Differential expression of calcium-binding proteins in the red nucleus of the developing and adult human brain

The adult human red nucleus consists of two parts: (1) the parvocellular part, which is clearly separated from (2) the magnocellular part. The latter and its rubrospinal projection is known to be rudimentary in the adult human brain. Information concerning the fetal or neonatal features of the red nucleus is sparse. This study is aimed at providing a detailed account of the distribution of three calcium-binding proteins: calretinin (CR), calbindin (CB), and parvalbumin (PV), which are known to be expressed in distinct neuronal populations. Special attention has been paid to transient phenomena. CB was the most abundant protein in the magnocellular part in fetal and perinatal brains; immunoreactive (ir) neurons appeared numerous and densely packed. In the adult only few and widely spaced ir nerve cells were present. CR-expression largely corresponds to that of CB, except that fewer neurons were immunolabelled. In double-labellings the majority of neurons expressed both CB and CR; a moderate number of nerve cells solely expressing CR was present in the magnocellular part. PV-ir fibers and a moderate number of small cells were observed in the fetal, perinatal as well as the adult parvocellular part. A few PV-ir neurons were seen in the magnocellular part of the fetal and perinatal brains. Our results indicated that: (1) the magnocellular and parvocellular parts of the red nucleus were well-demarcated portions from fetal life onwards, thus a dominance of the parvocellular part over the magnocellular occurred during development; (2) the magnocellular part was more prominent in the fetal period than in adulthood; (3) neurons in the red nucleus were heterogeneous with respect to the immunoreactivities towards the three calcium-binding proteins examined; (4) the transient prominence of the magnocellular part might be a substrate for a specific transitory pattern of motor behaviour.