Research report
Mirogabalin prevents repeated restraint stress-induced dysfunction in mice

https://doi.org/10.1016/j.bbr.2020.112506Get rights and content

Highlights

  • Mirogabalin is a recently launched ligand of the α2δ subunit of voltage-dependent calcium channels.

  • Mirogabalin prevents anxiety-like behavior and memory impairment induced by repeated restraint stress.

  • Mirogabalin prevents abnormal defecation induced by single and repeated restraint stress.

  • Mirogabalin directly inhibits restraint stress-induced hyperactivity in hippocampal neurons.

Abstract

Gabapentinoids, which are the common analgesics, are also thought to be an effective treatment for anxiety disorder, which is one of several psychiatric disorders triggered and exacerbated by stress. The aim of the present study was to investigate whether mirogabalin, a recently launched gabapentinoid, protects multiple brain functions against repeated restraint stress. Adult male ddY mice were restrained for 7 days (repeated restraint stress: 2 h/day) or for 30 min (single restraint stress). Mirogabalin (intraperitoneal, intracerebroventricular or intrahippocampal injection) was administered prior to the restraint stress. Y-maze, elevated-plus maze and c-Fos immunohistochemistry were performed to evaluate learning function, anxiety levels and hippocampal neuronal activities, respectively, after the 7th day of the repeated restraint stress. Intestinal function was evaluated in terms of defecation, which was scored after the 5th day of repeated restraint stress and by the number of fecal pellets excreted after a single session of restraint stress.

Repeated restraint stress induced memory dysfunction, anxiety-like behavior, an abnormal defecation score and increased hippocampal c-Fos expression. These changes were prevented by systemic administration of mirogabalin. Abnormal defecation was also induced by single restraint stress, and was inhibited by both systemic and central administration of mirogabalin, suggesting that the effect on the intestinal function was also mediated via the central nervous system. Enhancement of c-Fos expression by repeated stress was decreased by intrahippocampal injection of mirogabalin. Together, these observations suggest that mirogabalin protects multiple brain functions from repeated stress, which may be mediated by inhibition of hippocampal neuron hyperactivation.

Introduction

Chronic psychological stress contributes to mental and physical illnesses such as generalized anxiety disorders, major depressive disorder and irritable bowel syndrome [[1], [2], [3]]. The restraint stress protocol is a psychological stress model widely used in rodents, and produces significant stress responses without causing physical injury to the animal. The restraint stress model has been used to investigate the neurobiological, behavioral, and clinical aspects of stress in the development and expression of numerous disorders [[4], [5], [6], [7]]. Repeated restraint stress induces anxiety-like behavior, memory impairment [[8], [9], [10], [11]], anxiety-like behavior [[12], [13], [14]] and visceral sensitivity [15,16]. Acute and chronic restraint stress increases c-Fos expression, a marker of neuronal activity, in the hippocampus [[17], [18], [19]]. Chronic treatment with diazepam and imipramine reduces stress-induced c-Fos expression in the hippocampus [20], and deficient c-Fos expression in the hippocampus results in lower anxiety and faster habituation to stress in female mice [21], indicating that excessive hippocampal activity plays a role in stress responses.

Gabapentinoids, such as pregabalin and gabapentin, are anticonvulsants and analgesics used to treat neuropathic pain and partial seizure disorders. They are structurally related to the inhibitory neurotransmitter GABA. However, a series of experiments have shown that gabapentinoids have high affinity and selectivity for the α2δ subunit of voltage-dependent calcium channels in the peripheral and central nervous system (CNS) [22,23]. The predominant mechanism of action of gabapentinoids is considered to be inhibition of neurotransmitter release, including GABA [24], glutamate [25] and neuropeptides [26], at the presynaptic endings of neurons.

Gabapentinoids are also used for treatment of generalized anxiety disorder, and exert anxiolytic-like effects in normal and stressed (predator odor, tumor cells inoculation or ethanol-treated) rodents during the elevated-plus maze test [[27], [28], [29]]. In addition, clinical and animal studies have suggested that pregabalin may be beneficial for treatment of abdominal pain, bloating and diarrhea related to irritable bowel syndrome (IBS) [[30], [31], [32]]. Thus, gabapentinoids may also be effective for a wide range of psychiatric disorders. However, their effects on the abnormal symptoms induced by chronic psychological stress have not been fully investigated.

Mirogabalin is a novel gabapentinoid that has been recently launched for treatment of peripheral neuropathic pain including diabetic peripheral neuropathy and postherpetic neuralgia. Mirogabalin shows selective binding affinities and slower dissociation rates for the α2δ-1 subunit than the α2δ-2 subunit, and produces longer lasting analgesic effects at lower doses than pregabalin in animal models of neuropathic pain [33]. In the present study, we investigated (1) the effects of mirogabalin and pregabalin on repeated restraint stress-induced memory impairment, anxiety-like behavior and abnormal defecation in mice, (2) the effect of mirogabalin on the abnormal defecation induced by single restraint stress and its mediation of the central nervous system, and (3) the effect of the systemic and intrahippocampal administration of mirogabalin on c-Fos expression induced by repeated restraint stress.

Section snippets

Animals

All experiments were approved by the Institutional Animal Care and Use Committee of Kitasato University, and were carried out in accordance with the guidelines of the National Institutes of Health and the Japanese Pharmacological Society. Five- to 6-week-old male ddY mice (Japan SLC, Shizuoka, Japan) were kept in a controlled environment with controlled lighting (12 h light/dark cycle, lights on from 08:00 to 20:00) and temperature (23 ± 1 °C), and given free access to food and water. The ddY

Mirogabalin prevents anxiety-like behavior induced by repeated restraint stress

The time spent on the open-arms in the elevated-plus maze was measured to evaluate anxiety-like behavior after exposure to repeated restraint stress (Experiment 1: Fig. 2, and Supplementary Fig. 1). Repeated restraint stress decreased the time spent on the open arms, indicating an increase of anxiety-like behavior. Mirogabalin (30 mg/kg, Fig. 2A) and pregabalin (60 mg/kg, Supplementary Fig. 1) significantly and dose-dependently increased the time spent on the open-arms. When compared to the

Discussion

In the present study, we investigated the effects of mirogabalin on dysfunction resulting from repeated restraint stress, and demonstrated that mirogabalin as well as pregabalin prevented the induction of anxiety-like behavior, memory impairment and intestinal hyperactivity. Mirogabalin was more effective at lower doses than pregabalin, consistent with the former’s lower Kd value for the α2δ subunit [33]. Thus, gabapentinoids prevented chronic stress-induced dysfunctions via a mechanism

CRediT authorship contribution statement

Takashi Iwai: Conceptualization, Methodology, Writing - original draft. Akinori Kikuchi: Investigation. Misa Oyama: Validation. Shun Watanabe: Validation. Mitsuo Tanabe: Project administration, Funding acquisition, Writing - review & editing.

Declaration of Competing Interest

This study was funded by Daiichi Sankyo, Co., Ltd (Tokyo, Japan).

Acknowledgement

This study was supported by Daiichi Sankyo, Co., Ltd (Tokyo, Japan).

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