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occ1/Follistatin-related protein (Frp) is strongly expressed in the primary visual cortex (V1) of macaque monkeys, and its expression is strongly down-regulated by intraoculartetrodotoxin (TTX) injection. The pronounced area selectivity of occ1/Frp mRNA expression occurs in macaques and marmosets, but not in mice, rabbits and ferrets, suggesting thatocc1/Frp is an important clue to the evolution of the primate cerebral cortex. To further determine species differences, we examined the sensory-input dependency of occ1/FrpmRNA expression in mice in comparison with macaque V1. In macaque V1, occ1/FrpmRNA expression level significantly decreased with even 1-day monocular deprivation (MD) by TTX injection. In contrast to that in macaques, however, the occ1/Frp mRNA expression in the visual cortex in mice was not down-regulated by 1- to 7-day MD by TTX injection. Similarly, MD had no effect on occ1/Frp mRNA expression level in the dorsal lateral geniculate nucleus of mice. In addition, the extirpation of the cochlear or olfactory epitheliumhad no effect on occ1/Frp mRNA expression in either the cochlear nucleus or the olfactory bulb in mice. Thus, occ1/Frp mRNA expression is independent of sensory-input in mice. The results suggest that activity-dependent occ1/Frp mRNA expression is not common between mice and monkeys, and that primate V1 has acquired a unique gene regulatory mechanism that enables a rapid response to environmental changes. The characteristic feature of the activity dependency of occ1/Frp mRNA expression is discussed, in comparison with that of the expression of the immediate-early genes, c-fos and zif268.
Ever since Wong–Riley first reported in the late 1970s that histological staining using the chemical reactions of cytochrome oxidase (CO), a metabolic enzyme in the mitochondria, is useful to reveal the cytoarchitecture of the brain (Wong-Riley, 1979), the CO histochemistry method has been widely used in the field of neuroanatomy, especially in carnivores and primates. It has been suggested that CO activity is coupled with the spike activity of neurons (Wong-Riley, 1979). Most strikingly, the use of CO histochemistry was critical to the discovery of patchy functional sub-compartments in the supragranular layers of primate V1, which are referred to as “CO blobs/puffs/patches” (Horton, 1984). Additionally, CO histochemistry revealed sub-compartments of “thick stripes,” “thin stripes,” and “pale stripes” in the middle layer of the secondary visual cortex (V2), which have been shown to possess distinct connections with V1 and other cortical areas (Sincich and Horton, 2002). These three stripes are also functionally distinct, as binocular disparity coding neurons are clustered into thick stripes (Chen et al., 2008). As such, CO histochemistry has revealed many normally cryptic functional compartments of the mammalian brain. Nonetheless, in this article, we aim to question the interpretation of results from CO histochemistry as “activity maps” of the brain.