Molecular and neural basis of pleasant touch sensation

Aging-associated decrease of PGC-1α promotes pain chronification

Aging is generally associated with declining somatosensory function, which seems at odds with the high prevalence of chronic pain in older people. This discrepancy is partly related to the high prevalence of degenerative diseases such as osteoarthritis in older people. However, whether aging alters pain processing in the primary somatosensory cortex (S1), and if so, whether it promotes pain chronification is largely unknown. Herein, we report that older mice displayed prolonged nociceptive behavior following nerve injury when compared with mature adult mice. The expression of peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α) in S1 was decreased in older mice, whereas PGC-1α haploinsufficiency promoted prolonged nociceptive behavior after nerve injury. Both aging and PGC-1α haploinsufficiency led to abnormal S1 neural dynamics, revealed by intravital two-photon calcium imaging. Manipulating S1 neural dynamics affected nociceptive behavior after nerve injury: chemogenetic inhibition of S1 interneurons aggravated nociceptive behavior in naive mice; chemogenetic activation of S1 interneurons alleviated nociceptive behavior in older mice. More interestingly, adeno-associated virus-mediated expression of PGC-1α in S1 interneurons ameliorated aging-associated chronification of nociceptive behavior as well as aging-related S1 neural dynamic changes. Taken together, our results showed that aging-associated decrease of PGC-1α promotes pain chronification, which might be harnessed to alleviate the burden of chronic pain in older individuals.

Nicotine restores olfactory function by activation of prok2R/Akt/FoxO3a axis in Parkinson's disease

BACKGROUND

Olfactory dysfunction occurs frequently in Parkinson's disease (PD). In this study, we aimed to explore the potential biomarkers and underlying molecular pathways of nicotine for the treatment of olfactory dysfunction in 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-induced PD mice.

METHODS

MPTP was introduced into C57BL/6 male mice to generate a PD model. Regarding in vivo experiments, we performed behavioral tests to estimate the protective effects of nicotine in MPTP-induced PD mice. RNA sequencing and traditional molecular methods were used to identify molecules, pathways, and biological processes in the olfactory bulb of PD mouse models. Then, in vitro experiments were conducted to evaluate whether nicotine can activate the prok2R/Akt/FoxO3a signaling pathway in both HEK293T cell lines and primary olfactory neurons treated with 1-methyl-4-phenylpyridinium (MPP+). Next, prok2R overexpression (prok2R+) and knockdown (prok2R-) were introduced with lentivirus, and the Akt/FoxO3a signaling pathway was further explored. Finally, the damaging effects of MPP+ were evaluated in prok2R overexpression (prok2R+) HEK293T cell lines.

RESULTS

Nicotine intervention significantly alleviated olfactory and motor dysfunctions in mice with PD. The prok2R/Akt/FoxO3a signaling pathway was activated after nicotine treatment. Consequently, apoptosis of olfactory sensory neurons was significantly reduced. Furthermore, prok2R+ and prok2R- HEK293T cell lines exhibited upregulation and downregulation of the Akt/FoxO3a signaling pathway, respectively. Additionally, prok2R+ HEK293T cells were resistant to MPP+-induced apoptosis.

CONCLUSIONS

This study showed the effectiveness and underlying mechanisms of nicotine in improving hyposmia in PD mice. These improvements were correlated with reduced apoptosis of olfactory sensory neurons via activated prok2R/Akt/FoxO3a axis. These results explained the potential protective functions of nicotine in PD patients.

Out of touch? How trauma shapes the experience of social touch - Neural and endocrine pathways

Trauma can shape the way an individual experiences the world and interacts with other people. Touch is a key component of social interactions, but surprisingly little is known about how trauma exposure influences the processing of social touch. In this review, we examine possible neurobiological pathways through which trauma can influence touch processing and lead to touch aversion and avoidance in trauma-exposed individuals. Emerging evidence indicates that trauma may affect sensory touch thresholds by modulating activity in the primary sensory cortex and posterior insula. Disturbances in multisensory integration and oxytocin reactivity combined with diminished reward-related and anxiolytic responses may induce a bias towards negative appraisal of touch contexts. Furthermore, hippocampus deactivation during social touch may reflect a dissociative state. These changes depend not only on the type and severity of the trauma but also on the features of the touch. We hypothesise that disrupted touch processing may impair social interactions and confer elevated risk for future stress-related disorders.

Spinal Nmur2-positive Neurons Play a Crucial Role in Mechanical Itch

The dorsal spinal cord is crucial for the transmission and modulation of multiple somatosensory modalities, such as itch, pain, and touch. Despite being essential for the well-being and survival of an individual, itch and pain, in their chronic forms, have increasingly been recognized as clinical problems. Although considerable progress has been made in our understanding of the neurochemical processing of nociceptive and chemical itch sensations, the neural substrate that is crucial for mechanical itch processing is still unclear. Here, using genetic and functional manipulation, we identified a population of spinal neurons expressing neuromedin U receptor 2 (Nmur2+) as critical elements for mechanical itch. We found that spinal Nmur2+ neurons are predominantly excitatory neurons, and are enriched in the superficial laminae of the dorsal horn. Pharmacogenetic activation of cervical spinal Nmur2+ neurons evoked scratching behavior. Conversely, the ablation of these neurons using a caspase-3-based method decreased von Frey filament-induced scratching behavior without affecting responses to other somatosensory modalities. Similarly, suppressing the excitability of cervical spinal Nmur2+ neurons via the overexpression of functional Kir2.1 potassium channels reduced scratching in response to innocuous mechanical stimuli, but not to pruritogen application. At the lumbar level, pharmacogenetic activation of these neurons evoked licking and lifting behaviors. However, ablating these neurons did not affect the behavior associated with acute pain. Thus, these results revealed the crucial role of spinal Nmur2+ neurons in mechanical itch. Our study provides important insights into the neural basis of mechanical itch, paving the way for developing novel therapies for chronic itch. PERSPECTIVE: Excitatory Nmur2+ neurons in the superficial dorsal spinal cord are essential for mechanical but not chemical itch information processing. These spinal Nmur2+ neurons represent a potential cellular target for future therapeutic interventions against chronic itch. Spinal and supraspinal Nmur2+ neurons may play different roles in pain signal processing.

Therapeutic Potential of Targeting Prokineticin Receptors in Diseases

The prokineticins (PKs) were discovered approximately 20 years ago as small peptides inducing gut contractility. Today, they are established as angiogenic, anorectic, and proinflammatory cytokines, chemokines, hormones, and neuropeptides involved in variety of physiologic and pathophysiological pathways. Their altered expression or mutations implicated in several diseases make them a potential biomarker. Their G-protein coupled receptors, PKR1 and PKR2, have divergent roles that can be therapeutic target for treatment of cardiovascular, metabolic, and neural diseases as well as pain and cancer. This article reviews and summarizes our current knowledge of PK family functions from development of heart and brain to regulation of homeostasis in health and diseases. Finally, the review summarizes the established roles of the endogenous peptides, synthetic peptides and the selective ligands of PKR1 and PKR2, and nonpeptide orthostatic and allosteric modulator of the receptors in preclinical disease models. The present review emphasizes the ambiguous aspects and gaps in our knowledge of functions of PKR ligands and elucidates future perspectives for PK research. SIGNIFICANCE STATEMENT: This review provides an in-depth view of the prokineticin family and PK receptors that can be active without their endogenous ligand and exhibits "constitutive" activity in diseases. Their non- peptide ligands display promising effects in several preclinical disease models. PKs can be the diagnostic biomarker of several diseases. A thorough understanding of the role of prokineticin family and their receptor types in health and diseases is critical to develop novel therapeutic strategies with safety concerns.

In vivo recording of the circadian calcium rhythm in Prokineticin 2 neurons of the suprachiasmatic nucleus

Prokineticin 2 (Prok2) is a small protein expressed in a subpopulation of neurons in the suprachiasmatic nucleus (SCN), the primary circadian pacemaker in mammals. Prok2 has been implicated as a candidate output molecule from the SCN to control multiple circadian rhythms. Genetic manipulation specific to Prok2-producing neurons would be a powerful approach to understanding their function. Here, we report the generation of Prok2-tTA knock-in mice expressing the tetracycline transactivator (tTA) specifically in Prok2 neurons and an application of these mice to in vivo recording of Ca2+ rhythms in these neurons. First, the specific and efficient expression of tTA in Prok2 neurons was verified by crossing the mice with EGFP reporter mice. Prok2-tTA mice were then used to express a fluorescent Ca2+ sensor protein to record the circadian Ca2+ rhythm in SCN Prok2 neurons in vivo. Ca2+ in these cells showed clear circadian rhythms in both light-dark and constant dark conditions, with their peaks around midday. Notably, the hours of high Ca2+ nearly coincided with the rest period of the behavioral rhythm. These observations fit well with the predicted function of Prok2 neurons as a candidate output pathway of the SCN by suppressing locomotor activity during both daytime and subjective daytime.

Early tactile stimulation influences the development of Alzheimer's disease in gestationally stressed APP NL-G-F adult offspring NL-G-F/NL-G-F mice

Alzheimer's disease (AD) is associated with cerebral plaques and tangles, reduced synapse number, and shrinkage in several brain areas and these morphological effects are associated with the onset of compromised cognitive, motor, and anxiety-like behaviours. The appearance of both anatomical and behavioural symptoms is worsened by stress. The focus of this study was to examine the effect of neonatal tactile stimulation on AD-like behavioural and neurological symptoms on APP NL-G-F/NL-G-F mice, a mouse model of AD, who have been gestationally stressed. Our findings indicate that neonatal tactile stimulation improves cognition, motor skills, and anxiety-like symptoms in both gestationally stressed and non-stressed adult APP mice and that these alterations are associated with reduced Aβ plaque formation. Thus, tactile stimulation appears to be a promising non-invasive preventative strategy for slowing the onset of dementia in aging animals.

Tactile stimulation facilitates functional recovery and dendritic change following neonatal hemidecortication in rats

After large neocortical lesions, such as hemidecortication, children can show significant motor and cognitive impairments. It thus is of considerable interest to identify treatments that might enhance long-term functional outcome. We have previously shown that tactile stimulation enhances recovery from perinatal focal cortical lesions in rats, so the goal of the present experiment was to explore the effectiveness of postlesion tactile stimulation in reducing functional deficits associated with neonatal hemidecortication. Rats were given hemidecortications on postnatal day 10 (P10). Half of the group was then exposed to a daily tactile stimulation treatment for 15 min, three times a day for eleven days following the surgery. All groups were then tested on a number of behavioural tasks (Morris water task, skilled reaching, forelimb placing during spontaneous vertical exploration, and a sunflower seed opening task) beginning at P 120. The brains of the male animals were prepared for Golgi-Cox staining and subsequent analysis of dendritic arborisation and spine density. There were two main findings in this experiment: 1) Tactile stimulation improved cognitive ability and some motor performance after P 10 hemidecortication; and, 2) Tactile stimulation altered cortical organization after P10 hemidecortication. Tactile stimulation may provide an important noninvasive therapy after hemispherectomy in children.

Neural mechanisms of comforting: Prosocial touch and stress buffering

Comforting is a crucial form of prosocial behavior that is important for maintaining social unity and improving the physical and emotional well-being of social species. It is often expressed through affiliative social touch toward someone in distress, providing relief for their distressed state. In the face of increasing global distress, these actions are paramount to the continued improvement of individual welfare and the collective good. Understanding the neural mechanisms responsible for promoting actions focused on benefitting others is particularly important and timely. Here, we review prosocial comforting behavior, emphasizing synthesizing recent studies carried out using rodent models. We discuss its underlying behavioral expression and motivations, and then explore both the neurobiology of prosocial comforting in a helper animal and the neurobiology of stress relief following social touch in a recipient as part of a feedback loop interaction.

What are C-tactile afferents and how do they relate to "affective touch"?

Since their initial discovery in cats, low-threshold C-fiber mechanoreceptors have become a central interest of scientists studying the affective aspects of touch. Their pursuit in humans, here termed C-tactile (CT) afferents, has led to the establishment of a research field referred to as "affective touch", which is differentiated from "discriminative touch". Presently, we review these developments based on an automated semantic analysis of more than 1000 published abstracts as well as empirical evidence and the solicited opinions of leading experts in the field. Our review provides a historical perspective and update of CT research, it reflects on the meaning of "affective touch", and discusses how current insights challenge established views on the relation between CTs and affective touch. We conclude that CTs support gentle, affective touch, but that not every affective touch experience relies on CTs or must necessarily be pleasant. Moreover, we speculate that currently underappreciated aspects of CT signaling will prove relevant for the manner in which these unique fibers support how humans connect both physically and emotionally.

Prokineticin 2/PROK2 and Male Infertility

Male infertility represents about 50% of the causes of infertility in couples. The diagnosis process represents an important procedure for defining, when possible, the causes and approaching treatments (pharmacological, surgical) aimed at overcoming the problem. Several scientific studies have set out to discover early and indicative markers capable of providing information on the biological origin of infertility and increase current knowledge in the context of new potential therapeutic approaches. The prokineticin system (PROK) consists of the prokineticin 1 (PROK1) and prokineticin 2 (PROK2) proteins. Through the activation of two G-protein receptors (PROKR1 and PROKR2) regulate a wide range of biological functions, including gastrointestinal motility, circadian rhythm regulation, neurogenesis, angiogenesis, pain perception, and mood regulation. Several studies have highlighted the crucial role of the PROK system in the development and maturation of both male and female human reproductive organs. Particularly in men, the PROK system represents a new system useful to clarify some aspects of testicular pathophysiology and provide new potential hypotheses for therapeutic intervention. This narrative review aims to illustrate the state of the art regarding, in particular, the role of PROK2 in male infertility.

Effectiveness and functional magnetic resonance imaging outcomes of Tuina therapy in patients with post-stroke depression: A randomized controlled trial

OBJECTIVE

To investigate the effectiveness and functional magnetic resonance imaging (fMRI) outcomes of Tuina therapy in patients with post-stroke depression (PSD).

METHODS

This was a single-center, randomized, two-armed, controlled trial. Eighty-four patients with PSD were selected and randomly assigned to a Tuina therapy group or a routine rehabilitation control group. The patients underwent five 20-min treatment sessions per week over a period of 2 weeks. The primary outcome measure was change in Hamilton Depression Rating Scale (HAMD) score over the 2 weeks of intervention, whereas the secondary outcome measures were changes in Fugl-Meyer Assessment (FMA) score, Modified Barthel index (MBI), and Mini Mental State Examination (MMSE) score.

RESULTS

The Tuina group showed significantly improved HAMD scores compared to the routine rehabilitation control group (5.85, [2.54, 9.16]). For the secondary outcomes, the Tuina group showed better MMSE scores than the routine rehabilitation group (1.97, [1.19, 2.76]); however, there were no significant differences between the other secondary outcomes of both groups (P > 0.05). After 2 weeks, both groups showed a significant decrease in HAMD score compared to baseline. In addition, the Tuina group showed a significant decrease in MMSE score compared to baseline (2.35, [1.8, 2.9]); however, there were no significant differences in the MBI and FMA scores of the two group after the intervention (P > 0.05). Regarding fMRI results, the zALFF values of the right caudate nucleus, right putamen, right insula, left superior temporal gyrus, right parahippocampal gyrus, right hippocampus, left middle temporal gyrus, left angular gyrus, and left thalamus were higher in the Tuina group. In the Tuina group, the functional connectivity between the hippocampus and thalamus, and the thalamus and caudate nucleus, were significantly different (P <0.01). In addition, the zALFF value of the hippocampus was significantly negatively correlated with HAMD score. No serious adverse events were observed in both groups.

CONCLUSION

Tuina therapy administered 10 times within 2 weeks is safe and can effectively relieve depression and improve cognitive function in patients with PSD. This finding may be closely related to the effect of Tuina therapy on the activation and functional connectivity of the hippocampus.

CLINICAL TRIAL REGISTRATION

http://www.chictr.org.cn/showproj.aspx?proj=55151, identifier ChiCTR200003388.