Optogenetics and its application in pain and anxiety research

Optogenetics 2.0: challenges and solutions towards a quantitative probing of neural circuits

To exploit the full potential of optogenetics, we need to titrate and tailor optogenetic methods to emulate naturalistic circuit function. For that, the following prerequisites need to be met: first, we need to target opsin expression not only to genetically defined neurons per se, but to specifically target a functional node. Second, we need to assess the scope of optogenetic modulation, i.e. the fraction of optogenetically modulated neurons. Third, we need to integrate optogenetic control in a closed loop setting. Fourth, we need to further safe and stable gene expression and light delivery to bring optogenetics to the clinics. Here, we review these concepts for the human and rodent brain.

Optogenetic Neuromodulation in Inflammatory Pain

Inflammatory pain is one of the most prevalent forms of pain and negatively influences the quality of life. Neuromodulation has been an expanding field of pain medicine and is accepted by patients who have failed to respond to several conservative treatments. Despite its effectiveness, neuromodulation still lacks clinically robust evidence on inflammatory pain management. Optogenetics, which controls particular neurons or brain circuits with high spatiotemporal accuracy, has recently been an emerging area for inflammatory pain management and studying its mechanism. This review considers the fundamentals of optogenetics, including using opsins, targeting gene expression, and wavelength-specific light delivery techniques. The recent evidence on application and development of optogenetic neuromodulation in inflammatory pain is also summarised. The current limitations and challenges restricting the progression and clinical transformation of optogenetics in pain are addressed. Optogenetic neuromodulation in inflammatory pain has many potential targets, and developing strategies enabling clinical application is a desirable therapeutic approach and outcome.

Acid-sensing ion channel 1a in the central nucleus of the amygdala regulates anxiety-like behaviors in a mouse model of acute pain

Pain is commonly comorbid with anxiety; however, the neural and molecular mechanisms underlying the comorbid anxiety symptoms in pain (CASP) have not been fully elucidated. In this study, we explored the role of acid-sensing ion channel 1a (ASIC1a), located in GABAergic neurons from the central nucleus of the amygdala (GABA^CeA), in the regulation of CASP in an acute pain mouse model. We found that the mice displayed significant mechanical pain sensitization and anxiety-like behaviors one day post injection of complete Freud's adjuvant (CFA1D). Electrophysiological recordings from acute brain slices showed that the activity of GABA^CeA neurons increased in the CFA1D mice compared with that in the saline mice. In addition, chemogenetic inhibition of GABA^CeA neurons relieved mechanical pain sensitization and anxiety-like behaviors in the CFA1D mice. Interestingly, through pharmacological inhibition and genetic knockdown of ASIC1a in the central nucleus amygdala, we found that downregulation of ASIC1a relieved the hypersensitization of mechanical stimuli and alleviated anxiety-related behaviors, accompanied with reversing the hyperactivity of GABA^CeA neurons in the CFA 1D mice. In conclusion, our results provide novel insights that ASIC1a in GABA^CeA neurons regulates anxiety-like behaviors in a mouse model of acute pain.

Causally mapping human threat extinction relevant circuits with depolarizing brain stimulation methods

Laboratory threat extinction paradigms and exposure-based therapy both involve repeated, safe confrontation with stimuli previously experienced as threatening. This fundamental procedural overlap supports laboratory threat extinction as a compelling analogue of exposure-based therapy. Threat extinction impairments have been detected in clinical anxiety and may contribute to exposure-based therapy non-response and relapse. However, efforts to improve exposure outcomes using techniques that boost extinction - primarily rodent extinction - have largely failed to date, potentially due to fundamental differences between rodent and human neurobiology. In this review, we articulate a comprehensive pre-clinical human research agenda designed to overcome these failures. We describe how connectivity guided depolarizing brain stimulation methods (i.e., TMS and DBS) can be applied concurrently with threat extinction and dual threat reconsolidation-extinction paradigms to causally map human extinction relevant circuits and inform the optimal integration of these methods with exposure-based therapy. We highlight candidate targets including the amygdala, hippocampus, ventromedial prefrontal cortex, dorsal anterior cingulate cortex, and mesolimbic structures, and propose hypotheses about how stimulation delivered at specific learning phases could strengthen threat extinction.

Application of Comfort Therapy under eCASH Concept in Acute and Chronic Wound Treatment

INTRODUCTION

Given the new ideas on wound care offered by the eCASH (early Comfort using Analgesia, minimal Sedatives, and maximal Humane care) and the substantial differences in clinical treatment between acute and chronic wounds, we aimed to investigate the effect of comfort therapy under the eCASH concept on analgesic sedation and accelerated wound healing in patients with acute or chronic wounds.

METHODS

This randomized clinical study was conducted in two parts: acute wounds and chronic wounds. Patients with acute wounds were allocated into the acute wound control group (AWCG) and the acute wound experimental group (AWEG). Patients with chronic wounds were allocated into the chronic wound control group (CWCG) and two experimental groups, in which they received intermittent negative pressure therapy (IPTEG) and continuous negative pressure therapy (CPTEG). On the basis of the standard treatment for patients in the control group, eCASH therapy was used in the experimental groups. In addition, pain intensity and procedural anxiety were evaluated using the visual analogue score (VAS) and the Hamilton Anxiety Scale (HAM-A). In addition, clinical effects were assessed on the basis of the size of the surface area, rate of healing, and concentration of pro-inflammatory factors (IL-1, IL-6, TNF-α) and growth factors (VEGF, bFGF, TGF-β1).

RESULTS

Compared with the control group, the VAS score and HAM-A score in the experimental groups were significantly decreased after intervention (P < 0.05). After intervention, the levels of IL-1β, IL-6, and TNF-α in AWEG, IPTEG, and CPTEG were significantly lower than those in AWCG. In addition, the levels of VEGF, bFGF, and TGF-β1 in IPTEG and CPTEG were significantly higher than those in CWCG (P < 0.05).

CONCLUSION

These results indicated that comfort therapy under the eCASH concept has a significant effect on ameliorating the pain and anxiety of patients, reducing the inflammatory reaction during the period of wound healing in the treatment of acute and chronic wounds.

CLINICAL TRIAL REGISTRY

The trial has been registered in the Chinese Clinical Trial Registry (ChiCTR2200057981).

A network pharmacology approach to predict potential targets and mechanisms of "Ramulus Cinnamomi (cassiae) - Paeonia lactiflora" herb pair in the treatment of chronic pain with comorbid anxiety and depression

BACKGROUND

Traditional Chinese medicine (TCM) prescriptions have multiple bioactive properties. "Gui Zhi-Shao Yao" herb pair is widely used to treat chronic pain (CP), as well as anxiety and depression. However, its related targets and underlying mechanisms have not been deciphered.

METHODS

In this study, the network pharmacology method was used to explore the bioactive components and targets of "Gui Zhi-Shao Yao" herb pair and further elucidate its potential biological mechanisms of action in the treatment of CP with comorbid anxiety disorder (AD) and mental depression (MD).

RESULTS

Following a series of analyses, we identified 15 active compounds, hitting 130 potential targets. After the intersections the targets of this herb pair and CP, AD and MD - sorted by the value of degree - nine targets were identified as the vital ones: Akt1, IL6, TNF, PTGS2, JUN, CASP3, MAPK8, PPARγ and NOS3. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis results demonstrated 11 pathways, such as AGE-RAGE signalling pathway, IL-17 signalling pathway, TNF signalling pathway, which primarily participate in the pathological processes.

CONCLUSIONS

This study preliminarily predicted and verified the pharmacological and molecular mechanisms of "Gui Zhi-Shao Yao" herb pair for treating CP with comorbid AD and MD from a holistic perspective. In vivo and in vitro experiments will be required to further investigate the mechanisms.KEY MESSAGEA network pharmacology approach was applied to identify key targets and molecular mechanisms.Nine targets were regarded as the vital targets for chronic pain with comorbid anxiety and depression.Predicted 11 pathways were the potential therapy targets and pharmacological mechanism of "Gui Zhi-Shao Yao" herb pair.

Selective optogenetic activation of NaV1.7-expressing afferents in NaV1.7-ChR2 mice induces nocifensive behavior without affecting responses to mechanical and thermal stimuli

In small and large spinal dorsal root ganglion neurons, subtypes of voltage-gated sodium channels, such as NaV1.7, NaV1.8, and NaV1.9 are expressed with characteristically localized and may play different roles in pain transmission and intractable pain development. Selective stimulation of each specific subtype in vivo may elucidate its role of each subtype in pain. So far, this has been difficult with current technology. However, Optogenetics, a recently developed technique, has enabled selective activation or inhibition of specific neural circulation in vivo. Moreover, optogenetics had even been used to selectively excite NaV1.8-expressing dorsal root ganglion neurons to induce nocifensive behavior. In recent years, genetic modification technologies such as CRISPR/Cas9 have advanced, and various knock-in mice can be easily generated using such technology. We aimed to investigate the effects of selective optogenetic activation of NaV1.7-expressing afferents on mouse behavior. We used CRISPR/Cas9-mediated homologous recombination to generate bicistronic NaV1.7-iCre knock-in mice, which express iCre recombinase under the endogenous NaV1.7 gene promoter without disrupting NaV1.7. The Cre-driver mice were crossed with channelrhodopsin-2 (ChR2) Cre-reporter Ai32 mice to obtain NaV1.7iCre/+;Ai32/+, NaV1.7iCre/iCre;Ai32/+, NaV1.7iCre/+;Ai32/Ai32, and NaV1.7iCre/iCre;Ai32/Ai32 mice. Compared with wild-type mice behavior, no differences were observed in the behaviors associated with mechanical and thermal stimuli exhibited by mice of the aforementioned genotypes, indicating that the endogenous NaV1.7 gene was not affected by the targeted insertion of iCre. Blue light irradiation to the hind paw induced paw withdrawal by mice of all genotypes in a light power-dependent manner. The threshold and incidence of paw withdrawal and aversive behavior in a blue-lit room were dependent on ChR2 expression level; the strongest response was observed in NaV1.7iCre/iCre;Ai32/Ai32 mice. Thus, we developed a non-invasive pain model in which peripheral nociceptors were optically activated in free-moving transgenic NaV1.7-ChR2 mice.

DNA Directed Pro-Dopamine Regulation Coupling Subluxation Repair, H-Wave® and Other Neurobiologically Based Modalities to Address Complexities of Chronic Pain in a Female Diagnosed with Reward Deficiency Syndrome (RDS): Emergence of Induction of “Dopamine Homeostasis” in the Face of the Opioid Crisis

Addiction is a complex multifactorial condition. Established genetic factors can provide clear guidance in assessing the risk of addiction to substances and behaviors. Chronic stress can accumulate, forming difficult to recognize addiction patterns from both genetic and epigenetic (environmental) factors. Furthermore, psychological/physical/chemical stressors are typically categorized linearly, delaying identification and treatment. The patient in this case report is a Caucasian female, aged 36, who presented with chronic pain and partial disability following a surgically repaired trimalleolar fracture. The patient had a history of unresolved attention deficit disorder and an MRI scan of her brain revealed atrophy and functional asymmetry. In 2018, the patient entered the Bajaj Chiropractic Clinic, where initial treatment focused on re-establishing integrity of the spine and lower extremity biomechanics and graduated into cognitive behavior stabilization assisted by DNA pro-dopamine regulation guided by Genetic Addiction Risk Severity testing. During treatment (2018–2021), progress achieved included: improved cognitive clarity, focus, sleep, anxiety, and emotional stability in addition to pain reduction (75%); elimination of powerful analgesics; and reduced intake of previously unaddressed alcoholism. To help reduce hedonic addictive behaviors and pain, coupling of H-Wave with corrective chiropractic care seems prudent. We emphasize the importance of genetic assessment along with attempts at inducing required dopaminergic homeostasis via precision KB220PAM. It is hypothesized that from preventive care models, a new standard is emerging including self-awareness and accountability for reward deficiency as a function of hypodopaminergia. This case study documents the progression of a patient dealing with the complexities of an injury, pain management, cognitive impairment, anxiety, depression, and the application of universal health principles towards correction versus palliative care.

A Novel Photoswitchable Azobenzene-Containing Local Anesthetic Ethercaine with Light-Controlled Biological Activity In Vivo

Pain is a common symptom that impairs the quality of life for people around the world. Local anesthetics widely used for pain relief have a number of side effects, which makes the development of both new drugs and new ways to control their activity particularly important. Photopharmacology makes it possible to reduce the side effects of an anesthetic and control its biological activity in the body. The purpose of this work was to create a new light-controlled local anesthetic and study its biological activity in animals. A compound with a simple scheme of synthesis was chosen to shift the UV-Vis absorption band towards the visible range of the spectrum and was synthesized for the first time. Some computer calculations were performed to make sure that the aforementioned changes would not lead to loss of biological activity. The micellar form of the new compound was prepared, and in vivo biological studies were carried out in rabbits. The existence of a local anesthetic effect, which disappeared almost completely on irradiation with light (λ = 395 nm), was shown using the surface anesthesia model. Moreover, the possibility of multiple reversible changes in the biological activity of ethercaine under the action of light was demonstrated. The latter compound manifests no local irritating effect, either. The data obtained indicate the prospects for the development of new compounds based on azobenzene for light-controlled local anesthesia.

Olfactory Optogenetics: Light Illuminates the Chemical Sensing Mechanisms of Biological Olfactory Systems

The mammalian olfactory system has an amazing ability to distinguish thousands of odorant molecules at the trace level. Scientists have made great achievements on revealing the olfactory sensing mechanisms in decades; even though many issues need addressing. Optogenetics provides a novel technical approach to solve this dilemma by utilizing light to illuminate specific part of the olfactory system; which can be used in all corners of the olfactory system for revealing the olfactory mechanism. This article reviews the most recent advances in olfactory optogenetics devoted to elucidate the mechanisms of chemical sensing. It thus attempts to introduce olfactory optogenetics according to the structure of the olfactory system. It mainly includes the following aspects: the sensory input from the olfactory epithelium to the olfactory bulb; the influences of the olfactory bulb (OB) neuron activity patterns on olfactory perception; the regulation between the olfactory cortex and the olfactory bulb; and the neuromodulation participating in odor coding by dominating the olfactory bulb. Finally; current challenges and future development trends of olfactory optogenetics are proposed and discussed.

The role of the anterior pretectal nucleus in pain modulation: A comprehensive review

Descending pain modulation involves multiple encephalic sites and pathways that range from the cerebral cortex to the spinal cord. Behavioral studies conducted in the 1980s revealed that electrical stimulation of the pretectal area causes antinociception dissociation from aversive responses. Anatomical and physiological studies identified the anterior pretectal nucleus and its descending projections to several midbrain, pontine, and medullary structures. The anterior pretectal nucleus is morphologically divided into a dorsal part that contains a dense neuron population (pars compacta) and a ventral part that contains a dense fiber band network (pars reticulata). Connections of the two anterior pretectal nucleus parts are broad and include prominent projections to and from major encephalic systems associated with somatosensory processes. Since the first observation that acute or chronic noxious stimuli activate the anterior pretectal nucleus, it has been established that numerous mediators participate in this response through distinct pathways. Recent studies have confirmed that at least two pain inhibitory pathways are activated from the anterior pretectal nucleus. This review focuses on rodent anatomical, behavioral, molecular, and neurochemical data that have helped to identify mediators of the anterior pretectal nucleus and pathways related to its role in pain modulation.

A pyrazole-containing selenium compound modulates neuroendocrine, oxidative stress, and behavioral responses to acute restraint stress in mice

The contribution of oxidative stress has been described in numerous studies as one of the main pathways involved in the pathophysiology of anxiety and its comorbidities, such as chronic pain. Therefore, in this study, we investigated the anxiolytic-like, antiallodynic, and anti-hyperalgesic effects of 3,5-dimethyl-1-phenyl-4-(phenylselanyl)-1H-pyrazole (SePy) in response to acute restraint stress (ARS) in mice through the modulation of oxidative stress and neuroendocrine responses. Mice were restrained for 2 h followed by SePy (1 or 10 mg/kg, intragastrically) treatment. Behavioral, and biochemical tests were performed after further 30 min. The treatment with SePy reversed (i) the decreased time spent and the number of entries in the open arms of the elevated plus-maze apparatus, (ii) the decreased time spent in the central zone of the open field test and the increased number of grooming, (iii) the increased number of marbles buried, (iv) the increased response frequency of Von Frey Hair stimulation, and (v) the decreased latency time to nociceptive response in the hot plate test stress induced by ARS. Biochemically, SePy reversed ARS-induced increased levels of plasma corticosterone, and reversed the ARS-induced alterations in the levels of reactive species, lipid peroxidation, and superoxide dismutase and catalase activities in the prefrontal cortices and hippocampi of mice. Moreover, a molecular docking approach suggested that SePy may interact with the active site of the glucocorticoid receptor. Altogether, these results indicate that SePy attenuated anxiolytic-like behavior, hyperalgesia, and mechanical allodynia while modulating oxidative stress and neuroendocrine responses in stressed mice.

Behavioral, Biochemical and Electrophysiological Changes in Spared Nerve Injury Model of Neuropathic Pain

Neuropathic pain is a pathological condition induced by a lesion or disease affecting the somatosensory system, with symptoms like allodynia and hyperalgesia. It has a multifaceted pathogenesis as it implicates several molecular signaling pathways involving peripheral and central nervous systems. Affective and cognitive dysfunctions have been reported as comorbidities of neuropathic pain states, supporting the notion that pain and mood disorders share some common pathogenetic mechanisms. The understanding of these pathophysiological mechanisms requires the development of animal models mimicking, as far as possible, clinical neuropathic pain symptoms. Among them, the Spared Nerve Injury (SNI) model has been largely characterized in terms of behavioral and functional alterations. This model is associated with changes in neuronal firing activity at spinal and supraspinal levels, and induces late neuropsychiatric disorders (such as anxious-like and depressive-like behaviors, and cognitive impairments) comparable to an advanced phase of neuropathy. The goal of this review is to summarize current findings in preclinical research, employing the SNI model as a tool for identifying pathophysiological mechanisms of neuropathic pain and testing pharmacological agent.