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 pa rt, which is clearly separated from (2) the magnocellular part. The latter and its rubrospinal projection is known to be rudimentary in the adult huma n brain. Information concerning the fetal or neonatal features of the red n ucleus is sparse. This study is aimed at providing a detailed account of th e distribution of three calcium-binding proteins: calretinin (CR), calbindi n (CB), and parvalbumin (PV), which are known to be expressed in distinct n euronal populations. Special attention has been paid to transient phenomena . CB was the most abundant protein in the magnocellular part in fetal and p erinatal 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 neuron s were immunolabelled. In double-labellings the majority of neurons express ed both CB and CR; a moderate number of nerve cells solely expressing CR wa s 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 parv ocellular part. A few PV-ir neurons were seen in the magnocellular part of the fetal and perinatal brains. Our results indicated that: (I) the magnoce llular and parvocellular parts of the red nucleus were well-demarcated port ions from fetal life onwards, thus a dominance of the parvocellular part ov er the magnocellular occurred during development; (2) the magnocellular par t was more prominent in the fetal period than in adulthood; (3) neurons in the red nucleus were heterogeneous with respect to the immunoreactivities t owards the three calcium-binding proteins examined; (4) the transient promi nence of the magnocellular part might be a substrate for a specific transit ory pattern of motor behaviour.