Distribution Patterns of Subgroups of Inhibitory Neurons Divided by Calbindin 1.

The inhibitory neurons in the brain play an essential role in neural network firing patterns by releasing γ-aminobutyric acid (GABA) as the neurotransmitter. In the mouse brain, based on the protein molecular markers, inhibitory neurons are usually to be divided into three non-overlapping groups: parvalbumin (PV), neuropeptide somatostatin (SST), and vasoactive intestinal peptide (VIP)-expressing neurons. Each neuronal group exhibited unique properties in molecule, electrophysiology, circuitry, and function. Calbindin 1 (Calb1), a ubiquitous calcium-binding protein, often acts as a "divider" in excitatory neuronal classification. Based on Calb1 expression, the excitatory neurons from the same brain region can be classified into two subgroups with distinct properties. Besides excitatory neurons, Calb1 also expresses in part of inhibitory neurons. But, to date, little research focused on the intersectional relationship between inhibitory neuronal subtypes and Calb1. In this study, we genetically targeted Calb1-expression (Calb1+) and Calb1-lacking (Calb1-) subgroups of PV and SST neurons throughout the mouse brain by flexibly crossing transgenic mice relying on multi-recombinant systems, and the distribution patterns and electrophysiological properties of each subgroup were further demonstrated. Thus, this study provided novel insights and strategies into inhibitory neuronal classification.