CAJAL-RETZIUS NEURONS IN HUMAN CEREBRAL-CORTEX AT MIDGESTATION SHOW IMMUNOREACTIVITY FOR NEUROFILAMENT AND CALCIUM-BINDING PROTEINS

Along with subplate neurons, Cajal-Retzius cells (CRc) are the first n eurons to be generated in the cortical anlage. Studies of their chemic al content; such as neurofilament and caLcium-binding proteins, might give indications on their role in cortical development at midgestation in human fetuses (20-24 gestation weeks), when the CRc are morphologi cally mature. Cajal-Retzius cells were immunolabeled with antibodies t o subunits of neurofilament proteins SM131 and SM132. The SM132 antibo dies (directed against the nonphosphorylated epitope) specifically lab eled the CR cell bodies, dendrites, and proximal axons in a Golgilike fashion. Specific acetylcholinesterase activity is known to be typical of all the CRc, and double labeling for SM132 immunoreactivity and ac etylcholinesterase histochemistry demonstrated that all the CRc exhibi ted SM132 immunoreactivity. The SM131 antibodies (directed against the phosphorylated epitope) exclusively labeled the CRc axons, forming a dense positive network in the deep one-half of layer 1. This plexus wa s much denser than the one described with the Golgi method (Marin-Padi lla, 1990: J. Comp Neurol 239:89-105). Calbindin D-28k, parvalbumin, a nd calretinin immunoreactivities were visualized in the CRc. Double-la beling experiments showed that most of the CRc contained both calbindi n and calretinin and sometimes parvalbumin. These colocalizations reve aled a chemical heterogeneity within the CRc population even though th ey were described as morphologically homogeneous. These colocalization s of calcium-binding proteins in the CRc differed from the other nonpy ramidal cortical neurons where calbindin, calretinin, and parvalbumin are contained in different (mutually exclusive) neuronal populations. Based on the morphological features and differential chemical contents described for the CRc, different hypotheses on their possible role an d fate are discussed. (C) 1995 Wiley-Liss, Inc.