Distribution patterns of Wisteria floribunda agglutinin binding sites and parvalbumin-immunoreactive neurons in the human visual cortex: a double-labelling study.

Extracellular lattic-like coatings--known as perineuronal nets (PNs)--ensheath certain types of neurons in the mammalian neocortex. PNs and densely stippled zones in some cortical layers contain proteoglycans stainable e.g. with several plant lectins. The present study is focused on the binding sites of the plant lectin Wisteria floribunda agglutinin (WFA) and on its relationship to parvalbumin-immunoreactive (PARV-ir) neuronal constituents in the human visual cortical fields 17 and 18. Size and numbers of PNs varied not only between these two areas, but also between its layers. In area 17 the PNs appeared accumulated in two conspicuous bands which included layer IV, particularly layer IVb, and layer VI. Layer IVc of area 17 contained numerous small faintly stained PNs. In area 18 a two-tiered organization of PNs in layers IIIb-c and layer V was emphasized. The neuropil staining by WFA was much more intense in layers IIIb-c of area 18 than of area 17. In areas 17 and 18 the vast majority of PNs was associated with sub-populations of PARV-ir cells resembling several classes of GABAergic cortical interneurons. Among PARV-negative cells surrounded by PNs, only exceptionally pyramide-like neurons were detected. The patterns of lectin-labelling in the human visual primary and association cortex resembled those of macaque monkeys and differed from those in the visual cortex of rat and gerbil. These differences between mammals representing divergent modes of visual specialization may support the view that such extracellular matrix components in these occipital cortical areas are involved in visual information processing subserving fast inhibitory interneuronal actions.