Calcium-binding protein expression alone is insufficient to identify and classify GABAergic neurons in macaque cortex

Area of Science:

• Neuroscience
• Cell Biology
• Primate Cortex Research

Background:

• Neocortical GABAergic neuron classification traditionally relies on calcium-binding proteins (CBPs) like parvalbumin (PV), calbindin D-28K (CB), and calretinin (CR).
• In rodents, CB and CR co-expression led to a shift towards classification based on PV and signaling peptides somatostatin (SST) and vasoactive intestinal peptide (VIP).
• In macaques, CBP co-expression is rare, leading to the persistence of the CBP-based scheme despite questions about the GABAergic identity of these populations.

Purpose of the Study:

• To quantitatively evaluate the validity of calcium-binding proteins (CBPs) as a classification scheme for GABAergic neurons in macaque visual cortex.
• To determine if CBP-based classification accurately identifies GABAergic neuron subpopulations in macaques.
• To propose alternative or refined classification strategies for macaque GABAergic neurons.

Main Methods:

• Combined immunohistochemistry and in situ hybridization techniques.
• Quantitative analysis of CBP expression in relation to GABAergic markers in macaque visual cortex.
• Evaluation of staining intensity for distinguishing GABAergic subpopulations.

Main Results:

• Up to 50% of neurons expressing CBPs in the macaque visual cortex may not be GABAergic.
• GABAergic subpopulations within CBP classes cannot be reliably distinguished by staining intensity.
• The traditional CBP-based classification scheme is demonstrated to be invalid for macaque GABAergic neurons.

Conclusions:

• The CBP-based classification scheme is not a valid method for categorizing GABAergic neurons in the macaque neocortex.
• Co-labeling with signaling peptides somatostatin (SST) and vasoactive intestinal peptide (VIP) offers a viable approach to identify GABAergic subpopulations within CBP classes.
• Adopting the PV/SST/VIP classification scheme is a recommended alternative for accurately identifying GABAergic neuron subclasses in macaques.