Rates Of Cerebral Protein Synthesis Research Articles

Effects of axotomy on protein synthesis in the rat hypoglossal nucleus: examination of the influence of local recycling of leucine derived from protein degradation into the precursor pool.

The quantitative autoradiographic L-[1-14C] leucine method for the determination of regional rates of cerebral protein synthesis (lCPSleu) requires knowledge of the degree of recycling of leucine derived from protein degradation into the precursor pool for protein synthesis, which can be evaluated by measuring lambda i, the steady-state ratio of the leucine-specific activity in the precursor amino acid pool (tRNA-bound leucine) to that of the arterial plasma. To define the changes in lCPSleu during regeneration of the hypoglossal nerve, we examined the effects of axotomy on the value of lambda i. Because the concentration of tRNA-bound leucine in the hypoglossal nucleus is too low to measure, we measured the equivalent ratio for the total acid-soluble pool (psi i) and applied the linear relationship between lambda and psi found in the whole brain to calculate a value of lambda i in the ipsilateral and contralateral hypoglossal nuclei of 22 adult female rats 2, 18, 35, and 60 days after unilateral hypoglossal axotomy. Statistically significant but quantitatively inconsequential effects of axotomy on values of psi i and lambda i were found. Therefore, the mean value for lambda i (0.64) of the left and right hypoglossal nuclei in all 22 axotomized rats was used to calculate lCPSleu. In a separate group of 15 unilaterally axotomized rats, lCPSleu was determined by the autoradiographic technique; lCPSleu was increased on the axotomized side by 23% on day 2, 30% on day 18, and 13% on day 35. By postaxotomy day 60, lCPSleu had returned to normal.

The effect of an AMPA antagonist (NBQX) on postischemic neuron loss and protein synthesis in the rat brain.

Two groups of rats were subjected to 12 min of global cerebral ischemia and 6 days recirculation using the four-vessel occlusion model with hypotension and then treated with the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) antagonist NBQX [2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo (F) quinoxalinedione (Honoré et al. 1988]. One group was used for routine and quantitative histology and immunostaining for glial fibrillary acidic protein (GFAP). The second group was subjected to autoradiographic studies of regional cerebral protein synthesis, with special emphasis on the hippocampus, the frontal cortex, and the thalamus. It was found that neuroprotective treatment with NBQX normalized cerebral protein synthesis rate (CPSR) in all investigated regions 6 days after ischemia. In untreated ischemic animals CPSR was normalized in all regions except for the CA3 and thalamus, where it had increased by 29% and 41%, respectively. Treatment of controls with NBQX had no effect on CPSR after 6 days. The histological investigations revealed that NBQX did not protect vulnerable cells in the dentate hilus and the reticular thalamic nucleus (RTN). In these regions reactive astrocytosis visualized by GFAP immunostaining was equally pronounced in both ischemic and NBQX-treated animals, and most neurons in the RTN were eosinophilic. The 80-100% pyramidal neuron loss in CA1 was accompanied by a high degree of reactive astrocytosis, whereas the NBQX-treated animals showed no signs of astrocytosis in this region. The ischemic CA1 pyramidal layer was also massively invaded by microglia.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of regional rates of cerebral protein synthesis adjusted for regional differences in recycling of leucine derived from protein degradation into the precursor pool in conscious adult rats.

The quantitative autoradiographic L-[1-14C]leucine method for the determination of regional rates of cerebral protein synthesis in vivo takes into account recycling of unlabeled leucine derived from protein degradation into the precursor pool for protein synthesis. We have evaluated the degree of recycling by measuring the ratio of the apparent steady-state leucine specific activity in the precursor amino acid pool (tRNA-bound leucine) to that in the arterial plasma. In the whole brain of the conscious rat this ratio (lambda WB) equals 0.58. The equivalent ratio for leucine in the acid-soluble pool in whole brain (psi WB) is 0.49. A first-degree polynomial equation for lambda WB as a function of psi WB was fitted from paired determinations. To determine the degree of recycling in local regions of the brain, we have measured in individual brain regions (i) psi i and calculated lambda i assuming that the fitted equation also applies to these localized regions. Our results indicate that the degree of recycling into the precursor pool does vary regionally; lambda i in the individual regions varies from 0.62 in the hypoglossal nucleus to 0.50 in the globus pallidus. Local rates of protein synthesis were then determined by the autoradiographic technique with regional corrections for recycling of unlabeled leucine. Rates of leucine incorporation into protein averaged 6.1 nmol/g of tissue/min in the brain as a whole, with the rates in gray matter about twice those in white matter.

Regional cerebral protein synthesis after transient ischemia in the rat: Effect of the AMPA antagonist NBQX

Normothermic rats with 12 min, complete cerebral ischemia were treated with the AMPA antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo (F) quinoxalinedione (NBQX) [10], which prevents CA1 pyramidal neuron loss. Twenty hours after ischemia, cerebral protein synthesis rate (CPSR) was measured autoradiographically using [ 35S]methionine. Ischemia caused a 38% decrease of CPSR in CA1, and postischemic treatment with NBQX caused a 66% decrease in this region. Also treatment with NBQX alone resulted in a decrease (22% in CA1) of the CPSR. Since some evidence exists that the neuroprotective effect of NBQX is related to blockade of the fast AMPA-mediated transmission, the further decrease of the postischemic CPSR in CA1 could be a mere side effect.

The measurement of regional rates of cerebral protein synthesis in vivo

The measurement of regional rates of cerebral protein synthesis in vivo

Rates of cerebral protein synthesis are linked to slow wave sleep in the rat

Using L-[1- 14C]leucine autoradiography, rates of cerebral and local cerebral protein synthesis were studied during wakefulness, slow wave sleep (SWS) and REM sleep in the rat. In the cerebrum as a whole, the rate at which labelled leucine was incorporated into tissues was positively correlated with the occurrence of slow wave sleep. We failed to observe a significant correlation of protein synthesis rate with either wakefulness or REM sleep. As in the cerebrum as a whole, most discrete brain regions showed moderate positive correlations between the occurrence of SWS and rates of protein synthesis. There were no brain regions in which rates of protein synthesis showed striking correlations with sleep-wake states. Thus, the occurrence of SWS is associated with higher rates of protein synthesis throughout the brain. These data suggest that SWS sleep favors the restoration of cerebral proteins.

In vivo Cerebral Protein Synthesis Rates with Leucyl-Transfer RNA Used as a Precursor Pool: Determination of Biochemical Parameters to Structure Tracer Kinetic Models for Positron Emission Tomography

Leucine oxidation and incorporation into proteins were examined in the in vivo rat brain to determine rates and compartmentation of these processes for the purpose of structuring mathematical compartmental models for the noninvasive estimation of in vivo human cerebral protein synthesis rates (CPSR) using positron emission tomography (PET). Leucine specific activity (SA) in arterial plasma and intracellular free amino acids, leucyl-tRNA, alpha-ketoisocaproic acid (KIC), and protein were determined in whole brain of the adult rat during the first 35 min after intravenous bolus injection of L-[1-14C]leucine. Incorporation of leucine into proteins accounted for 90% of total brain radioactivity at 35 min. The lack of [14C]KIC buildup indicates that leucine oxidation in brain is transaminase limited. Characteristic specific activities were maximal between 0 to 2 min after bolus injection with subsequent decline following the pattern: plasma leucine greater than or equal to leucyl-tRNA approximately KIC greater than intracellular leucine. The time integral of leucine SA in plasma was about four times that of tissue leucine and twice those of leucyl-tRNA and KIC, indicating the existence of free leucine, leucyl-tRNA, and KIC tissue compartments, communicating directly with plasma, and separate secondary free leucine, leucyl-tRNA, and KIC tissue compartments originating in unlabeled leucine from proteolysis. Therefore, a relatively simple model configuration based on the key assumptions that (a) protein incorporation and catabolism proceed from a precursor pool communicating with the plasma space, and (b) leucine catabolism is transaminase limited is justified for the in vivo assessment of CPSR from exogenous leucine sources using PET in humans.

Estimation of Local Cerebral Protein Synthesis Rates with L-[1-11C]Leucine and PET: Methods, Model, and Results in Animals and Humans

We have estimated the cerebral protein synthesis rates (CPSR) in a series of normal human volunteers and monkeys using L-[1-11C]leucine and positron emission tomography (PET) using a three-compartment model. The model structure, consisting of a tissue precursor, metabolite, and protein compartment, was validated with biochemical assay data obtained in rat studies. The CPSR values estimated in human hemispheres of about 0.5 nmol/min/g agree well with hemispheric estimates in monkeys. The sampling requirements (input function and scanning sequence) for accurate estimates of model parameters were investigated in a series of computer simulation studies.

Measurement of local cerebral protein synthesis in vivo: influence of recycling of amino acids derived from protein degradation.

A quantitative autoradiographic method for the determination of local rates of protein synthesis in brain in vivo is being developed. The method employs L-[1-14C]leucine as the radiolabeled tracer. A comprehensive model has been designed that takes into account intracellular and extracellular spaces, intracellular compartmentation of leucine, and the possibility of recycling of unlabeled leucine derived from steady-state degradation of protein into the precursor pool for protein synthesis. We have evaluated the degree of recycling by measuring the ratio of the steady-state precursor pool distribution space for labeled leucine to that of unlabeled leucine. The values obtained were 0.58 in whole brain and 0.47 in liver. These results indicate that there is significant recycling of unlabeled amino acids derived from steady-state protein degradation in both tissues. Any method for the determination of rates of cerebral protein synthesis in vivo with labeled tracers that depends on estimation of precursor pool specific activity in tissue from measurements in plasma must take this recycling into account.

Cerebral Protein Synthesis and Ischemia

Publisher Summary This chapter describes the cerebral protein synthesis rates (CPSR) in detail for normal rat and gerbil brains. The in vitro results are used as a supplement to correct the end-point measurements of specific activities in the absence of knowledge about their time course during the 45 minutes of incorporation. This approach is applied to the study of regional cerebral protein synthesis in two models of cerebral ischemia. Functional and morphological investigations have revealed that irreversible neuronal damage may develop after as little as five minutes' ischemia in selectively vulnerable areas, whereas recovery from ischemia seems to be possible in other regions of the brain after ischemia as long as one hour. There are two series of experiments: a short-lasting ischemia induced by bilateral carotid occlusion in gerbils, and a prolonged ischemia induced by intrathoracal clamping of the innominate, subclavian and mammary arteries in monkeys, are presented.

The effects of aging on local rates of cerebral protein synthesis in rats.

The effects of aging on local rates of cerebral protein synthesis in rats.

Changes in protein synthesis underlying functional plasticity in immature monkey visual system.

Local rates of cerebral protein synthesis were determined in newborn rhesus monkeys subjected to either acute or chronic monocular visual deprivation. Chronic monocular deprivation resulted in decreased rates of protein synthesis in the laminae of the lateral geniculate nuclei innervated by the deprived eye whereas rates of protein synthesis were normal in geniculate laminae innervated by the functioning eye. Acute monocular deprivation produced no differential changes in rates of protein synthesis in any of the geniculate laminae.

Enhanced cerebral protein synthesis in developing hypothyroid rats: evidence for delayed maturation.

Abstract(1) Neonatal hypothyroidism resulted in a 40% increase in the incorporation of [14C]leucine into protein by cerebral cortical slices from 25‐day‐old rats. The uptake of the [14C]‐labelled amino acid into the acid‐soluble free amino acid pool was similar in hypothyroid and control groups which excluded the possibility that transport differences contributed to the observed differences in incorporation. (2) The conversion of [14C]leucine in the free amino acid pool to other metabolites was substantially greater in the hypothyroid state compared to euthyroid controls. (3) The correction of the incorporation data for radioactivity associated with [14C]leucine in the precursor pool, provided an estimate of cerebral protein synthetic rate which was markedly higher in thyroid hormone‐deficient‐rats compared to litter mate controls. (4) The administration of L‐thyroxine to hypothyroid animals for two successive days essentially returned the accelerated metabolism of the precursor pool leucine to normal but failed to ameliorate the increased incorporation into protein. (5) Incubations conducted in the presence of high exogenous leucine levels, to eliminate possible differences in intracellular free amino acid pool size, provided additional evidence for an increased rate of cerebral protein synthesis in 25‐day‐old hypothyroid rats compared to controls. (6) The results are compatible with a retardation in the normal developmental decline in the rate of cerebral protein synthesis associated with hypothyroidism.

Changes in the rates of protein synthesis in the brain of goldfish at various temperatures

Intraperitoneal injections of [ 14C] tyrosine suspension into goldfish produced a relatively constant specific activity of free tyrosine in the brain over an 8 hour experimental period. This made the measurement of the rate of cerebral protein synthesis in this time period possible. The increase of protein-bound [ 14C] tyrosine was linear with time and occured in most protein fractions. In the absence of a net increase of protein it was an indicator of the rate of cerebral protein turnover. Rates of incorporation of tyrosine into brain proteins were 0.52 per cent/hour at 34° and 0.026 per cent/hour at 10°, i.e., the rate at 34° was about 20-fold that at 10°. Temperature gradients of protein turnover were similar in fish and rat brain.

Effect of neonatal hypothyroidism and of thyroxine on l-[ 14C]leucine incorporation in protein in vivo and the relationship to ionic levels in the developing brain of the rat

Summary The rate of cerebral protein synthesis in vivo and changes in ionic levels have been investigated in infant rats following thyroid hormone deficiency induced at 1 day of age and after the administration of physiological levels of thyroxine from the 6th day of age. Following the injection of uniformly labelled l -[ 14 C]leucine in proportion to body weight, the rate of disappearance of the label from plasma and cerebral free amino acid pool was depressed in thyroid-deficient animals. The specific activity of cerebral protein-bound leucine expressed as a function of the specific activity of the label in the free amino acid pool was significantly reduced in hypothyroid rats, indicating a decrease in protein synthesis. It was inferred from the changes in cerebral Na + , K + , and Cl-ions in hypothyroid rats that the Na-K pump is altered and the transport of amino acids is adversely affected. Thyroxine therapy reversed the changes in cerebral protein synthesis and ionic concentration. It was concluded that the relationship between thyroid hormone action and brain protein synthesis is partially mediated through the effect of this hormone on ionic distribution and amino acid transport.