Changes in auditory brainstem responses in alpha-linolenic acid deficiency as a function of age in rats

Omega-3 fatty acids and health of auditory and vestibular systems: a comprehensive review

PURPOSE

The purpose of this study was to comprehensively review animal and human studies that explore the role of omega-3 PUFAs in maintaining the health of the auditory organ across all life stages.

METHODS

This narrative review involved searching Scopus, PubMed, Google Scholar, and Cochrane Library databases for relevant articles from December 1980 to July 2023.

RESULTS

some animal and human studies suggest that both deficiency and excessive intake of long-chain omega-3 PUFAs, particularly docosahexaenoic acid (DHA), can lead to auditory neural conduction impairment and reduced hearing acuity from fetal development to old age (presbycusis). These effects are likely to be dependent on the dosage. Some research indicates that an excessive intake of omega-3, rather than a deficiency, can result in nutritional toxicity and hearing impairments. Animal studies highlight the positive impact of omega-3 supplements with high DHA content in addressing hearing damage, but human research on this subject is limited. Furthermore, certain studies propose that omega-3 PUFAs may prevent or delay age-related hearing loss, with high plasma omega-3 concentration, particularly long-chain omega-3 PUFA, linked to reduced hearing loss. Additionally, consuming fish more than twice a week may be associated with a lower risk of hearing loss in adulthood, with these effects potentially influenced by age and gender. However, the majority of studies have been conducted on animals, and clinical trials are scarce. Research on the influence of omega-3 PUFAs on the peripheral and central vestibular systems remains limited.

CONCLUSION

This article delves into the impact of omega-3 on the auditory-vestibular system, exploring its influence on neurodevelopment, protection, and treatment. It not only highlights specific research gaps but also offers valuable insights for potential future studies.

Roles of the Unsaturated Fatty Acid Docosahexaenoic Acid in the Central Nervous System: Molecular and Cellular Insights

Fatty acids (FAs) are essential components of the central nervous system (CNS), where they exert multiple roles in health and disease. Among the FAs, docosahexaenoic acid (DHA) has been widely recognized as a key molecule for neuronal function and cell signaling. Despite its relevance, the molecular pathways underlying the beneficial effects of DHA on the cells of the CNS are still unclear. Here, we summarize and discuss the molecular mechanisms underlying the actions of DHA in neural cells with a special focus on processes of survival, morphological development, and synaptic maturation. In addition, we examine the evidence supporting a potential therapeutic role of DHA against CNS tumor diseases and tumorigenesis. The current results suggest that DHA exerts its actions on neural cells mainly through the modulation of signaling cascades involving the activation of diverse types of receptors. In addition, we found evidence connecting brain DHA and ω-3 PUFA levels with CNS diseases, such as depression, autism spectrum disorders, obesity, and neurodegenerative diseases. In the context of cancer, the existing data have shown that DHA exerts positive actions as a coadjuvant in antitumoral therapy. Although many questions in the field remain only partially resolved, we hope that future research may soon define specific pathways and receptor systems involved in the beneficial effects of DHA in cells of the CNS, opening new avenues for innovative therapeutic strategies for CNS diseases.

Long‑term treatment with salicylate enables NMDA receptors and impairs AMPA receptors in C57BL/6J mice inner hair cell ribbon synapse

Salicylate is widely used to produce animal models of tinnitus in mice and/or rats. The side effects on auditory function, including hearing loss and tinnitus, are considered the results of the auditory nerve dysfunction. A recent study indicated that chronic treatment with salicylate for several weeks reduces compressed action potential amplitude, which is contradictory to the studies reporting excessive activation of N-methyl-D-aspartate receptors (NMDAR) in tinnitus-induced animals. The specific aims of the experiment were to detect the effect of salicylate on the inner hair cells (IHCs), ribbon synapse, as well as the association between the hearing threshold and the number of mismatched ribbon synapses. In the present study, mice were injected intraperitoneally with a low dose of salicylate (200 mg/kg) for 14 days. The auditory brainstem response and otoacoustic emission were measured to assess auditory function of the mice. The postsynaptic regions of IHC were identified with two types of immunostaining targets: Postsynaptic density protein 95 and Glu2/3. The number of spheres was counted and the synapses were reconstructed in 3-dimensional images. Increases in distortion product otoacoustic emissions amplitudes of the salicylate group were detected, however, an elevation in the hearing threshold was also observed. A mismatch between pre-and post-ribbon synapses was observed. In addition, the cochlear components, including the numbers of outer hair cells and IHCs, were unlikely to be affected by salicylate. IHC ribbon synapses were more susceptible to salicylate stimuli. Furthermore, mismatch of pre- and post-ribbon synapses may indicate a competitive inhibition between NMDAR and α-amino-3-hydroxy-5-methyl-4-isoxa-zole-propionate receptors and dysfunction of ribbon synapses.

Gray and White Matter Brain Volume in Aged Rats Raised onn-3 Fatty Acid Deficient Diets

Omega-3 or n-3 fatty acids, especially docosahexaenoic acid, are important structural lipids in the brain. Their deficiency leads to a number of sensory, cognitive and behavioral effects. In previous studies, we showed that n-3 deficiency led to a decrease in the neuronal size of a number of brain regions in young rats. In particular, the neuronal size in the hippocampus CA1-CA3 layers decreased with a slight increase in the volumes of these layers. Therefore, we asked whether fatty acid deficiency could affect rat brain morphology in older animals. To address this question, we carried out gross morphological analysis using Magnetic Resonance Imaging on the gray and white matter volumes of brains in older rats (> 15 months) that were raised on n-3 deficient diets for three generations. We did not detect any differences in the total or regional gray and white matter volumes of brains of old rats maintained on a n-3 deficient or supplemented diet.

Neurophysiologic measures of auditory function in fish consumers: associations with long chain polyunsaturated fatty acids and methylmercury

BACKGROUND

Determining if associations exist between child neurodevelopment and environmental exposures, especially low level or background ones, is challenging and dependent upon being able to measure specific and sensitive endpoints. Psychometric or behavioral measures of CNS function have traditionally been used in such studies, but do have some limitations. Auditory neurophysiologic measures examine different nervous system structures and mechanisms, have fewer limitations, can more easily be quantified, and might be helpful additions to testing. To date, their use in human epidemiological studies has been limited. We reviewed the use of auditory brainstem responses (ABR) and otoacoustic emissions (OAE) in studies designed to determine the relationship of exposures to methyl mercury (MeHg) and nutrients from fish consumption with neurological development. We included studies of experimental animals and humans in an effort to better understand the possible benefits and risks of fish consumption.

OBJECTIVES

We reviewed the literature on the use of ABR and OAE to measure associations with environmental exposures that result from consuming a diet high in fish. We focused specifically on long chain polyunsaturated fatty acids (LCPUFA) and MeHg.

METHODS

We performed a comprehensive review of relevant studies using web-based search tools and appropriate search terms.

RESULTS

Gestational exposure to both LCPUFA and MeHg has been reported to influence the developing auditory system. In experimental studies supplemental LCPUFA is reported to prolong ABR latencies and human studies also suggest an association. Experimental studies of acute and gestational MeHg exposure are reported to prolong ABR latencies and impair hair cell function. In humans, MeHg exposure is reported to prolong ABR latencies, but the impact on hair cell function is unknown.

CONCLUSION

The auditory system can provide objective measures and may be useful in studying exposures to nutrients and toxicants and whether they are associated with children's neurodevelopment.

Animal studies of the functional consequences of suboptimal polyunsaturated fatty acid status during pregnancy, lactation and early post-natal life

Scores of animal studies demonstrate that seed oils replete with linoleic acid and very low in linolenic acid fed as the exclusive source of fat through pregnancy and lactation result in visual, cognitive, and behavioural deficits in the offspring. Commodity peanut, sunflower, and safflower oils fed to mother rats, guinea pigs, rhesus monkeys, and baboons induce predictable changes in tissue polyunsaturated fatty acid composition that are abnormal in free-living land mammals as well as changes in neurotransmitter levels, catecholamines, and signalling compounds compared with animals with a supply of ω3 polyunsaturated fatty acid. These diets consistently induce functional deficits in electroretinograms, reflex responses, reward or avoidance induced learning, maze learning, behaviour, and motor development compared with ω3 replete groups. Boosting neural tissue docosahexaenoic acid (DHA) by feeding preformed DHA enhances visual and cognitive function. Though no human randomized controlled trials on minimal ω3 requirements in pregnancy and lactation have been conducted, the weight of animal evidence compellingly shows that randomizing pregnant or lactating humans to diets that include high linoleate oils as the sole source of fat would be frankly unethical because they would result in suboptimal child development. Increasing use of commodity ω3-deficient oils in developing countries, many in the name of heart health, will limit brain development of the next generation and can be easily corrected at minimal expense by substituting high oleic acid versions of these same oils, in many cases blended with small amounts of α-linolenic acid oils like flax or perilla oil. Inclusion of DHA in these diets is likely to further enhance visual and neural development.

Excess omega-3 fatty acid consumption by mothers during pregnancy and lactation caused shorter life span and abnormal ABRs in old adult offspring

Consuming omega-3 fatty acids (omega-3 FA) during pregnancy and lactation is beneficial to fetal and infant development and might reduce the incidence and severity of preterm births by prolonging pregnancy. Consequently, supplementing maternal diets with large amounts of omega-3 FA is gaining acceptance. However, both over- and under-supplementation with omega-3 FA can harm offspring development. Adverse fetal and neonatal conditions in general can enhance age-related neural degeneration, shorten life span and cause other adult-onset disorders. We hypothesized that maternal over- and under-nutrition with omega-3 FA would shorten the offspring's life span and enhance neural degeneration in old adulthood. To test these hypotheses, female Wistar rats were randomly assigned to one of the three diet conditions starting from day 1 of pregnancy through the entire period of pregnancy and lactation. The three diets were Control omega-3 FA (omega-3/omega-6 ratio approximately 0.14), Excess omega-3 FA (omega-3/omega-6 ratio approximately 14.5) and Deficient omega-3 FA (omega-3/omega-6 ratio approximately 0% ratio). When possible, one male and female offspring from each litter were assessed for life span and sensory/neural degeneration (n=15 litters/group). The Excess offspring had shorter life spans compared to their Control and Deficient cohorts (mean+/-SEM=506+/-24, 601+/-14 and 585+/-21 days, p<or=0.004) when the study terminated on postnatal day 640. The Excess offspring had a higher incidence of presbycusis than the Control and Deficient groups (33.3, 4.3 and 4.5%, p=0.011) and a persistence of other sensory/neurological abnormalities and lower body weights in old adulthood. In conclusion, omega-3 FA over-nutrition or imbalance during pregnancy and lactation had adverse effects on life span and sensory/neurological function in old adulthood. The adverse outcomes in the Excess offspring were likely due to a "nutritional toxicity" during fetal and/or neonatal development that programmed them for life-long health disorders. The health implication is that consuming or administering large amounts of omega-3 FA during pregnancy and lactation seems inadvisable because of adverse effects on the offspring.

Abnormal neurological responses in young adult offspring caused by excess omega-3 fatty acid (fish oil) consumption by the mother during pregnancy and lactation

Consuming omega-3 fatty acids (omega-3 FA) during pregnancy and lactation benefits fetal and infant brain development and might reduce the severity of preterm births by prolonging pregnancy. However, diets that are relatively rich in omega-3 FA can adversely affect fetal and infant development and the auditory brainstem response (ABR), a measure of brain development and sensory function. We previously examined the offspring of female rats fed excessive, adequate or deficient amounts of omega-3 FA during pregnancy and lactation. The 24-day-old offspring in the Excess group, compared to the Control group, had postnatal growth retardation and poor hearing acuity and prolonged neural transmission times as evidenced by the ABR. The Deficient group was intermediate. The current study followed these offspring to see if these poor outcomes persisted into young adulthood. Based on prior findings, we hypothesized that the Excess and Deficient offspring would "catch-up" to the Control offspring by young adulthood. Female Wistar rats received one of the three diet conditions from day 1 of pregnancy through lactation. The three diets were the Control omega-3 FA condition (omega-3/omega-6 ratio approximately 0.14), the Excess omega-3 FA condition (omega-3/omega-6 ratio approximately 14.0) and Deficient omega-3 FA condition (omega-3/omega-6 ratio approximately 0% ratio). The Control diet contained 7% soybean oil; whereas the Deficient and Excess omega-3 FA diets contained 7% safflower oil and 7% fish oil, respectively. One male and female offspring per litter were ABR-tested as young adults using tone pip stimuli of 2, 4, 8 and 16 kHz. The postnatal growth retardation and prolonged neural transmission times in the Excess and Deficient pups had dissipated by young adulthood. In contrast, the Excess group had elevated ABR thresholds (hearing loss) at all tone pip frequencies in comparison to the Control and Deficient groups. The Deficient group had worse ABR thresholds than the Control group in response to the 8 kHz tone pips only. The Excess group also had ABR amplitude-intensity profiles suggestive of hyperacusis. These results are consistent with the Barker hypothesis concerning the fetal and neonatal origins of adult diseases. Thus, consuming diets that are excessively rich or deficient in omega-3 FA during pregnancy and lactation seems inadvisable because of risks for long-lasting adverse effects on brain development and sensory function.

The protective mechanism of antioxidants in cadmium-induced ototoxicity in vitro and in vivo

BACKGROUND

Several heavy metals have been shown to have toxic effects on the peripheral and central auditory system. Cadmium (Cd2+) is an environmental contaminant showing a variety of adverse effects. Given the current rate of release into the environment, the amount of Cd2+ present in the human body and the incidence of Cd2+-related diseases are expected to increase.

OBJECTIVE

The overall aim of this study was to gain further insights into the mechanism of Cd2+-induced ototoxicity.

METHODS

Cell viability, reactive oxygen species (ROS), mitochondrial membrane potential (MMP), cytochrome c (cyt c), phosphorylated extracellular signal-regulated protein kinase (p-ERK), caspases, morphologic change, and functional changes in HEI-OC1 cells, rat cochlear explants, and mouse cochlea after Cd2+ exposure were measured by flow cytometry, immunohistochemical staining, Western blot analysis, and auditory brainstem response (ABR) recording. Mechanisms underlying Cd2+ototoxicity were studied using inhibitors of different signaling pathways, caspases, and antioxidants.

RESULTS

Cd2+ exposure caused cell death, ROS generation, MMP loss, cyt c release, activation of caspases, ERK activation, apoptosis, and finally auditory threshold shift. Cd2+ toxicity interfered with inhibitors of cellular signaling pathways, such as ERK and c-jun N-terminal kinase, and with caspase inhibitors, especially inhibitors of caspase-9 and caspase-3. The antioxidants N-acetyl-l-cysteine and ebselen showed a significant protective effect on the Cd2+ toxicity.

CONCLUSIONS

Cd2+ is ototoxic with a complex underlying mechanism. However, ROS generation may be the cause of the toxicity, and application of antioxidants can prevent the toxic effect.

Excess and deficient omega-3 fatty acid during pregnancy and lactation cause impaired neural transmission in rat pups

Omega-3 fatty acids (omega-3 FA) consumption during pregnancy and lactation is beneficial to fetal and infant growth and may reduce the severity of preterm births. Thus, scientists and clinicians are recommending increasingly higher omega-3 FA doses for pregnant women and nursing babies for advancing the health of preterm, low birth weight, and normal babies. In contrast, some studies report that over-supplementation with omega-3 FA can have adverse effects on fetal and infant development by causing a form of nutritional toxicity. Our goal was to assess the effects of omega-3 FA excess and deficiency during pregnancy and lactation on the offspring's neural transmission as evidenced by their auditory brainstem responses (ABR). Female Wistar rats were given one of three diets from day 1 of pregnancy through lactation. The three diets were the Control omega-3 FA condition (omega-3/omega-6 ratio approximately 0.14), the Deficient omega-3 FA condition (omega-3/omega-6 ratio approximately 0%) and the Excess omega-3 FA condition (omega-3/omega-6 ratio approximately 14.0). The Control diet contained 7% soybean oil, whereas the Deficient diet contained 7% safflower oil and the Excess diet contained 7% fish oil. The offspring were ABR-tested on postnatal day 24. The rat pups in the Excess group had prolonged ABR latencies in comparison to the Control group, indicating slowed neural transmission times. The pups in the Excess group also showed postnatal growth restriction. The Deficient group showed adverse effects that were milder than those seen in the Excess group. Milk fatty acid profiles reflected the fatty acid profiles of the maternal diets. In conclusion, excess or deficient amounts of omega-3 FA during pregnancy and lactation adversely affected the offspring's neural transmission times and postnatal thriving. Consuming either large or inadequate amounts of omega-3 FA during pregnancy and lactation seems inadvisable because of the potential for adverse effects on infant development.

Dietary omega-3 fatty acids for women

This review details the specific needs of women for omega-3 fatty acids, including alpha linoleic acid (ALA) and the very long chain fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Omega-3 fatty acid (dietary or in capsules) ensures that a woman's adipose tissue contains a reserve of these fatty acids for the developing fetus and the breast-fed newborn infant. This ensures the optimal cerebral and cognitive development of the infant. The presence of large quantities of EPA and DHA in the diet slightly lengthens pregnancy, and improves its quality. Human milk contains both ALA and DHA, unlike that of other mammals. Conditions such as diabetes can alter the fatty acid profile of mother's milk, while certain diets, like those of vegetarians, vegans, or even macrobiotic diets, can have the same effect, if they do not include seafood. ALA, DHA and EPA, are important for preventing ischemic cardiovascular disease in women of all ages. Omega-3 fatty acids can help to prevent the development of certain cancers, particularly those of the breast and colon, and possibly of the uterus and the skin, and are likely to reduce the risk of postpartum depression, manic-depressive psychosis, dementias (Alzheimer's disease and others), hypertension, toxemia, diabetes and, to a certain extend, age-related macular degeneration. Omega-3 fatty acids could play a positive role in the prevention of menstrual syndrome and postmenopausal hot flushes. The normal western diet contains little ALA (less than 50% of the RDA). The only adequate sources are rapeseed oil (canola), walnuts and so-called "omega-3" eggs (similar to wild-type or Cretan eggs). The amounts of EPA and DHA in the diet vary greatly from person to person. The only good sources are fish and seafood, together with "omega-3" eggs.

Reduced auditory acuity in rat pups from excess and deficient omega-3 fatty acid consumption by the mother

Consumption of the nutrients omega-3 fatty acids (omega-3 FA) during pregnancy and lactation is considered beneficial to fetal and infant development. It may also reduce the incidence and severity of preterm births by prolonging gestational length. However several recent human and animal studies have reported that over-supplementation with omega-3 FA, especially in the form of fish oil, can have adverse effects on fetal and infant development and the auditory brainstem response (ABR). Our goal was to assess further the effects of omega-3 FA excess and deficiency during pregnancy and lactation on the offspring's auditory acuity as evidenced by their ABR thresholds. Female Wistar rats were given diets that were either deficient, adequate (control) or excess in omega-3 FA from day 1 of pregnancy through lactation. The offspring were ABR-tested at the postnatal age of 24 days. The rat pups in the Excess treatment condition had significantly elevated (worse) ABR thresholds, postnatal growth restriction, and a trend for increased postnatal mortality in comparison to the Control group. The Deficient group was intermediate. In conclusion, excess or deficient amounts of omega-3 FA during pregnancy and lactation in the laboratory rat adversely affected the offspring's auditory acuity. Postnatal thriving was also adversely affected. Consuming or administering large or inadequate amounts of omega-3 FA during pregnancy and lactation seems inadvisable because of the potential for adverse effects on infant development.

Overexpression of dopamine receptor genes and their products in the postnatal rat brain following maternal n-3 fatty acid dietary deficiency

A combination of PCR-Select cDNA subtraction and gene array hybridization was used to identify differentially expressed genomic markers in brains of rats fed for 3 weeks in utero and 2 weeks after birth on an n-3 polyunsaturated fatty acid (PUFA)-deficient diet supplied to dams. Total RNA was isolated, switch mechanism at 5'-end of the RNA transcripts (SMART) applied and used for PCR-Select subtraction of PUFA-deficient and adequately-fed control preparations. Subtracted and amplified ds-cDNA end-products were fragmented, terminally labeled with biotin-ddUTP and hybridized with a RN-U34A gene array. A 10-fold increase in potential genes with log2(Tester/Driver) = 1.4 was found compared with traditional gene array technology when the same chip was tested using non-subtracted targets. Reverse transcription-real-time relative PCR confirmed 30% of the transcripts. Among the validated transcripts, D1 and D2 receptors for dopamine (DA), were most prominent among a number of over-expressed neurotransmitter receptors and retinoic acid receptor (RXR alpha-2 and alpha-1). Immunohistochemical staining of brain sections from 2-week-old pups revealed a substantial enrichment of the D2 receptor in discrete regions of the mesolimbic and mesocortical pathways as well as in a large number of brain areas from the n-3 PUFA-deficient pups. Punches of the same areas run on western blots showed similar results. The overwhelming expression of D1 and D2 receptors may be attributed to a behavioral hypersensitivity caused by the possible impairment of DA production during brain development, which may have implications in certain disorders of the nervous system.

Hearing screening outcomes in infants of pregestational diabetic mothers

PURPOSE

Hearing screening results for newborns of diabetic mothers were compared with those of nondiabetic controls.

METHOD

This study was a retrospective chart review of mothers with pregestational diabetes mellitus and their neonates (n=73) who received newborn hearing screening between January 1, 2000, and May 1, 2002. A group of nondiabetic mothers and their infants (n=73), with birth dates that matched the diabetic group, served as controls. A 2-tiered hearing screening protocol, employing distortion product otoacoustic emission (DPOAE) and automated auditory brainstem response (A-ABR) screening techniques, was used.

RESULTS

The DPOAE screening failure rate was 5.5% (4/73) for babies in the nondiabetic control group and 11.0% (8/73) for infants of diabetic mothers; this difference was not statistically significant. The A-ABR failure rate was 9.1% (1/11) for the diabetic group compared with 0% (0/4) for the controls, but the A-ABR was measured for only a small number of participants in each group. The frequency of premature birth and abnormal birth weight was significantly greater for the infants of diabetic mothers compared with controls.

CONCLUSIONS

Given the greater frequency of prematurity and abnormal birth weight in the population of neonates born to diabetics, additional research using A-ABR is recommended.

[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.

Effects of dietary omega-3 polyunsaturated fatty acids on brain gene expression

Polyunsaturated fatty acids (PUFA) are essential structural components of the central nervous system. Their role in controlling learning and memory has been well documented. A nutrigenomic approach with high-density microarrays was used to reveal brain gene-expression changes in response to different PUFA-enriched diets in rats. In aged rats fed throughout life with PUFA-enriched diets, genes with altered expressions included transthyretin, alpha-synuclein, and calmodulins, which play important roles in synaptic plasticity and learning. The effect of perinatal omega-3 PUFA supply on gene expression later in life also was studied. Several genes showed similar changes in expression in rats fed omega-3-deficient diets in the perinatal period, regardless of whether they or their mothers were fed omega-3 PUFA-sufficient diets after giving birth. In this experiment, among the down-regulated genes were a kainate glutamate receptor and a DEAD-box polypeptide. Among the up-regulated genes were a chemokine-like factor, a tumor necrosis factor receptor, and cytochrome c. The possible involvement of the genes with altered expression attributable to different diets in different brain regions in young and aged rats and the possible mode of regulatory action of PUFA also are discussed. We conclude that PUFA-enriched diets lead to significant changes in expression of several genes in the central nervous tissue, and these effects appear to be mainly independent of their effects on membrane composition. The direct effects of PUFA on transcriptional modulators, the downstream developmentally and tissue-specifically activated elements might be one of the clues to understanding the beneficial effects of the omega-3 PUFA on the nervous system.

Electrophysiological findings in the Sprague-Dawley rat induced by moderate-dose carboplatin

Carboplatin is a second generation platinum-containing anti-tumor drug which selectively alters the micromechanical function of the inner hair cells (IHCs) of the organ of Corti in the chinchilla. Data from a recent study [Wake et al., Acta Otolaryngol. 116 (1996) 374-381], using the chinchilla model, have suggested that a moderate dose of carboplatin alters the efferent feedback loop gain of the OHCs. The present study was designed to evaluate the possible 'efferent feedback alteration mechanism' in the Sprague-Dawley rat using distortion product otoacoustic emissions (DPOAEs). A moderate dose of carboplatin (50 mg/kg body weight) was administered by a 30 min i.p. infusion. Pre- and 72-h post-treatment DPOAE and auditory brainstem response (ABR) recordings were acquired from a group of 12 rats. The animals were anesthetized with a ketamine-atropin anesthesia administered in two consecutive phases. The DPOAE responses (cubic distortion products) were recorded with four asymmetrical protocols: P1=60-50, P2=50-40, P3=40-30 and P4=30-20 dB SPL (sound pressure level), in the frequency range from 4.0 to 16 kHz. ABR responses were obtained for bipolar clicks and tone pips at the frequencies 8.0, 10.0, 20.0 and 30 kHz using stimuli in the range from 100 to 30 dB SPL. Significant ABR threshold shifts of 15 dB were observed at 30 kHz, and shifts of 10 dB at 20, 16 and 10 kHz. The comparison of pre- and post-treatment DPOAE responses did not reveal any significant changes for protocols P1, P2 and P4. Data from the P3 protocol indicated a decrease of the DPOAE amplitude. The findings from the rat model suggest that (a) moderate doses of carboplatin do not affect the efferent feedback loop OHC function and (b) the cochlear susceptibility to carboplatin across species is different, even at moderate-dose regimes.

The administration of pig brain phospholipids versus soybean phospholipids in the diet during the period of brain development in the rat results in greater increments of brain docosahexaenoic acid

Dietary porcine brain phospholipids are much more efficient than soybean phospholipids for ensuring a normal (optimal obtained with lab chow diet) level of docosahexaenoic acid (DHA) in tissues and brain subcellular fractions (brain myelin and nerve endings). Two weeks before mating, rats were divided into two groups (one group was subdivided into subgroups, fed with varying amounts of porcine brain phospholipids; the other group was divided into subgroups fed varying amounts of soybean phospholipids). Pups were killed when 21 days old. DHA (22:6(n-3)) increased up to normal levels in parallel with increasing amounts of (n-3) fatty acids (omega-3 fatty acids) in the diet, up to 60 mg with dietary porcine brain phospholipids and up to 200 mg with soybean phospholipids. Thus a smaller amount of dietary brain phospholipids resulted in the same level of DHA in tissues as a larger amount of dietary soybean phospholipids. In contrast, 22:5(n-6) declined when (n-3) fatty acids in the diet increased. It stabilized at 60 mg of (n-3) fatty acids/100 g diet with brain phospholipids, and approximately 200 mg/100 g diet with soybean phospholipids. As 22:5(n-6) replaced DHA in tissue when (n-3) fatty acids were not sufficient in the diet, this result shows that the recovery of a normal (and minimal) amount of 22:5(n-6) was obtained with lower dietary levels of brain phospholipids compared with soybean phospholipids.

What is the role of alpha-linolenic acid for mammals?

This review examines the data pertaining to an important and often underrated EFA, alpha-linolenic acid (ALA). It examines its sources, metabolism, and biological effects in various population studies, in vitro, animal, and human intervention studies. The main role of ALA was assumed to be as a precursor to the longer-chain n-3 PUFA, EPA and DHA, and particularly for supplying DHA for neural tissue. This paper reveals that the major metabolic route of ALA metabolism is beta-oxidation. Furthermore, ALA accumulates in specific sites in the body of mammals (carcass, adipose, and skin), and only a small proportion of the fed ALA is converted to DHA. There is some evidence that ALA may be involved with skin and fur function. There is continuing debate regarding whether ALA has actions of its own in relation to the cardiovascular system and neural function. Cardiovascular disease and cancer are two of the major burdens of disease in the 21st century, and emerging evidence suggests that diets containing ALA are associated with reductions in total deaths and sudden cardiac death. There may be aspects of the action and, more importantly, the metabolism of ALA that need to be elucidated, and these will help us understand the biological effects of this compound better. Additionally, we must not forget that ALA is part of the whole diet and should be seen in this context, not in isolation.

Ototoxic effects of cisplatin in a Sprague-Dawley rat animal model as revealed by ABR and transiently evoked otoacoustic emission measurements

The ototoxic effects of cisplatin in a Sprague-Dawley rat model were evaluated by recordings of auditory brainstem responses (ABR) and transiently evoked otoacoustic emissions (TEOAEs). The ABR responses were evoked from alternating clicks and 8, 10, 12, 16, 20 and 30 kHz tone pips in a range from 40 to 100 dB SPL range. The TEOAEs were recorded with a non-linear protocol, and were evoked by a 63.5 dB SPL click stimulus. Twenty five male Sprague-Dawley rats were used in the study, 20 animals were treated with cisplatin (16 mg/kg, body weight) and five animals served as controls. The data showed that 72 h after the cisplatin administration, the TEOAE and ABR variables were significantly altered. The relationship between the ABR and TEOAE variables was shown to be non-linear. The most significant relationships were observed between the TEOAE correlation and the ABR threshold values at 10, 12, and 16 kHz.

Nutritional (n-3) polyunsaturated fatty acids influence the behavioral responses to positive events in mice

The effect of (n-3) polyunsaturated fatty acid (PUFA) diet deficiency on behavioural responses to appetitive events was assessed in OF1 mice. Pups fed the same diet (deficient in alpha-linolenic acid or a standard control diet) as their dams were used aged 7 to 11 weeks. In a free choice model, the preference for a sucrose solution in both males and females was significantly lower in deficient than in control mice. Morphine conditioned place preference was obtained with the two diets at 8 and 16 mg/kg morphine, but the lower dose of 4 mg/kg induced a place preference in control but not in (n-3) deficient mice. Taken together, these results suggest that a nutritional (n-3) PUFA deficiency can alter the responsiveness to appetitive events.