Changes in hexokinase isoenzymes in regions of rat brain during thyroid deficiency

In this work, activities of hexokinase isoenzymes Type I and Type II were measured in the soluble and particulate fractions from the brain regions (cerebral hemispheres (cerebrum), cerebellum and brain stem) of the thyroidectomized adult rats as well as of the thyroidectomized rats administered with triiodothyronine. Thyroidectomy generally decreased the hexokinase activity associated with particulate and soluble fractions. Hexokinase Type II isoenzyme was more affected than the Type I isoenzyme. Administration of triiodothyronine to the hypothyroid rats abolished the effect of thyroidectomy. Adult brain enzymes have been generally considered not be affected by thyroid hormones. The data obtained in this work are suggestive of an effect of thyroid hormones on hexokinase in the adult brain. Since the effects of thyroidectomy on the energy metabolism of the heart tissue are well known, the heart tissue was also studied for comparison.     

Amino acid content in astroglial primary cultures from different brain regions during cultivation

Free amino acids in astroglial primary cultures obtained from newborn rat cerebral cortex, striatum and hippocampus were analyzed and compared during cultivation. Glutamate and taurine exhibited the highest concentrations. Aspartate and glutamate showed the highest values after 1 and 3 weeks of cultivation with lower values after 2 weeks in culture, while taurine, -alanine/hypotaurine and phosphoethanolamine showed the highest value after 2 weeks in culture. The non-neuroactive amino acids and -aminobutyric acid were present at a low level and the former showed the lowest concentration at 2 weeks of cultivation. Astrocytes from the different regions did generally not differ with respect to amino acid content. We conclude that the morphological and biochemical maturation of glia in culture is accompanied with marked quantitative changes in amino acid pattern.     

Seizures increase acetylcholine and choline concentrations in rat brain regions

Seizures induced by three convulsant treatment produced differential effects on the concentration of acetylcholine in rat brain. Status epilepticus induced by (i) coadministration of lithium and pilocarpine caused massive increases in the concentration of acetylcholine in the cerebral cortex and hippocampus, (ii) a high dose of pilocarpine did not cause an increase of acetylcholine, and (iii) kainate increased acetylcholine, but the magnitude was lower than with the lithium/pilocarpine model. The finding that the acetylcholine concentration increases in two models of status epilepticus in the cortex and hippocampus is in direct contrast with manyin vitro reports in which excessive stimulation causes depletion of acetylcholine. The concentration of choline increased during seizures with all three models. This is likely to be due to calcium- and agonist-induced activation of phospholipase C and/or D activity causing cleavage of choline-containing lipids. The excessive acetylcholine present during status epilepticus induced by lithium and pilocarpine was responsive to pharmacological manipulation. Atropine tended to decrease acetylcholine, similar to its effects in controls. The N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801, reduced the excessive concentration of acetylcholine, especially in the cortex. Inhibition of choline uptake by hemicholinium-3 (HC-3) administered icv reduced the acetylcholine concentration in controls and when given to rats during status epilepticus. These results demonstrate that the rat brain concentrations of acetylcholine and choline can increase during status epilepticus. The accumulated acetylcholine was not in a static, inactive compartment, but was actively turning-over and was responsive to drug treatments. Excessive concentrations of acetylcholine and/or choline may play a role in seizure maintenance and in the neuronal damage and lethality associated with status epilepticus.     

Changes in phosphofructokinase and pyruvate kinase in rat brain regions during alloxan-induced diabetes

Changes in the profile of two glycolytic enzymes, phosphofructokinase and pyruvate kinase, in different regions of rat brain were studied under alloxan-induced diabetes. A regional variation of the effect of diabetes on brain was noted - the cerebral hemispheres and cerebellum showed decreased activity of the enzymes, while the brain stem remained relatively unaffected. The changes in enzyme activities in the brain regions were more pronounced at the early days of diabetes, particularly at 8 days. Insulin administration to the diabetic animals restored the activity of the enzymes. The results indicate a regionally variable effect of diabetes on the two key glycolytic enzymes, and bring out a role of insulin in the regulation of brain glycolysis.     

Polyamine turnover in different regions of rat brain

The dynamics of the formation and disappearance of polyamines in rat brain have been examined after intraventricular administration of a tracer dose of [³H]putrescine. After 2 days [³H]putrescine was no longer detectable in any brain region examined. [³H] Spermidine and [³H] spermine were formed in all brain areas. In the midbrain, hypothalamus and cerebellum (regions which manifested the greatest initial accumulation of tritium) the specific radioactivity of spermidine declined with a half-life of 16-19 days. However, in areas with a low initial accumulation of tritium (the medulla-pons, internal capsule, cerebral cortex and corpus striatum) the specific radioactivity of spermidine changed very little between 2 and 19 days after the putrescine administration. Levels of [³H]spermine increased continuously in all brain areas for a 14-day period after the putrescine injection.     

Biochemical studies on histones of the central nervous system. III. Incorporation of [14C]-acetate into the histones of different rat brain regions during a learning experiment

Long term memory formation obviously is accompanied by changes in macromolecule synthesis within the brain structures involved. The regulation of this process was investigated in various rat brain regions using the model of histone acetylation with [14C]-acetate during the training session, as well as 5 min and 120 min upon completion of training. Almost at all three times and in most brain structures the acetylation rate was diminished in trained animals as compared to pseudo-conditioned rats. With the exception of hippocampus labeling in trained animals was even lower in comparison to passive controls.     

Changes in labeling of soluble and solubilized rat brain proteins using (3H)-leucine as precursor during a learning experiment.

This paper deals with an electrophoretic study on soluble and solubilized rat brain proteins during a brightness discrimination. After intraventricular injection of L-[3H]-leucine the most pronounced increase in relative specific activity was found for several soluble acidic protein-band complexes as well as for solubilized slow-migrating non-myelin proteins obtained from hippocampus of trained animals over the data obtained for active and passive controls.     

Changes in labeling of soluble and insoluble rat brain proteins using [3H]-tyrosine as precursor during a learning experiment.

The incorporation of intraventricularly injected L-[3H]-tyrosine into proteins from three rat brain regions was studied during the acquisition of a shock-motivated brightness discrimination. Separating the proteins by means of polyacrylamide gel electrophoresis revealed an increased labeling confined to only a few of the resolved slow-moving bands of soluble and, especially insoluble hippocampus proteins. The labeling of visual cortex proteins showed only minute changes, while the auditory cortex proteins exhibited no differences between trained and nontrained animals.     

Formal learning theory dissociates brain regions with different temporal integration

Learning can be characterized as the extraction of reliable predictions about stimulus occurrences from past experience. In two experiments, we investigated the interval of temporal integration of previous learning trials in different brain regions using implicit and explicit Pavlovian fear conditioning with a dynamically changing reinforcement regime in an experimental setting. With formal learning theory (the Rescorla-Wagner model), temporal integration is characterized by the learning rate. Using fMRI and this theoretical framework, we are able to distinguish between learning-related brain regions that show long temporal integration (e.g., amygdala) and higher perceptual regions that integrate only over a short period of time (e.g., fusiform face area, parahippocampal place area). This approach allows for the investigation of learning-related changes in brain activation, as it can dissociate brain areas that differ with respect to their integration of past learning experiences by either computing long-term outcome predictions or instantaneous reinforcement expectancies.     

Changes in activity and expression of phosphofructokinase in different rat brain regions after basal forebrain cholinergic lesion

Selective lesion of rat basal forebrain by the cholinergic immunotoxin 192IgG-saporin was used as an animal model to address the question of whether the changes in cortical glucose metabolism observed in patients with Alzheimer's disease may be related to impaired cholinergic transmission. At different times after creating the immunolesion, the isoenzyme pattern and steady-state mRNA levels of the key glycolytic enzyme phosphofructokinase were determined in cortex, hippocampus, basal forebrain and nucleus caudatus. The loss of cholinergic input was accompanied by a persistent decrease in choline acetytransferase and acetylcholine esterase activities in the cortical target areas similar to the cholinergic malfunction seen in Alzheimer's dementia. The basal forebrain lesion induced by the immunotoxin resulted in a transient increase in phosphofructokinase activity peaking on day 7 after inducing the lesion in cortical areas. In parallel, an increased steady-state level of phosphofructokinase mRNA was determined by RT/real-time PCR and in situ hybridization. In contrast, analysis by western blotting and quantitative PCR revealed no changes in the phosphofructokinase isoenzyme pattern after immunolesion. It is concluded that common metabolic mechanisms may underlie the degenerative and repair processes in denervated rat brain and in the diseased Alzheimer's brain.     

Changes in nucleic acid and protein content in different regions of the brain is rats reared in enriched and impoverished environments

The content of nucleic acids (DNA and RNA) and proteins in 1 mg of tissue and RNA/DNA and protein/DNA ratio in different brain structures (the neocortex, the hippocampus, the cerebellum, the brain-stem), as well as in the liver was studied in rats at different stages of postnatal ontogenesis (25 to 55 days) in the norm, under ecological deprivation and in an information-enriched medium, involving elaboration of conditioned reflexes. It was shown that intense physiological function of the brain cells in an information-enriched medium is attended with substantial enhancement of the RNA/DNA ratio, i.e. stimulation of transcribing activity of the cells genome. In conditions of ecological deprivation this value at first slightly increases, and the significantly diminishes in all the studied brain structures. Protein content in the nerve tissue is more stable in ontogenesis and changes but slightly at different afferentation levels. No significant changes were observed in any of the studied parameters in the lever tissue.     

Effect of dichloroacetate on acetyl-CoA content and acetylcholine synthesis in rat brain synaptosomes

In potassium-depolarized synaptosomes Ca²⁺ inhibited oxidation of pyruvate (30%) and decreased the level of acetyl-CoA in intrasynaptosomal mitochondria (32%). On the other hand, Ca²⁺ facilitated provision of acetyl-CoA to synaptoplasm, since under these condition no change of synaptoplasmic acetyl-CoA and twofold stimulation of acetylcholine synthesis were found. However, in Ca²⁺-activated synaptosomes both synaptoplasmic acetyl-CoA and acetylcholine synthesis were suppressed by 1 mM (–)hydroxycitrate by 27 and 29%, respectively. It was not the case in resting synaptosomes. Dichloroacetate (0.05 mM) partially reversed the inhibitory effect of Ca²⁺ on pyruvate metabolism in synaptosomes and whole brain mitochondria. In Ca²⁺-stimulated synaptosomes, the dichloroacetate overcame suppressive effects of (–)hydroxycitrate on the level of synaptoplasmic acetyl-CoA and acetylcholine synthesis, but not on citrate clevage. It is concluded that dichloroacetate may improve the metabolism of acetylcholine in activated cholinergic terminals by increasing the production of acetyl-CoA in mitochondria and increasing its provision through the mitochondrial membrane to synaptoplasm by the transport system, independent of the ATP-citrate lyase pathway.     

Age-dependent changes of nucleic acid labeling in different rat brain regions

The effects of aging on in vivo DNA and RNA labeling and on RNA content in various brain regions of 4-, 12-, and 24-month-old rats were investigated. No difference in [methyl-¹⁴C]thymidine incorporation into DNA of cerebral cortex and cerebelllum during aging was observed.The ratio of RNA/DNA content significantly decreased from 4 to 24 months of age in cerebral cortex, cerebellum and striatum. RNA labeling decreased by 15% in cerebral cortex of 24-month-old animals while in the other brain areas examined (cerebellum, hippocampus, hypothalamus, brainstem, striatum) did not change during aging.In the cerebral cortex, the ratio of the specific radioactivity of microsomal RNA to that of nuclear RNA, determined by in vivo experiments, was not affected by the aging process. A significant decrease of total, poly(A)+ RNA and poly(A)- RNA content was observed in the same brain area of 24-month-old rats compared to 4-month-old ones. Moreover, densitometric and radioactivity patterns obtained by gel electrophoresis of labeled RNA after in vitro experiments (tissue slices of cerebral cortex) showed a different ribosomal RNA processing during aging. In vivo chronic treatment with CDP-choline was able to increase RNA labeling in corpus striatum of 24-month-old animals.     

小鼠脑内甘氨酸含量在缺氧预适应中的变化

在小鼠重复缺氧预适应过程中,用HPLC方法,测定其全脑与不同脑区中的甘氨酸含量。结果表明,随着动物对低氧耐受性的增高,其全脑、间脑,特别是海马、脑干中的甘氨酸含量升高。结果提示,甘氨酸作为抑制性递质对低氧预适应的形成具有正面影响。