Monoamine uptake into synaptosomes from various regions of rat brain following lithium administration and withdrawal

A Positron Emission Tomography Study of Dopamine Transporter Density in Patients With Bipolar Disorder With Current Mania and Those With Recently Remitted Mania

Importance

Although dopamine is implicated in the pathophysiology of bipolar disorder (BD), the precise alterations in the dopaminergic system remain unknown.

Objective

To assess dopamine transporter (DAT) density in the striatum in patients with BD with current and recently remitted mania in comparison to healthy control individuals and its correlation with severity of manic symptoms.

Design, Setting, and Participants

This cross-sectional study conducted in a tertiary care referral center for mood disorders in Vancouver, British Columbia, Canada, recruited 26 patients with BD (9 with current mania; 17 with recently remitted mania) and 21 matched healthy control individuals. DAT density was measured using positron emission tomography with [11C]d-threo-methylphenidate (MP). The differences between the groups in nondisplaceable binding potential (BPND) for DAT was assessed using statistical parametric mapping. The study was conducted from November 2001 to February 2007 and the data were analyzed from November 2020 to December 2021.

Main Outcomes and Measures

DAT density as indexed by BPND for MP across groups; manic symptom severity as measured with the Young Mania Rating Scale (YMRS) and correlated with BPND values in patients with BD.

Results

Of 47 total participants (mean [SD] age, 37.8 [14.4] years), 27 (57.4%) were female; 26 individuals had BD (9 with current mania and 17 with recently remitted mania) and there were 21 healthy control individuals. MP BPND was significantly lower in patients with BD in the right putamen and nucleus accumbens (mean reduction [MR] = 22%; cluster level familywise error [FWE]-corrected P < .001) as well as left putamen and caudate (MR = 24%; cluster level FWE-corrected P < .001). The reduction in BPND was more extensive and pronounced in patients with current mania, while patients with recently remitted mania had lower BPND in the left striatum but not the right. There was a significant negative correlation between YMRS scores and MP BPND in the right striatum in patients with current mania (ρ = -0.93; 95% CI, -0.99 to -0.69; P < .001) and those with recently remitted mania (ρ = 0.64; 95% CI, -0.86 to -0.23; P = .005) but not in the left striatum in either group.

Conclusions and Relevance

These findings indicate that mania was associated with reduced DAT density and remitted mania was associated with DAT levels that approximated those present in individuals without BD. These results have potential implications for drug development for mania.

Neuropharmacological profile of a selective sigma ligand, igmesine: a potential antidepressant

Igmesine is a selective sigma (sigma(1)) ligand that was reported to exert antidepressant action through an unknown mechanism of action. A number of neurochemical measures were taken in this study in efforts to understand its mode of action. Following 21-day drug treatments, the actions of igmesine on a number of neurochemical measures were investigated. Data obtained showed significant decreases in the densities of beta-adrenergic but not 5-HT(1A), sigma(1) and GABA(B) receptors in fluoxetine (18%), desipramine (DMI, 32%) and igmesine (20%)-treated groups when compared with control. Tyrosine hydroxylase (TH) activity was significantly (30-32%) reduced in all treated groups. Further, fluoxetine and DMI excluding the igmesine-treated groups showed 85 and 40% reductions in serotonin (5-HT) and noradrenaline (NE) neuronal uptake, respectively. Following acute treatment, igmesine lacked activity for monoamine oxidase (MAO) A or B (IC(50)>10 microM). In in vivo studies, at behaviorally active doses, igmesine showed weak effects on the NE uptake but lacked activity in altering 5-HT and DA synthesis or antagonizing selective drug-induced depletion of monoamine neuronal uptake. N-methyl-D-aspartate (NMDA)-induced increases in cGMP was blocked by igmesine indicating that igmesine may interfere with the NMDA receptor/nitric oxide synthase/cGMP pathway. Although it appears that part of the pharmacological actions of igmesine is mediated by the monoaminergic system, there is still need to explore other possible mechanisms of antidepressant action.

Effects of a chronic lithium treatment on central dopamine neurotransporters

The objectives of this study were to characterize the effects of a chronic lithium (Li+) treatment on dopamine (DA) uptake sites, as well as on the levels of mRNA encoding for these transporters, and to determine the eventual reversibility of the treatment. Quantitative autoradiography was carried out on sections from rat brain using 3beta-(4-[125I]iodophenyl)tropane-2beta-carboxylic acid isopropyl ester ([125I]RT1-121) to label DA transporters, and mRNA levels were measured by in situ hybridization. Following chronic Li+ treatment (28 days), the labelling to DA transporters increased (60-90%) in all sections of the rostral and caudal neostriatum, whereas no alteration was observed in the other regions studied, namely the substantia nigra, the ventral tegmental area, and the dorsal raphe nucleus. These effects were reversed completely following a withdrawal period of 2 days without Li+. Also, there were no modifications in the labelling of DA transporters after only 2 days of Li+ treatment. In addition, we measured the levels of mRNA encoding for DA transporters in the substantia nigra and the ventral tegmental area; however, no alterations were observed following a chronic Li+ treatment, and thus the hypothesis of an increased synthesis is not supported. This could mean that the Li+ treatment modified the affinity of DA transporters for the radioligand, possibly a consequence of conformational changes induced by the disruption of the nerve terminal membrane environment; however, a modification in the number of transporters could not be ruled out. The results of this study further support the hypothesis of the implication of central dopaminergic transmission in the pathology and treatment of affective disorders.

Li+ stimulates ATP-regulated dopamine uptake in PC12 cells

Increased levels of dopamine have been associated with schizophrenia and mania; conversely, decreased levels of dopamine are associated with depression. Since the main mechanism for the termination of dopamine's pharmacological action is by re-uptake into the presynaptic cell, the speed of dopamine transport dramatically influences the concentration of dopamine present in the synaptic cleft, which in turn could determine brain disorders. Our preliminary studies have found that ATP can stimulate dopamine transport in rat synaptosomal preparation. We have also observed this ATP-regulated moiety of the dopamine uptake system when tested in PC12 cells. The large magnitude of ATP stimulation suggests that this dopamine uptake pathway may be important in the etiology and treatment of brain disorders. In order to test the relevance of ATP-stimulated dopamine uptake, we tested the effect of lithium salts on this system. Lithium chloride, one of the first drugs used in the treatment of mania, has become one of the most important agents utilized for the treatment of manic-depression and many schizoeffective disorders. Unfortunately, despite all efforts that have been made to explain lithium's mode of action, a clear cut biochemical mechanism has not been defined. We have found that lithium chloride, at therapeutic levels, is able to stimulate the ATP-regulated component of the dopamine uptake system by 49%. The further enhancement of dopamine re-uptake by lithium ions is consistent with its therapeutic effect. It is suggested that any substance that facilitates dopamine re-uptake could be of great importance in defining a useful treatment for mania and schizophrenia, as well as depression.

Lithium and serotonin function: implications for the serotonin hypothesis of depression

Lithium enjoys wide clinical use in the treatment of affective disorders, but the mechanism of its action in these conditions is still controversial. Recent studies have shown that lithium can interact with other antidepressant drugs to enhance their efficacy, perhaps by specific effects on serotonin (5-HT) function. A large body of independent evidence suggests that 5-HT function is abnormal in depression. This review documents preclinical evidence of lithium's effects on 5-HT function at the levels of precursor uptake, synthesis, storage, catabolism, release, receptors, and receptor-effector interactions. The weight of this evidence suggests that lithium's primary actions on 5-HT may be presynaptic, with many secondary postsynaptic effects. Studies in humans, using very different methodological approaches, generally suggest that lithium has a net enhancing effect on 5-HT function. These actions of lithium may serve to correct as-yet unspecified abnormalities of 5-HT function involved in the pathogenesis of depression.

Effects of lithium on alterations of pharmacokinetics of imipramine and on the related changes of monoamines in rat brain

Rats were given chronically i.p. imipramine (20 mg/kg), LiCl (1 mg/kg) or both drugs to examine the effects of lithium (Li) on the alterations of imipramine pharmacokinetics in the whole brain and on the imipramine-related changes of norepinephrine (NE) and serotonin (5-HT) levels in the brain. When rats were given Li for 3 days, followed by a single injection of imipramine, the concentrations of desipramine in the brain and serum were higher than those in the vehicle-treated rat, although the imipramine concentrations in both tissues did not differ in Li- and in vehicle-treated rats. In rats receiving both drugs for 10 days, the steady state levels of imipramine and desipramine in the brain were the same as those in the vehicle-treated rats but the steady state level of desipramine was reached earlier with Li treatments presumably because of the enhanced demethylation of imipramine. Consequently, the desipramine-dependent alterations of NE and 3-methoxy-4-hydroxyphenylglycol levels in the brain appeared to be induced earlier and more markedly when Li was given simultaneously. As the 5-hydroxyindole acetic acid (5-HIAA) levels were elevated in the brains of Li-treated rats and reduced in brains of imipramine-treated rats as compared with the level in vehicle-treated rats, the 5-HIAA level in rats receiving both drugs was equivalent to that in vehicle-treated rats.

A review of the biochemical and neuropharmacological actions of lithium

The pharmacological actions central to the therapeutic effects of lithium have not yet been established, despite almost 40 years of clinical use and scientific investigation. We review the biochemical and neuropharmacological data relating to this problem and attempt to identify profitable areas for further research.

Agonist-stimulation of cerebral phosphoinositide turnover following long-term treatment with antidepressants

Receptor-mediated stimulation of the formation of inositol phosphates (IP) in cerebral tissue may serve as a useful tool for studying long-term changes in the function of serotonin-2 (5-HT2), alpha-1-adrenergic (al), and muscarinic-cholinergic (musc) receptors. In this study we have evaluated the effects of chronic treatment with various antidepressants on receptor-mediated formation of IP in rat brain. Imipramine (IMI: 10 mg/kg/day; 14 days), Bupropion (BUPR: 40 mg/kg/day; 14 days), Lithium (Li: 0.5% in diet; 7 days) and electroshock treatment (EST: 20-30 mA/day; 7 days) were investigated. Cross-chopped slices of cerebral cortex from control and treated rats were prelabelled with myo-3H-inositol in HEPES buffer containing 11.1 mM LiCl. Accumulation of IP was measured in the presence and absence of serotonin (5-HT, 10 uM), norepinepherine (NE, 5 uM), and carbamylcholine (CCH, 100 uM). Values for agonist-stimulated IP formation in control rats were: 5-HT = 123 +/- 5%; NE = 268 +/- 16%; CCh = 205 +/- 21% of the basal level. The IP response to 5-HT was significantly lower following BUPR and higher following EST. Responses to NE and CCH were significantly lower following BUPR treatment but were not affected by the other antidepressant treatments. These observations are consistent with results of receptor-binding studies indicating up-regulation of 5-HT2 receptors by EST but are not consistent with studies showing down-regulation of 5-HT2 receptors by IMI and a lack of effect on 5-HT2 receptors by BUPR. Our results are not supportive of the notion, based mainly on [3H]prazosin binding studies, that al receptors are up-regulated by EST as well as by different antidepressant drugs.

Kinetics of the uptake of monoamines into synaptosomes from rat brain. Consequences of lithium treatment and withdrawal

The uptake systems for noradrenaline (NA) and 5-hydroxytryptamine (5-HT) into synaptosomal preparations from rat brain were found to consist of two components, a low-capacity and a high-capacity process. Administration of lithium (2 mequiv./kg) for 12 days was found to cause an increase in the activity of the low-capacity uptake process for NA, but to markedly inhibit the high-capacity system for this neurotransmitter. Following withdrawal of lithium, the activity of the low-capacity system returned to control values, but there was a profound enhancement of the high-capacity uptake process of NA. Both the low- and the high-capacity uptake systems for 5-HT were found to be inhibited by the administration of lithium. The reduced activity of the high-capacity system resulting from administration of lithium was still present 2 days after the cessation of treatment with the drug, whereas the low-capacity process was found to be further depressed. The uptake of dopamine (DA) into synaptosomal preparations appeared to be more complex than that of NA and 5-HT, since the shape of the substrate-velocity curve implied some form of multiple and co-operative process. The administration of lithium resulted in an enhancement of the uptake of DA in all regions of the brain examined, while 2 days of withdrawal from the drug caused a reduction to below control values in the amount of DA taken up. It therefore seems that alterations in monoaminergic uptake processes play a part in the mode of action of lithium, and may be involved in the genesis of the lithium-withdrawal phenomenon.

Short-term lithium administration enhances serotonergic neurotransmission: electrophysiological evidence in the rat CNS

Rats received lithium-containing chow for 48 h. Brain and plasma lithium concentrations ranged from 0.4 to 1.0 mEq/l. A first series of experiments served to assess the responsiveness of CA3 hippocampal pyramidal neurons to microiontophoretically applied serotonin (5-HT) and norepinephrine (NE). The response of the same neurons to electrical stimulation of the ventro-medial 5-HT pathway was measured after lithium treatment. The responsiveness to 5-HT and NE was not modified whereas the effect of activation of the ascending 5-HT pathway was increased two-fold by the lithium treatment. These neurons were activated to their physiological firing rate by means of small ejection currents of acetylcholine. A pretreatment with the 5-HT neurotoxin 5,7-dihydroxytryptamine abolished the response to the electrical stimulation in lithium-treated rats. In a second series of experiments, unitary recordings of 5-HT neurons were obtained from the dorsal raphe nucleus. The lithium treatment modified neither the number of spontaneously active 5-HT neurons nor their mean firing rate. These results provide direct electrophysiological evidence for the enhancement of 5-HT neurotransmission by short-term lithium treatment through its presynaptic action on 5-HT terminals.

Fenfluramine stimulation of serum cortisol in patients with major affective disorders and healthy controls: further evidence for a central serotonergic action of lithium in man

In order to investigate the influence of lithium long-term medication on serotonergic neurotransmission, fenfluramine stimulation (FFS) was used for the assessment of hormonal effects under serotonergic control. The cortisol plasma concentration following FFS was examined between 8 a.m. and 1 p.m. in 11 manic-depressive subjects under lithium prophylaxis and in 8 untreated euthymic patients. In addition, 11 healthy subjects with FFS, and 12 other subjects without FFS were investigated. The basal cortisol concentrations show considerable variation. Those of the lithium patients were in general found lower than those of the control groups. In both, the controls and the manic-depressive patients without lithium medication, no gross deviation from the expected physiological decline of morning cortisol values was found. A subtle effect of FFS in healthy subjects could be observed. In the lithium patients, however, a significant inversion of the cortisol secretion pattern with a steep increase between 10 and 12 a.m. could be demonstrated. It is concluded that FFS and lithium long-term medication exert an agonistic influence onto central serotonergic neurotransmission. Pharmacological challenge with fenfluramine may prove to be a useful tool for the investigation of serotonergic mechanisms in biological psychiatry.

Effects of lithium carbonate on serotonin uptake in rat blood platelets

1. Lithium carbonate administration to male rats for 1 to 4 weeks increased the affinity of platelet serotonin (5-HT) uptake (decreased Km) and decreased the rate of 5-HT uptake (Vmax) when the serum lithium levels were 0.5 meq/1 to 0.65 meq/l. When the serum levels were increased further to 1 meq/1, Vmax decreased further, without additional change in Km. 2. No effect on the kinetics of 5-HT uptake was observed when serum lithium levels were at 0.4 meq/1 or below. 3. Addition of lithium carbonate in vitro (1 meq/1) had no effect on the Km and Vmax of rat platelet 5-HT uptake. 4. The possible mechanism of the inhibitory effect of lithium treatment on platelet 5-HT uptake is discussed.