Ultrastructure of dopaminergic varicosities revealed by cryo-correlative light and electron microscopy.

Dopaminergic neurons are fundamental in governing motivation, movement, and many aspects of cognition. The targeted modulation of dopaminergic signaling serves as a cornerstone in developing therapeutic interventions for conditions such as Parkinson's disease, schizophrenia, and addiction. Despite the pivotal role of dopaminergic neurons, the ultrastructure of dopaminergic synapses remains poorly understood. Here, we establish and utilize a cryo-correlative light and electron microscopy process to investigate the micro/nanoscale architecture and organelle content of dopaminergic varicosities. Using cryo-electron tomography and subtomogram averaging, we demonstrate the ability to resolve in situ complex structures of the TRiC/CCT chaperone and the vacuolar-type ATPase. We combine our experimental setup with pharmacological treatments using dopamine or haloperidol, showing bidirectional modulation of vesicular content and mitochondrial calcium phosphate deposition. These findings contribute to our understanding of the composition and (re)organization of dopaminergic varicosities and provide a methodological platform for further studies of the structure and cell biology of dopaminergic neurons and their responses.