Hippocampal pyramidal cells: the reemergence of cortical lamination

The increasing resolution of tract-tracing studies has led to the definition of segments along the transverse axis of the hippocampal pyramidal cell layer, which may represent functionally defined elements. This review will summarize evidence for a morphological and functional differentiation of pyramidal cells along the radial (deep to superficial) axis of the cell layer. In many species, deep and superficial sublayers can be identified histologically throughout large parts of the septotemporal extent of the hippocampus. Neurons in these sublayers are generated during different periods of development. During development, deep and superficial cells express genes (Sox5, SatB2) that also specify the phenotypes of superficial and deep cells in the neocortex. Deep and superficial cells differ neurochemically (e.g. calbindin and zinc) and in their adult gene expression patterns. These markers also distinguish sublayers in the septal hippocampus, where they are not readily apparent histologically in rat or mouse. Deep and superficial pyramidal cells differ in septal, striatal, and neocortical efferent connections. Distributions of deep and superficial pyramidal cell dendrites and studies in reeler or sparsely GFP-expressing mice indicate that this also applies to afferent pathways. Histological, neurochemical, and connective differences between deep and superficial neurons may correlate with (patho-) physiological phenomena specific to pyramidal cells at different radial locations. We feel that an appreciation of radial subdivisions in the pyramidal cell layer reminiscent of lamination in other cortical areas may be critical in the interpretation of studies of hippocampal anatomy and function

High resolution immunogold analysis reveals distinct subcellular compartmentation of protein kinase Cγ and δ in rat Purkinje cells

High resolution immunogold cytochemistry was used to investigate the subcellular distribution of protein kinase Cγ and δ in Purkinje cells of the rat cerebellum. Postembedding incubation with an antibody raised to a peptide sequence near the C-terminus of protein kinase Cγ resulted in strong labelling along the dendrosomatic plasma membrane. A quantitative analysis indicated that this labelling reflected the existence of two pools of protein kinase Cγ; one membrane associated pool and one cytoplasmic pool located within 50 nm of the plasma membrane. The labelling along the plasma membrane showed a pronounced and abrupt increase when moving from the cell body into the axon initial segment. Gold particles signalling protein kinase Cγ were also enriched in putative Purkinje axon terminals in the dentate nucleus. The only organelle showing a consistent immunolabelling for protein kinase Cγ was the Golgi apparatus where the gold particles were restricted to the trans face. Protein kinase Cγ immunoreactivity also occurred in the Purkinje cell spines, with an enrichment in or near the postsynaptic density. Antibodies to protein kinase Cδ produced a very different labelling pattern in the Purkinje cells. Most of the gold particles were associated with rough endoplasmic reticulum, particularly with those cisternae that were located close to the nucleus or in the nuclear indentations. No significant protein kinase C5 immunolabelling was detected at the plasma membrane or in Purkinje cell spines. The present data point to a highly specific compartmentation of the two major protein kinase C isozyme in Purkinje cells and suggest that these isozymes act on different substrates and hence have different regulatory functions within these neurons