Lithium ions have a potent and selective inhibitory effect on cyclic GMP formation stimulated by neurotensin, angiotensin II and bradykinin

The NMDA receptor/nitric oxide pathway: a target for the therapeutic and toxic effects of lithium

Although lithium has largely met its initial promise as the first drug discovered in the modern era of psychopharmacology, to date no definitive mechanism for its effects has been established. It has been proposed that lithium exerts its therapeutic effects by interfering with signal transduction through G-protein-coupled receptor (GPCR) pathways or direct inhibition of specific targets in signaling systems, including inositol monophosphatase and glycogen synthase kinase-3 (GSK-3). Recently, increasing evidence has suggested that N-methyl-D-aspartate receptor (NMDAR)/nitric oxide (NO) signaling could mediate some lithium-induced responses in the brain and peripheral tissues. However, the probable role of the NMDAR/NO system in the action of lithium has not been fully elucidated. In this review, we discuss biochemical, preclinical/behavioral and physiological evidence that implicates NMDAR/NO signaling in the therapeutic effect of lithium. NMDAR/NO signaling could also explain some of side effects of lithium.

The effect of lithium chloride on morphine-induced tolerance and dependence in isolated guinea pig ileum

The chronic use of opioids is often accompanied by the development of tolerance and/or dependence upon these agents due to the adaptive changes in the response of the subject to the agent. On cellular level, these phases of altered responsiveness have been shown to be the sequelae of a combination of multiple independent components acting in concert. Changes in the number, affinity, or membrane trafficking of opioids receptors, the coupling of receptors to G-proteins or in associated second messenger systems have been implicated in underlying the aforementioned phenomena. Several observations have been shown that lithium is able to contradict the expected response in animals pre-treated with morphine. These facts clearly manifest the involvement of lithium in at least one of the diverse pathways that lead to morphine dependence and/or tolerance. The aim of the present study was to investigate the effect of lithium on acute morphine-induced tolerance and dependence in an in vitro model of isolated guinea pig ileum which has been extensively used for the assessment of these effects of opioids. Morphine inhibited electrically stimulated twitch of ileum in a concentration-dependent manner (pD(2)=7.27+/-0.16). Tolerance to this effect was induced by the incubation of ileum with 2xIC(50) of morphine for 2 h that induced a degree of tolerance of 14.7. The co-incubation of ileum with morphine along lithium chloride (1 mM) reduced the degree of tolerance significantly (P<0.001) and restored the sensitivity of ileum to the morphine inhibitory effect. Lithium chloride can also reduce the expression of tolerance to morphine significantly (P<0.01). Dependence was induced by incubation with 4xIC(50) of morphine for 2 h and was assessed based on naloxone-induced contractions (10(-5 )M). Lithium chloride (1 mM) can attenuate the development but not the expression of dependence to morphine as shown by the significant decrease in naloxone-induced contractions (P<0.05). These results suggest that lithium chloride can reduce the development and expression of acute tolerance to and development of dependence on morphine in the myenteric plexus of guinea pig ileum.

Inhibition of the morphine withdrawal syndrome and the development of physical dependence by lithium in mice

Due to the claim that lithium (Li+) reduces morphine self-administration in dependent rats, the effects of acute and chronic Li+ treatments on naloxone-precipitated withdrawal syndrome and physical dependence development to morphine in mice chronically treated with morphine, were evaluated. Morphine dependency was induced by the ingestion of morphine through drinking water in increasing doses for 10 days. Physical dependence to morphine was observed by precipitating an abstinence syndrome with naloxone (2 mg/kg, i.p.). In the acute experiments, Li+ (1 and 10 mg/kg, i.p.) was administered 1 hr prior to challenge with naloxone to morphine-dependent mice whereas for chronic studies, mice received morphine concomitant with Li+ (1200 mg/l) as drinking fluid for 10 days. Results obtained indicate that acute Li+ administration significantly reduced the withdrawal signs, and we were unable to induce some degree of morphine dependency in co-administration of Li+ to mice receiving chronic morphine treatment as compared to chronic morphine administration alone. The present study revealed that even in mice with very much lower serum Li+ levels than the commonly accepted therapeutic range there was a significant reduction in the withdrawal signs. It has been shown that Li+ and morphine have diverse effects on the transmembrane signal control systems. The interaction of Li+ and morphine might be through these systems.

Lithium lengthens the period of circadian rhythms in lesioned hamsters bearing SCN grafts

Lithium lengthens the free-running period of circadian rhythms in a wide variety of organisms. The object of the present study was to examine the effects of lithium treatment on free-running activity rhythms in suprachiasmatic nuclei lesioned (SCN-X) hamsters that had recovered circadian rhythmicity following transplantation of fetal anterior hypothalamic grafts containing the suprachiasmatic nuclei (SCN). The animals were housed individually in cages equipped with running wheels, and locomotor activity was monitored using a computer-based data acquisition system. At the end of the behavioral tests, animals were anesthetized and perfused. Brain sections were immunostained for vasoactive intestinal peptide (VIP) and vasopressin-associated neurophysin (NP) to evaluate the extent of the lesion and the presence of a functional graft. In both intact and in SCN-X grafted animals, lithium lengthened the period of free running activity without affecting the amount of activity or the precision of the rhythm.

Inositol trisphosphate, cyclic AMP, and cyclic GMP in rat brain regions after lithium and seizures

The mechanism of action of lithium, the primary treatment for bipolar affective disorder, is unknown but may involve inhibition of second messenger production in the brain. Therefore, the concentrations of three second messengers, inositol 1,4,5 trisphosphate (Ins 1,4,5P3), cyclic adenosine monophosphate (AMP), and cyclic guanosine monophosphate (GMP), were measured in rat cerebral cortex and hippocampus after acute or chronic lithium administration, as well as after treatment with the cholinergic agonist pilocarpine alone or in combination with lithium at a dose that induces seizures only in lithium pretreated rats. Neither acute nor chronic lithium treatment altered the hippocampal or cortical concentration of Ins 1,4,5P3, cyclic AMP, or cyclic GMP. Pilocarpine administered alone increased Ins 1,4,5P3 in both regions, did not alter cyclic AMP, and slightly increased cyclic GMP in the cortex. Coadministration of lithium plus pilocarpine caused large increases in the concentrations of all three second messengers and the production of each of them was uniquely attenuated: lithium reduced pilocarpine-induced increases of Ins 1,4,5P3 in the cortex at 60 min; chronic lithium administration reduced stimulated cyclic AMP production in the hippocampus; and chronic lithium treatment impaired stimulated cyclic GMP production in both regions. In summary, chronic lithium treatment appeared only to reduce Ins 1,4,5P3 and cyclic AMP concentrations after a long period of stimulation whereas cyclic GMP production was reduced by chronic lithium administration after both short and long periods of stimulation. Thus cyclic GMP was most sensitive to lithium and lithium attenuation of second messenger formation may be most important in excessively activated pathways.

Angiotensin II and atrial natriuretic factor receptor interactions at the blood-brain barrier

Data from several laboratories indicate that cerebral endothelial cells possess cell surface receptors for numerous vasoactive agents including angiotensin II (AII) and atrial natriuretic factor (ANF). The intracellular messengers of these receptors as well as possible receptor interactions were explored. ANF increased cGMP 10-fold over basal levels while incubation of the microvessels with AII did not significantly affect the level of this nucleotide. In contrast, AII significantly potentiated the increase in cGMP by ANF. Incubation of cerebral microvessels with AII resulted in a significant increase in the intracellular mediator of PI hydrolysis, 1,2-diacylglycerol (DG). ANF had no affect on DG or on the AII mediated increase of DG. Finally, data at the level of receptor binding indicated that while ANF decreased [3H]angiotensin binding to cerebral microvessels, AII had no effect on the binding of ANF to its receptor. The results of the present study demonstrate that AII can potentiate the regulation of cGMP by ANF and suggest the possibility of receptor interactions in control of blood-brain barrier function.

Potentiation by a sodium channel activator of effects of lithium ion on cyclic AMP, cyclic GMP and inositol phosphates

The effects of the lithium ion (Li+) on receptor-mediated synthesis of second messengers were determined, when cellular sodium channels were quiescent or excited, using the murine neuroblastoma clone (N1E-115). In this clone, lithium inhibited the receptor-mediated synthesis of cyclic AMP and cyclic GMP and it also increased the accumulation of inositol phosphates by a receptor-mediated process. When veratridine (20 microM) excited the sodium channel, the effects of lithium were potentiated. However, tetrodotoxin, a sodium channel blocker, completely prevented this potentiation. These results suggest that when neurons are depolarizing actively and intraneuronal levels of lithium increase by entry through the sodium channel, lithium has a more potent intracellular effect. As a result, lithium would have more potent and selective effects in those pathologically-active neurons underlying manic-depressive disorder.

Therapeutic concentrations of lithium and carbamazepine inhibit cGMP accumulation in human lymphocytes. A clinical model for a possible common mechanism of action?

Although a large variety of biochemical effects have been reported for lithium (Li) and carbamazepine (Cbm), the final molecular mechanism underlying their therapeutic efficacy for recurrent affective disorders is still unknown. The data presented here clearly indicate that therapeutic concentrations of both drugs inhibit sodium nitroprusside-induced accumulation of cGMP in human lymphocytes to about the same extent. The effect is not seen for other antidepressants, and shows pronounced interindividual variations in healthy volunteers. A similar effect of lithium and carbamazepine can also be demonstrated for the cGMP accumulation of central neurons using the model of dissociated cells of the mouse brain. The results are discussed in view of a common mechanism of action of both drugs. Furthermore, it is speculated that the individual sensitivity of the cGMP generating system of human lymphocytes to both drugs might be used to predict therapeutic response or nonresponse of the individual patient.

Mode of action of lithium in affective disorders. An influence on intracellular calcium functions

The inference that lithium acts by altering intracellular calcium functions is supported by the three areas considered above. First, recent work in other laboratories has broadened the range of lithium actions on calcium-dependent physiological functions. Second, a theoretical analysis of the coupling of calcium transport to the triphosphoinositide response presents a plausible mechanism by which lithium could limit the damage caused by deficient calcium transport. Third, we have recently reported that there is a direct enhancement of the calmodulin-activated membrane-bound calcium pump in lithium-treated bipolar subjects.

Lithium modulation of cortical cyclic nucleotides: evidence for the Yin-Yang hypothesis

Rats were subjected to chronic treatment with lithium chloride (0.2-0.3%) over a period of 3 weeks. The activity of cortical phosphodiesterase (EC 3.1.4.17) was determined simultaneously with cyclic AMP and cyclic GMP content and compared to control, untreated animals. Lithium, at therapeutic serum concentrations was found to suppress cyclic AMP levels with a concomitant increase in cyclic AMP-phosphodiesterase activity. A simultaneous two-fold increase in cyclic GMP was observed. Through the alteration of cortical cholinergic activity with physostigmine and the use of cyclic GMP as a cholinergic marker, we were able to demonstrate a novel cholinotropic property of lithium to stimulate synthesis of cyclic GMP. This effect appears to be linked, in a Yin-Yang mechanism, to the observed suppression of cyclic AMP induced by lithium through activation of cyclic AMP-phosphodiesterase.

Comparison of the stimulation of inositol phospholipid hydrolysis and of cyclic GMP formation by neurotensin, some of its analogs, and neuromedin N in neuroblastoma clone N1E-115

Neurotensin, some of its analogs, and neuromedin N were examined for comparison of their potencies at stimulating inositol phospholipid hydrolysis and cyclic GMP synthesis in intact murine neuroblastoma cells (clone N1E-115). Neurotensin(8-13) and acetylneurotensin(8-13) had the highest potencies for the stimulation of the hydrolysis of inositol phospholipid, which were about three times as potent as neurotensin (EC50 = 0.9 nM). On the other hand, fragments of the amino-terminal portion of neurotensin, such as neurotensin(1-6), neurotensin(1-8) and neurotensin(1-11), showed no ability to stimulate this hydrolysis. Neuromedin N, which is similar in structure to neurotensin(8-13) and which has been demonstrated to stimulate cyclic GMP formation [J.A. Gilbert and E. Richelson, Eur. J. Pharmac. 129, 379 (1986)], had EC50 values of 2.5 and 4.5 nM for release of [3H]inositol phosphates and stimulation of cyclic [3H]GMP respectively. A strong correlation was obtained between the EC50 values for neurotensin and several analogs in the stimulation of the release of inositol phosphates and the EC50 values for these peptides in the stimulation of cyclic GMP formation in neuroblastoma clone N1E-115 cells under similar experimental conditions. Thus, these two different biochemical effects of neurotensin and its analogs appear to be mediated by the same receptor site, which may also have been the site of action of neuromedin N in these cells.