Regional and subcellular localization of Li+ and other cations in the rat brain following long-term lithium administration

Lithium alters regional rat brain myo-inositol at 2 and 4 weeks: an ex-vivo magnetic resonance spectroscopy study at 18.8 T

Lithium has been the mainstay of treatment for bipolar disorder. Early studies suggest that lithium acts via inositol depletion. This study assesses the effect of 1, 2 and 4 weeks of lithium treatment on myo-inositol concentrations across several brain regions. Thirty-six Sprague-Dawley rats were treated for 2 weeks with an intraperitoneal injection of either 1 mmol/kg/day, twice daily lithium chloride (n=18) or placebo (2 ml/kg of saline) (n=18). The rats were separated into three groups: 1 week, 2 weeks and 4 weeks. Brains were dissected into prefrontal, temporal and occipital cortical areas, as well as hippocampus, and analyzed at 18.8 T. Myo-inositol was quantified using the Chenomx Profiler software. Lithium did not alter myo-inositol concentrations at 1 week. A significant reduction exists in myo-inositol concentrations in lithium-treated rats at 2 and 4 weeks, across all four brain regions. Studies suggest brain region-specific alterations in myo-inositol concentrations among bipolar patients. Our findings suggest that lithium-induced reduction of myo-inositol is more global.

Chronic lithium treatment with or without haloperidol fails to affect the morphology of the rat cerebellum

We used unbiased stereological principles to determine whether long-term administration of lithium at human therapeutic levels, with or without haloperidol, affects the number or sizes of cerebellar Purkinje cells or the volume of histological layers in the rat cerebellum. Twenty-eight rats were randomly divided into three groups, receiving either no treatment, lithium, or lithium combined with haloperidol. The serum lithium levels ranged from 0.50 to 0.77 mmol/l. Haloperidol was given at a daily dose of 1 mg/kg. After 30 weeks of treatment, the animals were killed and the cerebelli were histologically prepared. No statistically significant differences were observed between the groups with respect to the cerebellar measures.

Lithium ions enhance cysteine string protein gene expression in vivo and in vitro

Lithium is a well established pharmacotherapy for the treatment of recurrent manic-depressive illness. However, the mechanism by which lithium exerts its therapeutic action remains elusive. Here we report that lithium at 1 mM significantly increased the expression of cysteine string proteins (CSPs) in a pheochromocytoma cell line (PC12 cells) differentiated by nerve growth factor. These cells concomitantly exhibited increased expression of CSPs in their cell bodies and boutons. Enhanced CSP expression was also observed in the brain of rats fed a lithium-containing diet, which elevated serum lithium to a therapeutically relevant concentration of approximately 1.0 mM. However, both in vitro and in vivo, the expression of another synaptic vesicle protein, synaptophysin, and the t-SNARE, synaptosomal-associated protein of 25 kDa (SNAP-25), was not significantly altered by lithium. These observations indicate that lithium-induced changes of CSP gene expression may contribute to the therapeutic efficacy of this monovalent cation.

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.

Lithium induced changes in intracellular free magnesium concentration in isolated rat ventricular myocytes

We have examined the effect of exposing isolated rat ventricular myocytes to lithium while measuring cytosolic free magnesium ([Mg2+]i) and calcium ([Ca2+]i) levels with the fluorescent, ion sensitive probes mag-fura-2 and fura-2. There was a significant rise in [Mg2+]i after a 5 min exposure to a solution in which 50% of the sodium had been replaced by Li+, but not when the sodium had been replaced by bis-dimethylammonium (BDA). However, there were significant increases in [Ca2+]i when either Na+ substitute was used. The possibility that Li+, which enters the cells, interferes with the signal from mag-fura-2 was eliminated as Li+ concentrations up to 10 mM had no effect on the dye's fluorescence signal. A possible explanation for these findings is that Li+ displaces Mg2+ from intracellular binding sites. Having considered the binding constants for Mg2+ and Li+ to ATP, we conclude that Li+ can displace Mg2+ from Mg-ATP, thus causing a rise in [Mg2+]i. This work has implications for other studies where Li+ is used as a Na+ substitute.

Competition between Li+ and Mg2+ in neuroblastoma SH-SY5Y cells: a fluorescence and 31P NMR study

Because Mg2+ and Li+ ions have similar chemical properties, we have hypothesized that Li+/Mg2+ competition for Mg2+ binding sites is the molecular basis for the therapeutic action of lithium in manic-depressive illness. By fluorescence spectroscopy with furaptra-loaded cells, the free intracellular Mg2+ concentration within the intact neuroblastoma cells was found to increase from 0. 39 +/- 0.04 mM to 0.60 +/- 0.04 mM during a 40-min Li+ incubation in which the total intracellular Li+ concentration increased from 0 to 5.5 mM. Our fluorescence microscopy observations of Li+-free and Li+-loaded cells also indicate an increase in free Mg2+ concentration upon Li+ incubation. By 31P NMR, the free intracellular Mg2+ concentrations for Li+-free cells was 0.35 +/- 0. 03 mM and 0.80 +/- 0.04 mM for Li+-loaded cells (final total intracellular Li+ concentration of 16 mM). If a Li+/Mg2+ competition mechanism is present in neuroblastoma cells, an increase in the total intracellular Li+ concentration is expected to result in an increase in the free intracellular Mg2+ concentration, because Li+ displaces Mg2+ from its binding sites within the nerve cell. The fluorescence spectroscopy, fluorescence microscopy, and 31P NMR spectroscopy studies presented here have shown this to be the case.

Synapse-specific accumulation of lithium in intracellular microdomains: a model for uncoupling coincidence detection in the brain

Lithium's therapeutic specificity for the treatment of bipolar disorder may be attributable in part to an ability to target sites where there are high levels of synaptic activity. We show that glutamate receptors expressed in oocytes are highly permeable to lithium. Mathematical simulations of Li+ diffusion in mature dendritic spines suggest that in the presence of 1 mM extracellular lithium one synaptic current can increase Li+ concentration in the spine head by 4 mM with a decay time constant of about 15-20 ms. Two or more current spikes will produce oscillations between 6 and 8 mM or potentially higher. These results predict that the local intracellular lithium in dendritic spines can rise to high enough levels to uncouple second messenger mechanisms of coincidence detection.

Four weeks' inhalation exposure of rats to p-cymene affects regional and synaptosomal neurochemistry

Long-lasting effects of inhalation exposure to p-cymene (p-isopropyl-toluene; CAS No. 99-87-6) on regional and subcellular brain neurochemistry were studied. Male Long-Evans rats were exposed to 0, 50, or 250 p.p.m. p-cymene 6 hr/day, 5 days/week for four weeks followed by an exposure-free period of 8 weeks. Synaptosomes were isolated from whole brain minus cerebellum and used as an ex situ model for in situ conditions at the level of the presynaptic nerve terminal. There was no persistent effect on wet weight (regional) or regional noradrenaline (NA), dopamine (DA), or 5-hydroxytryptamine (5-HT) concentrations owing to exposure. Yield of synaptosomal protein was statistically significantly reduced in an exposure concentration-related manner (Control: 16.6 +/- 3.1; 50 p.p.m.: 9.2 +/- 2.1; 250 p.p.m.: 8.6 +/- 1.7 mg protein/g tissue, mean +/- I.S.D.). Synaptosomal NA and DA concentrations and acethycholinesterase, butyrylcholinesterase, and lactate dehydrogenase activities were statistically significantly increased when expressed relative to synaptosomal protein. It is hypothesized that a reduced density and number of synapses in situ are functionally compensated for by increased NA and DA release from noradrenergic and dopaminergic presynaptic nerve terminals. The applicability of the synaptosome as an ex situ neurochemical research model for the presynaptic CNS nerve terminal in situ for the study of solvent neurotoxicity in rats was further supported.

Effect of chronic lithium treatment with or without haloperidol on number and sizes of neurons in rat neocortex

The present study used stereological methods to determine whether long-term administration of lithium, with or without haloperidol, affects the number and average volume of neocortical neurons. Twenty-five rats were divided into three groups and given no treatment, lithium, or lithium combined with haloperidol. Serum lithium levels ranged from 0.5 to 0.8 mmol/l. Haloperidol was injected intraperitoneally at a daily dose of 1 mg/kg. After 30 weeks of treatment, the animals were killed and the brains were prepared. Neocortical volume, density of neurons, total number of neurons and mean volume of neurons were estimated. As no differences were found between the groups, the present study provides no evidence for quantitative morphological changes in the cerebral cortex due to long-term 'therapeutic' levels of lithium, with or without haloperidol.