Clozapine modulates retinoid homeostasis in human brain and normalizes serum retinoic acid deficit in patients with schizophrenia.

The atypical antipsychotic clozapine is one of the most potent drugs of its class, yet its precise mechanisms of action remain insufficiently understood. Recent evidence points toward the involvement of endogenous retinoic acid (RA) signaling in the pathophysiology of schizophrenia. Here we investigated whether clozapine may modulate RA-signaling. Effects of clozapine on the catabolism of all-trans RA (at-RA), the biologically most active metabolite of Vitamin A, were assessed in murine and human brain tissue and peripheral blood-derived mononuclear cells (PBMC). In patients with schizophrenia with and without clozapine treatment and matched healthy controls, at-RA serum levels and blood mRNA expression of retinoid-related genes in PBMCs were quantified. Clozapine and its metabolites potently inhibited RA catabolism at clinically relevant concentrations. In PBMC-derived microsomes, we found a large interindividual variability of the sensitivity toward the effects of clozapine. Furthermore, at-RA and retinol serum levels were significantly lower in patients with schizophrenia compared with matched healthy controls. Patients treated with clozapine exhibited significantly higher at-RA serum levels compared with patients treated with other antipsychotics, while retinol levels did not differ between treatment groups. Similarly, in patients without clozapine treatment, mRNA expression of RA-inducible targets CYP26A and STRA6, as well as at-RA/retinol ratio, were significantly reduced. In contrast, clozapine-treated patients did not differ from healthy controls in this regard. Our findings provide the first evidence for altered peripheral retinoid homeostasis in schizophrenia and suggest modulation of RA catabolism as a novel mechanism of action of clozapine, which may be useful in future antipsychotic drug development.

M1/M2 polarization in major depressive disorder: Disentangling state from trait effects in an individualized cell-culture-based approach.

Accumulating evidence indicates the specific involvement of inflammatory processes in major depressive disorder (MDD), particularly affecting innate immunity. Most immune alterations have so far been determined based on plasma or cerebrospinal fluid cytokine levels. To precisely characterize putative innate immune-mediated mechanisms in MDD pathogenesis, we sought to disentangle "state" from "trait" effects in a patient-specific cell model by quantifying the impact of patient-derived autologous sera (AS) on patient-specific monocyte-derived macrophages (Mo-MФs) polarization in vitro. Mo-MФs were generated from 28 patients with moderate to severe MDD and 28 age-, sex-, smoking status- and BMI-matched healthy controls (HC). Cells were treated either with AS or fetal calf serum (FCS) and polarized into M1 (LPS), M2 (IL-10, IL-4, TGF-ß) or M0 (unstimulated) macrophages. Polarization capacity was quantified by means of specific M1 (CCR7, CD86, CXCL10, IL-12p70, TNF-α, IL-6, IL-1ß, IL-12p40, IL-23, IP-10) and M2 (CD206, IL-10, TARC, IL-1RA) markers. Compared to HC, significantly increased M1-polarization was observed for MDD patients in the presence of FCS, however, polarization in AS enriched media determined an increased M2-polarization in patients. Moreover, female MDD patients exhibited increased M1- and decreased M2-polarization in both conditions compared to male MDD patients. Our data suggests that Mo-MФs derived from patients with MDD exhibit facilitated M1-polarization under traditional cell culture conditions and an increased potential for M2-polarization when cultured in AS. Striking inter-individual variation and pronounced gender effects highlight the potential utility of our personalized cell model-based approach to aid diagnostic and therapeutic decisions.

Inhibition of monoamine oxidase activity by repetitive transcranial magnetic stimulation: implications for inter-train interval and frequency.

Repetitive transcranial magnetic stimulation (rTMS) is a neuromodulation technique that stimulates cortical regions via time-varying electromagnetic fields; in several countries this technique has been approved as a treatment for major depressive disorder. One empirically established target in antidepressant pharmacotherapy is the flavin-containing monoamine oxidoreductase (MAO). The function of MAO enzymes is based on oxidation processes that may be sensitive towards strong electromagnetic fields. Therefore, we hypothesized that rTMS-induced electromagnetic fields impact the activity of this enzyme. Using crude synaptosomal cell preparations from human SH-SY5Y neuroblastoma cells and rat cortex as well as viable cells, we assessed the effects of rTMS on MAO-A and -B activity in a well-controlled in vitro set up. In short, samples were stimulated at maximal intensity with an equal number of total stimuli at frequencies of 5, 20, and 100 Hz. Sham stimulation was performed in parallel. Treatment at frequencies of 5 and 20 Hz significantly decreased mainly MAO-B activity in all tissue preparations and species, whereas 100 Hz stimulation remained without effect on any MAO activity. Our results support the hypothesis, that rTMS-induced electromagnetic fields affect MAO activity and provide further evidence for intracellular effects possibly contributing to therapeutic effects of this neuromodulatory method. On a cautionary note, however, our findings are solely based on in vitro evidence.

Anti-inflammatory effects of minocycline are mediated by retinoid signaling.

BACKGROUND: Minocycline is a lipophilic tetracycline of increasing appeal in neuroscience as it inhibits microglial activation, a mechanism involved in numerous neuropsychiatric disorders. Own data point towards retinoid-mediated effects of minocycline in murine brain and skin, and towards a vicious cycle of neuroinflammation which is driven by microglial activation-induced breakdown of local retinoids such as retinoic acid (RA). We therefore sought to study minocycline's anti-inflammatory effects on human microglial-like monocyte-derived cells in the context of retinoid signaling. RESULTS: As hypothesized, minocycline exposure resulted in a substantial increase of RA levels in the human monocytic cell line THP-1. While pro-inflammatory stimulation with lipopolysaccharides resulted in increased tryptophane-degrading indoleamine-2,3-dioxygenase IDO-expression and TNF-α levels in primary human monocyte-derived microglial-like cells, this effect was attenuated by minocycline only in the presence of retinoids. The anti-inflammatory effects of minocycline on TNF-α expression were completely abolished by a pharmacological blockage of retinoic acid receptors (RARs) using BMS-493 and unaffected by selectively blocking retinoid-X-receptors using UVI-3003. CONCLUSIONS: Our data indicate for the first time a RA-dependent, anti-inflammatory effect for minocycline in human microglial-like cells via inhibition of local RA turnover. The RA-dependent mode of action for minocycline appears to be predominantly mediated through RAR-signaling.

Clozapine-induced agranulocytosis: Evidence for an immune-mediated mechanism from a patient-specific in-vitro approach.

Use of the atypical antipsychotic clozapine (CZP) is compromised by the risk of potentially fatal agranulocytosis/granulocytopenia (CIAG). To address this, we have established a simple, personalized cell culture-based strategy to identify CIAG-susceptible patients, hypothesizing that an immunogenic and possibly haptene-based mechanism underlies CIAG pathophysiology. To detect a putative haptene-induced response to CZP in vitro exposure, a traditional lymphocyte stimulation assay was adapted and applied to patient-specific peripheral blood-derived mononuclear cells (PBMC). 6 patients with a history of CIAG, 6 patients under CZP treatment (without CIAG) and 12 matched healthy controls were studied. In vitro CZP exposure, even at strikingly low levels, resulted in significantly increased proliferation rates only in CIAG patients' PBMC. Other parameters including cell viability and mitogen-induced proliferation were also affected by in vitro CZP exposure, yet there was no significant difference between the groups. This personalized approach is a starting point for further investigations into a putative haptene-based mechanism underlying CIAG development, and may facilitate the future development of predictive testing.

Electroconvulsive therapy-induced brain plasticity determines therapeutic outcome in mood disorders.

There remains much scientific, clinical, and ethical controversy concerning the use of electroconvulsive therapy (ECT) for psychiatric disorders stemming from a lack of information and knowledge about how such treatment might work, given its nonspecific and spatially unfocused nature. The mode of action of ECT has even been ascribed to a "barbaric" form of placebo effect. Here we show differential, highly specific, spatially distributed effects of ECT on regional brain structure in two populations: patients with unipolar or bipolar disorder. Unipolar and bipolar disorders respond differentially to ECT and the associated local brain-volume changes, which occur in areas previously associated with these diseases, correlate with symptom severity and the therapeutic effect. Our unique evidence shows that electrophysical therapeutic effects, although applied generally, take on regional significance through interactions with brain pathophysiology.

Inhibition of retinoic acid catabolism by minocycline: evidence for a novel mode of action?

Retinoic acid (RA) represents an essential and highly potent endogenous retinoid with pronounced anti-inflammatory properties and potent anti-acne activity, and has recently been suggested to share a common anti-inflammatory mode of action with tetracycline antibiotics. We hypothesized that tetracyclines may directly interfere with RA homeostasis via inhibition of its local cytochrome P450 (CYP450)-mediated degradation, an essential component of tightly regulated skin RA homeostasis. To test this hypothesis, we performed controlled in vitro RA metabolism assays using rat skin microsomes and measured RA levels in a RA-synthesizing human keratinocyte cell line, both in the presence and in the absence of minocycline, a tetracycline popular in acne treatment. Interestingly, minocycline potently blocked RA degradation in rat skin microsomes, and strikingly enhanced RA levels in RA-synthesizing cell cultures, in a dose-dependent manner. These findings indicate a potential role for CYP-450-mediated RA metabolism in minocycline's pleiotropic mode of action and anti-acne efficacy and could account for the overlap between minocycline and RA-induced effects at the level of their molecular mode of action, but also clinically at the level of the rare side effect of pseudotumor cerebri, which is observed for both, RA and minocycline treatment.

Direct inhibition of retinoic acid catabolism by fluoxetine.

Recent evidence from animal and human studies suggests neuroprotective effects of the SSRI fluoxetine, e.g., in the aftermath of stroke. The underlying molecular mechanisms remain to be fully defined. Because of its effects on the cytochrome P450 system (CYP450), we hypothesized that neuroprotection by fluoxetine is related to altered metabolism of retinoic acid (RA), whose CYP450-mediated degradation in brain tissue constitutes an important step in the regulation of its site-specific auto- and paracrine actions. Using traditional pharmacological in vitro assays, the effects of fluoxetine on RA degradation were probed in crude synaptosomes from rat brain and human-derived SH-SY5Y cells, and in cultures of neuron-like SH-SY5Y cells. Furthermore, retinoid-dependent effects of fluoxetine on neuronal survival following glutamate exposure were investigated in rat primary neurons cells using specific retinoid receptor antagonists. Experiments revealed dose-dependent inhibition of synaptosomal RA degradation by fluoxetine along with dose-dependent increases in RA levels in cell cultures. Furthermore, fluoxetine's neuroprotective effects against glutamate excitotoxicity in rat primary neurons were demonstrated to partially depend on RA signaling. Taken together, these findings demonstrate for the first time that the potent, pleiotropic antidepressant fluoxetine directly interacts with RA homeostasis in brain tissue, thereby exerting its neuroprotective effects.

Do tetracyclines and erythromycin exert anti-acne effects by inhibition of P450-mediated degradation of retinoic acid?

For decades, retinoic acid (RA) is known as the most potent therapeutic option in the therapy of acne and altered homeostasis of endogenous retinoids has been discussed in the context of acne pathogenesis. Besides retinoids, antibiotics such as tetracyclines or erythromycin are well established in acne pharmacotherapy. Accumulating evidence points towards common molecular pathways being targeted by both RA and anti-acne antibiotics; however, a precise 'common denominator' connecting these chemically diverse anti-acne agents has not yet been identified. Interestingly, tetracyclines are associated with the occurrence of pseudotumor cerebri, a rare neurological side effect otherwise associated with retinoid intoxication or RA exposure. This association at the clinical level suggests an interaction between tetracyclines and endogenous RA signalling. As erythromycin does not cross the blood brain barrier, CNS side effects are not to be expected, yet not precluding a possible local interaction of erythromycin with endogenous RA metabolism in the skin. We hypothesize tetracyclines and erythromycin to locally inhibit endogenous RA metabolism in the skin and thus mimic therapeutic action of RA. This readily testable hypothesis suggests inhibition of endogenous RA metabolism and amplification of endogenous RA signalling as a mechanism underlying the biochemical actions of antibiotics in acne therapy. Elucidation of such interactions may ultimately enhance our understanding of acne therapy and pathogenesis and may yield a sound, scientific basis for hypothesis-driven development of novel therapeutic compounds.

UV-A emission from fluorescent energy-saving light bulbs alters local retinoic acid homeostasis.

Worldwide bans on incandescent light bulbs (ILBs) drive the use of compact fluorescent light (CFL) bulbs, which emit ultraviolet (UV) radiation. Potential health issues of these light sources have already been discussed, including speculation about the putative biological effects on light exposed tissues, yet the underlying mechanisms remain unclear. We hypothesized photoisomerization of all-trans retinoic acid (at-RA), a highly light sensitive morphogen, into biologically less active isomers, as a mechanism mediating biological effects of CFLs. Local at-RA is anti-carcinogenic, entrains molecular rhythms and is crucial for skin homeostasis. Therefore, we quantified the impact of CFL irradiation on extra- and intracellular levels of RA isomers using an epidermal cell culture model. Moreover, a biologically relevant impact of CFL irradiation was assessed using highly at-RA-sensitive human neuroblastoma cells. Dose-dependent conversion of extra- and intracellular at-RA into the biologically less active 13-cis-isomer was significantly higher in CFL vs. ILB exposure and completely preventable by employing a UV-filter. Moreover, pre-irradiation of culture media by CFL attenuated at-RA-specific effects on cell viability in human at-RA-sensitive cells in a dose-dependent manner. These findings point towards a biological relevance of CFL-induced at-RA decomposition, providing a mechanism for CFL-mediated effects on environmental health.

Quetiapine as combination treatment with citalopram in unipolar depression with prominent somatic symptoms: a randomised, double-blind, placebo-controlled pilot study.

BACKGROUND: Patients with major depressive disorder (MDD) accompanied by physical symptoms may be less responsive to antidepressant treatment. Quetiapine has been evaluated in the treatment of bipolar depression and has been recently approved as an add-on therapy for unipolar depression. Less is known about the efficacy of combination therapies in patients suffering from MDD with somatic symptoms. The aim of the present study was to evaluate the efficacy of quetiapine as adjunctive therapy to the SSRI citalopram in patients with MDD and somatic complaints. SUBJECTS AND METHODS: 41 inpatients with nonpsychotic DSM-IV MDD experiencing significant symptoms of somatic distress as defined by a baseline score on the SCL-90-R somatization subscale greater one standard deviation above adult nonpatient norms were randomly assigned to receive either citalopram 40 mg/day plus placebo (n=20) or citalopram 40 mg/day plus quetiapine, 300 to 600 mg/day (n=21) for 6 weeks. The primary outcome measure was the Hamilton Depression Rating Scale (HDRS) score. RESULTS: Mean changes in HDRS scores from baseline to week 6 using last-observation-carried-forward methods were -12.3±6.2 and -10.7±5.1 in the citalopram-quetiapine and citalopram-placebo group, respectively. Remission rates were significant higher in the citalopram-quetiapine-group (41.1%) than in the citalopram-placebo-group (26.3%), respectively. CONCLUSIONS: Although quetiapine as add-on to citalopram did not separate statistically from placebo on the HDRS score in improving depressive symptoms and somatic symptoms in patients with MDD and prominent somatic complaints, higher remission rates and other second outcome parameters showed advantages for quetiapine. Larger, double-blind, placebo-controlled trials of quetiapine as augmentation therapy in MDD with somatic symptoms are warranted.

Retinoid homeostasis in major depressive disorder.

The small, hormone-like molecule retinoic acid (RA) is a vital regulator in several neurobiological processes that are affected in depression. Next to its involvement in dopaminergic signal transduction, neuroinflammation, and neuroendocrine regulation, recent studies highlight the role of RA in homeostatic synaptic plasticity and its link to neuropsychiatric disorders. Furthermore, experimental studies and epidemiological evidence point to the dysregulation of retinoid homeostasis in depression. Based on this evidence, the present study investigated the putative link between retinoid homeostasis and depression in a cohort of 109 patients with major depressive disorder (MDD) and healthy controls. Retinoid homeostasis was defined by several parameters. Serum concentrations of the biologically most active Vitamin A metabolite, all-trans RA (at-RA), and its precursor retinol (ROL) were quantified and the individual in vitro at-RA synthesis and degradation activity was assessed in microsomes of peripheral blood-derived mononuclear cells (PBMC). Additionally, the mRNA expression of enzymes relevant to retinoid signaling, transport, and metabolism were assessed. Patients with MDD had significantly higher ROL serum levels and greater at-RA synthesis activity than healthy controls providing evidence of altered retinoid homeostasis in MDD. Furthermore, MDD-associated alterations in retinoid homeostasis differed between men and women. This study is the first to investigate peripheral retinoid homeostasis in a well-matched cohort of MDD patients and healthy controls, complementing a wealth of preclinical and epidemiological findings that point to a central role of the retinoid system in depression.

Gradient of electro-convulsive therapy's antidepressant effects along the longitudinal hippocampal axis.

Despite decades of successful treatment of therapy-resistant depression and major scientific advances in the field, our knowledge about electro-convulsive therapy's (ECT) mechanisms of action is still scarce. Building on strong empirical evidence for ECT-induced hippocampus anatomy changes, we sought to test the hypothesis that ECT has a differential impact along the hippocampus longitudinal axis. We acquired behavioural and brain anatomy magnetic resonance imaging (MRI) data in patients with depressive episode undergoing ECT (n = 9) or pharmacotherapy (n = 24) and healthy controls (n = 30) at two time points 3 months apart. Using whole-brain voxel-based statistical parametric mapping and topographic analysis focused on the hippocampus, we observed ECT-induced gradient of grey matter volume increase along the hippocampal longitudinal axis with predominant impact on its anterior portion. Clinical outcome measures showed strong correlations with both baseline volume and rate of ECT-induced change exclusively for the anterior, but not posterior hippocampus. We interpret our findings confined to the anterior hippocampus and amygdala as additional evidence of the regional specific impact of ECT that unfolds its beneficial effect on depression via the "limbic" system. Main limitations of the study are patients' polypharmacy, heterogeneity of psychiatric diagnosis, and long-time interval between scans.

Using routine MRI data of depressed patients to predict individual responses to electroconvulsive therapy.

Electroconvulsive therapy (ECT) is one of the most effective treatments in cases of severe and treatment resistant major depression. 60-80% of patients respond to ECT, but the procedure is demanding and robust prediction of ECT responses would be of great clinical value. Predictions based on neuroimaging data have recently come into focus, but still face methodological and practical limitations that are hampering the translation into clinical practice. In this retrospective study, we investigated the feasibility of ECT response prediction using structural magnetic resonance imaging (sMRI) data that was collected during ECT routine examinations. We applied machine learning techniques to predict individual treatment outcomes in a cohort of N = 71 ECT patients, N = 39 of which responded to the treatment. SMRI-based classification of ECT responders and non-responders reached an accuracy of 69% (sensitivity: 67%; specificity: 72%). Classification on additionally investigated clinical variables had no predictive power. Since dichotomisation of patients into ECT responders and non-responders is debatable due to many patients only showing a partial response, we additionally performed a post-hoc regression-based prediction analysis on continuous symptom improvements. This analysis yielded a significant relationship between true and predicted treatment outcomes and might be a promising alternative to dichotomization of patients. Based on our results, we argue that the prediction of individual ECT responses based on routine sMRI holds promise to overcome important limitations that are currently hampering the translation of such treatment biomarkers into everyday clinical practice. Finally, we discuss how the results of such predictive data analysis could best support the clinician's decision on whether a patient should be treated with ECT.

A simple approach to optimum pool size for pooled SARS-CoV-2 testing.

Systematic, large-scale testing of asymptomatic subjects is an important strategy in the management of the SARS-CoV-2 pandemic. In order to increase the capacity of laboratory-based molecular SARS-CoV-2 testing, it has been suggested to combine several samples and jointly measure them in a sample pool. While saving cost and labour at first sight, pooling efficiency depends on the pool size and the presently experienced prevalence of positive samples. Here we address the question of the optimum pool size at a given prevalence. We demonstrate the relation between analytical effort and pool size and delineate the effects of the target prevalence on the optimum pool size. Finally, we derive a simple-to-use formula and table that allow laboratories performing sample pooling to assess the optimum pool size at the currently experienced target prevalence rate.

Anxiety during ketamine infusions is associated with negative treatment responses in major depressive disorder.

About 20 to 30 percent of patients with Major Depressive Disorder (MDD) do not respond to standard treatment and are considered treatment-resistant. The N-methyl-d-aspartate (NMDA) glutamate receptor antagonist ketamine has demonstrated rapid antidepressant effects in treatment-resistant MDD, but it is unknown whether its acute psychological effects are related to the later antidepressant effect. Therefore, we investigated the association between antidepressant responses to ketamine and the quality of ketamine-induced psychological experiences in MDD. A total of 31 patients (M = 49.5 ±â€¯11.2 years, 16 women) were treated with three ketamine infusions per week (0.5 mg/ kg over 40 min) administered for two consecutive weeks. Depression severity was assessed using the Montgomery-Åsberg Depression Rating Scale (MADRS) at baseline, after four and 24 h and at end of treatment. The 5-Dimensional Altered States of Consciousness Rating Scale (5D-ASC) was applied four hours after the first infusion to assess the subjective quality of acute psychological effects. Patients with a ≥ 50% MADRS reduction from baseline to end of treatment were considered as responders. After six infusions, 17 of 31 patients (55%) showed a response to ketamine treatment, while 14 patients (45%) had no response. Anxiety-related experiences induced by ketamine were significantly higher in non-responders. Percentage MADRS reduction after four hours and individual levels of ketamine-induced anxiety were predictive of a response at end of treatment. The study demonstrated the considerable impact of ketamine-induced anxiety on the antidepressant efficacy of ketamine. It underpins the importance of considering patients' subjective experiences and underlines the possibility of a phenotypic response predictor.

Declarative and procedural memory consolidation during sleep in patients with borderline personality disorder.

Borderline personality disorder (BPD) is characterized by changes in subjective and objective measures of sleep quality. As recent findings point to the importance of sleep in memory consolidation, sleep-related memory consolidation was investigated in 15 female BPD patients (mean age 26.1+/-6.1 years) and 15 female healthy controls (mean age 25.6+/-6.8 years). Before and after the study night, declarative and procedural memory performance was tested by a paired associate list and a mirror tracing task. Subjective sleep quality was assessed by a sleep questionnaire, objective sleep quality was measured by a portable sleep recording device. During the study night the restorative value of sleep was significantly reduced in BPD patients (p<0.001), while objective sleep quality showed a trend for longer REM sleep duration (p=0.054). No significant differences were found regarding overnight performance improvement in the declarative and procedural memory tasks. Present findings suggest that declarative and procedural memory consolidation during sleep is intact in BPD patients.

Sleep-related memory consolidation in depression: an emerging field of research.

Sleep-related memory consolidation has received increasing attention in recent years. Because previous research has focused on healthy young adults, only very few studies have been conducted in patients with psychiatric disorders so far. The investigation of sleep-related memory consolidation in depression offers a wide range of future research opportunities and can therefore be regarded as an emerging field of research. This article gives a short overview of current knowledge of sleep-related memory consolidation in healthy young adults and builds a bridge to psychiatry and depression, where further research is urgently needed.

Retinoic Acid Enhances Apolipoprotein E Synthesis in Human Macrophages.

Apolipoprotein E (ApoE) represents a pivotal target in Alzheimer's disease (AD) and is modulated through retinoic acid (RA), an endogenous neuroprotective and anti-inflammatory compound. A major source of ApoE are microglia, which are pathologically activated in AD. Activated microglia are known to block RA signaling. This suggests a vicious cycle between inflammation, RA signaling, and ApoE homeostasis in AD pathogenesis. To test this hypothesis, we investigated effects of RA and proinflammatory activation on ApoE synthesis in primary human macrophage-derived microglial-like cells. Our results indicate that proinflammatory activation attenuates ApoE synthesis, an effect blocked by RA.

The relationship between REM sleep and memory consolidation in old age and effects of cholinergic medication.

BACKGROUND: Recent findings in young adults suggest that rapid eye movement (REM) sleep plays a role in procedural memory consolidation. The significance of REM sleep for memory consolidation in old age has not yet been investigated. METHODS: Effects of REM sleep manipulation on declarative and procedural memory consolidation were investigated in 107 healthy older adults, ages 60-82 years. Rapid eye movement sleep deprivation was achieved by REM sleep awakenings and compared with non-REM sleep awakenings. Rapid eye movement sleep augmentation was realized physiologically by REM sleep rebound and pharmacologically by administering an acetylcholinesterase inhibitor in a double-blind, placebo-controlled design. Memory performance was tested by a paired associate list and a mirror tracing task at 9:30 pm and 7:30 am with sleep intervening between 11:00 pm and 7:00 am. RESULTS: Although REM sleep deprivation led to a significant reduction in total and phasic REM sleep, memory consolidation remained unaffected. Both REM sleep augmentation groups showed a significant increase in phasic REM sleep, whereas only pharmacological cholinergic REM sleep manipulation exerted a significant positive effect on procedural memory consolidation. CONCLUSIONS: Because only after cholinergic stimulation of phasic REM sleep procedural memory consolidation is improved, cholinergic activation seems to be a crucial component of REM sleep-related memory consolidation in old age.