ISOFLURANE DEPTH SHAPES TRANSCRANIAL FOCUSED ULTRASOUND INDUCED NEUROMODULATION IN THE PREFRONTAL CORTEX IN MICE

Transcranial focused ultrasound (tFUS) is a non-invasive technique capable of modulating brain activity with promising therapeutic potential. tFUS is frequently applied under anesthesia due to the technical need for animal restraint. The objective of this study is to investigate how varying levels of isoflurane anesthesia might influence tFUS-induced neuronal responses. Calcium imaging with fiber photometry was used to monitor neuronal activity in response to tFUS targeting the infralimbic cortex (ILC) of mice while systematically varying isoflurane concentration (2%, 1%, and 0.5%) and tFUS parameters like pressure (0.15, 0.3, 0.45 MPa) and pulse duration (1.6 to 500 ms). Our findings demonstrated a time-locked response of the neuronal populations in the ILC to tFUS evidenced by an immediate rise in calcium signal that persists for 2 seconds following the pulse onset. The tFUS-induced calcium rise was the strongest under 2% isoflurane compared to both 1% and 0.5% isoflurane, highlighting a strong effect of anesthesia on tFUS-induced neuronal activation. Among the tested parameters, 0.3 MPa induced the most robust responses under 2% isoflurane. A relatively monotonic increase in calcium rise was observed when pulse duration increased from 1.6 ms to 500 ms at constant pressures across all isoflurane levels. Our study highlights the critical influence of isoflurane anesthesia on tFUS-induced neuronal activation. The strongest responses observed under 2% isoflurane could be attributed to lower baseline calcium levels and spontaneous activity. Our study poses critical questions that highlight the need for a systematic investigation of the anesthesia-neuromodulation interaction.