Cytoarchitectural and immunohistochemical characterization of calbindin and parvalbumin from the primary motor cortex of the marmoset ( <i>Callithrix jacchus</i> )

Abstract

The primary motor cortex (M1) contains specialized neurons involved in planning and initiating voluntary movements. Calcium-binding proteins (CBP) play a crucial role in modulating and promoting neuronal plasticity by buffering intracellular calcium. CBP are found in distinct neuronal subpopulations, knowledge of which can improve the understanding of locomotion networks. The marmoset monkey is an increasingly popular animal model for studying the neural basis of voluntary movement. Thus, understanding the structural and functional differences in the cortical motor system of marmosets compared to humans is necessary to fully appreciate the parallels and differences between model and target organisms. We analyzed the cytoarchitecture of neurons containing CBP calbindin (CB) and parvalbumin (PV) in marmoset M1. Marmoset M1 is a homogeneous agranular territory that emphasizes structures in layer V. Using visual contrast methodology, we observed stronger CB immunoreactivity (CBir) within layers I to III, while layers II, III, and V show greater PV immunoreactivity (PVir). CBir revealed a higher cell density in layer II and the presence of halo cells in layer V, while PVir revealed higher cell densities in layers II, III, and V, with PVir neurons being generally larger than CBir neurons. Based on these results, we can conclude that CBP immunostaining allows for the characterization of M1. Variations in laminar distribution suggest functional heterogeneity of the CBP-containing neurons in the cortical circuit.