Reconsolidation of sucrose instrumental memory in rats: The role of retrieval context

Ecocebo: How the interaction between environment and drug effects may improve pharmacotherapy outcomes

This narrative review describes the research on the effects of the association between environmental context and medications, suggesting the benefit of specific design interventions in adjunction to pharmacotherapy. The literature on Evidence-Based Design (EBD) studies and Neuro-Architecture show how contact with light, nature, and specific physical features of urban and interior architecture may enhance the effects of analgesic, anxiolytics, and antidepressant drugs. This interaction mirrors those already known between psychedelics, drugs of abuse, and setting. Considering that the physical feature of space is a component of the complex placebo configuration, the aim is to highlight those elements of built or natural space that may help to improve drug response in terms of efficacy, tolerability, safety, and compliance. Ecocebo, the integration of design approaches such as EBD and Neuro-Architecture may thus contribute to a more efficient, cost-sensitive, and sustainable pharmacotherapy.

Drug memory reconsolidation: from molecular mechanisms to the clinical context

Since its rediscovery at the beginning of the 21st Century, memory reconsolidation has been proposed to be a therapeutic target for reducing the impact of emotional memories that can go awry in mental health disorders such as drug addiction (substance use disorder, SUD). Addiction can be conceptualised as a disorder of learning and memory, in which both pavlovian and instrumental learning systems become hijacked into supporting drug-seeking and drug-taking behaviours. The past two decades of research have characterised the details of the molecular pathways supporting the reconsolidation of pavlovian cue-drug memories, with more recent work indicating that the reconsolidation of instrumental drug-seeking memories also relies upon similar mechanisms. This narrative review considers what is known about the mechanisms underlying the reconsolidation of pavlovian and instrumental memories associated with drug use, how these approaches have translated to experimental medicine studies, and the challenges and opportunities for the clinical use of reconsolidation-based therapies.

Procedures between training and reactivation influence the destabilization of instrumental sucrose memory

Memory destabilization and reconsolidation is hypothesized to be a fundamental mnemonic process that can underpin memory updating. Instrumental memories have been shown recently to be destabilized following a reactivation session that involves a change in instrumental reward contingency. However, the acquisition and performance of an instrumental response occurs in the presence of the learning of other reward-related memories. This may influence the ability of a given reactivation session to destabilize the previously learned instrumental memory. Here we present a series of experiments in male rats involving an instrumental memory trained on an FR1 schedule over 10 days, and then reactivated in a session that imposed a VR5 schedule of reinforcement. When MK-801 was injected prior to the VR5 reactivation session, it reliably impaired subsequent instrumental performance at test only when the reactivation session occurred 48 h, and not 24 h, after the end of training. The interposition between the end of training and the reactivation session of a context extinction session, an additional VR5 reactivation session, or indeed the simple experience of being handled and injected with vehicle, resulted in MK-801 no longer having an amnestic effect on test performance. While we do not have a clear account for the process and mechanism underpinning this apparent selectivity of the effect of the VR5 session to destabilize the instrumental memory, it does additionally highlight the need for greater understanding of the conditions that facilitate reactivation-induced memory destabilization.

Inhibition of Glycogen Synthase Kinase 3β Activity in the Basolateral Amygdala Disrupts Reconsolidation and Attenuates Heroin Relapse

Exposure to a heroin-associated conditioned stimulus can reactivate drug reward memory, trigger drug cravings, and induce relapse in heroin addicts. The amygdala, a brain region related to emotions and motivation, is involved in processing rewarding stimulus. Recent evidence demonstrated that disrupting the reconsolidation of the heroin drug memories attenuated heroin seeking which was associated with the basolateral amygdala (BLA). Meanwhile, neural functions associated with learning and memory, like synaptic plasticity, are regulated by glycogen synthase kinase 3 beta (GSK-3β). In addition, GSK-3β regulated memory processes, like retrieval and reconsolidation of cocaine-induced memory. Here, we used a heroin intravenous self-administration (SA) paradigm to illustrate the potential role of GSK-3β in the reconsolidation of drug memory. Therefore, we used SB216763 as a selective inhibitor of GSK-3β. We found that injecting the selective inhibitor SB216763 into the BLA, but not the central amygdala (CeA), immediately after heroin-induced memory retrieval disrupted reconsolidation of heroin drug memory and significantly attenuated heroin-seeking behavior in subsequent drug-primed reinstatement, suggesting that GSK-3β is critical for reconsolidation of heroin drug memories and inhibiting the activity of GSK-3β in BLA disrupted heroin drug memory and reduced relapse. However, no retrieval or 6 h after retrieval, administration of SB216763 into the BLA did not alter heroin-seeking behavior in subsequent heroin-primed reinstatement, suggesting that GSK-3β activity is retrieval-dependent and time-specific. More importantly, a long-term effect of SB216763 treatment was observed in a detectable decrease in heroin-seeking behavior, which lasted at least 28 days. All in all, this present study demonstrates that the activity of GSK-3β in BLA is required for reconsolidation of heroin drug memory, and inhibiting GSK-3β activity of BLA disrupts reconsolidation and attenuates heroin relapse.

The Mechanisms and Boundary Conditions of Drug Memory Reconsolidation

Drug addiction can be seen as a disorder of maladaptive learning characterized by relapse. Therefore, disrupting drug-related memories could be an approach to improving therapies for addiction. Pioneering studies over the last two decades have revealed that consolidated memories are not static, but can be reconsolidated after retrieval, thereby providing candidate pathways for the treatment of addiction. The limbic-corticostriatal system is known to play a vital role in encoding the drug memory engram. Specific structures within this system contribute differently to the process of memory reconsolidation, making it a potential target for preventing relapse. In addition, as molecular processes are also active during memory reconsolidation, amnestic agents can be used to attenuate drug memory. In this review, we focus primarily on the brain structures involved in storing the drug memory engram, as well as the molecular processes involved in drug memory reconsolidation. Notably, we describe reports regarding boundary conditions constraining the therapeutic potential of memory reconsolidation. Furthermore, we discuss the principles that could be employed to modify stored memories. Finally, we emphasize the challenge of reconsolidation-based strategies, but end with an optimistic view on the development of reconsolidation theory for drug relapse prevention.

Hippocampal gamma oscillations by sucrose instrumental memory retrieval in rats across sleep/wake cycle

Memory reconsolidation is a process allowing previously consolidated memories to be updated. In order for memory reconsolidation to occur, a memory first needs to be reactivated. It has been shown recently that memory retrieval during awake/sleep phases may affect susceptibility to memory reactivation. Given the importance of hippocampal gamma frequencies in memory processes, the purpose of the present research was to study changes in gamma bands power during retrieval of instrumental appetitive memories. Local field potentials were recorded in the CA1 area of dorsal hippocampus of Sprague Dawley rats during retrieval of instrumental appetitive memory performed either during light or dark phases of the circadian cycle. Appetitive memory retrieval was performed by using a protocol of sucrose self-administration in operant chambers equipped with levers (Piva et al., 2018): rats were first trained to self-administer sucrose pellets and, after a 14-days forced abstinence stage, memory retrieval stage consisted in training context exposure. At the retrival stage performed during the light phase, a decreased low-gamma power was observed in CA1 when rats were not lever pressing compared to when they were lever pressing (actual instrumental memory retrieval). Moreover, results showed an inverse correlation between gamma power and rate of responding when retrieval was performed in the dark phase. Our findings suggest that hippocampal gamma power is differently modulated when retrieval is performed during the light phase compared to the dark phase. Further investigations should explore the role of gamma oscillations as potential markers of instrumental appetitive memory reactivation in both light and dark conditions.

Protocols for instrumental memory reconsolidation in rodents: A methodological review

BACKGROUND

Memory reconsolidation enables the update of a previously consolidated memory trace after its reactivation. Although Pavlovian memory reconsolidation has been widely demonstrated, instrumental memory reconsolidation is still debated. Early studies suggested that instrumental memories did not undergo reconsolidation and therefore could not be disrupted, whereas other authors suggested that these memories are just more resistant to destabilization and reconsolidation in comparison to Pavlovian memories.

AIM AND RESULTS

The present paper reviews the behavioral protocols used to investigate appetitive instrumental memory reconsolidation in rodents and describes in detail the specific methods used for memory retrieval, with a critical analysis of the different experimental parameters.

CONCLUSIONS

The modalities under which the reconsolidation of appetitive (sucrose or drugs of abuse) instrumental memories occurs have been explored and partially elucidated. Further investigations are recommended on the boundary conditions that constrain instrumental memory reactivation.