the rat forebrain were studied in adult Wistar rats. For the analysis of time-dependent changes, the brains of 28 animals were irradiated with a constant energy density of 461 J/cm2. In this series, survival time ranged from 0.5 hours to 80 days. Immediately after irradiation, a circular lesion appeared on the surface of the brain. This lesion was surrounded by an edematous area intensively stained with Evans blue. At energy levels higher than 30 J, this circular edema contained numerous thrombosed vessels. Histopathologically, the lesion consisted of three distinct zones: the central coagulation necrosis was surrounded by a zone of delayed colliquation necrosis and by perifocal edema. At approximately 80 days after irradiation, the resulting cortical defect was covered by a pial membrane. Edematous changes of the brain cortex and the adjacent white matter were observed as early as 1 hour after irradiation. Within 16 hours, the perifocal edema spread over the white matter of both hemispheres, and it had disappeared by the 5th day after irradiation. In a second experiment, the energy density varied from 231 to 3077 J/cm2. This series consisted of 84 animals that were allowed to survive 48 hours. The size of the lesion depended on the level of energy applied, but the depth of the lesion varied less than the diameter at the brain surface.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional impairment of protein synthesis in the rat brain during bicuculline-induced seizures.

Protein synthesis was investigated in rats subjected to 30 min of bicuculline-induced seizures using biochemical and autoradiographic techniques. Incorporation studies were performed on freely convulsive animals following systemic administration of either a tracer dose of L-[1-14C]tyrosine or a flooding dose (7.5 mmol/kg) of L-[1-14C]valine. Using a tracer dose, amino acid incorporation was only moderately reduced (forebrain) or slightly enhanced (cerebellum/brainstem and spinal cord) but the specific radioactivity of [14C]tyrosine in the acid-soluble pool was increased 3- to 5-fold in experimental animals. After a flooding dose of [14C]valine the specific activity of the precursor amino acid was similar in control and convulsed animals. Under these conditions incorporation rates in forebrain and cerebellum/brainstem were reduced to 54 and 75%, respectively. Reduction of amino acid incorporation was even more pronounced in extraneural tissues, e.g. liver (6%), intestine (14%) and kidney (15%). Inhibition of protein synthesis in forebrain and cerebellum/brainstem was paralleled by a similar extent of polyribosome disaggregation in these regions (53 adn 78% of controls). In anaesthetized, mechanically ventilated rats, 30 min of seizure activity reduced forebrain polyribosomes to a similar extent (57%). Extraneural (hepatic) protein synthesis was also affected in physiologically controlled rats, but cerebellar polysomes were completely preserved. Autoradiographic studies using 3H-labelled amino acids were carried out to identify nerve cell populations most heavily affected. In freely convulsive rats both tracer dose and pool overloading revealed a similar regional pattern with preferential inhibition of amino acid incorporation in forebrain cortex, thalamus and the pyramidal cell layer of the hippocampus. These sites were also affected in the physiologically controlled animal, but the focal distribution of hippocampal and thalamic neurones with reduced protein synthesis differed from that in freely convulsive rats.

DNA Modification and Repair in Vivo: Towards a Biochemical Basis of Organ-Specific Carcinogenesis by Methylating Agents

The elucidation of the biological basis of organ-specific tumor induction by chemicals is a major objective of cancer research. For many carcinogens, the principal site of tumor induction has been shown to vary with species, dose, route of administration, and age or developmental stage. Some species also exhibit marked differences in their overall susceptibility to certain classes of chemical carcinogens. Accordingly, to accurately predict the adverse effects of genotoxic agents in humans, the basic mechanisms underlying organ and species specificity must first be understood.