Role of Glutamatergic Projections from Lateral Habenula to Ventral Tegmental Area in Inflammatory Pain-Related Spatial Working Memory Deficits

Knowledge mapping and emerging trends in cognitive impairment associated with chronic pain: A 2000-2024 bibliometric study

Chronic pain is commonly recognized as a distressing symptom or a standalone disease, with over half of those affected experiencing cognitive impairment, which significantly impacts their quality of life. Despite a recent surge in literature on cognitive impairment associated with chronic pain, a comprehensive bibliometric analysis in this field has yet to be conducted. In this study, we performed a bibliometric analysis on this topic. We retrieved English-language publications on chronic pain and cognitive impairment from 2000 to 2024 using the Web of Science Core Collection database. These publications were visually analyzed using tools such as VOSviewer, CiteSpace, and the R package "bibliometrix." We identified 1656 publications from 72 countries/regions across 722 journals on the topic of chronic pain and cognitive impairment. Publication numbers showed a steady increase, peaking in 2022. The United States led in contributions, with Harvard Medical School emerging as the most prominent institution involved. The journal Pain was the most prolific and frequently co-cited in this area. Among the authors, Stefan Duschek was the most productive, while Frederick Wolfe was the most frequently co-cited. Key research areas include investigating the bidirectional long-term effects between chronic pain and cognitive impairment and exploring the mechanisms underlying cognitive changes associated with chronic pain. In conclusion, this study highlights a global surge in research on cognitive impairment related to chronic pain. Emerging hotspots and future research trends point towards brain imaging mechanisms and neuronal circuit-mediated processes.

Reorganization of lateral habenula neuronal connectivity underlies pain-related impairment in spatial memory encoding

ABSTRACT

Dysfunctional hyperactivity of the lateral habenula nucleus (LHb) has emerged as a critical marker for pain-related mood impairments. Acting as a central hub, the LHb filters and disseminates pertinent information to other brain structures during learning. However, it is not well understood how intra-LHb activity is altered during cognitive demand under neuropathic pain conditions. To address this gap, we implanted an optrode structure to record neuronal activity in adult male CD (rat strain without definition) rats during the execution of a delayed nonmatch-to-sample (DNMS) spatial working memory (WM) task. We selectively modulated intra-LHb network activity by optogenetically inhibiting local LHb CaMKIIα (calcium calmodulin-dependent protein kinase II alpha)-expressing neurons during the delay phase of the DNMS task. Behavioral assessments were conducted using a persistent rodent model of neuropathic pain-spared nerve injury. Our results showed that the induction of neuropathic pain disrupted WM encoding accuracy and intra-LHb functional neuronal connectivity. This disruption was reversed by optogenetic inhibition of LHb CaMKIIα-expressing neurons, which also produced antinociceptive effects. Together, our findings provide insight into how intra-LHb networks reorganize information to support different task contexts, suggesting that the abnormal pain-related intra-LHb dynamic segregation of information may contribute to poor cognitive accuracy in male rodents during pain experiences.

Chronic Pain-Related Cognitive Deficits: Preclinical Insights into Molecular, Cellular, and Circuit Mechanisms

Cognitive impairment is a common comorbidity of chronic pain, significantly disrupting patients' quality of life. Despite this comorbidity being clinically recognized, the underlying neuropathological mechanisms remain unclear. Recent preclinical studies have focused on the fundamental mechanisms underlying the coexistence of chronic pain and cognitive decline. Pain chronification is accompanied by structural and functional changes in the neural substrate of cognition. Based on the developments in electrophysiology and optogenetics/chemogenetics, we summarized the relevant neural circuits involved in pain-induced cognitive impairment, as well as changes in connectivity and function in brain regions. We then present the cellular and molecular alternations related to pain-induced cognitive impairment in preclinical studies, mainly including modifications in neuronal excitability and structure, synaptic plasticity, glial cells and cytokines, neurotransmitters and other neurochemicals, and the gut-brain axis. Finally, we also discussed the potential treatment strategies and future research directions.

Orbitostriatal encoding of reward delayed gratification and impulsivity in chronic pain

Central robust network functional rearrangement is a characteristic of several neurological conditions, including chronic pain. Preclinical and clinical studies have shown the importance of pain-induced dysfunction in both orbitofrontal cortex (OFC) and nucleus accumbens (NAc) brain regions for the emergence of cognitive deficits. Outcome information processing recruits the orbitostriatal circuitry, a pivotal pathway regarding context-dependent reward value encoding. The current literature reveals the existence of structural and functional changes in the orbitostriatal crosstalk in chronic pain conditions, which have emerged as a possible underlying cause for reward and time discrimination impairments observed in individuals affected by such disturbances. However, more comprehensive investigations are needed to elucidate the underlying disturbances that underpin disease development. In this review article, we aim to provide a comprehensive view of the orbitostriatal mechanisms underlying time-reward dependent behaviors, and integrate previous findings on local and network malplasticity under the framework of the chronic pain sphere.

Burning Question: How Does Our Brain Process Positive and Negative Cues Associated with Thermosensation?

Whether it is the dramatic suffocating sensation from a heat wave in the summer or the positive reinforcement arising from a hot drink on a cold day; we can certainly agree that our thermal environment underlies our daily rhythms of sensation. Extensive research has focused on deciphering the central circuits responsible for conveying the impact of thermogenesis on mammalian behavior. Here, we revise the recent literature responsible for defining the behavioral correlates that arise from thermogenic fluctuations in mammals. We transition from the physiological significance of thermosensation to the circuitry responsible for the autonomic or behavioral responses associated with it. Subsequently, we delve into the positive and negative valence encoded by thermoregulatory processes. Importantly, we emphasize the crucial junctures where reward, pain, and thermoregulation intersect, unveiling a complex interplay within these neural circuits. Finally, we briefly outline fundamental questions that are pending to be addressed in the field. Fully deciphering the thermoregulatory circuitry in mammals will have far-reaching medical implications. For instance, it may lead to the identification of novel targets to overcome thermal pain or allow the maintenance of our core temperature in prolonged surgeries.

Whole-brain connections of glutamatergic neurons in the mouse lateral habenula in both sexes

BACKGROUND

The lateral habenula (LHb) is an epithalamus nucleus that is evolutionarily conserved and involved in various physiological functions, such as encoding value signals, integrating emotional information, and regulating related behaviors. The cells in the LHb are predominantly glutamatergic and have heterogeneous functions in response to different stimuli. The circuitry connections of the LHb glutamatergic neurons play a crucial role in integrating a wide range of events. However, the circuitry connections of LHb glutamatergic neurons in both sexes have not been thoroughly investigated.

METHODS

In this study, we injected Cre-dependent retrograde trace virus and anterograde synaptophysin-labeling virus into the LHb of adult male and female Vglut2-ires-Cre mice, respectively. We then quantitatively analyzed the input and output of the LHb glutamatergic connections in both the ipsilateral and contralateral whole brain.

RESULTS

Our findings showed that the inputs to LHbvGlut2 neurons come from more than 30 brain subregions, including the cortex, striatum, pallidum, thalamus, hypothalamus, midbrain, pons, medulla, and cerebellum with no significant differences between males and females. The outputs of LHbvGlut2 neurons targeted eight large brain regions, primarily focusing on the midbrain and pons nuclei, with distinct features in presynaptic bouton across different brain subregions. While correlation and cluster analysis revealed differences in input and collateral projection features, the input-output connection pattern of LHbvGlut2 neurons in both sexes was highly similar.

CONCLUSIONS

This study provides a systematic and comprehensive analysis of the input and output connections of LHbvGlut2 neurons in male and female mice, shedding light on the anatomical architecture of these specific cell types in the mouse LHb. This structural understanding can help guide further investigations into the complex functions of the LHb.

Dynamics of Lateral Habenula-Ventral Tegmental Area Microcircuit on Pain-Related Cognitive Dysfunctions

Chronic pain is a health problem that affects the ability to work and perform other activities, and it generally worsens over time. Understanding the complex pain interaction with brain circuits could help predict which patients are at risk of developing central dysfunctions. Increasing evidence from preclinical and clinical studies suggests that aberrant activity of the lateral habenula (LHb) is associated with depressive symptoms characterized by excessive negative focus, leading to high-level cognitive dysfunctions. The primary output region of the LHb is the ventral tegmental area (VTA), through a bidirectional connection. Recently, there has been growing interest in the complex interactions between the LHb and VTA, particularly regarding their crucial roles in behavior regulation and their potential involvement in the pathological impact of chronic pain on cognitive functions. In this review, we briefly discuss the structural and functional roles of the LHb-VTA microcircuit and their impact on cognition and mood disorders in order to support future studies addressing brain plasticity during chronic pain conditions.