Prazosin during threat discrimination boosts memory of the safe stimulus

Astrocytes Render Memory Flexible by Releasing D-Serine and Regulating NMDA Receptor Tone in the Hippocampus

BACKGROUND

NMDA receptor (NMDAR) hypofunction has been implicated in several psychiatric disorders with impairment of cognitive flexibility. However, the molecular mechanism of how NMDAR hypofunction with decreased NMDAR tone causes the impairment of cognitive flexibility has been minimally understood. Furthermore, it has been unclear whether hippocampal astrocytes regulate NMDAR tone and cognitive flexibility.

METHODS

We employed cell type-specific genetic manipulations, ex vivo electrophysiological recordings, sniffer patch recordings, cutting-edge biosensor for norepinephrine, and behavioral assays to investigate whether astrocytes can regulate NMDAR tone by releasing D-serine and glutamate. Subsequently, we further investigated the role of NMDAR tone in heterosynaptic long-term depression, metaplasticity, and cognitive flexibility.

RESULTS

We found that hippocampal astrocytes regulate NMDAR tone via BEST1-mediated corelease of D-serine and glutamate. Best1 knockout mice exhibited reduced NMDAR tone and impairments of homosynaptic and α₁ adrenergic receptor-dependent heterosynaptic long-term depression, which leads to defects in metaplasticity and cognitive flexibility. These impairments in Best1 knockout mice can be rescued by hippocampal astrocyte-specific BEST1 expression or enhanced NMDAR tone through D-serine supplement. D-serine injection in Best1 knockout mice during initial learning rescues subsequent reversal learning.

CONCLUSIONS

These findings indicate that NMDAR tone during initial learning is important for subsequent learning, and hippocampal NMDAR tone regulated by astrocytic BEST1 is critical for heterosynaptic long-term depression, metaplasticity, and cognitive flexibility.

Theta oscillations synchronize human medial prefrontal cortex and amygdala during fear learning

Numerous animal studies have demonstrated that fear acquisition and expression rely on the coordinated activity of medial prefrontal cortex (mPFC) and amygdala and that theta oscillations support interregional communication within the fear network. However, it remains unclear whether these results can be generalized to fear learning in humans. We addressed this question using intracranial electroencephalography recordings in 13 patients with epilepsy during a fear conditioning paradigm. We observed increased power and inter-regional synchronization of amygdala and mPFC in theta (4 to 8 hertz) oscillations for conditioned stimulus (CS+) versus CS-. Analysis of information flow revealed that the dorsal mPFC (dmPFC) led amygdala activity in theta oscillations. Last, a computational model showed that trial-by-trial changes in amygdala theta oscillations predicted the model-based associability (i.e., learning rate). This study provides compelling evidence that theta oscillations within and between amygdala, ventral mPFC, and dmPFC constitute a general mechanism of fear learning across species.

Doxazosin for the treatment of nightmare disorder: A diary-based case study

The α₁-adrenergic antagonist prazosin has showed good effect against posttraumatic stress disorder–related nightmares in several randomized controlled trials. The α₁-adrenergic antagonist doxazosin, which has a longer half-live than prazosin, has received far less attention in the treatment of such nightmares. Here, we report a case of a patient suffering from severe nightmares following an erroneous medical administration of adrenaline (causing severe physiological hyper-activation) who was treated with doxazosin. Over a period of 280 days, the patient kept a nightmare diary and took 0, 4, or 8 mg doxazosin. The analyses showed that 8 mg doxazosin (55.2% nightmare-free nights) worked better (odds ratio = 28.2; 95% confidence interval = 3.7–213.9) compared to nights without doxazosin (4.3% nightmare-free nights). Except dizziness, which was not regarded as particularly bothersome by the patient, doxazosin was well tolerated. It is concluded that doxazosin may be indicated as a pharmacological treatment for patients suffering from posttraumatic stress disorder–related nightmares.

Use of Prazosin for Pediatric Post-Traumatic Stress Disorder With Nightmares and/or Sleep Disorder: Case Series of 18 Patients Prospectively Assessed

OBJECTIVES

Few studies have investigated pharmacologic treatment for pediatric post-traumatic stress disorder (PTSD). Prazosin, an alpha-1 adrenergic receptor antagonist, has been studied and demonstrated to be efficacious in an adult population for PTSD related sleep disturbances; however, in the pediatric population, data is limited to case reports and retrospective case series. This study prospectively assessed the safety and effects of Prazosin on PTSD symptoms in a pediatric sample.

METHODS

Since 2016, 18 patients with PSTD under the age of 15 admitted in a child and adolescent psychiatric unit were challenged with prazosin as part of a treatment protocol. PTSD symptoms and adverse effects were collected weekly and prospectively assessed each month with validated clinical scales. All data were retrospectively analyzed. This treatment protocol and the evaluation of clinical data were approved by our Ethical committee for research on preexisting data at the University Teaching Hospital of Rouen.

RESULTS

Among the 18 patients (10 girls and 8 boys), 13 (72%) had experienced sexual abuse and 5 (28%) family violence. After 1 month of treatment with a mean prazosin dose of 2.16 ( ± 0.6) mg/day, the CGI-S score significantly decreased from 5.3 ( ± 0.9) to 2.9 ( ± 0.7) (improvement of 43%). The mean total UCLA-PTSD-RI score significantly decreased 11.4 points ( ± 5.4) during the first week and 37.9 ( ± 16) during the first month, leading to an improvement of 20% and 67%, respectively. The improvement was significant irrespective of trauma exposure or sex. No adverse effects were reported except for one patient (hypotension).

CONCLUSION

Consistent with prior case reports and retrospective reviews, our retrospective analysis of data prospectively and systematically assessed among 18 patients suggests that prazosin is well-tolerated and associated with improvement in symptoms for pediatric PTSD.

The effect of mindfulness training on extinction retention

Anxiety and trauma related disorders are highly prevalent, causing suffering and high costs for society. Current treatment strategies, although effective, only show moderate effect-sizes when compared to adequate control groups demonstrating a need to develop new forms of treatment or optimize existing ones. In order to achieve this, an increased understanding of what mechanisms are involved is needed. An emerging literature indicates that mindfulness training (MFT) can be used to treat fear and anxiety related disorders, but the treatment mechanisms are unclear. One hypothesis, largely based on findings from neuroimaging studies, states that MFT may improve extinction retention, but this has not been demonstrated empirically. To investigate this question healthy subjects either completed a 4-week MFT- intervention delivered through a smart-phone app (n = 14) or were assigned to a waitlist (n = 15). Subsequently, subjects participated in a two-day experimental protocol using pavlovian aversive conditioning, evaluating acquisition and extinction of threat-related responses on day 1, and extinction retention on day 2. Results showed that the MFT group displayed reduced spontaneous recovery of threat related arousal responses, as compared to the waitlist control group, on day 2. MFT did not however, have an effect on either the acquisition or extinction of conditioned responses day 1. This clarifies the positive effect of MFT on emotional functioning and could have implications for the treatment of anxiety and trauma related disorders.

Acute prazosin administration does not reduce stressor reactivity in healthy adults

RATIONALE

Norepinephrine plays a critical role in the stress response. Clarifying the psychopharmacological effects of norepinephrine manipulation on stress reactivity in humans has important implications for basic neuroscience and treatment of stress-related psychiatric disorders, such as posttraumatic stress disorder and alcohol use disorders. Preclinical research implicates the norepinephrine alpha-1 receptor in responses to stressors. The No Shock, Predictable Shock, Unpredictable Shock (NPU) task is a human laboratory paradigm that is well positioned to test cross-species neurobiological stress mechanisms and advance experimental therapeutic approaches to clinical trials testing novel treatments for psychiatric disorders.

OBJECTIVES

We hypothesized that acute administration of prazosin, a noradrenergic alpha-1 antagonist, would have a larger effect on reducing stress reactivity during unpredictable, compared to predictable, stressors in the NPU task.

METHODS

We conducted a double-blind, placebo-controlled, crossover randomized controlled trial in which 64 healthy adults (32 female) completed the NPU task at two visits (2 mg prazosin vs. placebo).

RESULTS

A single acute dose of 2 mg prazosin did not reduce stress reactivity in a healthy adult sample. Neither NPU startle potentiation nor self-reported anxiety was reduced by prazosin (vs. placebo) during unpredictable (vs. predictable) stressors.

CONCLUSIONS

Further research is needed to determine whether this failure to translate preclinical neuroscience to human laboratory models is due to methodological factors (e.g., acute vs. chronic drug administration, brain penetration, study population) and/or suggests limited clinical utility of noradrenergic alpha-1 antagonists for treating stress-related psychiatric disorders.

Post-retrieval oxytocin facilitates next day extinction of threat memory in humans

RATIONALE

Memories can return to a labile state and become amenable to modification by pharmacological and behavioral manipulations after retrieval. This process may reduce the impact of aversive memories and provide a promising therapeutic technique for the treatment of anxiety disorders. A growing body of evidence suggests that the mammalian neuropeptide oxytocin (OT) plays a role in the regulation of emotional memories in animals. However, the effects of OT on threat memory in humans remain largely unknown.

OBJECTIVES

This study aimed to investigate the effects of OT administration following threat memory retrieval on subsequent memory expression in human participants.

METHODS

In a double-blind, randomized, placebo-controlled, between-subject design, 61 healthy human individuals completed a 3-day experiment. All the participants underwent threat conditioning on day 1. On day 2, the participants were randomized to receive an intranasal dose of OT (40 IU) or placebo after memory retrieval, or an intranasal dose of OT (40 IU) without retrieval. On day 3, the participants were tested for extinction and reinstatement.

RESULTS

On day 3, all groups showed equivalent stimulus discrimination during the early phase of extinction. However, the group that received OT following a memory reminder showed a greater decline in stimulus discrimination by the late phase of extinction relative to the two other groups.

CONCLUSIONS

The results indicate that OT did not block reconsolidation to prevent the return of threat memory but rather interacted with post-retrieval processes to facilitate next day extinction. The study provides novel preliminary evidence for the role of OT in human threat memory.

Prazosin during fear conditioning facilitates subsequent extinction in male C57Bl/6N mice

RATIONALE

Recovery from a traumatic experience requires extinction of cue-based fear responses, a process that is impaired in post-traumatic stress disorder. While studies suggest a link between fear behavioral flexibility and noradrenaline signaling, the role of specific receptors and brain regions in these effects is unclear.

OBJECTIVES

Here, we examine the role of prazosin, an α1-adrenergic receptor (α1-AR) antagonist, in auditory fear conditioning and extinction.

METHODS

C57Bl/6N mice were subjected to auditory fear conditioning and extinction in combination with systemic (0.1-2 mg/kg) or local microinjections (3 or 6 mM) of the α1-AR antagonist prazosin into the prelimbic division of medial prefrontal cortex or basolateral amygdala. Conditioned fear and anxiety-like behaviors were compared with vehicle-injected control animals.

RESULTS

Mice that received systemic prazosin prior to fear conditioning exhibited similar initial levels of cue-elicited freezing compared to vehicle controls on the following day. However, at all doses tested, fear that was acquired during prazosin treatment was more readily extinguished, whereas anxiety-like behavior on the day of extinction was unaffected. A similar pattern of results was observed when prazosin was microinjected into the basolateral amygdala but not the prelimbic cortex. In contrast to pre-conditioning injections, prazosin administration prior to extinction had no effect on freezing.

CONCLUSIONS

Our results indicate that α1-AR activity during aversive conditioning is dispensable for memory acquisition but renders conditioned fear more impervious to extinction. This suggests that behavioral flexibility is constrained by noradrenaline at the time of initial learning via activation of a specific AR isoform.

Noradrenergic Modulation of Fear Conditioning and Extinction

The locus coeruleus norepinephrine (LC-NE) system plays a broad role in learning and memory. Here we begin with an overview of the LC-NE system. We then consider how both direct and indirect manipulations of the LC-NE system affect cued and contextual aversive learning and memory. We propose that NE dynamically modulates Pavlovian conditioning and extinction, either promoting or impairing learning aversive processes under different levels of behavioral arousal. We suggest that under high levels of stress (e.g., during/soon after fear conditioning) the locus coeruleus (LC) promotes cued fear learning by enhancing amygdala function while simultaneously blunting prefrontal function. Under low levels of arousal, the LC promotes PFC function to promote downstream inhibition of the amygdala and foster the extinction of cued fear. Thus, LC-NE action on the medial prefrontal cortex (mPFC) might be described by an inverted-U function such that it can either enhance or hinder learning depending on arousal states. In addition, LC-NE seems to be particularly important for the acquisition, consolidation and extinction of contextual fear memories. This may be due to dense adrenoceptor expression in the hippocampus (HPC) which encodes contextual information, and the ability of NE to regulate long-term potentiation (LTP). Moreover, recent work reveals that the diversity of LC-NE functions in aversive learning and memory are mediated by functionally heterogeneous populations of LC neurons that are defined by their projection targets. Hence, LC-NE function in learning and memory is determined by projection-specific neuromodulation that accompanies various states of behavioral arousal.