QUANTITATIVE AND QUALITATIVE CHANGES IN RIBONUCLEIC ACIDS OF RAT BRAIN DEPENDENT ON AGE AND TRAINING EXPERIMENTS

—Investigations of rat brain RNA were carried out by phenol extraction of the whole brain and chromatographic fractionation into ribosomal RNA and transfer RNA. (1) The amounts of both RNA species increase in the course of the animal's development reaching a maximum at about the tenth week of life. The ratio of both species remains constant throughout the growth to the twentieth week. After the rats had been trained how to reach their forage by balancing on a stressed rope, the rRNA content was found to be significantly higher, whereas the tRNA content was unchanged. (2) The portion of ribosomes bound in polysome complexes decreases with increasing age of rats. Conditioning of the animals brings about again an increase in polysome content. It is supposed that this reflects an enhanced synthesis of specific proteins in young developing rats and in the course of conditioning. (3) In young rats a second valine specific tRNA could be found as a minor component in addition to the major valyl-tRNA. This additional component disappears as the animals advance to an age of 3 weeks and it could not be detected in the brains of rats after training experiments. In tRNAs specific for the amino acids leucine, lysine and phenylalanine no kind of deviation could be stated.     

BIOCHEMICAL CHANGES IN RAT BRAIN ASSOCIATED WITH THE DEVELOPMENT OF THE BLOOD-BRAIN BARRIER

—Subcellular fractions from brains of 5, 10, 13, 16, 21, 30 day-old and adult rats were prepared. Protein content and various enzyme activities were assayed in all fractions and brain homogenates. γ-Glutamyl transpeptidase activity and 5′-nucleotidase were very low at 5 days of life but steadily increased, reaching adult concentrations at about 30 days after birth. Alkaline phosphatase, instead slowly decreased with maturation, while monoamine oxidase after an initial decrease, increased rapidly to adult levels. The relation between the appearance of enzymatic activity in brain and the blood-brain barrier function is discussed.     

CHANGES IN POLYSOMES OF THE DEVELOPING RAT BRAIN

Abstract— Rat brain polysomes were prepared from a deoxycholate-treated postmito-chondrial supernatant in the presence of 2% bentonite and 1 mg/ml of yeast RNA to prevent partial degradation during preparation.

• 1 The polysomal preparations had an absorption maximum at 260 mμ and an absorption minimum at 235 mμ. The ratio of absorption maximum to minimum and the RNA to protein ratio were 1·58 and 1·06 respectively in 6-day-old rat brain polysomes. The sedimentation patterns showed six distinct peaks with sedimentation coefficients of 235S, 185S, 173S, 135S, 100S and 80S, indicating that these preparations have the characteristics of pure heavy polysomes.

• 2 The rate of [¹⁴C]phenylalanine incorporation into brain polysomal protein was maximal at approximately 10 days of age and decreased thereafter. A similar progressive reduction with increasing age was found in the stimulation of phenylalanine incorporation by the addition of 60 μg/tube of polyuridylic acid. However, the incorporation of phenylalanine into young rat brain polysomes was usually greater even with the addition of polyuridylic acid than in the older animals.

• 3 The comparative studies on sucrose density gradient centrifugation of polysomes between young and adult rat brains showed a considerable decrease of heavy polysomes in the older animals.

• 4 The effect of various factors on the stability of brain polysomes from both ages has been studied. The rates of RNA, protein and acid-soluble phosphorus release from polysomes of the adult rat brains were usually greater in the presence of high salt concentration, ethylenediaminetetra-acetic acid and urea than those from the corresponding preparations of younger animals. On the basis of evidence obtained from the above results it suggested that the adult brain polysomes were more unstable than those of younger animals.

• 5 The amount of polysomal RNA linearly increased up to the first 20 days after birth and then levelled off. The ratio of G + C/A + U of polysomal RNA was less in the young rat brains, falling to 1·30 as compared to 1·50 in older animals. The differences were statistically significant at less than a 1% level of confidence.

• 6 Polysomal preparations also contained RNase, phosphomonoesterase, phospho-diesterase and 5′-nucleotidase activities which cannot be washed off. The specific activities of these enzymes were generally higher in young rat brains than those in the adult.

     

CHANGES OF THYMIDINE KINASE IN THE DEVELOPING RAT BRAIN

Abstract— Thymidine kinase (ATP: thymidine-5'-phosphotransferase EC 2.7.1.21) of the supernatant fraction from 6-day-old rat brain possessed a pH optimum of 8.0 and required the presence of 5mM-ATP and 2.5 mM-MgCl₂ for maximum activity. The activity was completely inhibited by addition of 1.8 mM-TTP. The enzyme activity was lost if the same supernatant fraction was refrozen and thawed. K_m was 2.8 × 10⁻⁶ M for [6-³H]thymidine.
Following subcellular fractionation of rat brain, the greatest proportion and highest specific activity of thymidine kinase was found in the supernatant fraction. Thymidine kinase activities reached a maximum at 6 days of age and then dropped sharply during maturation. Comparative studies of thymidine kinase activities of cerebrum, cerebellum and the remainder of the brain during growth indicated that the activity in the cerebellum was usually higher than those in the cerebrum and the remainder, and the biggest differences obtained at 6 days after birth corresponded with the peak in cerebellar activity.     

CHOLINE ACETYLTRANSFERASE CONTENT IN DISCRETE REGIONS OF THE RAT BRAIN STEM

—Choline acetyltransferase (ChAc) content of 50 separate rat brain stem nuclei and cerebellum removed by microdissection was determined using a sensitive radiometric assay. The distribution of ChAc activity is uneven, with extremely high levels in the cranial motor nuclei and the nucleus salivatorius. Low ChAc concentrations were observed in the cranial sensory nuclei, the nuclei of the reticular formation, the raphe nuclei and the nuclei of the acoustic system. The lowest ChAc levels were measured in the cerebellum. Comparison of the distribution of ChAc with histochemical localization of acetylcholinesterase revealed generally good agreement, and notable exceptions are discussed.     

QUANTITATIVE CHANGES IN THE CELLULARITY OF THE RAT SUBEPENDYMAL PLATE AFTER X-IRRADIATION

The brains of young adult rats were irradiated with a single dose of 8 Gy (800 rad) of 250 kVp X-rays. Within 2 weeks of treatment the cell population of the subependymal plate was reduced by 30%. During this period the cell cycle time remained unchanged but the labelling index was reduced. The cell population subsequently returned to normal after 39-52 weeks. Damage and subsequent recovery of the plate was due mainly to changes in the number of cells with small dark nuclei. Cells with small and large light nuclei were little affected. A model for the production and differentiation of cells in the subependymal region is proposed on the basis of age-related changes in the total number and proportions of the various cell types in the subependymal plate of normal rats. This is discussed both in terms of the radiation response of cells in the plate and the manifestation of delayed white matter necrosis after higher doses.     

不同年龄大鼠小脑浦肯野细胞超微结构的变化

对不同年龄雄性Ｗｉｓｔａｒ大鼠小脑蚓剖皮质浦肯野细胞的超微结构进行了观察。结果表明,随年龄增神经内的细胞器和内涵物发生了明显变化。浦肯野细胞内粗面内质网、高尔基复合体等细胞器数量有不同程度减少;微管增加;粗面内质网排列失序,网腔扩张;高尔基器排列紊乱,囊腔扩张;线粒体扩张或固缩,     

CHANGES WITH AGE IN WATER AND EXTRA-CELLULAR SPACE IN INCUBATED BRAIN TISSUE

Abstract— (1) Incubation in physiological saline at 37º caused brain slices from chick embryos to lose water (shrink), whereas slices from young chicks gained water (swell). Shrinkage decreased with age in embryonic brain, and swelling increased with age in chick's brain.
(2) Incubation at 0º diminished shrinkage in 8-day old embryos, caused an increasing degree of swelling in older embryos, and enhanced swelling in young chick's brain slices.
(3) Inulin equilibrated more rapidly with tissue water in embryonic than in young adult brains. Measured 'inulin space' values at 37º changed little with age, whereas 0º'inulin space' values significantly decreased with age. Calculated zero time 'inulin space' values also decreased with age.
(4) The measured 'inulin space' at 0º was larger than that measured at 37º (but not of the calculated zero time 'inulin space') in young embryos, then became progressively smaller, so that in young chicks the situation was reversed.
(5) The calculated extracellular space ranges from about 37 per cent (8-day old embryos) to about 14 per cent (15-day old chicks).
(6) Incubation in the absence of glucose had more effect on brain slices from young chicks than from embryos. The opposite was true when a hypotonic medium or a medium containing d -glutamate was used.     

EARLY CHANGES IN ACETYLCHOLINE POOLS IN THE HIPPOCAMPUS OF THE RAT BRAIN AFTER SEPTAL LESIONS

—After placement of lesions in the hippocampus by electrocoagulation, an increase in bound acetylcholine above control levels was shown. There was no concomitant rise in free acetylcholine. The rise in bound acetylcholine was not due to changes in levels of either acetylcholinesterase or choline acetyltransferase and it is suggested that the interruption of septal impulses and/or alterations in uptake or availability of substrates is responsible.     

SYNTHESIS OF GANGLIOSIDES DURING DEVELOPMENT AND ITS RELATION TO THE QUANTITATIVE CHANGES OF SUBCELLULAR PARTICLES OF RAT BRAIN

Abstract— Different subcellular fractions prepared from developing rat cerebrum were quantified by determinations of dried weights and protein contents. It was found that there is an increase of 2–2·5 times in the weights of synaptosomes and mitochondria/g of tissue during the first 20 days of extrauterine life.
A period of fast synthesis of gangliosides, with a similar pattern of increase for the different subcellular particles, was found during the first 15 days of life by study of the incorporation of injected d -[1-¹⁴C]glucosamine in rats at different stages of development. Attempts to find out if gangliosides from a certain fraction are precursors of those of other fractions indicated that in all fractions the gangliosides increase independently of the other fractions. It is concluded that the enzymic systems of synthesis of these glycolipids are present in vivo in all the fractions considered.     

CHANGES IN THE DNA SYNTHESIS PATTERN OF PARAMECIUM WITH INCREASED CLONAL AGE AND INTERFISSION TIME

The clonal age in paramecia refers to the total number of vegetative divisions a clone has undergone since its origin at autogamy (self-fertilization). As clonal age increases, the interfission time usually increases. The DNA synthesis pattern of cells of different ages was compared by autoradiographic analysis of the DNA synthesis of synchronized cells at various time intervals during the cell cycle (from one division to the next). The study showed that the G₁ period (the lag in DNA synthesis post division) was constant, irrespective of interfission time or clonal age; but the duration of the DNA synthesis period increased with increased interfission time or clonal age. Therefore, we have shown for the first time that the G₁ period is fixed, and the S period is increased in a eukaryotic unicellular organism as a function of interfission time and clonal age.     

抗体应答期间大鼠脑和胸腺中儿茶酚胺含量的变化

目的：探讨在抗体应答期间,脑和淋巴器官中儿茶酚胺（ＣＡｓ）含量的动态变化,籍以了解免疫状态对中枢和外周ＣＡｓ神经活动的影响。方法：用绵羊红细胞（ＳＲＢＣ）免疫大鼠,在免疫后第２￣７ｄ应用高效液相色谱－电化学检测法（ＨＰＬＣ－ＥＣＤ）测定大鼠下丘脑、海马、脑干和胸腺中云甲肾上腺素（ＮＡ）、肾上腺素（Ａ）、多巴胺（ＤＡ）和高香草酸（ＨＶＡ）的含量。结果：①下且脑和海马内ＮＡ在抗体应答期间升高,而胸腺中     

吡格列酮治疗STZ诱导糖尿病大鼠视网膜中TSP-1的变化

观察吡格列酮在治疗STZ诱导糖尿病大鼠视网膜中血小板反应素Ⅰ(thmmbospondin-1,TSP-1)的变化,探讨噻唑烷二酮类药物在糖尿病视网膜病变中的影响和可能作用机制。用链脲佐菌素(STZ)腹腔注射建立大鼠糖尿病模型,随机分正常对照组(C组),糖尿病安慰剂组(D组)和糖尿病吡格列酮治疗组(DP组),8周后取视网膜组织行免疫组织化学、RT-PCR半定量检测TSP- 1mRNA水平的变化,结果显示在糖尿病早期视网膜神经节细胞层、内核层中均有明显的TSP1表达,对比于糖尿病对照组,糖尿病治疗组视网膜单位面积表达TSP1的细胞数量要较二组对照组高;糖尿病治疗组、糖尿病对照组和正常对照组间TSP-1的荧光灰度值分别为528.2±47.78、493.4±39.36和417.7±28.74:内参照GAPDH的荧光灰度值分别为796.4±21.18、811.2±36.80和832.4±43.18,各组间TSP-1 mRNA表达有显著性差异,提示吡格列酮对糖尿病早期视网膜中TSP-1的表达变化有影响,吡格列酮可能在延缓糖尿病视网膜病变的发生发展中起一定的作用。     

SUSTAINED DRUG-INDUCED ELEVATION OF BRAIN GABA IN THE RAT1

Abstract— The contents of GABA, homocarnosine, and β-alanine can be raised in rat brain for long periods of time by the continued administration of phenelzine, aminooxyacetic acid (AOAA), or isonicotinic acid hydrazide (INH). These 3 compounds apparently act by preferential inhibition of the enzyme GABA aminotransferase (GABA-T). Oral administration of phenelzine (20 mg/kg per day) caused a 25–50 per cent increase in GABA levels in rat brain, but produced appreciable toxic side effects. A similar increase in GABA levels in brain resulted from oral administration to rats of INH in a dosage of 60 mg/kg per day, without production of any obvious toxic effects. Simultaneous administration of large doses of pyridoxine did not abolish the GABA-elevating effect of INH. Brain GABA levels in the rat were increased by approx. 50 per cent by daily injections of AOAA (2.5 mg/kg per day). At this low dosage, AOAA injections in rats could be continued for at least 6 weeks without producing evident toxic effects. Oral administration of large amounts of GABA, on the other hand, failed to increase the content of GABA in the brains of rats not treated with GABA-T inhibitors, and failed to produce any further increase of brain GABA levels in rats treated with AOAA.     

ELEVATION IN RAT BRAIN HISTAMINE CONTENT AFTER FOCUSED MICROWAVE IRRADIATION1

Abstract— —Microwave irradiation focused on the head of small rodents is now widely used as a means of more accurately measuring acetylcholine, choline, cyclic AMP, and several other important brain constituents. Because of its probable neurotransmitter role and rapid turnover, a similar approach was taken to study brain histamine. Histamine was measured by a modified radio-enzymatic method and was found to be nearly tripled in brains from microwave treated rats, compared to decapitation controls (124 vs 42 ng/g). Possible explanations include a microwave-induced inactivation of histamine breakdown, a microwave-induced redistribution of previously unmeasured histamine, and microwave-induced histidine decarboxylation. Brain histamine remained unchanged up to 30 min after decapitation and microwave heated brains from decapitated rats also had elevated histamine levels, indicating that brain histamine levels in decapitated rats do not represent the remainder of a rapidly depleting pool. No evidence for previously unmeasured histamine was found. Furthermore, microwave irradiation did not enhance the formation of [³H]histamine after intraventricular [³H]histidine administration, indicating a lack of microwave-induced histidine decarboxylation. It is concluded that the elevation in rat brain histamine after focused microwave irradiation is probably not artifactual, although the mechanism responsible for this phenomenon remains obscure.