Spontaneous recovery of reward memory through active forgetting of extinction memory

Focused Ultrasound Combined With Microbubbles Attenuate Symptoms in Heroin-Addicted Mice

OBJECTIVE

To explore the efficacy and mechanisms of stimulating the nucleus accumbens (NAc) in heroin-addicted mice using focused ultrasound and microbubbles (MBs).

METHODS

The conditioned place preference (CPP) method was employed to establish a heroin-addicted mice model. Mice were randomized into control (C), heroin (H), heroin + ultrasound (H + U) and H + U + MBs. Ultrasound (2 MHz fundamental frequency, 1.34 MPa peak-negative pressure, 1 MHz pulse repetition frequency, 5% duty cycle, 15 min/d, over 2 d) was applied to stimulate the NAc in the latter 2 groups. Whereas H + U + MBs received an injection of sulfur hexafluoride MBs during the stimulation. Subsequently, CPP scores, open-field test (OFT), and elevated plus-maze test (EPMT) were conducted to assess behavioral changes in addiction memory, anxiety and exercise status. HE staining was performed to detect pathological structures. Neurotransmitters such as dopamine (DA), serotonin (5-HT) and glutamate (Glu) were detected using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Transmission electron microscopy (TEM) was used to observe ultrastructural changes of synapses in NAc. Immunohistochemistry (IHC) was utilized to detect Cleaved Caspase-3 in the NAc region. Western blotting (WB) was used to detect the protein expression of Cleaved Caspase-3, Bax and Bcl-2 in NAc.

RESULTS

HE staining showed small patches of erythrocyte exudation were observed in the NAc and adjacent areas in H + U + MBs. The CPP scores of H + U + MBs were lower (p < 0.05) than H. After ultrasound treatment, all indices of the OFT and EPMT in H + U + MBs were significantly higher than H (p < 0.05). UPLC-MS/MS revealed that the levels of DA, 5-HT and Glu in H + U + MBs were lower than H (p < 0.01). TEM showed decrease the number of synapses (p < 0.05), and noticeable swelling of mitochondria, membrane damage, as well as damage to the cristae. Further detection by IHC and WB showed that the pro-apoptotic proteins Cleaved Caspase-3 and Bax increased and Bcl-2 decreased as anti-apoptotic proteins after ultrasound combined with MBs (p < 0.05).

CONCLUSION

Focused ultrasound combined with MBs stimulate the NAc can weaken the addictive memory and improve anxiety of heroin-related mice. The mechanical effect of ultrasound combined with the cavitation effect may be a potential treatment for addiction.

Active forgetting and neuropsychiatric diseases

Recent and pioneering animal research has revealed the brain utilizes a variety of molecular, cellular, and network-level mechanisms used to forget memories in a process referred to as "active forgetting". Active forgetting increases behavioral flexibility and removes irrelevant information. Individuals with impaired active forgetting mechanisms can experience intrusive memories, distressing thoughts, and unwanted impulses that occur in neuropsychiatric diseases. The current evidence indicates that active forgetting mechanisms degrade, or mask, molecular and cellular memory traces created in synaptic connections of "engram cells" that are specific for a given memory. Combined molecular genetic/behavioral studies using Drosophila have uncovered a complex system of cellular active-forgetting pathways within engram cells that is regulated by dopamine neurons and involves dopamine-nitric oxide co-transmission and reception, endoplasmic reticulum Ca2+ signaling, and cytoskeletal remodeling machinery regulated by small GTPases. Some of these molecular cellular mechanisms have already been found to be conserved in mammals. Interestingly, some pathways independently regulate forgetting of distinct memory types and temporal phases, suggesting a multi-layering organization of forgetting systems. In mammals, active forgetting also involves modulation of memory trace synaptic strength by altering AMPA receptor trafficking. Furthermore, active-forgetting employs network level mechanisms wherein non-engram neurons, newly born-engram neurons, and glial cells regulate engram synapses in a state and experience dependent manner. Remarkably, there is evidence for potential coordination between the network and cellular level forgetting mechanisms. Finally, subjects with several neuropsychiatric diseases have been tested and shown to be impaired in active forgetting. Insights obtained from research on active forgetting in animal models will continue to enrich our understanding of the brain dysfunctions that occur in neuropsychiatric diseases.

Diverse memory paradigms in Drosophila reveal diverse neural mechanisms

In this review, we aggregated the different types of learning and memory paradigms developed in adult Drosophila and attempted to assess the similarities and differences in the neural mechanisms supporting diverse types of memory. The simplest association memory assays are conditioning paradigms (olfactory, visual, and gustatory). A great deal of work has been done on these memories, revealing hundreds of genes and neural circuits supporting this memory. Variations of conditioning assays (reversal learning, trace conditioning, latent inhibition, and extinction) also reveal interesting memory mechanisms, whereas mechanisms supporting spatial memory (thermal maze, orientation memory, and heat box) and the conditioned suppression of innate behaviors (phototaxis, negative geotaxis, anemotaxis, and locomotion) remain largely unexplored. In recent years, there has been an increased interest in multisensory and multicomponent memories (context-dependent and cross-modal memory) and higher-order memory (sensory preconditioning and second-order conditioning). Some of this work has revealed how the intricate mushroom body (MB) neural circuitry can support more complex memories. Finally, the most complex memories are arguably those involving social memory: courtship conditioning and social learning (mate-copying and egg-laying behaviors). Currently, very little is known about the mechanisms supporting social memories. Overall, the MBs are important for association memories of multiple sensory modalities and multisensory integration, whereas the central complex is important for place, orientation, and navigation memories. Interestingly, several different types of memory appear to use similar or variants of the olfactory conditioning neural circuitry, which are repurposed in different ways.

Engineering, applications, and future perspectives of GPCR-based genetically encoded fluorescent indicators for neuromodulators

This review explores the evolving landscape of G-protein-coupled receptor (GPCR)-based genetically encoded fluorescent indicators (GEFIs), with a focus on their development, structural components, engineering strategies, and applications. We highlight the unique features of this indicator class, emphasizing the importance of both the sensing domain (GPCR structure and activation mechanism) and the reporting domain (circularly permuted fluorescent protein (cpFP) structure and fluorescence modulation). Further, we discuss indicator engineering approaches, including the selection of suitable cpFPs and expression systems. Additionally, we showcase the diversity and flexibility of their application by presenting a summary of studies where such indicators were used. Along with all the advantages, we also focus on the current limitations as well as common misconceptions that arise when using these indicators. Finally, we discuss future directions in indicator engineering, including strategies for screening with increased throughput, optimization of the ligand-binding properties, structural insights, and spectral diversity.

Genetic dissection of mutual interference between two consecutive learning tasks in Drosophila

Animals can continuously learn different tasks to adapt to changing environments and, therefore, have strategies to effectively cope with inter-task interference, including both proactive interference (Pro-I) and retroactive interference (Retro-I). Many biological mechanisms are known to contribute to learning, memory, and forgetting for a single task, however, mechanisms involved only when learning sequential different tasks are relatively poorly understood. Here, we dissect the respective molecular mechanisms of Pro-I and Retro-I between two consecutive associative learning tasks in Drosophila. Pro-I is more sensitive to an inter-task interval (ITI) than Retro-I. They occur together at short ITI (<20 min), while only Retro-I remains significant at ITI beyond 20 min. Acutely overexpressing Corkscrew (CSW), an evolutionarily conserved protein tyrosine phosphatase SHP2, in mushroom body (MB) neurons reduces Pro-I, whereas acute knockdown of CSW exacerbates Pro-I. Such function of CSW is further found to rely on the γ subset of MB neurons and the downstream Raf/MAPK pathway. In contrast, manipulating CSW does not affect Retro-I as well as a single learning task. Interestingly, manipulation of Rac1, a molecule that regulates Retro-I, does not affect Pro-I. Thus, our findings suggest that learning different tasks consecutively triggers distinct molecular mechanisms to tune proactive and retroactive interference.