Sparse Neurons Research Articles

Prenatal development of calbindin D-28K in human visual cortex.

The distribution of the calcium-binding protein calbindin D-28K (CB) was investigated in human fetal primary visual cortex. CB is present in Cajal-Retzius cells of layer I, in sparse neurons of the ventricular and intermediate zones (VZ, IZ), and in tangential fibres in IZ by 15 weeks (W) of gestation. Cajal-Retzius cells lose their staining by 30W. CB appears in layers II-VI mainly from 26W, following an inside-outside sequence. Until 34W, CB labelling is in somata and neuropil located primarily in layers IVA, IVC and V. Then reactive perikarya and puncta increase in layers II-IVA and deep IVB and C, but are reduced in infragranular layers from 34W to term. From 30W positive somata form clusters in the cell-rich bands in layers IV and V and labelled neuropil in layers III and IV has a periodic pattern from 34W. Also from 34W, numerous lightly reactive pyramidal cells are present in layers II to IVA in primary, but not secondary, visual cortex. Our results show precocious expression of CB before full laminar differentiation of the cortex and that some of this expression is transient.

NADPH diaphorase activity is inhibited by EDTA in neurons but not in choroid plexus epithelium

NADPH diaphorase histochemical staining was investigated in rat brain and choroid plexuses. All epithelial cells of the latter as well as some sparse neurons in striatum and cerebral cortex showed strong NADPH reaction product. While staining was homogeneous in neuronal cytoplasm, it was particulate in epithelial cells. Preincubation with EDTA (0.1 mM, 2 h) prevented appearance of NADPH diaphorase reaction in neurons but not in choroid plexuses. These data show that in rat brain two forms of NADPH diaphorase are present; they are specifically localized in neurons and choroidal cells, respectively.

Architectonics of the thalamus in the echidna (Tachyglossus aculeatus): search for the mediodorsal nucleus.

Architectural characteristics of the thalamus in echidnas and rats were compared in sections stained to reveal cell bodies, myelin, acetylcholinesterase, succinate dehydrogenase and cytochrome oxidase. Numerous species differences were noticed: in general, the thalamus is architecturally more homogeneous in echidnas than in rats, especially anteriorly. In this report we emphasize the presence of a relatively large structure localized in the anteromediodorsal part of the thalamus in echidnas. This structure, previously shown to project to the frontal cortex, contains very small amounts of acetylcholinesterase and the oxidative enzymes; in this respect it resembles the mediodorsal nucleus of rats. The same properties make this formation different from the anterodorsal and anteroventral nuclei in rats, the equivalents of which could not be identified in echidnas. The anteromediodorsal region of the thalamus in echidnas consists chiefly of two cytoarchitecturally different regions: the medial, 'polymorphic' part contains relatively small, densely packed, multiform perikarya, whereas the lateral, 'monomorphic' part is characterised by larger, sparse neurons with little cytoplasm and round, large, empty-looking nuclei in which the nucleolus is clearly seen. We conclude tentatively that this brain structure of echidnas corresponds to the mediodorsal nucleus in placental species. Further studies of connections and chemical properties will be essential to determine the degree of correspondence of the presumed 'frontal lobe system' in echidnas to that in other mammals.

Fine structure of cortical barrels in the mouse

Electron micrographs of sections of mouse neocortical layer IV, cut tangential to the pial surface, show the detailed organization of neuronal groups or 'barrels', which are related functionally to single facial vibrissae. Cortical barrels comprise 'sides' of stellate and small pyramidal neurons, groups of myelinated axons, and apical dendrites. The 'cores' comprise a neuropil of thalamic afferents, sparse neurons, converging basal dendrites of pyramidal cells and stellate cell dendrites. Some neurons of the 'sides' are attached through puncta adherentia.