Effects of chronic lithium treatment on protein kinase C and cyclic AMP-dependent protein phosphorylation

Lithium affects the circadian clock in the choroid plexus - A new role for an old mechanism

Lithium is an effective mood stabilizer, but the mechanism of its therapeutic action is not well understood. We investigated the effect of lithium on the circadian clock located in the ventricle barrier complex containing the choroid plexus (CP), a part of the glymphatic system that influences gross brain function via the production of cerebrospinal fluid. The mPer2^Luc mice were injected with lithium chloride (LiCl) or vehicle, and their effects on the clock gene Nr1d1 in CP were detected by RT qPCR. CP organotypic explants were prepared to monitor bioluminescence rhythms in real time and examine the responses of the CP clock to LiCl and inhibitors of glycogen synthase kinase-3 (CHIR-99021) and protein kinase C (chelerythrine). LiCl affected Nr1d1 expression levels in CP in vivo and dose-dependently delayed the phase and prolonged the period of the CP clock in vitro. LiCl and CHIR-99021 had different effects on 1] CP clock parameters (amplitude, period, phase), 2] dexamethasone-induced phase shifts of the CP clock, and 3] dynamics of PER2 degradation and de novo accumulation. LiCl-induced phase delays were significantly reduced by chelerythrine, suggesting the involvement of PKC activity. The effects on the CP clock may be involved in the therapeutic effects of lithium and hypothetically improve brain function in psychiatric patients by aligning the function of the CP clock-related glymphatic system with the sleep-wake cycle. Importantly, our data argue for personalized timing of lithium treatment in BD patients.

Lithium as a Neuroprotective Agent for Bipolar Disorder: An Overview

Lithium (Li+) is a first option treatment for adult acute episodes of Bipolar Disorder (BD) and for the prophylaxis of new depressed or manic episodes. It is also the preferred choice as maintenance treatment. Numerous studies have shown morphological abnormalities in the brains of BD patients, suggesting that this highly heritable disorder may exhibit progressive and deleterious changes in brain structure. Since treatment with Li+ ameliorates these abnormalities, it has been postulated that Li+ is a neuroprotective agent in the same way atypical antipsychotics are neuroprotective in patients diagnosed with schizophrenia spectrum disorders. Li+'s neuroprotective properties are related to its modulation of nerve growth factors, inflammation, mitochondrial function, oxidative stress, and programmed cell death mechanisms such as autophagy and apoptosis. Notwithstanding, it is not known whether Li+-induced neuroprotection is related to the inhibition of its putative molecular targets in a BD episode: the enzymes inositol-monophosphatase, (IMPase), glycogen-synthase-kinase 3β (GSK3), and Protein kinase C (PKC). Furthermore, it is uncertain whether these neuroprotective mechanisms are correlated with Li+'s clinical efficacy in maintaining mood stability. It is expected that in a nearby future, precision medicine approaches will improve diagnosis and expand treatment options. This will certainly contribute to ameliorating the medical and economic burden created by this devastating mood disorder.

Calcium in Signaling: Its Specificity and Vulnerabilities toward Biogenic and Abiogenic Metal Ions

Divalent calcium ion (Ca²⁺) plays an indispensable role as a second messenger in a myriad of signal transduction processes. Of utmost importance for the faultless functioning of calcium-modulated signaling proteins is their binding selectivity of the native metal cation over rival biogenic/abiogenic metal ion contenders in the intra/extracellular fluids. In this Perspective, we summarize recent findings on the competition between the cognate Ca²⁺ and other biogenic or abiogenic divalent cations for binding to Ca²⁺-signaling proteins or organic cofactors. We describe the competition between the two most abundant intracellular biogenic metal ions (Mg²⁺ and Ca²⁺) for Ca²⁺-binding sites in signaling proteins, followed by the rivalry between native Ca²⁺ and "therapeutic" Li⁺ as well as "toxic" Pb²⁺. We delineate the key factors governing the rivalry between the native and non-native cations in proteins and highlight key implications for the biological performance of the respective proteins/organic cofactors.

Trinuclear Calcium Site in the C2 Domain of PKCα/γ Is Prone to Lithium Attack

Lithium (Li⁺) is the first-line therapy for bipolar disorder and a candidate drug for various diseases such as amyotrophic lateral sclerosis, multiple sclerosis, and stroke. Despite being the captivating subject of many studies, the mechanism of lithium's therapeutic action remains unclear. To date, it has been shown that Li⁺ competes with Mg²⁺ and Na⁺ to normalize the activity of inositol and neurotransmitter-related signaling proteins, respectively. Furthermore, Li⁺ may co-bind with Mg²⁺-loaded adenosine or guanosine triphosphate to alter the complex's susceptibility to hydrolysis and mediate cellular signaling. Bipolar disorder patients exhibit abnormally high cytosolic Ca²⁺ levels and protein kinase C (PKC) hyperactivity that can be downregulated by long-term Li⁺ treatment. However, the possibility that monovalent Li⁺ could displace the bulkier divalent Ca²⁺ and inhibit PKC activity has not been considered. Here, using density functional theory calculations combined with continuum dielectric methods, we show that Li⁺ may displace the native dication from the positively charged trinuclear site in the C2 domain of cytosolic PKCα/γ. This would affect the membrane-docking ability of cytosolic PKCα/γ and reduce the abnormally high membrane-associated active PKCα/γ levels, thus downregulating the PKC hyperactivity found in bipolar patients.

Posttranslational modifications & lithium's therapeutic effect-Potential biomarkers for clinical responses in psychiatric & neurodegenerative disorders

Several neurodegenerative diseases and neuropsychiatric disorders display aberrant posttranslational modifications (PTMs) of one, or many, proteins. Lithium treatment has been used for mood stabilization for many decades, and is highly effective for large subsets of patients with diverse neurological conditions. However, the differential effectiveness and mode of action are not fully understood. In recent years, studies have shown that lithium alters several protein PTMs, altering their function, and consequently neuronal physiology. The impetus for this review is to outline the links between lithium's therapeutic mode of action and PTM homeostasis. We first provide an overview of the principal PTMs affected by lithium. We then describe several neuropsychiatric disorders in which PTMs have been implicated as pathogenic. For each of these conditions, we discuss lithium's clinical use and explore the putative mechanism of how it restores PTM homeostasis, and thereby cellular physiology. Evidence suggests that determining specific PTM patterns could be a promising strategy to develop biomarkers for disease and lithium responsiveness.

Is There Justification to Treat Neurodegenerative Disorders by Repurposing Drugs? The Case of Alzheimer's Disease, Lithium, and Autophagy

Lithium is the prototype mood-stabilizer used for acute and long-term treatment of bipolar disorder. Cumulated translational research of lithium indicated the drug's neuroprotective characteristics and, thereby, has raised the option of repurposing it as a drug for neurodegenerative diseases. Lithium's neuroprotective properties rely on its modulation of homeostatic mechanisms such as inflammation, mitochondrial function, oxidative stress, autophagy, and apoptosis. This myriad of intracellular responses are, possibly, consequences of the drug's inhibition of the enzymes inositol-monophosphatase (IMPase) and glycogen-synthase-kinase (GSK)-3. Here we review lithium's neurobiological properties as evidenced by its neurotrophic and neuroprotective properties, as well as translational studies in cells in culture, in animal models of Alzheimer's disease (AD) and in patients, discussing the rationale for the drug's use in the treatment of AD.

A Role for Phosphodiesterase 11A (PDE11A) in the Formation of Social Memories and the Stabilization of Mood

The most recently discovered 3',5'-cyclic nucleotide phosphodiesterase family is the Phosphodiesterase 11 (PDE11) family, which is encoded by a single gene PDE11A. PDE11A is a dual-specific PDE, breaking down both cAMP and cGMP. There are four PDE11A splice variants (PDE11A1-4) with distinct tissue expression profiles and unique N-terminal regulatory regions, suggesting that each isoform could be individually targeted with a small molecule or biologic. PDE11A4 is the PDE11A isoform expressed in brain and is found in the hippocampal formation of humans and rodents. Studies in rodents show that PDE11A4 mRNA expression in brain is, in fact, restricted to the hippocampal formation (CA1, possibly CA2, subiculum, and the adjacently connected amygdalohippocampal area). Within the hippocampal formation of rodents, PDE11A4 protein is expressed in neurons but not astrocytes, with a distribution across nuclear, cytoplasmic, and membrane compartments. This subcellular localization of PDE11A4 is altered in response to social experience in mouse, and in vitro studies show the compartmentalization of PDE11A4 is controlled, at least in part, by homodimerization and N-terminal phosphorylation. PDE11A4 expression dramatically increases in the hippocampus with age in the rodent hippocampus, from early postnatal life to late aging, suggesting PDE11A4 function may evolve across the lifespan. Interestingly, PDE11A4 protein shows a three to tenfold enrichment in the rodent ventral hippocampal formation (VHIPP; a.k.a. anterior in primates) versus dorsal hippocampal formation (DHIPP). Consistent with this enrichment in VHIPP, studies in knockout mice show that PDE11A regulates the formation of social memories and the stabilization of mood and is a critical mechanism by which social experience feeds back to modify the brain and subsequent social behaviors. PDE11A4 likely controls behavior by regulating hippocampal glutamatergic, oxytocin, and cytokine signaling, as well as protein translation. Given its unique tissue distribution and relatively selective effects on behavior, PDE11A may represent a novel therapeutic target for neuropsychiatric, neurodevelopmental, or age-related disorders. Therapeutically targeting PDE11A4 may be a way to selectively restore aberrant cyclic nucleotide signaling in the hippocampal formation while leaving the rest of the brain and periphery untouched, thus, relieving deficits while avoiding unwanted side effects.

PDE11A negatively regulates lithium responsivity

Lithium responsivity in patients with bipolar disorder has been genetically associated with Phosphodiesterase 11A (PDE11A), and lithium decreases PDE11A mRNA in induced pluripotent stem cell-derived hippocampal neurons originating from lithium-responsive patients. PDE11 is an enzyme uniquely enriched in the hippocampus that breaks down cyclic AMP and cyclic GMP. Here we determined whether decreasing PDE11A expression is sufficient to increase lithium responsivity in mice. In dorsal hippocampus and ventral hippocampus (VHIPP), lithium-responsive C57BL/6J and 129S6/SvEvTac mice show decreased PDE11A4 protein expression relative to lithium-unresponsive BALB/cJ mice. In VHIPP, C57BL/6J mice also show differences in PDE11A4 compartmentalization relative to BALB/cJ mice. In contrast, neither PDE2A nor PDE10A expression differ among the strains. The compartment-specific differences in PDE11A4 protein expression are explained by a coding single-nucleotide polymorphism (SNP) at amino acid 499, which falls within the GAF-B homodimerization domain. Relative to the BALB/cJ 499T, the C57BL/6J 499A decreases PDE11A4 homodimerization, which removes PDE11A4 from the membrane. Consistent with the observation that lower PDE11A4 expression correlates with better lithium responsiveness, we found that Pde11a knockout mice (KO) given 0.4% lithium chow for 3+ weeks exhibit greater lithium responsivity relative to wild-type (WT) littermates in tail suspension, an antidepressant-predictive assay, and amphetamine hyperlocomotion, an anti-manic predictive assay. Reduced PDE11A4 expression may represent a lithium-sensitive pathophysiology, because both C57BL/6J and Pde11a KO mice show increased expression of the pro-inflammatory cytokine interleukin-6 (IL-6) relative to BALB/cJ and PDE11A WT mice, respectively. Our finding that PDE11A4 negatively regulates lithium responsivity in mice suggests that the PDE11A SNPs identified in patients may be functionally relevant.

Role of Protein Kinase C in Bipolar Disorder: A Review of the Current Literature

Bipolar disorder (BD) is a major health problem. It causes significant morbidity and imposes a burden on the society. Available treatments help a substantial proportion of patients but are not beneficial for an estimated 40-50%. Thus, there is a great need to further our understanding the pathophysiology of BD to identify new therapeutic avenues. The preponderance of evidence pointed towards a role of protein kinase C (PKC) in BD. We reviewed the literature pertinent to the role of PKC in BD. We present recent advances from preclinical and clinical studies that further support the role of PKC. Moreover, we discuss the role of PKC on synaptogenesis and neuroplasticity in the context of BD. The recent development of animal models of BD, such as stimulant-treated and paradoxical sleep deprivation, and the ability to intervene pharmacologically provide further insights into the involvement of PKC in BD. In addition, the effect of PKC inhibitors, such as tamoxifen, in the resolution of manic symptoms in patients with BD further points in that direction. Furthermore, a wide variety of growth factors influence neurotransmission through several molecular pathways that involve downstream effects of PKC. Our current understanding identifies the PKC pathway as a potential therapeutic avenue for BD.

Adenylate cyclase regulates elongation of mammalian primary cilia

The primary cilium is a non-motile microtubule-based structure that shares many similarities with the structures of flagella and motile cilia. It is well known that the length of flagella is under stringent control, but it is not known whether this is true for primary cilia. In this study, we found that the length of primary cilia in fibroblast-like synoviocytes, either in log phase culture or in quiescent state, was confined within a range. However, when lithium was added to the culture to a final concentration of 100 mM, primary cilia of synoviocytes grew beyond this range, elongating to a length that was on average approximately 3 times the length of untreated cilia. Lithium is a drug approved for treating bipolar disorder. We dissected the molecular targets of this drug, and observed that inhibition of adenylate cyclase III (ACIII) by specific inhibitors mimicked the effects of lithium on primary cilium elongation. Inhibition of GSK-3beta by four different inhibitors did not induce primary cilia elongation. ACIII was found in primary cilia of a variety of cell types, and lithium treatment of these cell types led to their cilium elongation. Further, we demonstrate that different cell types displayed distinct sensitivities to the lithium treatment. However, in all cases examined primary cilia elongated as a result of lithium treatment. In particular, two neuronal cell types, rat PC-12 adrenal medulla cells and human astrocytes, developed long primary cilia when lithium was used at or close to the therapeutic relevant concentration (1-2 mM). These results suggest that the length of primary cilia is controlled, at least in part, by the ACIII-cAMP signaling pathway.

Decreased protein kinase C (PKC) in platelets of pediatric bipolar patients: effect of treatment with mood stabilizing drugs

Pediatric bipolar disorder (PBD) is a major public health concern, however, its neurobiology is poorly understood. We, therefore, studied the role of protein kinase C (PKC) in the pathophysiology of bipolar illness. We determined PKC activity and immunolabeling of various PKC isozymes (i.e., PKC alpha, PKC betaI, PKC betaII, and PKC delta) in the cytosol and membrane fractions of platelets obtained from PBD patients and normal control subjects. PKC activity and PKC isozymes were also determined after 8 weeks of pharmacotherapy of PBD patients (n=16) with mood stabilizers. PKC activity and the protein expression of PKC betaI and betaII, but not PKC alpha or PKC delta, were significantly decreased in both membrane as well as cytosol fractions of platelets obtained from medication-free PBD patients compared with normal control subjects. Eight weeks of pharmacotherapy resulted in significantly increased PKC activity but no significant changes in any of the PKC isozymes in PBD patients. These results indicate that decreases of specific PKC isozymes and decreased PKC activity may be associated with the pathophysiology of PBD and that pharmacotherapy with mood stabilizing drugs results in an increase and normalization of PKC activity along with improvement in clinical symptoms.

Sodium valproate at therapeutic concentrations changes Ca2+ response accompanied with its weak inhibition of protein kinase C in human astrocytoma cells

Sodium valproate (VPA) has been used clinically for treatment of not only epilepsy but also mood disorder. Although VPA is effective for treatment of epilepsy via inhibition of gamma-aminobutyric acid transaminase, it remains unknown why VPA is effective for the treatment of mood disorder. The authors examined the effect of VPA at therapeutic concentrations (300 and 600 microM) on the elevation of intracellular free calcium concentration ([Ca(2+)](i)) induced by carbachol, a muscarinic receptor agonist, in 1321N1 human astrocytoma cells. Treatment of the cells with 300 and 600 microM VPA for 2 min did not change the carbachol-induced [Ca(2+)](i) elevation. Treatment with 300 and 600 microM VPA for 48 h, however, reduced the elevation. Since we have shown that Li(+) reduced carbachol-induced [Ca(2+)](i) elevation in protein kinase C (PKC)-downregulated 1321N1 cells [Kurita, M., Mashiko, H., Rai, M., Kumasaka, T., Kouno, S., Niwa, S., Nakahata, N., 2002. Lithium chloride at a therapeutic concentration reduces Ca(2+)response in protein kinase C down-regulated human astrocytoma cells, Eur. J. Pharmacol. 442, 17-22.], the activity of PKC was examined. Treatment with VPA at the same concentrations for 24 or 48 h weakly reduced protein kinase C activity in membrane and cytosol fractions from the cells. On the other hand, the treatment of the cells with 600 microM VPA for 24 or 48 h slightly increased the B(max) value, but not the K(d) value, in the binding of [(3)H]quinuclidinyl benzylate, a muscarinic receptor ligand, to the membranes, suggesting that the number or affinity of muscarinic receptor did not decrease after VPA treatment. These results indicate that VPA at therapeutic concentrations slightly decreases the PKC activity and inhibits muscarinic receptor-mediated [Ca(2+)](i) elevation probably through change in the intracellular signaling pathway. VPA-induced reduction of PKC activity and [Ca(2+)](i) elevation may play a role in the treatment of mood disorder.

Modulation of phosphoinositide-protein kinase C signal transduction by omega-3 fatty acids: implications for the pathophysiology and treatment of recurrent neuropsychiatric illness

The phosphoinositide (PI)-protein kinase C (PKC) signal transduction pathway is initiated by pre- and postsynaptic Galphaq-coupled receptors, and regulates several clinically relevant neurochemical events, including neurotransmitter release efficacy, monoamine receptor function and trafficking, monoamine transporter function and trafficking, axonal myelination, and gene expression. Mounting evidence for PI-PKC signaling hyperactivity in the peripheral (platelets) and central (premortem and postmortem brain) tissues of patients with schizophrenia, bipolar disorder, and major depressive disorder, coupled with evidence that PI-PKC signal transduction is down-regulated in rat brain following chronic, but not acute, treatment with antipsychotic, mood-stabilizer, and antidepressant medications, suggest that PI-PKC hyperactivity is central to an underlying pathophysiology. Evidence that membrane omega-3 fatty acids act as endogenous antagonists of the PI-PKC signal transduction pathway, coupled with evidence that omega-3 fatty acid deficiency is observed in peripheral and central tissues of patients with schizophrenia, bipolar disorder, and major depressive disorder, support the hypothesis that omega-3 fatty acid deficiency may contribute to elevated PI-PKC activity in these illnesses. The data reviewed in this paper outline a potential molecular mechanism by which omega-3 fatty acids could contribute to the pathophysiology and treatment of recurrent neuropsychiatric illness.

Omega-3 fatty acids in bipolar disorder: clinical and research considerations

Several lines of evidence suggest that omega-3 fatty acids may be important in the pathophysiology, treatment or prevention of bipolar disorder (BD). Electronic and manual searches were conducted in order to review the literature relevant to the etiology and treatment of BDs with omega-3 fatty acids. We also present data from a randomized, double-blind, placebo-controlled pilot study conducted at three sites (N = 10) comparing an omega-3 fatty acid (docosahexaenoic acid, DHA) versus placebo, added to psychosocial treatment for women with BD who chose to discontinue standard pharmacologic treatment while attempting to conceive. While some epidemiologic and preclinical data support the role of omega-3 fatty acids in BD, clinical trials to date have yielded conflicting results. In our pilot study of 10 Caucasian women taking DHA while attempting to conceive (BP1 = 9, BPII = 1), age 27-42 years, DHA was well tolerated and suggests that a larger study would be feasible. The elucidation of the potential role of omega-3 fatty acids as a treatment for BD requires further study. The current data are not sufficient to support a recommendation of monotherapy treatment as a substitute for standard pharmacologic treatments. However, judicious monotherapy in selected clinical situations, or adjunctive use, may be warranted pending further data from adequately powered controlled clinical trials. Our pilot trial of DHA in women who plan to stop conventional psychotropics in order to conceive suggests that such trials are feasible.

Effect of chronic lithium treatment on the turnover of alpha2-adrenoceptors after chemical inactivation in rats

One of the most effective psychotherapeutic agents in the treatment of bipolar disease is lithium. Chronic lithium treatment affects some signal transduction mechanisms such as cAMP, cGMP, inositol 1,4,5 P(3), Gi protein, protein kinase C and can also modify gene expression in rat brain. In a previous study, we observed a greater inhibitory effect of lithium on cAMP production after blockade of alpha(2)-adrenoceptors in rat cerebral cortex. Here we examine the influence of chronic lithium treatment on turnover of alpha(2)-adrenoceptors after their inactivation by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) in rat cerebral cortex. After treatment with lithium for 10 days (120 mg/kg/day, i.p.), there was a significant increase in the appearance and disappearance rate constants of these adrenoceptors and a significant reduction of their half-life. These results suggest that chronic lithium administration alters the alpha(2)-adrenoceptor turnover in rat brain.

Cytokine production in bipolar affective disorder patients under lithium treatment

BACKGROUND

Our knowledge concerning immune functioning in bipolar affective disorder (BAD) is limited, while lithium's immunomodulatory effects seem multiple and conflicting. Our aim was to evaluate cytokine production and lithium's effect on it in BAD patients, using ELISPOT technique as a sensitive tool.

METHODS

Cytokine (IL-2, IL-6, IL-10 and IFN-gamma) production from isolated peripheral blood lymphocytes (PBLs) was evaluated (ELISPOT technique) in 40 euthymic BAD patients under chronic lithium treatment, in 20 healthy volunteers, and in 10 never medicated BAD patients before and after the introduction of lithium therapy. In all cases, cytokine plasma levels were also measured using ELISA.

RESULTS

BAD patients under chronic lithium treatment had significantly lower numbers of IL-2, IL-6, IL-10 and IFN-gamma secreting cells compared to healthy volunteers. The number of cytokine secreting cells decreased in never medicated patients after 3 months of lithium treatment. In vitro stimulation of PBLs with lithium did not affect the number of cytokine secreting cells either in the patients or in the healthy volunteers.

CONCLUSIONS

The significantly lower number of PBLs producing cytokines (IL-2, IL-6, IL-10 and IFN-gamma) in euthymic BAD patients under chronic lithium treatment result from the long-term (over 3 months) lithium administration. In vitro stimulation of PBLs with lithium did not change the number of cytokine producing cells. Our findings may be useful in elucidating possible downregulatory effects of lithium in humans.

Identification of PIK3C3 promoter variant associated with bipolar disorder and schizophrenia

BACKGROUND

Genes involved in phosphoinositide (PI) lipid metabolism are excellent candidates to consider in the pathogenesis of bipolar disorder (BD) and schizophrenia (SZ). One is PIK3C3, a member of the phosphatidylinositide 3-kinase family that maps closely to markers on 18q linked to both BD and SZ in a few studies.

METHODS

The promoter region of PIK3C3 was analyzed for mutations by single-strand conformation polymorphism analysis and sequencing. A case-control association study was conducted to determine the distribution of variant alleles in unrelated patients from three cohorts. Electromobility gel shift assays (EMSA) were performed to assess the functional significance of variants.

RESULTS

Two polymorphisms in complete linked disequilibrium with each other were identified, -432C- > T and a "C" insert at position -86. The -432T allele occurs within an octamer containing an ATTT motif resembling members of the POU family of transcription factors. In each population analyzed, an increase in -432T was found in patients. EMSAs showed that a -432T containing oligonucleotide binds to brain proteins that do not recognize -432C.

CONCLUSIONS

A promoter mutation in a PI regulator affecting the binding of a POU-type transcription factor may be involved in BD and SZ in a subset of patients.

Affective disorders, antidepressant drugs and brain metabolism

There is increasing evidence that affective disorders are associated with dysfunction of neurotransmitter postsynaptic transduction pathways and that chronic treatment with clinically active drugs results in adaptive modification of these pathways. Despite the close dependence of signal transduction on adenosine triphosphate (ATP) availability, the changes in energy metabolism in affective disorders are largely unknown. This question has been indirectly dealt with through functional imaging studies (PET, SPECT, MRS). Despite some inconsistencies, PET and SPECT studies suggest low activity in cortical (especially frontal) regions in depressed patients, both unipolar and bipolar, and normal or increased activity in the manic pole. Preliminary MRS studies indicate some alterations in brain metabolism, with reduced creatine phosphate and ATP levels in the brain of patients with affective disorders. However, the involvement of the energy metabolism in affective disorders is still debated. We propose direct neurochemical investigations on mitochondrial functional parameters of energy transduction, such as the activities of (a) the enzymatic systems of oxidative metabolic cycle (Kreb's cycle); (b) the electron transfer chain; (c) oxidative phosphorylation, and (d) the enzyme activities of ATP-requiring ATPases. These processes should be studied in affective disorders and in animals treated with antidepressant drugs or lithium.

Conditioned taste aversion and Ca/calmodulin-dependent kinase II in the parabrachial nucleus of rats

Bielavska and colleagues (Bielavska, Sacchetti, Baldi, & Tassoni, 1999) have recently shown that KN-62, an inhibitor of calcium/calmodulin-dependent kinase II (CaCMK), induces conditioned taste aversion (CTA) when introduced into the parabrachial nucleus (PBN) of rats. The aim of the present report was to assess whether activity of CaCMK in the PBN is changed during CTA. We induced CTA in one group of rats by pairing saccharin consumption with an ip injection of lithium chloride. Another group of rats received lithium alone (without being paired with saccharin consumption) to test whether lithium has an effect on CaCMK in the PBN, independent of those effects due to training. In animals receiving CTA training, CaCMK activity in extracts of PBN was reduced by approximately 30% at the postacquisition intervals of 12, 24, and 48 h, compared to control animals receiving saccharin with saline injection. By 120 h after CTA training, no effect on CaCMK was present. At those postacquisition intervals showing CaCMK activity effects due to CTA, there were no effects attributable to lithium alone. Lithium alone produced only a short-lasting reduction in CaCMK activity (at 20 min a 30% decrease, at 60 min a 23% decrease; and at 6, 12, and 24 h no decrease). The time course of lithium-induced effects differed markedly from that of CTA training. All changes were Ca2+/- -dependent; we did not observe any changes in Ca-independent activity. CTA effects on CaCMK were selective for PBN, insofar as we did not observe any CTA effects on CaCMK in the visual cortex, a brain region unrelated to taste pathways. Since CTA produces a relatively long-lasting reduction in CaCMK activity (lasting 2 days or more) specifically in the PBN, which is critical a relay for taste information, the reduction of CaCMK activity may enable the consolidation of taste memory in an aversive situation.

Inhibitory effects of omega-3 fatty acids on protein kinase C activity in vitro

Preliminary clinical data indicate that omega-3 fatty acids may be effective mood stabilizers for patients with bipolar disorder. Both lithium and valproic acid are known to inhibit protein kinase C (PKC) activity after subchronic administration in cell culture and in vivo. The current study was undertaken to determine the effects of the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on protein kinase C phosphotransferase activity in vitro. Various concentrations of DHA, EPA, and arachidonic acid (AA) were incubated with the catalytic domain of protein kinase C beta from rat brain. Protein kinase C activity was measured by quantifying incorporation of (32)P-PO(4) into a synthetic peptide substrate. Both DHA and EPA, as well as the combination of DHA and EPA, inhibited PKC activity at concentrations as low as 10 micromol l(-1). In contrast, arachidonic acid had no effect on PKC activity. Thus, PKC represents a potential site of action of omega-3 fatty acids in their effects on the treatment of bipolar disorder.

Concurrent measures of protein kinase C and phosphoinositides in lithium-treated bipolar patients and healthy individuals: a preliminary study

This study examined the hypothesis that lithium inhibits the PI signaling pathway in humans during in vivo administration by concurrently measuring PKC isozymes and platelet membrane phosphoinositides in lithium-treated patients and healthy individuals. The platelet membrane and cytosolic levels of PKC alpha, beta I, beta II, delta, and epsilon were measured using Western blotting. The relative platelet membrane contents of phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PIP), and phosphatidylinositol-4,5-bisphosphate (PIP(2)) were measured with two-dimensional thin-layer chromatography. Nine euthymic lithium-treated bipolar subjects and 11 healthy control subjects were studied. Compared to control subjects, lithium-treated bipolar patients had significantly lower levels of cytosolic PKC alpha isozyme (t-test=-3.24, d.f.=17, P=0.01) and PIP(2) platelet membrane levels (t-test=-2.51, d.f.=18, P=0.02), and a trend toward reduced levels of cytosolic PKC beta II isozyme (t=-2.17, d.f.=17, P=0.05). There was no significant correlation between PIP(2) and any of the PKC isozymes. These preliminary findings suggest that chronic lithium treatment may decrease the levels of both cytosolic PKC alpha isozyme and membrane PIP(2) in platelets of bipolar disorder patients.

Glycerophospholipids in brain: their metabolism, incorporation into membranes, functions, and involvement in neurological disorders

Neural membranes contain several classes of glycerophospholipids which turnover at different rates with respect to their structure and localization in different cells and membranes. The glycerophospholipid composition of neural membranes greatly alters their functional efficacy. The length of glycerophospholipid acyl chain and the degree of saturation are important determinants of many membrane characteristics including the formation of lateral domains that are rich in polyunsaturated fatty acids. Receptor-mediated degradation of glycerophospholipids by phospholipases A(l), A(2), C, and D results in generation of second messengers such as arachidonic acid, eicosanoids, platelet activating factor and diacylglycerol. Thus, neural membrane phospholipids are a reservoir for second messengers. They are also involved in apoptosis, modulation of activities of transporters, and membrane-bound enzymes. Marked alterations in neural membrane glycerophospholipid composition have been reported to occur in neurological disorders. These alterations result in changes in membrane fluidity and permeability. These processes along with the accumulation of lipid peroxides and compromised energy metabolism may be responsible for the neurodegeneration observed in neurological disorders.

Abnormalities of cAMP signaling in affective disorders: implication for pathophysiology and treatment

OBJECTIVE

During the last decade, much attention has been given to the role of signal transduction pathways in affective disorders. This review describes the possible role of the cAMP signaling in such disorders.

METHODS

Among the components of cAMP signaling, this review focuses on the cAMP-dependent phosphorylation system. We analyzed the basic components of the cAMP-dependent phosphorylation system and the preclinical evidence supporting their involvement in the biochemical action of antidepressants and mood stabilizers. The clinical data available until now, concerning the possible link between the cAMP-dependent phosphorylation system and the pathophysiology of affective disorders, are also reviewed.

RESULTS

The studies herein presented demonstrated that the levels and the activity of cAMP-dependent protein kinase are altered by antidepressants and mood stabilizers. Furthermore. these medications are able to modify the phosphorylation state, as well as the levels of some of the cAMP-dependent protein kinase substrates. More recently, clinical studies have reported abnormalities in the cAMP-dependent phosphorylation system in both peripheral cells and the postmortem brain of patients with affective disorders.

CONCLUSIONS

Overall, these studies support an involvement of cAMP signaling in affective disorders. The precise knowledge of the findings has the potential to improve the understanding of pharmacotherapy and to provide directions for the development of novel biochemical and genetic research strategies on the pathogenesis of affective disorders.

Pertussis vaccine and pertussis toxin increase lithium levels in rats: possible role of G-proteins

A single dose of lithium was injected intravenously or intraperitoneally in rats. Lithium levels in serum and tissues 5 or 24 hours later were elevated when the rats were pretreated with pertussis vaccine (PV). The vaccine was effective whether given locally (subcutaneous) or systemically (intravenous). Tests of heated (inactivated) PV suggested that pertussis toxin might be responsible for the effects of PV. Injection of purified pertussis toxin (PT) confirmed this suggestion. Elevation of serum urea nitrogen suggested that lithium levels were increased because the combination of PV or PT with lithium reduced renal excretory function which could cause retention of lithium. Inasmuch as PV and PT are known to inactivate the inhibitory G-proteins, these data suggest G-protein involvement in the elevation of lithium levels by PV and PT.

Signalling pathways in the brain: cellular transduction of mood stabilisation in the treatment of manic-depressive illness

The long-term treatment of manic-depressive illness (MDI) likely involves the strategic regulation of signalling pathways and gene expression in critical neuronal circuits. Accumulated evidence has identified signalling pathways, in particular the family of protein kinase C (PKC) isozymes, as targets for the long-term action of lithium. Chronic lithium administration produces a reduction in the expression of PKC alpha and epsilon, as well as a major PKC substrate, MARCKS, which has been implicated in long-term neuroplastic events in the developing and adult brain. More recently, studies have demonstrated robust effects of lithium on another kinase system, GSK-3beta, and on neuroprotective/neurotrophic proteins in the brain. Given the key roles of these signalling cascades in the amplification and integration of signals in the central nervous system, these findings have clear implications not only for research into the neurobiology of MDI, but also for the future development of novel and innovative treatment strategies.

Ziskind-Somerfeld Research Award. Protein kinase C signaling in the brain: molecular transduction of mood stabilization in the treatment of manic-depressive illness

Understanding the biology of the pharmacological stabilization of mood will undoubtedly serve to provide significant insight into the pathophysiology of manic-depressive illness (MDI). Accumulating evidence from our laboratories and those of other researchers has identified the family of protein kinase C isozymes as a shared target in the brain for the long-term action of both lithium and valproate. In rats chronically treated with lithium, there is a reduction in the hippocampus of the expression of two protein kinase isozymes, alpha and epsilon, as well as a reduction in the expression of a major PKC substrate, MARCKS, which has been implicated in long-term neuroplastic events in the developing and adult brain. In addition, we have been investigating the down-stream impact of these mood stabilizers on another kinase system, GSK-3 beta and on the AP-1 family of transcription factors. Further studies have generated promising preliminary data in support of the antimanic action of tamoxifen, and antiestrogen that is also a PKC inhibitor. Future studies must address the therapeutic relevance of these protein targets in the brain using innovative strategies in both animal and clinical investigations to ultimately create opportunities for the discovery of the next generations of mood stabilizers for the treatment of MDI.

Cyclic AMP responsive element binding protein phosphorylation and DNA binding is decreased by chronic lithium but not valproate treatment of SH-SY5Y neuroblastoma cells

Mood stabilizing drugs decrease central nervous system cyclic AMP signaling. We report here that chronic, but not acute treatment with lithium chloride in human neuroblastoma SH-SY5Y cells, inhibits phosphorylation of cyclic AMP responsive element binding protein and cyclic AMP responsive element DNA binding induced by the adenylyl cyclase activator forskolin, but has no effect on constitutive expression of cyclic AMP responsive element binding protein. These results are consistent with an effect of lithium to blunt the cyclic AMP signal transduction pathway. Such an effect is not shared by the other commonly prescribed mood stabilizer, sodium valproate. Our results suggest that cyclic AMP responsive element binding protein regulated gene expression may be relevant to the long-term prophylactic effect of lithium. Furthermore, sodium valproate, which is also effective in bipolar disorder, would appear to act on other pathways to bring about its therapeutic effects.

Increased membrane-associated protein kinase C activity and translocation in blood platelets from bipolar affective disorder patients

BACKGROUND

recent investigations have suggested that the phosphoinositide (PI) signal transduction system may be involved in the pathophysiology of bipolar affective disorders. Earlier studies in our laboratory have implicated altered PKC-mediated phosphorylation in bipolar affective disorder and in the clinical action of lithium. In the present study, we compared PKC activity and its translocation in platelets from subjects with bipolar affective disorder and three other groups.

METHODS

subjects included 44 with bipolar disorder (acute manic episode), 25 with acute major depression, 23 with schizophrenia in acute exacerbation and 43 controls free of personal or family history of an Axis I disorder. Blood platelet membrane and cytosol PKC activity was measured before and after in vitro stimulation with serotonin (5-HT), thrombin and the direct PKC activator, PMA. In addition, we examined 5-HT-, thrombin- and PMA-elicited translocations of PKC isozymes from cytosol to the membrane in platelets of control subjects.

RESULTS

in the basal state, manic subjects demonstrated higher membrane PKC activity than depressive and control subjects. The ratio of membrane to cytosol PKC activity was significantly higher in manic (1.10), as compared to control (0.84), depressed (0.93) or schizophrenic (0.93) subjects. Stimulation of platelets with 5-HT in vitro, resulted in greater membrane to cytosol ratio in the manic subjects compared to the three other groups. The responsiveness of platelets to PMA and thrombin was greater for manic subjects than for depressed and schizophrenic subjects, but not greater than the controls. In this measure both the schizophrenic and depressive groups were less active than controls. The results also demonstrate that platelets contain alpha-, beta-, delta- and zeta-PKC isozymes. While alpha- and beta-PKC isoforms were translocated from cytosol to membrane in response to serotonin, PMA and thrombin, serotonin also elicited the redistribution of delta-PKC and thrombin also activated zeta-PKC.

CONCLUSION

the results demonstrate that a heightened PKC-mediated signal transduction is associated with acute mania and suggest a decreased transduction in patients with unipolar depression or schizophrenia.

Region-selective effects of long-term lithium and carbamazepine administration on cyclic AMP levels in rat brain

The effect of lithium and carbamazepine in the treatment of bipolar affective disorder is well established. Although a number of biochemical effects have been found, the exact molecular mechanisms underlying their therapeutic actions have not been elucidated nor are the target regions in the brain identified. Taken into account the important role of the cyclic AMP second messenger system in the regulation of neuronal exitability and the indications of its involvement in the patophysiology of bipolar affective disorder, we have focused on the drug effects on cyclic AMP levels. The objectives of this investigation were to measure the effects on basal cyclic AMP levels, and to locate target regions within the rat brain after long-term administration of lithium and carbamazepine. Drug treatments were carried out for a period of 28 days. After either drug treatment the cyclic AMP level was increased 3-4 times in frontal cortex but unchanged in hippocampus, hypothalamus, thalamus, amygdala and in cerebellum. In neostriatum the cyclic AMP level was decreased to about 30% after treatment with lithium. We suggest the common region-selective effect, observed for both drugs in frontal cortex, to be essential for the therapeutic actions of lithium and carbamazepine.

Altered protein phosphorylation in the rat brain following chronic lithium and carbamazepine treatments

Lithium and carbamazepine (CBZ) alter levels of specific kinase-activating second messengers generated by adenylate cyclases and the phosphoinositide system. Thus, lithium and CBZ may change endogenous protein phosphorylation mediated by cyclic AMP-dependent protein kinase (PKA) and protein kinase C (PKC). The present study aimed at comparing the chronic effects of lithium and CBZ on protein phosphorylation in the rat brain by using quantitative autoradiography. Long-term treatments yielded plasma levels within the therapeutic range. In the particulate hippocampal fraction PKA-mediated phosphorylation of a 42 kDa protein and PKC-mediated phosphorylation of a 88 kDa protein were decreased after lithium treatment. In the cortical particulate fraction approximately 30% reduction in the PKA-mediated protein phosphorylation of several proteins was observed after lithium and CBZ treatments. In the same fraction, CBZ treatment significantly reduced PKC-mediated phosphorylation of several substrates by 30-40%. PKA activity was significantly reduced in cortex, but not in the hippocampus. Thus, both drugs exhibited fraction and region specificities.

Protein kinase C in the postmortem brain of teenage suicide victims

Increased serotonin2A (5-HT2A) receptors have been reported in the postmortem brain of suicide victims. To examine if this increase is associated with the dysregulation of postreceptor sites in the signaling cascade, we determined [3H]phorbol dibutyrate (PDBU) binding to protein kinase C (PKC) in postmortem brain samples (Brodmann's areas 8 and 9) obtained from teenage suicide victims and control subjects. [3H]PDBU binding to PKC was determined in membranal and cytosolic fractions. We observed that Bmax of [3H]PDBU binding sites was significantly decreased in both membranal and cytosolic fractions in brain samples from Brodmann's areas 8-9 compared to matched controls. These results thus suggest that PKC may play a role in the pathophysiology of suicidal behavior.

Inhibitory effect of lithium on cAMP dependent phosphorylation system

The aim of the present study was to assess the direct effect of lithium on cAMP dependent phosphorylation. The results show that lithium, but not rubidium, at therapeutic and high concentrations significantly decreases the cAMP stimulated MAP2 endogenous phosphorylation in microtubule fraction. An inhibitory effect of lithium has also been found using purified heat stable microtubule proteins phosphorylated by the catalytic subunit of PKA. These data suggest a direct effect of lithium on the cAMP dependent protein kinase.

Circadian variation in rat brain AP-1 DNA binding activity after cholinergic stimulation: modulation by lithium

The potential influence of a circadian rhythm and its modulation by lithium on the stimulation of AP-1 DNA binding activity by the cholinergic agonist pilocarpine was investigated in rat cerebral cortex. Stimulation of AP-1 binding after pilocarpine (30 mg/kg) was evident within 1 h and was maximally stimulated by 200% at 2 h. Pilocarpine-stimulated AP-1 binding exhibited a circadian rhythm in AP-1 binding measured at 0800, 1200, and 1600 hours, 2 h after pilocarpine. Pilocarpine-stimulated AP-1 binding at 0800 hours was approximately twice the level measured at 1600 hours. After acute lithium treatment, pilocarpine administration induced generalized seizures after about 20 min and stimulated AP-1 binding which increased continuously for 4.5 h, at which time the stimulation was 900% above control. A circadian variation was apparent in AP-1 binding stimulated by acute lithium plus pilocarpine, with stimulation at 0800 hours being 1.5 times that at 1600 hours. After chronic lithium and pilocarpine, which also produced seizures, there was no circadian variation in pilocarpine-stimulated AP-1 binding. Thus pilocarpine-induced AP-1 binding in rat cerebral cortex was influenced by a circadian rhythm, but this was abolished by chronic lithium administration.

Modulation by inositol of cholinergic- and serotonergic-induced seizures in lithium-treated rats

Hippocampal and cortical EEG recordings in rats were used to monitor the in vivo modulation by lithium of responses to agonists for 5HT2/5HT1c serotonergic (DOI) and cholinergic (pilocarpine) receptors and the influence of inositol administration. Administration of DOI (8 mg/kg) or pilocarpine (30 mg/kg) to rats pretreated with lithium acutely (3 mmol/kg) or chronically (dietary, 4 weeks) resulted in seizures, whereas these doses did not cause seizures without lithium pretreatment. This indicated that lithium most likely affects a signal transduction process common to both systems, which is the phosphoinositide second messenger system. To examine the potential influence of altered inositol levels on these responses, we tested the effects of infusions (10 mg, i.c.v.) of myo-inositol, a precursor of phosphoinositide synthesis, and of epi-inositol, an isomer not used for phosphoinositide synthesis. Administration of myo-inositol (10 mg) slightly reduced the incidence of seizures induced by acute lithium plus DOI but almost completely blocked seizures induced by acute lithium plus pilocarpine. This was surprising since seizures induced by acute lithium plus DOI were less severe than those after acute lithium plus pilocarpine, but myo-inositol was more effective in blocking the latter. Epi-inositol also blocked seizures under both conditions but it was less effective than myo-inositol after treatment with acute lithium plus pilocarpine. The latencies to seizures and/or severity of seizures were potentiated more by chronic than acute lithium pretreatment with both DOI and pilocarpine, but attenuation by myo-inositol was less with each agonist after chronic lithium compared with acute lithium treatment. Peripheral administration of a high dose of myo-inositol blocked seizures induced by acute lithium plus pilocarpine, but the inositol treatment itself was toxic and caused seizures prior to pilocarpine administration, so the mechanism of action cannot simply be attributed to increased brain inositol levels. These results demonstrate that lithium modulates the in vivo responses to DOI and pilocarpine, most probably through an effect on the phosphoinositide signal transduction system. They also show that centrally administered myo-inositol modifies responses to these agents, but the effectiveness of epi-inositol and other results leave unclear the mechanistic basis of its actions.

Distinctive rat brain immediate early gene responses to seizures induced by lithium plus pilocarpine

The mRNA levels of four immediate early genes (IEG) were measured in rat brain regions 60 min after administration of pilocarpine (30 mg/kg) to lithium-treated (3 mmol/kg) rats, during generalized convulsive status epilepticus. Northern blots demonstrated induction of the genes in the order of c-fos = jun-B > c-jun > jun-D with large increases in the cerebral cortex, hippocampus, and striatum, a smaller increase in the cerebellum, and less in the brainstem. The mRNA levels of these four IEG were measured in rat cerebral cortex and hippocampus at several times after administration of the cholinergic agonist pilocarpine (5 or 30 mg/kg) with or without lithium pretreatment (3 mmol/kg, 16 h prior, or chronic 4 week dietary administration). Treatment with pilocarpine (30 mg/kg) alone increased mRNA levels in the order of c-fos > jun-B > c-jun but did not change the jun-D mRNA level, and maximal c-fos and jun-B mRNA levels occurred earlier (30 min) in the cortex than in the hippocampus. Treatment with the lower dose of pilocarpine (5 mg/kg) alone caused only small increases in c-fos and jun-B mRNA levels and these responses were unaffected by lithium pretreatment. Lithium pretreatment potentiated IEG expression induced by 30 mg/kg pilocarpine, likely as a result of the seizures caused by this combination of drugs because pretreatment with anticonvulsants (diazepam or MK-801) blocked seizures and the enhanced IEG mRNA levels. The mRNA levels were increased during seizures in the order of c-fos > jun-B > c-jun > jun-D in the hippocampus and jun-B > c-fos > c-jun > jun-D in the cortex, and were increased for a longer duration as well as to a greater extent than after administration of pilocarpine alone. Administration of pilocarpine (30 mg/kg) to rats treated chronically with lithium caused increases similar to those measured with acute lithium pretreatment. Thus the induction of IEG by cholinergic stimulation varied with dose, time, and brain region, and unique responses were observed for each of the IEG. Lithium pretreatment did not impair IEG expression induced by the lower dose of pilocarpine and greatly enhanced expression of IEG after administration of the higher dose of pilocarpine concomitant with seizure activity.

The lymphoblast beta-adrenergic receptor in bipolar depressed patients: effect of chronic incubation with lithium chloride

We have recently reported a study of beta-adrenergic receptor binding characteristics in lymphoblast cell lines derived from patients with bipolar disorder (BD) and healthy, matched control subjects. In the present study we have investigated the effects of incubating cells from the same subjects with lithium chloride (1 mM) for 7 days prior to assay. There was no difference in beta-adrenergic receptor number between control and BD cell lines and incubation with lithium had no effect on receptor number in either group. Exposure of the cells to isoprenaline (1 nM) for 24 h immediately prior to assay caused significantly less down-regulation in BD cells (15 +/- 5%) than control cells (39 +/- 4%), as described previously. Incubation with lithium significantly increased the down-regulation response to isoprenaline in BD cells (39 +/- 6%) but not in control cells (30 +/- 7%). After lithium, the agonist-induced decrease in beta-AR number in BD cells was no longer significantly different from that in control cells. We conclude that lithium selectively enhanced the agonist down-regulation of beta-adrenergic receptors in cells derived from patients with bipolar disorder. The functional significance of this result and the potential biochemical mechanisms responsible for this effect are discussed.

Protein kinase C in nucleus parabrachialis: effect of drugs inducing conditioned taste aversion

A method for the dissection of the nucleus parabrachialis (NPB) from the coronal sections of frozen rat brain is described. The protein kinase C (PKC) activity was determined in the cytosol and particulate fractions of the pooled samples of the nucleus. The effect of the i.p. administration of the conditioned taste aversion-inducing agents LiCl and CuSO4 on PKC in the NPB and visual cortex (VC) was tested. 1 h after the LiCl injection, the portion of the membrane-bound PKC was increased by 23% (P < 0.01) above the level found after the saline injection. CuSO4 produced a 19% increase. Since the PKC activity in the cytosol declined, it is likely that the translocation of the enzyme took place. No changes in the PKC distribution in the VC samples could be detected. The results support the idea that the PKC translocation is not directly induced by the tested substances but that it rather reflects changes in the activity of the visceral system.

Hydrolysis of exogenous [3H]phosphatidylcholine by brain membranes and cytosol

Phosphatidylcholine, in addition to the widely studied inositol phospholipids is cleaved to produce second messengers in neuronal signal transduction processes. Because of the difficulty in labelling and measuring the metabolism of endogenous phosphatidylcholine in brain tissue, we investigated the utility of measuring the hydrolysis of exogenous labelled substrate incubated with rat cerebral cortical cytosol and membrane fractions as has been successful in studies of phosphoinositide hydrolysis. In the cytosol [3H]phosphatidylcholine was hydrolyzed at a linear rate for 60 min of incubation and GTP gamma S stimulated hydrolysis by 63%. The products of phospholipase C and phospholipase D, phosphorylcholine and choline, contributed only 44% of the [3H]phosphatidylcholine hydrolytic products in the cytosol, with phospholipase D activity slightly predominating. GTP gamma S stimulated cytosolic phospholipase C and reduced phospholipase D activity. [3H]Phosphatidylcholine was hydrolyzed much more slowly by membranes than by cytosol. In membranes the production of [3H]phosphorylcholine and [3H]choline were approximately equal, contributing 27% of the total [3H]phosphatidylcholine hydrolysis, and GTP gamma S only caused a slight stimulation of phospholipase C activity. Chronic lithium treatment (4 weeks) appeared to slightly reduce [3H]phosphatidylcholine metabolism in the cytosol and in membranes, but no statistically significant reductions were achieved. Cytosol and membrane fractions from postmortem human brain metabolized [3H]phosphatidylcholine slowly, and GTP gamma S had no effects. In summary, exogenous [3H]phosphatidylcholine was hydrolyzed by brain cytosol and membranes, and this was stimulated by GTP gamma S, but the complex contributions of multiple metabolic pathways complicates the application of this method for studying individual pathways, such as phospholipase D which contributes only a fraction of the total processes hydrolyzing exogenous [3H]phosphatidylcholine.

Lithium decreases membrane-associated protein kinase C in hippocampus: selectivity for the alpha isozyme

We investigated the effects of lithium on alterations in the amount and distribution of protein kinase C (PKC) in discrete areas of rat brain by using [3H]phorbol 12,13-dibutyrate quantitative autoradiography as well as western blotting. Chronic administration of lithium resulted in a significant decrease in membrane-associated PKC in several hippocampal structures, most notably the subiculum and the CA1 region. In contrast, only modest changes in [3H]phorbol 12,13-dibutyrate binding were observed in the various other cortical and subcortical structures examined. Immunoblotting using monoclonal anti-PKC antibodies revealed an isozyme-specific 30% decrease in hippocampal membrane-associated PKC alpha, in the absence of any changes in the labeling of either the beta (I/II) or gamma isozymes. These changes were observed only after chronic (4 week) treatment with lithium, and not after acute (5 days) treatment, suggesting potential clinical relevance. Given the critical role of PKC in regulating neuronal signal transduction, lithium's effects on PKC in the limbic system represent an attractive molecular mechanism for its efficacy in treating both poles of manic-depressive illness. In addition, the decreased hippocampal membrane-associated PKC observed in the present study offers a possible explanation for lithium-induced memory impairment.

Effects of chronic lithium treatment on platelet PKC isozymes in Alzheimer's and elderly control subjects

Patients with Alzheimer's disease (AD) have been reported to have abnormalities in peripheral cells similar to some of those found in the brain, including decreased levels of protein kinase C (PKC) in fibroblasts. Since increasing evidence suggests that lithium affects PKC function, we investigated the effects of 3 weeks of lithium administration on the immunolabeling of 4 PKC isozymes (alpha, beta, epsilon, and zeta) in particulate and soluble fractions from platelets of 7 patients with probable AD and 6 age-matched controls. AD patients had significantly less particulate or membrane-associated PKC zeta than normals during the placebo phase (P < 0.003). After 3 weeks of lithium treatment, AD patients had significantly less membrane-associated PKC alpha (P < 0.002), epsilon (P < 0.003), and zeta (P < 0.001) than normals. This is the first report of a difference in PKC in blood cells between AD and control subjects. These findings appear to indicate that some PKC isozymes may be differentially regulated in AD versus elderly controls, at least as evidenced in this peripheral cellular system.

Lithium modulation of phosphoinositide signaling system in rat cortex: selective effect on phorbol ester binding

Recent work indicates that the therapeutic action of lithium may be mediated through perturbation of postreceptor second messenger systems. To elucidate further the postreceptor cellular sites of action(s) of lithium, the effect of chronic lithium treatment on various components of the receptor-activated phosphoinositide pathway was investigated. We found that chronic administration of lithium (0.2% LiCl, 21 days) to adult male rats did not significantly affect phosphoinositide hydrolysis in cerebral cortical slices induced by carbachol (1 mM) or NaF (10 mM). Nor did the same treatment alter the carbachol (1 mM) potentiation of guanosine 5'-(gamma-thio)triphosphate (30 microM) stimulation of phosphoinositide hydrolysis (an index of receptor/G protein coupling) in cortical membranes. Immunoblotting studies revealed no changes in the levels of G alpha q/11 immunoreactivity in the cortex after chronic lithium treatment. The levels of protein kinase C, as revealed by specific binding of [3H]phorbol dibutyrate ([3H]PDBu), were significantly reduced in the cytosolic fraction and increased in the particulate fraction of rat cortex after chronic lithium, whereas the KD of [3H]PDBu binding remained relatively constant. A small and insignificant decrease in the density of [3H]inositol 1,4,5-trisphosphate binding was also found in the cortex. The above data suggest that chronic lithium treatment affects neither the muscarinic cholinergic-linked phosphoinositide turnover nor the putative G protein alpha subunit (G alpha q/11) responsible for phospholipase C activation. However, a possible translocation and activation of protein kinase C activity may be significant in the therapeutic effect of this mood-stabilizing agent.

Actions of lithium on the cyclic AMP signalling system in various regions of the brain--possible relations to its psychotropic actions. A study on the adenylate cyclase in rat cerebral cortex, corpus striatum and hippocampus

It has been estimated that in most industrialized countries 1 person out of every 1000 in the population is undergoing lithium treatment to stabilize their episodic mood disturbances due to manic-depressive illness. Lithium may stabilize mood swings by altering the action of certain neurotransmitters at the synaptic level in the brain. Recent research suggests that lithium alters neurotransmission by affecting neurotransmitter-coupled second messenger systems. A major second messenger system is the adenylate cyclase, which generates intracellular cAMP from ATP. The adenylate cyclases (type I-IV) are regulated by stimulatory and inhibitory receptors, which either stimulate or inhibit the adenylate cyclase activity. The stimulatory and inhibitory neurotransmitter-receptor signals are transferred to the catalytic unit of the adenylate cyclase by Gs and Gi, respectively. The activated receptor induces GTP stimulation of the heterotrimeric G protein, leading to a dissociation of the protein into the active alpha*GTP and the beta gamma complex. The former stimulates the catalytic unit of adenylate cyclase. The stimulation is terminated by a GTPase located on the alpha subunit that converts GTP to inactive GDP. At present, G proteins are known to play a central role in coupling receptors to effector proteins. In addition to extracellular regulation due to neurotransmitters, some adenylate cyclases (type I, III) are regulated by CaM as a consequence of enhanced intracellular concentrations of free Ca2+. The Ca(2+)-dependent stimulation of adenylate cyclase by CaM is assumed to occur by a direct effect on the catalytic unit. The catalytic units sensitive to Ca(2+)-CaM are also subjected to regulation by stimulatory and inhibitory neurotransmitter stimuli. Magnesium is essential for adenylate cyclase activity, since MgATP2- is the enzyme substrate. Furthermore, one Mg2+ site located on the G protein regulates both the receptor agonist affinity and the dissociation of the G protein during the activation cycle. A second Mg2+ site on the catalytic unit is responsible for Mg2+ regulation of the catalytic activity. The present work aimed at investigating the mechanisms by which lithium in vitro and after chronic treatment (ex vivo) affects adenylate cyclase activities in various regions of the rat brain. Lithium in vitro and ex vivo inhibited the selective stimulation of adenylate cyclase by Ca(2+)-CaM in the cerebral cortex. Furthermore, lithium in vitro interacted directly with the catalytic unit of adenylate cyclase.(ABSTRACT TRUNCATED AT 400 WORDS)

CNS signal transduction in the pathophysiology and pharmacotherapy of affective disorders and schizophrenia

Until recently, research on the neurochemical basis of affective disorders (AD) and schizophrenia (SCZ) focused on detecting postulated disturbances in presynaptic neurotransmitter release and metabolism, or postsynaptic receptor function. New insights into the molecular mechanisms involved in the propagation of neurotransmitter signals across biological membranes and in the regulation of neuronal responses have allowed the development of novel hypotheses, which may explain the altered postsynaptic neuroreceptor responsivity thought to be integral to the pathophysiology of these disorders. In this review we evaluate evidence from both basic science and clinical research implicating disturbances in postreceptor signal transduction in the pathophysiology and pharmacotherapy of AD and SCZ. Specific findings regarding potential postreceptor sites of pathophysiology are highlighted in each of these disorders, together with the growing body of data on the possible postreceptor loci of psychotropic drug action, especially lithium and antidepressants.

Chronic lithium treatment impairs phosphatidylinositol hydrolysis in membranes from rat brain regions

Membranes prepared from rat brain regions were used to measure the receptor-coupled and/or guanine nucleotide-binding protein (G protein)-mediated hydrolysis of exogenous [3H]phosphatidylinositol ([3H]PI). Guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) and NaF (in the presence of AlCl3) caused concentration-dependent stimulations of [3H]PI hydrolysis, supporting the conclusion that G proteins mediating [3H]PI hydrolysis can be activated in this preparation. Neither of these responses was altered by in vitro incubation with 8 mM LiCl, but both were reduced in hippocampal, striatal, and cortical membranes from rats that had been treated with lithium for 4 weeks compared with controls. Two cholinergic agonists, carbachol and pilocarpine, induced no hydrolysis of [3H]PI unless GTP gamma S was also present, in which case each equally stimulated [3H]PI hydrolysis above that obtained with GTP gamma S alone. In the presence of GTP gamma S several excitatory amino acid agonists stimulated [3H]PI hydrolysis to an extent similar to that of carbachol. After chronic lithium treatment, [3H]PI hydrolysis stimulated by carbachol was significantly attenuated, but the response to quisqualate was unaffected. Therefore, lithium added in vitro does not have an effect on cholinergic receptor- or G protein-mediated [3H]PI hydrolysis, but each of these is reduced by chronic lithium treatment. Because exogenous [3H]PI was provided as the substrate, it is evident that the inhibitory effect of chronic lithium treatment cannot be due to substrate depletion. Impaired function of G proteins appears to be the most likely mechanism accounting for attenuated [3H]PI hydrolysis after chronic administration of lithium.

Lithium chloride stimulates catecholamine synthesis and secretion in cultured bovine adrenal medullary cells

We examined the effects of lithium treatment on the synthesis and secretion of catecholamines in cultured bovine adrenal medullary cells. The treatment of cells with lithium (0.5-4 mmol/L) for 7 days caused an increase in basal and carbachol-stimulated synthesis of 14C-catecholamines from [14C]-tyrosine but not from [14C]-DOPA. Lithium treatment (4 mmol/L, 7 days) increased the activity of tyrosine hydroxylase in the cells. Lithium treatment (2-4 mmol/L, 7 days) also enhanced the secretion of catecholamines caused by carbachol, although the carbachol-induced influx of 45Ca2+ was reduced. Lithium (4 mmol/L, 7 days) potentiated the secretion of catecholamines evoked by the Ca2+ (1 mumol/L) from cells that were permeabilized by digitonin. The activity of protein kinase C in a soluble fraction was increased in lithium-treated cells (4 mmol/L, 7 days). These results demonstrate that lithium treatment increases the synthesis and secretion of catecholamines and the activity of protein kinase C in cultured adrenal medullary cells.