Heterodimerization of A2A and D2 Receptors in the Human Subthalamic Nucleus: Insights from Proximity Ligation Assay

The subthalamic nucleus (STh) is a key regulator of basal ganglia circuitry and a primary clinical target in various pathologies, most notably Parkinson’s disease (PD). While dopaminergic dysregulation is central to PD pathophysiology, the purinergic system is increasingly recognized as a critical modulator of dopaminergic tone. Colocalization of adenosine A₂A (A₂AR) and dopamine D₂ receptors (D₂R) has been reported in the STh, but their potential to form heterodimers in this region has not yet been assessed. In this study, we employ proximity ligation assay (PLA) on post-mortem human brain tissue to provide the first evidence of A₂AR–D₂R heterodimerization within the STh. Across donors, punctate PLA signal indicative of A₂AR–D₂R complexes was consistently observed throughout the STh, with quantitative analysis revealing a significant posterior enrichment. Puncta were primarily localised to dendritic and somatic regions, with abundant signal also observed around small non-neuronal nuclei of uncertain lineage. Within A₂AR–D₂R complexes, A₂AR activation reduces D₂R binding affinity, providing a mechanistic basis for the clinical use of A₂AR antagonists, such as istradefylline, in PD. Identifying these heterodimers in the human STh underscores this nucleus as a site of dopaminergic–adenosinergic integration and motivates targeted purinergic strategies in disorders marked by basal ganglia dysfunction.