It is now well established that lipids (fats) play a significant role in neuronal function within the brain. Moreover, that the lipid composition of the brain substantially influences subjective perception, mood and emotional behaviour. Interestingly, the lipid composition of the brain can be altered with long term changes in the diet, thus having a direct effect on mood and emotional behaviour. For example, a highly palatable diet, rich in 'healthy' fats has been shown to reduce anxiety-like behaviours, which suggests that by enhancing the general availability of lipids in the brain anxiolytic/anti-depressant effects may be further enriched.
Brain membranes contain a high proportion of polyunsaturated fatty acids (PUFA's), with n-3 fatty acids being the most prevalent in the brain's gray matter. n-3 PUFA's cannot be synthesised de novo by mammals but must be obtained from the diet. The incorporation of fatty acids into the brain occurs most efficiently during the suckling period, and requires more time during adulthood. When the brain levels of docosahexaenoic acid (DHA) in phospholipids are reduced by diet, a compensatory increase in docosapentanoic acid (DPA) levels is usually observed, dysregulating mood. Furthermore, the effects of n-3 fatty acid deprivation on brain content and behaviour can accumulate over the duration of a diet and over several generations, thus ongoing depletion's may impact on offspring. Interestingly, a DHA depleted diet affects the brain's DHA content in a region-selective manner with the pituitary gland, cortex, hippocampus, cerebellum and striatum being the most severely affected regions of the brain. The cortex, hippocampus, striatum and, most recently, the cerebellum are regions of the brain serving a multitude of different functions in behavioural organisation and performance, with dysfunction of the foregoing regions associated with depression and anxiety disorders.
Dopamine, Serotonin and DHA:
A reduction in brain DHA levels has been shown to affect different neurotransmitter systems altering the regulation of dopaminergic and serotonergic neuro-transmission, mechanisms known to be altered in depressed patients. This being so, changes in serotonin (5-HT) and dopamine (DA) receptor number or function, caused by changes in PUFA's, provide the theoretical rationale connecting fatty acids with the current neurotransmitter theories of depression. Overall, the majority of findings suggest that dopaminergic adaptations in the DA and 5-HT systems, compromising normal transmission, can play a major role in DHA deficiency, which can induce emotional dysregulation, resulting in depression.
Depression, Anxiety and Environmental Factors:
Depression and anxiety can be induced by environmental factors such as traumatic events or chronic stress. These factors have been shown to disrupt the regulation of lipid synthesis, and contribute to DHA deficit. Early studies have already suggested that an association exists between blood measures of fatty acid status and the severity of depression, as well as a depletion of n-3 fatty acid levels, particularly DHA, in red blood cell membranes. Moreover, lowered n-3 PUFA's have been observed in the serum of patients diagnosed with depression and anxiety.
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