Ultrasonic potentiation of ketamine neuromodulation

The psychiatric utility of ketamine is limited by its dissociative and systemic side effects. Recently, to enable precision ketamine pharmacotherapy, we introduced SonoKet, ketamine-loaded acoustically activatable liposomes that enable focused ultrasound (FUS)-targeted ketamine delivery to millimeter-sized brain regions. In initial studies, we observed that SonoKet uncaging targeted ketamine to the ultrasound-treated brain region, while inducing greater electrophysiologic and behavioral functional effects than dose-matched free ketamine. To further define these uncaging-potentiated neuromodulatory effects, we used solid-phase microextraction (SPME) coupled to LC-MS/MS to investigate the effect of ultrasound and SonoKet uncaging on key neurotransmitters in real-time. SPME probes were used to sample ketamine, its metabolites, and glutamate, GABA, serotonin (5-HT), and dopamine in the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), and retrosplenial cortex (RsC) of awake rats. Sampling occurred before and after intravenous administration of either SonoKet, free ketamine, or saline, with FUS targeted to either a frontolimbic or caudal brain region. FUS alone did not yield significant changes in neurotransmitter concentration, nor did it affect the pharmacodistribution of free ketamine. In contrast, FUS generally increased the neurotransmitter response to free ketamine, suggesting an ultrasonic potentiation of ketamine neuromodulation. SonoKet (0.75 mg/kg) uncaging with FUS elicited further elevations in glutamate, GABA, and 5-HT within the FUS-targeted region, along with an increase in dopamine in the NAc when the frontolimbic region was sonicated. These increases were similar to or higher than those induced by 10 mg/kg free ketamine alone or 0.75 mg/kg free ketamine combined with FUS, especially with frontolimbic SonoKet uncaging. Altogether, FUS potentiates ketamine-induced neuromodulation, with spatially specific and synergistically greater effects when ketamine is spatially localized via ultrasonic uncaging. This strategy could augment ketamine pharmacotherapy for psychiatric diseases, while limiting its dissociative and abuse liabilities.