Exfoliation of membrane ecto-enzymes in the form of micro-vesicles

Cultures from various normal and neoplastic cell lines exfoliated vesicles with 5'-nucleotidase activity which reflected the ecto-enzyme activity of the parent monolayer culture. The ratio of 5'-nucleotidase to ATPase activity in the microvesicles indicated that cellular ecto-ATPase was conserved in the exfoliative process. Phospholipids of the microvesicles contained significantly increased amounts of sphingomyelin and total polyunsaturated fatty acids. It was concluded that the shedded vesicles constituted a select portion of the plasma membrane. Examination by electron microscopy showed the vesicles had an average diameter of 500 to 1000 nm and often contained a second population of vesicles about 40 nm in diameter. As much as 70% of the plasma membrane ecto-5'-nucleotidase activity of a culture was released into the medium over a 24-h period. Phosphoesterhydrolases from C-6 glioma or N-18 neuroblastoma microvesicles dephosphorylated cell surface constituents when in contact with monolayer cultures. Exfoliated membrane vesicles may serve a physiologic function; it is proposed that they be referred to as exosomes.

Mechanisms of action of docosahexaenoic acid in the nervous system

This review describes (from both the animal and human literature) the biological consequences of losses in nervous system docosahexaenoate (DHA). It then concentrates on biological mechanisms that may serve to explain changes in brain and retinal function. Brief consideration is given to actions of DHA as a nonesterified fatty acid and as a docosanoid or other bioactive molecule. The role of DHA-phospholipids in regulating G-protein signaling is presented in the context of studies with rhodopsin. It is clear that the visual pigment responds to the degree of unsaturation of the membrane lipids. At the cell biological level, DHA is shown to have a protective role in a cell culture model of apoptosis in relation to its effects in increasing cellular phosphatidylserine (PS); also, the loss of DHA leads to a loss in PS. Thus, through its effects on PS, DHA may play an important role in the regulation of cell signaling and in cell proliferation. Finally, progress has been made recently in nuclear magnetic resonance studies to delineate differences in molecular structure and order in biomembranes due to subtle changes in the degree of phospholipid unsaturation.

A mutation in OTOF, encoding otoferlin, a FER-1-like protein, causes DFNB9, a nonsyndromic form of deafness

Using a candidate gene approach, we identified a novel human gene, OTOF, underlying an autosomal recessive, nonsyndromic prelingual deafness, DFNB9. The same nonsense mutation was detected in four unrelated affected families of Lebanese origin. OTOF is the second member of a mammalian gene family related to Caenorhabditis elegans fer-1. It encodes a predicted cytosolic protein (of 1,230 aa) with three C2 domains and a single carboxy-terminal transmembrane domain. The sequence homologies and predicted structure of otoferlin, the protein encoded by OTOF, suggest its involvement in vesicle membrane fusion. In the inner ear, the expression of the orthologous mouse gene, mainly in the sensory hair cells, indicates that such a role could apply to synaptic vesicles.

Behavioral deficits associated with dietary induction of decreased brain docosahexaenoic acid concentration

Docosahexaenoic acid (DHA), an n-3 fatty acid, is rapidly deposited during the period of rapid brain development. The influence of n-3 fatty acid deficiency on learning performance in adult rats over two generations was investigated. Rats were fed either an n-3 fatty acid-adequate (n-3 Adq) or -deficient (n-3 Def) diet for three generations (F1-F3). Levels of total brain n-3 fatty acids were reduced in the n-3 Def group by 83 and 87% in the F2 and F3 generations, respectively. In the Morris water maze, the n-3 Def group showed a longer escape latency and delayed acquisition of this task compared with the n-3 Adq group in both generations. The acquisition and memory levels of the n-3 Def group in the F3 generation seemed to be lower than that of the F2 generation. The 22:5n-6/22:6n-3 ratio in the frontal cortex and dams' milk was markedly increased in the n-3 Def group, and this ratio was significantly higher in the F3 generation compared with the F2 generation. These results suggest that learning and cognitive behavior are related to brain DHA status, which, in turn, is related to the levels of the milk/dietary n-3 fatty acids.

Arachidonic and docosahexaenoic acids are biosynthesized from their 18-carbon precursors in human infants

It is becoming clear that an adequate level of long-chain highly unsaturated fatty acids in the nervous system is required for optimal function and development; however, the ability of infants to biosynthesize long-chain fatty acids is unknown. This study explores the capacity of human infants to convert 18-carbon essential fatty acids to their elongated and desaturated forms, in vivo. A newly developed gas chromatography/negative chemical ionization/mass spectrometry method employing 2H-labeled essential fatty acids allowed assessment of this in vivo conversion with very high sensitivity and selectivity. Our results demonstrate that human infants have the capacity to convert dietary essential fatty acids administered enterally as 2H-labeled ethyl esters to their longer-chain derivatives, transport them to plasma, and incorporate them into membrane lipids. The in vivo conversion of linoleic acid (18:2n6) to arachidonic acid (20:4n6) is demonstrated in human beings. All elongases/desaturases necessary for the conversion of linolenic acid (18:3n3) to docosahexaenoic acid (22:6n3) are also active in the first week after birth. Although the absolute amounts of n-3 fatty acid metabolites accumulated in plasma are greater than those of the n-6 family, estimates of the endogenous pools of 18:2n6 and 18:3n3 indicate that n-6 fatty acid conversion rates are greater than those of the n-3 family. While these data clearly demonstrate the capability of infants to biosynthesize 22:6n3, a lipid that is required for optimal neural development, the amounts produced in vivo from 18:3n3 may be inadequate to support the 22:6n3 level observed in breast-fed infants.

A defect in harmonin, a PDZ domain-containing protein expressed in the inner ear sensory hair cells, underlies Usher syndrome type 1C

Usher syndrome type 1 (USH1) is an autosomal recessive sensory defect involving congenital profound sensorineural deafness, vestibular dysfunction and blindness (due to progressive retinitis pigmentosa)1. Six different USH1 loci have been reported. So far, only MYO7A (USH1B), encoding myosin VIIA, has been identified as a gene whose mutation causes the disease. Here, we report a gene underlying USH1C (MIM 276904), a USH1 subtype described in a population of Acadian descendants from Louisiana and in a Lebanese family. We identified this gene (USH1C), encoding a PDZ-domain-containing protein, harmonin, in a subtracted mouse cDNA library derived from inner ear sensory areas. In patients we found a splice-site mutation, a frameshift mutation and the expansion of an intronic variable number of tandem repeat (VNTR). We showed that, in the mouse inner ear, only the sensory hair cells express harmonin. The inner ear Ush1c transcripts predicted several harmonin isoforms, some containing an additional coiled-coil domain and a proline- and serine-rich region. As several of these transcripts were absent from the eye, we propose that USH1C also underlies the DFNB18 form of isolated deafness.

Dietary polyunsaturated fatty acids and depression: when cholesterol does not satisfy

Recent studies have both offered and contested the proposition that lowering plasma cholesterol by diet and medications increases suicide, homicide, and depression. Significant confounding factors include the quantity and distribution of dietary n-6 and n-3 polyunsaturated essential fatty acids that influence serum lipids and alter the biophysical and biochemical properties of cell membranes. Epidemiological studies in various countries and in the United States in the last century suggest that decreased n-3 fatty acid consumption correlates with increasing rates of depression. This is consistent with a well-established positive correlation between depression and coronary artery disease. Long-chain n-3 polyunsaturate deficiency may also contribute to depressive symptoms in alcoholism, multiple sclerosis, and post-partum depression. We postulate that adequate long-chain polyunsaturated fatty acids, particularly docosahexaenoic acid, may reduce the development of depression just as n-3 polyunsaturated fatty acids may reduce coronary artery disease.

Association of human herpes virus 6 (HHV-6) with multiple sclerosis: increased IgM response to HHV-6 early antigen and detection of serum HHV-6 DNA

Viruses have long been suggested to be involved in the etiology of multiple sclerosis (MS). This suggestion is based on (1) epidemiological evidence of childhood exposure to infectious agents and increase in disease exacerbations with viral infection; (2) geographic association of disease susceptibility with evidence of MS clustering; (3) evidence that migration to and from high-risk areas influences the likelihood of developing MS; (4) abnormal immune responses to a variety of viruses; and (5) analogy with animal models and other human diseases in which viruses can cause diseases with long incubation periods, a relapsing-remitting course, and demyelination. Many of these studies involve the demonstration of increased antibody titers to a particular virus, whereas some describe isolation of virus from MS material. However, no virus to date has been definitively associated with this disease. Recently, human herpesvirus 6 (HHV-6), a newly described beta-herpes virus that shares homology with cytomegalovirus (CMV), has been reported to be present in active MS plaques. In order to extend these observations, we have demonstrated increased IgM serum antibody responses to HHV-6 early antigen (p41/38) in patients with relapsing-remitting MS (RRMS), compared with patients with chronic progressive MS (CPMS), patients with other neurologic disease (OND), patients with other autoimmune disease (OID), and normal controls. Given the ubiquitous nature of this virus and the challenging precedent of correlating antiviral antibodies with disease association, these antibody studies have been supported by the detection of HHV-6 DNA from samples of MS serum as a marker of active viral infection.

Beneficial effects of dietary omega-3 polyunsaturated fatty acid on toxin-induced neuronal degeneration in an animal model of Parkinson's disease

In this study, we examined whether omega-3 (n-3) polyunsaturated fatty acids (PUFAs) may exert neuroprotective action in Parkinson's disease, as previously shown in Alzheimer's disease. We exposed mice to either a control or a high n-3 PUFA diet from 2 to 12 months of age and then treated them with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 140 mg/kg in 5 days). High n-3 PUFA dietary consumption completely prevented the MPTP-induced decrease of tyrosine hydroxylase (TH)-labeled nigral cells (P<0.01 vs. MPTP mice on control diet), Nurr1 mRNA (P<0.01 vs. MPTP mice on control diet), and dopamine transporter mRNA levels (P<0.05 vs. MPTP mice on control diet) in the substantia nigra. Although n-3 PUFA dietary treatment had no effect on striatal dopaminergic terminals, the high n-3 PUFA diet protected against the MPTP-induced decrease in dopamine (P<0.05 vs. MPTP mice on control diet) and its metabolite dihydroxyphenylacetic acid (P<0.05 vs. MPTP mice on control diet) in the striatum. Taken together, these data suggest that a high n-3 PUFA dietary intake exerts neuroprotective actions in an animal model of Parkinsonism.

Long chain polyunsaturated fatty acid formation in neonates: effect of gestational age and intrauterine growth

The present study was designed to evaluate the effect of gestational age and intrauterine growth on the long chain polyunsaturated fatty acid (LCP) synthesis from dietary precursors in neonates as reflected by plasma pools. These have been considered conditionally essential nutrients for normal growth, sensory maturation, and neurodevelopment. In vivo elongation/desaturation of deuterated d5-linoleic acid (d5-LA) to form arachidonic acid (AA), and d5-alpha-linolenic acid (d5-LNA) to form docosahexaenoic acid (DHA), was studied in 19 preterm appropriate-for-gestational-age (AGA) infants, 11 AGA term, and 11 intrauterine growth-retarded (IUGR) infants. They received a dose of 50 mg/kg body weight of d5-LA and d5-LNA enterally during the first days of life; d5-labeled derivatized fatty acids were determined in blood samples obtained at 24, 48, and 96 h after dosing. Lipids were extracted and fatty acids analyzed by gas chromatography and negative ion mass spectrometry. Mean concentrations, microg/mL, and d5/d0 for n-3 and n-6 precursor and products were computed at various times and were also integrated over the complete study period. Significantly higher time-integrated concentration of d5-AA and d5-DHA were observed in preterm infants relative to the other two groups. Time-integrated enrichment of DHA relative to LNA was 100-fold lower in preterms, 410-fold lower in term, and 27-fold lower in IUGR infants. Similar significant declines in product to precursor enrichments were noted for the n-6 series. A significant negative correlation of AA and DHA formation based on time-integrated d5/d0 ratios with gestational age was noted; product/ precursor enrichment versus gas chromatography for the n-6 series had an r of -0.5, p = 0.001, and for the n-3 series had an r of -0.6, p = 0.0001. Birth weight or weight adequacy did not add further strength to the relationship. We conclude that LCP formation from deuterated precursors occurs as early as 26 wk gestation, and in fact is more active at earlier gestational ages; growth retardation appears to slow down or diminish LCP formation. No quantitative estimates of LCP synthesis or nutritional sufficiency can be derived from these data.

Rats with low levels of brain docosahexaenoic acid show impaired performance in olfactory-based and spatial learning tasks

Studies were carried out to determine if decreased levels of central nervous system docosahexaenoic acid (DHA), a result of consuming an n-3-deficient diet, had an effect on learning- and memory-related behaviors in adult male rats. Females were reared on an n-3-deficient or n-3-adequate diet beginning at 21 d of life. Their male pups, the F2 generation, were weaned to the diet of the dam and tested at 9-12 wk of age. An olfactory-based discrimination and Morris water maze task were used to assess performance. Whole brain was collected after the behavioral experiments and central nervous system fatty acid content was analyzed in olfactory bulb total lipid extracts. F2 generation male rats consuming the n-3-deficient diet had an 82% decrease in DHA compared to rats consuming the n-3-adequate diet. The n-3-deficient animals made significantly more total errors in a 7-problem, 2-odor discrimination task compared to the n-3-adequate group. Furthermore, the escape latency in the Morris water maze task was significantly longer for the n-3-deficient rats compared to the n-3-adequate rats. These results indicate that rats with decreased DHA levels in the central nervous system perform poorer in these tasks compared to rats with higher DHA levels and suggest the presence of learning deficits in these animals.

Essential fatty acids predict metabolites of serotonin and dopamine in cerebrospinal fluid among healthy control subjects, and early- and late-onset alcoholics

BACKGROUND

Impulsive violence, suicide, and depression are strongly associated with low concentrations of cerebrospinal fluid 5-hydroxyindoleacetic acid (CSF 5-HIAA). Increased suicide and trauma reported in some cholesterol-lowering trials may be related to altered concentrations of polyunsaturated fatty acids rather than cholesterol, a possible surrogate marker.

METHODS

CSF 5-HIAA and homovanillic acid (HVA), total cholesterol, and plasma fatty acid concentrations were examined in 176 subjects, including 49 healthy volunteers, and 88 early- and 39 late-onset alcoholics.

RESULTS

Among each group, polyunsaturated fatty acids predicted both CSF 5-HIAA and CSF HVA concentrations, but total cholesterol was unrelated to either neurotransmitter metabolite. The relationships between plasma 22: 6n3 and CSF 5-HIAA were significantly different when healthy volunteers (r = .35) were compared to early-onset alcoholics (r = -.38) (p < .0002).

CONCLUSIONS

Dietary studies are indicated to determine if essential fatty acid supplementation can influence central nervous system serotonin and dopamine metabolism and modify impulsive behaviors related to these neurotransmitters.

The nervous system has an absolute molecular species requirement for proper function

A considerable body of biological evidence has accumulated that suggests that docosahexaenoic acid (22:6n3) is an essential component in the nervous system. Moreover, it appears from these studies that long chain polyunsaturates of the n-6 family such as arachidonate (20:4n6) and docosapentaenoate (22:5n6) cannot substitute for 22:6n3. This evidence is briefly reviewed and two hypotheses centering upon either biochemical or biophysical aspects of polyunsaturate function are presented and discussed. It is concluded that a bioactive metabolite of 22:6n3 is not responsible for its function in brain and that the best hypothesis asserts that a membrane function of a 22:6n3-containing species of phospholipid, such as phosphatidylserine, is critical for optimal neural function. Moreover, data are presented indicating that the biophysical properties of various highly unsaturated species of phospholipid are distinguishable. It is further contended that these species are not randomly distributed in membranes and thus the differences in physical properties may be amplified. It is concluded that a conceptual framework is needed in which the distinct membrane roles of phospholipid species may be understood as a function of the positions and numbers of double bonds. Only then may the critical role of the highly unsaturated n-3 polyunsaturates in the brain and retina be understood.

Transfer of omega-3 fatty acids across the blood-brain barrier after dietary supplementation with a docosahexaenoic acid-rich omega-3 fatty acid preparation in patients with Alzheimer's disease: the OmegAD study

OBJECTIVE

Little is known about the transfer of essential fatty acids (FAs) across the human blood-brain barrier (BBB) in adulthood. In this study, we investigated whether oral supplementation with omega-3 (n-3) FAs would change the FA profile of the cerebrospinal fluid (CSF).

METHODS

A total of 33 patients (18 receiving the n-3 FA supplement and 15 receiving placebo) were included in the study. These patients were participants in the double-blind, placebo-controlled randomized OmegAD study in which 204 patients with mild Alzheimer's disease (AD) received 2.3 g n-3 FA [high in docosahexaenoic acid (DHA)] or placebo daily for 6 months. CSF FA levels were related to changes in plasma FA and to CSF biomarkers of AD and inflammation.

RESULTS

At 6 months, the n-3 FA supplement group displayed significant increases in CSF (and plasma) eicosapentaenoic acid (EPA), DHA and total n-3 FA levels (P < 0.01), whereas no changes were observed in the placebo group. Changes in CSF and plasma levels of EPA and n-3 docosapentaenoic acid were strongly correlated, in contrast to those of DHA. Changes in DHA levels in CSF were inversely correlated with CSF levels of total and phosphorylated tau, and directly correlated with soluble interleukin-1 receptor type II. Thus, the more DHA increased in CSF, the greater the change in CSF AD/inflammatory biomarkers.

CONCLUSIONS

Oral supplementation with n-3 FAs conferred changes in the n-3 FA profile in CSF, suggesting transfer of these FAs across the BBB in adults.

Anandamide, an endogenous cannabinoid, inhibits Shaker-related voltage-gated K+ channels

Anandamide has been identified in porcine brain as an endogenous cannabinoid receptor ligand and is believed to be a counterpart to the psychoactive component of marijuana, delta 9-tetrahydrocannabinol (delta 9-THC). Here we report that anandamide directly inhibits (IC50, 2.7 muM) Shaker-related Kv1.2 K+ channels that are found ubiquitously in the mammalian brain. Delta 9-THC also inhibited Kv1.2 channels with comparable potency (IC50, 2.4 muM), as did several N-acyl-ethanolamides with cannabinoid receptor binding activity. Potassium current inhibition occurred through a pertussis toxin-insensitive mechanism and was not prevented by the cannabinoid receptor antagonist SR141716A. Utilizing excised patches of Kv1.2 channel-rich membrane as a rapid and sensitive bioassay, we found that phospholipase D stimulated the release of an endogenous anandamide-like K+ channel blocker from rat brain slices. Structure-activity studies were consistent with the possibility that the released blocker was either anandamide or another N-acyl-ethanolamide.

Nutritional deprivation of alpha-linolenic acid decreases but does not abolish turnover and availability of unacylated docosahexaenoic acid and docosahexaenoyl-CoA in rat brain

We applied our in vivo fatty acid method to examine concentrations, incorporation, and turnover rates of docosahexaenoic acid (22:6 n-3) in brains of rats subject to a dietary deficiency of alpha-linolenic acid (18:3 n-3) for three generations. Adult deficient and adequate rats of the F3 generation were infused intravenously with [4, 5-(3)H]docosahexaenoic acid over 5 min, after which brain uptake and distribution of tracer were measured. Before infusion, the plasma 22:6 n-3 level was 0.2 nmol ml(-1) in 18:3 n-3-deficient compared with 10.6 nmol ml(-1) in control rats. Brain unesterified 22:6 n-3 was not detectable, whereas docosahexaenoyl-CoA content was reduced by 95%, and 22:6 n-3 content in different phospholipid classes was reduced by 83-88% in deficient rats. Neither plasma or brain arachidonic acid (20:4 n-6) level was significantly changed with diet. Docosapentaenoic acid (22:5 n-6) reciprocally replaced 22:6 n-3 in brain phospholipids. Calculations using operational equations from our model indicated that 22:6 n-3 incorporation from plasma into brain was reduced 40-fold by 18:3 n-3 deficiency. Recycling of 22:6 n-3 due to deacylation-reacylation within phospholipids was reduced by 30-70% with the deficient diet, but animals nevertheless continued to produce 22:6 n-3 and docosahexaenoyl-CoA for brain function. We propose that functional brain effects of n-3 deficiency reflect altered ratios of n-6 to n-3 fatty acids.

A new tobamovirus infecting tomato crops in Jordan

In this study, we completed the whole genome sequence of a new tobamovirus isolated from tomato plants grown in greenhouses in Jordan during the spring of 2015. The 6393-nt single-stranded RNA (ssRNA) genome encodes four proteins, as do other tobamoviruses: two replication-related proteins of 126 kDa and 183 kDa, a 30-kDa movement protein (MP) and a 17.5-kDa coat protein (CP). Phylogenetic analysis showed that this virus does not group with either the tomato mosaic virus (ToMV) or the tobacco mosaic virus (TMV) clades. Instead, it stems from a branch leading to the TMV clade. Analysis of possible recombination events between this virus and representative isolates of closely related tomato-infecting tobamoviruses showed that at least one region originated by recombination. We provide evidence that we have identified a new tobamovirus, for which we propose the name "tomato brown rugose fruit virus".

In vivo conversion of linoleic acid to arachidonic acid in human adults

Human adults are shown to be capable of conversion of linoleic acid (LA, 18:2 n-6) to arachidonic acid (AA, 20:4 n-6) in vivo. It is confirmed that they can also convert alpha-linolenic acid (LNA, 18:3 n-3) to eicosapentaenoic acid (EPA, 20:5 n-3) and to docosahexaenoic acid (DHA, 22:6 n-3) in vivo. The time course and the maximal response for these processes during the first week after a single dose of the 18-carbon precursor is described. A stable-isotope method in which the protons of the C17 and C18 carbons are substituted with deuterium atoms is used in order to provide for a safe method for the study of human metabolism. High sensitivity and selectivity of detection is assured with negative ion, gas chromatography/mass spectrometry analysis. It is clear that human adults on an ad lib diet carry out EFA metabolism in vivo.

X-linked transposition of the great arteries and incomplete penetrance among males with a nonsense mutation in ZIC3

We report on a Lebanese family in which two maternal cousins suffered and died very early in life from cardiac malformations. Both presented with a transposition of the great arteries associated with one or several other cardiac defects. Various minor midline defects were also observed, but there were no situs abnormalities other than a persistent left superior vena cava in one. A maternal uncle of these two babies was born cyanotic and died on the third post-natal day. Analysis of the ZIC3 gene, revealed the presence of a mutation in the second exon leading to a truncation of the protein. Surprisingly, another maternal uncle of the two affected cousins also had the mutation but was not clinically affected. To our knowledge, this is the first instance of incomplete penetrance in a male for a mutation in a chromosome X gene.

A replication study of violent and nonviolent subjects: cerebrospinal fluid metabolites of serotonin and dopamine are predicted by plasma essential fatty acids

BACKGROUND

Among an independent group of subjects selected for their history of violent, impulsive behaviors and nonviolent control subjects, we attempted to replicate the finding that plasma docosahexaenoic acid concentrations were negatively correlated with cerebrospinal fluid 5-hydroxyindoleacetic acid (CSF 5-HIAA) concentrations.

METHODS

CSF 5-HIAA and homovanillic acid (HVA), fasting total cholesterol, and plasma fatty acid concentrations were examined in violent and nonviolent subjects matched for their severity of alcohol dependence.

RESULTS

Violent subjects had significantly higher lifetime violence and hostility ratings and lower concentrations of CSF 5-HIAA than nonviolent subjects. Plasma docosahexaenoic acid was negatively correlated with CSF 5-HIAA only among violent subjects.

CONCLUSIONS

This observational study suggests that dietary essential fatty acids may change neurotransmitter concentrations. Prospective dietary intervention trials will be required to determine if increasing dietary intake of docosahexaenoic acid will increase or decrease either CSF 5-HIAA concentrations or impulsive and violent behaviors.

n-3 fatty acid deficiency decreases phosphatidylserine accumulation selectively in neuronal tissues

We have previously shown that the docosahexaenoate (22:6n-3) status in membrane phospholipids influences the biosynthesis and accumulation of phosphatidylserine (PS) in brain microsomes and C6 glioma cells. In the present study, we investigated whether the observed effect of membrane docosahexaenoic acid status on PS accumulation is universal or occurs specifically in neuronal tissues. We observed that rat brain cortex, brain mitochondria, and olfactory bulb, where 22:6n-3 is highly concentrated, contain significantly higher levels of PS in comparison to liver and adrenal, where 22:6n-3 is a rather minor component. Phospholipid molecular species analysis revealed that in brain cortex, mitochondria, and olfactory bulb 18:0,22:6n-3 was the most abundant species representing 45-65% of total PS. In nonneuronal tissues such as liver and adrenal, 18:0,20:4n-6 was the major PS species. Dietary depletion of n-3 fatty acids during prenatal and postnatal developmental periods decreased the brain 22:6n-3 content by more than 80%, with a concomitant increase in 22:5n-6 in all tissues. Under these conditions, an approximately 30-35% reduction in total PS in rat brain cortex, brain mitochondria, and olfactory bulb was observed, while PS levels in liver and adrenal were unchanged. The observed reduction of PS content in neuronal membranes appears to be due to a dramatic reduction of 18:0,22:6n-3-PS without complete replacement by 18:0,22:5n-6-PS. These results establish that variations in membrane 22:6n-3 fatty acid composition have a profound influence on PS accumulation in neuronal tissues where 22:6n-3 is abundant. These data have implications in neuronal signaling events where PS is believed to play an important role.