Prominent Role ofn—3 Polyunsaturated Fatty Acids in Cortical Dopamine Metabolism

Interesterified fat consumption since gestation decreases striatal dopaminergic targets levels and gdnf impairing locomotion of adult offspring

Interesterified fat (IF) currently substitutes the hydrogenated vegetable fat (HVF) in processed foods. However, the IF consumption impact on the central nervous system (CNS) has been poorly studied. The current study investigated connections between IF chronic consumption and locomotor impairments in early life period and adulthood of rats and access brain molecular targets related to behavior changes in adulthood offspring. During pregnancy and lactation, female rats received soybean oil (SO) or IF and their male pups received the same maternal supplementation from weaning until adulthood. Pups' motor ability and locomotor activity in adulthood were evaluated. In the adult offspring striatum, dopaminergic targets, glial cell line-derived neurotrophic factor (GDFN) and lipid profile were quantified. Pups from IF supplementation group presented impaired learning concerning complex motor skill and sensorimotor behavior. The same animals showed decreased locomotion in adulthood. Moreover, IF group showed decreased immunoreactivity of all dopaminergic targets evaluated and GDNF, along with important changes in FA composition in striatum. This study shows that the brain modifications induce by IF consumption resulted in impaired motor control in pups and decreased locomotion in adult animals. Other studies about health damages induced by IF consumption may have a contribution from our current outcomes.

Omega-3 decreases D1 and D2 receptors expression in the prefrontal cortex and prevents amphetamine-induced conditioned place preference in rats

Amphetamine (AMPH) abuse is a serious public health problem due to the high addictive potential of this drug, whose use is related to severe brain neurotoxicity and memory impairments. So far, therapies for psychostimulant addiction have had limited efficacy. Omega-3 polyunsaturated fatty acids (n-3 PUFA) have shown beneficial influences on the prevention and treatment of several diseases that affect the central nervous system. Here, we assessed the influence of fish oil (FO), which is rich in n-3 PUFA, on withdrawal and relapse symptoms following re-exposure to AMPH. Male Wistar rats received d,l-AMPH or vehicle in the conditioned place preference (CPP) paradigm for 14 days. Then, half of each experimental group was treated with FO (3 g/kg, p.o.) for 14 days. Subsequently, animals were re-exposed to AMPH-CPP for three additional days, in order to assess relapse behavior. Our findings have evidenced that FO prevented relapse induced by AMPH reconditioning. While FO prevented AMPH-induced oxidative damages in the prefrontal cortex, molecular assays allowed us to observe that it was also able to modulate dopaminergic cascade markers (DAT, TH, VMAT-2, D1R and D2R) in the same brain area, thus preventing AMPH-induced molecular changes. To the most of our knowledge, this is the first study to show a natural alternative tool which is able to prevent psychostimulant relapse following drug withdrawal. This non-invasive and healthy nutraceutical may be considered as an adjuvant treatment in detoxification clinics.

Relationship between Erythrocyte Fatty Acid Composition and Psychopathology in the Vienna Omega-3 Study

This study investigated the relationship between erythrocyte membrane fatty acid (FA) levels and the severity of symptoms of individuals at ultra-high risk (UHR) for psychosis. Subjects of the present study consisted of 80 neuroleptic-naïve UHR patients. Partial correlation coefficients were calculated between baseline erythrocyte membrane FA levels, measured by gas chromatography, and scores on the Positive and Negative Syndrome Scale (PANSS), Global Assessment of Functioning Scale, and Montgomery–Asberg Depression Rating Scale (MADRS) after controlling for age, sex, smoking and cannabis use. Subjects were divided into three groups according to the predominance of positive or negative symptoms based on PANSS subscale scores; membrane FA levels in the three groups were then compared. More severe negative symptoms measured by PANSS were negatively correlated with two saturated FAs (myristic and margaric acids), one ω-9 monounsaturated FA (MUFA; nervonic acid), and one ω-3 polyunsaturated FA (PUFA; docosapentaenoic acid), and were positively correlated with two ω-9 MUFAs (eicosenoic and erucic acids) and two ω-6 PUFAs (γ-linolenic and docosadienoic acids). More severe positive symptoms measured by PANSS were correlated only with nervonic acid. No associations were observed between FAs and MADRS scores. In subjects with predominant negative symptoms, the sum of the ω-9 MUFAs and the ω-6:ω-3 FA ratio were both significantly higher than in those with predominant positive symptoms, whereas the sum of ω-3 PUFAs was significantly lower. In conclusion, abnormalities in FA metabolism may contribute to the neurobiology of psychopathology in UHR individuals. In particular, membrane FA alterations may play a role in negative symptoms, which are primary psychopathological manifestations of schizophrenia-related disability.

Therapeutic use of omega-3 fatty acids in bipolar disorder

Bipolar disorder (BD) is a severe, chronic affective disorder, associated with significant disability, morbidity and premature mortality. Omega-3 polyunsaturated fatty acids (PUFAs) play several important roles in brain development and functioning. Evidence from animal models of dietary omega-3 (n-3) PUFA deficiency suggest that these fatty acids are relevant to promote brain development and to regulate behavioral and neurochemical aspects related to mood disorders, such as stress responses, depression and aggression, as well as dopaminergic content and function. Preclinical and clinical evidence suggests roles for PUFAs in BD. n-3 PUFAs seem to be an effective adjunctive treatment for unipolar and bipolar depression, but further large-scale, well-controlled trials are needed to examine its clinical utility in BD. The use of n-3 as a mood stabilizer among BD patients is discussed here. This article summarizes the molecular pathways related to the role of n-3 as a neuroprotective and neurogenic agent, with a specific focus on BDNF. It is proposed that the n-3-BDNF association is involved in the pathophysiology of BD and represents a promising target for developing a novel class of rationally devised therapies.

Omega-3 fatty acids and monoamine neurotransmission

We proposed several years ago that the behavioral effects of n-3 PUFA deficiency observed in animal models might be mediated through the dopaminergic and serotonergic systems that are very involved in the modulation of attention, motivation and emotion. We evaluated this hypothesis in an extended series of experiments on rats chronically diet-deficient in alpha-linolenic acid, the precursor of long-chain n-3 PUFA, in which we studied several parameters of these neurotransmission systems. The present paper synthesizes the main data we obtained on interactions between n-3 PUFA status and neurotransmission in animal models. We demonstrated that several parameters of neurotransmission were affected, such as the vesicular pool of dopamine and serotonin, thus inducing several regulatory processes such as modification of cerebral receptors in specific brain areas. We also demonstrated that (i) a reversal diet with adequate n-6 and n-3 PUFA given during the lactating period to rats originating from alpha-linolenic acid-deficient dams was able to restore both the fatty acid composition of brain membranes and several parameters of the dopaminergic and serotonergic neurotransmission, and (ii) when given from weaning, this reversal diet allowed partial recovery of biochemical parameters, but no recovery of neurochemical factors. The occurrence of profound n-3 PUFA deficiency during the lactating period could therefore be an environmental insult leading to irreversible damage to specific brain functions. Strong evidence is now showing that a profound n-3 PUFA experimental deficiency is able to alter several neurotransmission systems, at least the dopaminergic and serotonergic. Whether these experimental findings can be transposed to human pathophysiology must be taken cautiously, but reinforces the hypothesis that strong links exist between the PUFA status, aspects of brain function such as neurotransmission processes and behavior.

Perinatal biochemistry and physiology of long-chain polyunsaturated fatty acids

Docosahexaenoic acid (DHA) and arachidonic acid (ARA) are important structural components of the central nervous system. These fatty acids are transferred across the placenta, are present in human milk, and are accumulated in the brain and retina during fetal and infant development. The high concentrations of DHA in the retina and of DHA and ARA in brain gray matter suggests that these fatty acids have important roles in retinal and neural function. Animal studies have shown that depletion of DHA from the retina and brain results in reduced visual function and learning deficits. The latter effects may be explained by changes in the membrane bilayer that alter membrane-associated receptors and signal transduction systems, ion channel activity, or direct effects on gene expression. DHA can be formed in the liver from alpha linolenic acid, but it is unclear if the rate of DHA synthesis in humans is sufficient to support optimal brain and retinal development. Although there is no evidence that the ability to form ARA from linoleic acid is limiting, supplementation with DHA reduces tissue ARA, possibly creating a conditional need for ARA in infants with a dietary intake of DHA. The amount of DHA in human milk varies widely and is positively correlated with visual and language development in breast-fed infants. Advances in understanding essential fatty acid requirements will benefit from intervention studies that use functionally relevant tests to probe the deficiency or adequacy of physiologically important pools of DHA and ARA in developing infants.

Behavioral Responses Are Altered in Piglets with Decreased Frontal Cortex Docosahexaenoic Acid

Docosahexaenoic acid [22:6(n-3)] is required in large amounts for membrane lipid synthesis during brain growth. The functional importance of differences in dietary fatty acid intakes that alter brain 22:6(n-3), however, is not well understood. We used a dietary approach to manipulate 22:6(n-3) in piglet brain and assessed the effects on behavior and change in behavior on an elevated plus maze after administration of L-dihydroxyphenylalanine (L-Dopa) or sulperide, a dopamine D2 receptor blocker. Piglets were fed 1.2% energy 18:2(n-6) and 0.05% energy 18:3(n-3) (low PUFA), or 10.7% energy 18:2(n-6), 1.1% energy 18:3(n-3), 0.3% energy 20:4(n-6) and 0.3% energy 22:6(n-3) (high PUFA) from 1 d of age and behavior assessed at 18-22 d of age. At 30 d of age, frontal cortex dopamine, and phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidyethanolamine (PE) and phosphatidylinositol (PI) fatty acids were quantified. Piglets fed the low PUFA diet had fewer arm entries on the maze than piglets fed the high PUFA diet, P = 0.02. L-Dopa increased the open (P = 0.005) and closed (P = 0.04) arm entries by piglets fed the low PUFA diet. Behavior did not differ between piglets fed the low and high PUFA diets when given L-Dopa. Frontal cortex PC, PS and PE 22:6(n-3) was lower and 22:5(n-6) was higher in piglets fed the low compared with the high PUFA diet, P < 0.01. Our work establishes the neonatal piglet as a model with which to study the behavioral effects of diet-induced changes in brain 22:6(n-3), and provides functional evidence that brain 22:6(n-3) is important in central dopamine metabolism.

The dopamine mesocorticolimbic pathway is affected by deficiency in n-3 polyunsaturated fatty acids

BACKGROUND

Several findings in humans support the hypothesis of links between n-3 polyunsaturated fatty acid (PUFA) status and psychiatric diseases.

OBJECTIVE

The involvement of PUFAs in central nervous system function can be assessed with the use of dietary manipulation in animal models. We studied the effects of chronic dietary n-3 PUFA deficiency on mesocorticolimbic dopamine neurotransmission in rats.

DESIGN

Using dual-probe microdialysis, we analyzed dopamine release under amphetamine stimulation simultaneously in the frontal cortex and the nucleus accumbens. The messenger RNA (mRNA) expression of vesicular monoamine transporter(2) and dopamine D(2) receptor was studied with the use of in situ hybridization. The protein expression of the synthesis-limiting enzyme tyrosine 3-monooxygenase (tyrosine 3-hydroxylase) was studied with the use of immunocytochemistry.

RESULTS

Dopamine release was significantly lower in both cerebral areas in n-3 PUFA-deficient rats than in control rats, but this effect was abolished in the frontal cortex and reversed in the nucleus accumbens by reserpine pretreatment, which depletes the dopamine vesicular storage pool. The mRNA expression of vesicular monoamine transporter(2) was lower in both cerebral areas in n-3 PUFA-deficient rats than in control rats, whereas the mRNA expression of D(2) receptor was lower in the frontal cortex and higher in the nucleus accumbens in n-3 PUFA-deficient rats than in control rats. Finally, tyrosine 3-monooxygenase immunoreactivity was higher in the ventral tegmental area in n-3 PUFA-deficient rats than in control rats.

CONCLUSIONS

Our results suggest that the mesolimbic dopamine pathway is more active whereas the mesocortical pathway is less active in n-3 PUFA-deficient rats than in control rats. This provides new neurochemical evidence supporting the effects of n-3 PUFA deficiency on behavior.

Neither the density nor function of striatal dopamine transporters were influenced by chronic n-3 polyunsaturated fatty acid deficiency in rodents

We hypothesized that the chronic dietary deficiency of n-3 polyunsaturated fatty acids (n-3 PUFAs) might affect the density and/or function of dopamine transporters (DAT), which have a major role in regulating the synaptic level of dopamine. This hypothesis was tested by investigating DAT in the striatum using three complementary methods in control and deficient rats. The density of DAT was determined by quantitative autoradiography using [(125)I]PE2I, a specific ligand of this transporter. Functional investigations were performed (i) in vitro by measuring [(3)H]dopamine uptake on synaptosomes, and (ii) in vivo using intracerebral microdialysis. The results demonstrated that neither the density nor the function of DAT were influenced by n-3 PUFA deficiency in the striatum. This suggests lower sensitivity to n-3 PUFA deficiency in the striatum than that previously observed in the frontal cortex.

Polyunsaturated fatty acids and cerebral function: focus on monoaminergic neurotransmission

More and more reports in recent years have shown that the intake of polyunsaturated fatty acids (PUFA) constitutes an environmental factor able to act on the central nervous system (CNS) function. We recently demonstrated that the effects of PUFA on behavior can be mediated through effects on the monoaminergic neurotransmission processes. Supporting this proposal, we showed that chronic dietary deficiency in alpha-linolenic acid in rats induces abnormalities in several parameters of the mesocortical and mesolimbic dopaminergic systems. In both systems, the pool of dopamine stored in presynaptic vesicles is strongly decreased. This may be due to a decrease in the number of vesicles. In addition, several other factors of dopaminergic neurotransmission are modified according to the system affected. The mesocortical system seems to be hypofunctional overall [e.g., decreased basal release of dopamine (DA) and reduced levels of dopamine D2 (DAD2) receptors]. In contrast, the mesolimbic system seems to be hyperfunctional overall (e.g., increased basal release of DA and increased levels of DAD2 receptors). These neurochemical changes are in agreement with modifications of behavior already described with this deficiency. The precise mechanisms explaining the effects of PUFA on neurotransmission remain to be clarified. For example, modifications of physical properties of the neuronal membrane, effects on proteins (receptors, transporters) enclosed in the membrane, and effects on gene expression and/or transcription might occur. Whatever the mechanism, it is therefore assumed that interactions exist among PUFA, neurotransmission, and behavior. This might be related to clinical findings. Indeed, deficits in the peripheral amounts of PUFA have been described in subjects suffering from neurological and psychiatric disorders. Involvement of the monoaminergic neurotransmission function has been demonstrated or hypothesized in several of these diseases. It can therefore be proposed that functional links exist among PUFA status, neurotransmission processes, and behavioral disorders in humans. Animal models are tools of choice for the understanding of such links. Improved prevention and complementary treatment of neurological and psychiatric diseases can be expected from these studies.

Chronic n-3 polyunsaturated fatty acid deficiency alters dopamine vesicle density in the rat frontal cortex

We studied the effects of a chronic deficiency in n-3 polyunsaturated fatty acids (n-3 PUFA) on the vesicle dopaminergic compartment in the frontal cortex of rats. Electronic micrographic analysis showed that the synaptic density and the clear vesicle density were similar in deficient and control rats. However, dopaminergic immunolabeling revealed a significantly decreased number of gold-labeled vesicles in the dopaminergic presynaptic terminals of the deficient rats. These findings demonstrate that dopamine cortical vesicles are specifically decreased in n-3 PUFA deficiency. The mechanism leading to this modification could involve several abnormalities (vesicle turn-over, membrane fluidity, vesicular monoamine transporter). This reduction in the dopaminergic vesicle pool constitutes the first structural support for the previously described modifications of dopamine metabolism in the frontal cortex. Such changes in dopamine neurotransmission could be involved in behavioral abnormalities occurring in n-3 PUFA deficient rats.