Lithium slows neuronal calcium regulation in the snail Helix pomatia

Inhibitory effects of lithium ion on intracellular Ca2+ mobilization in the rat hippocampal slices

Lithium is well established as a treatment of manic-depressive illness. As for the mechanism of action of lithium, it is proposed that lithium has effects on intracellular calcium ion (Ca2+) movement. But there are few reports in which the effects of lithium on intracellular Ca2+ movement are observed in the mammalian brain. We therefore examined the effects of lithium on intracellular Ca2+ changes in the rat hippocampal slices with a Ca2+ sensitive dye fura-2, and analyzed by means of a fluorescence microscope, a video-camera and photometrical devices. From the results of treatment with various noradrenergic agonists or antagonists, noradrenaline (NA)-induced intracellular Ca2+ change appears to be mainly mediated by alpha 1-adrenoceptors (AR) rather than alpha 2- or beta-AR. Furthermore, they are considered to be mediated by both alpha 1A-AR and alpha 1B-AR, and to be partly dependent on extracellular Ca2+. Lithium decreased NA-induced intracellular Ca2+ mobilization by attenuation of T1/2 rather than a change in the peak value, and antagonized ouabain-induced intracellular Ca2+ increase. Lithium may therefore suppress intracellular Ca2+ movement by enhancing the extrusion of intracellular Ca2+.

Carbachol potentiates Q current and activates a calcium-dependent non-specific conductance in rat hippocampus in vitro

Intracellular recordings were made from CA1 neurons in rat hippocampal slices maintained in vitro. When Na+ currents were blocked with tetrodotoxin and K+ conductances known to be sensitive to suppression by muscarinic agonists were blocked by 2 mM Ba2+, CA1 cells were depolarized by carbachol (3-10 microM) with an attendant conductance increase, whereas prior to Ba2+ the agonist produced a decrease or no change in conductance. Under voltage clamp at approximately -60 mV and in the presence of tetrodotoxin and Ba2+, carbachol (3-10 microM) induced a variable-latency biphasic inward current of up to 380 pA associated with a conductance increase of approximately 50%. The first phase was associated with an increase (more than 2-fold) of the Cs(+)-sensitive, hyperpolarization-activated cationic current, IQ. Carbachol also accelerated the kinetics of IQ at -100 mV with an average 24% reduction in its activation time constant. The second phase reflected an additional inward current that was Cs(+)-resistant, displayed little apparent voltage sensitivity and had a mean extrapolated reversal potential, determined in the presence of external Cs+ (< or = 5 mM), of approximately -20 mV. In a small proportion of cells the second phase of inward current was followed (or overlapped) by an outward current, also associated with a conductance increase, which reversed at approximately -70 mV. These carbachol actions were prevented by extracellular 300 microM Cd2+ and 2 mM Mn2+, by high levels (> 5 mM) of extracellular Mg2+ or Ca2+, and by omission of Ca2+ or reduction of extracellular Na+ to 25 mM by substitution of NaCl with Tris or N-methyl-D-glucamine. Carbachol action was not mimicked by oxotremorine (< or = 60 microM), but was irreversibly blocked by this drug. Likewise, atropine (100 nM) irreversibly and gallamine (10 microM) reversibly antagonized carbachol's action. The action of carbachol was blocked shortly after prior exposure of slices to 2-5 mM caffeine. Chronic or acute incubation of slices with 2 mM Li+ potentiated (between 1- and 2-fold) carbachol responses. The data indicate that muscarinic activation increases cationic flux by a calcium-dependent potentiation of IQ and activation of a non-selective conductance. The probability that inositol phospholipid metabolism is involved in triggering these events is discussed.

Lithium treatment blocks long-term synaptic depression in the striatum

We have studied the effect of acute and chronic lithium treatment on the activity of striatal neurons recorded from corticostriatal slices. Under control conditions, tetanic stimulation of glutamatergic corticostriatal terminals caused long-term depression (LTD) of excitatory synaptic potentials. Acute lithium treatment did not affect the peak of the induction phase, but it reduced the following phases of LTD. LTD was completely blocked in slices obtained from rats chronically injected with LiCl. Lithium treatment failed to affect the intrinsic membrane properties of striatal neurons and the presynaptic inhibitory effects of carbachol and t-ACPD. We suggest that the lithium-induced blockade of LTD may contribute to the therapeutic action of lithium salts in mania and depression.

Acute effects of lithium on synaptic transmission in rat hippocampus studied in vitro

Acute effects of lithium on synaptic transmissions in the CA1 neurones of rat hippocampus were examined. Perfusion of 2-10 mM lithium chloride (LiCl) produced a dose-dependent increase in the amplitude of field EPSPs, whereas change in the population spikes was variable. The increasing ratio of second field EPSP, which was examined by paired-pulse stimulation, was reduced about 10% by 5 mM LiCl. Intracellularly recorded EPSPs and IPSPs were facilitated by 10 mM LiCl, and the soma membrane was depolarized about 3.2 mV. Intracellular calcium concentration was measured in single hippocampal neurones using fura-2. Although calcium concentration at rest was approximately 30 nM and was increased to an average of 220 nM by 10(-5) M glutamate, 10 mM LiCl had no influence on it. The effects of Li on calcium-dependent processes were not manifested in this study. Variable changes of population spikes may be dependent on the balance between the excitatory and inhibitory postsynaptic potentials during lithium application.

Lithium enhances neuronal muscarinic excitation by presynaptic facilitation

The mechanisms underlying the psychotropic actions of lithium are not established, but modulation of endogenous brain neurotransmitter systems is likely to be important. Several interactions of lithium with muscarinic responses have been reported, including a marked potentiation of seizures produced by muscarinic agonists. Because the mechanism by which lithium augments muscarinic seizures may be related to the mechanism by which it produces its psychotropic effects, we have studied the interaction of lithium and muscarinic agonists in vitro. Using rat hippocampal slices, we found that a muscarinic agonist, pilocarpine, increased postsynaptic neuronal excitability, but simultaneously decreased synaptic transmission because of presynaptic inhibition. Lithium did not alter pilocarpine's postsynaptic excitatory actions, but reversed its presynaptic inhibitory action, leading to markedly increased action potential firing. These presynaptic effects are not caused by alterations in presynaptic action potential shape or reliability of conduction, and do not involve pertussis toxin-sensitive G proteins. Activation of protein kinase C with phorbol-12,13-dibutyrate, or inhibition with H-7 and sphingosine, did not affect muscarinic presynaptic inhibition, but abolished lithium's ability to enhance synaptic transmission, suggesting that this effect of lithium involves protein kinase C. We propose that presynaptic facilitation accounts for lithium's potentiation of muscarinic seizures. Since these effects occur with concentrations of lithium used clinically, similar presynaptic effects in endogenous brain neurotransmitter systems may be important for lithium's psychotropic actions.

Effects of lithium on platelet ionic intracellular calcium concentration in patients with bipolar (manic-depressive) disorder and healthy controls

Lithium is an effective drug in the treatment of both manic and depressive episodes of bipolar disorder. Lithium has been shown to block the metabolism of the intracellular second messenger inositol-1,4,5-trisphosphate which is involved in the rise in ionic intracellular calcium [( Ca++]i) which triggers neurotransmitter release and other cellular changes in secretory cells. We have measured the effect of lithium on [Ca++]i dynamics in platelets from bipolar patients stabilized with lithium treatment, and from healthy controls. Both resting [Ca++]i and the thrombin stimulated increase in [Ca++]i were higher in bipolar patients than in controls. Lithium added in vitro tended to increase the thrombin-stimulated rise in [Ca++]i. The use of the fluorescent Ca++ probe fura-2 in human platelets provides a useful method to investigate the mechanism of lithium's action in bipolar disorder and to study Ca++ related systems which may be abnormal in bipolar disorders.

Effect of lithium on Schwann cell proliferation stimulated by axolemma- and myelin-enriched fractions

Cultured Schwann cells stimulated with an axolemma- or myelin-enriched fraction incorporated 2.5 to three times as much [3H]thymidine when 10 mM lithium was added to the extracellular medium. The ability of lithium to enhance the mitogenic activity of either fraction was dose dependent. This result was not due to an increase in osmolarity, because addition of 10 mM NaCl had no effect on the amount of labeled thymidine accumulated by Schwann cells treated with either membrane fraction. In an earlier study, the effect of either membrane fraction could be potentiated with active phorbol esters. Lithium significantly enhanced the incorporation of [3H]thymidine into Schwann cells treated with a myelin-enriched fraction and phorbol esters. In contrast, lithium slightly increased the amount of labeled thymidine incorporated into Schwann cells stimulated with an axolemma-enriched fraction and phorbol esters. The mitogenic activity of either membrane fraction was impaired when the calcium channel blockers Mn2+ and nifedipine were added. Addition of lithium stimulated an increase in the amount of [3H]thymidine accumulated by Schwann cells treated with either the axolemma- or myelin-enriched fraction in the presence of either Mn2+ or nifedipine.

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.