Administration of riluzole to the basolateral amygdala facilitates fear extinction in rats

Update on neurobiological mechanisms of fear: illuminating the direction of mechanism exploration and treatment development of trauma and fear-related disorders

Fear refers to an adaptive response in the face of danger, and the formed fear memory acts as a warning when the individual faces a dangerous situation again, which is of great significance to the survival of humans and animals. Excessive fear response caused by abnormal fear memory can lead to neuropsychiatric disorders. Fear memory has been studied for a long time, which is of a certain guiding effect on the treatment of fear-related disorders. With continuous technological innovations, the study of fear has gradually shifted from the level of brain regions to deeper neural (micro) circuits between brain regions and even within single brain regions, as well as molecular mechanisms. This article briefly outlines the basic knowledge of fear memory and reviews the neurobiological mechanisms of fear extinction and relapse, which aims to provide new insights for future basic research on fear emotions and new ideas for treating trauma and fear-related disorders.

Randomized Controlled Trial of Riluzole Augmentation for Posttraumatic Stress Disorder: Efficacy of a Glutamatergic Modulator for Antidepressant-Resistant Symptoms

OBJECTIVE

Current pharmacologic treatments for posttraumatic stress disorder (PTSD) have shown limited efficacy, prompting a call to investigate new classes of medications. The current study investigated the efficacy of glutamate modulation with riluzole augmentation for combat-related PTSD symptoms resistant to treatment with selective serotonin reuptake inhibitors (SSRIs) or serotonin-norepinephrine reuptake inhibitors (SNRIs).

METHODS

A randomized, double-blind, placebo-controlled, parallel trial was conducted at Walter Reed National Military Medical Center and Syracuse VA Medical Center between December 2013 and November 2017. Veterans and active duty service members with combat-related PTSD (per the Clinician Administered PTSD Scale [CAPS]) who were not responsive to SSRI or SNRI pharmacotherapy were randomized to 8-week augmentation with a starting dose of 100 mg/d of riluzole (n = 36) or placebo (n = 38) and assessed weekly for PTSD symptoms, anxiety, depression, disability, and side effects.

RESULTS

Intent-to-treat analyses (N = 74) of the primary outcome (CAPS for DSM-IV) showed no significant between-group difference in change in overall PTSD symptoms (F = 0.64, P = .422), with a small effect size (d = 0.25). There was clinically significant within-group improvement in overall PTSD symptoms in both groups, with a greater mean (SD) decrease in CAPS score in the riluzole group (-21.1 [18.9]) than in the placebo group (-16.7 [17.2]). Exploratory analyses of PTSD symptom clusters showed significantly greater improvement on hyperarousal symptoms in the riluzole group as measured by the PTSD Checklist-Specific-Subscale D (d = 0.48) and near-significant findings on the CAPS Subscale D. Riluzole augmentation was not superior to placebo on change in depression, anxiety, or disability severity.

CONCLUSIONS

Although preliminary, the exploratory findings of this study offer some evidence that riluzole augmentation of an SSRI or SNRI may selectively improve PTSD hyperarousal symptoms without changes in overall PTSD symptoms, depression, anxiety, or disability. Additional investigation of the mechanism of the efficacy of riluzole for hyperarousal symptoms is warranted.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02155829.

Riluzole Exhibits No Therapeutic Efficacy on a Transgenic Rat model of Amyotrophic Lateral Sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a neurological disorder clinically characterized by motor system dysfunction, with intraneuronal accumulation of the TAR DNAbinding protein 43 (TDP-43) being a pathological hallmark. Riluzole is a primarily prescribed medicine for ALS patients, while its therapeutical efficacy appears limited. TDP-43 transgenic mice are existing animal models for mechanistic/translational research into ALS.

METHODS

We developed a transgenic rat model of ALS expressing a mutant human TDP-43 transgene (TDP-43M337V) and evaluated the therapeutic effect of Riluzole on this model. Relative to control, rats with TDP-43M337V expression promoted by the neurofilament heavy subunit (NEF) gene or specifically in motor neurons promoted by the choline acetyltransferase (ChAT) gene showed progressive worsening of mobility and grip strength, along with loss of motor neurons, microglial activation, and intraneuronal accumulation of TDP-43 and ubiquitin aggregations in the spinal cord.

RESULTS

Compared to vehicle control, intragastric administration of Riluzole (30 mg/kg/d) did not mitigate the behavioral deficits nor alter the neuropathologies in the transgenics.

CONCLUSION

These findings indicate that transgenic rats recapitulate the basic neurological and neuropathological characteristics of human ALS, while Riluzole treatment can not halt the development of the behavioral and histopathological phenotypes in this new transgenic rodent model of ALS.

Cognitive and hippocampal synaptic profiles in monosodium glutamate-induced obese mice

Obesity is a growing worldwide public health issue and is associated with a range of comorbidities, including cognitive deficits. The present study investigated synaptic changes in the hippocampus during the development of obesity. The treatment of newborn mice with monosodium-L-glutamate (MSG, 2 mg/g) induced obesity and recognition memory deficits in the novel object recognition (NOR) test at 16-17 weeks, but not at 8-9 weeks. Hippocampal synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD), and excitatory synaptic transmission at Schaffer collateral-CA1 (SC-CA1) synapses were compared between MSG-treated mice and age-matched control mice. LTP and fiber volley amplitudes were enhanced in MSG-treated mice at 16-17 weeks, but not at 8-9 weeks. Furthermore, the strength of paired-pulse facilitation (PPF) changed in MSG-treated mice at 16-17 weeks, but not at 8-9 weeks. These results suggest that enhanced LTP in the SC-CA1 synapses of MSG-induced obese mice involves presynaptic rather than postsynaptic mechanisms.

Novel pharmacological treatments for generalized anxiety disorder: Pediatric considerations

BACKGROUND

Pediatric anxiety disorders such as generalized anxiety disorder (GAD) are common, impairing, and often undertreated. Moreover, many youth do not respond to standard, evidence-based psychosocial or psychopharmacologic treatment. An increased understanding of the gamma-aminobutyric acid (GABA) and glutamate neurotransmitter systems has created opportunities for novel intervention development for pediatric GAD.

METHODS

This narrative review examines potential candidates for pediatric GAD: eszopiclone, riluzole, eglumegad (LY354740), pimavanserin, agomelatine.

RESULTS

The pharmacology, preclinical data, clinical trial findings and known side effects of eszopiclone, riluzole, eglumegad (LY354740), pimavanserin, agomelatine, are reviewed, particularly with regard to their potential therapeutic relevance to pediatric GAD.

CONCLUSION

Notwithstanding numerous challenges, some of these agents represent potential candidate drugs for pediatric GAD. Further treatment development studies of agomelatine, eszopiclone, pimavanserin and riluzole for pediatric GAD also have the prospect of informing the understanding of GABAergic and glutamatergic function across development.

Brain and Cognition for Addiction Medicine: From Prevention to Recovery Neural Substrates for Treatment of Psychostimulant-Induced Cognitive Deficits

Addiction to psychostimulants like cocaine, methamphetamine, and nicotine poses a continuing medical and social challenge both in the United States and all over the world. Despite a desire to quit drug use, return to drug use after a period of abstinence is a common problem among individuals dependent on psychostimulants. Recovery for psychostimulant drug-dependent individuals is particularly challenging because psychostimulant drugs induce significant changes in brain regions associated with cognitive functions leading to cognitive deficits. These cognitive deficits include impairments in learning/memory, poor decision making, and impaired control of behavioral output. Importantly, these drug-induced cognitive deficits often impact adherence to addiction treatment programs and predispose abstinent addicts to drug use relapse. Additionally, these cognitive deficits impact effective social and professional rehabilitation of abstinent addicts. The goal of this paper is to review neural substrates based on animal studies that could be pharmacologically targeted to reverse psychostimulant-induced cognitive deficits such as impulsivity and impairment in learning and memory. Further, the review will discuss neural substrates that could be used to facilitate extinction learning and thus reduce emotional and behavioral responses to drug-associated cues. Moreover, the review will discuss some non-pharmacological approaches that could be used either alone or in combination with pharmacological compounds to treat the above-mentioned cognitive deficits. Psychostimulant addiction treatment, which includes treatment for cognitive deficits, will help promote abstinence and allow for better rehabilitation and integration of abstinent individuals into society.

N-Methyl D-aspartate receptor subunit signaling in fear extinction

N-Methyl D-aspartate receptors (NMDAR) are central mediators of glutamate actions underlying learning and memory processes including those required for extinction of fear and fear-related behaviors. Consistent with this view, in animal models, antagonists of NMDAR typically impair fear extinction, whereas partial agonists have facilitating effects. Promoting NMDAR function has thus been recognized as a promising strategy towards reduction of fear symptoms in patients suffering from anxiety disorders and post-traumatic disorder (PTSD). Nevertheless, application of these drugs in clinical trials has proved of limited utility. Here we summarize recent advances in our knowledge of NMDAR pharmacology relevant for fear extinction, focusing on molecular, cellular, and circuit aspects of NMDAR function as they relate to fear extinction at the level of behavior and cognition. We also discuss how these advances from animal models might help to understand and overcome the limitations of existing approaches in human anxiety disorders and how novel, more specific, and personalized approaches might help advance future therapeutic strategies.

Administration of a delta opioid receptor agonist KNT-127 to the basolateral amygdala has robust anxiolytic-like effects in rats

RATIONALE

We previously reported that systemic administration of a selective delta opioid receptor (DOP) agonist, KNT-127, produced potent anxiolytic-like effects in rats. Interestingly, DOPs are highly distributed in the basolateral region of the amygdala (BLA).

OBJECTIVES

In this study, we investigated the effect of intra-BLA administration of KNT-127 on anxiety-like behaviors in rats.

METHODS AND RESULTS

In the elevated plus maze test, bilateral injection of KNT-127 into the BLA significantly and dose-dependently increased time spent in the open arms. The magnitude of KNT-127 (0.08 μg/0.2 μl)-induced anxiolytic-like effects was similar to muscimol (0.1 μg/0.2 μl), which is a selective agonist for the gamma amino butyric acid type A receptors. Further, anxiolytic-like effects of KNT-127 were abolished by pretreatment with naltrindole, a selective DOP antagonist, suggesting that KNT-127-induced anxiolytic-like effects are mediated by DOPs. These anxiolytic-like effects were confirmed using another innate anxiety model, the open field test. Interestingly, intra-BLA administration of KNT-127 also induced anxiolytic-like effects in the contextual fear conditioning test. Moreover, these effects were also abolished by naltrindole pretreatment. Finally, we demonstrated that intra-BLA administration of KNT-127 facilitates extinction learning of contextual fear in conditioned rats.

CONCLUSIONS

Altogether, our findings clearly demonstrate that intra-BLA administration of KNT-127 in rats has robust anxiolytic-like effects not only in innate anxiety-like behavioral tests but also in the contextual fear conditioning test.

Post-reexposure administration of riluzole attenuates the reconsolidation of conditioned fear memory in rats

Recently, we demonstrated that riluzole, which has been shown to block the glutamatergic system, facilitates fear extinction in rats. Here, we undertook experiments on contextual fear conditioning to clarify the actions of riluzole on the reconsolidation of fear memory in rats. We used the fast-acting benzodiazepine midazolam as a reconsolidation-inhibiting control drug. We demonstrated that riluzole (3 mg/kg) and midazolam (1 mg/kg) impaired the reconsolidation of contextual fear memory. Results from spontaneous recovery experiments also suggested that riluzole attenuated reconsolidation. Indeed, conditioned fear did not recover spontaneously 4 weeks after a short (3 min) reexposure and riluzole administration, whereas it recovered after a long (10 min) reexposure. Using western blotting, we demonstrated that a short reexposure increased the phosphorylation of cyclic adenosine monophosphate response element binding protein significantly in the dorsal part of hippocampus, but not in the medial prefrontal cortex. Interestingly, this phosphorylation was attenuated by riluzole with short reexposure. In addition, bilateral microinjection of riluzole (2 μM/0.2 μl/side) directly into the dorsal hippocampus clearly attenuated the reconsolidation. These findings suggested that the attenuating effect of riluzole on the reconsolidation of fear memory involves, at least in part, the dorsal part of the hippocampus. In conclusion, we demonstrated that riluzole attenuates the reconsolidation of fear memory in rats.