How can I measure brain acetylcholine levels in vivo? Advantages and caveats of commonly used approaches

Liquid/liquid junction microelectrodes for monitoring cholinergic transmitter in live mice brain in vivo

Acetylcholine (ACh) is an important neurotransmitter and biomarker for neurological disorders. The quantitative detection of ACh in vivo is critical but remains a challenge. In this work, we developed a novel micrometer-sized electrode based on interface between two immiscible electrolyte solutions (ITIES) to achieve in vivo measurement of ACh at high spatiotemporal resolution. The fabricated microITIES electrode was tested in vitro for ACh sensing using electrochemical methods including cyclical voltammetry and i-t amperometry in artificial cerebrospinal fluid (ACSF) solution. An increase in current was observed in both CV and i-t at -0.25 V (vs E1/2, TEA). Both CV and i-t showed a high sensitivity and a linear response with the linear range starting from as low as 0.5 μM. Then the electrode was applied for in vivo measurement of ACh in the living mouse brain. The electrode was implanted in the cortex of the mouse brain via stereotaxic surgery. The electrode was tested for exogenously applied ACh in vivo by local injection of ACh (500 nL, 0.5 M) twice. Repeated cyclic voltammograms were recorded before, during, and after both injections; the cyclic voltammograms showed a significant increase in current at ACh detection potential. The electrode was also tested for endogenously released ACh in vivo by the local injection of a high concentration KCl solution (500 nL and 1000 nL, 100 mM) to stimulate ACh release. Similarly, repeated cyclic voltammograms were recorded before, during, and after both injections; a significant increase in current at the ACh detection potential in the cyclic voltammograms was observed following each injection of KCl. These results validated the capability of the introduced microITIES electrode to measure exogenous and endogenous ACh in vivo.

Choline levels in the pregenual anterior cingulate cortex associated with unpleasant pain experience and anxiety

In vivo proton magnetic resonance spectroscopy is a non-invasive technique used to measure biochemical molecules such as choline, glutamate, glutamine, and γ-Aminobutyric acid (GABA), many of which are relevant to anxiety and pain. However, the relationship between these neurotransmitters/metabolites and their implications for anxiety and subjective experience of pain is not yet fully understood. The objective of this cross-sectional study was to investigate the association between anxiety and pain ratings with levels of total choline, glutamate and GABA in brain regions known to be involved in anxiety and emotional experience of pain, specifically pregenual anterior cingulate cortex (pgACC) and dorsal anterior cingulate cortex (dACC). The levels of the neurotransmitters/metabolites were measured using GABA-edited Mescher-Garwood PRESS for GABA measurements, with the OFF-sequence measurements for total choline (tCho) and Glx (combined glutamate + glutamine). The total choline (tCho) signal in our analysis included glycerophosphocholine (GPC) and phosphocholine (PC), which is consistent with standard practices in MRS studies. This approach ensures a robust estimation of tCho concentrations across participants. The study collected data from 38 participants (17 males and 21 females). The analysis revealed a significant correlation between anxiety ratings before a standardized pain provocation and the rated pain unpleasantness during the pain provocation. tCho correlated negatively with these parameters in pgACC. A linear regression analysis indicated that tCho levels in pgACC have a significant negative association with anxiety and perceived pain when controlling for age, depressive symptoms, and alcohol and tobacco intake. We also found that sex significantly moderates the relationship between pgACC choline levels and pain unpleasantness. The study suggests that levels of choline, an essential precursor of acetylcholine, are associated with anxiety and perceived pain. These levels may influence how Glx and GABA contribute to affective pain experiences by modulating the balance between excitatory and inhibitory signals. However, future research is needed to identify the mechanisms involved. Furthermore, the study indicates that sex is a significant factor in this relationship, with lower choline levels being associated with higher pain ratings in females but not in males. This highlights the significance of addressing sex as a biological factor in pain research to better understand the different responses to treatments and to facilitate the development of more effective interventions in the future.

Peripheral transcutaneous electrical stimulation to improve cognition: a review of the main effects in healthy humans and in mildly cognitively impaired patient populations

Peripheral nerve stimulation (PNS) is an ancient technique, up to now mainly used for pain management. The least invasive approach for PNS is transcutaneous electrical stimulation (TENS), which is performed by delivering mild electric currents through the skin and, depending on the stimulation pattern, activates the somatosensory Aβ-, Aδ- and C-fibers. In addition to its use for pain relief, accumulating data indicates that TENS can have broad-spectrum cognitive effects through the activation of neuromodulatory brain pathways. This review aims to summarize the current evidence on the cognitive effects of TENS, from healthy participants and mildly cognitively affected patients. Most studies on this topic have investigated the effects of TENS on memory, while fewer studies have explored attention, executive functions, and verbal fluency. Overall, promising evidence suggests that TENS may exert positive effects on specific cognitive functions. Further research is needed to build consensus on the most effective stimulation protocols, for both neurorehabilitation and enhancement, and to better understand the neurobiological mechanisms underlying the cognitive effects of TENS.

Flexible Acetylcholine Neural Probe with a Hydrophobic Laser-Induced Graphene Electrode and a Fluorous-Phase Sensing Membrane

This work develops the first laser-induced graphene (LIG)-based electrochemical sensor with a superhydrophobic fluorous membrane for a flexible acetylcholine (ACh) sensor. ACh regulates several physiological functions, including synaptic transmission and glandular secretion. The ACh sensing membrane is doped with a fluorophilic cation-exchanger that can selectively measure ACh based on the inherent selectivity of the fluorous phase for hydrophobic ions, such as ACh. The fluorous-phase sensor improves the selectivity for ACh over Na+ and K+ by 2 orders of magnitude (compared to traditional lipophilic membranes), thus lowering the detection limit in artificial cerebrospinal fluid (aCSF) from 331 to 0.38 μ M, thereby allowing measurement in physiologically relevant ranges of ACh. Engraving LIG under argon creates a hydrophobic surface with a 133.7° contact angle, which minimizes the formation of a water layer. The flexible solid-contact LIG fluorous sensor exhibited a slope of 59.3 mV/decade in aCSF and retained function after 20 bending cycles, thereby paving the way for studying ACh's role in memory and neurodegenerative diseases.

Recent Progress in Biosensors for Depression Monitoring-Advancing Personalized Treatment

Depression is currently a major contributor to unnatural deaths and the healthcare burden globally, and a patient's battle with depression is often a long one. Because the causes, symptoms, and effects of medications are complex and highly individualized, early identification and personalized treatment of depression are key to improving treatment outcomes. The development of wearable electronics, machine learning, and other technologies in recent years has provided more possibilities for the realization of this goal. Conducting regular monitoring through biosensing technology allows for a more comprehensive and objective analysis than previous self-evaluations. This includes identifying depressive episodes, distinguishing somatization symptoms, analyzing etiology, and evaluating the effectiveness of treatment programs. This review summarizes recent research on biosensing technologies for depression. Special attention is given to technologies that can be portable or wearable, with the potential to enable patient use outside of the hospital, for long periods.

Improving Neurological Health in Aging Via Neuroplasticity-Based Computerized Exercise: Protocol for a Randomized Controlled Trial

BACKGROUND

Our current understanding of how computerized brain training drives cognitive and functional benefits remains incomplete. This paper describes the protocol for Improving Neurological Health in Aging via Neuroplasticity-based Computerized Exercise (INHANCE), a randomized controlled trial in healthy older adults designed to evaluate whether brain training improves cholinergic signaling.

OBJECTIVE

INHANCE evaluates whether 2 computerized training programs alter acetylcholine binding using the vesicular acetylcholine transporter ligand [18F] fluoroethoxybenzovesamicol ([18F] FEOBV) and positron emission tomography (PET).

METHODS

In this phase IIb, prospective, double-blind, parallel-arm, active-controlled randomized trial, a minimum of 92 community-dwelling healthy adults aged 65 years and older are randomly assigned to a brain training program designed using the principles of neuroplasticity (BrainHQ by Posit Science) or to an active control program of computer games designed for entertainment (eg, Solitaire). Both programs consist of 30-minute sessions, 7 times per week for 10 weeks (35 total hours), completed remotely at home using either loaned or personal devices. The primary outcome is the change in FEOBV binding in the anterior cingulate cortex, assessed at baseline and posttest. Exploratory cognitive and behavioral outcomes sensitive to acetylcholine are evaluated before, immediately after, and 3 months following the intervention to assess the maintenance of observed effects.

RESULTS

The trial was funded in September 2019. The study received approval from the Western Institutional Review Board in October 2020 with Research Ethics Board of McGill University Health Centre and Health Canada approvals in June 2021. The trial is currently ongoing. The first participant was enrolled in July 2021, enrollment closed when 93 participants were randomized in December 2023, and the trial will conclude in June 2024. The study team will be unblinded to conduct analyses after the final participant exits the study. We expect to publish the results in the fourth quarter of 2024.

CONCLUSIONS

There remains a critical need to identify effective and scalable nonpharmaceutical interventions to enhance cognition in older adults. This trial contributes to our understanding of brain training by providing a potential neurochemical explanation of cognitive benefit.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04149457; https://clinicaltrials.gov/ct2/show/NCT04149457.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/59705.

Dynorphin modulates motivation through a pallido-amygdala cholinergic circuit

The endogenous opioid peptide dynorphin and its receptor κ-opioid receptor (KOR) have been implicated in divergent behaviors, but the underlying mechanisms remain elusive. Here we show that dynorphin released from nucleus accumbens dynorphinergic neurons exerts powerful modulation over a ventral pallidum (VP) disinhibitory circuit, thereby controlling cholinergic transmission to the amygdala and motivational drive in mice. On one hand, dynorphin acts postsynaptically via KORs on local GABAergic neurons in the VP to promote disinhibition of cholinergic neurons, which release acetylcholine into the amygdala to invigorate reward-seeking behaviors. On the other hand, dynorphin also acts presynaptically via KORs on dynorphinergic terminals to limit its own release. Such autoinhibition keeps cholinergic neurons from prolonged activation and release of acetylcholine, and prevents perseverant reward seeking. Our study reveals how dynorphin exquisitely modulate motivation through cholinergic system, and provides an explanation for why these neuromodulators are involved in motivational disorders, including depression and addiction.

Cholinergic Mechanisms in Gastrointestinal Neoplasia

Acetylcholine-activated receptors are divided broadly into two major structurally distinct classes: ligand-gated ion channel nicotinic and G-protein-coupled muscarinic receptors. Each class encompasses several structurally related receptor subtypes with distinct patterns of tissue expression and post-receptor signal transduction mechanisms. The activation of both nicotinic and muscarinic cholinergic receptors has been associated with the induction and progression of gastrointestinal neoplasia. Herein, after briefly reviewing the classification of acetylcholine-activated receptors and the role that nicotinic and muscarinic cholinergic signaling plays in normal digestive function, we consider the mechanics of acetylcholine synthesis and release by neuronal and non-neuronal cells in the gastrointestinal microenvironment, and current methodology and challenges in measuring serum and tissue acetylcholine levels accurately. Then, we critically evaluate the evidence that constitutive and ligand-induced activation of acetylcholine-activated receptors plays a role in promoting gastrointestinal neoplasia. We focus primarily on adenocarcinomas of the stomach, pancreas, and colon, because these cancers are particularly common worldwide and, when diagnosed at an advanced stage, are associated with very high rates of morbidity and mortality. Throughout this comprehensive review, we concentrate on identifying novel ways to leverage these observations for prognostic and therapeutic purposes.

Recent advances in cholinergic mechanisms: A preface for the ISCM2022 special issue

This preface introduces the Journal of Neurochemistry special issue on Cholinergic Mechanisms that highlights the progress in the molecular, structural, neurochemical, pharmacological, toxicological, and clinical studies of the cholinergic system which underline its complexity and impact on health and disease. This issue comprises of (systematic) reviews and original articles, the majority of which have been presented at the 17th International Symposium on Cholinergic Mechanisms (ISCM2022) held in Dubrovnik, Croatia in May 2022. The symposium brought together leading "Cholinergikers" to shed new light on cholinergic transmission, ranging from the molecular to the clinical and cognitive mechanisms.

Unraveling the Neural Circuits: Techniques, Opportunities and Challenges in Epilepsy Research

Epilepsy, a prevalent neurological disorder characterized by high morbidity, frequent recurrence, and potential drug resistance, profoundly affects millions of people globally. Understanding the microscopic mechanisms underlying seizures is crucial for effective epilepsy treatment, and a thorough understanding of the intricate neural circuits underlying epilepsy is vital for the development of targeted therapies and the enhancement of clinical outcomes. This review begins with an exploration of the historical evolution of techniques used in studying neural circuits related to epilepsy. It then provides an extensive overview of diverse techniques employed in this domain, discussing their fundamental principles, strengths, limitations, as well as their application. Additionally, the synthesis of multiple techniques to unveil the complexity of neural circuits is summarized. Finally, this review also presents targeted drug therapies associated with epileptic neural circuits. By providing a critical assessment of methodologies used in the study of epileptic neural circuits, this review seeks to enhance the understanding of these techniques, stimulate innovative approaches for unraveling epilepsy's complexities, and ultimately facilitate improved treatment and clinical translation for epilepsy.