Cellular architecture of the mouse hippocampus: a quantitative aspect of chemically defined GABAergic neurons with stereology

The structural organization of the central nervous system is an infrastructure of the modern neuroscience. Especially, anatomical research at the cellular level can serve as a fundamental resource to understand various novel findings from the molecular level to the system level. Of the decade, the importance of rigorous quantitative neuroanatomy is gradually realized, but earlier anatomical reports are usually presented in qualitative terms or quantified with biased methods. This article quantitatively describes the spatial distributions of chemically defined GABAergic neurons in the mouse hippocampus by using unbiased stereological techniques. We focus on the expression of nine major neurochemical markers: glutamic acid decarboxylase 67, three calcium binding proteins (parvalbumin, calretinin, calbindin D28K), four neuropeptides (somatostatin, neuropeptide Y, cholecystokinin, vasoactive intestinal protein) and neuronal nitric oxide synthase. Here we deal with their laminar distributions, numerical densities and the relative ratio to the total GABAergic neurons, with special reference to their differentiation along the dorsoventral axis of the mouse hippocampus. Furthermore, we estimate the absolute numbers of GABAergic neurons contained in a 300-mum-thick hypothetical slice. The present data outline the quantitative aspects of the cellular architecture of hippocampal GABAergic system and also give complementary information to the recent multidisciplinary analyses at the single cell level.