The expression patterns of the medium- and high-molecular-weight subunits of the neurofilament protein triplet have been extensively studied in several neuroanatomical studies. In the present study, we report the use of the low-molecular-weight neurofilament protein subunit (NF-L) as a reliable marker within the neurofilament protein family to reveal the regional architecture of mammalian neocortex. We document clearly its usefulness in anatomical parcellation studies and report unique expression patterns of NF-L throughout the mouse neocortex. NF-L was most abundant in the somatosensory cortex, the lateral secondary visual area, the granular insular cortex, and the motor cortex. Low NF-L staining intensity was observed in the agranular insular cortex, the prelimbic and infralimbic cortex, the anterior cingulate cortex, the visual rostromedial areas, the temporal association cortex, the ectorhinal cortex, and the lateral entorhinal cortex. NF-L immunoreactivity was present in the perikarya, dendrites, and proximal segment of axons primarily of pyramidal neurons, and was mainly located in layers II and III, and to a lesser extent in layers V and VI. Interestingly, Black-Gold myelin staining confirmed a close correlation between NF-L immunoreactivity and myelination patterns. The characteristic and distinctive distribution and laminar expression profiles of NF-L make it an excellent tool to assess accurately topographical boundaries among neocortical areas as illustrated herein in the adult mouse brain.

Glutamate is known to play a crucial role in the topographic reorganization of visual cortex after the induction of binocular central retinal lesions. In this study we investigated the possible involvement of the glial high-affinity Na + /K + -dependent glutamate transporters in cortical plasticity using western blotting and intracortical microdialysis. Basal extracellular glutamate levels and the re-uptake activity for glutamate have been determined by comparing the extracellular glutamate concentration before and during the blockage of glutamate removal from the synaptic cleft with the potent transporter inhibitor L-trans-pyrrolidine-3,4-dicarboxylic acid. In cats with central retinal lesions we observed increased basal extracellular glutamate concentrations together with a decreased re-uptake activity in non-deprived, peripheral area 17, compared with the sensory-deprived, central cortex of the same animal as well as the topographically matching regions of area 17 in normal subjects. Western blotting experiments revealed a parallel decrease in the expression level of the glial glutamate transporter proteins GLT-1 and GLAST in nondeprived cortex compared with sensory-deprived cortex of lesion cats and the corresponding regions of area 17 of normal subjects. This study shows that partial sensory deprivation of the visual cortex affects the removal of glutamate from the synaptic cleft and implicates a role for glial-neuronal interactions in adult brain plasticity.

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To screen for new region-specific protein markers we compared the proteome maps of the primary visual and somatosensory areas V1 and S1 in mouse brain using 2-D difference gel electrophoresis (2-D DIGE). Twenty-three protein spots showed a statistically significant difference in expression level between V1 and S1, with 52% appearing more abundantly in V1. Twenty-six proteins were mass spectrometrically identified in 22 spots. To assess the validity of this list of potential areal markers generated by 2-D DIGE, the effective area-specific distribution profile of creatine kinase brain subtype (CKB), a protein with a clearly higher expression level in S1, was monitored with in situ hybridization. The mRNA expression profile of CKB displayed a clear area-specific distribution, which allowed demarcation of S1 and its topographical borders with neighboring neocortical areas. This proteomic study demonstrates the innovative application of 2-D DIGE and MS to select new regional markers for neuroscience research.