Chronic administration of imipramine and lithium changes the phase-angle relationship between the activity and core body temperature circadian rhythms in rats

The impact of lithium on circadian rhythms and implications for bipolar disorder pharmacotherapy

Bipolar disorder (BD) is characterized by disrupted circadian rhythms affecting sleep, arousal, and mood. Lithium is among the most effective mood stabilizer treatments for BD, and in addition to improving mood symptoms, stabilizes sleep and activity rhythms in treatment responsive patients. Across a variety of experimental models, lithium has effects on circadian rhythms. However, uncertainty exists as to whether these actions directly pertain to lithium's therapeutic effects. Here, we consider evidence from mechanistic studies in animals and cells and clinical trials in BD patients that identify associations between circadian rhythms and the therapeutic effects of lithium. Most evidence indicates that lithium has effects on cellular circadian rhythms and increases morningness behaviors in BD patients, changes that may contribute to the therapeutic effects of lithium. However, much of this evidence is limited by cross-sectional analyses and/or imprecise proxy markers of clinical outcomes and circadian rhythms in BD patients, while mechanistic studies rely on inference from animals or small numbers of patients . Further study may clarify the essential mechanisms underlying lithium responsive BD, better characterize the longitudinal changes in circadian rhythms in BD patients, and inform the development of therapeutic interventions targeting circadian rhythms.

New targets for rapid antidepressant action

Current therapeutic options for major depressive disorder (MDD) and bipolar disorder (BD) are associated with a lag of onset that can prolong distress and impairment for patients, and their antidepressant efficacy is often limited. All currently approved antidepressant medications for MDD act primarily through monoaminergic mechanisms. Glutamate is the major excitatory neurotransmitter in the central nervous system, and glutamate and its cognate receptors are implicated in the pathophysiology of MDD, and in the development of novel therapeutics for this disorder. The rapid and robust antidepressant effects of the N-methyl-d-aspartate (NMDA) antagonist ketamine were first observed in 2000. Since then, other NMDA receptor antagonists have been studied in MDD. Most have demonstrated relatively modest antidepressant effects compared to ketamine, but some have shown more favorable characteristics. This article reviews the clinical evidence supporting the use of novel glutamate receptor modulators with direct affinity for cognate receptors: (1) non-competitive NMDA receptor antagonists (ketamine, memantine, dextromethorphan, AZD6765); (2) subunit (GluN2B)-specific NMDA receptor antagonists (CP-101,606/traxoprodil, MK-0657); (3) NMDA receptor glycine-site partial agonists (GLYX-13); and (4) metabotropic glutamate receptor (mGluR) modulators (AZD2066, RO4917523/basimglurant). We also briefly discuss several other theoretical glutamate receptor targets with preclinical antidepressant-like efficacy that have yet to be studied clinically; these include α-amino-3-hydroxyl-5-methyl-4-isoxazoleproprionic acid (AMPA) agonists and mGluR2/3 negative allosteric modulators. The review also discusses other promising, non-glutamatergic targets for potential rapid antidepressant effects, including the cholinergic system (scopolamine), the opioid system (ALKS-5461), corticotropin releasing factor (CRF) receptor antagonists (CP-316,311), and others.

Manipulating the sleep-wake cycle and circadian rhythms to improve clinical management of major depression

BACKGROUND

Clinical psychiatry has always been limited by the lack of objective tests to substantiate diagnoses and a lack of specific treatments that target underlying pathophysiology. One area in which these twin failures has been most frustrating is major depression. Due to very considerable progress in the basic and clinical neurosciences of sleep-wake cycles and underlying circadian systems this situation is now rapidly changing.

DISCUSSION

The development of specific behavioral or pharmacological strategies that target these basic regulatory systems is driving renewed clinical interest. Here, we explore the extent to which objective tests of sleep-wake cycles and circadian function - namely, those that measure timing or synchrony of circadian-dependent physiology as well as daytime activity and nighttime sleep patterns - can be used to identify a sub-class of patients with major depression who have disturbed circadian profiles.

SUMMARY

Once this unique pathophysiology is characterized, a highly personalized treatment plan can be proposed and monitored. New treatments will now be designed and old treatments re-evaluated on the basis of their effects on objective measures of sleep-wake cycles, circadian rhythms and related metabolic systems.

Chronobiology and mood disorders

The clinical observations of diurnal variation of mood and early morning awakening in depression have been incorporated into established diagnostic systems, as has the seasonal modifier defining winter depression (seasonal affective disorder, SAD). Many circadian rhythms measured in depressive patients are abnormal: earlier in timing, diminished in amplitude, or of greater variability. Whether these disturbances are of etiological significance for the role of circadian rhythms in mood disorders, or a consequence of altered behavior can only be dissected out with stringent protocols (eg, constant routine or forced desynchrony). These protocols quantify contributions of the circadian pacemaker and a homeostatic sleep process impacting on mood, energy, appetite, and sleep. Future studies will elucidate any allelic mutations in “circadian clock” –related or “sleep”-related genes in depression. With respect to treatment, antidepressants and mood stabilizers have no consistent effect on circadian rhythmicity. The most rapid antidepressant modality known so far is nonpharmacological: total or partial sleep deprivation in the second half of the night. The disadvantage of sleep deprivation, that most patients relapse after recovery sleep, can be prevented by coadministration of lithium, pindolol, serotonin (5-HT) reuptake inhibitors, bright light, or a subsequent phase-advance procedure. Phase advance of the sleep-wake cycle alone also has rapid effects on depressed mood, which lasts longer than sleep deprivation. Light is the treatment of choice for SAD and may prove to be useful for nonseasonal depression, alone or as an adjunct to medication. Chronobiological concepts emphasize the important role of zeitgebers to stabilize phase, light being the most important, but dark (and rest) periods, regularity of social schedules and meal times, and use of melatonin or its analogues should also be considered. Advances in chronobiology continue to contribute novel treatments for affective disorders.

Rapid-acting antidepressant strategies: mechanisms of action

Current antidepressants are ineffective in many depressed patients. Thus there is an urgent need to develop treatment strategies which have significantly faster response, can be sustained and have minimal side-effects. This paper reviews clinical data, potential biomarkers, mechanisms of action and future research directions for two proven strategies that produce marked improvement in severe depressive symptoms within 48 h, ketamine and sleep deprivation therapy (SDT). These treatments provide unequivocal evidence that the depressive process can be rapidly reversed in a subgroup of patients. Seventeen ketamine studies in over 150 patients showed a rapid response. Low-dose intravenous ketamine produced mild psychotomimetic effects but response has not been effectively sustained. SDT has been investigated in over 60 studies with a 40-60% response rate within 48 h. Although SDT is often used in Europe to initiate a rapid response, it is less utilized within the USA, in part, because it has a short duration when administered alone. We review data concerning chronotherapeutic strategies of bright-light therapy (BLT) and sleep-phase advance (SPA) which successfully sustain the antidepressant efficacy of SDT. Evidence is further discussed that a significant group of mood disorders have abnormal circadian rhythms which are known to be controlled by clock genes. It is hypothesized that chronotherapeutic manipulations can reset clock genes and thus, abnormalities in circadian rhythms. Further findings are reviewed that ketamine, in addition to its role as an NMDA antagonist, can also alter circadian rhythms. Thus, ketamine may share a critical mechanism with SDT.

New therapeutic targets for mood disorders

Existing pharmacological treatments for bipolar disorder (BPD) and major depressive disorder (MDD) are often insufficient for many patients. Here we describe a number of targets/compounds that clinical and preclinical studies suggest could result in putative novel treatments for mood disorders. These include: (1) glycogen synthase kinase-3 (GSK-3) and protein kinase C (PKC), (2) the purinergic system, (3) histone deacetylases (HDACs), (4) the melatonergic system, (5) the tachykinin neuropeptides system, (6) the glutamatergic system, and (7) oxidative stress and bioenergetics. The paper reviews data on new compounds that have shown antimanic or antidepressant effects in subjects with mood disorders, or similar effects in preclinical animal models. Overall, an improved understanding of the neurobiological underpinnings of mood disorders is critical in order to develop targeted treatments that are more effective, act more rapidly, and are better tolerated than currently available therapies.

Potential novel therapeutics for bipolar disorders

Existing pharmacological treatments for bipolar disorder (BPD), a severe recurrent mood disorder, are in general insufficient for many patients. Despite adequate doses and treatment duration, many individuals with this disease continue to experience mood episode relapses, residual symptoms, and functional impairment. This chapter reviews a number of targets/compounds that could result in putative novel treatments for BPD, including the dynorphin opioid neuropeptide system, the glutamatergic system, the purinergic system, the cholinergic system (muscarinic and nicotinic systems), the oxidative stress system, and the melatonergic system. The arachidonic acid cascade and intracellular signaling cascades (including glycogen synthase kinase 3 and protein kinase C) are also reviewed, as are agents that affect multiple targets (e.g., modafinil, Uridine RG2417). Further study of these and similar agents may improve our understanding of relevant drug targets and their clinical utility as potential therapeutics for this devastating disorder.

Bipolar disorder: candidate drug targets

Current pharmacotherapy for bipolar disorder is generally unsatisfactory for a large number of patients. Even with adequate modern bipolar pharmacological therapies, many afflicted individuals continue to have persistent mood episode relapses, residual symptoms, functional impairment, and psychosocial disability. Creating novel therapeutics for bipolar disorder is urgently needed. Promising drug targets and compounds for bipolar disorder worthy of further study include both systems and intracellular pathways and targets. Specifically, the purinergic system, the dynorphin opioid neuropeptide system, the cholinergic system (muscarinic and nicotinic systems), the melatonin and serotonin [5-hydroxytryptamine receptor 2C] system, the glutamatergic system, and the hypothalamic-pituitary adrenal axis have all been implicated. Intracellular pathways and targets worthy of further study include glycogen synthase kinase-3 protein, protein kinase C, and the arachidonic acid cascade.

Circadian activity rhythm abnormalities in ill and recovered bipolar I disorder patients

OBJECTIVES

Most physiological indicators of bipolar disorder (BPD) reflect current acute illness, and rarely have proved to be state-independent. Activity rhythms are highly abnormal in acute phases of BPD; we compared circadian activity rhythms in BPD I patients during ill and recovered states to those of normal controls to test the hypothesis that some abnormalities may persist.

METHODS

We compared 36 adult DSM-IV BPD I patients during acute mania or mixed states, and during full and sustained clinical recovery, to 32 healthy controls of similar age and sex distribution, using wrist-worn, piezoelectric actigraphic monitoring for 72 h and computed cosinor analysis of circadian activity rhythms.

RESULTS

We verified expected major differences between manic or mixed-state BPD I patients and matched normal controls, including phase advances averaging 2.1 h in ill BPD I patients and 1.8 h in recovered patients. Moreover, recovered BPD patients differed highly significantly from controls in several measures, including acrophase advance, higher percentage of nocturnal sleep, and lower average daily activity (mesor). Actigraphic measures among recovered BPD patients were independent of ratings of mania (on the Young Mania Rating Scale), depression (on the Hamilton Depression Rating Scale), or rating-scale scored subjective distress, as well as the type and dose of concurrent psychotropic medication.

CONCLUSIONS

These findings suggest that abnormal activity rhythms, including sustained phase advances, may represent enduring (trait) characteristics of BPD patients even during clinical recovery. If verified, such indices may be useful in supporting diagnoses and as an objective phenotype for genetic or other biological studies.

The behavioral actions of lithium in rodent models: leads to develop novel therapeutics

For nearly as long as lithium has been in clinical use for the treatment of bipolar disorder, depression, and other conditions, investigators have attempted to characterize its effects on behaviors in rodents. Lithium consistently decreases exploratory activity, rearing, aggression, and amphetamine-induced hyperlocomotion; and it increases the sensitivity to pilocarpine-induced seizures, decreases immobility time in the forced swim test, and attenuates reserpine-induced hypolocomotion. Lithium also predictably induces conditioned taste aversion and alterations in circadian rhythms. The modulation of stereotypy, sensitization, and reward behavior are less consistent actions of the drug. These behavioral models may be relevant to human symptoms and to clinical endophenotypes. It is likely that the actions of lithium in a subset of these animal models are related to the therapeutic efficacy, as well the side effects, of the drug. We conclude with a brief discussion of various molecular mechanisms by which these lithium-sensitive behaviors may be mediated, and comment on the ways in which rat and mouse models can be used more effectively in the future to address persistent questions about the therapeutically relevant molecular actions of lithium.

Influence of alpha-adrenoceptor agonists and antagonists on imipramine-induced hypothermia in mice

Effects of adrenoceptor agonists and antagonists on imipramine-induced hypothermia in mice were studied. Intraperitoneal injection of imipramine (10-40 mg x kg(-1)), alpha2-adrenoceptor agonist clonidine (0.05-0.1 mg x kg(-1)), alpha1-adrenoceptor agonist phenylephrine (6 mg x kg(-1)) and alpha1-adrenoceptor antagonist prazosin (1-4 mg x kg(-1)) but not alpha2-adrenoceptor antagonist yohimbine (1-4 mg x kg(-1)) induced significant hypothermia. The hypothermic response induced by imipramine (10-30 mg x kg(-1)) was not altered by clonidine (0.05-0.1 mg x kg(-1)) or phenylephrine (2-6 mg x kg(-1)). The response of imipramine (10-30 mg x kg(-1)) was reduced significantly by yohimbine (2 mg x kg(-1)) and was potentiated by prazosin (1 mg x kg(-1)). The hypothermic effect of clonidine (0.1 mg x kg(-1)) and imipramine (20 mg x kg(-1)) were also decreased significantly by different doses of yohimbine (1-4 mg x kg(-1)). The hypothermia induced by different doses of prazosin (1-4 mg x kg(-1)) was not altered by yohimbine (2 mg x kg(-1)) or by low dose of imipramine (10 mg x kg(-1)). It is concluded that alpha2-adrenoceptor mechanism may be involved in the hypothermic effect of imipramine.

Control of rat hypothalamic pro-opiomelanocortin neurons by a circadian clock that is entrained by the daily light-off signal

Previous studies have clearly demonstrated that the immediate-early gene, c-fos can regulate, through its protein product Fos, the expression of the pro-opiomelanocortin gene. In the present study, immunohistochemistry for Fos and beta-endorphin was used to assess the basal activity of hypothalamic pro-opiomelanocortin-producing neurons throughout a 12 h light/12 h dark cycle. Here, we showed that Fos is undetectable in most beta-endorphin neurons from late morning until 30 min after light offset in the evening, whereas Fos is spontaneously expressed in these neurons after 1 h following dark onset. The number of beta-endorphin neurons expressing Fos increases continuously during the first half of the dark phase, is maximal at the middle of this phase and decreases through late night and early morning, reaching a nadir 2-3 h after light onset. Acute shifts of lighting parameters allowed us to demonstrate that the light-off signal per se is neither sufficient nor necessary for Fos expression in beta-endorphin neurons. However, when recurrent, this signal is able to entrain Fos expression after a period of adaptation to the new light/dark schedule. Moreover, an expression of Fos in beta-endorphin neurons persists during subjective night in rat exposed to constant light or constant dark for two to three days. Thus, the occurrence of the daily rhythmic increase in the expression of Fos protein in hypothalamic pro-opiomelanocortin neurons exclusively at (subjective) night suggests that these neurons are, most likely, controlled by a (circadian) nocturnal oscillator. Our data also reveal an interesting property of this oscillator: its entrainment by the daily light-to-dark transition signal.

Organization of rat circadian rhythms during daily infusion of melatonin or S20098, a melatonin agonist

Daily administration of melatonin or S20098, a melatonin agonist, is known to entrain the free-running circadian rhythms of rats. The effects of the duration of administration on entrainment were studied. The animals demonstrated free-running circadian rhythms (running-wheel activity, body temperature, general activity) in constant darkness. Daily infusions of melatonin or S20098 for 1, 8, or 16 h entrained the circadian rhythms to 24 h. Two daily infusions of 1 h (separated by 8 h) entrained the activity peak within the shorter time interval. The entraining properties of melatonin and S20098 were similar and were affected neither by pinealectomy nor by infusion of 1- or 8-h duration. However, with 16-h infusion, less than half of the animals became entrained. Once entrained, the phase angle between the onset of infusion and the rhythms (onset of activity or acrophase of body temperature) increased with the duration of infusion. Before entrainment, the free-running period increased with the duration of infusion, an effect that was not predictable from the phase response curve.