Amygdaloid zif268 participated in the D-cycloserine facilitation effect on the extinction of conditioned fear

Dual-step pharmacological intervention for traumatic-like memories: implications from D-cycloserine and cannabidiol or clonidine in male and female rats

RATIONALE

Therapeutic approaches to mitigating traumatic memories have often faced resistance. Exploring safe reconsolidation blockers, drugs capable of reducing the emotional valence of the memory upon brief retrieval and reactivation, emerges as a promising pharmacological strategy. Towards this objective, preclinical investigations should focus on aversive memories resulting in maladaptive outcomes and consider sex-related differences to enhance their translatability.

OBJECTIVES

After selecting a relatively high training magnitude leading to the formation of a more intense and generalized fear memory in adult female and male rats, we investigated whether two clinically approved drugs disrupting its reconsolidation remain effective.

RESULTS

We found resistant reconsolidation impairment by the α2-adrenergic receptor agonist clonidine or cannabidiol, a major non-psychotomimetic Cannabis sativa component. However, pre-retrieval administration of D-cycloserine, a partial agonist at the glycine-binding site of the N-methyl-D-aspartate (NMDA) receptor complex, facilitated their impairing effects on reconsolidation. A similar reconsolidation blockade by clonidine or cannabidiol was achieved following exposure to a non-conditioned but generalized context after D-cycloserine administration. This suggests that sufficient memory destabilization can accompany generalized fear expression. Combining clonidine with cannabidiol without potentiating memory destabilization by D-cycloserine was ineffective.

CONCLUSIONS

These findings highlight the importance of NMDA receptor signaling in memory destabilization and underscore the efficacy of a dual-step pharmacological intervention in attenuating traumatic-like memories, even in a context different from the original learning environment.

A randomized pharmacological fMRI trial investigating D-cycloserine and brain plasticity mechanisms in learned pain responses

Learning and negative outcome expectations can increase pain sensitivity, a phenomenon known as nocebo hyperalgesia. Here, we examined how a targeted pharmacological manipulation of learning would impact nocebo responses and their brain correlates. Participants received either a placebo (n = 27) or a single 80 mg dose of D-cycloserine (a partial NMDA receptor agonist; n = 23) and underwent fMRI. Behavioral conditioning and negative suggestions were used to induce nocebo responses. Participants underwent pre-conditioning outside the scanner. During scanning, we first delivered baseline pain stimulations, followed by nocebo acquisition and extinction phases. During acquisition, high intensity thermal pain was paired with supposed activation of sham electrical stimuli (nocebo trials), whereas moderate pain was administered with inactive electrical stimulation (control trials). Nocebo hyperalgesia was induced in both groups (p < 0.001). Nocebo magnitudes and brain activations did not show significant differences between D-cycloserine and placebo. In acquisition and extinction, there were significantly increased activations bilaterally in the amygdala, ACC, and insula, during nocebo compared to control trials. Nocebo acquisition trials also showed increased vlPFC activation. Increased opercular activation differentiated nocebo-augmented pain aggravation from baseline pain. These results support the involvement of integrative cognitive-emotional processes in nocebo hyperalgesia.

The role of the basolateral amygdala and infralimbic cortex in (re)learning extinction

The basolateral amygdala complex (BLA) and infralimbic region of the prefrontal cortex (IL) play distinct roles in the extinction of Pavlovian conditioned fear in laboratory rodents. In the past decade, research in our laboratory has examined the roles of these brain regions in the re-extinction of conditioned fear: i.e., extinction of fear that is restored through re-conditioning of the conditioned stimulus (CS) or changes in the physical and temporal context of extinction training (i.e., extinction of renewed or spontaneously recovered fear). This paper reviews this research. It has revealed two major findings. First, in contrast to the acquisition of fear extinction, which usually requires neuronal activity in the BLA but not IL, the acquisition of fear re-extinction requires neuronal activity in the IL but can occur independently of neuronal activity in the BLA. Second, the role of the IL in fear extinction is determined by the training history of the CS: i.e., if the CS was novel prior to its fear conditioning (i.e., it had not been trained), the acquisition of fear extinction does not require the IL; if, however, the prior training of the CS included a series of CS-alone exposures (e.g., if the CS had been pre-exposed), the acquisition of fear extinction was facilitated by pharmacological stimulation of the IL. Together, these results were taken to imply that a memory of CS-alone exposures is stored in the IL, survives fear conditioning of the CS, and can be retrieved and strengthened during extinction or re-extinction of that CS (regardless of whether the extinction is first- or second-learned). Hence, under these circumstances, the initial extinction of fear to the CS can be facilitated by pharmacological stimulation of the IL, and re-extinction of fear to the CS can occur in the absence of a functioning BLA.

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.

Transcriptional Regulation Involved in Fear Memory Reconsolidation

Memory reconsolidation has been demonstrated to offer a potential target period during which the fear memories underlying fear disorders can be disrupted. Reconsolidation is a labile stage that consolidated memories re-enter after memories are reactivated. Reactivated memories, induced by cues related to traumatic events, are susceptible to strengthening and weakening. Gene transcription regulation and protein synthesis have been suggested to be required for fear memory reconsolidation. Investigating the transcriptional regulation mechanisms underlying reconsolidation may provide a therapeutic method for the treatment of fear disorders such as post-traumatic stress disorder (PTSD). However, the therapeutic effect of treating a fear disorder through interfering with reconsolidation is still contradictory. In this review, we summarize several transcription factors that have been linked to fear memory reconsolidation and propose that transcription factors, as well as related signaling pathways can serve as targets for fear memory interventions. Then, we discuss the application of pharmacological and behavioral interventions during reconsolidation that may or not efficiently treat fear disorders.