Dietary restriction of choline reduces hippocampal acetylcholine release in rats: in vivo microdialysis study

Modulation of Dietary Choline Uptake in a Mouse Model of Acid Sphingomyelinase Deficiency

Acid sphingomyelinase deficiency (ASMD) is a lysosomal storage disorder caused by mutations in the gene-encoding acid sphingomyelinase (ASM). ASMD impacts peripheral organs in all patients, including the liver and spleen. The infantile and chronic neurovisceral forms of the disease also lead to neuroinflammation and neurodegeneration for which there is no effective treatment. Cellular accumulation of sphingomyelin (SM) is a pathological hallmark in all tissues. SM is the only sphingolipid comprised of a phosphocholine group linked to ceramide. Choline is an essential nutrient that must be obtained from the diet and its deficiency promotes fatty liver disease in a process dependent on ASM activity. We thus hypothesized that choline deprivation could reduce SM production and have beneficial effects in ASMD. Using acid sphingomyelinase knock-out (ASMko) mice, which mimic neurovisceral ASMD, we have assessed the safety of a choline-free diet and its effects on liver and brain pathological features such as altered sphingolipid and glycerophospholipid composition, inflammation and neurodegeneration. We found that the choline-free diet was safe in our experimental conditions and reduced activation of macrophages and microglia in the liver and brain, respectively. However, there was no significant impact on sphingolipid levels and neurodegeneration was not prevented, arguing against the potential of this nutritional strategy to assist in the management of neurovisceral ASMD patients.

A Systematic Review of the Dietary Choline Impact on Cognition from a Psychobiological Approach: Insights from Animal Studies

The influence of dietary choline availability on cognition is currently being suggested by animal and human studies which have focused mainly on the early developmental stages. The aim of this review is to systematically search through the available rodent (rats and mice) research published during the last two decades that has assessed the effect of dietary choline interventions on cognition and related attentional and emotional processes for the entire life span. The review has been conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement guidelines covering peer-reviewed studies included in PubMed and Scopus databases. After excluding duplicates and applying the inclusion/exclusion criteria we have reviewed a total of 44 articles published in 25 journals with the contribution of 146 authors. The results are analyzed based on the timing and duration of the dietary intervention and the behavioral tests applied, amongst other variables. Overall, the available results provide compelling support for the relevance of dietary choline in cognition. The beneficial effects of choline supplementation is more evident in recognition rather than in spatial memory tasks when assessing nonpathological samples whilst these effects extend to other relational memory tasks in neuropathological models. However, the limited number of studies that have evaluated other cognitive functions suggest a wider range of potential effects. More research is needed to draw conclusions about the critical variables and the nature of the impact on specific cognitive processes. The results are discussed on the terms of the theoretical framework underlying the relationship between the brain systems and cognition.

Supplementation of fenugreek with choline-docosahexaenoic acid attenuates menopause induced memory loss, BDNF and dendritic arborization in ovariectomized rats

Cognitive impairment due to natural or surgical menopause is always associated with estrogen deficiency leading to reduced brain-derived neurotrophic factor (BDNF). Reduced BDNF levels in menopause affect neuronal maturation, survival, axonal and dendritic arborization and the maintenance of dendritic spine density. Conventional long-term estrogen replacement therapy reported causing the risk of venous thromboembolism and breast cancer. To overcome these undesirable effects, phytoestrogens have been used in menopause-induced condition without the risk of side effects. Therefore, the aim of the present study was to investigate the effect of dietary supplementation of fenugreek seed extract (FG) either alone or in combination with choline-DHA on BDNF and dendritic arborization of pyramidal neurons in CA1 and CA3 regions of the hippocampus in ovariectomized rats. Female Wistar rats of 9-10 months old were divided into six groups as normal control (NC); ovariectomy (OVX); OVX + FG; OVX + choline-DHA; OVX + FG + choline-DHA; and OVX + estradiol. All the groups, except NC, were ovariectomized. After 2 weeks of ovariectomy, dietary supplementation was initiated for a period of 30 days. After supplementation, behavioral studies, BDNF levels and dendritic arborization were estimated. Ovariectomized (OVX) rats showed reduced BDNF levels, dendritic branching points and dendritic intersections of pyramidal neurons in CA1 and CA3 regions of the hippocampus. OVX rats supplemented with FG with choline-DHA showed significantly improved BDNF levels, dendritic branching points and dendritic intersections. These results are demonstrating that FG with choline-DHA supplementation can be an alternative for estrogen replacement therapy to modulate menopause-induced learning and memory deficits.

Functional Expression of Choline Transporters in the Blood-Brain Barrier

Cholinergic neurons in the central nervous system play a vital role in higher brain functions, such as learning and memory. Choline is essential for the synthesis of the neurotransmitter acetylcholine by cholinergic neurons. The synthesis and metabolism of acetylcholine are important mechanisms for regulating neuronal activity. Choline is a positively charged quaternary ammonium compound that requires transporters to pass through the plasma membrane. Currently, there are three groups of choline transporters with different characteristics, such as affinity for choline, tissue distribution, and sodium dependence. They include (I) polyspecific organic cation transporters (OCT1-3: SLC22A1-3) with a low affinity for choline, (II) high-affinity choline transporter 1 (CHT1: SLC5A7), and (III) choline transporter-like proteins (CTL1-5: SLC44A1-5). Brain microvascular endothelial cells, which comprise part of the blood-brain barrier, take up extracellular choline via intermediate-affinity choline transporter-like protein 1 (CTL1) and low-affinity CTL2 transporters. CTL2 is responsible for excreting a high concentration of choline taken up by the brain microvascular endothelial cells on the brain side of the blood-brain barrier. CTL2 is also highly expressed in mitochondria and may be involved in the oxidative pathway of choline metabolism. Therefore, CTL1- and CTL2-mediated choline transport to the brain through the blood-brain barrier plays an essential role in various functions of the central nervous system by acting as the rate-limiting step of cholinergic neuronal activity.

The effect of paroxetine, venlafaxine and bupropion administration alone and combined on spatial and aversive memory performance in rats

BACKGROUND

The use of antidepressants in combination is common practice following non-response to single antidepressant agents. Nevertheless, the scientific literature lacks preclinical studies regarding the combined administration of antidepressants across multiple behavioral measures including, but not limited to, cognition. Hence, we aimed to determine the effects of paroxetine (PAR), venlafaxine (VEN) and bupropion (BUP) alone or combined (PAR+BUP or VEN+BUP) on spatial and affective memory tasks to advance the knowledge about the combined use of antidepressants in cognition.

METHODS

Adult rats received daily injections (15 days) of PAR (20mg/kg, ip), VEN (20mg/kg, ip), BUP (20mg/kg, ip) alone or combined and were submitted to behavioral measures of spatial memory (radial-arm maze - RAM), aversive memory (passive avoidance - PA), open field (OF) and forced swimming (FST) tests.

RESULTS

In the RAM, VEN or VEN+BUP impaired learning, while short-term memory (STM) was impaired by PAR, BUP and their combination. VEN+BUP improved STM as compared to BUP. PAR impaired long-term memory (LTM). VEN or BUP alone impaired STM and long-term fear memory, whilst PAR+BUP or VEN+BUP did not induce significant alterations.

CONCLUSIONS

The effects of VEN, PAR or BUP alone and in combination on measures of memory are variable and vary as a function of the pharmacodynamics profile of each drug as well as the specific memory paradigm.

Mechanistic basis of altered morphine disposition in nonalcoholic steatohepatitis

Morphine is metabolized in humans to morphine-3-glucuronide (M3G) and the pharmacologically active morphine-6-glucuronide (M6G). The hepatobiliary disposition of both metabolites relies upon multidrug resistance-associated proteins Mrp3 and Mrp2, located on the sinusoidal and canalicular membrane, respectively. Nonalcoholic steatohepatitis (NASH), the severe stage of nonalcoholic fatty liver disease, alters xenobiotic metabolizing enzyme and transporter function. The purpose of this study was to determine whether NASH contributes to the large interindividual variability and postoperative adverse events associated with morphine therapy. Male Sprague-Dawley rats were fed a control diet or a methionine- and choline-deficient diet to induce NASH. Radiolabeled morphine (2.5 mg/kg, 30 µCi/kg) was administered intravenously, and plasma and bile (0-150 or 0-240 minutes), liver and kidney, and cumulative urine were analyzed for morphine and M3G. The antinociceptive response to M6G (5 mg/kg) was assessed (0-12 hours) after direct intraperitoneal administration since rats do not produce M6G. NASH caused a net decrease in morphine concentrations in the bile and plasma and a net increase in the M3G/morphine plasma area under the concentration-time curve ratio, consistent with upregulation of UDP-glucuronosyltransferase Ugt2b1. Despite increased systemic exposure to M3G, NASH resulted in decreased biliary excretion and hepatic accumulation of M3G. This shift toward systemic retention is consistent with the mislocalization of canalicular Mrp2 and increased expression of sinusoidal Mrp3 in NASH and may correlate to increased antinociception by M6G. Increased metabolism and altered transporter regulation in NASH provide a mechanistic basis for interindividual variability in morphine disposition that may lead to opioid-related toxicity.

Chronic dietary choline supplementation modulates attentional change in adult rats

In two experiments adult rats were maintained on a diet enriched with added choline for 12 weeks prior to behavioral testing; control rats remained on the standard diet during this time. In Experiment 1 all rats received training in the Hall-Pearce negative transfer paradigm in which prior training with a conditioned stimulus (CS) paired with a small reinforcer retards further learning when the size of the reinforcer is increased. This effect, which has been attributed to a loss of associability by the CS, was obtained in control subjects but not in those given the supplement. Experiment 2 investigated the effect of prior nonreinforced exposure of the to-be-CS (latent inhibition). Such exposure retarded subsequent learning in control subjects, but latent inhibition was not obtained in those given the supplement. We conclude that the mechanism that reduces the attention paid to a stimulus that accurately predicts its consequences does not operate effectively after choline supplementation. These results are consistent with a role for the cholinergic system of the basal forebrain in modulation of attention.

Dietary choline deprivation impairs rat brain mitochondrial function and behavioral phenotype

Dietary choline deprivation (CD) is associated with behavioral changes, but mechanisms underlying these detrimental effects are not well characterized. For instance, no literature data are available concerning the CD effects on brain mitochondrial function related to impairment in cognition. Therefore, we investigated brain mitochondrial function and redox status in male Wistar rats fed a CD diet for 28 d. Moreover, the CD behavioral phenotype was characterized. Compared with rats fed a control diet (CTRL), CD rats showed lower NAD-dependent mitochondrial state III and state IV respiration, 40% lower complex I activity, and significantly higher reactive oxygen species production. Total glutathione was oxidatively consumed more in CD than in CTRL rats and the rate of protein oxidation was 40% higher in CD than in CTRL rats, reflecting an oxidative stress condition. The mitochondrial concentrations of cardiolipin, a phospholipid required for optimal activity of complex I, was 20% lower in CD rats than in CTRL rats. Compared with CTRL rats, the behavioral phenotype of CD rats was characterized by impairment in motor coordination and motor learning assessed with the rotarod/accelerod test. Furthermore, compared with CTRL rats, CD rats were less capable of learning the active avoidance task and the number of attempts they made to avoid foot shock was fewer. The results suggest that CD-induced dysfunction in brain mitochondria may be responsible for impairment in cognition and underline that, similar to the liver, the brain also needs an adequate choline supply for its normal functioning.

Effects of adult-onset choline deprivation on the activities of acetylcholinesterase, (Na+,K+)- and Mg2+-ATPase in crucial rat brain regions

Choline (Ch) plays an important role in brain neurotransmission, while Ch-deprivation (CD) has been linked to various pathophysiological states. Prolonged ingestion of Ch-deficient diet (CDD) is known to produce CD causing a reduction of rat brain acetylcholine (ACh) levels, as well as memory and growth disorders. The aim of this study was to investigate the effect of a 2-month adult-onset CD on the activities of acetylcholinesterase (AChE), (Na+,K+)- and Mg2+-ATPase in crucial brain regions of male rats. Adult rats were divided into two groups (control and CD). The CD group was fed with CDD for 2-months. At the end of the second month, rats were sacrificed by decapitation and the brain regions were rapidly removed. Enzyme activities were measured spectrophotometrically in the homogenated frontal cortex, hippocampus, hypothalamus, cerebellum, and pons. In CD rats, AChE activity was found statistically significantly increased in the hippocampus and the cerebellum (+28%, P<0.001 and +46%, P<0.001, respectively, as compared to control), while it was found unaltered in the other three regions (frontal cortex, hypothalamus and pons). (Na+,K+)-ATPase activity was found increased by CD in the frontal cortex (+30%, P<0.001), decreased in both hippocampus and hypothalamus (-68%, P<0.001 and -51%, P<0.001, respectively), and unaltered in both cerebellum and pons. No statistically significant changes were observed in the activities of Mg2+-ATPase in the frontal cortex and the hypothalamus, while statistically significant increases were recorded in the hippocampus (+21%, P<0.01), the cerebellum (+85%, P<0.001) and the pons (+19%, P<0.05), as compared to control levels. Our data suggest that adult-onset CD can have significant effects on the examined brain parameters in the examined crucial brain regions, as well as that CD is a metabolic disorder towards which different and brain region specific neurophysiological responses seem to occur. Following a 2-month adult-onset CD, the activity of AChE was found to be increased in the hippocampus and the cerebellum and unaltered in the other three regions (frontal cortex, hypothalamus and pons), while Na+,K+-ATPase activity was found to be increased in the frontal cortex, decreased in both hippocampus and hypothalamus, and unaltered in both cerebellum and pons. Moreover, Mg2+-ATPase activity was found to be unaltered in the frontal cortex and the hypothalamus, and increased in the hippocampus, the cerebellum and the pons. The observed differentially affected activities of AChE, (Na+,K+)-ATPase and Mg2+-ATPase (induced by CD) could result in modulations of cholinergic neurotransmission, neural excitability, metabolic energy production, Mg2+ homeostasis and protein synthesis (that might have a variety of neurophysiological consequences depending on the brain region in which they seem to occur).

Subsequent exposure to the choline uptake enhancer MKC-231 antagonizes phencyclidine-induced behavioral deficits and reduction in septal cholinergic neurons in rats

This study examined the effects of subsequent, subchronic, treatment with choline uptake enhancer MKC-231 on the behavioral and cellular deficits induced by repeated PCP exposure in rats. Prior subchronic PCP exposure resulted in increased locomotion following an acute PCP or cocaine challenge, but resulted in decreased locomotor activity in response to a carbachol-challenge. MKC-231 significantly antagonized the alterations in the locomotor responses to cocaine and carbachol, but not to PCP. In the novel object recognition test, repeated PCP exposure caused cognitive deficits in rats, and the PCP-induced cognitive deficits were antagonized by MKC-231. In contrast, no effects of PCP exposure were shown in the repeated passive avoidance test. Furthermore, repeated PCP exposure decreased a number of choline acetyltransferase (ChAT)-positive cells in the medial septum and increased dynorphin A expression in the ventral striatum. Moreover, MKC-231 significantly antagonized the changes in septal ChAT-positive cells, but not the changes in ventrostriatal dynorphin A expression. These results suggest that MKC-231 could be a therapeutic drug for the treatment of schizophrenia.

Elevation of serum cerebral injury markers correlates with serum choline decline after coronary artery bypass grafting surgery

The aims of this study were to determine circulating choline status and its relationship to circulating levels of S-100β protein and neuron-specific enolase, biochemical markers of cerebral injury and cognitive decline, after coronary artery bypass grafting (CABG) surgery. Preoperatively, patients scheduled for off-pump or on-pump CABG surgery had serum concentrations of 12.0±0.2 and 11.7±0.4μmol/L free choline and 2640±65 and 2675±115μmol/L phospholipid-bound choline, respectively. Serum free and bound choline levels decreased by 22–37% or 34–47% and 16–36% or 31–38% at 48h after off-pump or on-pump surgery, respectively. Serum S-100β and neuron-specific enolase increased from preoperative values of 0.083±0.009 and 6.3±0.2μg/L to 0.405±0.022 and 11.4±0.8μg/L, respectively, at 0h postoperatively and remained elevated for 48h after off-pump surgery. Serum free and bound choline concentrations were inversely correlated with the concentrations of S-100β (r=−0.798; p<0.001 and r=−0.734; p<0.001) and neuron-specific enolase (r=−0.840; p<0.001 and r=−0.728; p<0.001). In conclusion, CABG surgery induces a decline in serum free and phospholipid-bound choline concentrations. The decreased serum choline concentrations were inversely correlated with the elevated levels of circulating cerebral injury markers. Thus, a decline in circulating choline may be involved in postoperative cognitive decline.

Regional differences in gastrointestinal motility disturbances during acute necrotising pancreatitis

Patients with acute pancreatitis often suffer from intestinal motility disturbances but the mechanism of this dysfunction is largely unknown. We studied the effect of acute necrotising pancreatitis (ANP) on in vivo gastrointestinal motility and in vitro intestinal contractility in mice. ANP was induced non-invasively by feeding young female mice a choline-deficient ethionine-supplemented (CDE) diet during 72 h. Gastric emptying and intestinal transit were measured in vivo 15 min after intragastric gavage of a semiliquid Evans blue bolus. Gastric and intestinal neuromuscular function was determined in vitro on isolated muscle strips. ANP significantly decreased gastric emptying from 61.2 +/- 9.8 to 34.9 +/- 7.1% and intestinal transit from 63.4 +/- 5.6 to 32.5 +/- 5.4%. ANP did not affect receptor-dependent and receptor-independent gastric muscle contractions except the contractions to substance P, which were slightly inhibited. In intestinal muscle strips, ANP significantly decreased contractions to EFS, carbachol, PGF(2alpha), substance P and KCl. Our results show that ANP delays gastric emptying in vivo, associated with a specific reduction in substance P contractility in vitro. ANP also impairs intestinal transit in vivo, associated with a non-specific reduction of intestinal contractility in vitro. We conclude that ANP impairs gastrointestinal motility in mice with underlying regional differences in the pathogenic mechanisms.

Dopamine D2 receptor plays a role in memory function: implications of dopamine-acetylcholine interaction in the ventral hippocampus

RATIONALE

The role of the hippocampal dopaminergic system in mnemonic function has not been clarified yet.

OBJECTIVE

We previously reported that the dopamine D2 receptor (D2R) is involved in the regulation of acethylcholin (ACh) release in the hippocampus. In this study, we further investigated ACh-dopamine (DA) interaction in the hippocampus and its involvement in mnemonic function.

METHODS

For experiment 1, rats fed with Cholin (Ch)-deficient chow were used. We examined the effects of D2R antagonist, raclopride, on cognitive performance using a passive avoidance task. We further carried out in vivo microdialysis to assess the effect of infusion of D2R agonist, quinpirole, into the ventral hippocampus on its capacity to release ACh. For experiment 2, rats fed with normal chow were used. The performance of a radial arm maze task was assessed to examine the effects of hippocampal injection of D2R agonist, quinpirole, on memory impairment induced by scopolamine, a muscarinic ACh antagonist.

RESULTS

In experiment 1, rats fed with Ch-deficient chow showed impaired performances indicated by prolonged latency on retention trials of a passive avoidance task following the hippocampal injection of D2R antagonist, and showed reduced capacity to release ACh following the injection of D2R agonist compared with rats fed with normal chow. In experiment 2, memory impairment induced by the intraperitoneal injection of scopolamine was ameliorated by the injection of D2R agonist into the ventral hippocampus.

CONCLUSION

These results indicate the possible involvement of hippocampal ACh-DA interaction in mnemonic processing.

Septohippocampal acetylcholine: involved in but not necessary for learning and memory?

The neurotransmitter acetylcholine (ACh) has been accorded an important role in supporting learning and memory processes in the hippocampus. Cholinergic activity in the hippocampus is correlated with memory, and restoration of ACh in the hippocampus after disruption of the septohippocampal pathway is sufficient to rescue memory. However, selective ablation of cholinergic septohippocampal projections is largely without effect on hippocampal-dependent learning and memory processes. We consider the evidence underlying each of these statements, and the contradictions they pose for understanding the functional role of hippocampal ACh in memory. We suggest that although hippocampal ACh is involved in memory in the intact brain, it is not necessary for many aspects of hippocampal memory function.