The effect of thiamine deficiency on the acetylcoenzyme A and acetylcholine levels in the rat brain

Supplemental thiamine as a practical, potential way to prevent Alzheimer's disease from commencing

It is better to attempt stopping Alzheimer's disease (AD) before it starts than trying to cure it after it has developed. A cerebral scan showing deposition of either amyloid or tau identifies those elderly persons whose cognition is currently normal but who are at risk of subsequent cognitive loss that may develop into AD. Synaptic hypometabolism is usually present in such at-risk persons. Although inadequate adenosine triphosphate (ATP) may cause synaptic hypometabolism, that may not be the entire cause because, in fact, measurements in some of the at-risk persons have shown normal ATP levels. Thiamine deficiency is often seen in elderly, ambulatory persons in whom thiamine levels correlate with Mini-Mental State Examination scores. Thiamine deficiency has many consequences including hypometabolism, mitochondrial depression, oxidative stress, lactic acidosis and cerebral acidosis, amyloid deposition, tau deposition, synaptic dysfunction and abnormal neuro-transmission, astrocyte function, and blood brain barrier integrity, all of which are features of AD. Although the clinical benefits of administering supplementary thiamine to patients with AD or mild cognitive impairment have been mixed, it is more likely to succeed at preventing the onset of cognitive loss if administered at an earlier time, when the number of aberrant biochemical pathways is far fewer. Providing a thiamine supplement to elderly persons who still have normal cognition but who have deposition of either amyloid or tau, may prevent subsequent cognitive loss and eventual dementia. A clinical trial is needed to validate that possibility.

Acute Shoshin beriberi syndrome immediately post-kidney transplant with rapid recovery after thiamine administration

Pediatric kidney transplant surgery is usually well tolerated, despite suboptimal physical conditioning that may result from uremia and nutritional deficiencies that accompany end-stage kidney failure. Nutritional supplementation is used to overcome such deficiencies, especially for children needing dialysis. Thiamine, a water-soluble vitamin also known as vitamin B1, is a critical cofactor in energy metabolism and may be competitively inhibited by the antimetabolite oxythiamine, a uremic toxin that accumulates in kidney failure. We report a case of a thiamine deficiency syndrome leading to overwhelming cardiac dysfunction, metabolic instability, and hemodynamic compromise, after otherwise uneventful kidney transplant surgery. Prior to transplant, this 14-year-old boy was treated with peritoneal dialysis and received thiamine supplementation. Post-transplant, the patient first developed hyperglycemia, then lactic acidosis, and subsequently hemodynamic instability despite escalating treatment with volume resuscitation and inotropic medication. He made a rapid and complete recovery after administration of IV thiamine. This is the first reported case of Shoshin beriberi syndrome in a pediatric kidney transplant recipient. Inadequate dialysis may have been a key factor, with toxin accumulation and thiamine transporter downregulation contributing to his status. Functional thiamine deficiency should be considered as a potential treatable cause of early post-transplant hemodynamic instability.

Impact of exercise and vitamin B1 intake on hippocampal brain-derived neurotrophic factor and spatial memory performance in a rat model of stress

Chronic stress affects brain areas involved in learning and emotional responses through modulation of neurotropic factors or neurotransmitters. Therefore, we investigated the role of exercise and thiamine supplementation on spatial memory and on brain-derived neurotrophic factor (BDNF) and acetylcholine (Ach) content in the hippocampus of the stressed animals. Male Wistar rats were randomly assigned to 4 groups (8 rats/group): control group; stress group; swimming and stress group; and thiamine and stress group. All animals were assessed by a T maze for spatial memory or open field test for locomotion and anxiety. BDNF and Ach were estimated in the hippocampus. Chronic immobilization stress resulted in a significant decrease in BDNF and Ach levels in the hippocampus and impairment in spatial memory functions and decreased basal activity. However, either swimming training or thiamine intake for 30 d was proved to induce a significant increase both in BDNF and Ach in conjunction with improved performance in the T maze, marked anxiolytic effect and enhanced ambulation in the open field test, as compared to the stress group. Interestingly, swimming-exercised rats showed significantly higher levels of BDNF versus thiamine-receiving rats, while thiamine-receiving rats showed higher locomotor activity and less freezing behavior in the open field test compared to the swimming group. It was concluded that decreased BDNF and Ach after stress exposure could be a mechanism for the deleterious actions of stress on memory function; swimming exercise or vitamin B1 supplementation for 30 d was a protective tool to improve coping with chronic stress by modulating BDNF and Ach content along with enhancement of memory functions and motor activities.

Mild thiamine deficiency and chronic ethanol consumption modulate acetylcholinesterase activity change and spatial memory performance in a water maze task

Chronic thiamine deficiency may be responsible for pathologic changes in the brains of alcoholics, and subclinical episodes of this vitamin deficiency may cause cumulative brain damage. In the present work, the chronic effects of ethanol and its association to a mild thiamine deficiency episode (subclinical model) on neocortical and hippocampal acetylcholinesterase activity were assessed along with their possible association to spatial cognitive dysfunction. The results indicate that in the beginning of the neurodegenerative process, before the appearance of brain lesions, chronic ethanol consumption reverses the effects of mild thiamine deficiency on both spatial cognitive performance and acetylcholinesterase activity without having significant effects on any morphometric parameter.

Acetyl-CoA the key factor for survival or death of cholinergic neurons in course of neurodegenerative diseases

Glucose-derived pyruvate is a principal source of acetyl-CoA in all brain cells, through pyruvate dehydogenase complex (PDHC) reaction. Cholinergic neurons like neurons of other transmitter systems and glial cells, utilize acetyl-CoA for energy production in mitochondria and diverse synthetic pathways in their extramitochondrial compartments. However, cholinergic neurons require additional amounts of acetyl-CoA for acetylcholine synthesis in their cytoplasmic compartment to maintain their transmitter functions. Characteristic feature of several neurodegenerating diseases including Alzheimer’s disease and thiamine diphosphate deficiency encephalopathy is the decrease of PDHC activity correlating with cholinergic deficits and losses of cognitive functions. Such conditions generate acetyl-CoA deficits that are deeper in cholinergic neurons than in noncholinergic neuronal and glial cells, due to its additional consumption in the transmitter synthesis. Therefore, any neuropathologic conditions are likely to be more harmful for the cholinergic neurons than for noncholinergic ones. For this reason attempts preserving proper supply of acetyl-CoA in the diseased brain, should attenuate high susceptibility of cholinergic neurons to diverse neurodegenerative conditions. This review describes how common neurodegenerative signals could induce deficts in cholinergic neurotransmission through suppression of acetyl-CoA metabolism in the cholinergic neurons.

Thiamine (Vitamin B1)

Thiamine (vitamin B 1) was the first B vitamin to have been identified. It serves as a cofactor for several enzymes involved in energy metabolism. The thiamine-dependent enzymes are important for the biosynthesis of neurotransmitters and for the production of reducing substances used in oxidant stress defenses, as well as for the synthesis of pentoses used as nucleic acid precursors. Thiamine plays a central role in cerebral metabolism. Its deficiency results in dry beriberi, a peripheral neuropathy, wet beriberi, a cardiomyopathy with edema and lactic acidosis, and Wernicke—Korsakoff syndrome, whose manifestations consist of nystagmus, ophthalmoplegia, and ataxia evolving into confusion, retrograde amnesia, cognitive impairment, and confabulation. Patients on a strict thiamine-deficient diet display a state of severe depletion within 18 days. The most common cause of thiamine deficiency in affluent countries is either alcoholism or malnutrition in nonalcoholic patients. Treatment by thiamine supplementation is beneficial for diagnostic and therapeutic purposes.

Acetyl-CoA deficit in brain mitochondria in experimental thiamine deficiency encephalopathy

Several pathologic conditions are known to cause thiamine deficiency, which induce energy shortages in all tissues, due to impairment of pyruvate decarboxylation. Brain is particularly susceptible to these conditions due to its high rate of glucose to pyruvate-driven energy metabolism. However, cellular compartmentalization of a key energy metabolite, acetyl-CoA, in this pathology remains unknown. Pyrithiamine-evoked thiamine deficiency caused no significant alteration in pyruvate dehydrogenase and 30% inhibition of α-ketoglutarate dehydrogenase activities in rat whole forebrain mitochondria. It also caused 50% reduction of the metabolic flux of pyruvate through pyruvate dehydrogenase, 78% inhibition of its flux through α-ketoglutarate dehydrogenase steps, and nearly 60% decrease of intramitochondrial acetyl-CoA content, irrespective of the metabolic state. State 3 caused a decrease in citrate and an increase in α-ketoglutarate accumulation. These alterations were more evident in thiamine-deficient mitochondria. Simultaneously thiamine deficiency caused no alteration of relative, state 3-induced increases in metabolic fluxes through pyruvate and α-ketoglutarate dehydrogenase steps. These data indicate that a shortage of acetyl-CoA in the mitochondrial compartment may be a primary signal inducing impairment of neuronal and glial cell functions and viability in the thiamine-deficient brain.

Acetyl-CoA and acetylcholine metabolism in nerve terminal compartment of thiamine deficient rat brain

The decrease of pyruvate and ketoglutarate dehydrogenase complex activities is the main cause of energy and acetyl-CoA deficits in thiamine deficiency-evoked cholinergic encephalopathies. However, disturbances in pathways of acetyl-CoA metabolism leading to appearance of cholinergic deficits remain unknown. Therefore, the aim of this work was to investigate alterations in concentration and distribution of acetyl-CoA and in acetylcholine metabolism in brain nerve terminals, caused by thiamine deficits. They were induced by the pyrithiamine, a potent inhibitor of thiamine pyrophosphokinase. The thiamine deficit reduced metabolic fluxes through pyruvate and ketoglutarate dehydrogenase steps, yielding deficits of acetyl-CoA in mitochondrial and cytoplasmic compartments of K-depolarized nerve terminals. It also inhibited indirect transport of acetyl-CoA though ATP-citrate lyase pathway being without effect on its direct Ca-dependent transport to synaptoplasm. Resulting suppression of synaptoplasmic acetyl-CoA correlated with inhibition of quantal acetylcholine release (r = 0.91, p = 0.012). On the other hand, thiamine deficiency activated non-quantal acetylcholine release that was independent of shifts in intraterminal distribution of acetyl-CoA. Choline acetyltransferase activity was not changed by these conditions. These data indicate that divergent alterations in the release of non-quantal and quantal acetylcholine pools from thiamine deficient nerve terminals could be caused by the inhibition of acetyl-CoA and citrate synthesis in their mitochondria. They in turn, caused inhibition of acetyl-CoA transport to the synaptoplasmic compartment through ATP-citrate lyase pathway yielding deficits of cholinergic functions.

Mechanisms of neuronal cell death in Wernicke's encephalopathy

Wernicke's Encephalopathy (WE) is a serious neurological disorder resulting from thiamine deficiency, encountered in chronic alcoholics and in patients with grossly impaired nutritional status. Neuropathologic studies as well as Magnetic Resonance Imaging reveal selective diencephalic and brainstem lesions in patients with WE. The last decade has witnessed major advances in the understanding of pathophysiologic mechanisms linking thiamine deficiency to the selective brain lesions characteristic of WE. Activities of the thiamine-dependent enzyme alpha-ketoglutarate dehydrogenase, a rate-limiting tricarboxylic acid cycle enzyme are significantly reduced in autopsied brain tissue from patients with WE and from rats treated with the central thiamine antagonist, pyrithiamine. In the animal studies, evidence suggests that such enzyme deficits result in focal lactic acidosis, cerebral energy impairment and depolarization resulting from increased release of glutamate in vulnerable brain structures. It has been proposed that this depolarization may result in N-Methyl-D-Aspartate receptor-mediated excitotoxicity as well as increased expression of immediate early genes such as c-fos and c-jun resulting in apoptotic cell death. Other mechanisms involved in thiamine deficiency-induced cell loss may involve free radicals and alterations of the blood-brain barrier. Additional studies are still required to identify the site of the initial cellular insult and to explain the predilection of diencephalic and brainstem structures due to thiamine deficiency.

Influence of thiamine on the behavioral sensitivity to ethanol

Changes in sensitivity to ethanol's rate-decreasing effects on operant performance were examined in control rats and cohorts that received diet-induced or diet+pyrithiamine-induced thiamine deficiency. Seven groups of male Sprague-Dawley rats (12 rats/group) were trained in a 5-cycle lever-press operant task under a fixed-ratio 30 schedule of food reinforcement. Once trained to maintain consistent operant performance across all 5 cycles, each rat was tested with various doses of ethanol injected at the beginning of each time-out cycle. Each group of rats demonstrated equivalent saline baseline operant performance and ED50 for ethanol's rate-suppressing effects. Training sessions were suspended and rats received either a short- (9 days) or long-term (5-week) exposure to regular rat chow diet or thiamine-deficient diet, and received either saline or pyrithiamine injections in a 2 x 2 design. Three additional control groups were maintained on a regular rat chow diet and received supplemental injections of either thiamine+pyrithiamine injections, thiamine+saline injections, or saline+pyrithiamine injections. The controlled diet phase continued until the development of overt signs of thiamine deficiency, at which time thiamine supplements were administered for 4 days. In phase 3, all rats were retrained in the operant task and a second ethanol dose-effect function was generated. A history of thiamine deficiency and recovery failed to shift the behavioral dose-effect functions significantly for ethanol and their associated blood alcohol curves. Most interestingly, significant behavioral sensitization to ethanol's rate suppressant effects was demonstrated in the two control groups of rats receiving regular rat chow diet in combination with supplemental injections of thiamine and either saline or pyrithiamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of thiamin deficiency on energy metabolites in the turkey

The effects of thiamin deficiency on selected energy-related metabolites was investigated. A basal diet (B) was formulated to be 11% of NRC recommended level of 2 mg/kg of thiamin. Thiamin was added to this basal diet to generate the control diet (C). Twenty one-week-old female turkeys were fed either the B or C diet. On days four and five of the experiment, food intake was decreased significantly in B fed turkeys (P < 0.05). Plasma and brain samples were collected at this time. Brains were dissected and analyzed for ATP, ADP, uric acid, free fatty acids, glucose, and GABA. Adenosine triphosphate and the ATP/ADP ratio were decreased in the hindbrain (medulla-pons area) of thiamin deficient birds (P < 0.01). Uric acid was increased (P < 0.001) and free fatty acids were decreased (P < 0.0005) in the plasma of thiamin deficient birds. Based on the data, changes in ATP and ATP/ADP levels may be related to the anorectic behavior exhibited by the thiamin deficient bird.

Effect of a deficiency of thiamine on brain pyruvate dehydrogenase: enzyme assay by three different methods

A simple and rapid method based on the NADH-linked reduction of a tetrazolium dye was described for the determination of pyruvate dehydrogenase activity in rat brain homogenates. The method (method 3) gave a value of 36.06 +/- 1.24 nmol of pyruvate utilised/min/mg of whole brain protein. This value was higher than that obtained by measurement of the rate of decarboxylation of [1-14C]pyruvate (15.10 +/- 0.88 nmol/min/mg of protein; method 1) and was comparable with the rate of transfer of acetyl groups to an arylamine (39.04 +/- 1.32 nmol/min/mg of protein; method 2). A critique of the values reported by others by different methods was given. The pyruvate dehydrogenase activity in the mitochondria isolated from rat brain was in the "active" (nonphosphorylated) form. A deficiency of thiamine in rats was produced by treatment with pyrithiamine, an antagonist of thiamine. This treatment resulted in abnormal neurological signs, such as ataxia and convulsions. The measurement of the total activity of pyruvate dehydrogenase in the brain by all three methods showed no significant change in the enzymic activity in thiamine-deficient rats after treatment with pyrithiamine. The activities of the enzyme in the brains of pair-fed animals were similar to those in the controls.

GABA-transaminase and glutamic acid decarboxylase changes in the brain of rats treated with pyrithiamine

Pyrithiamine, a thiamine phosphokinase inhibitor, was fed to rats on a thiamine-deficient diet, producing weight loss, ataxia and loss of righting reflex in 10 days. Some rats were then sacrificed; others were returned to a normal diet, to be sacrificed only when their weight had returned to pre-experimental levels. Rats were sacrificed for assay of glutamic acid decarboxylase (GAD) and choline acetyltransferase (ChAT) activities in homogenates of eight brain regions or were perfused for gamma-aminobutyric acid transaminase (GABA-T) histochemistry. GAD activity was significantly reduced in symptomatic rats in the thalamus greater than cerebellum greater than midbrain greater than pons/medulla. GABA-T staining was similarly reduced, with greatest losses in the thalamus greater than inferior colliculus greater than pons greater than medulla. ChAT activity was not significantly altered in any brain area. Following return to a normal diet. GAD activity was significantly recovered in all areas except the thalamus. GABA-T staining recovered, at least partially, in all areas affected.

Activities of thiamine-dependent enzymes in two experimental models of thiamine-deficiency encephalopathy: 1. The pyruvate dehydrogenase complex

Chronic thiamine deprivation in the rat leads to selective neuropathological damage in brainstem structures whereas treatment with the central thiamine antagonist, pyrithiamine, results in more widespread damage. In order to further elucidate the neurochemical mechanisms responsible for this selective damage, the thiamine-dependent enzyme complex pyruvate dehydrogenase (PDHC) was measured in 10 brain structures in the rat during progression of thiamine deficiency produced by chronic deprivation or by pyrithiamine treatment. Feeding of a thiamine-deficient diet to adult rats resulted in 5-7 weeks in ataxia and loss of righting reflex accompanied by decreased blood transketolase activities. PDHC activities were selectively decreased by 15-30% in midbrain and pons (lateral vestibular nucleus). Thiamine treatment of symptomatic rats led to reversal of neurological signs and to concomitant reductions of the cerebral PDHC abnormalities. Daily pyrithiamine treatment led within 3 weeks to loss of righting reflex and convulsions and to decreased blood transketolase of a comparable magnitude to that observed in chronic thiamine-deprived rats. No significant regional alterations of PDHC, however, were observed in pyrithiamine-treated rats.

Correlation of enzymatic, metabolic, and behavioral deficits in thiamin deficiency and its reversal

To clarify the enzymatic mechanisms of brain damage in thiamin deficiency, glucose oxidation, acetylcholine synthesis, and the activities of the three major thiamin pyrophosphate (TPP) dependent brain enzymes were compared in untreated controls, in symptomatic pyrithiamin-induced thiamin-deficient rats, and in animals in which the symptoms had been reversed by treatment with thiamin. Although brain slices from symptomatic animals produced 14CO2 and 14C-acetylcholine from [U-14C]glucose at rates similar to controls under resting conditions, their K+-induced-increase declined by 50 and 75%, respectively. In brain homogenates from these same animals, the activities of two TPP-dependent enzymes transketolase (EC 2.2.1.1) and 2-oxoglutarate dehydrogenase complex (EC 1.2.4.2, EC 2.3.1.61, EC 1.6.4.3) decreased 60-65% and 36%, respectively. The activity of the third TPP-dependent enzyme, pyruvate dehydrogenase complex (EC 1.2.4.1, EC 2.3.1.12, EC 1.6.4.3) did not change nor did the activity of its activator pyruvate dehydrogenase phosphate phosphatase (EC 3.1.3.43). Although treatment with thiamin for seven days reversed the neurological symptoms and restored glucose oxidation, acetylcholine synthesis and 2-oxoglutarate dehydrogenase activity to normal, transketolase activity remained 30-32% lower than controls. The activities of other TPP-independent enzymes (hexokinase, phosphofructokinase, and glutamate dehydrogenase) were normal in both deficient and reversed animals.

Impairment of acetylcholine synthesis in thiamine deficient rats developed by prolonged tea consumption

The synthesis of whole brain acetylcholine is reduced in thiamine deficient rats produced by prolonged administration of tea. In those rats fed a normal diet and given tea (1:50, w/v) instead of drinking water for 20 weeks, the conversion of [14C] pyruvate to [14C]acetylcholine decreased by 35%. However, no neurological symptoms were observed. Administration of tea to rats fed a thiamine half-deficient diet for 7-8 weeks caused not only 60% decrease in acetylcholine synthesis but also neurological symptoms. This decreased synthesis of acetylcholine is related to a decline in pyruvate dehydrogenase activity. The results suggest that prolonged administration of tea to rats cause an impairment of acetyl CoA production resulting in a deficit in acetylcholine synthesizing capacity.

Choline and cholinergic neurons

Mammalian neurons can synthesize choline by methylating phosphatidylethanolamine and hydrolyzing the resulting phosphatidylcholine. This process is stimulated by catecholamines. The phosphatidylethanolamine is synthesized in part from phosphatidylserine; hence the amino acids methionine (acting after conversion to S-adenosylmethionine) and serine can be the ultimate precursors of choline. Brain choline concentrations are generally higher than plasma concentrations, but depend on plasma concentrations because of the kinetic characteristics of the blood-brain-barrier transport system. When cholinergic neurons are activated, acetylcholine release can be enhanced by treatments that increase plasma choline (for example, consumption of certain foods).

Norepinephrine-induced elevation of acetyl coenzyme A in rat pineal glands in culture

A micromethod for the determination of acetyl coenzyme A was developed and the relationship between the concentration of acetyl coenzyme A and the activity of rat pineal serotonin N-acetyltransferase was studied. Acetyl coenzyme A was determined by converting it into N-acetylserotonin using rat liver serotonin N-acetyltransferase. Subsequently, the hydroxy group of N-acetylserotonin was O-methylated by hydroxyindole-O-methyltransferase and S-[methyl-3H]adenosyl-l-methionine to form [3H]melatonin, which was then conveniently separated from S-[methyl-3H]adenosyl-l-methionine by thin-layer chromatography. The amount of radioactivity in melatonin is a measure of acetyl coenzyme A concentration. This method is sensitive and specific, since it can detect as low as 5 pmol of acetyl coenzyme A but not structurally related substances such as coenzyme A, adenosine diphosphate, cysteamine, D-panthothenic acid, or sodium acetate. After treating cultured rat pineal glands with l-norepinephrine (10 microM) for 6 hr, the concentration of acetyl coenzyme A was increased significantly from 3.26 +/- 0.37 to 10.24 +/- 0.93 pmol/gland, while the activity of serotonin N-acetyltransferase increased 68-fold. This result suggests that acetyl coenzyme A may play an important role in the norepinephrine-induced induction of serotonin N-acetyltransferase. Sensitivity and adaptability of this method can be utilized to measure acetyl coenzyme A in discrete regions of rat brain and in experimental conditions in which micromeasurement of acetyl coenzyme A may be required.

Thiamine and cholinergic transmission in the electric organ of Torpedo. I. Cellular localization and functional changes of thiamine and thiamine phosphate esters

The electric organ of Torpedo marmorata was found to contain as much as 120 +/- 24 nmol of thiamine per g of fresh tissue. The vitamin was distributed as nonesterified thiamine (32%), thiamine monophosphate (22%), thiamine diphosphate (8%), and an important proportion of thiamine triphosphate (38%). A high level of thiamine triphosphate was found in synaptosomes isolated from the electric organ. In contrast, the synaptic vesicles did not show any enrichment in thiamine, whereas they contained a marked peak of acetylcholine (ACh) and ATP. Thus thiamine seems to be very abundant in cholinergic nerve terminals; its localization is apparently extravesicular, either in the axoplasm or in association with plasma membrane. When calcium was reduced and magnesium increased in the external medium, the efficiency of transmission was diminished, owing to inhibition of ACh release; in a parallel manner the degree of thiamine phosphorylation was found to increase--this condition is known to modify the repartition of ACh between vesicular and extravesicular compartments. Electrical stimulation, which causes periodic variations of the level of ACh and ATP, also caused significant changes in thiamine esters. In addition, related changes of the vitamin and the transmitter were observed under other conditions, suggesting a functional link between the metabolism of thiamine and that of ACh in cholinergic nerve terminals.

Relation between the content of acetyl-coenzyme A and acetylcholine in brain slices

Slices of rat caudate nuclei were incubated in vitro in media containing, among other constituents, three different concentrations of glucose (0.5, 2 and 10 mM), 0.2 mM-choline, paraoxon as an inhibitor of cholinesterase, and 5 mM- or 30 mM-K+. After 30 and 60 min of incubation, the concentrations of acetyl-CoA, acetylcholine and choline in the tissue and of acetylcholine in the incubation medium were measured. The content of acetyl-CoA in the sliced varied in direct relation to the concentration of glucose in the incubation medium. The content of acetylcholine in the slices and, in experiments with high K+, also the amount of acetylcholine released into the incubation medium varied in direct relation to the concentration of glucose in the incubation medium and to the concentration of acetyl-CoA in the slices; the relation between the concentrations of acetyl-CoA and of acetylcholine in the slices was linear. It was concluded that the availability of acetyl-CoA had a decisive influence on both the rate of synthesis of acetylcholine and its steady-state concentration. The observations accord with the view that, at the ultimate level, the synthesis of acetylcholine is controlled by the Law of Mass Action.

Dietary folic acid and the activity of brain cholinergic and gamma-aminobutyric acid (GABA) enzymes

Charles River CD male rats were randomly divided into 3 groups of five each and placed on folate deficient, folate excess, and control diets respectively. glutamate decarboxylase GAD gamma-amino-butyrate aminotransferase (GABA-T), choline acetltransferase (ChAc), and acetylcholinesterase (AChE) were assayed in the rat brains after 6 weeks of dietary treatment. Neither folate deficiency nor folate supplementation influenced the enzymes associated with GABA and acetylcholine metabolism.

Effects of pyrithiamin and oxythiamin on acetylcholine levels and utilization in rat brain

Regional cerebral acetylcholine (ACh) levels and utilization rate were assessed in vivo in rats rendered thiamin deficient using the thiamin antagonists pyrithiamin or oxythiamin. ACh levels were significantly reduced in all brain regions of pyrithiamin treated rats and in the medulla-pons and striatum of oxythiamin treated rats compared to controls. ACh utilization was significantly reduced in the midbrain, striatum and hippocampus of pyrithiamin treated rats, but was reduced only in the striatum of oxythiamin treated rats compared to controls. Thus, there are some reductions in ACh levels and utilization that are unique to pyrithiamin induced deficiency and as such are distinct from oxythiamin/undernutrition related reductions. Since only pyrithiamin produces neurological symptoms, its unique ACh effects may be related to these symptoms.

Peripheral nerve changes in thiamine deficiency and starvation. An electron microscopic study

Electron microscopic investigations on sciatic and plantar nerves of thiamine deficient and starved rats show a distally pronounced axonal degeneration. The changes are present in starved and thiamine deficient animals, but the deficient animals are more severely affected. The earliest alterations consist of an increase of mitochondria and a proliferation of vesicular elements of the endoplasmic reticulum. They are followed by loop formations of the axon membrane, clustering and disintegration of neurotubules and neurofilaments, axonal shrinkage and finally myelin disruption. The distal accentuation of the early changes indicates a dying-back mechanism of axonal degeneration.

Purification and properties of rat brain pyruvate carboxylase

Rat brain pyruvate carboxylase was purified 2000-fold and some of its properties and kinetic parameters were investigated. The use of (NH4)2SO4 gradient solubilization on a Celite column and precipitation with polyethylene glycol permitted purification to an estimated 20% purity. Except for a few subtle kinetic differences this enzyme is indistinguishable from rat liver pyruvate carboxylase.