Difference in lithium transport between neurones and glia in primary culture

Brain lithium, N-acetyl aspartate and myo-inositol levels in older adults with bipolar disorder treated with lithium: a lithium-7 and proton magnetic resonance spectroscopy study

OBJECTIVES

We investigated the relationship between brain lithium levels and the metabolites N-acetyl aspartate (NAA) and myo-inositol (myo-Ino) in the anterior cingulate cortex of a group of older adults with bipolar disorder (BD).

METHODS

This cross-sectional assessment included nine subjects (six males and three females) with bipolar I disorder and currently treated with lithium, who were examined at McLean Hospital's Geriatric Psychiatry Research Program and Brain Imaging Center. The subjects' ages ranged from 56 to 85 years (66.0 +/- 9.7 years) and all subjects had measurements of serum and brain lithium levels. Brain lithium levels were assessed using lithium magnetic resonance spectroscopy. All subjects also had proton magnetic resonance spectroscopy to obtain measurements of NAA and myo-Ino.

RESULTS

Brain lithium levels were associated with higher NAA levels [df = (1, 8), Beta = 12.53, t = 4.09, p < 0.005] and higher myo-Ino levels [df = (1, 7), F = 16.81, p < 0.006]. There were no significant effects of serum lithium levels on any of the metabolites.

CONCLUSION

Our findings of a relationship between higher brain lithium levels and elevated NAA levels in older adult subjects with BD may support previous evidence of lithium's neuroprotective, neurotrophic, and mitochondrial function-enhancing effects. Elevated myo-Ino related to elevated brain lithium levels may reflect increased inositol monophosphatase (IMPase) activity, which would lead to an increase in myo-Ino levels. This is the first study to demonstrate alterations in NAA and myo-Ino in a sample of older adults with BD treated with lithium.

Method for measuring neurotoxicity of aggregating polypeptides with the MTT assay on differentiated neuroblastoma cells

Reliable in vitro assays are essential for study of the effects of neurotoxic compounds such as beta-amyloid peptides (Abeta). The MTT assay has been used in cultures of different cells, e.g. SH-SY5Y neuroblastoma cells, for the quantitative measurement of Abeta toxicity. In our laboratory differentiated SH-SY5Y cells were used in the MTT assay. Cell differentiation with 10 microM all-trans-retinoic acid resulted in a constant cell number. The cells possess highly developed neurites and exhibit high sensitivity against Abeta. Owing to the constant cell number in differentiated SH-SY5Y cultures the decrease of the redox activity is directly proportional to the neurotoxicity of the substances, no correction is needed. The results of the MTT assay of Abeta peptides on differentiated SH-SY5Y cells displayed a good correlation also with the in vivo results. The present experiments reveal an effective assay for the study of potentially neurotoxic compounds.

Brain lithium measurements with (7)Li magnetic resonance spectroscopy (MRS): a literature review

7Li magnetic resonance spectroscopy (MRS) has been successfully used in recent years as a new tool to measure brain tissue lithium concentrations in vivo. After demonstration of its feasibility in animal studies over a decade ago, human investigations have characterized the brain pharmacokinetics of lithium. Preliminary studies have investigated brain pharmacokinetic correlates of clinical response in the treatment of bipolar disorder patients, with indication of possible clinical relevance of 7Li MRS measures. In this paper we reviewed the accumulated literature in this area, and discuss possible directions for this research in the context of preliminary studies conducted by our group that demonstrated the feasibility of 7Li MRS at 3 T.

Correlation of anoxic neuronal responses and calbindin-D28k localization in stratum pyramidale of rat hippocampus

Immunohistochemical staining for the calcium-binding protein calbindin-D28k (CaBP) was combined with Lucifer Yellow (LY) identification and intracellular recording of changes in membrane parameters of pyramidal neurons in CA2, CA1, and the subiculum of rat hippocampal slices during brief exposure (4.0 +/- 0.19 min) to N2. Anoxia evoked either a depolarization or hyperpolarization of membrane potential (VM) (+21.5 +/- 2.79 mV above VM = -70.5 +/- 1.50 mV, n = 30 and -7.2 +/- 0.72 mV below VM = -68.2 +/- 1.34 mV, n = 24, respectively) and a fall in membrane resistance of approximately 20%. Differences in the response could be correlated with the presence or absence of CaBP and the localization of neurons in different layers of stratum pyramidale and sectors of the hippocampus. For neurons immunopositive for calbindin (CaBP(+)), depolarization was observed more frequently (83%) than hyperpolarization (17%); in contrast, 44% of responses of calbindin-negative (CaBP(-)) neurons were depolarizing and 56% were hyperpolarizing. Depolarizations of CaBP(+) neurons were more gradual in slope, and more rapidly reached a plateau in comparison with those recorded in CaBP(-) neurons. Responses of neurons in the superficial layer of stratum pyramidale (in which 79% of CaBP(+) pyramidal neurons were situated) were mainly depolarizing (91%), while for those in the deep layer (which contained 89% of the CaBP(-) cells) such responses were observed less often (45%). Depolarization was also more common than hyperpolarization for cells located in CA2/CA1c/CA1b (63%) than in the CA1a/subicular region (37%). The depolarizing response of the majority of pyramidal neurons which are CaBP(+), superficial, and closer to CA3 may reflect an efficient buffering of intracellular Ca2+, which maintains a low [Ca2+]i, steep gradient for Ca2+ influx and may facilitate the movement of Ca2+ away from points of entry. The neurons which are CaBP(-), deep, and closer to subiculum and in which N2 evokes hyperpolarization, on the other hand, may have a sustained elevation/accumulation of cytosolic Ca2+ which could activate K+ conductance, inhibit Ca2+ influx, and stabilize the membrane potential. These experiments provide a functional correlate for CaBP and suggest that it may have a significant role in Ca2+ homeostasis and the determination of selective neuronal vulnerability.

Lithium distribution in mania: single-dose pharmacokinetics and sympathoadrenal function

We examined lithium distribution after a single dose of 25 mEq in 14 drug-free manic patients. Lithium concentrations were measured in plasma, red blood cells, and urine. Maximum concentrations of lithium, times at which they were attained, and influx and efflux rate constants for extracellular fluid, red blood cell, and muscle-like compartments were estimated using a three-compartment pharmacokinetic model. Tissue lithium concentrations may continue to increase for hours after plasma lithium concentrations have peaked. Rate constants for absorption, excretion, and influx and efflux for the tissue compartments were similar to those previously reported for normal subjects. Rate constants for transport into and out of the tissue compartments correlated negatively with norepinephrine or epinephrine excretion and positively with the plasma/red cell Na+ gradient. Rate constants for efflux from red blood cell and muscle compartments correlated with measures of adrenocortical function and were higher in dexamethasone nonsuppressors than in suppressors. These data show that distribution of lithium may be related to sympathodrenal activity and Na+ distribution in manic patients.

Transport pathways for lithium ions in neuroblastoma x glioma hybrid cells at 'therapeutic' concentrations of Li+

The pathways of Li+ transport in neuroblastoma X glioma hybrid cells were studied at 2 mM external Li+. Five components of Li+ transport were identified. (1) A Na+-dependent Li+ countertransport system mediating Li+ transport in both directions across the plasma membrane. This transport pathway is insensitive to ouabain or external K+. It shows trans-stimulation (i.e. acceleration of Li+ extrusion by external Na+ and stimulation of Li+ uptake by internal Na+) and cis-inhibition (i.e. reduction of Li+ uptake by external Na+). (2) The Na+-K+ pump mediates Li+ uptake but not Li+ release in cells with physiological Na+ and K+ content. Li+ uptake by the pump in choline media is inhibited by both external Na+ and K+. In Na+ media, external K+ exhibits a biphasic effect: in concentrations up to about 1 mM, K+ accelerates, and at higher concentrations, K+ inhibits Li+ uptake by the pump. (3) Li+ can enter the voltage-dependent Na+ channel. Li+ uptake through this pathway is stimulated by veratridine and scorpion toxin, the stimulation being blocked by tetrodotoxin. Residual pathways comprise (4) a saturable component, which is comparable to basal Na+ uptake, and (5) a ouabain-resistant component promoting Li+ extrusion against an electrochemical gradient in choline media. The mechanisms for Li+ extrusion described here possibly explain how neuronal cells maintain the steady-state ratio of internal to external Li+ below 1 during chronic exposure to 1-2 mM external Li+.

Lithium entry into neural cells via sodium channels: a morphometric approach

Rat cerebral cortical explants prepared from 18-day-old embryos were grown for 18 days in vitro. Cultures were exposed to Na+, Li+ and choline+ media, respectively, in the presence or absence of tetrodotoxin and/or veratridine, and processed for electron-microscopy. Veratridine (50 microM) induced an increase in summated and mean areas of neuronal profiles in Na+- and Li+-media but not in the choline+-medium: the summated perimeters did not change. The mean value of the neuronal form factor was significantly elevated following exposure to veratridine in a Na+- or Li+-dependent manner, indicating that the shape of the sectioned neuronal elements shifted towards an (ideal) circle. Qualitative assessment revealed an increased electron-lucency of the cytoplasm of neuronal profiles in Na+- and Li+-media containing veratridine. The veratridine-induced neuronal changes were inhibited by simultaneous addition of tetrodotoxin (1 microM) to the media. In the case of the glial cells, the values of the summated area and form factor did not change in the various experimental groups. The area of the extracellular space per unit area of sections significantly decreased in the Na+- and Li+-media following veratridine exposure; this did not occur in the choline+-medium. The results indicate a considerable swelling of the neuronal elements, reflecting cation, Cl- and water uptake following prolonged sodium channel activation in the presence of Na+ or Li+ ions. The quantitative ultrastructural data strongly suggests an entry of Li+ ions into cultured rat cerebral cells via sodium channels.

A morphometric study of cultured rat cerebral synapses exposed to different cationic media

Quantitative techniques have been applied to compare the effects of high-K+, Mg2+ and Li+ media on the ultrastructure of cultured synapses alongside Na+-incubated controls. The explant cultures were prepared from 18-day-old embryonic rat cerebral cortices and maintained for 19 days in vitro. K+ -Stimulation for 25 min resulted in an increase in the mean perimeter and area of presynaptic terminals. Of these, the perimeter increase was the more pronounced, as indicated by a decrease in the value of the two-dimensional form factor. Reductions were also observed in the number of synaptic vesicles per presynaptic terminal, in the vesicle-terminal area ratio and in the synaptic vesicle density in an area adjacent to the presynaptic membrane, the latter two parameters being in positive linear correlation. The frequency of presynaptic cisternal/vacuolar profiles increased, and the synaptic curvature shifted in a positive direction. Synaptic length did not change following K+-exposure. Qualitative assessment indicated the presence of a network subjacent to the post-synaptic thickening and swelling of the postsynaptic ending after K+-stimulation. Incubation and fixation in Mg2+-media of two concentrations resulted in an increase in the number and area ratio of synaptic vesicles per terminal, and an elevation in the synaptic vesicle density in the higher Mg2+ concentration medium. Li+-treatment reduced the number of synaptic vesicles per terminal, the vesicle-terminal area ratio, and the vesicle density in the vicinity of the presynaptic membrane, while the synaptic curvature shifted in the positive direction. These changes were less pronounced than those characteristic of synapses in the K+ medium.

Lithium distribution across the membrane of motoneurons in the isolated frog spinal cord

Lithium sensitive microelectrodes were used to investigate the transmembrane distribution of lithium ions (Li+) in motoneurons of the isolated frog spinal cord. After addition of 5 mmol.1(-1) LiCl to the bathing solution the extracellular diffusion of Li+ was measured. At a depth of 500 micrometers, about 60 min elapsed before the extracellular Li+ concentration approached that of the bathing solution. Intracellular measurements revealed that Li+ started to enter the cells soon after reaching the motoneuron pool and after up to 120 min superfusion, an intra - to extracellular concentration ratio of about 0.7 was obtained. The resting membrane potential and height of antidromically evoked action potentials were not altered by 5 mmol.1(-1) Li+.

Acute and chronic effects of lithium in therapeutically relevant concentrations on potassium uptake into astrocytes

Potassium uptake into astrocytes in primary cultures was measured by the aid of 42K. Acute application of lithium in concentrations of 1 and 5 mM, but not 0.5 und 0.25 mM, exerted a significant inhibition of the potassium uptake rates. This effect is due to a partial impairment of the ouabain-sensitive part of the uptake into the cells caused by a lithium interaction with the extracellular K+-activated site of the Na+, K+-ATPase. After 14 days of exposure of the astrocytes to 1 mM lithium, the potassium uptake remained lower in the presence of lithium than in its absence. However, the cells had adjusted to the chronic presence of lithium by increasing their potassium uptake to such an extent that, during the exposure to 1 mM lithium, it was indistinguishable from that in cultures from the same batches grown in the absence of lithium and measured in the absence of this compound. The interference by lithium with potassium uptake into astrocytes may well be related to the inhibition of potassium clearance in the CNS described in the literature.

The influence of external sodium and potassium on lithium uptake by primary brain cell cultures at "therapeutic" lithium concentration

The ionic regulating of lithium homeostasis and steady-state intra:extracellular lithium distribution in the brain can be approached by experimental methods using intact nerve cells in vitro. Primary cultures prepared from chick embryonic brain were applied to study the effect of extracellular sodium and potassium on the lithium uptake of nerve cells at 'therapeutic' lithium concentration (1.5 mM). Lithium influx and the level of steady-state intracellular lithium were significantly reduced by increasing the external sodium concentration. At physiological extracellular sodium level, the steady-state content of lithium in the brain cells was about half of that observed in the presence of 10 mM sodium in the incubation media and the value of the intra:extracellular lithium distribution ratio was below 1. External potassium (0.5 - 3mM) strongly inhibited lithium uptake of the nerve cells. Ouabain (10(-4)M) had no effect on this potassium-sensitive lithium uptake in Tyrode media. Sodium influx studied by isotope tracer methodology was higher in cultures preloaded with lithium as compared to that of the controls. It can be concluded that sodium and potassium ions, at physiological concentrations, significantly influence lithium uptake as well as the intra:extracellular lithium distribution in brain cell cultures.