Effect of lithium on concentrations of glutamate and GABA levels in amygdala and hypothalamus of rat

Lithium Enhances the GABAergic Synaptic Activities on the Hypothalamic Preoptic Area (hPOA) Neurons

Lithium (Li+) salt is widely used as a therapeutic agent for treating neurological and psychiatric disorders. Despite its therapeutic effects on neurological and psychiatric disorders, it can also disturb the neuroendocrine axis in patients under lithium therapy. The hypothalamic area contains GABAergic and glutamatergic neurons and their receptors, which regulate various hypothalamic functions such as the release of neurohormones, control circadian activities. At the neuronal level, several neurotransmitter systems are modulated by lithium exposure. However, the effect of Li+ on hypothalamic neuron excitability and the precise action mechanism involved in such an effect have not been fully understood yet. Therefore, Li+ action on hypothalamic neurons was investigated using a whole-cell patch-clamp technique. In hypothalamic neurons, Li+ increased the GABAergic synaptic activities via action potential independent presynaptic mechanisms. Next, concentration-dependent replacement of Na+ by Li+ in artificial cerebrospinal fluid increased frequencies of GABAergic miniature inhibitory postsynaptic currents without altering their amplitudes. Li+ perfusion induced inward currents in the majority of hypothalamic neurons independent of amino-acids receptor activation. These results suggests that Li+ treatment can directly affect the hypothalamic region of the brain and regulate the release of various neurohormones involved in synchronizing the neuroendocrine axis.

Akkouh I, Hughes T, Frei E, A. Andreassen O, Djurovic S. Using iPSC Models to Understand the Role of Estrogen in Neuron-Glia Interactions in Schizophrenia and Bipolar Disorder

Schizophrenia (SCZ) and bipolar disorder (BIP) are severe mental disorders with a considerable disease burden worldwide due to early age of onset, chronicity, and lack of efficient treatments or prevention strategies. Whilst our current knowledge is that SCZ and BIP are highly heritable and share common pathophysiological mechanisms associated with cellular signaling, neurotransmission, energy metabolism, and neuroinflammation, the development of novel therapies has been hampered by the unavailability of appropriate models to identify novel targetable pathomechanisms. Recent data suggest that neuron-glia interactions are disturbed in SCZ and BIP, and are modulated by estrogen (E2). However, most of the knowledge we have so far on the neuromodulatory effects of E2 came from studies on animal models and human cell lines, and may not accurately reflect many processes occurring exclusively in the human brain. Thus, here we highlight the advantages of using induced pluripotent stem cell (iPSC) models to revisit studies of mechanisms underlying beneficial effects of E2 in human brain cells. A better understanding of these mechanisms opens the opportunity to identify putative targets of novel therapeutic agents for SCZ and BIP. In this review, we first summarize the literature on the molecular mechanisms involved in SCZ and BIP pathology and the beneficial effects of E2 on neuron-glia interactions. Then, we briefly present the most recent developments in the iPSC field, emphasizing the potential of using patient-derived iPSCs as more relevant models to study the effects of E2 on neuron-glia interactions.

Metabonomic analysis identifies molecular changes associated with the pathophysiology and drug treatment of bipolar disorder

Bipolar affective disorder is a severe and debilitating psychiatric condition characterized by the alternating mood states of mania and depression. Both the molecular pathophysiology of the disorder and the mechanism of action of the mainstays of its treatment remain largely unknown. Here, (1)H NMR spectroscopy-based metabonomic analysis was performed to identify molecular changes in post-mortem brain tissue (dorsolateral prefrontal cortex) of patients with a history of bipolar disorder. The observed changes were then compared to metabolic alterations identified in rat brain following chronic oral treatment with either lithium or valproate. This is the first study to use (1)H NMR spectroscopy to study post-mortem bipolar human brain tissue, and it is the first to compare changes in disease brain with changes induced in rat brain following mood stabilizer treatment. Several metabolites were found to be concordantly altered in both the animal and human tissues. Glutamate levels were increased in post-mortem bipolar brain, while the glutamate/glutamine ratio was decreased following valproate treatment, and gamma-aminobutyric acid levels were increased after lithium treatment, suggesting that the balance of excitatory/inhibitory neurotransmission is central to the disorder. Both creatine and myo-inositol were increased in the post-mortem brain but depleted with the medications. Lastly, the level of N-acetyl aspartate, a clinically important metabolic marker of neuronal viability, was found to be unchanged following chronic mood stabilizer treatment. These findings promise to provide new insight into the pathophysiology of bipolar disorder and may be used to direct research into novel therapeutic strategies.

Effect of Lithium on Rat Cerebrum Under Different Dietary Protein Regimens

This study was designed to investigate the effects of lithium in adult rat brain under different dietary protein regimens. Lithium as carbonate was given at a dose of 1.1 g/kg diet to female rats fed normal (18% protein), low protein (8% protein), and high protein (30% protein) diets for 30 days. Lithium treatment resulted in a significant decrease in the levels of norepinephrine, dopamine, and serotonin in the cerebrum of the rat brain. Further, administration of lithium to rats fed low protein (LP) and high protein (HP) diets also showed a significant decrease in the levels of norepinephrine and dopamine but caused no significant change in the serotonin concentration. Lithium administration to normal diet, LP, and HP groups resulted in a significant increase in the activities of acetylcholinesterase and monoamine oxidase. Lithium treatment led to decrease in the activity of enzyme Na+ K+ ATPase in all groups. On the second day, the LP group showed enhanced transfer latency (TL), a dependent variable to study elevated plus-maze test, whereas HP diet went from 34% reduction to normal. On the other hand, lithium administration restored the already enhanced TL in the LP group. The study concludes that lithium treatment to protein-deficient cases may not further aggravate the effects of protein-deficient conditions, but it may afford protection.

Magnetic resonance spectroscopic measurement of cerebral gamma-aminobutyric acid concentrations in patients with bipolar disorders

BACKGROUND

Animal models of depression and psychopharmacological mechanisms of action suggest the importance of the gamma-amino butyric acid (GABA) system in the pathophysiology of mood disorders. Mood stabilizers have overlapping effects on GABAergic neurotransmission, and antidepressant use has been associated with alterations in GABAB receptor function. Magnetic resonance spectroscopy (MRS) provides an opportunity to noninvasively assess cerebral GABA concentrations in anterior paralimbic circuits that have been implicated in mood disorders.

METHODS

In bipolar disorder patients and healthy control subjects, we used MRS with a modified GABA-edited point resolved spectroscopy sequence (TE 68 ms, TR 1500 ms, 512 averages, total scan time 26 min) to assess GABA in an 18-cm3 occipital voxel. In addition, in another cohort of bipolar disorder patients and healthy control subjects, we similarly assessed GABA in a 12.5-cm3 medial prefrontal/anterior cingulate (MPF/AC) voxel. The concentration of GABA was referenced to creatine (Cr) from unedited spectra.

RESULTS

In bipolar patients and controls, we consistently detected 3.0 p.p.m. GABA peaks in occipital lobe and MPF/AC. In 16 bipolar (nine bipolar I and seven bipolar II) disorder patients, compared with six healthy control subjects, mean occipital GABA/Cr concentration was 61% higher. In addition, in 15 bipolar (five bipolar I, nine bipolar II, and one bipolar not otherwise specified) disorder patients, compared with six healthy control subjects, mean MPF/AC GABA/Cr concentration tended to be 41% higher.

CONCLUSIONS

Patients with bipolar disorders may have increased cerebral GABA concentrations. Although this was more evident in the occipital lobe, MPC/AC GABA disturbance may be of greater potential interest in view the more established role of MPF/AC in affective processing. Additional studies are warranted to assess changes in GABAergic neurotransmission and the influences of diagnosis, mood state, and medication status in bipolar disorder patients.

Lithium reduced synaptic transmission and increased neuronal excitability without altering endogenous serotonin, norepinephrine and dopamine in rat hippocampal slices in vitro

1. Extracellular field potentials were recorded in the CA1 pyramidal cell layer following stimulation of stratum radiatum in rat hippocampal slices during superfusion with different concentrations (1, 2, 5, 10, 20, and 30 mM) of lithium (Li+). Control slices were exposed similarly to choline (Ch+) or sodium (Na+). 2. At high concentrations (greater than or equal to 10 mM), Li+, Ch+ and Na+ reduced the amplitude of the field excitatory postsynaptic potential (EPSP). However, Li+ increased, whereas Ch+ and Na+ reduced the population spike amplitude. Thus, Li+ specifically enhanced the excitability of CA1 pyramidal cells. 3. Electrophysiologically monitored slices, plus an additional group exposed to Li+, Ch+ or Na+ without concomitant field potential recordings, were processed for measurement of endogenous levels of serotonin (5-HT), norepinephrine (NE) and dopamine (DA). The mean endogenous levels of 5-HT and NE were not significantly different in 1-30 mM Li+, Ch+ and Na+. Dopamine contents were unchanged after exposure to Li+ and Na+, but were reduced by Ch+. 4. The non-specific effects of Li+ on synaptic transmission and its specific effects on neuronal excitability appeared independent of changes in endogenous 5-HT, NE and DA levels.

Chronic lithium treatment and status epilepticus induced by lithium and pilocarpine cause selective changes of amino acid concentrations in rat brain regions

We measured the effects of four weeks of dietary lithium treatment and of status epilepticus induced by administration of pilocarpine to lithium-treated rats on the concentrations of amino acids in four regions of rat brain: cerebral cortex, hippocampus, striatum, and substantia nigra. To ensure accurate quantitation of the amino acids, animals were sacrificed by focussed beam microwave irradiation and amino acids were measured using a fully validated triple-column ion-exchanged amino acid analyzer with post-column o-phthalaldehyde derivatization and fluorometric detection. The concentrations of four amino acids, threonine, methionine, lysine and tyrosine, were increased significantly in two to four brain regions by chronic lithium treatment. Their concentrations remained elevated, or were further increased, during status epilepticus. The concentrations of eight amino acids and ammonia were not altered by lithium treatment but increased in concentration during status epilepticus in some brain regions. Glycine, serine, arginine and citrulline were decreased by chronic lithium treatment. Status epilepticus increased the concentrations of these four amino acids above that found in the lithium-treated samples in some of the brain regions that were examined. Six amino acids and glutathione were generally unaltered by both treatments. These results are related to the effects of lithium treatment and are compared with changes reported by others following treatment with a variety of convulsive stimuli.

Perfusion with lithium modifies neurophysiological responses in the CA1 region of the hippocampal slice preparation

The effects of acute lithium exposure on extracellular electrophysiological responses in the CA1 region of the in vitro hippocampus were investigated. Field potentials were assessed while perfusing slices with normal media or media in which LiCl was substituted for NaCl in 30, 20, 10 and 2 mM amounts. Lithium concentration in the slice following 20 min perfusion with 20 mM lithium was determined to be about 14 mM. At the higher concentrations, lithium exposure depressed the presynaptic fiber volley and antidromic population spike. On the other hand, the population EPSP and orthodromic population spike were enhanced. No significant changes were found at 2 mM. The findings are compatible with one action of lithium being on the excitability of axons and synaptic terminals. Comparisons were drawn between previous studies involving chronic lithium exposure and the present results. In this acute preparation lithium effects, as reflected in the population EPSP, were in opposition to those found with chronic lithium exposure. Changes demonstrated in this preparation in fiber volley and antidromic population spike paralleled those found with chronic lithium exposure.

Lithium mechanisms in bipolar illness and altered intracellular calcium functions

Calcium functions as an intracellular second messenger, transducing a variety of hormonal, electrical, and mechanical stimuli by activating a wide range of enzymes. There is evidence, ranging from definitive to strongly presumptive in quality, that lithium can alter many calcium-dependent processes. The list of enzyme systems dependent on calcium and altered by lithium includes adenylate cyclase, glycogen synthase, inositol-1-phosphatase, and calcium adenosine triphosphatase (ATPase). Lithium also interferes with calcium regulation of receptor sensitivity, parathyroid hormone release, microtubule structure, and other systems. All of the neural mechanisms that are hypothesized to explain various psychopharmacological treatments of bipolar illness involve functions that are critically controlled by calcium. Moreover, in every instance, a known action of lithium on calcium function could account for lithium's therapeutic or prophylactic results. From these considerations the dual hypotheses emerge that bipolar illnesses arise from disorders in calcium-regulated functions and that lithium acts by reversing or counterbalancing the effects of these calcium dysfunctions.

GABA and circadian timekeeping: implications for manic-depression and sleep disorders

Circadian rhythms, evident in a wide variety of physiological and behavioural parameters, are under the control of central neural pacemakers, the best characterized of which is the suprachiasmatic nucleus of the hypothalamus. The neurophysiological mechanisms involved in central pacemaker function are unknown. Recent biochemical, pharmacological and behavioural evidence suggests that the inhibitory transmitter gamma-aminobutyric acid (GABA), present in the small interneurones of the suprachiasmatic nucleus, plays an important role in circadian timekeeping. This has enabled the formulation of strategies for treatment of patients with manic depressive illness and certain sleep disorders in which disorders of circadian timekeeping may be fundamental.

Clinical and neuropathological aspects of long-term damage to the central nervous system after lithium medication

A female patient, who died at the age of 61 and had suffered from several manic-depressive psychoses for more than 30 years, developed three phases of intoxication under lithium therapy. There was a 15-year history of electro- and Pentetrazol-induced convulsive therapy prior to lithium medication; neuroleptics were still administered during lithium therapy. The last lithium intoxication, 3 years prior to death was during a low-dosage therapy with normal lithium levels followed by severe lasting impairment: akinesia, rigidity, dysarthria, ataxia, and an organic alteration in character. For the first time, neuropathological findings could be established in such a case: extensive damage to granule and Purkinje cells in the cerebellum; gliosis in the dentate nucleus, the inferior olives, and the nucleus ruber; cytoplasmic inclusions in various nerve cells of the cranial nerve nuclei; cytoplasmic vacuoles, especially in the cells of the supra-optic nucleus. Surprisingly little damage could be found in the substantia nigra and in the neostriatum. The clinical course as well as the pattern and intensity of the brain damage oppose an interpretation as a consequence of preceding convulsive shock therapy.

Lithium effects on rat brain glucose metabolism in long-term lithium-treated rats studied in vivo

The time course of lithium effects on several brain energy metabolites has been investigated in rats. The rats were injected once daily with lithium chloride and killed by freezing in liquid nitrogen 1--8 h after the last injection. The effect of lithium was most marked in the period in which the brain lithium concentration was increasing, whereas the effect was wearing off when the brain lithium concentration had stabilized, even though the lithium concentration was higher. These results led to the hypothesis that the effect of lithium on several parameters depends on the increase in lithium concentration following the administration of lithium, rather than on the absolute concentration of lithium.

Lithium protection against oxygen toxicity in rats: ammonia and amino acid metabolism

1. The use of Li pre-treatment in rats before high pressure oxygen exposure has been reported effective in controlling convulsions. This is an effect which is better demonstrated if exposure to oxygen follows shortly after Li injection than exposure following several hours later. 2. This study has investigated the hypothesis that the protective action of Li may be exerted, in the short term, by its removing ammonia from the blood and alleviating the latter's known toxic action. 3. A normal Li distribution time profile in unstressed rat brain and blood following intraperitoneal injection has been established. Brain and blood ammonia, amino acids and Li concentrations were also measured in Li-treated animals exposed and convulsed by oxygen. These measurements were made both shortly (15 min) and also several hours after (24 hr) Li treatment. Ammonia and amino acid values in Li-protected groups were compared to normal unstressed animal values and also to values in animals convulsed by oxygen unprotected by Li pre-treatment. 4. In rat brain abd blood significant (P less than 0-001) elevation of ammonia and glutamine and depression of gamma-amino butyric acid (brain only) and glutamate was noted following oxygen treatment in unprotected animals. Prior injection of Li 15 min before high pressure oxygen exposure delayed convulsions twice as long. Additionally if these animals were only exposed to oxygen for a period of time equal to that which would normally produce convulsions in unprotected animals, brain and blood ammonia and amino acids were maintained near to unstressed animal levels. Concomitantly, blood Li concentrations were considerably depressed below the values one would expect from the previously determined Li distribution time profile. 5. In rats exposed to high pressure oxygen 24 hr after Li treatment there was no protective action against high pressure oxygen convulsion, rather a potentiating effect for convulsion was seen. 6. These data present compelling evidence for the controlling effect of Li in rats, on rising blood ammonia concentration which occurs in high pressure oxygen exposure. The effect might well be due to the known chelating properties of Li with ammonia.

Effect of lithium and other alkali metals on brain chemistry and behavior. I. Glutamic acid and GABA in brain regions

Glutamic acid and GABA concentrations were measured in brain areas of rats injected with the chloride salts of Li+, Na+, K", Rb+ or Cs+ for 5 days. Regional changes in brain glutamic acid and GABA were found in animals after lithium, rubidium or cesium, but not potassium, compared to sodium treatments. Increased glutamic acid and GABA levels, caused by lithium and rubidium, were found in brain structures (hypothalamus and amygdala) known to be involved in emotional behavior. Whether these changes are associated with the effective use of lithium and, perhaps, of rubidium in affective disorders remains obscure.

Inhibition of L-alanine aminotransferase by lithium salts

Pharmacologic concentrations of either LiCl, LiN03 and LiF or the lithium salts of pyruvic or glutamic acids inhibit the formation of alanine arising from the transamination of glutamate in the presence of pyruvate. Lithium pyruvate is the most effective inhibitor, while the addition of K+ to the incubation reaction can effectively reduce this inhibition. Some possible modes of action of the lithium ion is presented.