Depressive-like behaviours and decreased dendritic branching in the medial prefrontal cortex of mice with tumors: A novel validated model of cancer-induced depression

Glioma induces atypical depression-like behaviors in mice through the 5-HT and glutamatergic synapse pathways

Glioma patients often undertake psychiatric disorders such as depression and anxiety. There are several clinical epidemiological studies on glioma-associated depression, but basic research and corresponding animal experiments are still lacking. Here, we observed that glioma-bearing mice exhibited atypical depression-like behaviors in orthotopic glioma mouse models. The concentrations of monoamine neurotransmitters were detected by enzyme-linked immunosorbent assay (ELISA), revealing a decrease in 5-hydroxytryptamine (5-HT) levels in para-glioma tissues. The related gene expression levels also altered, detected by quantitative RT-PCR. Then, we developed a glioma-depression comorbidity mouse model. Through sucrose preference test (SPT), forced swimming test (FST), tail suspension test (TST) and other tests, we found that the occurrence of glioma could lead to changes in depression-like behaviors in a chronic unpredictable mild stress (CUMS) mouse model. The results of RNA sequencing (RNA-seq) indicated that the altered expression of glutamatergic synapse related genes in the paratumor tissues might be one of the main molecular features of the comorbidity model. Our findings suggested that the presence of glioma caused and altered depression-like behaviors, which was potentially related to the 5-HT and glutamatergic synapse pathways.

Microglia contribute to mammary tumor-induced neuroinflammation in a female mouse model

Following diagnosis but before treatment, up to 30% of breast cancer patients report behavioral side effects (e.g., anxiety, depression, memory impairment). Our rodent mammary tumor model recapitulates aspects of these behavioral sequelae, as well as elevated circulating and brain inflammatory mediators. Neuroinflammation is a proposed mechanism underlying the etiology of mood disorders and cognitive deficits, and therefore may be contributing to tumor-associated behavioral side effects. The cellular mechanisms by which tumor-induced neuroinflammation occurs remain unknown, making targeted treatment approaches inaccessible. Here, we tested the hypotheses that microglia are the primary cells driving tumor-induced neuroinflammation and behavioral side effects. Young adult female BALB/c mice were induced with a 67NR mammary tumor; tumor-free controls underwent a sham surgery. Mammary tumors increased IBA1+ and GFAP+ staining in the amygdala and hippocampus relative to tumor-free controls. However, tumors did not alter gene expression of Percoll-enriched microglia isolated from the whole brain. While cognitive, social, and anhedonia-like behaviors were not altered in tumor-bearing mice, tumors increased central tendency in the open-field test; microglia depletion did not reverse this effect. Brain region RT-qPCR data indicated that microglia depletion attenuated tumor-induced elevations of neuroinflammatory gene expression in a region- and mediator-specific manner. These results indicate a causal role of microglia in tumor-induced neuroinflammation. This research advances our understanding of the cellular mechanisms underlying tumor-induced neuroinflammation in order to understand how brain responses (e.g., behavior) may be altered with subsequent cancer-related immune challenges.

Accumulation and neuroprotective effects of lithium on hepatocellular carcinoma mice model

AIM

The peripheral tumor growth is accompanied by the accumulation of inflammatory mediators in the blood that can negatively influence blood-brain barrier function and neuronal structure and develop the cancer-associated depression. The aim of the study was to evaluate the neurobiological effects of lithium on hepatocellular carcinoma mice model.

METHODS

In this study we analyzed the locomotor activity of lithium-treated tumor-bearing mice using the Phenomaster instrument. Inductively coupled plasma mass-spectral analysis was used to determine lithium levels in blood, brain, liver, kidneys, tumors and muscle tissues. The prefrontal cortex neurons ultrastructure was assessed by transmission electron microscopy. Expression of BDNF, GRP78, EEA1, LAMP1, and LC3 beta in neurons was determined by immunohistochemical analysis.

RESULTS

A decrease in locomotor activity was found in animals with tumors. At the same time, the low expression levels of the neurotrophic factor BDNF and early endosomal marker EEA1 were revealed, as well as the decreased amount of synaptic vesicles and synapses was shown. Signs of endoplasmic reticulum stress and autophagy development in neurons of animals with tumors were noted. Lithium carbonate administration had a corrective effect on animal's behavior and the prefrontal cortex neurons structure.

CONCLUSIONS

In summary, lithium can restore the neuronal homeostasis in tumor-bearing mice.

TET2 deficiency promotes anxiety and depression-like behaviors by activating NLRP3/IL-1β pathway in microglia of allergic rhinitis mice

BACKGROUND

Anxiety and depression-like behaviors in allergic rhinitis (AR) are attracting attention, while the precise mechanism has not been clearly elucidated. Recent evidence shows that neuroinflammation in anterior cingulate cortex (ACC) may be the core of these neuropsychiatric symptoms in AR. Here, we investigated the molecular link between the anxiety and depression-like behaviors and neuroinflammation in ACC.

METHODS

Mice were sensitized and challenged with ovalbumin (OVA) to induce AR. Nasal inflammation levels were assessed by H&E staining and PAS staining. Anxiety and depression-like behaviors were evaluated by behavioral experiments including open field test, forced swimming test, and sucrose preference test. Neuronal impairment was characterized via Nissl staining and 18FDG-PET. The role of ten-eleven translocation 2 (TET2) in AR-related anxiety and depression was assessed by Tet2-/- mice. In addition, the murine BV2 microglial cell line was utilized to explore the molecular mechanisms by which TET2 mediates neuroinflammation. The levels of TET2, NLRP3 and their downstream molecules were detected by immunohistochemistry, Western blot, Dot blot and ELISA. The effects of metformin on depression-like behaviors in AR mice were also evaluated.

RESULTS

AR mice showed significant anxiety and depression-like behaviors, which associated with the activation of ACC. Loss of TET2 activated the NLRP3/IL-1β pathway of microglia in AR mice, further accelerating the anxiety and depression-like behaviors. In addition, knockdown of TET2 activated the NLRP3/IL-1β pathway in BV2 cells. Metformin improved the neuropsychiatric symptoms of AR mice by reducing the activation of NLRP3/IL-1β pathway after upregulating TET2.

CONCLUSION

TET2 deficiency activates the NLRP3/IL-1β pathway of microglia in the ACC, promoting the pathological process of anxiety and depression-like behavior in AR. Metformin could be effective in treating neuroinflammation by regulating microglia via TET2 up-regulation, indicating that metformin is a potential way to treat anxiety and depression-like behaviors in AR.

Whey protein isolate attenuates depression-like behavior developed in a mouse model of breast tumor

Increasing evidence indicates that tryptophan (Trp) metabolism disturbance controls hippocampal 5-hydroxytryptamine (5-HT) and thereby affecting depression-like behavior, in which the gut microbiota (GM) might be involved. This study investigated the effect of Trp-rich whey protein isolate (WPI) on depressive-like behavior in 4T1 tumor-bearing mice. Female BALB/c mice were subcutaneously inoculated with murine 4T1 mammary carcinoma cells and received 2 g/kg of WPI by gavage daily for 21 days. The results showed that WPI exerted no significant effects on tumor weight and volume, but abrogated tumor-induced depression-like behavior, as evidenced by remarkably increased time and distance in the center of the open-field test, decreased immobility time in the tail suspension test, increased time and number of entries to the open arms in the elevated plus maze and sucrose preference. Moreover, WPI promoted the hippocampal Trp, 5-hydroxytryptophan (5-HTP), 5-HT, 5-hydroxyindoleacetic acid (5-HIAA) levels and inhibited kynurenine (Kyn) through up-regulating serotonin transporter (SERT) and down-regulating indoleamine 2, 3-dioxygenase (IDO). WPI showed an enriched microbial diversity indicated by increased Shannon index and decreased Simpson index, reduced the abundances of Proteobacteria, Rikenellaceae_RC9_gut_group, Alloprevotella and Prevotellaceae_UCG-001, and increased the abundance of unclassified_k__norank_d__Bacteria in tumor-bearing mice (P < 0.05). At level 3, WPI enhanced the function of microbial gene related to Trp metabolism in the KEGG pathways (P < 0.05). Our results suggest that WPI exhibits a potent antidepressant-like effect via the regulation of hippocampal Trp metabolism and alteration of GM composition and function, and it may be an effective prevention for cancer-related depression.

Understanding the initiation, delivery and processing of bone cancer pain from the peripheral to the central nervous system

Bone cancer pain is a complex condition characterized by persistent, sudden, spontaneous pain accompanied by hyperalgesia that typically arises from bone metastases or primary bone tumors, causing severe discomfort and significantly diminishing cancer patients' quality of life and confidence in their ability to overcome the disease. It is widely known that peripheral nerves are responsible for detecting harmful stimuli, which are then transmitted to the brain via the spinal cord, resulting in the perception of pain. In the case of bone cancer, tumors and stromal cells within the bone marrow release various chemical signals, including inflammatory factors, colony-stimulating factors, chemokines, and hydrogen ions. Consequently, the nociceptors located at the nerve endings within the bone marrow sense these chemical signals, generating electrical signals that are then transmitted to the brain through the spinal cord. Subsequently, the brain processes these electrical signals in a complex manner to create the sensation of bone cancer pain. Numerous studies have investigated the transmission of bone cancer pain from the periphery to the spinal cord. However, the processing of pain information induced by bone cancer within the brain remains unclear. With the continuous advancements in brain science and technology, the brain mechanism of bone cancer pain would become more clearly understood. Herein, we focus on summarizing the peripheral nerve perception of the spinal cord transmission of bone cancer pain and provide a brief overview of the ongoing research regarding the brain mechanisms involved in bone cancer pain.

Targeting Underlying Inflammation in Carcinoma Is Essential for the Resolution of Depressiveness

In modern clinical practice and research on behavioral changes in patients with oncological problems, there are several one-sided approaches to these problems. Strategies for early detection of behavioral changes are considered, but they must take into account the specifics of the localization and phase in the course and treatment of somatic oncological disease. Behavioral changes, in particular, may correlate with systemic proinflammatory changes. In the up-to-date literature, there are a lot of useful pointers on the relationship between carcinoma and inflammation and between depression and inflammation. This review is intended to provide an overview of these similar underlying inflammatory disturbances in both oncological disease and depression. The specificities of acute and chronic inflammation are considered as a basis for causal current and future therapies. Modern therapeutic oncology protocols may also cause transient behavioral changes, so assessment of the quality, quantity, and duration of behavioral symptoms is necessary to prescribe adequate therapy. Conversely, antidepressant properties could be used to ameliorate inflammation. We will attempt to provide some impetus and present some unconventional potential treatment targets related to inflammation. It is certain that only an integrative oncology approach is justifiable in modern patient treatment.

Neuroinflammation in the medial prefrontal cortex exerts a crucial role in bone cancer pain

Bone cancer pain (BCP) is one of the most common types of pain in cancer patients which compromises the patient's functional status, quality of life, and survival. Central hyperalgesia has increasingly been identified as a crucial factor of BCP, especially in the medial prefrontal cortex (mPFC) which is the main cortical area involved in the process of pain and consequent negative emotion. To explore the genetic changes in the mPFC during BCP occurrence and find possible targets for prediction, we performed transcriptome sequencing of mPFC in the BCP rat model and found a total of 147 differentially expressed mRNAs (DEmRNAs). A protein-protein interaction (PPI) network revealed that the DEmRNAs mainly participate in the inflammatory response. Meanwhile, microglia and astrocytes were activated in the mPFC of BCP rats, further confirming the presence of neuroinflammation. In addition, Gene Ontology (GO) analysis showed that DEmRNAs in the mPFC are mainly involved in antigen processing, presentation of peptide antigen, and immune response, occurring in the MHC protein complex. Besides, the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that DEmRNAs are mainly enriched in the pathways of phagosome, staphylococcus aureus infection, and antigen processing, in which MHCII participate. Furthermore, immunostaining showed that MHCII is mainly located in the microglia. Microglia are believed to be involved in antigen processing, a key cause of BCP. In vivo, minocycline (MC) treatment inhibits the activation of microglia and reduces the expression of MHCII and proinflammatory cytokines, thereby alleviating BCP and pain-related anxiety. Taken together, our study identified differentially expressed genes in the BCP process and demonstrated that the activation of microglia participates in the inflammatory response and antigen process, which may contribute to BCP.

Ovarian status modulates endocrine and neuroinflammatory responses to a murine mammary tumor

Patients with breast cancer have increased circulating inflammatory markers and mammary tumors increase neuroinflammation in rodent models. Menopausal status is not only important in the context of breast cancer as circulating estrogen influences tumor progression, but also because estrogen is anti-inflammatory and an essential modulator of endocrine function in the brain and body. Here, we manipulated "menopause" status (ovary-intact and ovariectomized) in an estrogen receptor (ER)+ mouse mammary tumor model to determine the extent to which ovarian status modulates: 1) tumor effects on estrogen concentrations and signaling in the brain, 2) tumor effects on estrogen-associated neurobiology and inflammation, and 3) the ability for tumor resection to resolve the effects of a tumor. We hypothesized that reduced circulating estradiol (E2) after an ovariectomy exacerbates tumor-induced peripheral and central inflammation. Notably, we observed ovarian-dependent modulation on tumor-induced peripheral outcomes, including E2-dependent processes and, to a lesser degree, circulating inflammatory markers. In the brain, ovariectomy exacerbated neuroinflammatory markers in select brain regions and modulated E2-related neurobiology due to a tumor and/or resection. Overall, our data suggest that ovarian status has moderate implications for tumor-induced alterations in neuroendocrinology and neuroinflammation and mild effects on peripheral inflammatory outcomes in this murine mammary tumor model.

Quercetin Alleviates the Progression of Breast Cancer-Related Depression via Inhibiting the Pyroptosis and Promoting the Immune Response

Background. Breast cancer-related depression (BCRD) seriously inhibits the life quality of patients with breast cancer. The Xiaoyao Kangai Jieyu Formula is known to inhibit the progression of depression. However, the detailed function of the Xiaoyao Kangai Jieyu Formula in BCRD remains unclear. Methods. Network pharmacology was constructed to assess the downstream target of the Xiaoyao Kangai Jieyu Formula in BCRD. In addition, the tail suspension test, sucrose preference test, and forced swimming test were used to test the symptom of depression in mice. Fluoro-Jade B staining was performed to observe the structure of neurons. RT-qPCR and western blot were applied to evaluate mRNA and protein levels. Besides, ELISA was performed to test the inflammatory responses and the immune response-related cytokines. Results. Quercetin was identified as the key component of the Xiaoyao Kangai Jieyu Formula. Quercetin significantly inhibited BCRD-induced neuron pyroptosis via downregulation of PYD and card domain containing (ASC), NLR family pyrin domain containing 3 (NLRP3), and caspase-1, and quercetin could reverse BCRD-caused inhibition of neuron viability. Quercetin significantly attenuated the symptom of BCRD in mice, and it could reverse the contents of 5-hydroxytryptamine (5-HT), dopamine (DA), and neutrophil elastase (NE) in mice. Moreover, quercetin could promote the immune responses in xenograft mice via upregulation of interleukin- (IL-) 2, interferon-γ (IFN-γ), and IL-10. Conclusion. Quercetin, the active ingredient of the Xiaoyao Kangai Jieyu Formula, effectively mitigated the progression of BCRD by inhibiting pyroptosis, promoting immune response, and improving serum metabolism.

The underestimated sex: a review on female animal models of depression

Major depression (MD) is the most common psychiatric disorder, predicted to affect around 264 million people worldwide. Although the etiology of depression remains elusive, the interplay between genetics and environmental factors, such as early life events, stress, exposure to drugs and health problems appears to underlie its development. Whereas depression is twice more prevalent in women than in men, most preclinical studies are performed in male rodents. In fact, females' physiology and reproductive experience are associated with changes to brain, behavior and endocrine profiles that may influence both stress, an important precipitating factor for depression, and response to treatment. These specificities emphasize the need to choose the most suitable models and readouts in order to better understand the pathophysiological mechanisms of depression in females. With this review, we aim to provide an overview of female animal models of depression highlighting the major differences between models, regarding behavioral, physiological, and molecular readouts, but also the major gaps in research, attending to the role of etiological factors, protocol variability and sex.

Electroacupuncture Attenuates Chronic Inflammatory Pain and Depression Comorbidity through Transient Receptor Potential V1 in the Brain

Chronic pain is one of the highest costs in clinical therapy, often appearing comorbid with depression. They present with overlapping clinical conditions and common pathological pathways especially in neuroinflammation, both of which can be reversed by electroacupuncture (EA). Transient receptor potential V1 receptor (TRPV1) is a Ca[Formula: see text] permeable ion channel that responds to brain inflammation and has a known role in the development of chronic pain and depression. Here, we investigate the role of TRPV1 and its related molecules in a mouse model of inflammation-induced chronic pain and depression using Complete Freund's adjuvant (CFA). We measured inflammatory mediators in plasma and evaluated the TRPV1 signaling pathway in the medial prefrontal cortex (mPFC), hypothalamus, and periaqueductal gray (PAG) of the mouse brain. Mechanical and thermal hyperalgesia as well as depressive-like behaviors were induced using the open field test and forced swimming test. Therapeutic effects were observed in EA and Trpv1[Formula: see text] mice in measures of chronic pain and depression. Inflammatory mediators induced by CFA injection were attenuated by EA and Trpv1 deletion. TRPV1 and downstream molecules were significantly decreased in the mPFC, hypothalamus, and PAG of mice, effects which were reversed by EA and Trpv1 knockout. We provide novel evidence that these inflammatory mediators modulate the TRPV1 signaling pathway and suggest new potential therapeutic targets for chronic pain and depression.

Cancer blues? A promising judgment bias task indicates pessimism in nude mice with tumors

In humans, affective states can bias responses to ambiguous information: a phenomenon termed judgment bias (JB). Judgment biases have great potential for assessing affective states in animals, in both animal welfare and biomedical research. New animal JB tasks require construct validation, but for laboratory mice (Mus musculus), the most common research vertebrate, a valid JB task has proved elusive. Here (Experiment 1), we demonstrate construct validity for a novel mouse JB test: an olfactory Go/Go task in which subjects dig for high- or low-value food rewards. In C57BL/6 and Balb/c mice faced with ambiguous cues, latencies to dig were sensitive to high/low welfare housing: environmentally-enriched animals responded with relative 'optimism' through shorter latencies. Illustrating the versatility of this validated JB task across different fields of research, it further allowed us to test hypotheses about the mood-altering effects of cancer in male and female nude mice (Experiment 2). Males, although not females, treated ambiguous cues as intermediate; and males bearing subcutaneous lung adenocarcinomas also responded more pessimistically to these than did healthy controls. To our knowledge, this is the first evidence of a valid mouse JB task, and the first demonstration of pessimism in tumor-bearing animals. This task still needs to be refined to improve its sensitivity. However, it has great potential for investigating mouse welfare, the links between affective state and disease, depression-like states in animals, and hypotheses regarding the neurobiological mechanisms that underlie affect-mediated biases in judgment.

Transient receptor potential V1 (TRPV1) modulates the therapeutic effects for comorbidity of pain and depression: The common molecular implication for electroacupuncture and omega-3 polyunsaturated fatty acids

Chronic pain and depression are conditions that are highly comorbid and present with overlapping clinical presentations and common pathological biological pathways in neuroinflammation, both of which can be reversed by the use of electroacupuncture (EA) and omega-3 polyunsaturated fatty acids (PUFAs). Transient receptor potential V1 (TRPV1), a Ca²⁺ permeable ion channel that can be activated by inflammation, is reported to be involved in the development of chronic pain and depression. Here, we investigated the role of TRPV1 and its related pathways in the murine models of cold stress-induced nociception and depression. Female C57BL/6 wild type and TRPV1 knockout mice were subjected to intermittent cold-stress (ICS) to initiate depressive-like and chronic pain behaviors, respectively. The Bio-Plex ELISA technique was utilized to analyze inflammatory mediators in mice plasma. The western blot and immunostaining techniques were used to analyze the presence of TRPV1 and related molecules in the medial prefrontal cortex (mPFC), hippocampus, periaqueductal gray (PAG), and amygdala. The ICS model significantly induced chronic pain (mechanical: 2.55 ± 0.31 g; thermal: 8.12 ± 0.87 s) and depressive-like behaviors (10.95 ± 0.95% in the center zone; 53.14 ± 4.01% in immobility). The treatment efficacy of EA, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) were observed in both nociceptive and depression test results. Inflammatory mediators were increased after ICS induction and further reversed by the use of EA, EPA and DHA. A majority of TRPV1 proteins and related molecules were significantly decreased in the mPFC, hippocampus and PAG of mice. This decrease can be reversed by the use of EA, EPA and DHA. In contrast, these molecules were increased in the mice's amygdala, and were attenuated by the use of EA, EPA and DHA. Our findings indicate that these inflammatory mediators can regulate the TRPV1 signaling pathway and initiate new potential therapeutic targets for chronic pain and depression treatment.

The antioxidant and immunomodulatory compound 3-[(4-chlorophenyl)selanyl]-1-methyl-1H-indole attenuates depression-like behavior and cognitive impairment developed in a mouse model of breast tumor

Psychiatric alterations are often found in patients with breast cancer even before the initiation of adjuvant therapy, resulting in a poor quality of life. It has become accepted that neuroinflammation and oxidative stress are involved in the pathophysiology of depression and cognitive impairment. Herein, we tested the hypothesis that treatment with the antioxidant and immunomodulatory selenium-containing compound 3-[(4-chlorophenyl)selanyl]-1-methyl-1H-indole (CMI)could attenuate behavioral and neurochemical alterations in a mammary (4T1) tumor model. Female BALB/c mice were subcutaneously inoculated with 4T1 cancer cells (1 × 10⁵ cells/mice) or PBS. From days 14 to 20, mice received daily gavage with canola oil or CMI. On day 21, mice were submitted to behavioral tests followed by euthanasia. We found that CMI did not alter tumor growth, body weight, and body temperature in tumor-bearing mice. Importantly, treatment with CMI abrogated tumor-induced depression-like behavior and cognitive impairment. By the time CMI improved the behavioral alterations, it had reduced tumor-induced neuroinflammation (altered expression of NFκB, IL-1β, TNF-α, IL-10, IDO, and COX-2) and oxidative stress (altered expression of iNOS and Nrf2, and levels of reactive species, nitric oxide, lipid peroxidation, and superoxide dismutase activity) in the prefrontal cortices and hippocampi of mice. A molecular docking approach suggested the ability of CMI to inhibit the activity of iNOS and COX-2. Together, our results indicate that CMI treatment may attenuate depression and cognitive impairment in 4T1 tumor-bearing mice, and be a groundbreaking strategy for the treatment of cancer-related psychiatric symptoms to improve the quality of life of cancer patients.

Behavioral coping strategies predict tumor development and behavioral impairment after chronic social stress in mice

The aims of this study were to identify behavioral strategies to cope with social defeat, evaluate their impact on tumor development and analyze the contributions of both to changes in physiology and behavior produced by chronic defeat stress. For this purpose, OF1 mice were inoculated with B16F10 melanoma cells and subjected to 18 days of repeated defeat stress in the presence of a resident selected for consistent levels of aggression. Combined cluster and discriminant analyses of behavior that manifested during the first social interaction identified three types of behavioral profiles: active/aggressive (AA), passive/reactive (PR) and an intermediate active/non-aggressive (ANA) profile. Animals that showed a PR coping strategy developed more pulmonary metastases at the end of the social stress period than animals in other groups. The ANA but not AA group also showed higher tumor metastases than non-stressed subjects. In addition, the ANA group differed from the other groups because it displayed the highest corticosterone levels after the first interaction. Chronic stress reduced sucrose consumption, which indicates anhedonia, in all the stressed groups. However, the PR subjects exhibited a longer immobility time and swam for less time than other subjects in the forced swim test (FST), and they travelled a shorter distance in the open field test (OFT). In this test, the ANA group also travelled smaller distances than the non-stressed group, but the difference was more moderate. In contrast, tumor development but not stress increased behaviors associated with anxiety in the OFT (e.g., time in the center) in all tumor-bearing subjects. In summary, although the effects of social stress and tumor development on behavior were rather moderate, the results indicate the importance of behavioral coping strategies in modulating the effects of chronic stress on health.

Medial prefrontal cortex in neurological diseases

The medial prefrontal cortex (mPFC) is a crucial cortical region that integrates information from numerous cortical and subcortical areas and converges updated information to output structures. It plays essential roles in the cognitive process, regulation of emotion, motivation, and sociability. Dysfunction of the mPFC has been found in various neurological and psychiatric disorders, such as depression, anxiety disorders, schizophrenia, autism spectrum disorders, Alzheimer's disease, Parkinson's disease, and addiction. In the present review, we summarize the preclinical and clinical studies to illustrate the role of the mPFC in these neurological diseases.

Activation of hippocampal microglia in a murine model of cancer-induced pain

Introduction

Pain is a common and debilitating comorbidity of metastatic breast cancer. The hippocampus has been implicated in nociceptive processing, particularly relating to the subjective aspect of pain. Here, a syngeneic mouse model was used to characterize the effects of peripheral tumors on hippocampal microglial activation in relation to cancer-induced pain (CIP).

Materials and methods

Mice were systemically treated with the colony-stimulating factor 1 receptor inhibitor Pexidartinib prior to intrafemoral (IF) or subcutaneous 4T1 carcinoma cell inoculation. Spontaneous and evoked nociceptive responses were quantitated throughout tumor development, and contralateral hippocampi were collected via endpoint microdissection for RNA analysis. Additionally, IF tumor-bearing animals were sacrificed on days 5, 10, 15, and 20 post 4T1 cell inoculation, and brain sections were immunofluorescently stained for Iba1, a marker of activated microglia.

Results

Ablation of these neuroimmune cells with the CSF1R inhibitor Pexidartinib delayed the onset and severity of cancer-induced nociceptive behaviors in IF tumor-bearing animals, adding to the body of literature that demonstrates microglial contribution to the development and maintenance of CIP. Furthermore, in untreated IF tumor-bearing mice, nociceptive behaviors appeared to progress in parallel with microglial activation in hippocampal regions. Immunofluorescent Iba1+ microglia increased in the dentate gyrus and cornu ammonis 1 hippocampal regions in IF tumor-bearing animals over time, which was confirmed at the mRNA level using relevant microglial markers.

Conclusion

This is the first experimental evidence to demonstrate the effects of peripheral tumor-induced nociception on hippocampal microglial activation. The increase in hippocampal microglia observed in the present study may reflect the emotional and cognitive deficits reported by patients with CIP.

Solid peripheral tumor leads to systemic inflammation, astrocyte activation and signs of behavioral despair in mice

Prevalence of depression is higher in patients with cancer than in the general population. Sustained systemic inflammation has been associated with depressive behavior and it has been reported that depressed patients commonly display alterations in their immune system. We previously showed that cancer in mice induces a systemic environment that promotes neutrophil activation and leukocytosis. We thus hypothesized that the peripheral systemic response to a solid tumor leads to endothelial activation, which may promote inflammatory changes in the brain with behavioral consequences. Using the Lewis lung carcinoma (LLC) model, we show that tumor growth induces a progressive increase in peripheral inflammation as observed by elevated interleukin-6 (IL-6). In behavioral studies, tumor-bearing mice showed no sign of motor, coordination or short term working memory deficits as assessed by rotarod, balance-beam, and novel object recognition tests. However, there was an impairment in the grip strength test and interestingly, an anxious and despair-like phenotype in the elevated plus-maze, and tail suspension tests, respectively. Immunostaining of perfused brains revealed fibrin accumulation in the vasculature with some leakage into the parenchyma, a process known to activate endothelial cells. Taken together, our results suggest that the inflamed and prothrombotic systemic environment created by the growth of a peripherally-located solid tumor induces endothelial activation, accumulation of fibrin in the brain and astrocyte activation, perhaps leading to depressive-like behavior.

Imaging Neurons within Thick Brain Sections Using the Golgi-Cox Method

The Golgi-Cox method of neuron staining has been employed for more than two hundred years to advance our understanding of neuron morphology within histological brain samples. While it is preferable from a practical perspective to prepare brain sections at the greatest thickness possible, in order to increase the probability of identifying stained neurons that are fully contained within single sections, this approach is limited from a technical perspective by the working distance of high-magnification microscope objectives. We report here a protocol to stain neurons using the Golgi-Cox method in mouse brain sections that are cut at 500 μm thickness, and to visualize neurons throughout the depth of these sections using an upright microscope fitted with a high-resolution 30X 1.05 N.A. silicone oil-immersion objective that has an 800 μm working distance. We also report two useful variants of this protocol that may be employed to counterstain the surface of mounted brain sections with the cresyl violet Nissl stain, or to freeze whole brains for long-term storage prior to sectioning and final processing. The main protocol and its two variants produce stained thick brain sections, throughout which full neuron dendritic trees and dendrite spines may be reliably visualized and quantified.

Behavioural Effects of Using Sulfasalazine to Inhibit Glutamate Released by Cancer Cells: A Novel target for Cancer-Induced Depression

Despite the lack of robust evidence of effectiveness, current treatment options for cancer-induced depression (CID) are limited to those developed for non-cancer related depression. Here, anhedonia-like and coping behaviours were assessed in female BALB/c mice inoculated with 4T1 mammary carcinoma cells. The behavioural effects of orally administered sulfasalazine (SSZ), a system x_c⁻ inhibitor, were compared with fluoxetine (FLX). FLX and SSZ prevented the development of anhedonia-like behaviour on the sucrose preference test (SPT) and passive coping behaviour on the forced swim test (FST). The SSZ metabolites 5-aminosalicylic acid (5-ASA) and sulfapyridine (SP) exerted an effect on the SPT but not on the FST. Although 5-ASA is a known anti-inflammatory agent, neither treatment with SSZ nor 5-ASA/SP prevented tumour-induced increases in serum levels of interleukin-1β (IL-1β) and IL-6, which are indicated in depressive disorders. Thus, the observed antidepressant-like effect of SSZ may primarily be attributable to the intact form of the drug, which inhibits system x_c⁻. This study represents the first attempt at targeting cancer cells as a therapeutic strategy for CID, rather than targeting downstream effects of tumour burden on the central nervous system. In doing so, we have also begun to characterize the molecular pathways of CID.

Overview of Glutamatergic Dysregulation in Central Pathologies

As the major excitatory neurotransmitter in the mammalian central nervous system, glutamate plays a key role in many central pathologies, including gliomas, psychiatric, neurodevelopmental, and neurodegenerative disorders. Post-mortem and serological studies have implicated glutamatergic dysregulation in these pathologies, and pharmacological modulation of glutamate receptors and transporters has provided further validation for the involvement of glutamate. Furthermore, efforts from genetic, in vitro, and animal studies are actively elucidating the specific glutamatergic mechanisms that contribute to the aetiology of central pathologies. However, details regarding specific mechanisms remain sparse and progress in effectively modulating glutamate to alleviate symptoms or inhibit disease states has been relatively slow. In this report, we review what is currently known about glutamate signalling in central pathologies. We also discuss glutamate's mediating role in comorbidities, specifically cancer-induced bone pain and depression.