Astrocytic α7 nicotinic acetylcholine receptors play an essential role in regulating glutamate dynamics and memory flexibility in the hippocampus

Astrocytes regulate hippocampal excitatory transmission by controlling glutamate dynamics, yet the contribution of cholinergic signaling to these processes remains poorly understood. Here, we investigated the role of astrocytic α7 nicotinic acetylcholine receptors (α7-nAChRs) in regulating glutamate homeostasis, synaptic plasticity, and memory flexibility in the hippocampus. Using ultrastructural analyses, functional imaging of glutamate, calcium, and sodium, electrophysiology, and behavioral approaches, we studied α7-nAChR knockout mice (α7KO) and an AAV-based mouse model enabling astrocyte-specific re-expression of α7-nAChRs (α7KI-astro). Electron microscopy revealed abundant α7nAChR expression in astrocytic processes at excitatory synapses in the hippocampal CA1 region. In α7KO mice, astrocytic calcium signaling and glutamate uptake were impaired. These alterations of glutamate dynamics were accompanied by reduced expression and altered localization of the glutamate transporter GLT-1, retraction of perisynaptic astrocytic processes, and deficits in synaptic fatigue, vesicle recycling, long-term depression, and memory flexibility. In α7KI-astro mice, calcium signaling, glutamate dynamics, synaptic plasticity, and memory flexibility were restored. Similarly, pharmacological enhancement of GLT-1 activity with ceftriaxone rescued both synaptic and behavioral deficits. Together, these findings identify astrocytic α7-nAChRs as critical regulators of glutamate homeostasis and hippocampal function, revealing a cholinergic mechanism through which astrocytes influence synaptic plasticity and cognitive flexibility.