PubMed Health⌕ Search

Biomedical subjects

Alexei R Koudinov

Publications and source records attributed to Alexei R Koudinov.

8 recordsLinked to original sources
PubMed2005

Direct detection of brain acetylcholine synthesis by magnetic resonance spectroscopy.

The cholinergic system is an important modulatory neurotransmitter system in the brain. Changes in acetylcholine concentration have been previously determined directly in animal models and human brain biopsy specimens, and indirectly, by the effects of drugs, in living humans. Here, we developed a method for direct determination of acetylcholine synthesis in living brain tissue. The method is based on administration of choline, enriched with carbon-13 (stable isotope) in the two methylene positions, and detection of labeled acetylcholine and all other metabolic fates of choline, by carbon-13 magnetic resonance spectroscopy. We tested this method in rat brain slices and found it to be specific for acetylcholine synthesis in both the cortex and hippocampus. This method is potentially useful as a research tool for exploring the cholinergic system role in cognitive processes and memory storage as well as in diseases in which the malfunction of the cholinergic system has been implicated.

Acetylcholine↗
PubMed2004

Cholesterol homeostasis failure as a unifying cause of synaptic degeneration.

We previously showed that fine tuning of neural cholesterol dynamics is essential for basic synapse function, plasticity and behavior. Significant experimental evidence indicates that cholinergic function, ionotropic and metabotropic receptor machinery, excessive tau phosphorylation, the change of amyloid beta (Abeta or Abeta) biochemistry, neural oxidative stress reactions, and other features of neurodegeneration also depend on fine tuning of brain cholesterol homeostasis. This evidence suggest that (i) cholesterol homeostasis break is the unifying primary cause of sporadic and familial Alzheimer's disease (AD), neuromuscular diseases (particularly inclusion-body myositis), Niemann-Pick's type C disease and Down syndrome, and (ii) explains the overlap of neurodegenerative hallmarks across the spectrum of neurodegenerative diseases. Provided is evidence-based explanation of why extremely rare (but scientifically popular) cases of AD associated with mutations in amyloid beta protein precursor (APP) and presenilin (PS) genes, are translated into the disorder via membrane cholesterol sensitivity of APP processing by secretases and Abeta generation. The reciprocal effect of Abeta on cholesterol synthesis, cellular uptake, efflux and esterification is summarized, as well as the potential implication of such biological function for the compensatory Abeta-assisted restoration of the synaptic long-term potentiation (LTP) and resulting inability of tackling amyloid to cure AD.

Alzheimer Disease↗
PubMed2004

Alzheimer's amyloid-beta (A beta) is an essential synaptic protein, not neurotoxic junk.

Despite a decade long universal publication in favor of the view on amyloid-beta (A beta) as Alzheimer's disease culprit (solely neurotoxic for neurons and brain tissue), current scientific evidence leaves little doubt that A beta serves an essential role at synapse and in synaptic structure-functional plasticity that underlie learning and memory. Therefore, the change of A beta biology in Alzheimer's disease (as well as in a number of other human pathologies, including cardiovascular disease, neuromuscular junction disorders, NPC and Down's syndrome) may represent a physiological mechanism to compensate for impaired brain structure or function. In our own recent study A beta 1-40 rescued long term potentiation (LTP, a major model for activity-dependent CNS plasticity), while cholesterol synthesis inhibition abolished the restorative action of the A beta peptide. This study confirms that A beta protein is a functional player in synaptic structure-functional plasticity and in cholesterol neurochemical pathways. The article also calls for a need to critically re-evaluate a universal belief that transgenic mice with a transgene for amyloid-beta protein precursor (A beta PP) are a true model for Alzheimer's type neurodegeneration.

Alzheimer Disease↗
PubMed2003

Cholesterol, synaptic function and Alzheimer's disease.

We experimentally modeled neuronal cholesterol imbalance by creating an acute biochemical increase in cholesterol turnover in rat hippocampal slices. This kind of experimental set-up impairs the redistribution of cholesterol from one cell to another via lipoprotein transport. While increasing cholesterol removal or immediately afterwards, we evoked and recorded two brain waveforms, paired pulse facilitation (PPF) and long-term potentiation (LTP), which indicate neurotransmission and synaptic plasticity, respectively. We found that the lack of cholesterol supply to neurons impaired both PPF and LTP. From additional immunofluorescent analysis of the slices, we could demonstrate that the cholesterol imbalance also caused neurodegeneration of hippocampal neural cell processes and the appearance of tau protein pathology in the mossy fibers. We also analyzed rats fed a cholesterol diet and discovered that they had increased hippocampal cholesterol biosynthesis and impaired LTP. Cholesterol-fed rats were also characterized by Alzheimer's-like brain amyloid that we did not observe in the model of acute cholesterol imbalance. Our data and research by others suggest that biological cholesterol homeostasis dysregulation itself plays a key role in synaptic plasticity impairment and neuronal degeneration, and is the primary cause for several Alzheimer's disease hallmarks not limited to brain amyloids. Moreover, changes in the neurochemistry of amyloid beta, tau, neuronal cytoskeleton, and oxidative stress reactions due to Alzheimer's likely represent physiological transitory mechanisms that aim to compensate impaired brain cholesterol dynamics and/or associated neurotransmission and synaptic plasticity failure. Part of this article was published as netprint and is available under the URL http://clinmed.netprints.org/cgi/content/full/2001100005v1.

Acetates↗
PubMed2002

Choline in the aging brain.

Proton magnetic resonance spectroscopy has been increasingly utilized in brain research to monitor non-invasively metabolites such as N-acetyl aspartate (NAA), creatine (Cr) and choline (Cho). We present here studies of the effect of aging on the ratios of these metabolites measured in the rat brain in vivo and on choline transport and lipid synthesis in rat brain slices, in vitro. The in vivo studies indicated that the ratios of Cho/NAA and Cho/Cr increased in the aged hippocampus, whereas the ratio of Cr/NAA was similar in the aged and adult hippocampus. These three ratios remained similar in the cortex of adult and aged rats. The in vitro studies revealed that in the aged cortex and the aged hippocampus the activity of the low-affinity choline uptake increased, possibly compensating for a decrease in the high-affinity uptake activity and the rate of choline diffusion. The incorporation of choline into phospholipids exhibited high and low affinity kinetics which were not modified by aging.

Aging↗