Unpredictable Chronic Mild Stress Paradigm Established Effects of Pro- and Anti-inflammatory Cytokine on Neurodegeneration-Linked Depressive States in Hamsters with Brain Endothelial Damages

Neuroinflammation in the prefrontal-amygdala-hippocampus network is associated with maladaptive avoidance behaviour

Maladaptive avoidance behaviour is often observed in patients suffering from anxiety and trauma- and stressor-related disorders. The prefrontal-amygdala-hippocampus network is implicated in learning and memory consolidation. Neuroinflammation in this circuitry alters network dynamics, resulting in maladaptive avoidance behaviour. The two-way active avoidance test is a well-established translational model for assessing avoidance responses to stressful situations. While some animals learn the task and show adaptive avoidance (AA), others show strong fear responses to the test environment and maladaptive avoidance (MA). Here, we investigated if a distinct neuroinflammation pattern in the prefrontal-amygdala-hippocampus network underlies the behavioural difference observed in these animals. Wistar rats were tested 8 times and categorized as AA or MA based on behaviour. Brain recovery followed for the analysis of neuroinflammatory markers in this network. AA and MA presented distinct patterns of neuroinflammation, with MA showing increased astrocyte, EAAT-2, IL-1β, IL-17 and TNF-ɑ in the amygdala. This neuroinflammatory pattern may underlie these animals' fear response and maladaptive avoidance. Further studies are warranted to determine the specific contributions of each inflammatory factor, as well as the possibility of treating maladaptive avoidance behaviour in patients with psychiatric disorders with anti-inflammatory drugs targeting the amygdala.

Suppressive role of lovastatin in intracerebral hemorrhage through repression of autophagy

Statins possess critical function in the brain. Here, we intended to investigate the role of lovastatin in brain damage after intracerebral hemorrhage (ICH). A collagenase-induced ICH rat model was established followed by lovastatin treatment. Then, the effect of lovastatin on ICH-induced brain damage was explored with cognitive function, learning and memory abilities, and neurological damage of rats analyzed. Besides, brain water content, number of degenerate neurons, Nissl's body, and apoptosis of neurons were detected. Oxidative stress levels, inflammation, and autophagy levels in ICH were measured after treatment of lovastatin. Lovastatin improved the cognitive impairment of rats, enhanced their spatial learning and memory abilities, reduced nervous system damage, lesion area, and brain water content after ICH. Lovastatin was capable of reducing the number of degenerated neurons, the apoptosis level, autophagy level, and increasing the number of Nissl's body. Lovastatin inhibited the oxidative stress response and inflammatory factors in the brain tissue after ICH, and increased the expression of anti-inflammatory factor IL-10. Lovastatin inhibited AMPK/mTOR signaling pathway after ICH. Our study highlighted the suppressive role of lovastatin in ICH-induced brain damage.

The hippocampus in stress susceptibility and resilience: Reviewing molecular and functional markers

Understanding the individual variability that comes with the likelihood of developing stress-related psychopathologies is of paramount importance when addressing mechanisms of their neurobiology. This article focuses on the hippocampus as a region that is highly influenced by chronic stress exposure and that has strong ties to the development of related disorders, such as depression and post-traumatic stress disorder. We first outline three commonly used animal models that have been used to separate animals into susceptible and resilient cohorts. Next, we review molecular and functional hippocampal markers of susceptibility and resilience. We propose that the hippocampus plays a crucial role in the differences in the processing and storage of stress-related information in animals with different stress susceptibilities. These hippocampal markers not only help us attain a more comprehensive understanding of the various facets of stress-related pathophysiology, but also could be targeted for the development of new treatments.

New Insights into the Pivotal Role of the Amygdala in Inflammation-Related Depression and Anxiety Disorder

Depression and anxiety disorders are the two most prevalent psychiatric diseases that affect hundreds of millions of individuals worldwide. Understanding the etiology and related mechanisms is of great importance and might yield new therapeutic strategies to treat these diseases effectively. During the past decades, a growing number of studies have pointed out the importance of the stress-induced inflammatory response in the amygdala, a kernel region for processing emotional stimuli, as a potentially critical contributor to the pathophysiology of depression and anxiety disorders. In this review, we first summarized the recent progress from both animal and human studies toward understanding the causal link between stress-induced inflammation and depression and anxiety disorders, with particular emphasis on findings showing the effect of inflammation on the functional changes in neurons in the amygdala, at levels ranging from molecular signaling, cellular function, synaptic plasticity, and the neural circuit to behavior, as well as their contributions to the pathology of inflammation-related depression and anxiety disorders. Finally, we concluded by discussing some of the difficulties surrounding the current research and propose some issues worth future study in this field.

Association between increased inflammatory cytokine expression in the lateral habenular nucleus and depressive-like behavior induced by unpredictable chronic stress in rats

Depression induced by unpredictable chronic stress (UCS) has been widely studied using animal models. However, its underlying pathological mechanisms remain unclear. Increased inflammatory cytokines (ICs) in the central nervous system (CNS) are closely related to depressive disorder. UCS was used as an animal model in this study to investigate how UCS-induced changes in cytokine signaling lead to depression. We found that UCS could increase ICs in the CNS, especially in the habenular nucleus (Hb). UCS resulted in decreased expression of Menin in Hb and increased the activation of the NF-κB signaling pathway. Local administration of tumor necrosis factor-α in the lateral Hb (LHb) could induce depressive-like behavior in rats. The anti-inflammatory drug aspirin and the NF-κB inhibitor pyrrolidine dithiocarbamate could alleviate depressive-like behavior. This phenomenon was not observed for local administration in the dorsal raphe nucleus and paraventricular nucleus. These results indicate that LHb is the main central target for ICs to regulate depressive-like behaviors. We also found that LHb lesions could improve the inflammatory response in the hippocampus, reduce the activation of the NF-κB signaling pathway and the expression of ICs, and increase the expression of brain-derived neurotrophic factor and its receptor tropomyosin receptor kinase B, collectively improving the neuroinflammation caused by UCS. Moreover, LHb lesions improve not only hippocampal neurogenesis damage caused by UCS by activating the PI3K/mTOR signaling pathway but also hippocampal function by reducing the expression of apoptosis-related proteins, including phosphorylated p53, Bax, Bcl2, and cleaved-caspase3. In conclusion, our study sheds light on the pathogenesis of ICs-induced depression. Anti-inflammation in the CNS could be a new strategy in the treatment of depression.

Increased use of ketamine for the treatment of depression: Benefits and concerns

Ketamine was initially used as an anesthetic which could induce cognitive impairment and psychomimetic effects. In initial randomized controlled trials (RCTs) that mostly included a small sample size and were investigator-initiated, ketamine reportedly exerted antidepressant effects 1 to 2 h after a single intravenous infusion in patients with major depressive episodes, particularly treatment-resistant depression (TRD). Interest in ketamine was reported in systematic reviews and meta-analyses, however, many were primarily focused on the rapid onset of ketamine effects without equal attention to its safety and tolerability. Furthermore, several meta-analyses were based on many duplicated RCTs. The initial trends emphasized the clinical utility of ketamine as an antidepressant. The development of esketamine nasal spray by a pharmaceutical company led to an RCT with a large sample size and segmented therapeutic strategy, which provided results applicable to patients with TRD in the real-world clinical environment. However, possible effects of ketamine on cognitive function have not yet been investigated in RCTs. In numerous studies, chronic, recreational use of ketamine reportedly substantially impaired cognitive function in most domains. Although results of several human and animal studies indicated the therapeutic use of ketamine for treatment of depression did not induce cognitive impairment, this issue should be further investigated. Based on the current knowledge about ketamine, future antidepressants are expected to be glutamatergic drugs without ketamine-like adverse events (e.g., psychomimetic symptoms and cognitive impairment), but having only ketamine-like therapeutic properties (e.g., rapid antidepressants effects without time lag).

Role of PPARs in Progression of Anxiety: Literature Analysis and Signaling Pathways Reconstruction

Peroxisome proliferator-activated receptor (PPAR) group includes three isoforms encoded by PPARG, PPARA, and PPARD genes. High concentrations of PPARs are found in parts of the brain linked to anxiety development, including hippocampus and amygdala. Among three PPAR isoforms, PPARG demonstrates the highest expression in CNS, where it can be found in neurons, astrocytes, and glial cells. Herein, the highest PPARG expression occurs in amygdala. However, little is known considering possible connections between PPARs and anxiety behavior. We reviewed possible connections between PPARs and anxiety. We used the Pathway Studio software (Elsevier). Signal pathways were created according to previously developed algorithms. SNEA was performed in Pathway Studio. Current study revealed 14 PPAR-regulated proteins linked to anxiety. Possible mechanism of PPAR involvement in neuroinflammation protection is proposed. Signal pathway reconstruction and reviewing aimed to reveal possible connection between PPARG and CCK-ergic system was conducted. Said analysis revealed that PPARG-dependent regulation of MME and ACE peptidase expression may affect levels of nonhydrolysed, i.e., active CCK-4. Impairments in PPARG regulation and following MME and ACE peptidase expression impairments in amygdala may be the possible mechanism leading to pathological anxiety development, with brain CCK-4 accumulation being a key link. Literature data analysis and signal pathway reconstruction and reviewing revealed two possible mechanisms of peroxisome proliferator-activated receptors involvement in pathological anxiety: (1) cytokine expression and neuroinflammation mechanism and (2) regulation of peptidases targeted to anxiety-associated neuropeptides, primarily CCK-4, mechanism.

Anti-inflammatory and antioxidant effects of muscarinic acetylcholine receptor (mAChR) activation in the rat hippocampus

Recently we found that acute treatment with Oxotremorine (Oxo), a non-selective mAChRs agonist, up-regulates heat shock proteins and activates their transcription factor heat shock factor 1 in the rat hippocampus. Here we aimed to investigate: a) if acute treatment with Oxo may regulate pro-inflammatory or anti-inflammatory cytokines and oxidative stress in the rat hippocampus; b) if chronic restraint stress (CRS) induces inflammatory or oxidative alterations in the hippocampus and whether such alterations may be affected by chronic treatment with Oxo. In the acute experiment, rats were injected with single dose of Oxo (0.4 mg/kg) and sacrificed at 24 h, 48 h and 72 h. In the CRS experiment, the rats were exposed for 21 days to the CRS and then were treated with Oxo (0.2 mg/kg) for further 10 days. The acute Oxo treatment showed an ability to significantly reduce reactive oxygen species (ROS), singlet oxygen (¹O₂), pro-inflammatory cytokines levels (IL-1β and IL-6) and phosphorylated NF-κB-p65. Acute Oxo treatment also increased superoxide dismutase (SOD)-2 protein levels and stimulated SOD activity. No differences were detected in the anti-inflammatory cytokine levels, including IL-10 and TGF-β1. In the group of rats exposed to the CRS were found increased hippocampal IL-1β and IL-6 levels, together with a reduction of SOD activity level. These changes produced by CRS were counteracted by chronic Oxo treatment. In contrast, the upregulation of ROS and ¹O₂ levels in the CRS group was not counteracted by chronic Oxo treatment. The results revealed a hippocampal anti-inflammatory and antioxidant effect of Oxo treatment in both basal conditions and anti-inflammatory in the CRS rat model.

BXD recombinant inbred strains participate in social preference, anxiety and depression behaviors along sex-differences in cytokines and tactile allodynia

Depression and anxiety are the most common psychiatric disorders, representing a major public health concern. Dysregulation of oxidative and inflammatory systems may be associated with psychiatric disorders, such as depression and anxiety. Due to the need to find appropriate animal models to the understanding of such disorders, we queried whether 2 BXD recombinant inbred (RI) mice strains (BXD21/TyJ RI and BXD84/RwwJ RI mice) and C57BL/6 wild-type mice show differential performance in depression and anxiety related behaviors and biomarkers. Specifically, we assessed social preference, elevated plus maze, forced swim, and Von Frey tests at 3-4 months-of-age, as well as activation of cytokines and antioxidant mRNA levels in the cortex at 7 months-of-age. We report that (1) the BXD84/RwwJ RI strain exhibits anxiety disorder and social avoidance-like behavior (2) BXD21/TyJ RI strain shows a resistance to depression illness, and (3) sex-dependent cytokine profiles and allodynia with elevated inflammatory activity were inherent to male BXD21/TyJ RI mice. In conclusion, we provide novel data in favor of the use of BXD recombinant inbred mice to further understand anxiety and depression disorders.