Fatty acid composition of lipids of human brain myelin and synaptosomes: changes in phenylketonuria and Down's syndrome

Fatty Acids: A Safe Tool for Improving Neurodevelopmental Alterations in Down Syndrome?

The triplication of chromosome 21 causes Down syndrome (DS), a genetic disorder that is characterized by intellectual disability (ID). The causes of ID start in utero, leading to impairments in neurogenesis, and continue into infancy, leading to impairments in dendritogenesis, spinogenesis, and connectivity. These defects are associated with alterations in mitochondrial and metabolic functions and precocious aging, leading to the early development of Alzheimer’s disease. Intense efforts are currently underway, taking advantage of DS mouse models to discover pharmacotherapies for the neurodevelopmental and cognitive deficits of DS. Many treatments that proved effective in mouse models may raise safety concerns over human use, especially at early life stages. Accumulating evidence shows that fatty acids, which are nutrients present in normal diets, exert numerous positive effects on the brain. Here, we review (i) the knowledge obtained from animal models regarding the effects of fatty acids on the brain, by focusing on alterations that are particularly prominent in DS, and (ii) the progress recently made in a DS mouse model, suggesting that fatty acids may indeed represent a useful treatment for DS. This scenario should prompt the scientific community to further explore the potential benefit of fatty acids for people with DS.

Peroxisomes of the Brain: Distribution, Functions, and Associated Diseases

Peroxisomes are versatile cell organelles that exhibit a repertoire of organism and cell-type dependent functions. The presence of oxidases and antioxidant enzymes is a characteristic feature of these organelles. The role of peroxisomes in various cell types in human health and disease is under investigation. Defects in the biogenesis of the organelle and its function lead to severe debilitating disorders. In this manuscript, we discuss the distribution and functions of peroxisomes in the nervous system and especially in the brain cells. The important peroxisomal functions in these cells and their role in the pathology of associated disorders such as neurodegeneration are highlighted in recent studies. Although the cause of the pathogenesis of these disorders is still not clearly understood, emerging evidence supports a crucial role of peroxisomes. In this review, we discuss research highlighting the role of peroxisomes in brain development and its function. We also provide an overview of the major findings in recent years that highlight the role of peroxisome dysfunction in various associated diseases.

Early postnatal oleic acid administration enhances synaptic development and cognitive abilities in the Ts65Dn mouse model of Down syndrome

OBJECTIVES

The brains of individuals with Down syndrome (DS) present defects in neurogenesis and synaptogenesis during prenatal and early postnatal stages that are partially responsible for their cognitive disabilities. Because oleic and linolenic fatty acids enhance neurogenesis, synaptogenesis, and cognitive abilities in rodents and humans, in this study we evaluated the ability of these compounds to restore these altered phenotypes in the Ts65Dn (TS) mouse model of DS during early postnatal stages.

METHODS

TS and euploid mice were treated with oleic or linolenic acid from PD3 to PD15, and the short- and long- term effects of these acids on neurogenesis and synaptogenesis were evaluated. The effects of these treatments on the cognitive abilities of TS mice during early adulthood were also evaluated.

RESULTS

Administration of oleic or linolenic acid did not modify cell proliferation immediately after treatment discontinuation or several weeks later. However, oleic acid increased the total number of DAPI+ cells (+ 26%), the percentage of BrdU+ cells that acquired a neural phenotype (+ 9.1%), the number of pre- (+ 29%) and post-synaptic (+ 32%) terminals and the cognitive abilities of TS mice (+ 18.1%). In contrast, linolenic acid only produced a slight cognitive improvement in TS mice. (+12.1%).

DISCUSSION

These results suggest that early postnatal administration of oleic acid could palliate the cognitive deficits of DS individuals.

Prenatal Administration of Oleic Acid or Linolenic Acid Reduces Neuromorphological and Cognitive Alterations in Ts65dn Down Syndrome Mice

BACKGROUND

The cognitive impairments that characterize Down syndrome (DS) have been attributed to brain hypocellularity due to neurogenesis impairment during fetal stages. Thus, enhancing prenatal neurogenesis in DS could prevent or reduce some of the neuromorphological and cognitive defects found in postnatal stages.

OBJECTIVES

As fatty acids play a fundamental role in morphogenesis and brain development during fetal stages, in this study, we aimed to enhance neurogenesis and the cognitive abilities of the Ts65Dn (TS) mouse model of DS by administering oleic or linolenic acid.

METHODS

In total, 85 pregnant TS females were subcutaneously treated from Embryonic Day (ED) 10 until Postnatal Day (PD) 2 with oleic acid (400 mg/kg), linolenic acid (500 mg/kg), or vehicle. All analyses were performed on their TS and Control (CO) male and female progeny. At PD2, we evaluated the short-term effects of the treatments on neurogenesis, cellularity, and brain weight, in 40 TS and CO pups. A total of 69 TS and CO mice were used to test the long-term effects of the prenatal treatments on cognition from PD30 to PD45, and on neurogenesis, cellularity, and synaptic markers, at PD45. Data were compared by ANOVAs.

RESULTS

Prenatal administration of oleic or linolenic acid increased the brain weight (+36.7% and +45%, P < 0.01), the density of BrdU (bromodeoxyuridine)- (+80% and +115%; P < 0.01), and DAPI (4',6-diamidino-2-phenylindole)-positive cells (+64% and +22%, P < 0.05) of PD2 TS mice with respect to the vehicle-treated TS mice. Between PD30 and PD45, TS mice prenatally treated with oleic or linolenic acid showed better cognitive abilities (+28% and +25%, P < 0.01) and a higher density of the postsynaptic marker PSD95 (postsynaptic density protein 95) (+65% and +44%, P < 0.05) than the vehicle-treated TS animals.

CONCLUSION

The beneficial cognitive and neuromorphological effects induced by oleic or linolenic acid in TS mice suggest that they could be promising pharmacotherapies for DS-associated cognitive deficits.

Overexpression of DYRK1A inhibits choline acetyltransferase induction by oleic acid in cellular models of Down syndrome

Histological brain studies of individuals with DS have revealed an aberrant formation of the cerebral cortex. Previous work from our laboratory has shown that oleic acid acts as a neurotrophic factor and induces neuronal differentiation. In order to characterize the effects of oleic acid in a cellular model of DS, immortalized cell lines derived from the cortex of trisomy Ts16 (CTb) and normal mice (CNh) were incubated in the absence or presence of oleic acid. Oleic acid increased choline acetyltransferase expression (ChAT), a marker of cholinergic differentiation in CNh cells. However, in trisomic cells (CTb line) oleic acid failed to increase ChAT expression. These results suggest that the overdose of specific genes in trisomic lines delays differentiation in the presence of oleic acid by inhibiting acetylcholine production mediated by ChAT. The dual-specificity tyrosine (Y) phosphorylation-regulated kinase 1A (DYRK1A) gene is located on human chromosome 21 and encodes a proline-directed protein kinase. It has been proposed that DYRK1A plays a prominent role in several biological functions, leading to mental retardation in DS patients. Here we explored the potential role of DYRK1A in the modulation of ChAT expression in trisomic cells and in the signaling pathways of oleic acid. Down-regulation of DYRK1A by siRNA in trisomic CTb cells rescued ChAT expression up to levels similar to those of normal cells in the presence of oleic acid. In agreement with these results, oleic acid was unable to increase ChAT expression in neuronal cultures of transgenic mice overexpressing DYRK1A. In summary, our results highlight the role played by DYRK1A in brain development through the control of ChAT expression. In addition, the overexpression of DYRK1A in DS models prevented the neurotrophic effect of oleic acid, a fact that may account for mental retardation in DS patients.

Median nerve conduction velocity and central conduction time measured with somatosensory evoked potentials in thyroxine-treated infants with Down syndrome

OBJECTIVE

The aim of this study was to determine whether thyroxine treatment would improve nerve conduction in infants with Down syndrome.

METHODS

A single-center, nationwide, randomized, double-blind, clinical trial was performed. Neonates with Down syndrome were assigned randomly to thyroxine (N = 99) or placebo (N = 97) treatment for 2 years. Daily thyroxine doses were adjusted regularly to maintain plasma thyrotropin levels in the normal range and free thyroxine concentrations in the high-normal range. The outcome measures were nerve conduction velocity and central conduction time, determined through median nerve somatosensory evoked potential recording, at the age of 24 months.

RESULTS

At the age of 24 months, somatosensory evoked potential recordings for 81 thyroxine-treated and 84 placebo-treated infants were available for analysis. Nerve conduction velocity and central conduction time did not differ significantly between the 2 treatment groups (nerve conduction velocity: thyroxine: 51.0 m/second; placebo: 50.1 m/second; difference: 0.9 m/second; central conduction time: thyroxine: 8.83 milliseconds; placebo: 8.73 milliseconds; difference: 0.1 milliseconds).

CONCLUSIONS

Postnatal thyroxine treatment of infants with Down syndrome did not alter somatosensory evoked potential-measured peripheral or central nerve conduction significantly. The absence of favorable effects suggests that pathologic mechanisms other than mild postnatal hypothyroidism underlie the impaired nerve conduction. The absence of adverse effects suggests that longstanding plasma free thyroxine concentrations in the high-normal range are not harmful to nerve maturation.

Astrocyte-synthesized oleic acid behaves as a neurotrophic factor for neurons

Unlike in the adult brain, the newborn brain specifically takes up serum albumin during the postnatal period, coinciding with the stage of maximal brain development. Here we shall summarize our knowledge about the role played by albumin in brain development. The role of this protein in brain development is intimately related to its ability to carry fatty acids. Thus, albumin stimulates oleic acid synthesis by astrocytes from the main metabolic substrates available during brain development. Astrocytes internalize albumin in vesicle-like structures by receptor-mediated endocytosis, which is followed by transcytosis, including passage through the endoplasmic reticulum (ER). The presence of albumin in the ER activates the sterol regulatory element-binding protein-1 (SREBP-1) and increases stearoyl-CoA 9-desaturase (SCD) mRNA, the key enzyme in oleic acid synthesis. Oleic acid released by astrocytes is used by neurons for the synthesis of phospholipids and is specifically incorporated into growth cones. In addition, oleic acid promotes axonal growth, neuronal clustering, and the expression of the axonal growth associated protein, GAP-43. All of these observations indicate neuronal differentiation. The effect of oleic acid on GAP-43 synthesis is brought about by the activation of protein kinase C. The expression of GAP-43 is significantly increased by the presence of albumin in neurons co-cultured with astrocytes, indicating that neuronal differentiation takes place by the presence of oleic acid synthesized and released by astrocytes in situ. In conclusion, during brain development the presence of albumin could play an important role by triggering the synthesis and release of oleic acid by astrocytes, thereby inducing neuronal differentiation.

Neuronal differentiation is triggered by oleic acid synthesized and released by astrocytes

Unlike in the adult brain, the newborn brain specifically takes up serum albumin during the postnatal period, coinciding with the stage of maximal brain development. Here we report that albumin stimulates oleic acid synthesis by astrocytes from the main metabolic substrates available during brain development. Oleic acid released by astrocytes is used by neurons for the synthesis of phospholipids and is specifically incorporated into growth cones. Oleic acid promotes axonal growth, neuronal clustering, and expression of the axonal growth-associated protein-43, GAP-43; all these observations indicating neuronal differentiation. The effect of oleic acid on GAP-43 synthesis is brought about by the activation of protein kinase C, since it was prevented by inhibitors of this kinase, such as H-7, polymyxin or sphingosine. The expression of GAP-43 was significantly increased in neurons co-cultured with astrocytes by the presence of albumin indicating that neuronal differentiation takes place in the presence of oleic acid synthesized and released by astrocytes in situ. In conclusion, during brain development the presence of albumin could play an important role by triggering the synthesis and release of oleic acid by astrocytes, which induces neuronal differentiation.

Antioxidant enzymes and fatty acid status in erythrocytes of Down syndrome patients

The excess of genetic information in patients with Down syndrome (DS) produces an increase in the catalytic activity of superoxide dismutase (SOD1), an antioxidant enzyme coded on chromosome 21. It has been suggested that an increase in oxidative stress in DS patients may cause adverse effects in the cell membranes through the oxidation of polyunsaturated fatty acids (PUFAs). The aim of this study was to evaluate the cellular antioxidant system by determining the catalytic activity of the SOD1, glutathione peroxidase (GPx), catalase (CAT), and glutathione reductase (GR) enzymes and the concentrations of α-tocopherol in red blood cells (RBCs) in a group of 72 DS patients. The profile of fatty acids in the phospholipids of RBC membranes was also evaluated. The activity of the erythrocyte antioxidant enzymes is significantly higher in the DS group than in the control group (SOD1, 635 ± 70 U/g Hb vs 476 ± 67 U/g Hb; CAT, 1843 ± 250 U/g Hb vs 1482 ± 250 U/g Hb; GPx, 23.2 ± 5.3 U/g Hb vs 21.5 ± 3.6 U/g Hb; and GR, 9.32 ± 1.4 U/g Hb vs 6.9 ± 1.3 U/g Hb, respectively). No differences were observed in RBC α-tocopherol concentrations between the two groups studied. Long-chain n6 PUFA (C20:3n6, C20:4n6) concentrations were increased in DS patients, suggesting enhanced Δ-6-desaturase activity. The long-chain n3 PUFA (docosahexenoic acid) does not appear to be affected by increased oxidative stress, probably because of the existence of compensatory antioxidant mechanisms.

Reduced N-acetylaspartate in the brain observed on in vivo proton magnetic resonance spectroscopy in patients with mental retardation

Volume-selective proton magnetic resonance spectroscopy (1H-MRS) of the brain was performed with a 1.5T magnet in 28 patients with unclassified mental retardation (MR) and in 25 age-matched healthy children. Peaks of N-acetylaspartate (NAA), choline (Cho), and creatine (Cr), but not of lactate, were observed in both groups on 1H-MRS. In all our subjects of this age range, 1H-MRS revealed an increase with advancing age in the ratio of NAA/Cho (P = .0031), but no developmental change in the NAA/Cr and Cho/Cr ratios. The NAA/Cho ratio was lower in patients with MR than in controls (P = .0016). The NAA/Cr ratio tended to be lower in the MR group, and the Cho/Cr ratio did not differ between patients with MR and controls. These results suggest that in patients with MR, NAA decreases and a disorder and/or dysfunction of neurons in the brain exists.

Growth hormone response after administration of L-dopa, clonidine, and growth hormone releasing hormone in children with Down syndrome

We studied the response of growth hormone secretion after the administration of L-dopa, clonidine, and growth hormone releasing hormone in eight growth-retarded children with Down syndrome aged 1 to 6.5 years. After L-dopa administration, five children had low growth hormone secretion (M = 3.7 ng/ml, SD = 2.12 at 30 min) and three children had elevated growth hormone levels (> 30 ng/ml). After clonidine administration, six children had relatively low growth hormone levels (M = 3.15 ng/ml, SD = 2.53 at 60 min) and two children had high levels (38.3 ng/ml and 16.8 ng/ml, respectively). There was a better response after growth hormone releasing hormone administration; only one child had a growth hormone level of < 10 ng/ml. Most of the children had a modified response of growth hormone secretion subsequent to the various stimulation tests. All children, however, were able to secrete some growth hormone (> or = 10 ng/ml) at least during one of the stimulation tests. In comparison with peak growth hormone levels reported in normal children, our cohort had significantly lower growth hormone levels only after clonidine administration. It is postulated that children with Down syndrome have both anatomical and biochemical hypothalamic derangements that may result in decreased growth hormone secretion and reduced linear growth. In addition, other mechanisms that may be in part responsible for the observed growth retardation are discussed.

The role of alterations in free radical metabolism in mediating cognitive impairments in Down's syndrome

Down's syndrome (DS) is a genetic disorder involving an excess of chromosome 21 (trisomy 21) in approximately 96% of the cases and comprises approximately 15% of the population with mental retardation (Heller, 1969). In addition to the constitutional mental deficiencies associated with the syndrome many DS patients develop dementia associated with Alzheimer's disease (AD) in their later years of life (Thase et al., 1984). The genetic locus for Cu,Zn-superoxide dismutase (SOD1), a key enzyme in free radical metabolism, is located on chromosome 21, and the activity level of this enzyme is elevated by approximately 50% in a variety of cells of DS patients (see Kedziora and Bartosz, 1988; Sinet, 1982). Because alterations in free radical metabolism may be involved in neuronal death and may be associated with a number of pathological manifestations of DS, it is important to understand the role of free radical metabolism in cognitive impairments of DS, the topic discussed in this chapter.

Synaptic dysgenesis

Synapse formation is a complex, incompletely understood process that has received only limited investigation in man despite the importance of synaptic dysfunction in common disorders such as epilepsy and mental retardation. This review explores synaptic differentiation, focussing on the morphologic maturation of synapses. Since differentiation depends on many antecedent developmental events, synaptogenesis can be affected by several factors: errors in neuronal proliferation, migration, and differentiation. The challenge to the neurobiologist is to detect and evaluate the minor alterations in neuronal differentiation that could account for the structural basis of the clinical manifestations. Trisomy 21 is an example of a condition in which the cytoarchitecture of the cerebral cortex is not obviously altered, yet mental retardation is consistently present; research neurobiologic techniques are making possible documentation of its structural basis. Epilepsy is another example in which examination of surgically removed cerebral cortex reveals subtle cortical dysplasias helpful in understanding the basis for the abnormal electrical discharge. Further exploration of synaptogenesis, particularly the influence of gene products and epigenetic factors on synapse maturation, will increase our understanding of the pathogenesis of conditions in which "morphology" seems normal but function is abnormal.

Enhanced production of superoxide anion by microglia from trisomy 16 mice

Disruption of normal oxygen radical metabolism in the CNS may contribute to the neuropathological changes associated with Down syndrome (trisomy 21) and its mouse counterpart, the trisomy 16 (Ts16) mouse. One potent source of oxyradicals is the CNS-specific macrophage, the microglial cell. We prepared primary glial cultures from the cerebral cortices of Ts16 and normal littermate mice taken at day 15 of gestation. Microglia were isolated from confluent cultures after 14 days in vitro and assayed for superoxide anion production using a cytochrome C reduction assay. Stimulation by either opsonized zymosan (OPZ) or phorbol myristate acetate (PMA), produced significantly higher levels (2.8-20 fold) of superoxide per mg protein in Ts16 microglial cultures. Resting, i.e. unstimulated secretion, was not significantly different from littermate controls. Astrocyte enriched cultures, stimulated by OPZ, exhibited low levels of superoxide production which was higher in Ts16 mice than normal littermates. Microglial enriched cultures from rat neonatal cerebral cortices were exposed for 24 h to medium from the Ts16 glial cultures. Superoxide production in the Ts16 media treated rat microglia was significantly higher than in those treated with littermate conditioned media.

Lipid abnormalities in the brain in adult Down's syndrome and Alzheimer's disease

Quantitative analysis by HPTLC of the major lipid classes and dolichol, and of fatty acyl groups of separated phosphoglycerides by capillary GLC, has been carried out on the gray matter of frontal cerebral cortex of brains from six Down's syndrome (DS) and six Alzheimer's disease (AD) adults, and six each of two corresponding sets of age-matched controls; specimens of DS and control cerebellum and corpus callosum were also analyzed. In DS frontal cortex, but not in AD frontal cortex, compared to their respective controls there was a decrease in the fraction of phosphatidylethanolamine (PE) and an increase in the fractions of sphingomyelin (SPM) and phosphatidylserine (PS). Abnormalities were not found in the proportions of major lipid classes in DS cerebellum or corpus callosum. The concentration of dolichol was elevated for age in the frontal cortex of DS and of AD. In the phosphoglycerides of DS frontal cortex, the fatty acyl composition showed small, but statistically significant, differences from those of age-matched controls, and some slight abnormalities were also detected in DS corpus callosum. The alterations in DS frontal cortex included decreases in (n-6) and increases in (n-3) groups in choline and ethanolamine phosphoglycerides (CPG and EPG), as had previously been found in EPG and serine phosphoglyceride (SPG) of the DS fetal brain. In DS frontal cortex, the proportion of 22:4(n-6) groups was decreased in SPG, and in inositol phosphoglyceride (IPG) 18:1(n-9) was increased. There were also small but significant alterations in DS frontal cortex in the fractions of shorter chain groups in CPG. In marked contrast, most of the fatty acyl abnormalities seen in DS were absent in the AD frontal cortex. It is therefore suggested that some abnormalities in the composition of cerebral membranes present prenatally in DS may persist into adulthood, and are not directly related to AD-type pathology.

The neurobiologic consequences of Down syndrome

Trisomy of the whole or distal part of human chromosome 21 (HSA 21) (Ts21) results in Down Syndrome (DS), which is characterized in part by mental retardation and associated neurological abnormalities. Structural abnormalities observed frequently include reduced brain weight, decreased number and depth of sulci in the cerebral cortices, neuronal heterotopias, and reduced numbers of specific populations of neurons, such as granule cells, in the cerebral cortices. Abnormalities in the structure of cells, primarily of the dendrites, are observed in portions of the neuraxis, such as the hippocampus, cerebellum, and cerebral cortices. Functional abnormalities in membrane properties in peripheral structures and in neurotransmitter enzyme systems in both peripheral and central structures are observed also. Brains of DS individuals over the age of 40 exhibit the characteristic neuropathologic and neurochemical stigmata of Alzheimer's disease (AD). The cholinergic and noradrenergic systems appear to be particularly vulnerable. To elucidate the mechanisms responsible for these abnormalities, identification of the genes located in the distal part of HSA 21 and the systematic study of animal model systems with close genetic homology are essential.

Genetic basis for a mouse model of Down syndrome

The Trisomy 16 (Ts16) mouse has been proposed as a model for Down Syndrome (DS) in humans, based on genetic homology between mouse chromosome 16 (MMU 16) and human chromosome 21 (HSA 21). Translocations of HSA 21 resulting in trisomy for only a portion of the genetic information contained on this chromosome can result in a DS phenotype. Thus, these translocations help to define a "DS region" of the chromosome. A number of genes from this DS region of HSA 21 have been mapped to MMU 16. Techniques for localizing genes on chromosomes have been used to identify the portion of MMU 16 which corresponds to the DS region of HSA 21. This region appears to be highly conserved between mouse and human, providing further support for a mouse model of DS.

Altered composition of polyunsaturated fatty acyl groups in phosphoglycerides of Down's syndrome fetal brain

We have observed recently that in vitro lipoperoxidation is enhanced in Down's syndrome brain homogenates of prenatal age. As this may relate to the composition of polyunsaturated acyl groups (PUFA) in phospholipids, we have examined the PUFA of ethanolamine and serine phosphoglycerides (EPG and SPG), which are particularly rich in PUFA, in the same series of cerebral cortex specimens of Down's syndrome and age-matched control fetuses. Although the total percentages of PUFA in the two phosphoglycerides were not altered, compared with controls the ratio of PUFA of the (n-3) series to those of the (n-6) series was very significantly elevated in Down's syndrome, from 0.32 to 0.55 in EPG and from 0.60 to 0.97 in SPG. In particular, docosahexaenoyl, 22:6(n-3), groups were uniformly increased in Down's syndrome compared with controls by 54% and 33% in EPG and SPG, respectively, while arachidonoyl, 20:4(n-6), groups were decreased by 16% and 30%, respectively. Similar changes occur during normal development, but the (n-3) to (n-6) ratio of PUFA in these phosphoglycerides of Down's syndrome at the fifth month of gestation resembled that of normal human cerebral grey matter at term. However, other developmental indices related to PUFA composition were not significantly affected. It seems therefore that in the developing Down's syndrome brain there may be a distortion of the normal transformations of essential fatty acids and of their incorporation into phosphoglycerides. The disproportion between docosahexaenoyl and arachidonoyl groups in membrane phosphoglycerides during prenatal development in Down's syndrome may also result in disturbances of the proper functioning, and the ontogenetic integration, of membrane enzymes and transport processes.

Superoxide dismutase, glutathione peroxidase and lipoperoxidation in Down's syndrome fetal brain

Certain aspects of the metabolism of oxygen derivatives were investigated in the cerebral cortex from Down's syndrome (trisomy 21) fetuses. In comparison with controls of similar gestational age, the specific activity of the cytosolic Cu/Zn-dependent superoxide dismutase (SOD-I) was significantly elevated by 60 +/- 5%. This is consistent with a gene dosage effect, as the gene coding for SOD-I is on chromosome 21. In order to determine whether the increase in SOD-I activity is associated with an adaptive rise in glutathione peroxidase (GSHPx), as has been observed in other tissues, the activity of this enzyme was also estimated but was found not to be altered in the Down's syndrome brain. In addition, in vitro lipoperoxidation, estimated by the formation of malondialdehyde (MDA) on incubation of homogenates fortified with ascorbate and Fe2+, was significantly elevated (36 +/- 4%) in cerebral cortex of the Down's syndrome fetuses. The concentration of total combined polyunsaturated fatty acids (PUFA) was not significantly altered in the tissue, although there is evidence for differences in the composition of certain phospholipids. It is proposed that, on account of the evidence for a potential perturbation of oxygen free radical metabolism (notably an increased SOD-I activity not compensated by a rise in GSHPx) and for enhanced in vitro peroxidizability of PUFA, there may be increased lipoperoxidative damage in the Down's syndrome brain prenatally.

Abnormal electric membrane properties of Down's syndrome DRG neurons in cell culture

Cell cultures were prepared from normal and Down's syndrome dorsal root ganglia (DRG). Both pre- and postnatal specimens were utilized; 8 normal and 4 Down's. Cultures were maintained in medium with normal (4 mM) and elevated (20 mM) potassium (K) since the latter was found to enhance neuron survival. After various period of incubation, cultures were transferred to normal K medium and their electrical membrane properties (EMP) determined using intracellular recording techniques. An analysis of variance was performed with 5 covariates: developmental stage, culture duration, K concentration, type of action potential, and neuronal surface area. This analysis indicated that the Down's neurons had abnormal EMP, the most affected being the after hyperpolarization (-41%), membrane time constant (+30%), threshold rheobasic depolarization (-22%), rate of falling phase of action potential (-20%), specific membrane resistance (+18%) and absolute refractory period (+12%). All differences were also observed when samples of normal and Down's neurons were matched for the 5 covariates mentioned above, take separately. If the abnormal EMP observed in the present study for Down's DRG neurons in culture occurred for CNS neurons in situ they would disrupt the normal function of the nervous system and could therefore constitute the neurobiological basis of the mental retardation observed in Down's syndrome.