A comparative perspective on minicolumns and inhibitory GABAergic interneurons in the neocortex

Abstract

Neocortical columns are functional and morphological units whose architecture may have been under selective evolutionary pressure in different mammalian lineages in response to encephalization and specializations of cognitive abilities. Inhibitory interneurons make a substantial contribution to the morphology and distribution of minicolumns within the cortex. In this context, we review differences in minicolumns and GABAergic interneurons among species and discuss possible implications for signaling among and within minicolumns. Furthermore, we discuss how abnormalities of both minicolumn disposition and inhibitory interneurons might be associated with neuropathological processes, such as Alzheimer's disease, autism, and schizophrenia. Specifically, we explore the possibility that phylogenetic variability in calcium-binding protein-expressing interneuron subtypes is directly related to differences in minicolumn morphology among species and might contribute to neuropathological susceptibility in humans.

Keywords: calbindin; calcium-binding proteins; calretinin; evolution; neuropathology; parvalbumin.

Figure 1

Minicolumn widths collated from the literature for the Class Mammalia. The following sources were used: Escobar et al. (1986), White and Peters (1993), Peters and Yilmaz (1993), Feldman and Peters (1974), Favorov and Diamond (1990), Tommerdahl et al. (1993), Gabbott and Bacon (1996), Peters and Walsh (1972), Peters and Kara (1987), Kohn et al. (1997), Fleischauer et al. (1972), DeFelipe et al. (1990), Peters and Sethares (1991), Peters and Sethares (1996), Peters and Sethares (1997), Buxhoeveden et al. (2001a), Von Bonin and Mehler (1971), Kaas et al. (1981), Buxhoeveden et al. (2002a), Schlaug et al. (1995), Seldon (1981), del Rio and DeFelipe (1997a), Buldyrev et al. (2000); and Casanova and Tilquist (2008). Note that in certain cases an average minicolumn width had been computed by calculating the mean based on the minimum and maximum values reported in each study. Numbers refer to Brodmann areas.

Figure 2

Schematic representation of the major calcium-binding protein-ir interneuron subtypes. Roman numerals indicate cortical layers, wm = white matter.

Figure 3

Examples of CB (A), CR (B), and PV (C) immunostaining in layers II/III of chimpanzee motor cortex. Scale bar = 50 μm.

Figure 4

Examples of CB (A), CR (B), and PV (C) immunostaining from layer I through layer VI in baboon parietal cortex. Scale bar = 500 μm.