Psilocybin modulates nucleus accumbens activity via astrocytic transcriptional regulation

Psilocybin is a serotonergic hallucinogen that acts primarily through 5-HT₂A receptor signaling, yet the mechanisms by which it regulates mesolimbic inhibitory tone remain poorly understood. Here we investigated how psilocybin and structurally related synthetic tryptamines modulate inhibitory signaling in the nucleus accumbens (NAc) and whether astrocyte-associated mechanisms contribute to this process. Psilocybin-like tryptamines that generalized to the psilocybin cue increased NAc neuronal activity while reducing extracellular GABA levels, identifying diminished NAc GABAergic tone as a neurochemical correlate of psilocybin-like behavioral responses. Consistent with this interpretation, local pharmacological modulation of NAc GABA receptor signaling altered psilocybin-appropriate responding. We next examined the cellular and molecular basis of this GABAergic regulation. Ex vivo whole-cell recordings revealed that psilocin, the active metabolite of psilocybin, reduced tonic GABA current in NAc medium spiny neurons without affecting miniature inhibitory postsynaptic currents, indicating preferential modulation of tonic rather than miniature synaptic inhibition. Cell-type-specific analyses further showed that psilocybin selectively reduced intracellular GABA levels in astrocytes, but not neurons. Psilocybin increased astrocytic NFATc4 and ALDH5A1 protein expression together with enhanced H3K27 acetylation, and ChIP–qPCR analysis showed increased NFATc4 occupancy at the Aldh5a1 promoter. Consistent with upstream serotonergic signaling, psilocin-induced calcium responses in astrocytes were attenuated by 5-HT₂A receptor antagonism. Together, these findings support a model in which psilocybin modulates mesolimbic inhibitory tone through astrocyte-associated regulation of NAc GABA homeostasis. Our findings further identify astrocytic NFATc4-associated transcriptional regulation as a mechanism linked to ALDH5A1 expression, astrocytic GABA homeostasis and tonic inhibitory regulation in the NAc.