Drummond, G. T. | Search bioRxiv

bioRxiv2024

Astrocytic modulation of population encoding in mouse visual cortex via GABA transporter 3 revealed by multiplexed CRISPR/Cas9 gene editing

Astrocytes, which are increasingly recognized as pivotal constituents of brain circuits governing a wide range of functions, express GABA transporter 3 (Gat3), an astrocyte-specific GABA transporter responsible for maintenance of extra-synaptic GABA levels. Here, we examined the functional role of Gat3 in astrocyte-mediated modulation of neuronal activity and information encoding. First, we developed a multiplexed CRISPR construct applicable for effective genetic ablation of Gat3 in the visual cortex of adult mice. Using in vivo two-photon calcium imaging of visual cortex neurons in Gat3 knockout mice, we observed changes in spontaneous and visually driven single neuronal response properties such as response magnitudes and trial-to-trial variability. Gat3 knockout exerted a pronounced influence on population-level neuronal activity, altering the response dynamics of neuronal populations and impairing their ability to accurately represent stimulus information. These findings demonstrate that Gat3 in astrocytes profoundly shapes the sensory information encoding capacity of neurons and networks within the visual cortex.

neuroscience↗

bioRxiv2024

Cortical norepinephrine-astrocyte signaling critically mediates learned behavior

Updating behavior based on feedback from the environment is a crucial means by which organisms learn and develop optimal behavioral strategies1-3. Norepinephrine (NE) release from the locus coeruleus (LC) has been shown to mediate learned behaviors4-6 such that in a task with graded stimulus uncertainty and performance, a high level of NE released after an unexpected outcome causes adaptations in subsequent behavior7. Yet, how the transient activity of LC-NE neurons, lasting tens of milliseconds, alters neuronal activity and influences behavior several seconds later is unclear. Here, we show that NE released after an unexpected outcome acts directly on cortical astrocytes via 1 adrenergic (Adra1a) receptors to elicit sustained increases in intracellular calcium. Chemogenetic blockade of astrocytic calcium dynamics prevents trial-to-trial behavioral adaptation. NE stimulation of astrocytes elicits ATP release, and imaging ATP levels in the cortex reveals an increase in extracellular ATP in response to an unexpected outcome. Blocking ATP-driven signaling to neuronal adenosine A1 receptors also prevents post-reinforcement behavioral adaptation. Finally, high density neuronal recordings in prefrontal cortex reveal that a surprising outcome alters the neuronal representation of the stimulus on the subsequent trial without sustained changes in cortical activity; blocking either astrocyte calcium dynamics or A1 receptors occludes these post-reinforcement changes in single-neuron and population neuronal encoding of task variables underlying behavioral changes. Together, these data demonstrate that astrocytes play an essential role in norepinephrine-driven learned behavior: they have prolonged calcium responses to transient norepinephrine release and convey task-relevant reinforcement information across behavioral intervals, enabling selective updating of neuronal task representations to support adaptive behavior.

neuroscience↗