Cholinergic Tone Research Articles

The mechanisms shaping CA2 pyramidal neuron action potential bursting induced by muscarinic acetylcholine receptor activation.

Recent studies have revealed that hippocampal area CA2 plays an important role in hippocampal network function. Disruption of this region has been implicated in neuropsychiatric disorders. It is well appreciated that cholinergic input to the hippocampus plays an important role in learning and memory. While the effect of elevated cholinergic tone has been well studied in areas CA1 and CA3, it remains unclear how changes in cholinergic tone impact synaptic transmission and the intrinsic properties of neurons in area CA2. In this study, we applied the cholinergic agonist carbachol and performed on-cell, whole-cell, and extracellular recordings in area CA2. We observed that under conditions of high cholinergic tone, CA2 pyramidal neurons depolarized and rhythmically fired bursts of action potentials. This depolarization depended on the activation of M1 and M3 cholinergic receptors. Furthermore, we examined how the intrinsic properties and action-potential firing were altered in CA2 pyramidal neurons treated with 10 µM carbachol. While this intrinsic burst firing persisted in the absence of synaptic transmission, bursts were shaped by synaptic inputs in the intact network. We found that both excitatory and inhibitory synaptic transmission were reduced upon carbachol treatment. Finally, we examined the contribution of different channels to the cholinergic-induced changes in neuronal properties. We found that a conductance from Kv7 channels partially contributed to carbachol-induced changes in resting membrane potential and membrane resistance. We also found that D-type potassium currents contributed to controlling several properties of the bursts, including firing rate and burst kinetics. Furthermore, we determined that T-type calcium channels and small conductance calcium-activated potassium channels play a role in regulating bursting activity.

Low acetylcholine during early sleep is important for motor memory consolidation.

The synaptic homeostasis theory of sleep proposes that low neurotransmitter activity in sleep optimizes memory consolidation. We tested this theory by asking whether increasing acetylcholine levels during early sleep would weaken motor memory consolidation. We trained separate groups of adult mice on the rotarod walking task and the single pellet reaching task, and after training, administered physostigmine, an acetylcholinesterase inhibitor, to increase cholinergic tone in subsequent sleep. Post-sleep testing showed that physostigmine impaired motor skill acquisition of both tasks. Home-cage video monitoring and electrophysiology revealed that physostigmine disrupted sleep structure, delayed non-rapid-eye-movement sleep onset, and reduced slow-wave power in the hippocampus and cortex. Additional experiments showed that: (1) the impaired performance associated with physostigmine was not due to its effects on sleep structure, as 1 h of sleep deprivation after training did not impair rotarod performance, (2) a reduction in cholinergic tone by inactivation of cholinergic neurons during early sleep did not affect rotarod performance, and (3) stimulating or blocking muscarinic and nicotinic acetylcholine receptors did not impair rotarod performance. Taken together, the experiments suggest that the increased slow wave activity and inactivation of both muscarinic and nicotinic receptors during early sleep due to reduced acetylcholine contribute to motor memory consolidation.

Treatment with Dimethyl Fumarate Enhances Cholinergic Transmission in Multiple Sclerosis.

Dimethyl fumarate (DMF) exerts anti-inflammatory effects in multiple sclerosis by activating the Nrf2 antioxidant pathway, which is also stimulated by acetylcholine via alpha-7 nicotinic acetylcholine receptors. In animal models, Nrf2 potentiates cholinergic synaptic plasticity. The aim of this study was to test whether treatment with DMF modulates cholinergic pathways in relapsing-remitting multiple sclerosis (RRMS). Patients starting DMF (20) or IFN-β 1a (20) and healthy subjects (20) were enrolled. Short-latency afferent inhibition (SAI), which is a transcranial stimulation measure of central cholinergic transmission, was recorded in patients and controls at baseline and, in patients only, after 6months of treatment. Patients treated with DMF also underwent autonomic function testing to further explore peripheral and central cholinergic tone. At baseline, SAI was similar in patients and in controls (p = 0.983). Treatment with DMF significantly increased SAI (p = 0.01), while IFNβ had no effect (p = 0.80). In the cold face test, DMF treatment also increased reflex bradycardia (p = 0.013), and reduced diastolic blood pressure variation (p = 0.010), further indicating its ability to stimulate cholinergic transmission. Treatment of MS patients with DMF results in increased cholinergic stimulation, with possible implications for neuroinflammation and neuroprotection.

Activation of Prejunctional P2x2/3 Heterotrimers by ATP Enhances the Cholinergic Tone in Obstructed Human Urinary Bladders.

The objective of this study was to investigate the role of ATP in cholinergic neurotransmission in the urinary bladder of control men and of patients obstructed as a result of benign prostatic hyperplasia (BPH). Human detrusor samples were collected from 41 patients who submitted to transvesical prostatectomy resulting from BPH and 26 male organ donors. The release of [3H]acetylcholine ([3H]ACh) was evoked by electrical field stimulation (10 Hz, 200 pulses) in urothelium-denuded detrusor strips. Myographic recordings were performed to test detrusor strip sensitivity to ACh and ATP. Nerve-evoked [3H]ACh release was 1.5-fold higher in detrusor strips from BPH patients compared with controls. This difference was abolished after desensitization of ionotropic P2X1-3 receptors with an ATP analog, α,β-methylene ATP (30 μM, applied for 15 minutes). TNP-ATP (10 nM, a preferential P2X2/3 antagonist) and A317491 (100 nM, a selective P2X3 antagonist) were about equipotent in decreasing nerve-evoked [3H]ACh release in control detrusor strips, but the selective P2X1 receptor antagonist NF023 (3 μM) was devoid of effect. The inhibitory effect of TNP-ATP (10 nM) increased from 27% ± 9% to 43% ± 6% in detrusor strips of BPH patients, but the effect of A317491 (100 nM) [3H]ACh release unaltered (20% ± 2% vs. 24% ± 4%). The amplitude of ACh (0.1-100 μM)-induced myographic recordings decreased, whereas sensitivity to ATP (0.01-3 mM) increased in detrusor strips from BPH patients. Besides the well characterized P2X1 receptor-mediated contractile activity of ATP in pathologic human bladders, we show here for the first time that cholinergic hyperactivity in the detrusor of BPH patients is facilitated by activation of ATP-sensitive P2X2/3 heterotrimers. SIGNIFICANCE STATEMENT: Bladder outlet obstruction often leads to detrusor overactivity and reduced bladder compliance in parallel to atropine-resistant increased purinergic tone. Our data show that P2X1 purinoceptors are overexpressed in the detrusor of patients with benign prostatic hyperplasia. Besides the P2X1 receptor-mediated detrusor contractions, ATP favors nerve-evoked acetylcholine release via the activation of prejunctional P2X2/3 excitatory receptors in these patients Thus, our hypothesis is that manipulation of the purinergic tone may be therapeutically useful to counteract cholinergic overstimulation in obstructed patients.

Altered motor, anxiety-related and attentional task performance at baseline associate with multiple gene copies of the vesicular acetylcholine transporter and related protein overexpression in ChAT::Cre+ rats

Transgenic rodents expressing Cre recombinase cell specifically are used for exploring mechanisms regulating behavior, including those mediated by cholinergic signaling. However, it was recently reported that transgenic mice overexpressing a bacterial artificial chromosome containing choline acetyltransferase (ChAT) gene, for synthesizing the neurotransmitter acetylcholine, present with multiple vesicular acetylcholine transporter (VAChT) gene copies, resulting in altered cholinergic tone and accompanying behavioral abnormalities. Since ChAT::Cre+ rats, used increasingly for understanding the biological basis of CNS disorders, utilize the mouse ChAT promotor to control Cre recombinase expression, we assessed for similar genotypical and phenotypical differences in such rats compared to wild-type siblings. The rats were assessed for mouse VAChT copy number, VAChT protein expression levels and for sustained attention, response control and anxiety. Rats were also subjected to a contextual fear conditioning paradigm using an unconditional fear-inducing stimulus (electrical foot shocks), with blood samples taken at baseline, the fear acquisition phase and retention testing, for measuring blood plasma markers of hypothalamic–pituitary–adrenal gland (HPA)-axis activity. ChAT::Cre+ rats expressed multiple mouse VAChT gene copies, resulting in significantly higher VAChT protein expression, revealed anxiolytic behavior, hyperlocomotion and deficits in tasks requiring sustained attention. The HPA-axis was intact, with unaltered circulatory levels of acute stress-induced corticosterone, leptin and glucose. Our findings, therefore, reveal that in ChAT::Cre+ rats, VAChT overexpression associates with significant alterations of certain cognitive, motor and affective functions. Although highly useful as an experimental tool, it is essential to consider the potential effects of altered cholinergic transmission on baseline behavior in ChAT::Cre rats.

Alterations in NMDAR-mediated signaling within the laterodorsal tegmental nucleus are associated with prenatal nicotine exposure

Cigarette smoking during pregnancy has been clinically associated with a variety of poorbehavioral outcomes for the exposed individuals, including higher risks for drug abuse and development of attention/deficit-hyperactive disorder (ADHD). Experimental studies support the hypothesis that nicotine might contribute to these risks, since prenatal nicotine exposure (PNE) in rodents was associated with greater addiction liability, hyperactivity, social impairments and a wide range of emotional and cognitive deficits. Alterations of glutamate signaling within brain regions involved in behavioral circuits could contribute to these outcomes. The pontine laterodorsal tegmental nucleus (LDT) exerts cholinergic modulation within the ventral tegmental area, nucleus accumbens, and cortical-projecting thalamic centers and PNE-associated alterations in LDT glutamate signaling could impact cholinergic output to these LDT targets. We have previously demonstrated that PNE alters AMPA-mediated signaling within LDT neurons, and in the present investigation, we focused on changes of NMDA receptors (NMDARs) and presence of silent synapses as an indicator of metaplastic processes in LDT cells associated with PNE treatment. PNE was associated with a decreased functional presence of GluN2B NMDAR subunits in synapses of large, putatively cholinergic neurons, whereas an increased function of this subunit was detected in small, likely GABAergic cells. In addition, PNE was associated with functional alterations of extrasynaptic NMDARs in putative cholinergic neurons, suggestive of an increased presence of GluN3A-containing NMDARs. An increased number of silent synapses was exclusively seen in the small cells. When taken together, we hypothesize that NMDA-mediated signaling changes within LDT neurons following PNE treatment would result in reductions of excitatory cholinergic modulatory tone in target brain regions, which would be expected to contribute to the behavioral deficits found among these individuals.

Autonomic modulation of the electrical substrate in mice haploinsufficient for cardiac sodium channels: a model of the Brugada syndrome.

A murine line haploinsufficient in the cardiac sodium channel has been used to model human Brugada syndrome: a disease causing sudden cardiac death due to lethal ventricular arrhythmias. We explored the effects of cholinergic tone on electrophysiological parameters in wild-type and genetically modified, heterozygous, Scn5a+/- knockout mice. Scn5a+/- ventricular slices showed longer refractory periods than wild-type both at baseline and during isoprenaline challenge. Scn5a+/- hearts also showed lower conduction velocities and increased mean increase in delay than did littermate controls at baseline and blunted responses to isoprenaline challenge. Carbachol exerted limited effects but reversed the effects of isoprenaline with coapplication. Scn5a+/- mice showed a reduction in conduction reserve in that isoprenaline no longer increased conduction velocity, and this was not antagonized by muscarinic agonists.

FV 1 Cholinergic brain structure and sensory-afferent modulation of motor cortex excitability

Introduction The basal forebrain provides important output within the cholinergic system. The cholinergic system may also influence the effects of paired associative stimulation (PAS), a plasticity inducing protocol involving paired median nerve and motor cortex stimulation, and short latency afferent inhibition (SAI) in which a median nerve sensory afferent stimulus induces short lasting conditioning effects on motor cortex excitability. The responses to either PAS or SAI can be variable. Here we hypothesized that the basal forebrain structural characteristics, or those of the thalamus as important sensory-afferent relay station with cholinergic input, relate to the functional influence of the cholinergic system measured using PAS or SAI. We therefore asked whether structural variability in these cholinergic brain areas could explain some of that functional variability observed with PAS or SAI. Material and methods Forty healthy volunteers (12 male; mean age 60, range 26–81) underwent a facilitatory PAS protocol with an inter-stimulus interval (ISI) of around 25 ms. An LTP-like facilitatory response was defined as an increase post-PAS of MEP amplitude of at least 10% relative to pre-PAS MEP size. SAI employed median nerve condition of motor cortex stimulation with inhibitory as well as facilitatory ISIs. We obtained T1 MPRAGE sequences on a 3T MRI scanner. MRI data were processed using Statistical Parametric Mapping and the CAT12 Toolbox (http://www.neuro.uni-jena.de/cat/) implemented in Matlab 2015a. Volumes of the basal forebrain were determined using a stereotactic atlas based on combined postmortem MRI and histological examination of cholinergic nuclei. As it is based on the histological examination of a single brain specimen and may not generalize across individuals, we also used volumes of right and left BFCS as obtained from the CAT12 toolbox. We used ANOVA models for group comparisons of responders and non-responders to PAS or SAI. Results Nineteen participants (48%) had an LTP-like response to PAS. Age, sex, or motor thresholds did not predict the PAS response. SAI had inhibitory effects in 80% of participants (n = 32). There was no association between the amount of PAS effects and the SAI response. Basal forebrain and right thalamus volumes were larger in SAI responders while volumes were similar in PAS responders and non-responders. Discussion The results suggest that a larger basal forebrain cholinergic output system, and a larger thalamus as sensory-afferent relay station that receives cholinergic input facilitate the short lasting modulation of motor cortex excitability in the SAI paradigm. This could be because of higher cholinergic tone. The cholinergic system may be less important in longer lasting modulation of motor cortex excitability in the PAS paradigm where an LTP-like response may involve more GABA-ergic neurotransmission.

A Cross-Recurrence Analysis of the Pupil Size Fluctuations in Steady Scotopic Conditions.

Pupil size fluctuations during stationary scotopic conditions may convey information about the cortical state activity at rest. An important link between neuronal network state modulation and pupil fluctuations is the cholinergic and noradrenergic neuromodulatory tone, which is active at cortical level and in the peripheral terminals of the autonomic nervous system (ANS). This work aimed at studying the low- and high-frequency coupled oscillators in the autonomic spectrum (0–0.45 Hz) which, reportedly, drive the spontaneous pupillary fluctuations. To assess the interaction between the oscillators, we focused on the patterns of their trajectories in the phase-space. Firstly, the frequency spectrum of the pupil signal was determined by empirical mode decomposition. Secondly, cross-recurrence quantification analysis was used to unfold the non-linear dynamics. The global and local patterns of recurrence of the trajectories were estimated by two parameters: determinism and entropy. An elliptic region in the entropy-determinism plane (95% prediction area) yielded health-related values of entropy and determinism. We hypothesize that the data points inside the ellipse would likely represent balanced activity in the ANS. Interestingly, the Epworth Sleepiness Scale scores scaled up along with the entropy and determinism parameters. Although other non-linear methods like Short Time Fourier Transform and wavelets are usually applied for analyzing the pupillary oscillations, they rely on strong assumptions like the stationarity of the signal or the a priori knowledge of the shape of the single basis wave. Instead, the cross-recurrence analysis of the non-linear dynamics of the pupil size oscillations is an adaptable diagnostic tool for identifying the different weight of the autonomic nervous system components in the modulation of pupil size changes at rest in non-luminance conditions.

THE USE OF COGNITIVE AND ERP BIOMARKERS OF CHOLINERGIC FUNCTION IN NOVEL TESTS OF MUSCARINIC POSITIVE ALLOSTERIC MODULATORS

Introduction The decline of cholinergic functioning is associated with increased cognitive decline and the development of Alzheimer's disease (AD) pathology. At present, there is no pharmacological agent that slows the progression the disease. Muscarinic post positive allosteric modulators (PAMs) are a new class of compounds aiming to restore cholinergic functioning in patients suffering from AD pathology. PAMs of the M1 receptor can potentiate the response of the M1 receptor to acetylcholine, without inducing the harmful side-effects. This is due to the fact that PAMs do not bind at the target site, rather they boost the signal of acetylcholine when is engaged at the orthosteric receptor. The downside of using PAMs is that they have low affinity to radioactive ligands, so this reduces the utility of PET imaging. This creates a challenge in how to establish functional efficacy of the compound in both preclinical and clinical trials. Methods To address this challenge, we plan on using cognitive tasks and electroencephalography (qEEG) to identify dose-depended changes in cholinergic functioning. These functional biomarkers allow us to develop more detailed models of how M1PAMs may influence downstream cognitive processing. The cognitive and EEG measures presented have been shown to modulate cholinergic tone, therefore we should be able to identify effective target engagement. Results Cognitive tasks tested spatial and sustained attention, episodic and working memory, perceptual vigilance and psychomotor speed. Tasks recorded by EEG tested auditory and visual discrimination using oddball tasks, and incidental memory. Conclusions These cognitive and electrophysiological results will assist in establishing functional targets for future studies using M1PAMs. This research was funded by Funding for this research comes from an Alzheimer's Association and the Alzheimer's Drug Discovery Foundation.

Cholinergic striatal neurons are increased in HSAN V homozygous mice despite reduced NGF bioavailability

The neurotrophin Nerve growth factor (NGF) plays a critical role in the mature and developing nervous system. A point mutation (R100W) in the NGFB gene was found in patients with Hereditary Sensory and Autonomic Neuropathy type V (HSAN V), which leads to pain insensitivity. In a previous work it has been shown that the mutation provokes a reduced secretion of mature NGF. In this study we generated and analyzed homozygous NGFR100W/R100W mice to understand whether the reduced NGF bioavailability can contribute to the clinical phenotype of the homozygous condition. We found that the majority of NGFR100W/R100W mice were born normal but failed to reach the first month of age. This early lethality was rescued by daily treatment with wild type NGF. In addition, we found that the density of cholinergic neurons of homozygous mice was unaffected in the medial septum and in the nucleus basalis of Meynert, whereas, suprisingly, it was increased specifically in the striatum. Due to the known action of the striatal cholinergic tone in modulating pain, our findings support the hypothesis that a central mechanism, linked to the NGFR100W-dependent increase of the striatal cholinergic tone, can contribute to the pain insensitivity observed in HSAN V patients.

Autonomic control of cardiovascular adjustments associated with orthostasis in the scansorial snake Boa constrictor.

Orthostatic hypotension is a phenomenon triggered by a change in the position or posture of an animal, from a horizontal to a vertical head-up orientation, characterised by a blood pooling in the lower body and a reduction in central and cranial arterial blood pressure (PA). This hypotension elicits systemic vasoconstriction and tachycardia, which generally reduce blood pooling and increase PA Little is known about the mediation and importance of such cardiovascular adjustments that counteract the haemodynamic effects of orthostasis in ectothermic vertebrates, and some discrepancies exist in the information available on this subject. Thus, we sought to expand our knowledge on this issue by investigating it in a more elaborate way, through an in vivo pharmacological approach considering temporal circulatory changes during head-up body inclinations in unanaesthetised Boa constrictor To do so, we analysed temporal changes in PA, heart rate (fH) and cardiac autonomic tone associated with 30 and 60deg inclinations, before and after muscarinic blockade with atropine, double blockade with atropine and propranolol, and α1-adrenergic receptor blockade with prazosin. Additionally, the animals' fH variability was analysed. The results revealed that, in B. constrictor: (1) the orthostatic tachycardia is initially mediated by a decrease in cholinergic tone followed by an increase in adrenergic tone, a pattern that may be evolutionarily conserved in vertebrates; (2) the orthostatic tachycardia is important for avoiding an intense decrease in PA at the beginning of body inclinations; and (3) α1-adrenergic orthostatic vasomotor responses are important for the maintenance of PA at satisfactory values during long-term inclinations.

Autonomic cardiac regulation facilitates acute heat tolerance in rainbow trout: in situ and in vivo support.

Acute warming in fish increases heart rate (fH) and cardiac output to peak values, after which performance plateaus or declines and arrhythmia may occur. This cardiac response can place a convective limitation on systemic oxygen delivery at high temperatures. To test the hypothesis that autonomic cardiac regulation protects cardiac performance in rainbow trout during acute warming, we investigated adrenergic and cholinergic regulation during the onset and progression of cardiac limitations. We explored the direct effects of adrenergic stimulation by acutely warming an in situ working perfused heart until arrhythmia occurred, cooling the heart to restore rhythmicity and rewarming with increasing adrenergic stimulation. Adrenergic stimulation produced a clear, dose-dependent increase in the temperature and peak fH achieved prior to the onset of arrhythmia. To examine how this adrenergic protection functions in conjunction with cholinergic vagal inhibition in vivo, rainbow trout fitted with ECG electrodes were acutely warmed in a respirometer until they lost equilibrium (CTmax) with and without muscarinic (atropine) and β-adrenergic (sotalol) antagonists. Trout exhibited roughly equal and opposing cholinergic and adrenergic tone on fH that persisted up to critical temperatures. β-Adrenergic blockade significantly lowered peak fH by 14-17%, while muscarinic blockade significantly lowered the temperature for peak fH by 2.0°C. Moreover, muscarinic and β-adrenergic blockers injected individually or together significantly reduced CTmax by up to 3°C, indicating for the first time that cardiac adrenergic stimulation and cholinergic inhibition can enhance acute heat tolerance in rainbow trout at the level of the heart and the whole animal.

Respiratory sinus arrhythmia is a major component of heart rate variability in undisturbed, remotely monitored rattlesnakes, Crotalus durissus.

ECG recordings were obtained using an implanted telemetry device from the South American rattlesnake, Crotalus durissus, held under stable conditions without restraining cables or interaction with researchers. Mean heart rate (fH) recovered rapidly (<24 h) from anaesthesia and operative procedures. This preceded a more gradual development of heart rate variability (HRV), with instantaneous fH increasing during each lung ventilation cycle. Atropine injection increased mean fH and abolished HRV. Complete autonomic blockade revealed a cholinergic tonus on the heart of 55% and an adrenergic tonus of 37%. Power spectral analysis of HRV identified a peak at the same frequency as ventilation. This correlation was sustained after temperature changes and it was more evident, marked by a more prominent power spectrum peak, when ventilation is less episodic. This HRV component is homologous to that observed in mammals, termed respiratory sinus arrhythmia (RSA). Evidence for instantaneous control of fH indicated rapid conduction of activity in the cardiac efferent nervous supply, as supported by the description of myelinated fibres in the cardiac vagus. Establishment of HRV 10 days after surgical intervention seems a reliable indicator of the re-establishment of control of integrative functions by the autonomic nervous system. We suggest that this criterion could be applied to other animals exposed to natural or imposed trauma, thus improving protocols involving animal handling, including veterinarian procedures.

Galantamine reversed early postoperative cognitive deficit via alleviating inflammation and enhancing synaptic transmission in mouse hippocampus

Postoperative cognitive dysfunction (POCD) is commonly seen in patients undergoing major surgeries and may persist. Although neuroinflammation is one of the important contributors to the development of POCD, the mechanisms underlying POCD remain unclear. We performed stabilized tibial fracture operation in male mice. In comparison with sham mice (anesthesia only), the surgery mice exhibited cognitive deficits in a fear conditioning paradigm at postsurgery day 3-7, and increased numbers of microglia and elevated levels of pro-inflammatory cytokines (IL-1β, IL-6 and TNF-α) without change of anti-inflammatory cytokines (IL-4 and IL-10) in the hippocampus. Electrophysiological recordings from CA1 hippocampal neurons revealed that POCD mice exhibited impairment in AMPA receptor-mediated evoked excitatory postsynaptic currents (eEPSCs) without alteration in the rectification property of AMPA receptors. Interestingly, daily intraperitoneal administration of galantamine, an inhibitor of acetylcholinesterase, reversed cognitive dysfunction in surgery mice and attenuated accumulation of microglia and protein levels of IL-1β, IL-6 and TNF-α in the hippocampus. Additionally, galantamine potentiated AMPA receptor-mediated eEPSCs in the hippocampus more prominent in surgery mice than in sham mice. Therefore, enhancement of cholinergic tone in the hippocampus might be a therapeutic strategy for early POCD in terms of suppression of inflammation and normalization of excitatory synaptic transmission.

Cholinergic Mechanisms of Target Oddball Stimuli Detection: The Late "P300-Like" Event-Related Potential in Rats.

Event-related potentials (ERPs) and oscillations (EROs) provide powerful tools for studying the brain's synaptic function underlying information processing. The P300 component of ERPs indexing attention and working memory shows abnormal amplitude and latency in neurological and psychiatric diseases that are sensitive to pharmacological agents. In the active auditory oddball discriminant paradigm, behavior and auditory-evoked potentials (AEPs) were simultaneously recorded in awake rats to investigate whether P300-like potentials generated in rats responding to rare target oddball tones are sensitive to subcutaneous modulation of the cholinergic tone by donepezil (1 mg/kg) and scopolamine (0.64 mg/kg). After operant training, rats consistently discriminate rare target auditory stimuli from frequent irrelevant nontarget auditory stimuli by a higher level of correct lever presses (i.e., accuracy) in target trials associated with a food reward. Donepezil attenuated the disruptive effect of scopolamine on the level of accuracy and premature responses in target trials. Larger P300-like peaks with early and late components were revealed in correct rare target stimuli trials as compared to frequent tones. Donepezil enhanced the peak amplitude of the P300-like component to target stimuli and evoked slow theta and gamma oscillations, whereas scopolamine altered the amplitude of the P300-like component and EROs to target stimuli. Pretreatment with donepezil attenuated effects of scopolamine on the peak amplitude of the P300-like component and on EROs. This study provides evidence that AEP P300-like responses can be elicited by rats engaged in attentive and memory processing of target stimuli and outline the relevance of the cholinergic system in stimulus discrimination processing. The findings highlight the sensitivity of this translational index for investigating brain circuits and/or novel pharmacological agents, which modulate cholinergic transmission associated with increased allocation of attentional resources.

Neurophysiological signals as predictive translational biomarkers for Alzheimer\u2019s disease treatment: effects of donepezil on neuronal network oscillations in TgF344-AD rats

BackgroundTranslational research in Alzheimer’s disease (AD) pathology provides evidence that accumulation of amyloid-β and hyperphosphorylated tau, neuropathological hallmarks of AD, is associated with complex disturbances in synaptic and neuronal function leading to oscillatory abnormalities in the neuronal networks that support memory and cognition. Accordingly, our recent study on transgenic TgF344-AD rats modeling AD showed an age-dependent reduction of stimulation-induced oscillations in the hippocampus, and disrupted long-range connectivity together with enhanced neuronal excitability in the cortex, reflected in greatly increased expression of high-voltage spindles, an epileptic absence seizure-like activity. To better understand the translational value of observed oscillatory abnormalities in these rats, we examine here the effects of donepezil, an acetylcholine esterase inhibitor clinically approved for AD treatment.MethodsBrainstem nucleus pontis oralis stimulation-induced hippocampal oscillations were recorded under urethane anesthesia in adult (6-month-old) and aged (12-month-old) TgF344-AD and wild-type rats. Spontaneous cortical activity was monitored in a cohort of freely behaving aged rats implanted with frontal and occipital cortical electroencephalography (EEG) electrodes.ResultsSubcutaneous administration of donepezil significantly augmented stimulation-induced hippocampal theta oscillation in aged wild-type rats and both adult and aged TgF344-AD rats, which have been previously shown to have diminished response to nucleus pontis oralis stimulation. Moreover, in adult TgF344-AD rats, donepezil also significantly increased theta phase-gamma amplitude coupling in the hippocampus during stimulation. However, neither of these effects were significantly changed in adult wild-type rats. Under freely behaving conditions, donepezil treatment had the opposite effect on cortical oscillatory connectivity in TgF344-AD and wild-type rats, and it reduced the occurrence of high-voltage spindle activity in TgF344-AD rats.ConclusionsTogether, these results imply that pharmacologically enhancing cholinergic tone with donepezil could partially reverse oscillatory abnormalities in TgF344-AD rats, which is in line with its clinical effectiveness in AD patients. Therefore, our study suggests good translational opportunities for these neurophysiological signals recorded in TgF344-AD rats, and their application could be considered in drug discovery efforts for developing therapies with disease-modifying potential.

Pharmacological Modulation of Right Ventricular Endocardial-Epicardial Gradients in Brugada Syndrome.

Background We explored the hypothesis that increased cholinergic tone exerts its proarrhythmic effects in Brugada syndrome (BrS) through increasing dispersion of transmural repolarization in patients with spontaneous and drug-induced BrS. Methods BrS and supraventricular tachycardia patients were studied after deploying an Ensite Array in the right ventricular outflow tract and a Cardima catheter in the great cardiac vein to record endo and epicardial signals, respectively. S1-S2 restitution curves from the right ventricular apex were conducted at baseline and after edrophonium challenge to promote increased cholinergic tone. The local unipolar electrograms were then analyzed to study transmural conduction and repolarization dynamics. Results The study included 8 BrS patients (5 men:3 women; mean age, 56 years) and 8 controls patients with supraventricular tachycardia (5 men:3 women; mean age, 48 years). Electrophysiological studies in controls demonstrated shorter endocardial than epicardial right ventricular activation times (mean difference: 26 ms; P<0.001). In contrast, patients with BrS showed longer endocardial than epicardial activation time (mean difference: -15 ms; P=0.001). BrS hearts, compared with controls, showed significantly larger transmural gradients in their activation recovery intervals (mean intervals, 20.5 versus 3.5 ms; P<0.01), with longer endocardial than epicardial activation recovery intervals. Edrophonium challenge increased such gradients in both controls (to a mean of 16 ms [ P<0.001]) and BrS (to 29.7 ms; P<0.001). However, these were attributable to epicardial and endocardial activation recovery interval prolongations in control and BrS hearts, respectively. Dynamic changes in repolarization gradients were also observed across the BrS right ventricular wall in BrS. Conclusions Differential contributions of conduction and repolarization were identified in BrS which critically modulated transmural dispersion of repolarization with significant cholinergic effects only identified in the patients with BrS. This has important implications for explaining the proarrhythmic effects of increased vagal tone in BrS, as well as evaluating autonomic modulation and epicardial ablation as therapeutic strategies.

Midazolam is effective to reduce cortical network activity in organotypic cultures during severe cholinergic overstimulation with soman

Intoxication with organophosphorus compounds can result in life-threatening organ dysfunction and refractory seizures. Sedation or hypnosis is essential to facilitate mechanical ventilation and control seizure activity. The range of indications for midazolam includes both hypnosis and seizure control. Since benzodiazepines cause sedation and hypnosis by dampening neuronal activity of the cerebral cortex, we investigated the drug’s effect on action potential firing of cortical neurons in brain slices. Extensive cholinergic overstimulation was induced by increasing acetylcholine levels and simultaneously treating the slices with soman to block acetylcholinesterase activity. At control conditions midazolam reduced discharge rates (median/95% confidence interval) from 8.8 (7.0–10.5) Hz (in the absence of midazolam) to 2.2 (1.4–2.9) Hz (10 μM midazolam) and 1.6 (0.9–2.2) Hz (20 μM midazolam). Without midazolam, cholinergic overstimulation significantly enhanced neuronal activity to 13.1 (11.0–15.2) Hz. Midazolam attenuated firing rates during cholinergic overstimulation to 6.5 (4.8–8.2) Hz (10 μM midazolam) and 4.1 (3.3–6.0) Hz (20 μM midazolam), respectively. Thus, high cholinergic tone attenuated the drug’s efficacy only moderately. These results suggest that midazolam is worth being tested as a promising drug to induce sedation and hypnosis in patients suffering from severe organophosphorous intoxication.

Blue Light Enhances Bacterial Clearance and Reduces Organ Injury During Sepsis.

The physiology of nearly all mammalian organisms are entrained by light and exhibit circadian rhythm. The data derived from animal studies show that light influences immunity, and these neurophysiologic pathways are maximally entrained by the blue spectrum. Here, we hypothesize that bright blue light reduces acute kidney injury by comparison with either bright red or standard, white fluorescent light in mice subjected to sepsis. To further translational relevance, we performed a pilot clinical trial of blue light therapy in human subjects with appendicitis. Laboratory animal research, pilot human feasibility trial. University basic science laboratory and tertiary care hospital. Male C57BL/6J mice, adult (> 17 yr) patients with acute appendicitis. Mice underwent cecal ligation and puncture and were randomly assigned to a 24-hour photoperiod of bright blue, bright red, or ambient white fluorescent light. Subjects with appendicitis were randomized to receive postoperatively standard care or standard care plus high-illuminance blue light. Exposure to bright blue light enhanced bacterial clearance from the peritoneum, reduced bacteremia and systemic inflammation, and attenuated the degree of acute kidney injury. The mechanism involved an elevation in cholinergic tone that augmented tissue expression of the nuclear orphan receptor REV-ERBα and occurred independent of alterations in melatonin or corticosterone concentrations. Clinically, exposure to blue light after appendectomy was feasible and reduced serum interleukin-6 and interleukin-10 concentrations. Modifying the spectrum of light may offer therapeutic utility in sepsis.