Rat brain acetylcholinesterase turnover in vivo: use of a radioactive methylphosphonothiate irreversible inhibitor

Reduced clearance of proteins labeled with diisopropylfluorophosphate in portacaval-shunted rats

Portacaval shunting is a model for hepatic encephalopathy that causes chronic hyperammonemia, disruption of metabolic, signaling, and neurotransmitter systems, and progressive morphological changes. Exposure of cultured cells to ammonia raises intralysosomal pH and inhibits proteolysis, and the present study tested the hypothesis that proteolytic capacity is diminished in portacaval-shunted rats. Proteins were labeled in vivo with tracer doses of diisopropylfluorophosphate (DFP) and clearance of label was assayed. This approach labeled proteins independent of protein synthesis, which is reported to be altered in shunted rats, and avoided complications arising from re-utilization of labeled amino acids that causes underestimation of degradation rate. Characterization of DFP labeling showed that protein labeling was fast, about 50% of the label was released during a 24 h interval, labeling by DFP metabolites was negligible, inhibition of brain acetylcholinesterase was not detectable, and labeling by [(3)H]- and [(14)C]DFP was equivalent. To assay degradative capacity, proteins were first labeled with [(3)H]DFP, followed by labeling with [(14)C]DFP that was given 24 or 72 h later. The (3)H/(14)C ratio in each animal was used as a relative measure of removal of (3)H-labeled proteins. (3)H/(14)C ratios were generally significantly higher in portacaval-shunted rats than in controls, consistent with reduced proteolytic capacity. Assays of amino acid incorporation into brain protein generally replicated literature reports, supporting the conclusion that protein synthesis unlikely to be markedly inhibited and amino acid recycling influences calculated protein synthesis rates in shunted rats. Therapeutic strategies to reduce ammonia level would help normalize lysosomal functions and protein and lipid turnover.

Resurrecting clinical pharmacology as a context for Alzheimer disease drug development

Commercial priorities have been identified as negative factors in drug development. We trace the problem to inattention to sound clinical pharmacology practices. When properly applied, clinical pharmacology and associated drug development sciences can, hand in hand, facilitate success in commercial drug development.

Reaction of the organism to stress: the survival attractor concept

This paper outlines a phenomenological approach for describing physiological reactions occurring immediately after vital threats. This exemplified by data taken from previous studies relative to chemical intoxications of rats by a neurotoxical drug. The survival rate of the animals and the variations of their cerebral acetylcholinesterase activity are both reported as a function of the drug concentration, and with respect to their age. The collecting of the results may be described as the cusp, a bifurcation set of Thom's Catastrophe Theory. The young animals react by a vital burst which modifies the shape of the cusp. A new fold or pocket takes place, changing it to the butterfly bifurcation set. This pocket supports the survival attractor concept, which appears reactional, transitory and variable in its intensity. In the last part of the paper, an extension of this concept is proposed to the visual domain. Some of patients who have suddenly and partially lost their visual acuity can recover some visual capacity by developing a new ability to see in weak contrasts. This reaction may be described as a visual survival attractor.

Demonstration of functional acetylcholinesterase on the soma of individual neurones of Aplysia by in vivo microspectrophotometry

The presence of functional acetylcholinesterase is demonstrated in vivo on somatic membranes of single ganglionic neurones of Aplysia using concurrently microspectrophotometry and electrophysiology. The similarity of the effects of an irreversible blocker of acetylcholinesterase and of phospholipase C from Bacillus cereus suggests that acetylcholinesterase is anchored in the membrane via phosphatidylinositol.

Spectrophotometry in vivo, a technique for local and direct enzymatic assays: application to brain acetylcholinesterase

In vivo enzymology is not widely studied due to the lack of a well-adapted technology. We have developed a system that allows local and long-term spectrophotometric assays in brain tissue of live animals. It utilizes a miniaturized optical probe consisting of a multibarrel micropipette for reagent injections and optical fibers for light absorption measurements. We have applied this system to the colorimetric determination of brain acetylcholinesterase activity in rats. The reproducibility of the assay was demonstrated by repetitive assays over 24 hr, its specificity was established through the use of a highly specific organophosphorus inhibitor, and the activities measured in different brain areas agreed with the known distribution of acetylcholinesterase. No electroencephalographic abnormalities and no change in vigilance level were observed in the experimental animals. This methodology should prove to be useful for the colorimetric measurement of different enzymes or metabolites in various organs.

Recovery of cholinesterases in soman-injected superior cervical ganglion of the rat in the presence and absence of innervation

We have previously described the procedure for quantitative separation of extracellular and intracellular ChEs using mild treatment of rat superior cervical ganglion with papain. Here, this procedure was used in order to investigate the recovery of ChEs in the two pools after irreversible inhibition by soman which was directly injected into the ganglion. After such treatment only ganglion ChEs were totally inhibited, whereas the activity of ChEs in preganglionic neurons and their axons remained unaffected. Comparing in innervated and decentralized ganglia the pattern of recovery rate and ultrastructural reappearance of ChEs after local inhibition, with that reported after systemic ChEs inhibition, it was possible to distinguish between the indirect effects of innervation on the recovery rate and pattern of ChEs of ganglion origin and the direct contribution to the total ganglion enzyme activity of ChEs originating in the preganglionic elements. The absence of nerve contracts affects mostly extracellular activity, particularly AChE, whereas the intracellular activity of AChE was only slightly decreased and the activity of nsChE was somewhat increased. This increase coincides with the enhanced cytochemical reaction of nsChE in some nonneuronal cells in the ganglion. Actinomycyn D decreased the rate of initial rapid phase of recovery of intracellular ChEs when injected in the ganglion daily for three days, whereas the recovery of extracellular ChEs was already decreased the first day of Actinomycyn D application. This indicates that the externalization of the enzyme is more affected than its synthesis by inhibition the translation step.(ABSTRACT TRUNCATED AT 250 WORDS)