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-'4C]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 steadystate 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.The autoradiographic deoxyglucose method (1) for measurement of local cerebral glucose utilization provides a useful model for the design of methods to determine local rates of biochemical processes within tissues in vivo. We have used the same general approach to develop a method for the quantitative determination of local rates of protein synthesis, or, more precisely, amino acid incorporation into protein, in the nervous system (2, 3). The method is an application of the basic principles for the assay of rates of chemical reactions with isotopes adapted for the special conditions encountered in vivo (4). Briefly, the total amount of labeled product specific to the reaction of interest (in this case labeled protein) formed in the selected tissue over an interval of time is divided by the integrated specific activity (SA) of the precursor pool over the same interval and corrected for any isotope effect (4). This relationship can be expressed as follows:
Verbal fluency tasks are widely applied in a variety of languages, but whether the quality and quantity of responses are comparable across structurally different writing systems is debatable. For example, since there are no letters in a logographic, non-alphabetic language such as Chinese, the mechanisms speakers use to generate a list of words in a letter fluency task might be structurally different than those used by speakers of alphabetic languages. In this study, we investigated lexical retrieval strategies and approaches in letter and category fluency tasks among monolingual Mandarin speakers compared to monolingual English speakers. We found that the responses of Mandarin speakers are both qualitatively and quantitatively different in letter fluency, and qualitatively different in category fluency. These results suggest that differences in task completion among non-English-speaking populations are important to consider when using this extensively utilised cognitive and linguistic measure in research and clinic.
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