Testing the validity of<Emphasis Type="Italic"> c-fos</Emphasis> expression profiling to aid the therapeutic classification of psychoactive drugs

Rationale

Different stimuli, including pharmacological stimuli, induce different neuroanatomical profiles of c-fos expression. Can these profiles be used in classifying psychoactive drugs and predicting therapeutic utility?

Objective

To test the validity of c-fos expression profiling to aid therapeutic classification.

Methods

Anxiolytics, antidepressants, antipsychotics and psychostimulants were compared. (i) A meta-analysis was performed and profiles compiled from literature reports of changes in c-fos expression in rat brain regions, measured by in situ hybridisation histochemistry or immunohistochemistry, after acute injection of psychoactive drugs. (ii) Male rat brains were profiled for changes in c-fos mRNA expression induced by acute injection of psychoactive drugs.

Results

(i) The meta-analysis showed that anxiolytics activate few (mostly stress-related) brain regions; antidepressants activate more regions, including the central amygdaloid nucleus; antipsychotics activate more regions still, including the nucleus accumbens and striatal areas; and psychostimulants activate the greatest number of all, including the most cortical regions (especially the piriform cortex). Profiles also varied within drug classes. (ii) Our experimental profiles confirmed and extended meta-analysis profiles, showing more downregulation. (iii) Sites activated by mirtazapine (an antidepressant not previously profiled) matched those of the antidepressant imipramine.

Conclusions

(i) Differences between drug classes support their classification by means of c-fos profiling. Differences within classes may reflect mechanistic variations. (ii) Greater downregulation in our experiments might be because of inclusion of low, clinically relevant, drug doses and fuller coverage of brain regions. (iii) The agreement between mirtazapine and imipramine increases our confidence in the validity of c-fos expression profiling to aid drug classification and predict therapeutic utility.

     

Occurrence of mirtazapine-induced delirium in organic brain disorder

Mirtazapine is the first of a new class of antidepressants, the noradrenergic and specific serotonergic antidepressants. Its antidepressant effect appears to be related to its dual enhancement of both noradrenergic neurotransmission and serotonin 5-HT1 receptor-mediated serotonergic neurotransmission. Mirtazapine has demonstrated superior tolerability to the tricyclic antidepressants, primarily on account of its relative absence of anticholinergic, adrenergic and serotonin-related adverse effects. We observed mirtazapine-induced delirium in one organically depressed and two major depressed patients with subclinical brain disease. The appearance of hallucinations, psychomotoric agitation and cognitive changes after initiation of mirtazapine, and their prompt improvement after drug discontinuation, led to the impression that these were drug-induced phenomena. One possible hypothesis for the observed deliria is a central increase of norepinephrine after acute administration of mirtazapine. Subclinical brain disease might have favoured the occurrence of delirium in the three cases.     

Overlapping and distinct brain regions associated with the anxiolytic effects of chlordiazepoxide and chronic fluoxetine.

Little is known about the sites of action for the behavioral effects of chronic antidepressants. The novelty-induced hypophagia (NIH) test is one of few animal behavioral tests sensitive to acute benzodiazepines and chronic antidepressants. The goals of these experiments were to examine patterns of brain activation associated with the behavioral response to novelty and identify regions that could regulate the anxiolytic effects of acute benzodiazepine and chronic antidepressant treatments, measured using the NIH test. In the first experiment, rats were treated acutely with the anxiolytic, chlordiazepoxide (2.5 or 5 mg/kg, i.p.). In separate experiments, animals were implanted with osmotic minipumps delivering vehicle or fluoxetine (5 or 20 mg/kg per day s.c.) for 3 or 28 days. NIH was assessed by giving animals access to a familiar palatable food in a novel environment. Associated brain areas were identified using c-fos immunohistochemistry. NIH was mitigated by acute chlordiazepoxide and chronic fluoxetine. Both drugs reversed novelty-induced changes in c-fos expression in the lateral division of the posterolateral part of the bed nucleus of the stria terminalis (STLP), cingulate cortex (Cg), and dorsal field CA2 of the hippocampus (dCA2). Chronic fluoxetine additionally increased c-fos expression in the anterior nucleus accumbens (aAcb) and the piriform cortex (Pir). The effects of the drugs on c-fos expression in many regions correlated with anxiolytic efficacy. These findings identified brain regions where the effects of chronic antidepressants and benzodiazepines may converge to produce anxiolytic activity, as well as distinct sites of action for the two classes of drugs.     

Immediate-early gene expression in the central nucleus of the amygdala is not specific for anxiolytic or anxiogenic drugs

The lateral, basal, and central nuclei of the amygdala are part of a circuitry that instantiates many fear and anxious behaviors. One line of support indicates that immediate-early gene (IEG) expression (e.g., c-fos and egr-1 (zif268)) is increased in these nuclei following fear conditioning. Other research finds that anxiogenic drugs working through various mechanisms induce IEG expression in the central nucleus of the amygdala (CeA) suggesting that expression is a neural marker for fear and anxiety. However, several studies have also found that anxiolytic drugs induce IEG expression in the CeA. Expression of egr-1 in the CeA and lateral nucleus of the amygdala following administration of anxiolytic and anxiogenic benzodiazepine and serotonin agonists and antagonists was investigated. The first experiment determined behaviorally active anxiolytic and anxiogenic doses for two anxiogenic drugs (FG 7142 and mCPP) and two anxiolytic drugs (diazepam and buspirone). The effects of anxiogenic and anxiolytic doses of these drugs on egr-1 expression in the amygdala were then tested in a second experiment. All four drugs increased egr-1 in the CeA indicating that increased egr-1 mRNA expression in the CeA is not specific to anxiolytic or anxiogenic effects of the drugs. We suggest that IEG expression in the CeA may be due to activation of circuits that are associated with systemic physiological homeostasis perturbed by a number of drugs including anxiogenic and anxiolytic compounds.     

[11C]Mirtazapine binding in depressed antidepressant nonresponders studied by PET neuroimaging

Rationale  Lack of benefit from antidepressant drug therapy is a major source of human suffering, affecting at least 25% of people with major depressive disorder. We want to know whether nonresponse to antidepressants can be linked to aberrant neuroreceptor binding. Objective  This study aims to assess the antidepressant binding in brain regions of depressed nonresponders compared with healthy controls. Materials and methods  Healthy volunteers and depressed subjects who had failed to benefit from at least 2 antidepressant treatments were recruited by newspaper advertisements. All subjects had received no antidepressant medication for at least 2 months before positron emission tomography (PET) that was carried out with [¹¹C]mirtazapine. Kinetic parameters of [¹¹C]mirtazapine were determined from PET data in selected brain regions by the simplified reference tissue model. Results  Binding potentials of [¹¹C]mirtazapine in cerebral cortical regions were lower in depressed nonresponders than in healthy controls. Removal rates of [¹¹C]mirtazapine were higher in diencephalic regions of depressed nonresponders than in healthy controls. Conclusions  PET neuroimaging with [¹¹C]mirtazapine showed aberrant neuroreceptor binding in brain regions of depressed subjects who had failed to benefit from treatment with antidepressant drugs.     

Ketamine and Serotonergic Psychedelics: Common Mechanisms Underlying the Effects of Rapid-Acting Antidepressants

BackgroundThe glutamatergic modulator ketamine has created a blueprint for studying novel pharmaceuticals in the field. Recent studies suggest that “classic” serotonergic psychedelics (SPs) may also have antidepressant efficacy. Both ketamine and SPs appear to produce rapid, sustained antidepressant effects after a transient psychoactive period.MethodsThis review summarizes areas of overlap between SP and ketamine research and considers the possibility of a common, downstream mechanism of action. The therapeutic relevance of the psychoactive state, overlapping cellular and molecular effects, and overlapping electrophysiological and neuroimaging observations are all reviewed.ResultsTaken together, the evidence suggests a potentially shared mechanism wherein both ketamine and SPs may engender rapid neuroplastic effects in a glutamatergic activity-dependent manner. It is postulated that, though distinct, both ketamine and SPs appear to produce acute alterations in cortical network activity that may initially produce psychoactive effects and later produce milder, sustained changes in network efficiency associated with therapeutic response. However, despite some commonalities between the psychoactive component of these pharmacologically distinct therapies—such as engagement of the downstream glutamatergic pathway—the connection between psychoactive impact and antidepressant efficacy remains unclear and requires more rigorous research.ConclusionsRapid-acting antidepressants currently under investigation may share some downstream pharmacological effects, suggesting that their antidepressant effects may come about via related mechanisms. Given the prototypic nature of ketamine research and recent progress in this area, this platform could be used to investigate entirely new classes of antidepressants with rapid and robust actions.     

Cytisine, a partial agonist of high-affinity nicotinic acetylcholine receptors, has antidepressant-like properties in male C57BL/6J mice

The nicotine in tobacco is thought to modulate neuronal systems regulating mood. Moreover, it appears possible that blockade rather than activation of beta2-containing (beta2*) nicotinic acetylcholine receptors (nAChRs) may lead to antidepressant-like effects. We used cytisine, a partial agonist of alpha4/beta2*nAChRs and a full agonist at alpha3/beta4*nAChRs, in several tests of antidepressant efficacy. Further, we used c-fos expression to identify potential neurobiological correlates of the antidepressant-like effects of cytisine. Cytisine had antidepressant-like effects in several animal models of antidepressant efficacy. In addition, immunohistochemical analyses indicated that cytisine could reduce c-fos immunoreactivity in the basolateral amygdala by approximately 50%. These data show that cytisine acts like classical antidepressants in rodent models of antidepressant efficacy. In addition, cytisine's ability to block alpha4/beta2*nAChRs may be responsible for its antidepressant-like properties, and these may be mediated through a reduction of neuronal activity in the basolateral amygdala. These studies also suggest that both antagonists and partial agonists of alpha4/beta2*nAChRs would be interesting targets for the development of novel antidepressant drugs.     

Antinociceptive effects of the antidepressants amitriptyline, duloxetine, mirtazapine and citalopram in animal models of acute, persistent and neuropathic pain

The effects of acute, systemic administration of amitriptyline, duloxetine and mirtazapine (antidepressant drugs that variously affect extracellular noradrenaline and serotonin levels) and the selective serotonin reuptake inhibitor (SSRI) citalopram were compared in rat models of experimental pain. None of the drugs (all 3-30 mg/kg, i.p.) affected acute nociceptive responses as measured in the tail flick test. In the hot plate test, duloxetine and mirtazapine significantly increased (P<0.05) the nociceptive response latency, whereas amitriptyline and citalopram were ineffective. In the formalin test, duloxetine and citalopram significantly attenuated, whereas amitriptyline and mirtazapine increased, second phase flinching behaviour (all P<0.05). However, amitriptyline and mirtazapine reduced second phase licking behaviour. In the chronic constriction injury model of neuropathic pain, thermal hyperalgesia of the injured hindpaw was significantly attenuated by all four drugs (P<0.05); only amitriptyline and duloxetine fully reversed thermal hypersensitivity. None of the drugs tested attenuated mechanical allodynia. In contrast amitriptyline, duloxetine and mirtazapine significantly reduced mechanical hyperalgesia (P<0.05); citalopram was ineffective. No drug-related effects on motor performance in the rotarod test were observed. These results (a) highlight the difficulty in correlating antinociceptive effects of drugs from different antidepressant classes across a range of animal pain models and (b) suggest that antidepressants that variously affect both noradrenaline and serotonin levels have more potent and efficacious antinociceptive effects than SSRIs (as exemplified by citalopram), against a range of pain-like behaviours in an animal model of neuropathic pain.     

Usefulness of antidepressants for improving the neuropathic pain-like state and pain-induced anxiety through actions at different brain sites.

Clinically, it is well known that chronic pain induces depression, anxiety, and a reduced quality of life. There have been many reports on the relationship between pain and emotion. We previously reported that chronic pain induced anxiety with changes in opioidergic function in the central nervous system. In this study, we evaluated the anxiolytic-like effects of several types of antidepressants under a chronic neuropathic pain-like state and searched for the brain site of action where antidepressants show anxiolytic or antinociceptive effects. Sciatic nerve-ligated mice exhibited thermal hyperalgesia and tactile allodynia from days 7 to 28 after nerve ligation. At 4 weeks after ligation, these mice showed a significant anxiety-related behavior in the light-dark test and the elevated plus-maze test. Under these conditions, repeated administration of antidepressants, including the tricyclic antidepressant (TCA) imipramine, the serotonin noradrenaline reuptake inhibitor (SNRI) milnacipran, and the selective serotonin reuptake inhibitor (SSRI) paroxetine, significantly prevented the anxiety-related behaviors induced by chronic neuropathic pain. These antidepressants also produced a significant reduction in thermal hyperalgesia and tactile allodynia. Moreover, the microinjection of paroxetine into the basolateral amygdala or cingulate cortex reduced anxiety-related behavior, and microinjection into the primary somatosensory cortex significantly attenuated thermal hyperalgesia. These findings suggest that serotonergic antidepressants are effective for treating anxiety associated with chronic neuropathic pain and may be useful for treating neuropathic pain with emotional dysfunction such as anxiety. Furthermore, SSRIs show anxiolytic and antinociceptive effects by acting on different brain regions.     

Differential expression of IEG mRNA in rat brain following acute treatment with clozapine or haloperidol: a semi-quantitative RT-PCR study

Antipsychotic drugs have been shown to modulate immediate early gene (IEG) expression in rat brain regions that are associated with schizophrenia, which may be directly linked to their immediate therapeutic benefit. In this study, we analysed the expression profile of a series of IEGs (c-fos, c-jun, fra-1, Krox-20, Krox-24, arc, sgk-1, BDNF and NARP) in six rat brain regions (prefrontal cortex, hippocampus, striatum, nucleus accumbens, thalamus and cerebellum). Rats (n=5) were administered either clozapine (20 mg/kg i.p.), haloperidol (1 mg/kg i.p.) or the appropriate vehicle with pre-treatment times of 1, 6 and 24 h. IEG expression was analysed in these regions by Taqman RT-PCR. The spatial and temporal profile of IEG induction following antipsychotic drug treatment correlates with regions associated with the efficacy and side effect profile of each drug. In particular, sgk-1 expression levels after antipsychotic drug treatment may have predictive value when investigating the profile of a novel antipsychotic drug.     

Different actions for acute and chronic administration of mirtazapine on serotonergic transmission associated with raphe nuclei and their innervation cortical regions

The atypical antidepressant, mirtazapine enhances noradrenergic transmission, but its effects on serotonergic transmission remain to be clarified. The present study determined the effects of acute and chronic administration of mirtazapine on serotonergic transmissions in raphe nuclei and their innervation regions, frontal and entorhinal cortex, using multiple-probes microdialysis with real-time PCR and western blotting. Acute administration of mirtazapine did not affect extracellular serotonin level in raphe nuclei or cortex; however, chronic administration increased extracellular serotonin level in raphe nuclei without affecting that in cortex. Blockade of 5-HT1A receptor, but not that of the 5-HT2A/2C receptor, enhanced the effects of acute administration of mirtazapine on extracellular serotonin level in raphe nuclei. Chronic mirtazapine administration reduced the inhibitory function associated with somatodendritic 5-HT1A receptor in raphe nuclei, but enhanced postsynaptic 5-HT1A receptor in serotonergic innervated cortical regions. Chronic administration reduced the expression of mRNA and protein of serotonin transporter and 5-HT1A receptor in raphe nuclei, but not in the cortices. These results suggested that acute administration of mirtazapine probably activated serotonergic transmission, but its stimulatory action was abolished by activated inhibitory 5-HT1A receptor. Chronic administration of mirtazapine resulted in increased extracellular serotonin level via reduction of serotonin transporter with reduction of somatodendritic 5-HT1A autoreceptor function in raphe nuclei. These pharmacological actions of mirtazapine include its serotonergic profiles as noradrenergic and specific serotonergic antidepressant (NaSSA).     

Optimizing antidepressant treatment: efficacy and tolerability

It has been suggested that dual-action antidepressants acting on both serotonin and noradrenaline pathways in the brain may offer superior therapeutic benefit over classical antidepressants, particularly in severe depression. Directly acting dual-action antidepressant drugs include venlafaxine and milnacipran. In addition, mirtazapine and nefazodone, may indirectly potentiate serotonergic and noradrenergic transmission, although evidence that they do indeed do so in vivo is limited. Meta-analysis of clinical trials suggests that venlafaxine has a more rapid onset of action than selective serotonin reuptake inhibitors (SSRIs), and the same may also be true for milnacipran and mirtazapine. Efficacy, both in terms of extent of antidepressant effect and in the proportion of patients responding, is probably superior to that of SSRIs, at least for venlafaxine and milnacipran. In terms of tolerability, all dual-action drugs clearly appear to be better tolerated than tricyclic antidepressants. Mirtazapine and nefazodone have specific side-effect profiles as a result of their antagonist action at biogenic amine and other receptors. Milnacipran, and to a lesser extent venlafaxine, are slightly better tolerated than SSRIs.     

[N-methyl-11C]Mirtazapine for positron emission tomography neuroimaging of antidepressant actions in humans

Rationale Many actions of antidepressant drugs cannot yet be studied using positron emission tomography (PET) neuroimaging due to lack of suitable radioligands. We believe that mirtazapine, radiolabeled with C-11, might be suitable for PET neuroimaging of ₂-adrenoceptors in selected regions of the living human brain.Objective To determine the regional central biodistribution and pharmacokinetics of [N-methyl-¹¹C]mirtazapine in humans.Methods Five healthy volunteers received an intravenous injection of [N-methyl-¹¹C]mirtazapine for evaluating its metabolism, biodistribution and pharmacokinetics.Results [N-methyl-¹¹C]Mirtazapine entered the brain readily, with initial clearance from blood to tissue (K₁) ranging from 0.31 ml/ml/min in amygdala to 0.54 ml/ml/min in thalamus. The rate of metabolism of [N-methyl-¹¹C]mirtazapine in the bloodstream was relatively slow, with 20–40% of [¹¹C]-derived radioactivity still present as parent compound at 60 min post-injection. The clearance of [N-methyl-¹¹C]mirtazapine from the tissue compartment (k₂) ranged from a low of 0.03 min^–1 in amygdala to a high of 0.06–0.07 min^–1 in thalamus and cerebellum. The volume of distribution (V_e) of [N-methyl-¹¹C]mirtazapine was markedly greater in hippocampus and amygdala (11.3–12.0) than in cerebellum (6.7), with intermediate levels in the thalamus (9.4).Conclusions [N-methyl-¹¹C]Mirtazapine has suitable properties for PET neuroimaging. We envision [N-methyl-¹¹C]mirtazapine as a molecular probe for PET imaging of antidepressant actions at sites such as ₂-adrenoceptors in the living human brain.     

Involvement of the endocannabinoid system in the ability of long-term tricyclic antidepressant treatment to suppress stress-induced activation of the hypothalamic-pituitary-adrenal axis.

The efficacy of antidepressants has been linked in part to their ability to reduce activity of the hypothalamic-pituitary-adrenal (HPA) axis; however, the mechanism by which antidepressants regulate the HPA axis is largely unknown. Given that recent research has demonstrated that endocannabinoids can regulate the HPA axis and exhibit antidepressant potential, we examined the hypothesis that the endocannabinoid system is regulated by long-term antidepressant treatment. Three-week administration of the tricyclic antidepressant desipramine (10 mg/kg/day) resulted in a significant increase in the density of the cannabinoid CB(1) receptor in the hippocampus and hypothalamus, without significantly altering endocannabinoid content in any brain structure examined. Furthermore, chronic desipramine treatment resulted in a reduction in both secretion of corticosterone and the induction of the immediate early gene c-fos in the medial dorsal parvocellular region of the paraventricular nucleus of the hypothalamus (PVN) following a 5 min exposure to swim stress. Acute treatment with the CB(1) receptor antagonist, AM251 (1 mg/kg), before exposure to swim stress, completely occluded the ability of desipramine to reduce both corticosterone secretion and induction of c-fos expression in the PVN. Collectively, these data demonstrate that CB(1) receptor density in the hippocampus and hypothalamus is increased by chronic tricyclic antidepressant treatment, and suggest that this upregulation could contribute to the ability of tricyclic antidepressants to suppress stress-induced activation of the HPA axis.     

Effects of antidepressants on the brain/plasma distribution of corticosterone.

It is well established that hypothalamic-pituitary-adrenal (HPA) axis dysregulation, characterized by elevated circulating cortisol concentrations and impaired negative feedback inhibition, is associated with affective disorders. As normalization of the HPA axis function and mood-stabilizing effects occur simultaneously during antidepressant treatment, it is likely that these effects are either directly or indirectly dependent. Although data concerning the outward transport of glucocorticoids from the brain by P-glycoprotein (Pgp) are inconsistent, it has been hypothesized that antidepressants exert their clinical activity in parts by inhibiting Pgp, subsequently leading to enhanced brain glucocorticoid levels and the normalization of the HPA axis function. Here, we report on the effects of different antidepressants (amitriptyline, fluoxetine, mirtazapine, St John's wort extract) on the brain/plasma distribution of corticosterone in mice after acute and subchronic treatment. The four antidepressants exerted different effects on the corticosterone concentration in brain and plasma. Changes in corticosterone levels were highly correlated, suggesting passive diffusion between both tissues. St John's wort extract and fluoxetine elevated brain and plasma corticosterone concentrations after subchronic treatment. Mirtazapine and amitriptyline had no effect on corticosterone concentration after subchronic treatment, possibly because both are also potent antagonists at the 5-HT2 receptor, which mediates HPA axis stimulation by serotonergic stimuli. In addition, St John's wort is the only antidepressant tested which slightly elevated Pgp protein level in the brain.     

Pharmacological principles of antidepressant efficacy

Both noradrenaline (NA) and serotonin (5-HT) appear to be involved in depression. Evidence suggests that dual-acting antidepressants, i.e. those that affect both monoamine systems, such as tricyclic antidepressants and the noradrenergic and specific serotonergic antidepressant mirtazapine, may have greater efficacy and a faster onset of action than drugs that act on a single monoamine system only, such as the selective serotonin reuptake inhibitors (SSRIs). Cell firing is reduced by SSRIs in the short-term, but is increased by mirtazapine, probably due to its actions on both NA (via alpha(2) antagonism) and 5-HT (via alpha(1)-stimulation by NA). This may help to explain clinical evidence suggesting that mirtazapine has a faster onset of action than the more selective antidepressants.     

Short-Term Duloxetine Administration Affects Neural Correlates of Mood-Congruent Memory

It is unknown how antidepressants reverse mood-congruent memory bias, a cognitive core factor causing and maintaining depression. Using a double-blind, placebo-controlled, cross-over design, we investigated the effect of a short-term treatment (14 days) with the dual reuptake inhibitor duloxetine on neural correlates of mood-congruent and mood-incongruent memory formation and retrieval in healthy volunteers who underwent a sad mood induction procedure. Duloxetine did not affect acute mood state or memory performance, but interacted with brain processes mediating mood-congruent memory. It decreased activity related to successful memory formation for mood-congruent and -incongruent items in a set of brain regions comprising the putamen and the middle frontal gyrus, as well as the middle and the anterior cingulate cortex. Duloxetine specifically increased amygdala activity related to successful memory retrieval for mood-incongruent items. Here we show that short-term administration of duloxetine affects the neural correlates of emotional memory formation and retrieval in a set of brain regions whose processing is related to affective state and its regulation. While duloxetine suppressed the neural correlates of emotional memory formation in general, it specifically enhanced amygdala processes associated with mood-incongruent memory retrieval. This pattern of results shows how an antidepressant may reduce emotional memory formation and reverse mood-congruent processing biases at retrieval.     

Hypertensive urgency induced by an interaction of mirtazapine and clonidine

Mirtazapine is a new antidepressant with a tetracyclic chemical structure that is not related to selective serotonin reuptake inhibitors, tricyclic antidepressants, or monoamine oxidase inhibitors. The antidepressant effect results from stimulation of the noradrenergic system through antagonism at central (alpha2-inhibitory receptors. Clonidine exerts its antihypertensive effect by stimulating these receptors to cause a reduction in endogenous release of norepinephrine. Therefore, the two agents have mechanisms of action that potentially oppose one another. We report a case of hypertensive urgency that ensued after a patient stabilized on clonidine began taking mirtazapine.     

Antidepressants and their effect on sleep

Given the relationship between sleep and depression, there is inevitably going to be an effect of antidepressants on sleep. Current evidence suggests that this effect depends on the class of antidepressant used and the dosage. The extent of variation between the effects of antidepressants and sleep may relate to their mechanism of action. This systematic review examines randomised-controlled trials (RCTs) that have reported the effect that antidepressants appear to have on sleep. RCTs are not restricted to depressed populations, since several studies provide useful information about the effects on sleep in other groups. Nevertheless, the distinction is made between those studies because the participant's health may influence the baseline sleep profiles and the effect of the antidepressant. Insomnia is often seen with monoamine oxidase inhibitors (MAOIs), with all tricyclic antidepressants (TCAs) except amitriptyline, and all selective serotonin reuptake inhibitors (SSRIs) with venlafaxine and moclobemide as well. Sedation has been reported with all TCAs except desipramine, with mirtazapine and nefazodone, the TCA-related maprotiline, trazodone and mianserin, and with all MAOIs. REM sleep suppression has been observed with all TCAs except trimipramine, but especially clomipramine, with all MAOIs and SSRIs and with venlafaxine, trazodone and bupropion. However, the effect on sleep varies between compounds within antidepressant classes, differences relating to the amount of sedative or alerting (insomnia) effects, changes to baseline sleep parameters, differences relating to REM sleep, and the degree of sleep-related side effects.     

Effects of acute and subacute antidepressant treatment on kindled seizures in rats

The effects of acute and subacute administration of the tricyclic antidepressants imipramine and amitriptyline, and the atypical antidepressants mianserin and iprindole, on seizures kindled from the amygdala and the cortex were examined. Whereas amitriptyline selectively antagonized seizures kindled from the amygdala after a single dose, neither amitriptyline nor imipramine was any more effective in antagonizing seizures kindled from the amygdala than from the cortex following subacute treatment. Both acute and subacute administration of iprindole failed to significantly alter seizures kindled from either site. Although only the highest acute dose of mianserin tested selectively attenuated amygdaloid seizures, a lower dose that was ineffective when given acutely, was selective when given subacutely. In contrast to an earlier report, the present findings suggest that kindling may not be a particularly useful model for the evaluation of potential antidepressant agents.