Increased adenylyl cyclase type 1 mRNA, but not adenylyl cyclase type 2 in the rat hippocampus following antidepressant treatment

Forebrain overexpression of type 1 adenylyl cyclase promotes molecular stability and behavioral resilience to physical stress

The ability to cope with stress is essential for emotional stability and mental health. It is also hypothesized that factors promoting resilience to stress may offer treatment strategies for maladaptive disorders such as anxiety and depression. Here, we find that physical restraint reduces the expression of type 1 adenylyl cyclase (Adcy1), a neurospecific synaptic enzyme that positively regulates the cAMP signaling cascade. Conversely, an increase of forebrain Adcy1 expression in transgenic mouse (i.e., Adcy1 ^tg mouse) predisposes individuals to molecular stability and behavioral resilience. Transgenic overexpression of Adcy1 prevents the physical restraint-induced down-regulation of brain-derived neurotrophic factor (BDNF) and neuropeptide Y (NPY). Further, Adcy1 ^tg mice maintain regular locomotive activity in novelty exploration and voluntary wheel running following physical restraint. Adcy1 ^tg mice show higher corticosterone and lower basal glucocorticoid receptor (GR) expression, along with a higher MR (mineralocorticoid receptor) to GR ratio in the hippocampus. Further, Adcy1 ^tg mice show reduced immobility under acute physical stress conditions in the forced swimming test and are more sensitive to the antidepressant desipramine. Our results demonstrate a novel function of Adcy1 in stress coping and suggest Adcy1 as a potential target to antagonize stress vulnerability and promote antidepressant efficacy.

Adenylyl cyclase 7 and neuropsychiatric disorders: A new target for depression?

Adenylyl cyclases (ACs) are enzymes that catalyze the production of cyclic adenosine monophosphate (cAMP) from adenosine triphosphate (ATP). Humans express nine isoforms of membranous ACs and a soluble AC. Studies with genetic knockout or overexpression rodent models have indicated that AC isoforms may be targeted to achieve specific therapeutic outcomes. AC1, for instance, has been suggested and pursued as a target for relieving pain. Notably, previous studies examining genetically modified mice as well as human genetic polymorphisms have suggested a link between AC7 activity and depressive disorders. In the present review we present an overview on AC function and discuss the most recent developments to target AC isoforms for drug therapies. We next focus on discussing the available literature on the molecular and animal pharmacology of AC7 highlighting the available studies on the role of AC7 in depressive disorders. In addition, we discuss other possible physiological functions of AC7 relating to ethanol effects and the immune system and conclude with considerations about pharmacological modulation of AC7.

CNS Target Identification and Validation: Avoiding the Valley of Death or Naive Optimism?

There are many challenges along the path to the approval of new drugs to treat CNS disorders, one of the greatest areas of unmet medical need with a large societal burden and health-care impact. Unfortunately, over the past two decades, few CNS drug approvals have succeeded, leading many pharmaceutical companies to deprioritize this therapeutic area. The reasons for the failures in CNS drug discovery are likely to be multifactorial. However, selecting the most biologically plausible molecular targets that are relevant to the disorder is a critical first step to improve the probability of success. In this review, we outline previous methods for identifying and validating novel targets for CNS drug discovery, and, cognizant of previous failures, we discuss potential new strategies that may improve the probability of success of developing novel treatments for CNS disorders.

Regulation of Calcium-Independent Phospholipase A2 Expression by Adrenoceptors and Sterol Regulatory Element Binding Protein-Potential Crosstalk Between Sterol and Glycerophospholipid Mediators

Calcium-independent phospholipase A2 (iPLA2) is an 85-kDa enzyme that releases docosahexaenoic acid (DHA) from glycerophospholipids. DHA can be metabolized to resolvins and neuroprotectins that have anti-inflammatory properties and effects on neural plasticity. Recent studies show an important role of prefrontal cortical iPLA2 in hippocampo-prefrontal cortical LTP and antidepressant-like effect of the norepinephrine reuptake inhibitor (NRI) antidepressant, maprotiline. In this study, we elucidated the cellular mechanisms through which stimulation of adrenergic receptors could lead to increased iPLA2 expression. Treatment of SH-SY5Y neuroblastoma cells with maprotiline, another tricyclic antidepressant with noradrenaline reuptake inhibiting properties, nortriptyline, and the adrenergic receptor agonist, phenylephrine, resulted in increased iPLA2β mRNA expression. This increase was blocked by inhibitors to alpha-1 adrenergic receptor, mitogen-activated protein (MAP) kinase or extracellular signal-regulated kinase (ERK) 1/2, and sterol regulatory element-binding protein (SREBP). Maprotiline and phenylephrine induced binding of SREBP-2 to sterol regulatory element (SRE) region on the iPLA2 promoter, as determined by electrophoretic mobility shift assay (EMSA). Together, results indicate that stimulation of adrenoreceptors causes increased iPLA2 expression via MAP kinase/ERK 1/2 and SREBP, and suggest a possible mechanism for effect of CNS noradrenaline on neural plasticity and crosstalk between sterol and glycerophospholipid mediators, that may play a role in physiological or pathophysiological processes in the brain and other organs.

Potential molecular and cellular mechanism of psychotropic drugs

Psychiatric disorders are among the most debilitating of all medical illnesses. Whilst there are drugs that can be used to treat these disorders, they give sub-optimal recovery in many people and a significant number of individuals do not respond to any treatments and remain treatment resistant. Surprisingly, the mechanism by which psychotropic drugs cause their therapeutic benefits remain unknown but likely involves the underlying molecular pathways affected by the drugs. Hence, in this review, we have focused on recent findings on the molecular mechanism affected by antipsychotic, mood stabilizing and antidepressant drugs at the levels of epigenetics, intracellular signalling cascades and microRNAs. We posit that understanding these important interactions will result in a better understanding of how these drugs act which in turn may aid in considering how to develop drugs with better efficacy or increased therapeutic reach.

The genetics of selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are among the most widely prescribed drugs in psychiatry. Based on the fact that SSRIs increase extracellular monoamine levels in the brain, the monoamine hypothesis of depression was introduced, postulating that depression is associated with too low serotonin, dopamine and noradrenaline levels. However, several lines of evidence indicate that this hypothesis is too simplistic and that depression and the efficacy of SSRIs are dependent on neuroplastic changes mediated by changes in gene expression. Because a coherent view on global gene expression is lacking, we aim to provide an overview of the effects of SSRI treatment on the final targets of 5-HT receptor signal transduction pathways, namely the transcriptional regulation of genes. We address gene polymorphisms in humans that affect SSRI efficacy, as well as in vitro studies employing human-derived cells. We also discuss the molecular targets affected by SSRIs in animal models, both in vivo and in vitro. We conclude that serotonin transporter gene variation in humans affects the efficacy and side-effects of SSRIs, whereas SSRIs generally do not affect serotonin transporter gene expression in animals. Instead, SSRIs alter mRNA levels of genes encoding serotonin receptors, components of non-serotonergic neurotransmitter systems, neurotrophic factors, hypothalamic hormones and inflammatory factors. So far little is known about the epigenetic and age-dependent molecular effects of SSRIs, which might give more insights in the working mechanism(s) of SSRIs.

Role of AC-cAMP-PKA Cascade in Antidepressant Action of Electroacupuncture Treatment in Rats

Adenylyl cyclase (AC)-cyclic adenosine monophosphate (cAMP)-cAMP-dependent protein kinase A (PKA) cascade is considered to be associated with the pathogenesis and treatment of depression. The present study was conducted to explore the role of the cAMP cascade in antidepressant action of electroacupuncture (EA) treatment for chronic mild stress (CMS)-induced depression model rats. The results showed that EA improved significantly behavior symptoms in depression and dysfunction of AC-cAMP-PKA signal transduction pathway induced by CMS, which was as effective as fluoxetine. Moreover, the antidepressant effects of EA rather than Fluoxetine were completely abolished by H89, a specific PKA inhibitor. Consequently, EA has a significant antidepressant treatment in CMS-induced depression model rats, and AC-cAMP-PKA signal transduction pathway is crucial for it.

Antidepressant-like effects of curcumin on serotonergic receptor-coupled AC-cAMP pathway in chronic unpredictable mild stress of rats

Serotonergic receptors take their physiologic effects by affecting adenylyl cyclase (AC) catalytic activity and cyclic adenosine monophosphate (cAMP) concentration. AC-cAMP second messenger pathway has been recently suggested to play an important role in depression. Therefore, the compound that regulates the signal pathway may have potential as antidepressant. Curcumin is the main component of Curcuma longa L, a well-known indigenous herb with comprehensive bioactivities. In the present study, we investigated the effects of chronic unpredictable mild stress (CUMS) and curcumin on behaviours and serotonergic receptor-coupled AC-cAMP signal pathway in rats. Curcumin produced beneficial effects on the stressed rats by effectively improving CUMS-induced low sucrose consumption and reducing serum corticosterone levels in rats. Moreover, curcumin enhanced AC activity and cAMP levels in platelet and various brain regions, and up-regulated mRNA expressions of AC subtypes AC 2, AC 8 and cAMP response element binding protein (CREB) in the hippocampus, cortex and hypothalamus of the CUMS rats. Curcumin also attenuated CUMS-induced reductions of 5-hydroxytryptamine (5-HT) levels and high expressions of central 5-HT(1A/1B/7) receptors in rats. These results suggested that the potent antidepressant property of curcumin might be attributed to its improvement of AC-cAMP pathway as well as CREB via suppressing central 5-HT(1A/1B/7) receptors in the CUMS rats. Our findings provided a basis for examining the interaction of serotonergic receptors and AC-cAMP pathway in depression and curcumin treatment.

Chronic antidepressants potentiate via sigma-1 receptors the brain-derived neurotrophic factor-induced signaling for glutamate release

Up-regulation of BDNF (brain-derived neurotrophic factor) has been suggested to contribute to the action of antidepressants. However, it is unclear whether chronic treatment with antidepressants may influence acute BDNF signaling in central nervous system neurons. Because BDNF has been shown by us to reinforce excitatory glutamatergic transmission in cultured cortical neurons via the phospholipase-gamma (PLC-gamma)/inositol 1,4,5-trisphosphate (IP3)/Ca2+ pathway (Numakawa, T., Yamagishi, S., Adachi, N., Matsumoto, T., Yokomaku, D., Yamada, M., and Hatanaka, H. (2002) J. Biol. Chem. 277, 6520-6529), we examined in this study the possible effects of pretreatment with antidepressants on the BDNF signaling through the PLC-gamma)/IP3/Ca2+ pathway. Furthermore, because the PLC-gamma/IP3/Ca2+ pathway is regulated by sigma-1 receptors (Hayashi, T., and Su, T. P. (2001) Proc. Natl. Acad. Sci. U. S. A. 98, 491-496), we examined whether the BDNF signaling is modulated by sigma-1 receptors (Sig-1R). We found that the BDNF-stimulated PLC-gamma activation and the ensued increase in intracellular Ca2+ ([Ca2+]i) were potentiated by pretreatment with imipramine or fluvoxamine, so was the BDNF-induced glutamate release. Furthermore, enhancement of the interaction between PLC-gamma and TrkB (receptor for BDNF) after imipramine pretreatment was observed. Interestingly, BD1047, a potent Sig-1R antagonist, blocked the imipramine-dependent potentiation on the BDNF-induced PLC-gamma activation and glutamate release. In contrast, overexpression of Sig-1R per se, without antidepressant pretreatment, enhances BDNF-induced PLC-gamma activation and glutamate release. These results suggest that antidepressant pretreatment selectively enhance the BDNF signaling on the PLC-gamma/IP3/Ca2+ pathway via Sig-1R, and that Sig-1R plays an important role in BDNF signaling leading to glutamate release.

Nitric oxide synthesis is required for exercise-induced increases in hippocampal BDNF and phosphatidylinositol 3' kinase expression

Previous studies have shown that running exercise, either alone or in combination with antidepressant treatment, results in increased hippocampal BDNF levels. Nitric oxide (NO) is an important signaling molecule that has neuronal survival-promoting properties and has been shown to play an important role in plasticity associated with activating interventions. Herein, we administered the NO synthase (NOS) inhibitor, N-nitro-L-arginine methyl ester (L-NAME), in conjunction with the monoamine oxidase inhibitor (MAOI) antidepressant, tranylcypromine, and voluntary wheel-running exercise to determine whether the enhancement in full-length BDNF mRNA occurring with these interventions is dependent upon NO synthesis. Our results demonstrate that both chronic exercise and chronic exercise-plus-tranylcypromine lead to enhanced hippocampal BDNF mRNA and protein expression. NOS inhibition prevents this effect of chronic exercise, but only partly prevents the effects of the exercise/antidepressant combination. Thus, the robust enhancement in BDNF mRNA occurring with exercise appears to be NO synthesis-dependent, but the intervention including antidepressant may enhance BDNF expression through alternative intracellular mechanisms. In addition, because exercise and antidepressants have both been shown to activate survival-promoting genes, we evaluated the levels of hippocampal phosphatidylinositol 3' kinase (PI-3K), an important signaling molecule within a principal neuronal survival-promoting intracellular pathway. Like BDNF mRNA and protein, exercise increases the expression of PI-3K, whereas concomitant NOS inhibition prevents this increase in PI-3K immunoreactivity above control levels. Our results are discussed in light of possible overlapping, but distinct intracellular pathways activated by exercise and antidepressant treatment to bring about enhancements in BDNF expression and other survival-promoting effects. These findings further demonstrate the potential therapeutic potential of chronic exercise to supplement pharmacotherapeutic treatment of mood disorders.

Candidate genes for antidepressant response to selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) can safely and successfully treat major depression, although a substantial number of patients benefit only partially or not at all from treatment. Genetic polymorphisms may play a major role in determining the response to SSRI treatment. Nonetheless, it is likely that efficacy is determined by multiple genes, with individual genetic polymorphisms having a limited effect size. Initial studies have identified the promoter polymorphism in the gene coding for the serotonin reuptake transporter as moderating efficacy for several SSRIs. The goal of this review is to suggest additional plausible polymorphisms that may be involved in antidepressant efficacy. These include genes affecting intracellular transductional cascades; neuronal growth factors; stress-related hormones, such as corticotropin-releasing hormone and glucocorticoid receptors; ion channels and synaptic efficacy; and adaptations of monoaminergic pathways. Association analyses to examine these candidate genes may facilitate identification of patients for targeted alternative therapies. Determining which genes are involved may also assist in identifying future, novel treatments.

Invited review: the evolution of antidepressant mechanisms

Present antidepressants are all descendents of the serendipitous findings in the 1950s that the monoamine oxidase inhibitor iproniazid and the tricyclic antidepressant imipramine were effective antidepressants. The identification of their mechanism of action, and those of reserpine and amphetamine, in the 1960s, led to the monoamine theories of depression being postulated; first, with noradrenaline then 5-hydroxytryptamine being considered the more important amine. These monoamine theories of depression predominated both industrial and academic research for four decades. Recently, in attempts to design new drugs with faster onsets of action and more universal therapeutic action, downstream alterations common to current antidepressants are being examined as potential antidepressants. Additionally, the use of animal models has identified a number of novel targets some of which have been subjected to clinical trials in humans. However, monoamine antidepressants remain the best current medications and it may be some time before they are dislodged as the market leaders.

Noradrenergic and serotonergic blockade inhibits BDNF mRNA activation following exercise and antidepressant

Antidepressants and physical exercise have been shown to increase the transcription of hippocampal brain-derived neurotrophic factor (BDNF). Much evidence regarding the initial actions of antidepressant medications as well as exercise leads to the hypothesis that noradrenergic (NE) and/or serotonergic (5-HT) activation is a key element in the BDNF transcriptional elevation common to both interventions. Currently, we used short-term beta-adrenergic, 5-HT(1A), or 5-HT(2A/C) receptor blockade to characterize the influence of NE and 5-HT systems on BDNF transcription during physical exercise and antidepressant treatment. In situ hybridization revealed that beta-adrenergic blockade significantly blunted the BDNF mRNA elevations due to exercise, and also inhibited the modest elevations in the CA3 and dentate gyrus following short-term treatment with tranylcypromine. In contrast, 5-HT(2A/C) blockade only minimally altered exercise-induced BDNF mRNA levels, but inhibited up-regulation of BDNF transcription via tranylcypromine. Finally, 5-HT(1A) blockade did not inhibit exercise-induced BDNF mRNA elevations, but significantly enhanced levels above those achieved with exercise alone in the CA4. These results suggest that NE activation via beta-adrenergic receptors may be essential for both exercise and antidepressant-induced BDNF regulation. 5-HT(1A) and 5-HT(2A/C) activation, on the other hand, appear to be most important for antidepressant-induced BDNF regulation, but may also participate significantly in exercise-induced regulation in the CA4.

Imipramine treatment up-regulates the expression and function of mGlu2/3 metabotropic glutamate receptors in the rat hippocampus

We examined the effect of a chronic imipramine treatment (10 mg/kg, i.p., once daily for 21 days) on the expression and function of metabotropic glutamate (mGlu) receptors in discrete regions of the rat brain. Chronic imipiramine treatment up-regulated the expression of mGlu2/3 receptor proteins in the hippocampus, nucleus accumbens, cerebral cortex and corpus striatum. Expression of mGlu1a receptor protein was increased exclusively in the hippocampus, whereas no changes in the expression of mGlu4 and mGlu5 receptors or Homer-1a protein were detected. Using hippocampal slices, we examined the stimulation of polyphosphoinositide (PI) hydrolysis induced by mGlu receptor agonists in control and imipramine-treated rats. Imipramine treatment amplified the PI response to the non subtype-selective mGlu receptor agonist, 1S,3R-aminocyclopentane-1,3-dicarboxylated (1S,3R-ACPD) in both hippocampal and cortical slices, but failed to affect the response to the selective mGlu1/5 receptor agonist, S-3,5-dihydroxyphenylglycine (DHPG). Amplification was restored when DHPG was combined with the selective mGlu2/3 receptor agonist, LY379268. In addition, 1S,3R-ACPD-stimulated PI hydrolysis was no longer enhanced in imipramine-treated rats when the mGlu2/3 component of the PI response was abrogated by the antagonist, LY341495. In contrast, the ability of LY379268 to inhibit forskolin-stimulated cAMP formation was reduced in hippocampal slices of rats chronically treated with imipramine. Taken together, these results suggest that neuroadaptive changes in the expression and function of mGlu2/3 receptors occur in response to chronic antidepressants.

Antidepressants and neuroplasticity

OBJECTIVE

We review the literature on the cellular changes that underlie the structural impairments observed in brains of animals exposed to stress and in subjects with depressive disorders. We discuss the molecular, cellular and structural adaptations that underlie the therapeutic responses of different classes of antidepressants and contribute to the adaptive plasticity induced in the brain by these drugs.

METHODS

We review results from various clinical and basic research studies.

RESULTS

Studies demonstrate that chronic antidepressant treatment increases the rate of neurogenesis in the adult hippocampus. Studies also show that antidepressants up-regulate the cyclic adenosine monophosphate (cAMP) and the neurotrophin signaling pathways involved in plasticity and survival. In vitro and in vivo data provide direct evidence that the transcription factor, cAMP response element-binding protein (CREB) and the neurotrophin, brain derived-neurotrophic factor (BDNF) are key mediators of the therapeutic response to antidepressants.

CONCLUSIONS

These results suggest that depression maybe associated with a disruption of mechanisms that govern cell survival and neural plasticity in the brain. Antidepressants could mediate their effects by increasing neurogenesis and modulating the signaling pathways involved in plasticity and survival.

Isoform-specific changes of adenylate cyclase mRNA expression in rat brains following chronic electroconvulsive shock

1. Electroconvulsive shock (ECS) has been reported to regulate the cAMP signaling system at various levels, suggesting that the cAMP system is involved in the therapeutic mechanism. 2. Chronic ECS has been suggested to change the expressions of adenylate cyclase (AC) genes, which constitute at least 9 families. However, little is known about its effect on the expression of AC. Therefore, to understand how chronic ECS alters the expression of AC genes in the brain, the authors analyzed the expression of 9 AC isoforms at the transcriptional level in rat hippocampus and cerebellum by quantitative RT-PCR following chronic ECS treatment. 3. Chronic ECS treatment was found to induce differential changes in the expression of AC isoforms in an isoform- and brain region-specific manner in the rat hippocampus and cerebellum. 4. Thus, it is concluded that chronic ECS induces differential changes in the expression of AC isoform mRNA in an isoform- and brain region-specific manner in the rat hippocampus and cerebellum. This suggests that the differential expression of AC isoforms might be an important mechanism by which chronic ECS treatment regulates the cAMP signaling system in rat brains.

Increased hippocampal BDNF immunoreactivity in subjects treated with antidepressant medication

BACKGROUND

The cAMP signaling pathway, and its downstream neurotrophic factor BDNF, are major targets of antidepressant medications. Abnormalities in this pathway have previously been reported in postmortem brain of subjects with mood disorders. This study was designed to test whether the diagnosis of a mood disorder, or treatment with an antidepressant or mood stabilizer was associated with changes in hippocampal BDNF in postmortem brain.

METHODS

Frozen postmortem anterior hippocampus sections were obtained from the Stanley Foundation Neuropathology Consortium. Tissue from subjects with major depression, bipolar disorder, schizophrenia and nonpsychiatric control subjects were stained for BDNF using immunohistochemistry.

RESULTS

Increased BDNF expression was found in dentate gyrus, hilus and supragranular regions in subjects treated with antidepressant medications at the time of death, compared with antidepressant-untreated subjects. Furthermore, there was a trend toward increased BDNF expression in hilar and supragranular regions in depressed subjects treated with antidepressants, compared with the subjects not on these medications at the time of death.

CONCLUSIONS

These findings are consistent with recent studies measuring CREB levels in this same subject sample, and support current animal and cellular models of antidepressant function.

Signaling: cellular insights into the pathophysiology of bipolar disorder

Clinical studies over the years have provided evidence that monoamine signaling and hypothalamic-pituitary-adrenal axis disruption are integral to the pathophysiology of bipolar disorder. A full understanding of the pathophysiology from a molecular to a systems level must await the identification of the susceptibility and protective genes driving the underlying neurobiology of bipolar disorder. Furthermore, the complexity of the unique biology of this affective disorder, which includes the predisposition to episodic and often progressive mood disturbance, and the dynamic nature of compensatory processes in the brain, coupled with limitations in experimental design, have hindered our progress to date. Imaging studies in patient populations have provided evidence of a role for anterior cingulate, amygdala, and prefrontal cortex in the pathophysiology of bipolar disorder. More recent research strategies designed to uncover the molecular mechanisms underlying our pharmacologic treatments and their interaction in the regulation of signal transduction as well as more advanced brain imaging studies remain promising approaches. This experimental strategy provides data derived from the physiologic response of the system in affected individuals and addresses the critical dynamic interaction with pharmacologic agents that effectively modify the clinical expression of the pathophysiology.