Brain Choline Acetyltransferase Activity Research Articles

Digoxin Exhibits Neuroprotective Properties in a Rat Model of Dementia

Alzheimer's disease (AD) is by far the most common cause of cognitive impairment in older adults. Current treatments are entirely focused on the symptoms of AD. A complex etiology for AD has been proposed recently, in which AD leads in elevated levels of inflammation. We previously studied digoxin's involvement in the sporadic-AD intracerebroventricular (ICV)-streptozotocin (STZ) animal model due to its anti-inflammatory and neuroprotective characteristics. 18 adult sprague-dawley rats were split into three groups: control (n = 6), STZ + Saline (n = 6), and STZ + Digoxin (n = 6). Twelve AD-induced rats were split into two groups using stereotaxy five days after STZ injection (3mg/kg) into both lateral ventricles: one group got digoxin (0.1mg/kg/day, i.p.) for three weeks, while the other group received saline. Following treatment, each subject was subjected to a passive avoidance learning (PAL) test, followed by brain tissue harvesting. The levels of tumor necrosis factor-alpha (TNF-α) and choline acetyl transferase (ChAT) were measured in the brain, and neurons were counted using Cresyl violet staining in cornu ammonis-1 (CA1) and cornu ammonis-3 (CA3) cornu ammonis (CA3). ICV-STZ significantly shortened PAL latency, increased brain TNF-α levels, decreased brain ChAT activity, and decreased hippocampus neuron number. On the other hand, digoxin significantly reduced all of these STZ-induced deleterious effects. Digoxin significantly rescued rats from memory loss caused by ICV-STZ by decreasing hippocampal cell death, neuroinflammation, and cholinergic deficiency. These findings suggest that digoxin may be beneficial in treating cognitive impairment and Alzheimer's disease.

Exenatide reduces TNF-α expression and improves hippocampal neuron numbers and memory in streptozotocin treated rats

Recent studies suggest a possible link between type 2 diabetes and Alzheimer's disease (AD). Glucogan-like peptide 1 (GLP-1) facilitates insulin release from pancreas under hyperglycemic conditions. In addition to its metabolic effects, GLP-1 and its long-lasting analogs, including exenatide can stimulate neurogenesis and improve cognition in rodent AD model. The aim of the present study was to investigate the effects of exenatide on hippocampal cellularity, cognitive performance and inflammation response in a rat model of AD. Fourteen rats were used to create AD model using intracerebroventricular (ICV) streptozotocin (STZ) infusion while 7 rats were administered 0.9% NaCl only (sham-operated group). Following stereotaxic surgery, STZ received rats were randomly distributed into two groups, and treated with either saline or exenatide 20µgr/kg/day through intraperitoneally for two weeks. Then, cognitive performance (passive avoidance learning), brain tumor necrosis factor alpha (TNF-α) levels, choline acetyltransferase (ChAT) activity and hippocampal neuronal count were determined. While the brain TNF-α levels were significantly high in the saline-treated STZ group, exenatide treatment suppressed the increase in TNF-α levels. Saline-treated STZ group showed reduced ChAT activity compared to sham group. However, exenatide significantly preserved brain ChAT activity. The cognitive performance was also impaired in saline group while exenatide improved memory in rats. Moreover, exenatide treatment significantly prevented the decrease in hippocampal neurons. Overall, the results of the present study clearly indicated exenatide might have beneficial effects on impaired cognitive performance and hippocampal neuronal viability in AD by suppressing the inflammation response and increasing cholinergic activity.

Choline transporter 1 maintains cholinergic function in choline acetyltransferase haploinsufficiency.

Choline acetyltransferase (ChAT), the enzyme that synthesizes the neurotransmitter acetylcholine (ACh), is thought to be present in kinetic excess in cholinergic neurons. The rate-limiting factor in ACh production is the provision of choline to ChAT. Cholinergic neurons are relatively unique in their expression of the choline transporter 1 (CHT1), which exhibits high-affinity for choline and catalyzes its uptake from the extracellular space to the neuron. Multiple lines of evidence indicate that the activity of CHT1 is a key determinant of choline supply for ACh synthesis. We examined the interaction of ChAT and ChT activity using mice heterozygous for a null mutation in the Chat gene (Chat+/-). In these mice, brain ChAT activity was reduced by 40-50% relative to the wild type, but brain ACh levels as well as ACh content and depolarization-evoked ACh release in hippocampal slices were normal. However, the amount of choline taken up by CHT1 and ACh synthesized de novo from choline transported by CHT1 in hippocampal slices, as well as levels of CHT1 mRNA in the septum and CHT1 protein in several regions of the CNS, were 50-100% higher in Chat+/- than in Chat+/+ mice. Thus, haploinsufficiency of ChAT leads to an increased expression of CHT1. Increased ChT activity may compensate for the reduced ChAT activity in Chat+/- mice, contributing to the maintenance of apparently normal cholinergic function as reflected by normal performance of these mice in several behavioral assays.

Effects of Gestational Exposure to Chlorpyrifos on Postnatal Central and Peripheral Cholinergic Neurochemistry

The effects of gestational exposure to the commonly used organophosphorus insecticide chlorpyrifos (O,O-diethyl O-[3,5,6-trichloro-2-pyridinyl]phosphorothioate) on postnatal central and peripheral cholinergic neurochemistry were investigated. Pregnant rats were orally dosed daily with chlorpyrifos (0, 3, 5, or 7 mg/kg) in corn oil from gestation day 6 to 20. Pups were sacrificed on postnatal days 1, 3, 6, 9, and 12 for the determination of brain, heart, lung, and serum cholinesterase, and brain choline acetyltransferase activities, along with liver carboxylesterase activity. Exposure to chlorpyrifos did not produce signs of overt toxicity to the dams or developing offspring. Cholinesterase activities were inhibited in a dose-related manner, with brain cholin-esterase inhibition of about 26%, 32%, and 45% on postnatal day 1. Inhibition of brain cholineste-rase persisted in all treatment groups until postnatal day 6 and in the medium and high-dosage groups through postnatal day 9. Liver carboxylesterase activity was also inhibited in a dose-related manner, with a recovery profile parallel to that of brain cholinesterase. Choline acetyltransferase activity was decreased by about 13% in the high-dosage group on postnatal days 9 and 12. These results indicate that gestational exposure to chlorpyrifos results in relatively persistent inhibition of brain cholinesterase and a delayed depression of choline acetyltransferase at a time when brain cholinesterase activity had returned to control levels in the high-dosage group.

Apolipoprotein E: A pharmacogenetic target for the treatment of Alzheimer's disease

The discovery that the apolipoprotein E4 (apoE4) allele is strongly linked to both sporadic and familial late-onset Alzheimer's disease (AD) raises the possibility that a dysfunction of the lipid transport system could seriously affect lipid homeostasis in the brain. We recently proposed that the abnormally low concentrations of apoE observed in the brains of apoE4 AD subjects could compromise cholesterol, fatty acid, and phospholipid transport in the central nervous system. This, in turn, would indirectly impair the cholinergic system, which, in contrast to other neurotransmitters in the central nervous system, relies heavily on lipids to synthesize acetylcholine. Several independent investigators have now confirmed the original observation of an inverse relationship between apoE4 allele copy number and residual brain choline acetyltransferase activity and nicotinic-receptor binding sites in the brains of subjects with AD. More importantly, it has been shown that the presence of the apoE4 allele differentially affects the quality and size of drug responsiveness in subjects with AD treated with cholinomimetic and noncholinomimetic agents. We also examine the role of apoE as a potent therapeutic target for AD.

Effects of ginsenosides on maze performance and brain choline acetyltransferase activity in scopolamine-treated young rats and aged rats

In young adult rats with scopolamine-induced cognitive impairment, choline acetyltransferase activity was increased in the medial septum, but not in the diagonal band, caudate and hippocampus, 30 min after the injection of ginsenosides Rg1 or Re. Rb1 and Rd had no effect on choline acetyltransferase activity. Aged rats showed a smaller number of initial correct responses in the radial-arm maze and a lower choline acetyltransferase activity in the medial septum, diagonal band, caudate and hippocampus than did young adult rats. Repeated i.p. injections of Rg1 increased the number of initial correct responses and the activity of choline acetyltransferase in the medial septum, but not in the diagonal band, caudate and hippocampus, in aged rats. These results suggest that Rg1 and Re may contribute the ameliorative effects through an increase of choline acetyltransferase activity in the medial septum.

Decompensation of hepatic and cerebral acyl-CoA metabolism in BALB/cByJ mice by chronic riboflavin deficiency: restoration by acety1-L-carnitine

BALB/cByJ mice have an autosomal recessive deficiency of short-chain acyl-CoA dehydrogenase (SCAD) and show elevated excretion of urinary butyrylglycine, ethylmalonate, and methylsuccinate, which resembles the SCAD deficiency disorder in children. These mice are clinically normal, perhaps because of an efficient acyl-CoA conjugation system. We attempted to decompensate the acyl-CoA metabolism in mutant mice by chronic treatment with a riboflavin-deficient diet for 3 weeks to potentiate the SCAD deficiency. We studied the urinary profiles of organic acids, acylglycines, hepatic and cerebral profiles of carnitines, and ammonia to assess the potentiation of this disorder. Cerebral activity of choline acetyltransferase (ChAT) was determined to study the effects of acyl-CoA accumulation on the cholinergic system. The results indicate that in riboflavin-deficient mutant mice, the excretion of ethylmalonate, methylsuccinate, butyrylglycine, and dicarboxylic acids was enhanced. Hepatic and cerebral free and esterified carnitines were reduced, indicating a potentiation of the secondary carnitine deficiency. Hepatic ammonia levels, but not cerebral ammonia or glutamine levels, were elevated, indicating a tendency towards secondary hyperammonemia. Brain choline acetyltransferase activity was significantly reduced in striatum, implying a reduced availability of cerebral acetyl-CoA or a decreased cerebral transport of choline: Most of these changes were partially or completely restored by a concomitant treatment with acetyl-L-carnitine (ALCAR). In summary, we conclude that BALB/cByJ mice with SCAD deficiency, but with a functional urea cycle, might have an adequate adaptive mechanism to adjust to an excessive acyl-CoA load without hyperammonemia at the cerebral level. However, any deficiency of vitamins or cofactors in the diet could disturb an adaptation to this disorder and produce an effect on the cholinergic system.

Ameliorating Effects of SDZ ENA 713 on Age-Associated Decreases in Learning Performance and Brain Choline Acetyltransferase Activity in Rats

In the present study, we have investigated the effects of SDZ ENA 713 on spatial learning deficits in aged rats. Using the same animals, the effect of SDZ ENA 713 on choline acetyltransferase was simultaneously studied to obtain a basis for the behavioral study. In the aged rats, the spatial learning and choline acetyltransferase activity in the frontal cortex were significantly deteriorated compared with young adult rats. SDZ ENA 713 (0.2 mg/kg) significantly shortened the time to reach a hidden platform without affecting swim rates in the water maze task. SDZ ENA 713 (0.1 and 0.2 mg/kg) inhibited aging-induced decreases in choline acetyltransferase activity in the frontal cortex. These results suggest that SDZ ENA 713 ameliorates aging-induced learning deficits and cholinergic dysfunction in rats.

Memory deficits and cholinergic impairments in apolipoprotein E-deficient mice

Apolipoprotein E-deficient mice provide a useful system for studying the role of apolipoprotein E (apoE) in the function of distinct neuronal systems. In the present study we focused on the cholinergic system of these mice. This was pursued by measurements of specific biochemical, physiological and cognitive parameters. Morris Water Maze tasks revealed impairments in working memory but not in reference memory of the apoE-deficient mice. Measurements of brain choline acetyltransferase activities revealed them to be markedly lower in the hippocampus and frontal cortex of the apoE-deficient mice than in the corresponding brain areas of the controls, but unaltered in other brain areas. In addition, hypothermia induced by the centrally acting muscarinic agonist, oxotremorine, was reduced in the apoE-deficient mice as compared to controls. These results show that apoE-deficient mice have cholinergic deficits and highlight the importance of this mouse model for studying the interactions between apoE and the cholinergic nervous system.

Thyroxine normalizes polychlorinated biphenyl (PCB) dose-related depression of choline acetyltransferase (ChAT) activity in hippocampus and basal forebrain of 15-day-old rats

Neonatal exposure to the toxic chemical polychlorinated biphenyl (PCB) induces hypothyroidism (depressed thyroid hormones). Neonatal rats made hypothyroid by other means (chemical or surgical) have subnormal activity of choline acetyltransferase (ChAT), which catalyzes synthesis of acetylcholine, in the hippocampus and basal forebrain. The present study examined whether neonatal rats with PCB-induced hypothyroidism had depressed ChAT activity in these two brain areas, and whether alterations in ChAT activity were secondary to hypothyroidism rather than/in addition to a direct effect of PCB. Neonatal rats were exposed to PCB by feeding pregnant female rats chow containing various concentrations of PCB (0, 62.5, 125 or 250 ppm) throughout pregnancy and lactation. During postnatal days 4–14, neonatal rats exposed to the highest concentration of PCB were injected with either saline, triiodothyronine (T 3), or thyroxine (T 4), or were not injected at all. Circulating thyroid hormone levels (T 4 and T 3) and brain ChAT activity were determined at 15 days of age. All concentrations of PCB depressed circulating T 4 levels and ChAT activity in a dose-r response manner, but did not modify T 3 levels. Injections of T 4, but not T 3, elevated ChAT activity in PCB-exposed rats to near control levels. Thus, altered ChAT activity in PCB- exposed rats may partially result from the hypothyroidism accompanying PCB poisoning. The possible molecular mechanism(s) of action of PCB on brain ChAT activity remains unclear.

Effect of chronic treatment with aluminum compound on rat brain choline acetyltransferase activity.

Effect of chronic treatment with aluminum compound on rat brain choline acetyltransferase activity.

Effects of postnatal aluminum exposure on choline acetyltransferase activity and learning abilities in the rat

Young rats were treated by gastric intubation with aluminum lactate (0, 100, and 200 mg Al/kg/day) from postnatal days 5 to 14 to determine the treatment's influence on brain choline acetyltransferase activity and learning abilities. The results indicated that aluminum concentrations in the cerebral areas increased in parallel to plasma aluminum at the dose of 200 mg. In the same case, choline acetyltransferase activity was reduced. At postnatal days 50 and 100, the treated rats did not show alterations in their learning abilities in the 2 tests which are based on different motivations (avoidance of an aversive light or alimentary motivation) and different ways of achievement (pressing on a lever or running in a maze). A low reduction in the general activity, particularly in the radial maze test, was only observed in rats treated with 200 mg Al/kg/day.

Muscle-derived factors reverse the cholinotoxic effects of ethanol during early neuroembryogenesis in the chick embryo

The interaction between muscle-derived factors and ethanol on cholinergic neuronal expression was studied in the chick embryo during early neuroembryogenesis using choline acetyltransferase (ChAT) as cholinergic neuronal marker. Ethanol (10 mg/50 μl) and limb muscle extract (130 μg protein/50 μl) (LME) were administered in ovo either alone or concomitantly at embryonic days 1–3 (E1–E3); or ethanol was given E1–E3 and followed by LME at E4–E7. All groups were sacrificed at embryonic day 8 (E8) and ChAT activity was assayed in homogenates of whole brain and of spinal cord. As previously reported 6,8,31, ethanol at E1–3 produced a 30% decrease in brain ChAT activity and 35% in spinal cord. Concomitant administration of ethanol and LME at embryonic days E1–E3 eliminated the decrease in choline acetyltransferase activity produced by ethanol in the brain, but not in the spinal cord. On the other hand, administration of LME at embryonic days E4–E7 to embryos pretreated with ethanol at embryonic days E1–E3, raised ChAT activity to control level in the spinal cord, but only partially restored ChAT activity in the brain. In view of the alleged neurotrophic effects of muscle-derived factors on neuronal survival and neuronal growth, we interpret these findings to suggest that LME in addition to its ability to decrease natural neuronal death, may prevent death resulting from neurotoxicity.

Hoe 288: Indications on the memory‐enhancing effects of a peptidase inhibitor

AbstractSeveral neuropeptides have recently been found to be involved in motivational, memory, and learning processes. Therefore, we tested the hypothesis that the peptidase (EC 3.4.15.1) inhibitor Hoe 288 modulated cognitive functions. Hoe 288 exhibited nootropic effects in uphill avoidance in mice (30 mg/kg orally administered [p.o.]). Scopolamineinduced amnesia in mice and rats was antagonized after subchronic administration for two or three days (1–10 mg/kg p.o. or intraperitoneally [i.p.]) in step‐through avoidance and an eight‐arm‐radial maze, respectively. The resulting bell‐shaped dose‐response curves had a maximum effect at 3 mg/kg. To elucidate the underlying neurochemical effects, ex vivo experiments in rats were performed: acute or repeated administration of Hoe 288 (0.03 – 3 mg/kg i.p.) induced a significant decrease of acetylcholine (ACh) content in certain brain areas that lasted up to 6 hr after treatment. The reduced brain ACh content was most likely due to an enhanced ACh release, as coadministration of the choline uptake inhibitor hemicholinium‐3 (HC‐3) and Hoe 288 potentiated the decrease of ACh induced by HC‐3. Choline acetyltransferase activity in brain increased after acute and subchronic administration of the peptidase inhibitor. Receptor‐mediated effects of ACh were estimated indirectly by its stimulation of guanylate cyclase. Hoe 288 increased cGMP content in a comparable dose range (0.3 – 1 mg/kg i.p.). The converting enzyme inhibitor Hoe 288 was shown to influence acquisition and retention of information in rodents, and the effects on ACh metabolism are in concordance with results obtained with potential nootropics in animal experiments.

Brain choline acetyltransferase activity and neuropeptide Y concentrations in Alzheimer's disease

Choline acetyltransferase (ChAT) activity and neuropeptide Y (NPY) levels in post-mortem tissues from patients with histologically proven Alzheimer's disease were compared with age-matched neurologically normal control individuals. Despite the high NPY concentrations in human cerebral cortex, no significant abnormalities were found. However, ChAT activity was reduced throughout the cortex, without a relationship to areas of functional deficit, as previously identified using fluorodeoxyglucose. These results lend further support to the concept of Alzheimer's disease as a highly selective neurodegenerative disorder.

Progressive supranuclear palsy: Relationship between extrapyramidal disturbances, dementia, and brain neurotransmitter markers

Biochemical markers for the major neurotransmitter systems were measured in the brains of 5 patients who had died with neuropathologically confirmed progressive supranuclear palsy. A marked nigrostriatal dopamine deficiency, observed in 4 of the 5 patients, was sufficient to explain the parkinsonian features (especially bradykinesia) observed in patients with progressive supranuclear palsy. Dopamine concentrations, however, were normal in the nucleus accumbens, hypothalamus, and temporal cortex. Brain noradrenalin, serotonin, gamma-aminobutyric acid, and aspartic acid levels were generally normal. Normal brain choline acetyltransferase activity (the marker enzyme for cholinergic neurons) in the 2 patients with severe dementia suggests that, at least in some patients, the cognitive impairment in this disorder is likely to be related to noncholinergic neurotransmitter system changes. The glutamic acid concentration was elevated in many brain areas in 3 of the 5 patients studied.

Brain cholinergic, behavioral, and morphological development in rats exposed in utero to methylparathion

The purpose of this study was to determine the effects of subchronic administration of the organophosphate methylparathion (MPTH) during gestation on behavior and development of brain cholinergic neurons in the offspring. Pregnant rats received daily po doses of MPTH from Day 6 through Day 20 of gestation at doses causing no (1.0 mg/kg) or minimal (1.5 mg/kg) visible signs of maternal toxicity. Acetylcholinesterase (AChE) and choline acetyltransferase (CAT) activities, and [ 3H]quinuclidinyl benzilate (QNB) binding to muscarinic receptors, were determined in several brain regions at 1, 7, 14, 21, and 28 days postnatal age and in maternal brain at Day 19 of gestation. Prenatal exposure to 1.5 mg MPTH/kg reduced AChE and increased CAT activity in all brain regions at each developmental period and in maternal brain. Similar exposure to 1.0 mg MPTH/kg caused a significant but smaller and less persistent reduction in AChE activity but no change in brain CAT activity of the offspring. Both doses of MPTH decreased the B max of 3H-QNB binding in maternal frontal cortex but did not alter the postnatal pattern of 3H-QNB binding. In parallel studies, prenatal exposure to MPTH did not affect a variety of behaviors. However, cage emergence, accommodated locomotor activity, and operant behavior in a mixed paradigm were impaired in rats exposed to 1.0 but not to 1.5 mg/kg MPTH. No morphological changes were observed in hippocampal or cerebellar tissue. Thus, subchronic prenatal exposure to MPTH altered postnatal development of cholinergic neurons and caused subtle alterations in selected behaviors of the offspring.

Alzheimer's disease: Choline acetyltransferase activity in brain tissue from clinical and pathological subgroups

Choline acetyltransferase activity was measured postmortem in five brain regions to determine if such activity provided biochemical support for clinical and pathological subgrouping of Alzheimer's disease. Seven patients with Alzheimer's disease were divided into groups based on age at onset, severity of neuropathological changes, history of myoclonus, family history of dementia, cerebellar amyloid plaques, and congophilic angiopathy. Thirty-two age-matched normal control subjects and 17 neurological control patients with Huntington's disease were also studied. Patients with early-onset and late-onset Alzheimer's disease did not differ in the clinical duration of their disease. Choline acetyltransferase activity was significantly lower in patients with early-onset Alzheimer's disease than in age-matched control subjects in frontal cortex, temporal cortex, hippocampus, and cerebellum. In contrast, choline acetyltransferase activity in patients with late-onset Alzheimer's disease was significantly lower than in age-matched control subjects only in hippocampus. There was a tendency for choline acetyltransferase activity to be lower in cortex from patients with early-onset Alzheimer's disease compared with cortex from the late-onset group, and this difference was significant in temporal cortex. Choline acetyltransferase activity was also measured in the substantia innominata from 9 patients with Alzheimer's disease and 5 age-matched control subjects. Subjects with early-onset Alzheimer's disease had significantly lower choline acetyltransferase activity in substantia innominata than did control subjects. Patients with Alzheimer's disease and a history of myoclonus had significantly lower choline acetyltransferase activity than did affected patients without myoclonus. Multivariate regression analysis showed myoclonus to be the single best predictor of low brain choline acetyltransferase activity. These results provide further evidence for clinical, pathological, and biochemical heterogeneity in Alzheimer's disease.

Acetylcholine, choline and choline acetyltransferase activity in the developing brain of normal and hypothyroid rats.

Abstract— Acetylcholine, choline and choline acetyltransferase activity were measured in the whole brains of normal and hypothyroid rats during development. At 1 day postpartum, brain acetylcholine was 73 per cent of adult levels. Propylthiouracil‐induced hypothyroidism up to age 20 days did not alter brain acetylcholine concentrations, but at 30 days resulted in significantly decreased levels. At day 1, brain choline was 20 per cent higher than adult levels and decreased between days 8 and 10. In hypothyroid rats this phenomenon did not occur until days 15–20. At day 1 postnatally, choline acetyltransferase activity was only 7 per cent of adult levels, then between days 5 and 20 rose to 77 per cent of adult levels. Beginning at day 8, hypothyroidism resulted in significantly decreased enzyme levels. This effect could be reversed at day 17 by concurrent tri‐iodothyronine substitution therapy. In hypothyroid rats, maximum brain choline acetyltransferase activity was 30 per cent less than normal adult levels.