Differential modulation of the anterior cingulate and insular cortices on anxiogenic-like responses induced by empathy for pain

Emotional contagion and cognitive empathy regulate the effect of depressive symptoms on empathy-related brain functional connectivity in patients with chronic back pain

BACKGROUND

Chronic pain and depression share common neural mechanisms, but their impacts on empathy are different. It is unclear how comorbid depressive symptoms affect empathy-related brain function in patients with chronic pain.

METHODS

A total of 29 healthy participants and 107 patients with chronic back pain (CBP) were included in this study. All subjects underwent a functional MRI scan with concurrent empathic stimulation. Multiple linear regression, moderation analysis, and mediation analysis were used to explore the impacts of chronic pain and comorbid depression on empathy.

RESULTS

The interaction between the pain intensity and the depressive symptoms affected the functional connectivity (FC) of the insula-middle frontal gyrus (MFG), and the severity of the self-rating depression scale (SDS) scores moderated the effect of the pain on the left insula-left MFG FC. Within the CBP group, the emotional contagion (EC) scores served as a mediator in the association between the SDS scores and the FC of the left middle cingulate cortex (MCC)-inferior temporal gyrus (ITG), and the level of cognitive empathy (CE) moderated the effect of the SDS scores on the left MCC-ITG FC.

LIMITATIONS

There is a lack of research on the effects of depressive symptoms on empathy in individuals with different types of chronic pain.

CONCLUSION

Depressive symptoms were strongly associated with the emotional contagion in patients with chronic back pain. Furthermore, the emotional contagion and the cognitive empathy regulated the effect of the comorbid depressive symptoms on the MCC-ITG connectivity in patients with chronic back pain.

Pharmacological Manipulation of Corticotropin-Releasing Factor Receptors in the Anterior and Posterior Subregions of the Insular Cortex Differently Affects Anxiety-Like Behaviors in the Elevated Plus Maze in Rats

Neuroimaging data in humans and neurobiological studies in rodents have suggested an involvement of the insular cortex (IC) in anxiety manifestations. However, the local neurochemical mechanisms involved are still poorly understood. Corticotropin-releasing factor (CRF) neurotransmission has been described as a prominent neurochemical mechanism involved in the expression of anxiety-like behaviors, but the brain sites related are poorly understood. Additionally, several findings indicate that control of physiological and behavioral responses by the IC occurs in a site-specific manner along its rostrocaudal axis. Thus, this study is aimed at evaluating the effect of CRF receptor agonism and antagonism within the anterior and posterior subregions of the IC in controlling anxiety-related behaviors in the elevated plus maze (EPM). For this, independent groups (six groups) of animals received bilateral microinjections of vehicle, the selective CRF1 receptor antagonist CP376395, or CRF into either the anterior or posterior subregions of the IC. Ten minutes later, the behavior in the EPM was evaluated for five minutes. Treatment of the anterior IC with CP376395, but not with CRF, increased the time and number of entries into the open arms of the EPM. CRF, but not the CRF1 receptor antagonist, microinjected into the posterior IC also increased exploration of the EPM open arms. Taken together, these data indicate that CRFergic neurotransmission in the anterior IC is involved in the expression of anxiety-related behaviors in the EPM. This neurochemical mechanism does not seem to be activated within the posterior IC during exposure to the EPM, but the effects caused by CRF microinjection indicate that activation of CRF receptors in this IC subregion might evoke anxiolytic-like effects.

Effects of stress contagion on anxiogenic- and orofacial inflammatory pain-like behaviors with brain activation in mice

The conditions of stress contagion are induced in bystanders without direct experiences of stressful events. This study determined the effects of stress contagion on masseter muscle nociception in mice. Stress contagion was developed in the bystanders after cohabitating with a conspecific mouse subjected to social defeat stress for 10 days. On Day 11, stress contagion increased anxiety- and orofacial inflammatory pain-like behaviors. The c-Fos and FosB immunoreactivities evoked by masseter muscle stimulation were increased in the upper cervical spinal cord, while c-Fos expressions were increased in the rostral ventromedial medulla, including the lateral paragigantocellular reticular nucleus and nucleus raphe magnus in stress contagion mice. The level of serotonin in the rostral ventromedial medulla was increased under stress contagion, while the number of serotonin positive cells was increased in the lateral paragigantocellular reticular nucleus. Stress contagion increased c-Fos and FosB expressions in the anterior cingulate cortex and insular cortex, both of which were positively correlated with orofacial inflammatory pain-like behaviors. The level of brain-derived neurotrophic factor was increased in the insular cortex under stress contagion. These results indicate that stress contagion can cause neural changes in the brain, resulting in increased masseter muscle nociception, as seen in social defeat stress mice.

Disorders in the gut and liver are involved in depression contagion between isosexual post-stroke depression mice and the healthy cohabitors

Despite the accumulated evidence that pair housing could attenuate post-stroke depression (PSD), but less attention has been paid to the healthy cohabitors, and the underlying mechanisms remain unclear. This study aimed to determine whether there is depressive contagion between PSD mice and their healthy cohabitors. PSD was induced by middle cerebral artery occlusion (MCAO) plus restraint stress for four weeks. Three days after MCAO, the mice were restrained two hours per day and isosexually pair-housed for four weeks. The results showed that, compared with the partners pair housed with normal control mice (Ctrl group), the partners pair housed with PSD mice (CH group) displayed depressive-like behaviors, including decreased sucrose preference rate, significantly shorter duration in the center arena and reduced total distance in the open-field test, and extended immobile time in forced swimming test and tail-suspension test without sex differences. Regarding the change in the body weight, only the males showed a significant reduction on days 17 and 24 after treatment. Furthermore, the CH group showed significantly increased corticosterone and decreased oxytocin (OXT) levels in serum, while the mRNA levels of OXT, vasopressin and oxytocin receptor were remarkably upregulated in the hypothalamus of the CH group. However, there was no significant change in the vasopressin receptor V1a. Interestingly, compared with the Ctrl group, there was a significant decrease in butyrate in serum of the CH group. Consistently, they had mild liver dysfunction with increased alanine transaminase, extended hepatic sinus surrounded by enhanced SLC22A9, and significantly increased Iba1-positive macrophages. Moreover, the expression of tight junction protein (Occludin and ZO-1) obviously decreased in the colon with increasing Iba1-positive cells. These results suggest that isosexual pair-housing with PSD mice causes the healthy partners to develop depressive-like behaviors with disturbances in the gut and liver.

Anterior cingulate cortex, but not amygdala, modulates the anxiogenesis induced by living with conspecifics subjected to chronic restraint stress in male mice

Cohabitation with a partner undergoing chronic restraint stress (CRE) induces anxiogenic-like behaviors through emotional contagion. We hypothesized that the anterior cingulate cortex (ACC) and the amygdala would be involved in the modulation of this emotional process. This study investigated the role of the ACC and amygdala in empathy-like behavior (e.g., anxiety-like responses) induced by living with a mouse subjected to CRE. Male Swiss mice were housed in pairs for 14 days and then allocated into two groups: cagemate stress (one animal of the pair was subjected to 14 days of restraint stress) and cagemate control (no animal experienced stress). Twenty-four hours after the last stress session, cagemates had their brains removed for recording FosB labeling in the ACC and amygdala (Exp.1). In experiments 2 and 3, 24 h after the last stress session, the cagemates received 0.1 μL of saline or cobalt chloride (CoCl₂ 1 mM) into the ACC or amygdala, and then exposed to the elevated plus-maze (EPM) for recording anxiety. Results showed a decrease of FosB labeling in the ACC without changing immunofluorescence in the amygdala of stress cagemate mice. Cohabitation with mice subjected to CRE provoked anxiogenic-like behaviors. Local inactivation of ACC (but not the amygdala) reversed the anxiogenic-like effects induced by cohabitation with a partner undergoing CRE. These results suggest the involvement of ACC, but not the amygdala, in anxiety induced by emotional contagion.

Evaluation of the posterior insular cortex involvement in anxiogenic response to emotional stress in male rats: Functional topography along the rostrocaudal axis

The insular cortex (IC) is engaged in behavioral and physiological responses to emotional stress. Control of physiological functions and behavioral responses has been reported to occur in a site-specific manner along the rostrocaudal axis of the IC. However, a functional topography of the IC regulation of anxiogenic responses caused by stress has never been evaluated. Therefore, we investigated the role of rostrocaudal subregions in the posterior IC in anxiogenic-like effect caused by exposure to acute restraint stress in male rats. For this, rats received bilateral microinjection of the non-selective synaptic inhibitor CoCl₂ or vehicle into either the rostral, intermediate or caudal portions of the posterior IC before exposure to acute restraint stress. Then, behavior in the elevated plus maze (EPM) was evaluated immediately after restraint stress. The behavior of non-stressed animals in the EPM was also investigated. We observed that acute restraint stress decreased the exploration of the EPM open arms in animals treated with vehicle in all regions of the posterior IC, thus indicating an anxiogenic-like effect. The avoidance of the EPM open arms was completely inhibited in animals subjected to microinjection of CoCl₂ into the intermediate posterior IC. Nevertheless, the same pharmacological treatment into either the rostral or caudal subregions of the posterior IC did not affect the restraint-evoked behavioral changes in the EPM. Taken together, these results suggest that regulation of anxiogenic-like effect to emotional stress along the rostrocaudal axis of the posterior IC might occur in a site-specific manner, indicating a role of the intermediate subregion.

The Reversal of Empathy-Induced Hypernociception in Male Mice by Intra-Amygdala Administration of Midazolam and Cannabidiol Depends on 5-HT3 Receptors

Introduction: Empathy is a fundamental prosocial behavior. It has been defined as perception, awareness, and understanding of others' emotional states, including painful processes. Mice living in pairs with conspecific chronic suffering from constriction injury exhibit pain hypersensitivity mediated by the amygdaloid complex. Nevertheless, the underlying mechanisms in the amygdala responsible for this response remain to be determined. This study investigated if the anxiolytic benzodiazepine midazolam (MDZ) and cannabidiol (CBD), a phytocannabinoid with multiple molecular targets, would attenuate this behavioral change. We also investigated if serotonergic and γ-aminobutyric acid (GABA)ergic mechanisms in the amygdala are involved in this effect. Materials and Methods: Male Swiss mice were housed in pairs for 28 days. The pairs were divided into two groups on the 14th day: cagemate nerve constriction and cagemate sham. On the 24th day, cagemates underwent a stereotaxic surgery and, on the 28th day, were evaluated on the writhing test. Results: The results showed that living with chronic pain leads to hypernociception in the cagemate and increases the expression of 5-HT₃ receptor (5-HT₃R) and glutamic acid decarboxylase 67 within the amygdala. MDZ (3.0 and 30 nmol) and CBD (30 and 60 nmol) attenuated the hypernociceptive behavior. The 5-HT₃R antagonist ondansetron (0.3 nmol) prevented the antinociceptive effects of MDZ and CBD. Conclusion: These findings indicate that 5-HT₃R and GABAergic mechanisms within the amygdala are involved in the pain hypersensitivity induced by the empathy for pain model. They also suggest that MDZ and CBD could be a new potential therapy to alleviate emotional pain disorders.

Emotional contagion and prosocial behavior in rodents

Empathy is critical to adjusting our behavior to the state of others. The past decade dramatically deepened our understanding of the biological origin of this capacity. We now understand that rodents robustly show emotional contagion for the distress of others via neural structures homologous to those involved in human empathy. Their propensity to approach others in distress strengthens this effect. Although rodents can also learn to favor behaviors that benefit others via structures overlapping with those of emotional contagion, they do so less reliably and more selectively. Together, this suggests evolution selected mechanisms for emotional contagion to prepare animals for dangers by using others as sentinels. Such shared emotions additionally can, under certain circumstances, promote prosocial behavior.

Mice Cohabiting With Familiar Conspecific in Chronic Stress Condition Exhibit Methamphetamine-Induced Locomotor Sensitization and Augmented Consolation Behavior

Recognizing and sharing emotions are essential for species survival, but in some cases, living with a conspecific in distress condition may induce negative emotional states through empathy-like processes. Studies have reported that stressors promote psychiatric disorders in both, those who suffer directly and who witness these aversive episodes, principally whether social proximity is involved. However, the mechanisms underlying the harmful outcomes of emotional contagion need more studies, mainly in the drug addiction-related behaviors. Here, we investigated the relevance of familiarity and the effects of cohabitation with a partner submitted to chronic stress in the anxiety-like, locomotor sensitization, and consolation behaviors. Male Swiss mice were housed in pairs during different periods to test the establishment of familiarity and the stress-induced anxiety behavior in the elevated plus maze. Another cohort was housed with a conspecific subjected to repeated restraint stress (1 h/day) for 14 days. During chronic restraint the allogrooming was measured and after the stress period mice were tested in the open field for evaluation of anxiety and locomotor cross-sensitization induced by methamphetamine. We found that familiarity was established after 14 days of cohabitation and the anxiogenic behavior appeared after 14 days of stress. Repeated restraint stress also increased anxiety in the open field test and induced locomotor cross-sensitization in the stressed mice and their cagemates. Cagemates also exhibited an increase in the consolation behavior after stress sessions when compared to control mice. These results indicate that changes in drug abuse-related, consolation, and affective behaviors may be precipitated through emotional contagion in familiar conspecifics.

5-HT3 receptor within the amygdaloid complex modulates pain hypersensitivity induced by empathy model of cohabitation with a partner in chronic pain condition in mice

Cohabitation with a partner undergoing chronic pain induces pain hypersensitivity. Among a lot of other neurochemical pathways, the serotonin (5-HT) role, specifically the 5-HT₃ receptor (5-HT₃R), in the amygdala has never been evaluated in this model. Here we studied the effects of the amygdala's chemical inhibition, its neuronal activation pattern, and 5-HT, 5-HIAA, and 5-HT turnover within the amygdala. Furthermore, the systemic and intra-amygdala 5-HT₃R activation and blockade in mice that cohabited with a conspecific subjected to chronic constriction injury were investigated. Male Swiss mice were housed in partners for 28 days. The dyads were divided into two groups on the 14^th day: cagemate nerve constriction (CNC) and cagemate sham (CS). On the 24^th day, cagemates underwent a stereotaxic surgery (when necessary) and, on the 28^th day, they were evaluated on the writhing test. The amygdala inactivation promotes pain-hypersensitivity behaviors in groups and dyads; cohabitation with a partner with chronic pain did not change FosB-labeled cells in the amygdala's nucleus and increases 5-HT turnover in cagemates. Systemic and intra-amygdala 5-HT₃R activation attenuated and enhanced the number of writhes, respectively. In contrast, 5-HT₃R blockade reduced hypersensitivity pain response. Results suggest the involvement of amygdala serotonergic signaling via 5-HT₃R in empathy-like behavior.