Evidence that lithium induces a glutamatergic: nitric oxide-mediated response in rat brain

The neuropsychiatric manifestations of COVID-19: Interactions with psychiatric illness and pharmacological treatment

The recent outbreak of the corona virus disease (COVID-19) has had major global impact. The relationship between severe acute respiratory syndrome coronavirus (SARS-CoV-2) infection and psychiatric diseases is of great concern, with an evident link between corona virus infections and various central and peripheral nervous system manifestations. Unmitigated neuro-inflammation has been noted to underlie not only the severe respiratory complications of the disease but is also present in a range of neuro-psychiatric illnesses. Several neurological and psychiatric disorders are characterized by immune-inflammatory states, while treatments for these disorders have distinct anti-inflammatory properties and effects. With inflammation being a common contributing factor in SARS-CoV-2, as well as psychiatric disorders, treatment of either condition may affect disease progression of the other or alter response to pharmacological treatment. In this review, we elucidate how viral infections could affect pre-existing psychiatric conditions and how pharmacological treatments of these conditions may affect overall progress and outcome in the treatment of SARS-CoV-2. We address whether any treatment-induced benefits and potential adverse effects may ultimately affect the overall treatment approach, considering the underlying dysregulated neuro-inflammatory processes and potential drug interactions. Finally, we suggest adjunctive treatment options for SARS-CoV-2-associated neuro-psychiatric symptoms.

Nitric oxide: Antidepressant mechanisms and inflammation

Millions of individuals worldwide suffers from mood disorders, especially major depressive disorder (MDD), which has a high rate of disease burden in society. Although targeting the biogenic amines including serotonin, and norepinephrine have provided invaluable links with the pharmacological treatment of MDD over the last four decades, a growing body of evidence suggest that other biologic systems could contribute to the pathophysiology and treatment of MDD. In this chapter, we highlight the potential role of nitric oxide (NO) signaling in the pathophysiology and thereby treatment of MDD. This has been investigated over the last four decades by showing that (i) levels of NO are altered in patients with major depression; (ii) modulators of NO signaling exert antidepressant effects in patients with MDD or in the animal studies; (iii) NO signaling could be targeted by a variety of antidepressants in animal models of depression; and (iv) NO signaling can potentially modulate the inflammatory pathways that underlie the pathophysiology of MDD. These findings, which hypothesize an NO involvement in MDD, can provide a new insight into novel therapeutic approaches for patients with MDD in the future.

Nitric oxide involvement in additive antidepressant-like effect of agmatine and lithium in mice forced swim test

Lithium is still the main agent in the management of mood disorders such as depression. Likewise, agmatine protects the central nervous system (CNS) against depression. The aim of the present study was to examine the possible additive antidepressant-like effect of agmatine and lithium in mice forced swim test (FST) as well as exploration of the probable involvement of nitric oxide (NO) pathway in this response. Results showed that pretreatment with a subeffective dose of agmatine (0.01 mg/kg) augmented the antidepressant-like effect of lithium subeffective dose (3 mg/kg) (P < 0.001). L-NG-nitroarginine methyl ester (L-NAME, nonspecific nitric oxide synthase [NOS] inhibitor) at doses of 10 and 30 mg/kg, and 7-nitroindazole (7-NI, neuronal NOS inhibitor) at doses of 15 and 30 mg/kg potentiated the antidepressant-like effect of the subeffective combination of lithium (3 mg/kg) and agmatine (0.001 mg/kg) (P < 0.001, P < 0.01, respectively). However, various doses of aminoguanidine (25 and 50 mg/kg, inducible NOS inhibitor) failed to alter the immobility time of the same combination (P > 0.05). Moreover, pretreatment with subeffective doses of L-arginine (substrate for NOS, 300 and 750 mg/kg) reversed the augmenting antidepressant-like effect of agmatine (0.01 mg/kg) on lithium (3 mg/kg) (P < 0.001). Our results revealed that agmatine enhances the antidepressant-like effects of lithium and the NO pathway might mediate this phenomenon. In addition, constitutive NOS plays a dramatic role in this response.

Pathologic role of nitrergic neurotransmission in mood disorders

Mood disorders are chronic, recurrent mental diseases that affect millions of individuals worldwide. Although over the past 40 years the biogenic amine models have provided meaningful links with the clinical phenomena of, and the pharmacological treatments currently employed in, mood disorders, there is still a need to examine the contribution of other systems to the neurobiology and treatment of mood disorders. This article reviews the current literature describing the potential role of nitric oxide (NO) signaling in the pathophysiology and thereby the treatment of mood disorders. The hypothesis has arisen from several observations including (i) altered NO levels in patients with mood disorders; (ii) antidepressant effects of NO signaling blockers in both clinical and pre-clinical studies; (iii) interaction between conventional antidepressants/mood stabilizers and NO signaling modulators in several biochemical and behavioral studies; (iv) biochemical and physiological evidence of interaction between monoaminergic (serotonin, noradrenaline, and dopamine) system and NO signaling; (v) interaction between neurotrophic factors and NO signaling in mood regulation and neuroprotection; and finally (vi) a crucial role for NO signaling in the inflammatory processes involved in pathophysiology of mood disorders. These accumulating lines of evidence have provided a new insight into novel approaches for the treatment of mood disorders.

Roles of Gasotransmitters in Synaptic Plasticity and Neuropsychiatric Conditions

Synaptic plasticity is important for maintaining normal neuronal activity and proper neuronal functioning in the nervous system. It is crucial for regulating synaptic transmission or electrical signal transduction to neuronal networks, for sharing essential information among neurons, and for maintaining homeostasis in the body. Moreover, changes in synaptic or neural plasticity are associated with many neuropsychiatric conditions, such as schizophrenia (SCZ), bipolar disorder (BP), major depressive disorder (MDD), and Alzheimer's disease (AD). The improper maintenance of neural plasticity causes incorrect neurotransmitter transmission, which can also cause neuropsychiatric conditions. Gas neurotransmitters (gasotransmitters), such as hydrogen sulfide (H2S), nitric oxide (NO), and carbon monoxide (CO), play roles in maintaining synaptic plasticity and in helping to restore such plasticity in the neuronal architecture in the central nervous system (CNS). Indeed, the upregulation or downregulation of these gasotransmitters may cause neuropsychiatric conditions, and their amelioration may restore synaptic plasticity and proper neuronal functioning and thereby improve such conditions. Understanding the specific molecular mechanisms underpinning these effects can help identify ways to treat these neuropsychiatric conditions.

Lithium in the treatment of bipolar disorder: pharmacology and pharmacogenetics

After decades of research, the mechanism of action of lithium in preventing recurrences of bipolar disorder remains only partially understood. Lithium research is complicated by the absence of suitable animal models of bipolar disorder and by having to rely on in vitro studies of peripheral tissues. A number of distinct hypotheses emerged over the years, but none has been conclusively supported or rejected. The common theme emerging from pharmacological and genetic studies is that lithium affects multiple steps in cellular signaling, usually enhancing basal and inhibiting stimulated activities. Some of the key nodes of these regulatory networks include GSK3 (glycogen synthase kinase 3), CREB (cAMP response element-binding protein) and Na(+)-K(+) ATPase. Genetic and pharmacogenetic studies are starting to generate promising findings, but remain limited by small sample sizes. As full responders to lithium seem to represent a unique clinical population, there is inherent value and need for studies of lithium responders. Such studies will be an opportunity to uncover specific effects of lithium in those individuals who clearly benefit from the treatment.

A Review of Biomarkers in Mood and Psychotic Disorders: A Dissection of Clinical vs. Preclinical Correlates

Despite significant research efforts aimed at understanding the neurobiological underpinnings of mood (depression, bipolar disorder) and psychotic disorders, the diagnosis and evaluation of treatment of these disorders are still based solely on relatively subjective assessment of symptoms as well as psychometric evaluations. Therefore, biological markers aimed at improving the current classification of psychotic and mood-related disorders, and that will enable patients to be stratified on a biological basis into more homogeneous clinically distinct subgroups, are urgently needed. The attainment of this goal can be facilitated by identifying biomarkers that accurately reflect pathophysiologic processes in these disorders. This review postulates that the field of psychotic and mood disorder research has advanced sufficiently to develop biochemical hypotheses of the etiopathology of the particular illness and to target the same for more effective disease modifying therapy. This implies that a "one-size fits all" paradigm in the treatment of psychotic and mood disorders is not a viable approach, but that a customized regime based on individual biological abnormalities would pave the way forward to more effective treatment. In reviewing the clinical and preclinical literature, this paper discusses the most highly regarded pathophysiologic processes in mood and psychotic disorders, thereby providing a scaffold for the selection of suitable biomarkers for future studies in this field, to develope biomarker panels, as well as to improve diagnosis and to customize treatment regimens for better therapeutic outcomes.

Lithium increases nitric oxide levels in subjects with bipolar disorder during depressive episodes

BACKGROUND

Altered nitric oxide (NO) signaling has been associated with the pathophysiology of Bipolar Disorder (BD), directly affecting neurotransmitter release and synaptic plasticity cascades. Lithium has shown to regulate NO levels in preclinical models. However, no study has addressed peripheral NO levels in unmedicated BD. Also, lithium's effects on NO levels have not been studied in humans.

METHODS

Plasma NO was evaluated in subjects with BD I and II during a depressive episode (n = 26). Subjects had a score of ≥18 in the 21-item Hamilton Depression Rating Scale and were followed-up during a 6-week trial with lithium. Plasma NO levels were also compared to matched healthy controls (n = 28). NO was determined by chemiluminescence method.

RESULTS

Lithium treatment significantly increased plasma NO levels after 6 weeks of treatment in comparison to baseline levels in bipolar depression (p = 0.016). Baseline NO levels during depressive episodes showed no difference when matching up to healthy controls (p = 0.66).

CONCLUSION

The present findings suggest that lithium upregulates NO signaling in unmedicated BD with short illness duration. Further studies with larger samples are needed to confirm the effects of lithium on NO pathway and its association with synaptic plasticity and therapeutics of BD.

Effects of lithium on inflammation

Lithium is an effective medication for the treatment of bipolar affective disorder. Accumulating evidence suggests that inflammation plays a role in the pathogenesis of bipolar disorder and that lithium has anti-inflammatory effects that may contribute to its therapeutic efficacy. This article summarizes the studies which examined the effects of lithium on pro- and anti-inflammatory mediators. Some of the summarized data suggest that lithium exerts anti-inflammatory effects (e.g., suppression of cyclooxygenase-2 expression, inhibition of interleukin (IL)-1β and tumor necrosis factor-α production, and enhancement of IL-2 and IL-10 synthesis). Nevertheless, there is a large body of data which indicates that under certain experimental conditions lithium also exhibits pro-inflammatory properties (e.g., induction of IL-4, IL-6 and other pro-inflammatory cytokines synthesis). The reviewed studies utilized various experimental model systems, and it is thus difficult to draw an unequivocal conclusion regarding the effect of lithium on specific inflammatory mediators.

Suppression of memory acquisition following co-administration of lithium and atorvastatin through nitric oxide pathway in mice

PURPOSE

The aim of this study was to investigate the interactive effect of lithium and atorvastatin on cognitive performance and the role of NO as a potential mechanism involved in this interaction.

MATERIALS AND METHODS

Memory performance was evaluated in a two-trial recognition Y-maze test and a step-through passive avoidance task in mice. Lithium (5, 10, 20 or 40 mg/kg, i.p.) and atorvastatin (1 mg/kg, p.o.) were administered 1 h before each trial, L-NAME, a non-specific NO synthase inhibitor (3, 10 mg/kg, i.p.); aminoguanidine, a specific inducible NO synthase (iNOS) inhibitor (100 mg/kg); and L-arginine, a NO precursor (750 mg/kg) were administered 30 min before training sessions. The level of plasma NO end-products (NOx) was determined using Griess reagent protocol.

RESULTS

1) Lithium (40 mg/kg) impaired the acquisition of spatial recognition memory; 2) lithium did not affect the retrieval phase of spatial memory; 3) atorvastatin (1 mg/kg) significantly impaired the memory performance, when co-administered with the sub-effective dose of lithium (10 mg/kg), but did not affect the status when administered with lithium (5 mg/kg); 4) L-NAME (10 mg/kg) and aminoguanidine (100 mg/kg) dramatically decreased memory performance in mice received sub-effective doses of both lithium (5 mg/kg) and atorvastatin (1 mg/kg); 5) L-arginine (750 mg/kg) improved the memory acquisition in mice administered lithium (10 mg/kg) and atorvastatin (1 mg/kg); 6) lithium did not affect the cognitive performance in the passive avoidance test. All results were compatible and confirmed with in vitro determination of plasma NOx levels.

CONCLUSIONS

Lithium, dose dependently, impaired acquisition phase of spatial recognition memory. Lithium and atorvastatin co-administration impaired spatial recognition memory mediating by nitrergic pathway. In addition to L-arginine, our data from L-NAME and aminoguanidine also support the involvement of NO pathway in this interaction.

Nitrergic, glutamatergic and gabaergic systems in lithium toxicity

We examined the role of nitrergic, glutamatergic and gamma-aminobutyric acid (GABA)-ergic systems in the mechanism(s) underlying lithium induced acute toxicity. With this aim, lithium (18 mEq/kg, i.p.) intoxicated rats were observed for 3 hr recording their clinical signs and death. Lithium exposure at the dose used produced central nervous system (CNS) depression. Pre-treatment of N(w)-nitro-L-arginine methyl ester (L-NAME) a nonselective nitric oxide synthase inhibitor (10 mg/kg, i.p.), 7-nitroindazole (7-NI) a selective neuronal nitric oxide synthase inhibitor (25 mg/kg, i.p.), nitric oxide precursor L-arginine (1,000 mg/kg, i.p.) and MK-801 a noncompetitive antagonist of N-methyl-D-aspartic acid class of glutamate receptors (0.5 mg/kg, i.p.) all increased CNS depression and mortality in lithium group however, no change was seen in GABA receptor agonist GABA (1,000 mg/kg, i.p.) or D-arginine (1,000 mg/kg, i.p.) a biologically inactive enantiomer of L-arginine pre-treated rats. Glutamic acid decarboxylase (GAD) enzyme activity was measured in hippocampus, cerebral cortex and cerebellum of the different groups of animals. GAD enzyme activity reduced in cerebral cortex but not altered in hippocampus or cerebellum by lithium as compared to the control (saline) group. We conclude that an interaction with nitrergic and glutamatergic systems may have a role in the acute toxicity of lithium in rats.The inhibition of glutamate metabolism may arise from this interaction and the involvement of GABA-ergic system should be further investigated in this toxicity.

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.

Lithium chloride disrupts consolidation of morphine-induced conditioned place preference in male mice: the nitric oxide/cyclic GMP signaling pathway

Lithium effects on brain functions such as cognition, attention, learning and memory are well-established for ages; however, the way it affects these functions and its precise mechanism of action remains unknown. The purpose of this study was to determine the effects of lithium on the consolidation of morphine-associated conditioned place preference and the possible involvement of the NO/cGMP pathway. Using an unbiased conditioned place preference (CPP) model, the effects of lithium (1-100 mg/kg, i.p.), nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (5-100 mg/kg, i.p.), nitric oxide precursor L-arginine (50-150 mg/kg, i.p.) and phosphodiesterase inhibitor sildenafil (5-40 mg/kg, i.p.) on the consolidation of morphine-induced CPP were assessed. In addition, the possible interaction between lithium, L-arginine and sildenafil or subeffective doses of lithium and L-NAME on the consolidation of morphine-induced contextual memory was evaluated. NMRI mice were used in all studies. Lithium (5-30 mg/kg, i.p.), immediately after conditioning trials, significantly reduced the time spent by mice in the reward-paired compartment. Although post-training administration of L-arginine, sildenafil or L-NAME had no significant effect on the consolidation of CPP, concomitant administration of L-arginine (50-150 mg/kg) and sildenafil (5-10 mg/kg) with lithium (30 mg/kg) prevented the impairing effect of lithium. Also, co-administration of sub-effective doses of lithium (1 mg/kg) and L-NAME (5 mg/kg) disrupted consolidation of CPP. However, delayed administration of effective doses of lithium, which shows specific effect on memory consolidation, did not affect morphine-induced CPP. Lithium seems to inhibit consolidation of morphine-induced CPP and this impairing effect might be via nitric oxide/cyclic GMP pathway.

Chronic lithium treatment protects the rat kidney against ischemia/reperfusion injury: the role of nitric oxide and cyclooxygenase pathways

Ischemia/reperfusion injury is a major problem in renal transplantation. Several evidences represent lithium preconditioning effect against ischemia/reperfusion injury in various tissues. In this study our aim was to investigate the protective effect of chronic lithium administration on renal ischemia/reperfusion injury in rats. Ischemia/reperfusion injury was induced by clamping left renal pedicle for 60 min, 2 weeks after right nephrectomy. Lithium-treated animals received lithium-chloride in drinking water for 30days. In order to investigate the role of nitric oxide (NO) and cyclooxygenase (COX) pathways in renoprotective effect of lithium, N(ω)-nitro-L-arginine methyl ester hydrochloride (L-NAME, NO synthase inhibitor) and indomethacin (COX inhibitor) were used, respectively. Serum creatinine, blood urea nitrogen and renal histology were assessed 24h after inducing ischemia/reperfusion injury. Dimercaptosuccinic acid scan was also performed 48 h following operation. Chronic lithium treatment in ischemia/reperfusion injury groups significantly decreased creatinine (1.09±0.16 mg/dl), blood urea nitrogen (59.0±13.38 mg/dl), histological damage (7.83%±4.02%) and improved cortical function compared with non-lithium treated animals (4.45±0.44, 176.66±12.24 mg/dl and 83.5%±3.5%, respectively) (P<0.001). Either L-NAME or indomethacin administration partially reversed the protective effect of lithium, while simultaneous blockade of NO and COX pathways completely abolished lithium renoprotective effect. Our results indicate that lithium ameliorates renal ischemia/reperfusion injury through NO and/or COX pathways. We propose that lithium pre-treatment as a simple and practical intervention to boost the renal viability and function after ischemia/reperfusion injury may be promising in the setting of transplantation.

Involvement of nitric oxide-cGMP pathway in the anticonvulsant effects of lithium chloride on PTZ-induced seizure in mice

Lithium is still the mainstay in the treatment of affective disorders as a mood stabilizer. Lithium also shows some anticonvulsant properties. While the underlying mechanisms of action of lithium are not yet exactly understood, we used a model of clonic seizure induced by pentylenetetrazole (PTZ) in male NMRI mice to investigate whether the anticonvulsant effect of lithium is mediated via NO-cGMP pathway. Injection of a single effective dose of lithium chloride (25 mg/kg) intraperitoneally (i.p.) increased significantly the seizure threshold (P<0.01). The anticonvulsant properties of the effective dose of lithium were prevented by pre-treatment with the per se non-effective doses of L-ARG [the substrate for nitric oxide synthase; NOS] (30 and 50 mg/kg) or sildenafil [a phosphodiesterase 5 inhibitor] (10 and 20 mg/kg). L-NAME [a non-specific NOS inhibitor] (5, 15 and 30 mg/kg), 7-NI [a specific neural NOS inhibitor] (30 and 60 mg/kg) or MB [a guanylyl cyclase inhibitor] (0.5 and 1 mg/kg) augmented the anticonvulsant effect of a sub-effective dose of lithium (10 mg/kg, i.p.). Whereas several doses of aminoguanidine [an inducible NOS inhibitor] (20, 50 and 100 mg/kg) failed to alter the anticonvulsant effect of lithium. Our findings demonstrated that nitric oxide-cyclic GMP pathway could be involved in the anticonvulsant properties of the lithium chloride. In addition, the role of constitutive NOS versus inducible NOS is prominent in this phenomenon.

Protective effects of lithium on acetic acid-induced colitis in rats

Inflammatory bowel disease (IBD) is a multifactorial disease with unknown etiology characterized by oxidative stress, leukocyte infiltration, and rise in inflammatory cytokines such as tumor necrosis factor (TNF-alpha). Lithium, as a therapeutic agent for bipolar disorder, exerts some anti-inflammatory properties. In this study we have investigated the effects of lithium on acetic-acid-induced colitis in rats. Lithium (5, 10, and 20 mg/kg) was administered 1 h before the introduction of acetic acid. Colonic status was investigated 24 h following colitis induction through macroscopic, histological, and biochemical analyses. Lithium (20 mg/kg) ameliorated macroscopic and microscopic scores. These observations were accompanied by a reduction in the degree of both neutrophil infiltration, indicated by decreased myeloperoxidase activity, and lipid peroxidation, as measured by a decline in malondialdehyde content in inflamed colon as well as a decrease in TNF-alpha levels. These findings suggest that lithium exerts beneficial effects on experimental colitis and therefore might be useful in the treatment of IBD.

Antinociceptive effect of chronic lithium on visceral hypersensitivity in a rat model of diarrhea-predominant irritable bowel syndrome: The role of nitric oxide pathway

BACKGROUND AND AIM

Lithium, a widely used drug in bipolar-affective disorders, plays gastro-protective roles. The effects of lithium on several tissues are mediated through nitric oxide (NO), which regulates gastrointestinal motility and mucosal integrity. The aim of this study was to investigate the protective effect of chronic lithium administration on visceral hypersensitivity and to investigate the role of NO as a potential mechanism of lithium in a rat model of irritable bowel syndrome.

METHODS

Colitis was induced by the intracolonic administration of acetic acid. After subsidence of inflammation on the seventh experimental day, nociception and defecation parameters were measured. A subgroup of animals had been pretreated with lithium carbonate (600 mg/L) for 35 days. Thereafter, either a non-selective NO synthase (NOS) inhibitor (N-nitro-L-arginine methyl ester [L-NAME], 10 mg/kg), a selective NOS inhibitor (aminoguanidine, 100 mg/kg), or saline were administered intraperitoneally 1 h before measurements.

RESULTS

Chronic lithium attenuated the visceral hypersensitivity, increased the nociceptive threshold, and decreased stool frequency. L-NAME and aminoguanidine decreased the nociceptive threshold and reduced the protective effects of lithium on visceral hypersensitivity. Stool frequency was increased in both the lithium-treated and water-treated groups by L-NAME administration, but not aminoguanidine. The form of defecation in the lithium-treated rats shifted toward hard stools rather than being soft and formless, but NOS inhibitors did not change the stool consistency pattern.

CONCLUSION

The results indicate the antinociceptive property of chronic lithium on visceral hypersensitivity. As this effect was lowered by NOS inhibitors, NO might play a role in the protective effect of lithium to some extent.

Nitric oxide involvement in the antidepressant-like effects of acute lithium administration in the mouse forced swimming test

In the present study we evaluated the involvement of l-arginine/nitric oxide (NO)/cGMP pathway in the antidepressant-like effects of acute lithium administration in the mouse forced swimming test (FST). Lithium, at 30 and 100 mg/kg, significantly reduced the immobility times of mice in the FST, whereas at lower doses (0.5, 5 and 10 mg/kg) had no effect on the immobility time. The NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), at 10 and 30 mg/kg, and the selective neuronal NOS inhibitor N(omega)-propyl-L-arginine (L-NPA), at 5 and 15 mg/kg, had no significant effects on the FST, whereas they significantly decreased the immobility time at 100 and 30 mg/kg, respectively. Combination of non-effective dose of lithium (10 mg/kg) with low doses of L-NAME (30 mg/kg) or L-NPA (15 mg/kg) significantly reduced the immobility times in the FST. Moreover, the guanylyl cyclase inhibitor ODQ at 50 mg/kg significantly decreased the immobility time of mice, whereas it had not significant effects on the FST at 2, 10 and 20 mg/kg. Combination of lithium (10 mg/kg) with 20 mg/kg ODQ significantly decreased the immobility times in the FST. Non-effective doses of L-arginine (750 mg/kg) or sildenafil (5 mg/kg) significantly reversed the antidepressant-like effect of 30 mg/kg lithium in the FST. Neither of the drugs had effect on the locomotor activity. These data indicate the involvement of L-arginine/NO/cGMP pathway in the antidepressant-like effect of lithium in the mouse FST and also might suggest the concurrent administration of NOS inhibitors and lithium as an appropriate strategy for treatment of depression.

Nitric oxide involvement in the effect of acute lithium administration on the nonadrenergic noncholinergic-mediated relaxation of rat gastric fundus

INTRODUCTION

Lithium has largely met its initial promise as the first drug to be discovered in the modern era of psychopharmacology. However, the mechanism for its action remains an enigma. The aim of the present study was to verify the effect of acute lithium administration on the nonadrenergic noncholinergic (NANC)-mediated relaxation of rat isolated gastric fundus and to evaluate the role of nitric oxide pathway in this manner.

MATERIALS AND METHODS

The isolated rat gastric fundus strips were precontracted with 0.5 microM serotonin and electrical field stimulation (EFS) was applied at 5 Hz frequency to obtain NANC-mediated relaxation in the presence or absence of lithium (0.1, 0.5, 1 and 5 mM). Also, effects of combining lithium (0.1 mM) with the NO synthase (NOS) inhibitor L-NAME (0.03 microM) or the guanylyl cyclase inhibitor ODQ (1 microM) on relaxant responses to EFS was investigated. Moreover, effects of combining lithium (1 mM) with 0.1 mM L-arginine (a precursor of NO) on neurogenic relaxation were assessed. Also, the effect of lithium (1 mM) on relaxation to sodium nitroprusside (SNP; 1 nM-0.1 mM) and glyceryltrinitrate (GTN; 0.1-10 microM) was investigated.

RESULTS

The NANC-mediated relaxation was significantly (P<0.001) reduced by lithium in a dose- and time-dependent manner. Combination of lithium (0.1 mM) with L-NAME (0.03 microM), which separately had partial inhibitory effect on relaxations, significantly (P<0.001) reduced the NANC-mediated relaxation of gastric fundus. ODQ (1 microM) significantly inhibited the neurogenic relaxations in the presence or absence of lithium (0.1 and 1 mM). Although L-arginine at 0.1 mM had no effect on relaxation to EFS, it prevented the inhibition by lithium (1 mM) of relaxant responses to EFS. Also, SNP and GTN produced concentration-dependent relaxation in precontracted rat gastric fundus which was not altered by lithium incubation (1 mM).

DISCUSSION

Our experiments indicated that lithium likely by interfering with L-arginine/NO pathway in nitrergic nerve can result in impairment of NANC-mediated relaxation of rat gastric fundus.

Effect of chronic lithium administration on endothelium-dependent relaxation of rat mesenteric bed: role of nitric oxide

The mechanism of action of lithium, an effective treatment for bipolar disease, is still unknown. In this study, the mesenteric vascular beds of control rats and rats that were chronically treated with lithium were prepared by the McGregor method, and the mesenteric vascular bed vasorelaxation responses were examined. NADPH-diaphorase histochemistry was used to determine the activity of NOS (nitric oxide synthase) in mesenteric vascular beds. We demonstrated that ACh-induced vasorelaxation increased in the mesenteric vascular bed of rats treated with lithium. Acute Nο-nitro-l-arginine methyl ester (l-NAME) administration in the medium blocked ACh-induced vasorelaxation in the control group more effectively than in lithium-treated rats, while the vasorelaxant response to sodium nitroprusside, a NO donor, was not different between lithium-treated and control groups. Acute aminoguanidine administration blocked ACh-induced vasorelaxation of lithium-treated rats, but had no effect in the control rats. Furthermore, NOS activity, determined by NADPH-diaphorase staining, was significantly greater in the mesenteric vascular beds from chronic lithium-treated rats than in those from control rats. These data suggest that the enhanced ACh-induced endothelium-derived vasorelaxation in rat mesenteric bed from chronic lithium-treated rats might be associated with increased NOS activity, likely via iNOS. Simultaneous acute l-NAME and indomethacin administration suggests the possible upregulation of EDHF (endothelium-derived hyperpolarizing factor) in lithium-treated rats.

Appearance of antidepressant-like effect by sildenafil in rats after central muscarinic receptor blockade: evidence from behavioural and neuro-receptor studies

The phosphodiesterase (PDE) 5 inhibitor sildenafil has been shown to display psychotropic actions in humans and animals, and has been used for the treatment of antidepressant-associated erectile dysfunction. However, its effects on the neurobiology of depression are unknown. Nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) inhibition is anti-depressant in animals, and increasing cGMP with sildenafil is anxiogenic in rodents. Substantial cholinergic-nitrergic interaction exists in the brain, while sildenafil shows modulatory actions on cholinergic transmission. Depression is also associated with increased cholinergic drive. Here we report that sildenafil increases muscarinic acetylcholine receptor (mAChR) signaling in human neuroblastoma cells. We also show that fluoxetine (20 mg/kg/day x 7 days), as well as a combination of sildenafil (10 mg/kg/day x 7 days) plus the antimuscarinic atropine (1 mg/kg/day x 7 days) demonstrates significant, comparable antidepressant-like effects in the rat forced swim test (FST) and also reduces cortical beta-adrenergic receptor (beta-AR) density, while sildenafil or atropine alone did not. Importantly, sildenafil did not modify fluoxetine's response. Sildenafil thus demonstrates antidepressant-like effects but only after central muscarinic receptor blockade, providing evidence for cholinergic-nitrergic interactions in the neurobiology of depression.

Effect of lithium on endothelium-dependent and neurogenic relaxation of rat corpus cavernosum: Role of nitric oxide pathway

INTRODUCTION

Some studies have reported erectile dysfunction in patients receiving lithium through a mechanism that has not yet been defined. The aim of the present study was to verify the effect of acute lithium administration on the nonadrenergic noncholinergic (NANC)- and endothelium-mediated relaxation of rat isolated corpus cavernosum.

MATERIALS AND METHODS

The isolated rat corporeal strips were precontracted with phenylephrine hydrochloride (7.5 microM) and electrical field stimulation (EFS) was applied at different frequencies (2, 5, 10, and 15 Hz) to obtain NANC-mediated relaxation or relaxed by adding cumulative doses of acetylcholine (10nM-1mM) to obtain endothelium-dependent relaxation in the presence or absence of lithium (0.3, 0.5, 1, and 5mM). Also, effects of combining lithium (0.3mM) with 30 nM and 0.1 nM L-NAME (an NO synthase inhibitor) on NANC- and acetylcholine-mediated relaxation was investigated, respectively. Moreover, effects of combining lithium (1mM) with 0.1mM and 10 microM L-arginine (a precursor of NO) on NANC- and endothelium-mediated relaxation was assessed, respectively. Also, the effect of lithium (1mM) on relaxation to sodium nitroprusside (SNP; 1nM-1mM), an NO donor, was investigated.

RESULTS

The NANC-mediated relaxation was significantly (P<0.001) reduced by 1 and 5mM, but not by 0.3 and 0.5mM lithium. Lithium significantly (P<0.001) attenuated the maximum response to acetylcholine in a concentration-dependent manner. Combination of lithium (0.3mM) with 30 and 0.1 nM L-NAME, which separately had a minimum effect on NANC- and endothelium-mediated relaxation, significantly (P<0.001) reduced the NANC- and endothelium-mediated relaxation, respectively. Although L-arginine at 10 microM and 0.1mM did not alter the relaxant responses to acetylcholine and EFS, it improved the inhibition by lithium (1mM) of relaxant responses to acetylcholine and EFS, respectively. Also, SNP produced similar concentration-dependent relaxations from both groups.

DISCUSSION

Our experiments indicated that lithium likely by interfering with NO pathway in both endothelium and nitrergic nerve can result in impairment of both the endothelium- and NANC-mediated relaxation of rat corpus cavernosum.

Role of nitric oxide in the gastro-protective effect of lithium

BACKGROUND AND AIM

Lithium is widely used for the management of neuropsychiatric symptoms in bipolar disorders. A few studies have shown that lithium has a protective effect against gastric damage with an unknown mechanism. Some of the actions of lithium are mediated through nitric oxide (NO), which has an important role in the regulation of gastric wall blood flow as well as gastric mucosal integrity. The aim of this study was to test the hypothesis if the gastro-protective effect of lithium is mediated through NO.

METHODS

Male Wistar rats were pre-treated with either a non-selective NO synthase inhibitor (N(G)-nitro-l-arginine, 10mg/kg), a selective inducible NO synthase inhibitor (aminoguanidine, 100mg/kg) or saline. Lithium carbonate (10, 20, 50 and 100mg/kg) was then administered intraperitoneally 1h before the induction of gastric mucosal damage. Gastric damage was induced by either water immersion stress or ethanol gavage in rats.

RESULTS

Lithium had a significant protective effect in both stress and ethanol-induced gastric damage, but it needed in ethanol-induced gastric damage a higher dose than in the stress induced lesion. Lithium carbonate doses 20 and 50mg/kg produced plasma concentrations that were in the range of human therapeutic Li levels (0.6-1.0muM). Pre-treatment of animals with N(G)-nitro-l-arginine (20 and 40mg/kg) reduced the protective effect of lithium against ethanol-induced gastric damage, but not in stress-induced damage. Aminoguanidine administration showed no effect on the damage reduction either in control or lithium treated rats.

CONCLUSIONS

The results indicate that NO might play a role in the gastro-protective effect of lithium against ethanol-induced gastric damage in rats.

Lithium inhibits the modulatory effects of morphine on susceptibility to pentylenetetrazole-induced clonic seizure in mice: involvement of a nitric oxide pathway

Lithium has been reported to inhibit opioid-induced properties. The present study examined the effect of acute and chronic administration of lithium chloride (LiCl) on morphine's biphasic modulation of susceptibility to pentylenetetrazole (PTZ)-induced clonic seizure in mice. We also examined the possible involvement of nitric oxide (NO) pathway in lithium effect. Both acute (0.1 and 1 mg/kg) and chronic (same doses, 21 consecutive days) administration of LiCl completely inhibited the anticonvulsant and proconvulsant effects of morphine (at doses 1 and 30 mg/kg, respectively). A very low and per se noneffective dose of LiCl (0.05 mg/kg) significantly inhibited both phases of morphine effect when administered concomitant with a noneffective low dose of naloxone (0.1 mg/kg). The NO synthase inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME) at a per se noneffective dose of 0.3 mg/kg potentiated the inhibitory effects of low doses of LiCl (0.01 and 0.05 mg/kg) on both phases of morphine effect. l-arginine, a NO synthase substrate, at a per se noneffective dose of 30 mg/kg reversed the inhibitory effects of lithium (1 mg/kg). Lithium is capable of antagonizing both modulatory effects of morphine on seizure susceptibility even at relatively low doses. These inhibitory effects of lithium may also involve NO synthesis.

Early suppression of striatal cyclic GMP may predetermine the induction and severity of chronic haloperidol-induced vacous chewing movements

Haloperidol persists in brain tissue long after discontinuation while haloperidol-induced tardive dyskinesia often worsens after withdrawal of the drug. The mechanism of haloperidol-associated tardive dyskinesia is unknown, although neurotoxic pathways are suspected. Nitric oxide (NO) synthase (NOS) inhibitors exacerbate haloperidol-induced catalepsy, while haloperidol itself is a potent neuronal NOS inhibitor in vitro. Since NO and cGMP are involved in striatal neural plasticity, this study investigates a possible relation between cGMP and extrapyramidal symptoms as early predictors of haloperidol-associated tardive dyskinesia. Sprague-Dawley rats were administered either water or oral haloperidol (0.25 mg/kg/d p.o.) for 17 weeks, followed by 3 weeks withdrawal. Saline (i.p.) or the nNOS/guanylate cyclase inhibitor, methylene blue (5 mg/kg/d i.p.), were co-administered with haloperidol for the first three weeks of treatment. Vacous chewing movements (VCM's) were continuously monitored, followed by the determination of striatal cGMP and peripheral serum nitrogen oxide (NOx) levels. Chronic haloperidol engendered significant VCM's, with acute withdrawal associated with significantly reduced striatal cGMP levels as well as reduced serum NOx. Furthermore, suppressed cGMP levels were maintained and VCM's were significantly worse after early administration of methylene blue to the chronic haloperidol group. However, serum NOx was unchanged from control. We conclude that the central effects of chronic haloperidol on striatal NO-cGMP function persist for up to 3 weeks post-withdrawal. Moreover, suppression of striatal cGMP constitutes an early neuronal insult that determines the presence and intensity of haloperidol-associated motor dysfunction.

Withdrawal-associated changes in peripheral nitrogen oxides and striatal cyclic GMP after chronic haloperidol treatment

The irreversible nature of haloperidol-induced tardive dyskinesia suggests a neurotoxic etiology, although the causes are unknown. Since nitric oxide demonstrates neurotoxic as well as neuroprotectant properties, and antipsychotics can inhibit nitric oxide (NO) synthase in vitro, this study investigates the NO-cGMP pathway as a pre-determining factor in chronic haloperidol-associated dyskinesia in rats. Sprague-Dawley rats were administered either water, oral haloperidol (0.25 mg/kg per day po), the guanylyl cyclase-nNOS inhibitor, methylene blue (MB; 5 mg/kg per day ip) or haloperidol plus MB for 3 weeks. In a second protocol, rats received water or haloperidol orally for 17 weeks, followed by 3 weeks withdrawal. Either saline (ip) or MB (ip) was administered for 3 weeks prior to haloperidol withdrawal. Vacous chewing movements (VCMs) were continuously monitored, followed by the determination of serum nitrogen oxides (NO(x)) and striatal cGMP at week 20. Chronic haloperidol engendered significant VCMs, with acute withdrawal resulting in significantly reduced plasma NO(x) and striatal cGMP. Furthermore, NO(x) and cGMP suppression was amplified by pre-withdrawal MB administration. Sub-acute haloperidol similarly induced incremental VCMs, but without effect on NO(x) or cGMP. However, haloperidol plus MB also induced significantly greater VCMs with decreased cGMP compared to haloperidol alone. Thus, NO(x)-cGMP inhibition persists pronounced after long-term haloperidol treatment and withdrawal. MB potentiation of these effects suggests that haloperidol inhibits a NO-dependent neuro-protective response to oxidative stress in the striatum that may pre-determine TD development.

Correlation between hypermetabolism and neuronal damage during status epilepticus induced by lithium and pilocarpine in immature and adult rats

The correlation between seizure-induced hypermetabolism and subsequent neuronal damage was studied in 10-day-old (P10), 21-day-old (P21), and adult rats subjected to lithium-pilocarpine status epilepticus (SE). Local CMRglc (LCMRglc) values were measured by the [14C]2-deoxyglucose method for a duration of 45 minutes starting at 60 minutes after the onset of SE, and neuronal damage was assessed by cresyl violet staining at 6 days after SE. In P21 and adult rats, LCMRglc values were increased by 275 to 875% in all thalamic, cortical, forebrain, and hypothalamic regions plus the substantia nigra. In addition, at P21 there were also large increases in LCMRglc in brainstem regions. In P10 rats, metabolic increases were mostly located in cortical and forebrain regions plus the substantia nigra but did not affect hypothalamic, thalamic, or brainstem areas. In adult rats, there was an anatomical correlation between hypermetabolism and neuronal damage. At P21, although hypermetabolism occurred in regions with damage, the extent of damage varied considerably with the animals and ranged from an almost negligible to a very extended degree. Finally, in P10 rats, although quite pronounced hypermetabolism occurred, there was no neuronal damage induced by the seizures. Thus, in the present model of epilepsy, the correlation between marked hypermetabolism and neuronal damage can be shown in adult rats. Conversely, immature rats can sustain major metabolic activations that lead either to a variable extent of damage, as seen at P21, or no damage, as recorded at P10.