GABAergic modulation with classical benzodiazepines prevent stress-induced neuro-immune dysregulation and behavioral alterations

Abstract

Objective Psychosocial stress is associated with altered immunity, anxiety, and depression. Repeated social defeat (RSD), a model of social stress, triggers egress of inflammatory myeloid progenitor cells (MPCs; CD11b+ /Ly6Chi) that traffic to the brain, promoting anxiety-like behavior. In parallel, RSD enhances neuroinflammatory signaling and long-lasting social avoidant behavior. Lorazepam and clonazepam are routinely prescribed anxiolytics that act by enhancing GABAergic activity in the brain. Besides binding to the central benzodiazepine binding site (CBBS) in the central nervous system (CNS), lorazepam binds to the translocator protein (TSPO) with high affinity causing immunomodulation. Clonazepam targets the CBBS and has low affinity for the TSPO. Here the aims were to determine if lorazepam and clonazepam would: 1) prevent stress-induced peripheral and central inflammatory responses, and 2) block anxiety and social avoidance behavior in mice subjected to RSD. Methods C57/BL6 mice were divided into experimental groups, and treated with either lorazepam (0.10mg/kg), clonazepam (0.25 mg/kg) or vehicle (0.9%NaCl). Behavioral data and tissues were collected the morning after the last cycle of RSD. Results Lorazepam and clonazepam were effective in attenuating mRNA expression of CRH in the hypothalamus and corticosterone in plasma in mice subjected to RSD. Both drugs blocked stress-induced levels of IL-6 in plasma. Lorazepam and clonazepam had different effects on stress-induced enhancement of myelopoiesis and inhibited trafficking of monocytes and granulocytes in circulation. Furthermore, lorazepam, but not clonazepam, inhibited splenomegaly and the production of pro-inflammatory cytokines in the spleen following RSD. Additionally, lorazepam and clonazepam, blocked stress-induced accumulation of macrophages (CD11b+/CD45high) in the CNS. In a similar manner, both lorazepam and clonazepam prevented neuroinflammatory signaling and reversed anxiety-like and depressive-like behavior in mice exposed to RSD. Conclusion These data support the notion that lorazepam and clonazepam, aside from exerting anxiolytic and antidepressant effects, may have therapeutic potential as neuroimmunomodulators during psychosocial stress. The reversal of RSD-induced behavioral outcomes may be due to the enhancement of GABAergic neurotransmission, or some other off-target effect. The peripheral actions of lorazepam, but not clonazepam, seem to be mediated by TSPO activation.

Stress-Induced Microglia Activation and Monocyte Trafficking to the Brain Underlie the Development of Anxiety and Depression

“…Pretreatment with propranolol in mice subjected to RSD, and the use of IL-1 receptor type-1 knockout (IL-1R KO) mice in the RSD model, inhibited stress-associated increase in serum IL-6 comparable to home caged controls [42]. In the same manner, treatment with antidepressant imipramine and benzodiazepines, lorazepam and clonazepam, significantly attenuated corticosterone and norepinephrine levels in plasma of mice subjected to RSD and decreased levels of IL-6 in plasma after six cycles of stress compared to home cage controls ( [17]; unpublished data from Sheridan et al). These data generated in different studies suggest that the production of IL-6 might also be from another cellular source different from peripheral immune cells.…”

“…Administered cytokines stimulate the expression and release of corticotrophin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), and cortisol, all of which are altered in depressed patients [2]. Likely, mice exposed to RSD have increased levels of pro-inflammatory cytokines in plasma, paralleled with an increased mRNA expression of CRH in the hypothalamus (HYPO), high blood levels of ACTH, and corticosterone in plasma [17,31].…”

“…Some clinically relevant murine models include repeated social defeat (RSD) [3,8], inescapable tail-shock [9,12], restraint stress [10,11], and chronic unpredictable stress or chronic mild stress [13][14][15][16]. RSD, a model of psychosocial stress in mice, provides a valuable and predictable probe to study the mechanisms leading to stress-related alterations in inflammation in both the periphery and CNS [17]. These inflammatory responses are frequently associated with anxiety-and depressive-like behaviors [7,18,19].…”

“…Analysis of peripheral inflammatory markers in the blood of patients with mood disorders reveals elevated levels of interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) levels [24][25][26][27][28]. In rodents, RSD causes an increase in pro-inflammatory molecules released into circulation [17]. Specifically, RSD causes an increase of IL-6, TNF-α, keratinocyte chemoattractant, macrophage inflammatory protein-2 (CCL8/MCP-2), and monocyte chemoattractant protein-1 (CCL2/MCP-1) [3].…”

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“…We explored this in each study mentioned within the paper and found significant variability in washout period use and duration, concomitant anxiolytic and mood stabiliser use. These factors may further contribute to the possibility of artefacts given their potential effects on the immune system (for review see [76,77]). …”