Acute and chronic escitalopram alter EEG gamma oscillations differently: relevance to therapeutic effects

40-Hz Temporally Interfering Electrical Stimulation Over the Temporal Lobe Induced Antidepressant-Like Effects in Chronic Unpredictable Mild Stress Rats

Temporally interfering (TI) electrical stimulation provides a promising noninvasive and focused stimulation for neuropsychiatric disorders. However, the feasible stimulation strategy and potential effects require further study. Our previous studies have identified gamma oscillatory abnormalities of temporal regions in depressed patients and rats. We accordingly aim to develop an effective TI antidepressant strategy. The stimulation strategy was firstly determined by modeling and simulation, and verified by c-Fos immunofluorescence staining. 32 rats were randomized into control (n = 8) and depression (n = 24) groups induced by chronic unpredictable mild stress (CUS), which were exposed to stimulation for 5 days, 20 mins per day. The behavioral and electrophysiology experiments were performed to examine the antidepressant-like effects of TI, using transcranial alternating current stimulation (tACS) as a positive control. In the electrophysiology experiment, local field potential (LFP) signals were recorded from bilateral primary auditory cortex (A1) before and after stimulation. We found that TI activated more c-Fos-positive cells in A1 target than tACS, exhibiting better stimulation focality. Both TI and tACS significantly ameliorated depression-like behaviors compared to sham group, and TI made more improvements. Furthermore, TI largely restored the gamma deficits by increasing gamma power and phase locking value (PLV) compared with tACS. And the gamma-band deficits were found remarkably correlated with depression-like behaviors. Overall, TI ameliorated depression-like behaviors in CUS rats, which may be associated with the restoration of aberrant gamma oscillations. With the advantages of both spatial targeting and noninvasive character, TI holds great promise for the clinical application of depression.

Long-term administration of paroxetine increases cortical EEG beta and gamma band activities in healthy awake rats

Understanding the electrophysiological properties of antidepressant medications is important to resolve the response heterogeneity of these drugs in clinical practice. Administration of paroxetine, a selective serotonin reuptake inhibitor, has been shown to increase serotonin levels that affect cortical activities in healthy subjects. However, the extent to which cortical oscillations can be altered by ongoing administration of paroxetine is not known. Here, we develop EEG biomarkers showing long-term effects of paroxetine. EEG changes were analyzed using Neuroscan in healthy wakeful rats administered paroxetine (4 mg/kg/day) for six weeks. Subsequent EEG recordings taken at 3 and 6 weeks after treatment showed differences in cortical oscillations obtained from both hemispheres and frontal-central-parietal regions. Chronic paroxetine administration resulted in an increase in gamma band activity. Comparison of EEG frequency bands of paroxetine and saline groups showed an enhancement in higher frequency activities at third weeks after the treatment. Higher activity of alpha oscillations in the temporal cortex was persistent at sixth week of the administration. Overall, our results suggest that chronic paroxetine administration affects cortical oscillations across an expansive network.

Unique Effects of (R)-Ketamine Compared to (S)-Ketamine on EEG Theta Power in Rats

Differences in the pharmacological effects of (S)-ketamine and (R)-ketamine are at the focus of research. Clinical data and our rat studies confirmed the antidepressant effect of (S)- but not (R)-ketamine, with similar differences in quantitative electroencephalogram (EEG) and sleep effects. In contrast, studies mainly on mice showed some stronger, preferable effects of (R)-ketamine. EEG theta (5-9 Hz) rhythm originates from the hippocampus, and its power is associated with cognitive functions, attention, and decreased anxiety. To find a brain parameter that is not associated with the antidepressant effect of drugs and may confirm potent in vivo effects of (R)-ketamine in rats, theta EEG power-inducing effects of the two enantiomers were measured and compared for 23 h. EEG-equipped Wistar rats were treated with (R)-ketamine (7.5, 15, 30 mg/kg i.p.), (S)-ketamine (7.5 and 15 mg/kg i.p.), or vehicle at the beginning of the passive phase. Frontoparietal EEG, electromyogram, and motor activity were recorded. (R)-ketamine but not (S)-ketamine dose-dependently increased EEG theta power during wakefulness and rapid eye movement (REM) sleep for 23 h. These results suggest that (R)-ketamine has an effect on a hippocampal function that was not affected by (S)-ketamine and may be associated with neural plasticity and memory encoding.

(S)-Ketamine but Not (R)-Ketamine Shows Acute Effects on Depression-Like Behavior and Sleep-Wake Architecture in Rats

BACKGROUND

Racemic ketamine consists of two enantiomers, namely (R)-ketamine and (S)-ketamine, with distinguishable pharmacological properties. Both enantiomers have been reported to show rapid antidepressant effects in rodents. Currently, the (S)-enantiomer has been approved for the treatment of major depression, whereas (R)-ketamine failed to show antidepressant effect in recent clinical studies. Major depressive disorder is frequently characterized by disinhibition of rapid eye movement (REM) sleep and disruption of non-REM (NREM) sleep. Racemic ketamine and most conventional antidepressants affect these parameters. However, it remains largely unknown which enantiomer is responsible for these effects.

METHODS

Here, we compared acute effects of the two ketamine enantiomers (15 mg/kg i.p.) on different sleep-wake stages in freely moving, EEG-equipped rats. We also evaluated the antidepressant-like activity of the enantiomers in a chronic restraint stress model of depression.

RESULTS

(S)-ketamine but not (R)-ketamine increased REM sleep latency and decreased REM sleep time at 2 and 3 hours, and increased electroencephalogram delta power during NREM sleep. In addition, only (S)-ketamine increased wakefulness and decreased NREM sleep in the first 2 hours. In the forced swimming test, only (S)-ketamine decreased the immobility time of chronically stressed rats.

CONCLUSION

Effects of the two ketamine enantiomers on rat sleep-wake architecture and behavior are markedly different when administered in the same dose. (S)-ketamine remarkably affects the sleep-wake cycle and very likely sleep-related neuroplasticity, which may be relevant for its antidepressant efficacy. Our results regarding (R)-ketamine's lack of effect on vigilance and behavior are in line with recent clinical studies.

Predicting Prognostic Effects of Acupuncture for Depression Using the Electroencephalogram

Depression is considered to be a major public health problem with significant implications for individuals and society. Patients with depression can be with complementary therapies such as acupuncture. Predicting the prognostic effects of acupuncture has a big significance in helping physicians make early interventions for patients with depression and avoid malignant events. In this work, a novel framework of predicting prognostic effects of acupuncture for depression based on electroencephalogram (EEG) recordings is presented. Specifically, EEG, as a widely used measurement to evaluate the therapeutic effects of acupuncture, is utilized for predicting prognostic effects of acupuncture. Max-relevance and min-redundancy (mRMR), with merits of removing redundant information among selected features and remaining high relevance between selected features and response variable, is employed to select important lead-rhythm features extracted from EEG recordings. Then, according to the subject Hamilton Depression Rating Scale (HAMD) scores before and after acupuncture for eight weeks, the reduction rate of HAMD score is calculated as a measure of the prognostic effects of acupuncture. Finally, five widely used machine learning methods are utilized for building the predicting models of prognostic effects of acupuncture for depression. Experimental results show that nonlinear machine learning methods have better performance than linear ones on predicting prognostic effects of acupuncture using EEG recordings. Especially, the support vector machine with Gaussian kernel (SVM-RBF) can achieve the best and most stable performance using the mRMR with both evaluating criteria of FCD and FCQ for feature selection. Both mRMR-FCD and mRMR-FCQ obtain the same best performance, where the accuracy and F 1 score are 84.61% and 86.67%, respectively. Moreover, lead-rhythm features selected by mRMR-FCD and mRMR-FCQ are analyzed. The top seven selected lead-rhythm features have much higher mRMR evaluating scores, which guarantee the good predicting performance for machine learning methods to some degree. The presented framework in this work is effective in predicting the prognostic effects of acupuncture for depression. It can be integrated into an intelligent medical system and provide information on the prognostic effects of acupuncture for physicians. Informed prognostic effects of acupuncture for depression in advance and taking interventions can greatly reduce the risk of malignant events for patients with mental disorders.

Cannabinoids and sleep-wake cycle: The potential role of serotonin

Cannabis sativa (Marijuana) has a long history as a medicinal plant and Δ9-tetrahydrocannabinol (Δ9-THC) is the most active component in this plant. Cannabinoids are interesting compounds with various modulatory effects on physiological processes and cognitive functions. The use of cannabinoids is a double-edged sword, because they induce both adverse and therapeutic properties. One of the most important roles of cannabinoids is modulating sleep-wake cycle. Sleep, its cycle, and its mechanism are highly unknown. Also, the effects of cannabinoids on sleep-wake cycle are so inconsistent. Thus, understanding the role of cannabinoids in modulating sleep-wake cycle is a critical scientific goal. Cannabinoids interact with many neurotransmitter systems. In this review article, we chose serotonin due to its important role in regulating sleep-wake cycle. We found that the interaction between cannabinoids and serotonergic signaling especially in the dorsal raphe is extensive, unknown, and controversial.

EEG and Sleep Effects of Tramadol Suggest Potential Antidepressant Effects with Different Mechanisms of Action

Tramadol is a widely used, centrally acting, opioid analgesic compound, with additional inhibitory effects on the synaptic reuptake of serotonin and noradrenaline, as well as on the 5-HT₂ and NMDA receptors. Preclinical and clinical evidence also suggests its therapeutic potential in the treatment of depression and anxiety. The effects of most widely used antidepressants on sleep and quantitative electroencephalogram (qEEG) are well characterized; however, such studies of tramadol are scarce. Our aim was to characterize the effects of tramadol on sleep architecture and qEEG in different sleep–wake stages. EEG-equipped Wistar rats were treated with tramadol (0, 5, 15 and 45 mg/kg) at the beginning of the passive phase, and EEG, electromyogram and motor activity were recorded. Tramadol dose-dependently reduced the time spent in rapid eye movement (REM) sleep and increased the REM onset latency. Lower doses of tramadol had wake-promoting effects in the first hours, while 45 mg/kg of tramadol promoted sleep first, but induced wakefulness thereafter. During non-REM sleep, tramadol (15 and 45 mg/kg) increased delta and decreased alpha power, while all doses increased gamma power. In conclusion, the sleep-related and qEEG effects of tramadol suggest antidepressant-like properties, including specific beneficial effects in selected patient groups, and raise the possibility of a faster acting antidepressant action.

Acute 5-HT2C Receptor Antagonist SB-242084 Treatment Affects EEG Gamma Band Activity Similarly to Chronic Escitalopram

Serotonin 2C receptors (5-HT_2CRs) are implicated in the pathomechanism and treatment of anxiety and depression. Recently, as a new biomarker of depression, alterations in the gamma power of the electroencephalogram (EEG) have been suggested. Chronic treatment with the selective serotonin reuptake inhibitor (SSRI) antidepressant escitalopram has been shown to cause sleep-wake stage-dependent alterations in gamma power. However, despite the antidepressant potency of 5-HT_2CR-antagonists, there is no data available regarding the effects of selective 5-HT_2CR-antagonists on gamma activity. Therefore, we investigate the acute effect of the 5-HT_2CR-antagonist SB-242084 on gamma power in different vigilance stages when given in monotherapy, or in combination with chronic escitalopram treatment. We administered SB-242084 (1 mg/kg, intraperitoneally) or vehicle to EEG-equipped rats after a 21-day-long pretreatment with escitalopram (10 mg/kg/day, via osmotic minipumps) or vehicle. Frontoparietal EEG, electromyogram, and motor activity were recorded during the first 3 h of passive phase, after the administration of SB-242084. Quantitative EEG analysis revealed that acute SB-242084 increased gamma power (30-60 Hz) in light and deep slow-wave sleep, and passive wakefulness. However, in active wakefulness, rapid eye movement sleep, and intermediate stage, no change was observed in gamma power. The profile of the effect of SB-242084 on gamma power was similar to that produced by chronic escitalopram. Moreover, SB-242084 did not alter chronic escitalopram-induced effects on gamma. In conclusion, the similarity in the effect of the 5-HT_2CR-antagonist and chronic SSRI on gamma power provides further evidence for the therapeutic potential of 5-HT_2CR-antagonists in the treatment of depression and/or anxiety.

Hormonal regulation of circuit function: sex, systems and depression

Major depressive disorder (MDD) is a debilitating chronic illness that is two times more prevalent in women than in men. The mechanisms associated with the increased female susceptibility to depression remain poorly characterized. Aberrant neuronal oscillatory activity within the putative depression network is an emerging mechanism underlying MDD. However, innate sex differences in network activity and its contribution to depression vulnerability have not been well described. In this review, current evidence of sex differences in neuronal oscillatory activity, including the influence of sex hormones and female cycling, will first be described followed by evidence of disrupted neuronal circuit function in MDD and the effects of antidepressant treatment. Lastly, current knowledge of sex differences in MDD-associated aberrant circuit function and oscillatory activity will be highlighted, with an emphasis on the role of sex steroids and female cycling. Collectively, it is clear that there are significant gaps in the literature regarding innate and pathologically associated sex differences in network activity and that the elucidation of these differences is invaluable to our understanding of sex-specific vulnerabilities and therapies for MDD.

Evaluation of human electroencephalogram change for sensory effects of fragrance

BACKGROUND

The stabilizing effect of lavender and the arousal effect of peppermint essential oils are acknowledged and used widely in aromatherapy and the cosmetics industry. However, no evaluation method confirms the effects of essential oils through quantitative and objective electroencephalogram (EEG) results; instead, only a psychological and subjective method exists. Therefore, this study aims to create a new emotional cosmetic evaluation paradigm using EEG values. Moreover, it enables quantitative interpretation of the results in addition to the subjective survey outcomes.

METHODS

For this study, 12 healthy female Korean participants were recruited and three fragrances were used. The EEG results were collected for 3 minutes (1 minute each before, during, and after inhalation of every fragrance).

RESULTS

The quantitative EEG outcomes indicate changes in the participant's brainwaves before and after inhalation. Significant changes in the EEG were observed. Based on the results, the effects of fragrances were confirmed to be stabilizing for lavender, and arousing for peppermint and coffee aroma. Furthermore, the subjective questionnaire results indicate similar tendency as that of the quantitative EEG results.

CONCLUSION

In addition to psychological and subjective assessments, our emotional evaluation method can verify the cosmetic fragrance effects through quantitative and objective results.