Effects of pharmacological agents, sleep deprivation, hypoxia and transcranial magnetic stimulation on electroencephalographic rhythms in rodents: Towards translational challenge models for drug discovery in Alzheimer’s disease

Cariprazine modulates sleep architecture in rats

BACKGROUND

Cariprazine is a dopamine D₃-preferring D₃/D₂ receptor partial agonist compound recently introduced to treat schizophrenia and bipolar disorder. Although cariprazine is clinically classified as a low-somnolence drug, to date no detailed polysomnographic study is available on its effect on sleep.

AIMS

This study examined the acute systemic effects of cariprazine on the rat sleep architecture and electroencephalography spectral power.

METHODS

Sprague Dawley rats were recorded during their normal sleep period for four hours, and their sleep stages were classified.

RESULTS

Cariprazine (0.3 mg/kg i.p.) reduced the time spent in rapid eye movement (REM) sleep and increased REM latency. This dose of cariprazine decreased the gamma (40-80 Hz) band frequency oscillations and increased the theta (4-9 Hz) and alpha (9-15 Hz) frequencies during the wake periods but not during slow-wave sleep. The 0.03 mg/kg dose of cariprazine only increased the alpha power during the wake periods, while the 0.003 mg/kg dose was without any effect.

CONCLUSION

Taken together, the present results suggest that the REM-suppressing effect of cariprazine may be related to its effectiveness in improving depressive symptoms, as various drugs with similar REM-reducing properties effectively treat the depressive state, whereas the gamma power-reducing effect of cariprazine may be indicative of its efficacy in schizophrenia or mania, as similar effects have been observed with other D₂ and 5-HT₂ receptor antagonist drugs. These data contribute to our understanding of the complex mechanism of action that may stand behind the clinical efficacy of cariprazine.

TMS-EEG Co-Registration in Patients with Mild Cognitive Impairment, Alzheimer's Disease and Other Dementias: A Systematic Review

An established method to assess effective brain connectivity is the combined use of transcranial magnetic stimulation with simultaneous electroencephalography (TMS–EEG) because TMS-induced cortical responses propagate to distant anatomically connected brain areas. Alzheimer’s disease (AD) and other dementias are associated with changes in brain networks and connectivity, but the underlying pathophysiology of these processes is poorly defined. We performed here a systematic review of the studies employing TMS–EEG co-registration in patients with dementias. TMS–EEG studies targeting the motor cortex have revealed a significantly reduced TMS-evoked P30 in AD patients in the temporo-parietal cortex ipsilateral to stimulation side as well as in the contralateral fronto-central area, and we have demonstrated a deep rearrangement of the sensorimotor system even in mild AD patients. TMS–EEG studies targeting other cortical areas showed alterations of effective dorsolateral prefrontal cortex connectivity as well as an inverse correlation between prefrontal-to-parietal connectivity and cognitive impairment. Moreover, TMS–EEG analysis showed a selective increase in precuneus neural activity. TMS–EEG co-registrations can also been used to investigate whether different drugs may affect cognitive functions in patients with dementias.

Minocycline Treatment Reverses Sound Evoked EEG Abnormalities in a Mouse Model of Fragile X Syndrome

Fragile X Syndrome (FXS) is a leading known genetic cause of intellectual disability. Many symptoms of FXS overlap with those in autism including repetitive behaviors, language delays, anxiety, social impairments and sensory processing deficits. Electroencephalogram (EEG) recordings from humans with FXS and an animal model, the Fmr1 knockout (KO) mouse, show remarkably similar phenotypes suggesting that EEG phenotypes can serve as biomarkers for developing treatments. This includes enhanced resting gamma band power and sound evoked total power, and reduced fidelity of temporal processing and habituation of responses to repeated sounds. Given the therapeutic potential of the antibiotic minocycline in humans with FXS and animal models, it is important to determine sensitivity and selectivity of EEG responses to minocycline. Therefore, in this study, we examined if a 10-day treatment of adult Fmr1 KO mice with minocycline (oral gavage, 30 mg/kg per day) would reduce EEG abnormalities. We tested if minocycline treatment has specific effects based on the EEG measurement type (e.g., resting versus sound-evoked) from the frontal and auditory cortex of the Fmr1 KO mice. We show increased resting EEG gamma power and reduced phase locking to time varying stimuli as well as the 40 Hz auditory steady state response in the Fmr1 KO mice in the pre-drug condition. Minocycline treatment increased gamma band phase locking in response to auditory stimuli, and reduced sound-evoked power of auditory event related potentials (ERP) in Fmr1 KO mice compared to vehicle treatment. Minocycline reduced resting EEG gamma power in Fmr1 KO mice, but this effect was similar to vehicle treatment. We also report frequency band-specific effects on EEG responses. Taken together, these data indicate that sound-evoked EEG responses may serve as more sensitive measures, compared to resting EEG measures, to isolate minocycline effects from placebo in humans with FXS. Given the use of minocycline and EEG recordings in a number of neurodegenerative and neurodevelopmental conditions, these findings may be more broadly applicable in translational neuroscience.

Critical role of CA1 muscarinic receptors on memory acquisition deficit induced by total (TSD) and REM sleep deprivation (RSD)

AIM

Despite different theories regarding sleep physiological function, an overall census indicates that sleep is useful for neural plasticity which eventually strengthens cognition and brain performance. Different studies show that sleep deprivation (SD) leads to impaired learning and hippocampus dependent memory. According to some studies, cholinergic system plays an important role in sleep (particularly REM sleep), learning, memory, and its retrieval. So this study has been designed to investigate the effect of CA1 Cholinergic Muscarinic Receptors on memory acquisition deficit induced by total sleep deprivation (TSD) and REM sleep deprivation (RSD).

METHOD

A modified water box (locomotor activity may be provide a limiting factor in this method of SD) or multiple platforms were used for induction of TSD or RSD, respectively. Inhibitory passive avoidance apparatus has been used to determine the effects of SD and its changes by physostigmine (as cholinesterase inhibitor) or scopolamine (muscarinic receptor antagonist) on memory formation. Because locomotor activity and pain perception induce critical roles in passive avoidance memory formation, we also measured these factors by open field and hot-plate instruments, respectively.

RESULTS

The results showed that TSD and RSD for 24 hours impaired memory formation but they did not alter locomotor activity. TSD also induced analgesia effect, but RSD did not alter it. Intra-CA1 injection of physostigmine (0.0001μg/rat) and scopolamine (0.01μg/rat) did not alter memory acquisition in the sham-TSD or sham-RSD, by themselves. Moreover, intra-CA1 injection of sub-threshold dose of physostigmine (0.0001μg/rat) and scopolamine (0.01μg/rat) could restore the memory acquisition deficit induced by RSD, while scopolamine could restore TSD-induced amnesia. Both drugs reversed analgesia induced by TSD. None of previous interventions altered locomotor activity.

CONCLUSION

According to this study, CA1 cholinergic muscarinic receptors play an important role in amnesia induced by both TSD and RSD. However further studies are needed for showing cellular and molecular mechanisms of surprising result of similar pharmacological effects using compounds with opposite profiles.

Changes of Functional and Directed Resting-State Connectivity Are Associated with Neuronal Oscillations, ApoE Genotype and Amyloid Deposition in Mild Cognitive Impairment

The assessment of effects associated with cognitive impairment using electroencephalography (EEG) power mapping allows the visualization of frequency-band specific local changes in oscillatory activity. In contrast, measures of coherence and dynamic source synchronization allow for the study of functional and effective connectivity, respectively. Yet, these measures have rarely been assessed in parallel in the context of mild cognitive impairment (MCI) and furthermore it has not been examined if they are related to risk factors of Alzheimer’s disease (AD) such as amyloid deposition and apolipoprotein ε4 (ApoE) allele occurrence. Here, we investigated functional and directed connectivities with Renormalized Partial Directed Coherence (RPDC) in 17 healthy controls (HC) and 17 participants with MCI. Participants underwent ApoE-genotyping and Pittsburgh compound B positron emission tomography (PiB-PET) to assess amyloid deposition. We observed lower spectral source power in MCI in the alpha and beta bands. Coherence was stronger in HC than MCI across different neuronal sources in the delta, theta, alpha, beta and gamma bands. The directed coherence analysis indicated lower information flow between fronto-temporal (including the hippocampus) sources and unidirectional connectivity in MCI. In MCI, alpha and beta RPDC showed an inverse correlation to age and gender; global amyloid deposition was inversely correlated to alpha coherence, RPDC and beta and gamma coherence. Furthermore, the ApoE status was negatively correlated to alpha coherence and RPDC, beta RPDC and gamma coherence. A classification analysis of cognitive state revealed the highest accuracy using EEG power, coherence and RPDC as input. For this small but statistically robust (Bayesian power analyses) sample, our results suggest that resting EEG related functional and directed connectivities are sensitive to the cognitive state and are linked to ApoE and amyloid burden.

Quantitative EEG After Brain Stimulation and Cognitive Training in Alzheimer Disease

PURPOSE

Medications are the currently accepted symptomatic treatment of Alzheimer disease (AD), but their impact on delaying the progression of cognitive deficits and functional impairment is limited. The authors aimed to explore long-term electrophysiological effects of repetitive transcranial magnetic stimulation interlaced with cognitive training on quantitative electroencephalography (EEG) in patients with AD.

METHODS

Quantitative EEG was assessed on non-repetitive transcranial magnetic stimulation interlaced with cognitive training treatment days before treatment and after each treatment phase in seven patients with mild AD.

RESULTS

After 4.5 months (54 sessions) of treatment, a significant increase of delta activity over the temporal region was found compared with pretreatment values. Nonsignificant increases of the log EEG power were found for alpha band over the frontal and temporal regions, beta band over the frontal region, theta band over the frontal, temporal, and parieto-occipital regions, and delta band over the frontal and parieto-occipital regions. Nonsignificant decreases were found for alpha over the parieto-occipital region, and for beta over the temporal and parieto-occipital regions. A positive correlation was found between log alpha power over the frontal and temporal regions at 6 weeks and Mini-Mental State Examination (MMSE) scores at 6 weeks and 4.5 months, and between log alpha power over the parieto-occipital regions and MMSE scores at 6 weeks. A negative correlation was found between log alpha power over the frontal and temporal regions at 6 weeks and baseline Alzheimer's Disease Assessment Scale-cognitive subscale scores.

CONCLUSIONS

Repetitive transcranial magnetic stimulation interlaced with cognitive training has long-term effects on quantitative EEG in patients with mild AD. Further research on the quantitative EEG long-term effects of transcranial magnetic stimulation interlaced with cognitive training is required to confirm the authors' data.

Classification of Healthy Subjects and Alzheimer's Disease Patients with Dementia from Cortical Sources of Resting State EEG Rhythms: A Study Using Artificial Neural Networks

Previous evidence showed a 75.5% best accuracy in the classification of 120 Alzheimer's disease (AD) patients with dementia and 100 matched normal elderly (Nold) subjects based on cortical source current density and linear lagged connectivity estimated by eLORETA freeware from resting state eyes-closed electroencephalographic (rsEEG) rhythms (Babiloni et al., 2016a). Specifically, that accuracy was reached using the ratio between occipital delta and alpha1 current density for a linear univariate classifier (receiver operating characteristic curves). Here we tested an innovative approach based on an artificial neural network (ANN) classifier from the same database of rsEEG markers. Frequency bands of interest were delta (2–4 Hz), theta (4–8 Hz Hz), alpha1 (8–10.5 Hz), and alpha2 (10.5–13 Hz). ANN classification showed an accuracy of 77% using the most 4 discriminative rsEEG markers of source current density (parietal theta/alpha 1, temporal theta/alpha 1, occipital theta/alpha 1, and occipital delta/alpha 1). It also showed an accuracy of 72% using the most 4 discriminative rsEEG markers of source lagged linear connectivity (inter-hemispherical occipital delta/alpha 2, intra-hemispherical right parietal-limbic alpha 1, intra-hemispherical left occipital-temporal theta/alpha 1, intra-hemispherical right occipital-temporal theta/alpha 1). With these 8 markers combined, an accuracy of at least 76% was reached. Interestingly, this accuracy based on 8 (linear) rsEEG markers as inputs to ANN was similar to that obtained with a single rsEEG marker (Babiloni et al., 2016a), thus unveiling their information redundancy for classification purposes. In future AD studies, inputs to ANNs should include other classes of independent linear (i.e., directed transfer function) and non-linear (i.e., entropy) rsEEG markers to improve the classification.

Pharmaco-EEG Studies in Animals: An Overview of Contemporary Translational Applications

The contemporary value of animal pharmaco-electroencephalography (p-EEG)-based applications are strongly interlinked with progress in recording and neuroscience analysis methodology. While p-EEG in humans and animals has been shown to be closely related in terms of underlying neuronal substrates, both translational and back-translational approaches are being used to address extrapolation issues and optimize the translational validity of preclinical animal p-EEG paradigms and data. Present applications build further on animal p-EEG and pharmaco-sleep EEG findings, but also on stimulation protocols, more specifically pharmaco-event-related potentials. Pharmaceutical research into novel treatments for neurological and psychiatric diseases has employed an increasing number of pharmacological as well as transgenic models to assess the potential therapeutic involvement of different neurochemical systems and novel drug targets as well as underlying neuronal connectivity and synaptic function. Consequently, p-EEG studies, now also readily applied in modeled animals, continue to have an important role in drug discovery and development, with progressively more emphasis on its potential as a central readout for target engagement and as a (translational) functional marker of neuronal circuit processes underlying normal and pathological brain functioning. In a similar vein as was done for human p-EEG studies, the contribution of animal p-EEG studies can further benefit by adherence to guidelines for methodological standardization, which are presently under construction by the International Pharmaco-EEG Society (IPEG).

Classification of Single Normal and Alzheimer's Disease Individuals from Cortical Sources of Resting State EEG Rhythms

Previous studies have shown abnormal power and functional connectivity of resting state electroencephalographic (EEG) rhythms in groups of Alzheimer's disease (AD) compared to healthy elderly (Nold) subjects. Here we tested the best classification rate of 120 AD patients and 100 matched Nold subjects using EEG markers based on cortical sources of power and functional connectivity of these rhythms. EEG data were recorded during resting state eyes-closed condition. Exact low-resolution brain electromagnetic tomography (eLORETA) estimated the power and functional connectivity of cortical sources in frontal, central, parietal, occipital, temporal, and limbic regions. Delta (2-4 Hz), theta (4-8 Hz), alpha 1 (8-10.5 Hz), alpha 2 (10.5-13 Hz), beta 1 (13-20 Hz), beta 2 (20-30 Hz), and gamma (30-40 Hz) were the frequency bands of interest. The classification rates of interest were those with an area under the receiver operating characteristic curve (AUROC) higher than 0.7 as a threshold for a moderate classification rate (i.e., 70%). Results showed that the following EEG markers overcame this threshold: (i) central, parietal, occipital, temporal, and limbic delta/alpha 1 current density; (ii) central, parietal, occipital temporal, and limbic delta/alpha 2 current density; (iii) frontal theta/alpha 1 current density; (iv) occipital delta/alpha 1 inter-hemispherical connectivity; (v) occipital-temporal theta/alpha 1 right and left intra-hemispherical connectivity; and (vi) parietal-limbic alpha 1 right intra-hemispherical connectivity. Occipital delta/alpha 1 current density showed the best classification rate (sensitivity of 73.3%, specificity of 78%, accuracy of 75.5%, and AUROC of 82%). These results suggest that EEG source markers can classify Nold and AD individuals with a moderate classification rate higher than 80%.

On-Going Frontal Alpha Rhythms Are Dominant in Passive State and Desynchronize in Active State in Adult Gray Mouse Lemurs

The gray mouse lemur (Microcebus murinus) is considered a useful primate model for translational research. In the framework of IMI PharmaCog project (Grant Agreement n°115009, www.pharmacog.org), we tested the hypothesis that spectral electroencephalographic (EEG) markers of motor and locomotor activity in gray mouse lemurs reflect typical movement-related desynchronization of alpha rhythms (about 8–12 Hz) in humans. To this aim, EEG (bipolar electrodes in frontal cortex) and electromyographic (EMG; bipolar electrodes sutured in neck muscles) data were recorded in 13 male adult (about 3 years) lemurs. Artifact-free EEG segments during active state (gross movements, exploratory movements or locomotor activity) and awake passive state (no sleep) were selected on the basis of instrumental measures of animal behavior, and were used as an input for EEG power density analysis. Results showed a clear peak of EEG power density at alpha range (7–9 Hz) during passive state. During active state, there was a reduction in alpha power density (8–12 Hz) and an increase of power density at slow frequencies (1–4 Hz). Relative EMG activity was related to EEG power density at 2–4 Hz (positive correlation) and at 8–12 Hz (negative correlation). These results suggest for the first time that the primate gray mouse lemurs and humans may share basic neurophysiologic mechanisms of synchronization of frontal alpha rhythms in awake passive state and their desynchronization during motor and locomotor activity. These EEG markers may be an ideal experimental model for translational basic (motor science) and applied (pharmacological and non-pharmacological interventions) research in Neurophysiology.

Cognitive Impairment After Sleep Deprivation Rescued by Transcranial Magnetic Stimulation Application in Octodon degus

Sleep is indispensable for maintaining regular daily life activities and is of fundamental physiological importance for cognitive performance. Sleep deprivation (SD) may affect learning capacity and the ability to form new memories, particularly with regard to hippocampus-dependent tasks. Transcranial magnetic stimulation (TMS) is a non-invasive procedure of electromagnetic induction that generates electric currents, activating nearby nerve cells in the stimulated cortical area. Several studies have looked into the potential therapeutic use of TMS. The present study was designed to evaluate how TMS could improve learning and memory functions following SD in Octodon degus. Thirty juvenile (18 months old) females were divided into three groups (control, acute, and chronic TMS treatment-with and without SD). TMS-treated groups were placed in plastic cylindrical cages designed to keep them immobile, while receiving head magnetic stimulation. SD was achieved by gently handling the animals to keep them awake during the night. Behavioral tests included radial arm maze (RAM), Barnes maze (BM), and novel object recognition. When TMS treatment was applied over several days, there was significant improvement of cognitive performance after SD, with no side effects. A single TMS session reduced the number of errors for the RAM test and improved latency and reduced errors for the BM test, which both evaluate spatial memory. Moreover, chronic TMS treatment brings about a significant improvement in both spatial and working memories.

The use of EEG parameters as predictors of drug effects on cognition

It has been shown to be difficult to predict whether cognition-enhancing effects of drugs in animal studies have the same effect in humans. Various issues in translating findings from animal to human studies can be identified. Here we discuss whether EEG could be considered as a possible tool to translate the effects of cognition enhancers across species. Three different aspects of EEG measures are evaluated: frequency bands, event-related potentials, and coherence analysis. On basis of the comparison of these measures between species, and effects of drugs that improve or impair memory performance (mainly cholinergic drugs), it appears that event-related potentials and coherence analyses could be considered as potential translational tools to study cognition-enhancing drug effects in rodents and animals.

Pharmacology of a novel central nervous system-penetrant P2X7 antagonist JNJ-42253432

In the central nervous system, the ATP-gated Purinergic receptor P2X ligand-gated ion channel 7 (P2X7) is expressed in glial cells and modulates neurophysiology via release of gliotransmitters, including the proinflammatory cytokine interleukin (IL)-1β. In this study, we characterized JNJ-42253432 [2-methyl-N-([1-(4-phenylpiperazin-1-yl)cyclohexyl]methyl)-1,2,3,4-tetrahydroisoquinoline-5-carboxamide] as a centrally permeable (brain-to-plasma ratio of 1), high-affinity P2X7 antagonist with desirable pharmacokinetic and pharmacodynamic properties for in vivo testing in rodents. JNJ-42253432 is a high-affinity antagonist for the rat (pKi 9.1 ± 0.07) and human (pKi 7.9 ± 0.08) P2X7 channel. The compound blocked the ATP-induced current and Bz-ATP [2'(3')-O-(4-benzoylbenzoyl)adenosine-5'-triphosphate tri(triethylammonium)]-induced release of IL-1β in a concentration-dependent manner. When dosed in rats, JNJ-42253432 occupied the brain P2X7 channel with an ED50 of 0.3 mg/kg, corresponding to a mean plasma concentration of 42 ng/ml. The compound blocked the release of IL-1β induced by Bz-ATP in freely moving rat brain. At higher doses/exposure, JNJ-42253432 also increased serotonin levels in the rat brain, which is due to antagonism of the serotonin transporter (SERT) resulting in an ED50 of 10 mg/kg for SERT occupancy. JNJ-42253432 reduced electroencephalography spectral power in the α-1 band in a dose-dependent manner; the compound also attenuated amphetamine-induced hyperactivity. JNJ-42253432 significantly increased both overall social interaction and social preference, an effect that was independent of stress induced by foot-shock. Surprisingly, there was no effect of the compound on either neuropathic pain or inflammatory pain behaviors. In summary, in this study, we characterize JNJ-42253432 as a novel brain-penetrant P2X7 antagonist with high affinity and selectivity for the P2X7 channel.

Transcranial magnetic stimulation (TMS)/repetitive TMS in mild cognitive impairment and Alzheimer's disease

Several Transcranial Magnetic Stimulation (TMS) techniques can be applied to noninvasively measure cortical excitability and brain plasticity in humans. TMS has been used to assess neuroplastic changes in Alzheimer's disease (AD), corroborating findings that cortical physiology is altered in AD due to the underlying neurodegenerative process. In fact, many TMS studies have provided physiological evidence of abnormalities in cortical excitability, connectivity, and plasticity in patients with AD. Moreover, the combination of TMS with other neurophysiological techniques, such as high-density electroencephalography (EEG), makes it possible to study local and network cortical plasticity directly. Interestingly, several TMS studies revealed abnormalities in patients with early AD and even with mild cognitive impairment (MCI), thus enabling early identification of subjects in whom the cholinergic degeneration has occurred. Furthermore, TMS can influence brain function if delivered repetitively; repetitive TMS (rTMS) is capable of modulating cortical excitability and inducing long-lasting neuroplastic changes. Preliminary findings have suggested that rTMS can enhance performances on several cognitive functions impaired in AD and MCI. However, further well-controlled studies with appropriate methodology in larger patient cohorts are needed to replicate and extend the initial findings. The purpose of this paper was to provide an updated and comprehensive systematic review of the studies that have employed TMS/rTMS in patients with MCI and AD.