A study of gamma-aminobutyric acid uptake in normal and Down's syndrome platelets

Huntington's disease: the neuroexcitotoxin aspartate is increased in platelets and decreased in plasma

The neural degeneration observed in the striata of patients with Huntington's disease (HD) can be reproduced by excitatory NMDA receptor agonists such as aspartate and glutamate in striatal cell cultures and in striata of vertebrates injected with these substances. Therefore, we decided to investigate the role of aspartate and glutamate in HD. Aspartate, glutamate, glutamine, and phenylalanine were measured in platelets and plasma of HD patients and age- and sex-matched healthy controls (C), using HPLC methods. In HD platelets the mean aspartate concentration was significantly (p < 0.01) increased (8.9 +/- 3.8 (SD) nmol/mg protein, n = 28) compared to C (4.6 +/- 1.4 (SD) nmol/mg protein, n = 24), whereas plasma aspartate was significantly (p < 0.01) decreased in HD (0.092 +/- 0.023 (SD) mg/dl, n = 16) versus C (0.179 +/- 0.109 (SD) mg/dl, n = 21). The increase in platelet aspartate should be a direct or indirect consequence of the dominant gene defect in HD. It might therefore be present in neurons as well, especially since platelets share many characteristics with neurons. Hence, chronically increased release of aspartate with consecutive overstimulation of postsynaptic neurons via NMDA receptors might be responsible for the damage observed in striatal target cells of corticostriatal glutamatergic and aspartatergic projection fibers in HD.

Effect of vigabatrin (GVG) on serotonin (5-HT) uptake and release of human platelets in vitro

In platelets from healthy persons the effect of gamma-vinyl-GABA (GVG) on 5-HT uptake, storage, release and the kinetic parameters Km and Vmax of platelet 5-HT high affinity uptake was investigated in vitro. 5-HT uptake, storage and release in response to increasing GVG concentrations (0-7.74 mM) at a constant incubation time (60 min) and in dependence on time (0-90 min) at a constant GVG concentration (7.74 mM) remained unchanged. Concerning the high affinity 5-HT uptake, GVG (7.74 mM) caused a slight decrease of Vmax from 83.3 +/- 35.0 (SD) pmol 5-HT/10(8) pl./min to 77.0 +/- 33.4 (SD) pmol 5-HT/10(8) pl./min and a significant elevation of Km from 4.2 +/- 1.1 (SD) x 10(-7) M to 6.7 +/- 1.8 (SD) x 10(-7) M (P < 0.002) to about 160% of the control. This means a competitive inhibition of 5-HT uptake induced by GVG. Altogether, the effects of GVG on platelet 5-HT transport appear to be weak. An alteration of the platelet 5-HT system was demonstrated only at therapeutically nonrelevant high GVG concentrations. If platelets represent a model for 5-HT transport processes in presynaptic serotonergic neurons it is concluded that GVG has no effect on serotonergic activity.

Studies on choline transport enhancement into fibroblasts from normals and Alzheimer's donors

Human dental fibroblasts transport choline actively. This transport is inhibitable by hemicholinium-3. In this paper, choline transport into fibroblasts of normal donors (four cell lines) and into those of Alzheimer victims (four cell lines, age and sex matched to the normals) is accelerated by methylated xanthines, nicotine, and dexamethasone. At a caffeine concentration of 10 microM the stimulation of choline transport into normal cells averages 128% and into Alzheimer donor cells, 45%. 1 microM Dexamethasone stimulates choline influx by 86% in normal cells and 36% in Alzheimer cells. Nicotine enhances choline transport by 35% in normal cells and by 16% in Alzheimer cells. The implication is that if Alzheimer's disease is a cholinergic disorder, it may be amenable to transport-directed chemotherapies.

Sleep in the Down syndrome

Polysomnographic recordings were obtained for 10 Down syndrome (DS) children (6 males and 4 females, 9 months to 7 years old) and 16 age-matched normal controls. The present study was conducted to study the sleep characteristics of DS patients of this age group. The percentage of each sleep stage, rapid eye movements (REMs)/min, time intervals between REMs(I)/min, times of awakening in the middle of sleep, body movements (BMs) and twitch movements (TMs) were studied. I/min was divided into three frequencies: I less than 1 sec, l less than or equal to I less than 2 sec and I greater than or equal to 2 sec. Two of the 10 patients showed an increase in the percentage of REM sleep. In the group aged 1 to 5 years old, the REMs/min and I/min (I less than 1 sec) values were higher than those in normal controls (p less than 0.05). Many times of awakening in the middle of sleep (greater than or equal to 5 times and/or greater than or equal to 60 min) were observed in 4 cases. The frequency of BMs in total sleep was higher than that in controls (p less than 0.01). Five of the 10 cases showed an abnormal pattern as to the frequency of BMs during each sleep stage. The frequency of TMs was less than that in controls (total sleep and stage 1, p less than 0.05; stage REM, p less than 0.01). Seven of 9 cases showed an abnormal pattern as to the frequency of TMs during each sleep stage.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization and localization of high-affinity GABA uptake in slices of the rabbit oviduct

The characteristics of [3H]gamma-aminobutyric acid (GABA) uptake by slices of the rabbit oviduct were studied, and the GABA-accumulating structures were identified by histoautoradiography. A high-affinity (Km = 5 microM), sodium-dependent GABA uptake system was demonstrated which showed significant segmental variation along the oviduct with a maximal capacity (21 nmol/g tissue per h) at the fimbriated ampullary end of the organ. The uptake showed optimum values at pH 7.4 and 37 degrees C and could be influenced by changes of K+ and Ca2+ concentrations in the medium. Unlabelled GABA, ouabain and beta-alanine completely inhibited the uptake process, whereas known inhibitors of neuronal GABA uptake (L-diaminobutyric acid, nipecotic acid) produced only partial inhibition even at high doses. In autoradiographic experiments, epithelial secretory cells were predominantly labelled by [3H]GABA. These findings indicate the presence of a non-neuronal GABA uptake system in the oviductal epithelium and do not support the earlier hypothesis of GABAergic innervation in the oviduct.

GABA uptake in embryonic palate mesenchymal cells of two mouse strains

To obtain further evidence that the inhibitory neurotransmitter GABA functions in palate development, the presence of an active GABA uptake mechanism was sought using primary cultures of embryonic palate mesenchymal cells. Uptake was compared from cells of two inbred mouse strains in which the SWV strain shows greater sensitivity than the AJ strain to effects of GABA on palate morphogenesis and of diazepam in producing cleft palate. Palate cells were capable of accumulating [3H]GABA by saturable uptake mechanisms characteristic of a high and low affinity active transport as indicated by temperature, Na+ ion and carrier dependence as well as Km and Vmax values that were comparable to other biological systems. The Vmax of the high-affinity uptake system from cells of the SWV strain was 1.8 fold higher than that of the AJ. GABA uptake was also observed in fibroblasts from various sources including embryonic mouse limb cells, human skin fibroblasts and 3T3 cells. When active GABA uptake was measured in skin fibroblasts from the mouse SWV and AJ strains, the rate of uptake from SWV cells under high affinity conditions was also 1.8 fold greater than in AJ cells. Thus active GABA uptake appears to be genetically regulated in non-neural cells which may contribute to differential responses to GABA.

Uptake of gamma-aminobutyric acid by human blood platelets: comparison with CNS uptake

Human blood platelets show a sodium and temperature dependent uptake of gamma-aminobutyric acid (GABA) and other neuroactive amino acids. The most potent inhibitors tested of platelet GABA uptake were taurine and beta-alanine, while nipecotic acid and cis-3-aminocyclohexanecarboxylic acid were relatively weak inhibitors. These results suggest GABA is transported by a beta-amino acid uptake process in human platelets. Thus, platelet GABA uptake may more closely resemble glial rather than neuronal uptake.

Benzodiazepine receptors on human blood platelets

Binding studies conducted on membrane preparation from human platelets using (3H) Ro5-4864 and (3H) diazepam showed specific and saturable binding. Scatchard analysis revealed a single class of binding sites with KD = 10.8 +/- 0.9 nM and Bmax = 775 +/- 105 fmol/mg protein for (3H) Ro5-4864 and KD = 10.5 +/- 1.1 nM and Bmax = 133 +/- 19 fmol/mg for (3H) diazepam. We were unable to detect any GABA binding site on crude membrane preparation, nor did GABA enhance the binding of (3H) Ro5-4864 or (3H) diazepam. This suggests that benzodiazepine receptors are uncoupled to GABA system on human platelets. Ro15-1788, a specific antagonist for "central type" benzodiazepine (BDZ) binding sites was inactive in displacing (3H) Ro5-4864 from membrane receptors, while PK 11195 (a specific ligand for the "peripheral type" receptor) was the most potent of the drugs tested in inhibiting (3H) Ro5-4864 binding. These results indicate that human blood platelets bear "peripheral-type" BDZ receptor. Moreover, we could not detect any (3H) propyl beta carboline specific binding on platelet membranes. Results on benzodiazepine receptors on human circulating lymphocytes are also reported and similarity in pharmacological properties with platelet benzodiazepine receptors is suggested.

Down's syndrome in adults: brain metabolism

The cerebral metabolic rate for glucose, as measured with positron emission tomography and fluorine-18-labeled 2-deoxy-D-glucose, was significantly higher in four healthy young subjects with trisomy 21 syndrome (Down's syndrome) than the mean rate in healthy young controls. The rate of cerebral glucose utilization in the frontal lobe of a 51-year-old subject with Down's syndrome was significantly lower than the rate in the young subjects with this syndrome, but approximated the rate in middle-aged controls. Thus glucose utilization by the brain appears to be excessive in young adults with Down's syndrome but may decline with age in some brain regions.