Research Areas
Glia-neuron interactions during development of defensive behaviors
Defensive behaviors like freezing and escaping are crucial for survival. While these behaviors are innate, discerning between threatening and harmless stimuli must be acquired through life experience. Conditions such as chronic stress or anxiety can induce disproportionate responses, perturbing normal development with long lasting repercussions. Yet how defensive responses are established in developing animals, and the role of astrocytes (and other glia) in this process, remains largely unknown.
We analyzed defensive responses to a visual looming threat across development in mice and quantified changes of synapses and glia in relevant brain regions, sSC and dPAG. Our behavioral analysis showed that adolescent mice primarily escape from the visual threat, while adults exhibited mainly freezing. Further, we observed that animals rapidly adapt to the looming threat and that adult females are more responsive than males. These age-dependent behaviors correlated with dynamic changes in synapse, astrocyte, and microglia numbers in the dPAG, suggesting its involvement in the developmental switch from escaping to freezing (Albrecht et al., 2025).
Current work is focused on region specific perturbations of synaptic and glial proteins in the sSC and dPAG, and analysis of additional types of threat responses and brain regions involved. Given the strong link between abnormal threat response and anxiety disorders, especially in adolescence, our work will provide important molecular targets for future translational investigations.
Deciphering astrocyte calcium activity in regulating synapses and behavior during development
A central challenge in the field is understanding how astrocyte activity is defined and expressed, as they do not fire action potentials. Astrocytes respond to neuronal activity by alterations in intracellular calcium levels, while manipulating astrocytic calcium has detrimental implications on synapses (Farhy-Tselnicker et al. 2021), circuits, and behavior (Imrie and Farhy-Tselnicker 2025). Yet the cellular mechanisms linking calcium release and synaptic modulation are unknown.
We analyzed synapse development in the visual circuit of mice lacking the type 2 inositol triphosphate receptors (IP3R2 KO), a central mediator of ER store-released calcium in astrocytes. Our results show a developmental stage-dependent decrease in glutamatergic synapses, diminished light-evoked neuronal activation, and perturbed visually triggered defensive behaviors. We also observe reduced morphological complexity of IP3R2 KO astrocytes, suggesting a mechanistic link between astrocytic calcium, growth, and synaptic support (Imrie et al. 2026).
Our current work focuses on analyzing the consequences of IP3R2 removal from astrocytes on neuronal activity using calcium imaging in acute brain slices and identifying the calcium-dependent astrocytic proteins that regulate astrocytic morphogenesis and glutamatergic synapse development. By investigating the causes and consequences of astrocyte calcium signals that link synapse regulation, circuit function, and behavioral outputs, our work provides critical foundational insights advancing the field of astrocyte biology.
Regulation of synaptic rhythmicity by astrocytic circadian clock
The circadian clock regulates many biological processes including synaptic function. Synapse number and activity, and cognitive function (e.g., learning and memory) change throughout the circadian cycle, while disruptions to the circadian cycle (such as irregular sleep or food intake) are linked with disorders including depression and Alzheimer’s disease.
We are specifically focused on characterizing the hitherto unknown role of the astrocytic molecular clock in synaptic development, determining the effects of astrocytic clock dysfunction on learning and memory in young and adult mice, and determining how astrocytic calcium activity is involved. We have established astrocyte specific conditional knockout mouse models and experimental assays, including protocols for measuring time-of-day-dependent learning and memory, locomotion, and anxiety (Mar et al. 2025) and made exciting discoveries demonstrating perturbed circadian activity in IP3R2 KO mice.
To target astrocytes as therapeutics for circadian pathologies, it is imperative to first define the uncharacterized mechanisms by which the astrocytic clock regulates synapses and is itself controlled.
Astrocyte-secreted proteins drive the development of distinct synapse types
Astrocytes release proteins such as glypicans (GPC4) and thrombospondins (TSP1) that regulate distinct aspects of synapse formation (Farhy-Tselnicker et al. 2017; Farhy-Tselnicker et al. 2021), however, how neurons respond to these diverse signals to produce the correct synapse number and type is unknown.
Using phosphoproteomics, we identified glycogen synthase kinase 3β (GSK3β) as a neuronal candidate to relay these astrocytic signals. GSK3β is a known regulator of synapse function and plasticity, yet its role in mediating astrocyte-regulated synapse formation is unknown. We observed GSK3β activation in GPC4-treated neurons, while treating neurons with TSP1 increased GSK3β inhibition. Importantly, we show that global GSK3β inhibition blocks synapse formation, while activated GSK3β levels are decreased in GPC4 knockout mice. Our data (Gray et al. in preparation) suggest the hypothesis that GSK3β acts as a molecular switch promoting distinct synapse types in response to astrocytic proteins.
GSK3β is an attractive therapeutic target for Alzheimer’s disease (AD). Current strategies seek to inhibit GSK3β, however, our data show that synapse formation requires GSK3β activation. Thus, inhibiting GSK3β may paradoxically perturb synaptogenesis, curbing cognitive improvements in AD patients. Our work will uncover how GSK3β activity regulates synapses, enabling future translational success.
Re-defining the synaptic transcriptome of astrocytes
A recent explosion of RNA sequencing studies has allowed us, for the first time, to directly compare gene expression across cell types. We conducted meta-analysis of published transcriptomes (including Farhy-Tselnicker et al. 2021) to discover that astrocytes express a staggering number of genes considered by the field as “neuronal synaptic”, such as postsynaptic density proteins and glutamate receptors. Literature review revealed that research has primarily focused on their function in neurons, while their astrocytic roles are unknown (Imrie, Gray et al. 2024).
We are currently analyzing datasets from different developmental stages, single-cell RNA sequencing, and proteomics, and developing in vivo assays using AAVs and genetic mouse models to validate and manipulate these genes in astrocytes (Gray et al. in preparation). Current therapeutic strategies for neurological disorders employ a “neuron-centric” approach to targeting synaptic genes. However, since astrocytes also express these genes, such strategies risk failure by overlooking their contribution to the pathology. By revealing the astrocytic roles of these genes, our work will inform the development of new and more effective therapies.