Harmine impairs memory performance of treated rats and nontreated cagemates

Ayahuasca-enhanced extinction of fear behaviour: Role of infralimbic cortex 5-HT2A and 5-HT1A receptors

BACKGROUND AND PURPOSE

Ayahuasca (AYA) is a botanical psychedelic with promising results in observational and small clinical trials for depression, trauma and drug use disorders. Its psychoactive effects primarily stem from N,N-dimethyltryptamine (DMT). However, there is a lack of research on how and where AYA acts in the brain. This study addressed these questions by examining the extinction of aversive memories in AYA-treated rats.

EXPERIMENTAL APPROACH

We focused on the 5-HT1A and 5-HT2A receptors, as DMT exhibits a high affinity for both of them, along with the infralimbic cortex in which activity and plasticity play crucial roles in regulating the mnemonic process under analysis.

KEY RESULTS

A single oral treatment with AYA containing 0.3 mg·kg-1 of DMT increased the within-session extinction of contextual freezing behaviour without affecting its recall. This protocol, when repeated twice on consecutive days, enhanced extinction recall. These effects were consistent for both 1- and 21-day-old memories in males and females. AYA effects on fear extinction were independent of changes in anxiety and general exploratory activity: AYA- and vehicle-treated animals showed no differences when tested in the elevated plus-maze. The 5-HT2A receptor antagonist MDL-11,939 and the 5-HT1A receptor antagonist WAY-100635 infused into the infralimbic cortex respectively blocked within- and between-session fear extinction effects resulting from repeated oral administration of AYA.

CONCLUSION AND IMPLICATIONS

Our findings highlight complementary mechanisms by which AYA facilitates the behavioural suppression of aversive memories in the rat infralimbic cortex. These results suggest potential beneficial effects of AYA or DMT in stress-related disorders.

Evidence on the impairing effects of Ayahuasca on fear memory reconsolidation

RATIONALE

To uncover whether psychedelic drugs attenuate fear memory responses would advance the development of better psychedelic-based treatments for posttraumatic stress disorder (PTSD). Ayahuasca (AYA), a psychedelic brew containing indolamine N, N-dimethyltryptamine (DMT) and β-carbolines, facilitates fear extinction and improves neural plasticity. Upon retrieval, fear memory undergoes labilization and reconsolidation; however, the effects of AYA on this memory stabilization phase are unknown.

OBJECTIVES

We aimed to investigate the effects of AYA treatment on fear memory reconsolidation.

METHODS

Fear-conditioned Wistar rats received AYA (60, 120, or 240 mg/kg) or H₂O orally via gavage o.g. 20 min before, immediately, or 3 h after a short retrieval session. Analysis of AYA through liquid chromatography-tandem mass spectrometry was used to determine the content of DMT and β-carbolines in AYA.

RESULTS

AYA impaired fear memory reconsolidation when given 20 min before or 3 h after memory retrieval, with the dose of 60 mg/kg being effective at both moments. This dose of AYA was devoid of anxiolytic effect. Importantly, during retrieval, AYA did not change fear expression. The lack of retrieval abolished the reconsolidation impairing effect of AYA. The effects of AYA treatment 20 min before or 3 h after memory retrieval lasted at least 22 days, suggesting no spontaneous recovery of fear memory. Fear memory impairments induced by AYA treatment, at both moments, do not show reinstatement.

CONCLUSIONS

Our findings support the view that a low dose of AYA treatment impairs early and late stages of memory reconsolidation instead of facilitating fear extinction.