Chronic treatment with the monoamine oxidase inhibitor phenelzine increases hypothalamic-pituitary-adrenocortical activity in male C57BL/6 mice: relevance to atypical depression

Safinamide, an inhibitor of monoamine oxidase, modulates the magnitude, gating, and hysteresis of sodium ion current

BACKGROUND

Safinamide (SAF), an α-aminoamide derivative and a selective, reversible monoamine oxidase (MAO)-B inhibitor, has both dopaminergic and nondopaminergic (glutamatergic) properties. Several studies have explored the potential of SAF against various neurological disorders; however, to what extent SAF modulates the magnitude, gating, and voltage-dependent hysteresis [Hys(V)] of ionic currents remains unknown.

METHODS

With the aid of patch-clamp technology, we investigated the effects of SAF on voltage-gated sodium ion (NaV) channels in pituitary GH3 cells.

RESULTS

SAF concentration-dependently stimulated the transient (peak) and late (sustained) components of voltage-gated sodium ion current (INa) in pituitary GH3 cells. The conductance-voltage relationship of transient INa [INa(T)] was shifted to more negative potentials with the SAF presence; however, the steady-state inactivation curve of INa(T) was shifted in a rightward direction in its existence. SAF increased the decaying time constant of INa(T) induced by a train of depolarizing stimuli. Notably, subsequent addition of ranolazine or mirogabalin reversed the SAF-induced increase in the decaying time constant. SAF also increased the magnitude of window INa induced by an ascending ramp voltage Vramp. Furthermore, SAF enhanced the Hys(V) behavior of persistent INa induced by an upright isosceles-triangular Vramp. Single-channel cell-attached recordings indicated SAF effectively increased the open-state probability of NaV channels. Molecular docking revealed SAF interacts with both MAO and NaV channels.

CONCLUSION

SAF may interact directly with NaV channels in pituitary neuroendocrine cells, modulating membrane excitability.

Recruitment of Corticotropin-Releasing Hormone (CRH) Neurons in Categorically Distinct Stress Reactions in the Mouse Brain

Corticotropin-releasing hormone (CRH) neurons in the paraventricular hypothalamic nucleus (PVH) are in the position to integrate stress-related information and initiate adaptive neuroendocrine-, autonomic-, metabolic- and behavioral responses. In addition to hypophyseotropic cells, CRH is widely expressed in the CNS, however its involvement in the organization of the stress response is not fully understood. In these experiments, we took advantage of recently available Crh-IRES-Cre;Ai9 mouse line to study the recruitment of hypothalamic and extrahypothalamic CRH neurons in categorically distinct, acute stress reactions. A total of 95 brain regions in the adult male mouse brain have been identified as containing putative CRH neurons with significant expression of tdTomato marker gene. With comparison of CRH mRNA and tdTomato distribution, we found match and mismatch areas. Reporter mice were then exposed to restraint, ether, high salt, lipopolysaccharide and predator odor stress and neuronal activation was revealed by FOS immunocytochemistry. In addition to a core stress system, stressor-specific areas have been revealed to display activity marker FOS. Finally, activation of CRH neurons was detected by colocalization of FOS in tdTomato expressing cells. All stressors resulted in profound activation of CRH neurons in the hypothalamic paraventricular nucleus; however, a differential activation of pattern was observed in CRH neurons in extrahypothalamic regions. This comprehensive description of stress-related CRH neurons in the mouse brain provides a starting point for a systematic functional analysis of the brain stress system and its relation to stress-induced psychopathologies.

Selective effects of dorsal raphé nucleus glucocorticoid receptor deletion on depression-like behavior in female C57BL/6J mice

We have shown differing effects of glucocorticoid receptor (GR) deletion from the dorsal raphé nucleus (DRN) and locus coeruleus (LC) on depression-relevant behavior in male mice, but DRN GR deletion has not been tested in female mice. Female floxed GR mice were given DRN injections of AAV2/9 pseudotype viral vectors transducing Cre recombinase to produce DRN GR gene deletion (Cre) and compared with mice receiving DRN injections of AAV2/9 transducing green fluorescent protein (GFP). Social interaction, a measure of depression-like withdrawal, was unaffected by DRN GR deletion, but forced swim immobility, a measure of despair-like passivity, was reduced in female Cre vs. GFP mice. Behavioral effects were not attributable to changes in basal corticosterone or LC GR deletion. Combined with our prior studies, the current findings suggest that DRN GR have sex-independent effects to promote forced swim immobility, but influence social interaction only in male mice. Differential effects of DRN GR deletion in female mice may provide insight into the greater incidence of depression and specific depression symptoms in women.

Privileged scaffolds as MAO inhibitors: Retrospect and prospects

This review aims to be a comprehensive, authoritative, critical, and readable review of general interest to the medicinal chemistry community because it focuses on the pharmacological, chemical, structural and computational aspects of diverse chemical categories as monoamine oxidase inhibitors (MAOIs). Monoamine oxidases (MAOs), namely MAO-A and MAO-B represent an enormously valuable class of neuronal enzymes embodying neurobiological origin and functions, serving as potential therapeutic target in neuronal pharmacotherapy, and hence we have coined the term "Neurozymes" which is being introduced for the first time ever. Nowadays, therapeutic attention on MAOIs engrosses two imperative categories; MAO-A inhibitors, in certain mental disorders such as depression and anxiety, and MAO-B inhibitors, in neurodegenerative disorders like Alzheimer's disease (AD) and Parkinson's disease (PD). The use of MAOIs declined due to some potential side effects, food and drug interactions, and introduction of other classes of drugs. However, curiosity in MAOIs is reviving and the recent developments of new generation of highly selective and reversible MAOIs, have renewed the therapeutic prospective of these compounds. The initial section of the review emphasizes on the detailed classification, structural and binding characteristics, therapeutic potential, current status and future challenges of the privileged pharmacophores. However, the chemical prospective of privileged scaffolds such as; aliphatic and aromatic amines, amides, hydrazines, azoles, diazoles, tetrazoles, indoles, azines, diazines, xanthenes, tricyclics, benzopyrones, and more interestingly natural products, along with their conclusive SARs have been discussed in the later segment of review. The last segment of the article encompasses some patents granted in the field of MAOIs, in a simplistic way.

A Polysomnographic Study of Parkinson's Disease Sleep Architecture

Sleep disturbance is a common nonmotor phenomenon in Parkinson's disease (PD) affecting patient's quality of life. In this study, we examined the association between clinical characteristics with sleep disorders and sleep architecture patterns in a PD cohort. Patients underwent a standardized polysomnography study (PSG) in their “on medication” state. We observed that male gender and disease duration were independently associated with obstructive sleep apnea (OSA). Only lower levodopa equivalent dose (LED) was associated with periodic limb movement disorders (PLMD). REM sleep behavior disorder (RBD) was more common among older patients, with higher MDS-UPDRS III scores, and LED. None of the investigated variables were associated with the awakenings/arousals (A/A). Sleep efficiency was predicted by amantadine usage and age, while sleep stage 1 was predicted by dopamine agonists and Hoehn & Yahr severity. The use of MAO-B inhibitors and MDS-UPDRS part III were predictors of sleep stages 2 and 3. Age was the only predictor of REM sleep stage and gender for total sleep time. We conclude that sleep disorders and architecture are poorly predictable by clinical PD characteristics and other disease related factors must also be contributing to these sleep disturbances.

Increased antidepressant sensitivity after prefrontal cortex glucocorticoid receptor gene deletion in mice

Our laboratory has previously shown that antidepressants regulate glucocorticoid receptor (GR) expression in the prefrontal cortex (PFC). To determine if PFC GR are involved in antidepressant effects on behavior or hypothalamic-pituitary-adrenocortical (HPA) axis activity, we treated floxed GR male mice with saline or 15 or 30 mg/kg/d imipramine after PFC injection of adeno-associated virus 2/9 vectors transducing expression of Cre recombinase, to knock-down GR (PFC-GRKD), or green fluorescent protein (PFC-GFP), to serve as a control. The pattern of virally transduced GR deletion, common to all imipramine treatment groups, included the infralimbic, prelimbic, and medial anterior cingulate cortex at its largest extent, but was confined to the prelimbic and anterior cingulate cortex at its smallest extent. PFC GR knock-down increased behavioral sensitivity to imipramine, with imipramine-treated PFC-GRKD but not PFC-GFP mice exhibiting significant decreases in depression-like immobility during forced swim. PFC GR deletion did not alter general locomotor activity. The 30 mg/kg dose of imipramine increased plasma corticosterone levels immediately after a 5-min forced swim, but PFC GR knock-down had no significant effect on plasma corticosterone under these experimental conditions. We conclude that PFC GR knock-down, likely limited to the medial prelimbic and anterior cingulate cortices, can increase behavioral sensitivity to antidepressants. These findings indicate a novel role for PFC GR in influencing antidepressant response.

Hypothalamic-pituitary-adrenocortical axis: neuropsychiatric aspects

Evidence of aberrant hypothalamic-pituitary-adrenocortical (HPA) activity in many psychiatric disorders, although not universal, has sparked long-standing interest in HPA hormones as biomarkers of disease or treatment response. HPA activity may be chronically elevated in melancholic depression, panic disorder, obsessive-compulsive disorder, and schizophrenia. The HPA axis may be more reactive to stress in social anxiety disorder and autism spectrum disorders. In contrast, HPA activity is more likely to be low in PTSD and atypical depression. Antidepressants are widely considered to inhibit HPA activity, although inhibition is not unanimously reported in the literature. There is evidence, also uneven, that the mood stabilizers lithium and carbamazepine have the potential to augment HPA measures, while benzodiazepines, atypical antipsychotics, and to some extent, typical antipsychotics have the potential to inhibit HPA activity. Currently, the most reliable use of HPA measures in most disorders is to predict the likelihood of relapse, although changes in HPA activity have also been proposed to play a role in the clinical benefits of psychiatric treatments. Greater attention to patient heterogeneity and more consistent approaches to assessing treatment effects on HPA function may solidify the value of HPA measures in predicting treatment response or developing novel strategies to manage psychiatric disease.

Glucocorticoid receptor deletion from the dorsal raphé nucleus of mice reduces dysphoria-like behavior and impairs hypothalamic-pituitary-adrenocortical axis feedback inhibition

Glucocorticoids can cause depression and anxiety. Mechanisms for glucocorticoid effects on mood are largely undefined. The dorsal raphé nucleus (DRN) produces the majority of serotonin in the brain, and expresses glucocorticoid receptors (GR). Because we previously showed that antidepressants used to treat depression and anxiety decrease DRN GR expression, we hypothesized that deleting DRN GR would have anxiolytic- and antidepressant-like effects. We also hypothesized that DRN GR deletion would disinhibit activity of the hypothalamic-pituitary-adrenal (HPA) axis. Adeno-associated virus pseudotype AAV2/9 expressing either Cre recombinase (DRNGRKO mice) or GFP (DRN-GFP mice) was injected into the DRN of floxed GR mice to test these hypotheses. Three weeks after injection, mice underwent 21 days of social defeat or control handling and were tested for anxiety-like behavior (open-field test, elevated-plus maze), depression-like behavior [sucrose preference, forced-swim test (FST), tail-suspension test (TST)], social interaction, and circadian and stress-induced HPA activity. DRN GR deletion decreased anxiety-like behavior in control but not in defeated mice. DRN GR deletion decreased FST and tended to decrease TST despair-like behavior in both control and defeated mice, but did not affect sucrose preference. Exploration of social (a novel mouse) as well as neutral (an empty box) targets was increased in DRNGRKO mice, suggesting that DRN GR deletion also promotes active coping. DRN GR deletion increased stress-induced HPA activity without strongly altering circadian HPA activity. We have shown a novel role for DRN GR to mediate anxiety- and despair-like behavior and to regulate HPA negative feedback during acute stress.

Sensitivity of depression-like behavior to glucocorticoids and antidepressants is independent of forebrain glucocorticoid receptors

The location of glucocorticoid receptors (GR) implicated in depression symptoms and antidepressant action remains unclear. Forebrain glucocorticoid receptor deletion on a C57B/6×129×CBA background (FBGRKO-T50) reportedly produces increased depression-like behavior and elevated glucocorticoids. We further hypothesized that forebrain GR deletion would reduce behavioral sensitivity to glucocorticoids and to antidepressants. We have tested this hypothesis in mice with calcium calmodulin kinase IIα-Cre-mediated forebrain GR deletion derived from a new founder on a pure C57BL/6 background (FBGRKO-T29-1). We measured immobility in forced swim or tail suspension tests after manipulating glucocorticoids or after dose response experiments with tricyclic or monoamine oxidase inhibitor antidepressants. Despite forebrain GR deletion that was at least as rapid and more extensive than reported in the mixed-strain FBGRKO-T50 mice (Boyle et al. 2005), and possibly because of their different founder, our FBGRKO-T29-1 mice did not exhibit increases in depression-like behavior or adrenocortical axis hormones. Nevertheless, FBGRKO-T29-1 mice were at least as sensitive as floxed GR controls to the depressive effects of glucocorticoids and the effects of two different classes of antidepressants. FBGRKO-T29-1 mice also unexpectedly exhibited increased mineralocorticoid receptor (MR) gene expression. Our results reinforce prior evidence that antidepressant action does not require forebrain GR, and suggest a correlation between the absence of depression-like phenotype and combined MR up-regulation and central amygdala GR deficiency. Our findings demonstrate that GR outside the areas targeted in FBGRKO-T29-1 mice are involved in the depressive effects of glucocorticoids, and leave open the possibility that these GR populations also contribute to antidepressant action.

Lack of elevations in glucocorticoids correlates with dysphoria-like behavior after repeated social defeat

Activity of the hypothalamic-pituitary-adrenocortical (HPA) axis is often abnormal in depression and could hold clues for better treatment of this debilitating disease. However, it has been difficult to use HPA activity as a depression biomarker because both HPA hyperactivity and HPA hypoactivity have been reported in depression. Melancholic depression has typically been associated with HPA hyperactivity, while atypical depression has been linked with HPA hypoactivity. Many animal models of chronic stress recapitulate behavioral aberrations and elevated HPA activity that could represent a model for melancholic depression. However, there are no animal models that could be used to elucidate the etiology or treatment of atypical depression. We have used repeated social defeat in mice to test the hypothesis that this chronic stress would induce dysphoria-like behavior associated with HPA hypoactivity in a subset of subjects. Intruder mice were placed in the home cage of an aggressive resident mouse for 5 min/d for 30 days. The majority of intruder mice had elevated basal plasma corticosterone (High Morning Corticosterone, or HMC) and adrenal 11β hydroxylase mRNA levels relative to control mice that were handled daily. However, a subset of intruder mice (Low Morning Corticosterone; LMC) exhibited basal plasma corticosterone and 11β hydroxylase mRNA levels that were indistinguishable from control levels. Significant changes in emotional behavior only occurred in LMC mice, which exhibited anxiety-like increases in activity and defecation during tail suspension and anhedonia-like decreases in sucrose preference. Relative to HMC mice, LMC mice also showed increases in gene expression of mineralocorticoid receptor in CA2 hippocampus, consistent with the possibility that HPA activity in this group is constrained by increased sensitivity to glucocorticoid negative feedback. LMC mice also exhibited increased c-fos gene expression compared to HMC mice in the paraventricular hypothalamus and lateral septum suggesting that central pathways fail to habituate to chronic stress even though adrenocortical activity is not stimulated. We conclude that LMC mice showed adrenocortical hyporesponsiveness, which in combination with the behavioral abnormalities in this group may represent a model for the HPA hypoactivity associated with atypical depression.

The MAO inhibitor phenelzine improves functional outcomes in mice with experimental autoimmune encephalomyelitis (EAE)

Multiple sclerosis (MS) and the animal model, experimental autoimmune encephalomyelitis (EAE), are both accompanied by motor and non-motor symptoms. Pathological changes in the activities of key neurotransmitters likely underlie many of these symptoms. We have previously described disturbances in the levels of 5-hydroxytryptamine (5-HT/serotonin), noradrenaline (NE) and γ-aminobutyric acid (GABA) in a mouse model of EAE. The potential therapeutic effect of a drug that targets these three neurotransmitters, the antidepressant and anti-panic drug phenelzine (PLZ), was assessed in mice with MOG(35-55) induced EAE. The neurotransmitter content of EAE and control tissue after PLZ administration was first evaluated by HPLC. The ability of PLZ treatment to modulate EAE disease course and clinical signs was then assessed. Daily PLZ treatment, starting seven days after disease induction, delayed EAE onset, reduced disease severity in the chronic phase and was associated with substantial improvements in exploratory behavior and a novel measure of sickness and/or depression. Upon completion of the experiment, PLZ's effects on histopathological markers of the disease were examined. No differences were observed in T cell infiltration, microglia/macrophage reactivity, demyelination or axonal injury in PLZ-treated spinal cords. However, EAE mice treated with PLZ showed a normalization of 5-HT levels in the ventral horn of the spinal cord that might account for the improvements in behavioral outcomes. These results demonstrate the therapeutic potential of MAO inhibitors such as PLZ in MS. Additionally, the behavioral changes observed in EAE mice indicate that alterations in non-motor or 'affective' measures may be valuable to consider in addition to traditional measures of gross locomotor function.

Stress risk factors and stress-related pathology: neuroplasticity, epigenetics and endophenotypes

This paper highlights a symposium on stress risk factors and stress susceptibility, presented at the Neurobiology of Stress workshop in Boulder, CO, in June 2010. This symposium addressed factors linking stress plasticity and reactivity to stress pathology in animal models and in humans. Dr. J. Radley discussed studies demonstrating prefrontal cortical neuroplasticity and prefrontal control of hypothalamo-pituitary-adrenocortical axis function in rats, highlighting the emerging evidence of the critical role that this region plays in normal and pathological stress integration. Dr. M. Kabbaj summarized his studies of possible epigenetic mechanisms underlying behavioral differences in rat populations bred for differential stress reactivity. Dr. L. Jacobson described studies using a mouse model to explore the diverse actions of antidepressants in brain, suggesting mechanisms whereby antidepressants may be differentially effective in treating specific depression endophenotypes. Dr. R. Yehuda discussed the role of glucocorticoids in post-traumatic stress disorder (PTSD), indicating that low cortisol level may be a trait that predisposes the individual to development of the disorder. Furthermore, she presented evidence indicating that traumatic events can have transgenerational impact on cortisol reactivity and development of PTSD symptoms. Together, the symposium highlighted emerging themes regarding the role of brain reorganization, individual differences, and epigenetics in determining stress plasticity and pathology.

Co-species housing in mice and rats: effects on physiological and behavioral stress responsivity

Co-species housing of mice and rats is common practice at most breeding facilities and research laboratories, neglecting the possible effects on the animals. We investigated physiological as well as behavioral stress-reactivity in mice and rats which were either derived from a co-species or species-separated housing condition at the breeding facilities. The animals were kept under the housing condition they were used to or assigned to the opposite one. Co-species housing had a significant impact on acute stress reactivity in mice and rats but only if they were used to this housing condition throughout their lives. Moreover, the stress-effects appeared to be long lasting. Assigning animals, derived from a species-separated housing condition, to co-species housing led to chronic stress in mice and affected experimental behavior of rats. Our findings led to the conclusion that co-species housing in mice and rats should be avoided, supporting the recommendations by the U.S. National Institutes of Health (NIH) and the Dutch Ministry of Health, Welfare and Sport (VWS). In order to support the interpretation, facilitate the reproducibility and comparability and subsequently the generalizability of experimental results, breeding facilities should at least provide detailed information about their housing conditions.

Glucocorticoid status affects antidepressant regulation of locus coeruleus tyrosine hydroxylase and dorsal raphé tryptophan hydroxylase gene expression

Brainstem monoaminergic nuclei express glucocorticoid receptors (GR), and glucocorticoids have been shown to inhibit expression of enzymes involved in monoamine synthesis. Monoamine deficits have been implicated in depression pathology. However, it is unknown if antidepressants regulate brainstem GR, and if glucocorticoids might influence antidepressant effects on monoamine-synthesizing enzymes. Our lab has found opposing effects of the monoamine oxidase inhibitor phenelzine and the tricyclic antidepressant imipramine on HPA activity and forebrain GR gene expression. We therefore hypothesized that phenelzine and imipramine would also affect brainstem GR gene expression differentially, and that antidepressant-induced changes in GR expression would correlate with effects on monoamine-synthesizing enzyme expression. Using in situ hybridization, we measured effects of chronic antidepressant treatment on brainstem GR, locus coeruleus and ventral tegmental area (VTA) tyrosine hydroxylase (TH), and dorsal raphé tryptophan hydroxylase (TPH2) gene expression in male C57BL/6 mice that were adrenalectomized and replaced with defined levels of corticosterone. GR expression was decreased by phenelzine in the locus coeruleus and decreased by imipramine in the dorsal raphé. Phenelzine increased locus coeruleus TH and imipramine increased dorsal raphé TPH2 gene expression in a glucocorticoid-dependent manner, suggesting that increases in these enzymes were due to relief of inhibitory glucocorticoid signaling. We did not find antidepressant effects on GR or TH expression in the VTA or on mineralocorticoid receptor (MR) expression in any of the nuclei examined. Our findings represent a potential mechanism through which antidepressants and glucocorticoids could alter both HPA activity and mood via effects on brainstem GR, norepinephrine, and serotonin.

Differential effects of the antidepressants tranylcypromine and fluoxetine on limbic cannabinoid receptor binding and endocannabinoid contents

The goal of this study was to determine whether the endocannabinoid system is altered by chronic antidepressant treatment. The effects of 3-week administration of the monoamine oxidase inhibitor, tranylcypromine (10 mg/kg) and the selective serotonin reuptake inhibitor, fluoxetine (5 mg/kg) on cannabinoid CB(1) receptor densities and endocannabinoid contents were determined in limbic brain regions of the rat. Tranylcypromine significantly reduced tissue content of the endocannabinoid N-arachidonylethanolamine (anandamide) in the prefrontal cortex, hippocampus and hypothalamus and increased 2-arachidonoylglycerol content in the prefrontal cortex. Tranylcypromine treatment significantly increased CB(1) receptor binding density in the prefrontal cortex and hippocampus, but not in the hypothalamus. Treatment with fluoxetine increased CB(1) receptor density in the prefrontal cortex, but had no effect on endocannabinoid contents in any brain region examined. These data suggest that monoaminergic neurotransmission can regulate the endocannabinoid system and further indicates a role of the endocannabinoid system in affective illness and its treatment.

Differential effects of imipramine and phenelzine on corticosteroid receptor gene expression in mouse brain: potential relevance to antidepressant response

Although glucocorticoid feedback sensitivity of the hypothalamic-pituitary-adrenal (HPA) axis is frequently impaired in depression, atypical depression may exhibit increased feedback sensitivity. Because monoamine oxidase inhibitors (MAOI) are often more effective than tricyclic antidepressants (TCA) for atypical depression, we hypothesized that to normalize HPA function in atypical depression, MAOI would differ from TCA in decreasing rather than increasing feedback sensitivity. Consistent with this hypothesis and prior evidence for opposing effects on HPA feedback in mice, we report contrasting effects of chronic MAOI (phenelzine) and TCA (imipramine) treatment on neural corticosteroid receptor gene expression in adrenalectomized male C57BL/6 mice with fixed glucocorticoid levels. Our findings corroborate prior reports of antidepressant-induced increases in hippocampal mineralocorticoid (MR) and glucocorticoid receptor (GR) expression. However, hippocampal effects were neither sustained nor representative of effects in other brain regions. Imipramine typically increased and phenelzine decreased GR expression in other feedback-related brain regions such as the paraventricular hypothalamus and prefrontal cortex. Imipramine effects were limited to feedback-related regions, whereas phenelzine had additional effects to decrease accumbens GR and central amygdala MR expression. Our results suggest an expansion of the corticosteroid receptor hypothesis of depression to include drug- and brain region-specific actions of antidepressants to decrease as well as increase corticosteroid receptor expression and feedback sensitivity. Our findings further suggest how antidepressants could improve glucocorticoid regulation of HPA activity without also facilitating the adverse effects of glucocorticoids on mood.

The therapeutic potential of monoamine oxidase inhibitors

Monoamine oxidase inhibitors were among the first antidepressants to be discovered and have long been used as such. It now seems that many of these agents might have therapeutic value in several common neurodegenerative conditions, independently of their inhibition of monoamine oxidase activity. However, many claims and some counter-claims have been made about the physiological importance of these enzymes and the potential of their inhibitors. We evaluate these arguments in the light of what we know, and still have to learn, of the structure, function and genetics of the monoamine oxidases and the disparate actions of their inhibitors.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Circadian regulation of mouse topoisomerase I gene expression by glucocorticoid hormones

Because glucocorticoid hormones modulate various biological processes, the endogenous rhythm of their secretion is thought to be an important factor affecting the efficacy and/or toxicity of many drugs. Topoisomerase I (Topo I) is a nuclear target of the anticancer drug camptothecin (CPT). In this study, we demonstrate that Topo I expression in tumor-bearing mice and the efficacy of CPT on the tumor are affected by the 24-h variation in circulating glucocorticoid levels. A single administration of corticosterone (CORT) to the tumor-bearing mice resulted in a significant increase in Topo I mRNA levels not only in the tumor masses but also in other healthy tissues such as liver and skeletal muscle. The CORT-induced increase in Topo I mRNA was suppressed by pretreating the mice with RU486, a glucocorticoid receptor antagonist. Significant 24-h oscillations in the Topo I mRNA levels were observed in the tumor and healthy liver without exogenous CORT, and were eliminated by adrenalectomy of the mice. This result suggests that endogenous glucocorticoid hormones are involved in the circadian regulation of Topo I gene expression. Furthermore, the anti-tumor efficacy of the Topo I inhibitor CPT-11 on the tumor-bearing mice was enhanced by administering the drug at the time when the Topo I activity was increased. Our present results demonstrate that glucocorticoid is involved in the 24-h oscillation mechanism of Topo I gene expression and suggest that monitoring the circadian rhythm in Topo I activity is useful for choosing the most appropriate time of day to administer of Topo I inhibitors.