Chronic Gq activation of ventral hippocampal neurons and astrocytes differentially affects memory and behavior

Chronic Chemogenetic Activation of Astrocytes in the Murine Mesopontine Region Leads to Disturbances in Circadian Activity and Movement

We have previously shown that neuromodulatory actions on astrocytes can elicit metabotropic glutamate- and N-methyl-D-aspartate receptor-dependent tonic changes in excitability in the mesopontine region. Although in vitro experiments explored robust effects, the in vivo significance of our findings remained unknown. In this project, chronic chemogenetic activation of mesopontine astrocytes and its actions on movement, circadian activity, acoustic startle and spatial memory were tested. The control group of young adult male mice where mesopontine astrocytes expressed only the mCherry fluorescent tag was compared to the group expressing the hM3D(Gq) chemogenetic actuator. Chronic chemogenetic astrocyte activation reduced the amplitude of the acoustic startle reflex and increased the locomotion speed in the resting period. Gait alterations were also demonstrated but no change in the spatial memory was explored. As a potential background of these findings, chronic astrocytic activation decreased the cholinergic neuronal number to 54% and reduced the non-cholinergic neuronal number to 76% of the control. In conclusion, chronic astrocytic activation and the consequential decrease in the neuronal number led to disturbances in movement and circadian activity resembling brainstem-related symptoms of progressive supranuclear palsy, raising the possibility that astrocytic overactivation is involved in the pathogenesis of this disease.

Astrocyte regulation of behavioral outputs: the versatile roles of calcium

Behavior arises from coordinated brain-wide neural and glial networks, enabling organisms to perceive, interpret, and respond to stimuli. Astrocytes play an important role in shaping behavioral output, yet the underlying molecular mechanisms are not fully understood. Astrocytes respond to intrinsic and extrinsic cues with calcium (Ca2+) fluctuations, which are highly heterogeneous across spatio-temporal scales, contexts, and brain regions. This heterogeneity allows astrocytes to exert dynamic regulatory effects on neuronal function but has made it challenging to understand the precise mechanisms and pathways linking astrocytic Ca2+ to specific behavioral outcomes, and the functional relevance of these signals remains unclear. Here, we review recent literature uncovering roles for astrocytic Ca2+ signaling in a wide array of behaviors, including cognitive, homeostatic, and affective focusing on its physiological roles, and potential pathological implications. We specifically highlight how different types of astrocytic Ca2+ signals are linked to distinct behavioral outcomes and discuss limitations and unanswered questions that remain to be addressed.

Somatostatin neurons detect stimulus-reward contingencies to reduce neocortical inhibition during learning

Learning involves the association of discrete events in the world to infer causality, likely through a cascade of changes at input- and target-specific synapses. Transient or sustained disinhibition may initiate cortical circuit plasticity important for association learning, but the cellular networks involved have not been well defined. Using recordings in acute brain slices, we show that whisker-dependent sensory association learning drives a durable, target-specific reduction in inhibition from somatostatin (SST)-expressing GABAergic neurons onto pyramidal (Pyr) neurons in superficial but not deep layers of mouse somatosensory cortex. Critically, SST output was not altered when stimuli and rewards were unpaired, indicating that these neurons are sensitive to stimulus-reward contingency. Depression of SST output onto Pyr neurons could be phenocopied by chemogenetic suppression of SST activity outside of the training context. Thus, neocortical SST neuron output can undergo long-lasting modifications to selectively disinhibit superficial layers of sensory neocortex during learning.

Activation of the hippocampal CA1 astrocyte Gq and Gi G protein-coupled receptors exerts a protective effect against attention deficit hyperactivity disorder

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) is characterized by symptoms such as inattention, hyperactivity and impulsiveness, which significantly impact the healthy development of children. Our prior research demonstrated that exposure to S-Ketamine during pregnancy can lead to the development of ADHD, and existing studies have established a close association between astrocytes and the onset and progression of ADHD. The activation and inhibition of astrocytes are closely linked to neuropsychiatric dysfunction, and astrocytic NOD-like receptor protein 3 (NLRP3) has been reported to contribute to alterations in mental state and cognitive deficits. Thus, this study aims to investigate the role of astrocytes in ADHD by selectively modulating astrocyte function through Gq and Gi G protein-coupled receptors (GPCRs) and by specifically targeting the knockout of NLRP3.

METHODS

Pregnant C57BL/6 J mice or mice with a specific deletion of NLRP3 in astrocytes were administered intraperitoneal injections of 15 mg/kg of S-ketamine for 5 consecutive days from gestational day 14 to 18 to establish an ADHD model. To modulate astrocyte activity in the hippocampal CA1 region, we administered astrocyte-specific Gq-Adeno-associated virus (AAV) or Gi-AAV into the CA1 and maintained treatment with CNO. At 21 days postnatally, we conducted open field test (OFT), novel object recognition (NOR), elevated plus maze (EPM) and fear conditioning (FC) in the offspring mice. Additionally, on postnatal day 21, we implanted electrodes in the CA1 region of the offspring mice for neurophysiological monitoring and investigated local field potentials (LFP) during NOR on postnatal day 27. Lastly, pathological assessments were conducted after euthanasia.

RESULTS

Both the activation and inhibition of astrocytes in the hippocampal CA1 region improved impulsive-like behaviors and cognitive function in ADHD mice, reduced the power of theta (θ) oscillations during novel object exploration and decreased NLRP3-associated inflammatory factors, including cleaved caspase-1 and IL-18. Furthermore, compared to WT mice, astrocyte-specific NLRP3 conditional knockout mice demonstrated significantly reduced impulsive behavior and cognitive deficits, as well as a decrease in θ oscillation power and a reduction in NLRP3-associated inflammatory factors.

CONCLUSIONS

Our data provide compelling evidence that the activation of astrocytes alleviated impulsive-like behaviors and cognitive dysfunction, possibly by reducing NLRP3-associated pyroptosis following changes in calcium levels within the astrocytes. The activation of astrocytes can be a potential therapeutic target for ADHD.

Astrocytes in Rodent Anxiety-Related Behavior: Role of Calcium and Beyond

Anxiety is a physiological, emotional response that anticipates distal threats. When kept under control, anxiety is a beneficial response, helping animals to maintain heightened attention in environments with potential dangers. However, an overestimation of potential threats can lead to an excessive expression of anxiety that, in humans, may evolve into anxiety disorders. Pharmacological treatments show variable efficacy among patients, highlighting the need for more efforts to better understand the pathogenesis of anxiety disorders. Mounting evidence suggests that astrocytes, a type of glial cells, are active partners of neurons in brain circuits and in the regulation of behaviors under both physiological and pathological conditions. In this review, I summarize the current literature on the role of astrocytes from different brain regions in modulating anxious states, with the goal of exploring novel cerebral mechanisms to identify potential innovative therapeutic targets for the treatment of anxiety disorders.

Effects of chemogenetic virus injection and clozapine administration in spinal cord injury

Neuromodulation therapy using chemogenetic stimulation has shown potential in enhancing motor recovery and neuroregeneration following spinal cord injury (SCI). These therapeutic benefits are hypothesized to result from the promotion of neuroplasticity, particularly when administered during the acute phase of injury. In this study, we investigated the effects of chemogenetic stimulation using Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) in conjunction with clozapine, a ligand for receptor activation. DREADDs enable targeted, reversible neuromodulation, facilitating the histological characterization of engineered neurons. We utilized these receptors to modulate G-protein-coupled receptor (GPCR) signaling pathways, leading to the activation or inhibition of intracellular signaling. The objective was to determine whether the administration of DREADDs and clozapine (0.1 ​mg/kg) could enhance motor function and neuronal recovery, particularly when applied during the acute phase of SCI. Weekly behavioral assessments demonstrated significant improvements in motor skills and neuronal regeneration in treated animals compared to controls, with the most pronounced effects observed when stimulation was initiated early after injury. These enhancements in neuroplasticity were reflected in improved ladder rung test scores and Basso, Beattie, and Bresnahan (BBB) scale results in DREADDs-treated rats. Histological analyses, including immunohistochemistry (IHC) staining, Western blotting, and quantitative reverse transcription PCR (qRT-PCR), confirmed that the treatment group exhibited a higher density of neurons, increased signaling protein expression, and reduced inflammatory markers. These findings suggest that chemogenetic stimulation, particularly when administered during the acute phase, effectively promotes neuroregeneration and motor recovery. Future research should focus on assessing the long-term safety and efficacy of chemogenetic virus injection and clozapine administration, with an emphasis on the timing of intervention.

Astrocytes in the Ventral Hippocampus Bidirectionally Regulate Innate and Stress-Induced Anxiety-Like Behaviors in Male Mice

The mechanisms of anxiety disorders, the most common mental illness, remain incompletely characterized. The ventral hippocampus (vHPC) is critical for the expression of anxiety. However, current studies primarily focus on vHPC neurons, leaving the role for vHPC astrocytes in anxiety largely unexplored. Here, genetically encoded Ca2+ indicator GCaMP6m and in vivo fiber photometry calcium imaging are used to label vHPC astrocytes and monitor their activity, respectively, genetic and chemogenetic approaches to inhibit and activate vHPC astrocytes, respectively, patch-clamp recordings to measure glutamate currents, and behavioral assays to assess anxiety-like behaviors. It is found that vHPC astrocytic activity is increased in anxiogenic environments and by 3-d subacute restraint stress (SRS), a well-validated mouse model of anxiety disorders. Genetic inhibition of vHPC astrocytes exerts anxiolytic effects on both innate and SRS-induced anxiety-related behaviors, whereas hM3Dq-mediated chemogenetic or SRS-induced activation of vHPC astrocytes enhances anxiety-like behaviors, which are reversed by intra-vHPC application of the ionotropic glutamate N-methyl-d-aspartate receptor antagonists. Furthermore, intra-vHPC or systemic application of the N-methyl-d-aspartate receptor antagonist memantine, a U.S. FDA-approved drug for Alzheimer's disease, fully rescues SRS-induced anxiety-like behaviors. The findings highlight vHPC astrocytes as critical regulators of stress and anxiety and as potential therapeutic targets for anxiety and anxiety-related disorders.

Chronic activation of a negative engram induces behavioral and cellular abnormalities

Negative memories engage a brain and body-wide stress response in humans that can alter cognition and behavior. Prolonged stress responses induce maladaptive cellular, circuit, and systems-level changes that can lead to pathological brain states and corresponding disorders in which mood and memory are affected. However, it is unclear if repeated activation of cells processing negative memories induces similar phenotypes in mice. In this study, we used an activity-dependent tagging method to access neuronal ensembles and assess their molecular characteristics. Sequencing memory engrams in mice revealed that positive (male-to-female exposure) and negative (foot shock) cells upregulated genes linked to anti- and pro-inflammatory responses, respectively. To investigate the impact of persistent activation of negative engrams, we chemogenetically activated them in the ventral hippocampus over 3 months and conducted anxiety and memory-related tests. Negative engram activation increased anxiety behaviors in both 6- and 14-month-old mice, reduced spatial working memory in older mice, impaired fear extinction in younger mice, and heightened fear generalization in both age groups. Immunohistochemistry revealed changes in microglial and astrocytic structure and number in the hippocampus. In summary, repeated activation of negative memories induces lasting cellular and behavioral abnormalities in mice, offering insights into the negative effects of chronic negative thinking-like behaviors on human health.

Astrocytes control recent and remote memory strength by affecting the recruitment of the CA1→ACC projection to engrams

The maturation of engrams from recent to remote time points involves the recruitment of CA1 neurons projecting to the anterior cingulate cortex (CA1→ACC). Modifications of G-protein-coupled receptor pathways in CA1 astrocytes affect recent and remote recall in seemingly contradictory ways. To address this inconsistency, we manipulated these pathways in astrocytes during memory acquisition and tagged c-Fos-positive engram cells and CA1→ACC cells during recent and remote recall. The behavioral results were coupled with changes in the recruitment of CA1→ACC projection cells to the engram: Gq pathway activation in astrocytes caused enhancement of recent recall alone and was accompanied by earlier recruitment of CA1→ACC projecting cells to the engram. In contrast, Gi pathway activation in astrocytes resulted in the impairment of only remote recall, and CA1→ACC projecting cells were not recruited during remote memory. Finally, we provide a simple working model, hypothesizing that Gq and Gi pathway activation affect memory differently, by modulating the same mechanism: CA1→ACC projection.

Neuronal activation of Gαq EGL-30/GNAQ late in life rejuvenates cognition across species

Loss of cognitive function with age is devastating. EGL-30/GNAQ and Gαq signaling pathways are highly conserved between C. elegans and mammals, and murine Gnaq is enriched in hippocampal neurons and declines with age. We found that activation of EGL-30 in aged worms triples memory span, and GNAQ gain of function significantly improved memory in aged mice: GNAQ(gf) in hippocampal neurons of 24-month-old mice (equivalent to 70- to 80-year-old humans) rescued age-related impairments in well-being and memory. Single-nucleus RNA sequencing revealed increased expression of genes regulating synaptic function, axon guidance, and memory in GNAQ-treated mice, and worm orthologs of these genes were required for long-term memory extension in worms. These experiments demonstrate that C. elegans is a powerful model to identify mammalian regulators of memory, leading to the identification of a pathway that improves memory in extremely old mice. To our knowledge, this is the oldest age at which an intervention has improved age-related cognitive decline.