Midbrain dopamine drives splenic immunity through a brain-to-body circuit.

Midbrain dopamine neurons are well-known to shape central nervous system function, yet there is growing evidence for their influence on the peripheral immune systems. Here we demonstrate that midbrain dopamine neurons form a circuit to the spleen via a multisynaptic pathway from the dorsal vagal complex (DVC) through the celiac ganglion. Midbrain dopamine neurons modulate the activity of D1-like and D2-like dopamine receptor-expressing DVC neurons. In vivo activation of midbrain dopamine neurons induced dopamine release in the DVC and increased immediate early gene expression in both the DVC and celiac ganglion, indicating enhanced neuronal activity. Activation of this midbrain-to-spleen circuit reduced spleen weight and decreased naïve CD4 + T-cell populations without affecting total T-cell numbers. These findings unveil a functional midbrain-DVC-celiac ganglion-spleen pathway, through which midbrain dopamine neurons modulate splenic immunity. These novel insights into the neural regulation of the immune system have important implications for diseases involving altered dopamine neurotransmission and highlight potential targets for immunotherapeutic interventions.