Hippocampal Cajal–Retzius cells project to the entorhinal cortex: retrograde tracing and intracellular labelling studies

Abstract

Cajal-Retzius (CR) cells are characteristic horizontally orientated, early-generated transient neurons in the marginal zones of the neocortex and hippocampus that synthesize the extracellular matrix protein reelin. They have been implicated in the pathfinding of entorhino-hippocampal axons, but their role in this process remained unclear. Here we have studied the axonal projection of hippocampal CR cells. Following injection of the carbocyanine dye DiI into the entorhinal cortex of aldehyde-fixed rat embryos and young postnatal rats, neurons in the outer molecular layer of the dentate gyrus and stratum lacunosum-moleculare of the hippocampus proper with morphological characteristics of CR cells were retrogradely labelled. In a time course analysis, the first retrogradely labelled CR cells were observed on embryonic day 17. This projection of hippocampal CR cells to the entorhinal cortex was confirmed by retrograde tracing with Fast Blue in new-born rats and by intracellular biocytin filling of CR cells in acute slices from young postnatal rat hippocampus/entorhinal cortex and in entorhino-hippocampal slice cocultures using infrared videomicroscopy in combination with the patch-clamp technique. In double-labelling experiments CR cells were identified by their immunocytochemical staining for reelin or calretinin, and their interaction with entorhino-hippocampal axons labelled by anterograde tracers was analysed. Future studies need to investigate whether this early transient projection of hippocampal CR cells to the entorhinal cortex is used as a template by the entorhinal axons growing to their target layers in the hippocampus.

Borna Disease Virus Replication in Organotypic Hippocampal Slice Cultures from Rats Results in Selective Damage of Dentate Granule Cells

“…Hippocampi were dissected from rat pups (P0 to P2) and cut into 350-m sections with a tissue chopper under sterile conditions. Hippocampal sections were transferred into petri dishes containing cold buffer solution of minimum essential medium supplemented with 2 mM glutamine at pH 7.3 and further cultivated on humidified porous membranes (Millicell Cell Culture Inserts CM30; Millipore Corporation) for various periods (14, 21, or 28 days) in slice culture medium as previously described (6). The medium was changed three times per week.…”

The Repulsive Guidance Molecule RGMa Is Involved in the Formation of Afferent Connections in the Dentate Gyrus

“…These complex slices (n ϭ 62) were cultivated on porous membranes (Millicell, Millipore Corporation, Bedford, MA) for 7 d in vitro (DIV 7) and fed with medium as described previously (Ceranik et al, 1999). The cocultures were treated in different sets of experiments either with a functional RGMa Ab (1 g/ml) (n ϭ 18) or with phosphatidylinositolspecific phospholipase C (PI-PLC) (Sigma) at two different concentrations (5 and 10 U/ml) (n ϭ 36).…”

Novel and Transient Populations of Corticotropin-Releasing Hormone-Expressing Neurons in Developing Hippocampus Suggest Unique Functional Roles: A Quantitative Spatiotemporal Analysis

“…Recent data indicate roles for hippocampal Cajal-Retzius cells in the pathfinding of entorhinal axons (Ceranik et al, 2000a) and as transient postsynaptic targets for these axons . These actions of Cajal-Retzius cells may involve reelin, as evident from the severe cytoarchitectonic malformations in reelin-deficient (reeler) mice (for review, see Frotscher, 1998).…”