A brief exposure to ketamine can produce lasting changes in behavior and mood. In larval zebrafish, a short ketamine treatment suppressed the passive "giving-up" response that normally occurs when swimming fails to produce forward movement. Whole-brain imaging showed that ketamine initially hyperactivates a circuit involving norepinephrine and astrocytes, which controls this passivity. After ketamine is removed, the same circuit becomes less sensitive to futility, resulting in long-term increased perseverance. Experiments using pharmacology, chemogenetics, and optogenetics confirmed that norepinephrine and astrocytes are both necessary and sufficient for this effect. In adult mice, astrocytes in the cortex were similarly activated during a futility test, and ketamine also caused astrocyte hyperactivation. The cross-species conservation of this mechanism suggests new strategies for treating affective disorders.
Ketamine, a mood-altering compound, suppresses passivity induced by futility in larval zebrafish, similar to effects in rodent learned helplessness models. Brain-wide imaging in behaving zebrafish shows ketamine elevates intracellular calcium in astroglia for many minutes, followed by persistent calcium downregulation after washout. This calcium elevation depends on astroglial α1-adrenergic receptors and is required for suppression of passivity. Chemo- and optogenetic experiments show that the aftereffects of glial calcium elevation are sufficient to suppress passivity by inhibiting neuronal-astroglial integration of behavioral futility. Imaging in mouse cortex reveals ketamine elevates astroglial calcium through conserved pathways, suggesting ketamine exerts its behavioral effects by persistently modulating evolutionarily ancient neuromodulatory systems spanning neurons and astroglia.