A quantitative analysis of bestrophin 1 cellular localization in mouse cerebral cortex

Aim: Calcium-activated ligand-gated chloride channels, beyond their role in maintaining anion homeostasis, modulate neuronal excitability by facilitating nonvesicular neurotransmitter release. BEST1, a key member of this family, is permeable to γ-aminobutyric acid (GABA) and glutamate. While astrocytic BEST1 is well-studied and known to regulate neurotransmitter levels, its distribution and role in other brain cell types remain unclear. This study aimed to reassess the localization of BEST1 in the mouse cerebral cortex. Methods: We examined the localization and distribution of BEST1 in the mouse parietal cortex using light microscopy, confocal double-labeling with markers for astrocytes, neurons, microglia, and oligodendrocyte precursor cells, and 3D reconstruction techniques. Results: In the cerebral cortex, BEST1 is more broadly distributed than previously thought. Neurons are the second most abundant BEST1+ cell type in the cerebral cortex, following astrocytes. BEST1 is diffusely expressed in neuronal somatic and neuropilar domains and is present at glutamatergic and GABAergic terminals, with a prevalence at GABAergic terminals. We also confirmed that BEST1 is expressed in cortical microglia and identified it in oligodendrocyte precursor cells, albeit to a lesser extent. Conclusions: Together, these findings suggest that BEST1's role in controlling neurotransmission may extend beyond astrocytes to include other brain cells. Understanding BEST1's function in these cells could offer new insights into the molecular mechanisms shaping cortical circuitry. Further research is needed to clarify the diverse roles of BEST1 in both normal and pathophysiological conditions.