Effect of a diet-induced n-3 PUFA depletion on cholinergic parameters in the rat hippocampus

Brain docosahexaenoic acid status and learning in young rats submitted to dietary long-chain polyunsaturated fatty acid deficiency and supplementation limited to lactation

N-3 fatty acid deficiency has been related to decreased docosahexaenoic acid (DHA) and increased docosapentaenoic acid (DPA) levels in brain and to learning disadvantages. The influence of n-3 deficiency and supplementation on brain fatty acids and learning were investigated in young rats. Newborn Wistar rats were assigned to three groups of cross-foster mothers. The control group (C) was nursed by mothers that received essential fatty acids during pregnancy and lactation, and the deficient group (D) was nursed by mothers that did not receive those fatty acids. The supplemental group (S) had the same conditions as D, receiving an additional DHA and arachidonic acid supplement during lactation. Cerebral cortex and hippocampus fatty acid composition was examined using thin-layer and capillary column gas chromatography, and learning was measured by passive-avoidance procedure. D brains showed low DHA and high DPA levels, but S brain composition was similar to C. Learning in the S group was unaffected, but in the D group, it was poorer than C. Learning was directly correlated with DHA levels and inversely with DPA levels in brain. Low DHA and high DPA brain levels both were correlated with poor learning. DPA seems not to be a suitable brain functional analogue of DHA, and DHA supplementation reversed both biochemical and learning adverse effects observed in n-3 deficiency.

Lipid homeostasis and apolipoprotein E in the development and progression of Alzheimer's disease

Extracellular amyloid plaques, intracellular neurofibrillary tangles, and loss of basal forebrain cholinergic neurons in the brains of Alzheimer's disease (AD) patients may be the end result of abnormalities in lipid metabolism and peroxidation that may be caused, or exacerbated, by beta-amyloid peptide (Abeta). Apolipoprotein E (apoE) is a major apolipoprotein in the brain, mediating the transport and clearance of lipids and Abeta. ApoE-dependent dendritic and synaptic regeneration may be less efficient with apoE4, and this may result in, or unmask, age-related neurodegenerative changes. The increased risk of AD associated with apoE4 may be modulated by diet, vascular risk factors, and genetic polymorphisms that affect the function of other transporter proteins and enzymes involved in brain lipid homeostasis. Diet and apoE lipoproteins influence membrane lipid raft composition and the properties of enzymes, transporter proteins, and receptors mediating Abeta production and degradation, tau phosphorylation, glutamate and glucose uptake, and neuronal signal transduction. The level and isoform of apoE may influence whether Abeta is likely to be metabolized or deposited. This review examines the current evidence for diet, lipid homeostasis, and apoE in the pathogenesis of AD. Effects on the cholinergic system and response to cholinesterase inhibitors by APOE allele carrier status are discussed briefly.

[The role of nutritional factors on the structure and function of the brain: an update on dietary requirements]

The brain is an organ elaborated and functioning from substances present in the diet. Dietary regulation of blood glucose level (via ingestion of food with a low glycemic index ensuring a low insulin level) improves the quality and duration of intellectual performance, if only because at rest the adult brain consumes 50 p. 100 of dietary carbohydrates, 80 p. 100 of them for energy purposes. The nature of the amino acid composition of dietary proteins contributes to good cerebral function; tryptophan plays a special role. Many indispensable amino acids present in dietary proteins help to elaborate neurotransmitters and neuromodulators. Omega-3 fatty acids provided the first coherent experimental demonstration of the effect of dietary nutrients on the structure and function of the brain. First it was shown that the differentiation and functioning of cultured brain cells requires omega-3 fatty acids. It was then demonstrated that alpha-linolenic acid (ALA) deficiency alters the course of brain development, perturbs the composition and physicochemical properties of brain cell membranes, neurones, oligodendrocytes, and astrocytes (ALA). This leads to physicochemical modifications, induces biochemical and physiological perturbations, and results in neurosensory and behavioral upset. Consequently, the nature of polyunsaturated fatty acids (in particular omega-3) present in formula milks for infants (premature and term) conditions the visual and cerebral abilities, including intellectual abilities. Moreover, dietary omega-3 fatty acids are certainly involved in the prevention of some aspects of cardiovascular disease (including at the level of cerebral vascularization), and in some neuropsychiatric disorders, particularly depression, as well as in dementia, notably Alzheimer's disease. Their deficiency can prevent the satisfactory renewal of membranes and thus accelerate cerebral aging. Iron is necessary to ensure oxygenation, to produce energy in the cerebral parenchyma, and for the synthesis of neurotransmitters. The iodine provided by the thyroid hormone ensures the energy metabolism of the cerebral cells. The absence of iodine during pregnancy induces severe cerebral dysfunction, leading to cretinism. Manganese, copper, and zinc participate in enzymatic mechanisms that protect against free radicals, toxic derivatives of oxygen. The use of glucose by nervous tissue implies the presence of vitamin B1. Vitamin B9 preserves memory during aging, and with vitamin B12 delays the onset of signs of dementia, provided it is administered in a precise clinical window, at the onset of the first symptoms. Vitamins B6 and B12, among others, are directly involved in the synthesis of neurotransmitters. Nerve endings contain the highest concentrations of vitamin C in the human body. Among various vitamin E components, only alpha-tocopherol is involved in nervous membranes. The objective of this update is to give an overview of the effects of dietary nutrients on the structure and certain functions of the brain.

Alterations in hippocampal phospholipid profile by prenatal exposure to ethanol

It has been suggested that hippocampus-related cognitive processes are especially sensitive to ethanol. To provide an insight into the biochemical mechanisms underlying the hippocampus-related functional deficits associated with prenatal ethanol exposure, we investigated the effects of chronic ethanol exposure on the phospholipid profile in developing rat hippocampi. High-performance liquid chromatography/electrospray ionization-mass spectrometry analysis revealed that ethanol lowered the levels of total phosphatidylserine (PS) by 15-20% at all ages examined, primarily owing to the reduction in 1-stearoyl-2-docosahexaenoyl-PS (18:0,22:6n-3-PS) species. Ethanol exposure also led to a decrease in phosphatidylcholine (PC) and an increase in phosphatidylethanolamine (PE), but the total phospholipid content was not significantly changed. At the fatty acid level, ethanol exposure significantly decreased the 22:6n-3 content at postnatal days 0 and 21, with a slight increase in 22:5n-6, without changing the total fatty acid content significantly. In conclusion, ethanol depleted PS, especially 22:6-containing species, and PC from hippocampal membranes with concomitant increase in PE. Alteration of the phospholipid profile in the hippocampus resulting from exposure to ethanol during prenatal and developmental stages may have significant implications with respect to the cognitive dysfunction observed in fetal alcohol syndrome.

Serotoninergic neurotransmission is affected by n-3 polyunsaturated fatty acids in the rat

We explored the effects of chronic alpha-linolenic acid dietary deficiency on serotoninergic neurotransmission. In vivo synaptic serotonin (5-HT) levels were studied in basal and pharmacologically stimulated conditions using intracerebral microdialysis in the hippocampus of awake 2-month-old rats. We also studied the effects of reversion of the deficient diet on fatty acid composition and serotoninergic neurotransmission. A balanced (control) diet was supplied to deficient rats at different stages of development, i.e. from birth, 7, 14 or 21 days of age. We demonstrated that chronic n-3 polyunsaturated fatty acid dietary deficiency induced changes in the synaptic levels of 5-HT both in basal conditions and after pharmacological stimulation with fenfluramine. Higher levels of basal 5-HT release and lower levels of 5-HT-stimulated release were found in deficient than in control rats. These neurochemical modifications were reversed by supply of the balanced diet provided at birth or during the first 2 weeks of life through the maternal milk, whereas they persisted if the balanced diet was given from weaning (at 3 weeks of age). This suggests that provision of essential fatty acids is durably able to affect brain function and that this is related to the developmental stage during which the deficiency occurs.

Docosahexaenoic acid in the diet: its importance in maintenance and restoration of neural membrane function

The central nervous system has the second highest concentration of lipids after adipose tissue. Long chain fatty acids, particularly arachidonic acid and docosahexaenoic acid, are integral components of neural membrane phospholipids. Alterations in neural membrane phospholipid components cannot only influence crucial intracellular and intercellular signaling but also alter many membrane physical properties such as fluidity, phase transition temperature, bilayer thickness, and lateral domains. A deficiency of docosahexaenoic acid markedly affects neurotransmission, membrane-bound enzyme and ion channel activities, gene expression, intensity of inflammation, and immunity and synaptic plasticity. Docosahexaenoic acid deficiency is associated with normal aging, Alzheimer disease, hyperactivity, schizophrenia, and peroxisomal disorders. Although the molecular mechanism of docosahexaenoic acid involvement in the disorders remains unknown, the supplementation of docosahexaenoic acid in the diet restores gene expression and modulates neurotransmission. Also, improvements are seen in signal transduction processes associated with behavioral deficits, learning activity, peroxisomal disorders, and psychotic changes in schizophrenia, depression, hyperactivity, stroke, and Alzheimer disease.