Ultrasonic Modulation of Astrocytic and Neuronal Calcium Dynamics in Mouse Cortex

Background

Astrocytes are abundant in the brain and their calcium signaling is reported to have an important effect on neuronal activity in both physiological and pathological conditions. Low-frequency focused ultrasound (FUS) has recently emerged as a powerful noninvasive neuromodulation approach, yet its impact on astrocyte calcium dynamics in different brain states in vivo is poorly understood.

Objective

This study aimed to elucidate the effects of non-thermal FUS on astrocyte calcium dynamic with in vivo cellular-resolution and cell-type-specific recording and identify whether the influences of FUS on cortical astrocytes and neurons are distinctive and state dependent.

Methods

Here we combined a customized 0.521MHz FUS transducer with two-photon microscopy, allowing simultaneous single-cell resoultion imaging and FUS stimulation at intensities of 0.91 or 1.5 W/cm ² to examine astrocyte and neuronal calcium responses in somatosensory cortex of both awake and lightly anesthetized mice. Functional clustering analysis was performed to identify calcium response activated or inhibited subpopulations.

Results

In awake mice, FUS significantly enhanced the amplitude, frequency, and temporal integral of astrocyte calcium transients, while suppressing neuronal calcium activity and reducing the proportion of activated neuronal subpopulations. In contrast, lightly anesthetized mice displayed a blunted yet increased astrocyte response and negligible neuronal modulation under FUS, suggesting that baseline suppression from anesthesia partially masks FUS effects.

Conclusions

Our study demonstrated that FUS elicited distinctive, state-dependent effects on cortical astrocytes and neurons, highlighting astrocytes as previously underappreciated targets of ultrasound neuromodulation. These findings will pave the way for FUS-based therapies targeting astrocyte–neuron interactions in conditions involving abnormal brain excitability.

Highlights

• Low duty cycle low frequency focused ultrasound induced negligible heat effects.

• Ultrasound markedly enhanced astrocyte calcium transients in awake mice.

• Ultrasound suppressed neuronal calcium activity in awake mice.

• The effects of ultrasound on both cell types were reduced under light anesthesia.