EFFECTS OF IMIDAZOLEACETIC ACID ON BRAIN AMINO ACIDS AND BODY TEMPERATURE IN MICETunnicliff, G.; Wein, J.; Roberts, E.
doi: 10.1111/j.1471-4159.1972.tb05111.xpmid: 5072379
Free amino acids have been studied in the brains of fasted mice (18 h) injected intraperitoneally with a 3 mmol/kg dose of imidazole‐4‐acetic acid (IMA). Groups of mice were killed by cervical dislocation and their brains were removed before injection or at 5, 15, 30, 60, 90 and 120 min after injection and treated immediately with perchloric acid. Amino acid analyses were performed on the perchlorate extracts. Of the 16 amino acids evaluated quantitatively, only glutamic acid and glutamine showed progressive changes during the period of observation, the glutamic acid falling and glutamine levels rising. Serine and threonine levels were increased significantly above the control values from 30 min after the injection to the end of the experiment. Rectal temperatures (measured with a thermistor probe) after injection of IMA showed a progressive reduction from the control levels throughout the period of observation. An essentially linear correlation was noted between the decreases in body temperature and the differences between the glutamic acid and glutamine values for the first 90 min post‐injection. Our data suggest that IMA affects mechanisms of temperature regulation, possibly in the hypothalamus, and that, among other processes, the activities of glutaminase and of serine and threonine dehydratases in brain might be reduced when brain temperatures fall.
BRAIN PROTEINS: QUALITATIVE AND QUANTITATIVE CHANGES, SYNTHESIS AND DEGRADATION DURING FETAL DEVELOPMENT OF THE RABBITCain, D. F.; Ball, E. D.; Dekaban, A. S.
doi: 10.1111/j.1471-4159.1972.tb05113.xpmid: 5072381
The composition and metabolism of the proteins of the cerebral pallium of the rabbit during the final one‐third of the gestational period were measured. During this period, the brain increased in size almost 10‐fold and the migration of neuroblasts to form the cerebral cortex became complete. Concurrent with the marked structural changes, the solubility characteristics and electrophoretic distribution of various brain proteins showed little change. However, at the time of birth and in the adult, significant differences in gel electrophoresis patterns were apparent. The rate of synthesis of protein in brain slices from the fetus of 20 days gestation was 3‐fold higher per mg of tissue than in the neonate and about 30‐fold higher than in the adult. Activities of acidic and neutral proteases per unit weight were virtually the same and nearly constant throughout the late fetal period. However, during this stage, while rapid growth persists, the total protein synthetic activity of the pallium predominated over the total proteolytic activity, whereas sometime after birth the ratios of these activities reversed consequent to a shutdown of the synthetic process.
THE REGIONAL AND SUBCELLULAR DISTRIBUTION OF CATECHOL‐ O ‐METHYL TRANSFERASE IN THE RAT BRAINBroch, O. J.; Fonnum, F.
doi: 10.1111/j.1471-4159.1972.tb05115.xpmid: 4403687
Catechol‐O‐methyl transferase (COMT) activities determined in different regions of rat brain showed small variations. Highest activities were found in the hypothalamus and corpora quadrigemina, and lowest activities in the hippocampus and corpus striatum. The regional distribution of COMT was thus at variance with the distribution of DOPA decar‐ boxylase in this study and with the distribution of catecholamines and tyrosine hydroxylase reported in the literature. Determinations of the subcellular distribution of COMT in rat forebrain showed that 50 per cent of the activity was recovered in the high speed supernatant fluid and about 33 per cent in the crude mitochondrial fraction. Further separation of the latter by discontinuous sucrose gradients showed that the particulate COMT was found in the synaptosomal fraction in an occluded form. Full enzyme activity was only obtained after treatment with a detergent or after resuspension in water. After hypo‐osmotic rupture of the crude mitochondrial fraction, COMT was recovered in the cytoplasmic fraction. The subcellular distribution of COMT was very similar to the ones of lactate dehydrogenase and DOPA decarboxylase. The proportions of soluble COMT obtained from homogenates of various regions of the brain differed from that of choline acetyl transferase and DOPA decarboxylase but were similar to that of lactate dehydrogenase. In conclusion, COMT is a cytoplasmic enzyme almost evenly distributed in the CNS. Its distribution does not resemble the distributions of the catecholamines or of the enzymes participating in the synthesis of catecholamines.
INCORPORATION OF PHENYLALANINE, TYROSINE AND TRYPTOPHAN INTO PROTEIN OF HOMOGENATES FROM DEVELOPING RAT BRAIN: KINETICS OF INCORPORATION AND RECIPROCAL INHIBITIONOja, S. S.
doi: 10.1111/j.1471-4159.1972.tb05116.xpmid: 5072383
The kinetics of the incorporation into protein of (3H)phenylalanine, (3H)tyrosine and (3H)tryptophan were studied with homogenates prepared from whole brain of 1‐, 7‐, 21‐ and 60‐day‐old rats. The maximal velocities (Vmax)of incorporation of phenylalanine and tyrosine decreased and the apparent Michaelis‐constants (Km) for all three amino acids increased with increasing age of the rats. Tyrosine had the smallest and tryptophan the largest Km values in all age groups. Phenylalanine competitively inhibited the incorporation of tyrosine, but tyrosine inhibited non‐competitively the incorporation of phenylalanine. Tryptophan inhibited competitively the incorporation of phenylalanine, but at least partially non‐competitively the incorporation of tyrosine. Phenylalanine and tyrosine did not significantly affect the incorporation of tryptophan in homogenates from 60‐day‐old rats. In 1‐day‐old rats only a very large excess of phenylalanine or tyrosine inhibited detectably. The Ki for phenylalanine in the incorporation of tyrosine was significantly smaller in 1‐ than in 60‐day‐old rats. In every case the inhibition presumably occurred at a single rate‐limiting step in the complicated process of incorporation of amino acids into protein.
THE PATTERN OF METHYLATION OF RNA IN PERIPHERAL NERVE OF THE CHICK DURING DEVELOPMENTMezei, Catherine; Hu, Y.‐W.
doi: 10.1111/j.1471-4159.1972.tb05117.xpmid: 5072384
The pattern of the methylation of RNA was investigated in organ cultures of the sciatic nerve of the chicken. Nerve tissue from 14‐day embryos, 17‐day embryos and 3‐day‐ old chicks was incubated with (methyl‐3H)methionine or with (2‐14C)uridine and (methyl‐3H)methionine simultaneously for various periods of time. Subsequently, RNA was extracted from the tissues and the purified preparations were fractionated by polyacrylamide gel electrophoresis. The electrophoretic patterns of the rapidly labelled RNA changed during the three developmental stages. The incorporation of both uridine and the methyl groups from methionine was highest in the‘heavy’RNA species of the 14‐day embryonic nerve during the 0.5 and 1.0 h incubation periods. In contrast, in the nerves of 3‐day‐old chicks during a 0.5 h pulse with both precursors, methylation was almost entirely limited to the transfer RNA species. Furthermore, the incorporation of uridine in the nerves from 3‐day‐old animals revealed the presence of a heterogeneous population of rapidlylabelled, unmethylated species of RNA, most of which migrated between the smaller ribosomal RNA and transfer RNA components of the bulk RNA. The pattern of uridine incorporation and the methylation of the rapidly‐labelled RNA of the 17‐day embryonic nerve represented a transitional state between that of the 14‐day embryos and that of the 3‐day‐old chicks. The 17‐day embryonic stage of development corresponded to the phase of the onset of rapid deposition of myelin lipids in the sciatic nerve. Pulse‐chase experiments on the embryonic nerves indicated that a number of methylated precursors of ribosomal RNA and labile, heterogeneous, probably DNA‐like RNA were synthesized.
METABOLISM OF THE ASPARTYL MOIETY OF N ‐ACETYL‐ l ‐ASPARTIC ACID IN THE RAT BRAINNadler, J. V.; Cooper, J. R.
doi: 10.1111/j.1471-4159.1972.tb05119.xpmid: 5072386
The metabolism of N‐acetyl‐l‐aspartic acid (NAA) was studied in rat brain. (Aspartyl‐U‐14C)NAA was metabolized predominantly by deacylation. Studies of NAA biosynthesis from l‐(U‐14C)aspartic acid have confirmed previous reports that NAA turns over slowly in rat brain. However, intracerebrally‐injected N‐acetyl‐l‐(U‐14C)asparticacid was rapidly metabolized. Exogenous NAA appears to be taken up rapidly into a small, metabolically‐active pool. This pool serves as substrate for a tricarboxylic acid cycle associated with the production of glutamate for the biosynthesis of glutamine. The bulk of the NAA content in brain appears to be relatively inactive metabolically.
EFFECTS OF SODIUM FLUOROACETATE ON THE METABOLISM OF N ‐ACETYLASPARTATE AND ASPARTATE IN MOUSE BRAINNadler, J. V.; Horwitch, P.; Cooper, J. R.
doi: 10.1111/j.1471-4159.1972.tb05120.xpmid: 5072387
A subconvulsant dose of sodium fluoroacetate inhibited the metabolic utilization of intracerebrally‐administered N‐acetyl‐l‐(U‐14C)asparticacid and the labelling of glutamine from this precursor in mouse brain, but not the labelling of glutamate or aspartate. A convulsant dose also inhibited the utilization of l‐(U‐14C)aspartic acid. When intraperitoneal injection of a convulsant dose of sodium fluoroacetate was followed by intracerebral injection of N‐acetyl‐l‐(U‐14C)asparticacid, the levels of N‐acetylaspartate, aspartate and glutamate in brain were lowered, while the glutamine content was increased. The specific radioactivity of glutamine relative to that of glutamate was much lower when these compounds were labelled from l‐(U‐14C)aspartic acid than when N‐acetyl‐l‐(U‐14C)aspartic acid was used as the precursor. Intracerebral injection of tracer amounts of l‐(U‐14C)aspartic acid reduced the content of N‐acetylaspartate in brain and raised the glutamine content. Sodium fluoroacetate had no additional effect on the relative specific radioactivity of glutamine or the content of N‐acetylaspartate, aspartate, glutamate or glutamine when l‐(U‐14C)aspartic acid was the precursor. We consider the results to be consistent with a selective inhibition both by sodium fluoroacetate and by exogenous aspartic acid of the tricarboxylic acid cycle in brain associated with the biosynthesis of glutamine. We suggest that the activity of this pathway may regulate the metabolism of N‐acetylaspartate and aspartate.