Elsevier

Neuroscience

Volume 88, Issue 1, January 1999, Pages 93-105
Neuroscience

Area- and lamina-specific organization of a neuronal subpopulation defined by expression of latexin in the rat cerebral cortex

https://doi.org/10.1016/S0306-4522(98)00185-7Get rights and content

Abstract

The aim of the present study was to investigate the density, laminar distribution, size, morphology, and neurotransmitter phenotype of rat cortical neurons expressing latexin, an inhibitor of carboxypeptidase A. Immunohistochemical analyses established that latexin-immunoreactive neurons are restricted essentially to the infragranular layers of lateral cortical areas in the rat. The overall density, laminar or sublaminar localization, and cell size distribution of latexin-positive neurons differed substantially across cytoarchitectonic areas within lateral cortex. Numerous latexin-positive neurons had the morphology of modified pyramidal cells especially of layer VI. The vast majority of latexin-positive neurons were glutamate-immunoreactive in the six lateral neocortical areas examined, while neurons immunoreactive for both latexin and GABA were virtually absent. Thus the majority of latexin-positive neurons are likely to be excitatory projection neurons.

The area- and lamina-specific distribution of the latexin-expressing subpopulation of glutamate-immunoreactive neurons is a distinctive feature that may contribute to the functional specialization of the lateral cortical areas.

Section snippets

Animals

Wistar male rats (Sankyo; Shizuoka, Japan) aged 45–55 days were used.

Timm staining

To facilitate the identification of cortical areas, sections were stained by the Timm method,[16]with certain modifications compatible with simultaneous detection of latexin immunoreactivity. Rats (n=3) were deeply anaesthetized with pentobarbital (50 mg/kg) and perfused sequentially, first with 100 ml of 0.1% sodium sulphide in 0.15 M sodium phosphate buffer (pH 7.4), then with 250 ml of 0.5% glutaraldehyde in the same buffer,

Density and laminar distribution of latexin-immunoreactive neurons

As described in our previous reports,2, 3latexin-immunoreactive neurons were found in the lateral part of the neocortex and in the adjacent ventral periallocortex. With the modified fixation protocol, the pattern of Timm staining in the cerebral cortex was similar to that reported by Zilles et al.[84]and by Pérez-Clausell.[59]We found that the density of latexin-immunoreactive neurons in the cerebral cortex co-varies with the subdivision of the lateral cortex into areas defined by the Nissl and

Density and laminar distribution of latexin-immunoreactive neurons and their correlation with cortical area organization

We have established that latexin-positive neurons are abundant in the infragranular layers of the lateral cortical fields, but are very rare or completely absent from dorsal and medial cortical fields. Furthermore, we have demonstrated that the density and laminar distributions of latexin-positive neurons co-vary in relation to cytoarchitectonic area boundaries as defined by Zilles and colleagues,82, 83with the exception of Oc2L.

Interestingly, latexin-positive neurons were dense throughout the

Acknowledgements

The authors wish to thank Drs Edward G. Jones, Heinz Künzle, Toshio Terashima and Keiko Takiguchi-Hayashi for their comments on the manuscript. This work was supported in part by a research grant from the Human Frontier Science Program (RG-11/96 B).

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