Changing distribution patterns of synaptophysin-immunoreactive structures in the human dorsal striatum of the fetal brain.

Within the striatum two compartments, matrix and patches, can be distinguished by differences in the expression of neuroactive substances, afferent and efferent connections and time of neurogenesis. The present study was done to demonstrate the pattern of synaptophysin (SYN) expression which is indicative of synaptogenesis in the human fetal striatum (15th-32nd weeks of gestation) with special reference to developmental changes. From the 15th to the 22nd gestational weeks an intense diffuse SYN immunolabelling of striatal patches is observed. In the matrix SYN-immunoreactive fiber bundles are seen until the 20th week. Thereafter, the matrix is nearly devoid of SYN-immunoreactive structures. From the 28th week of gestation the matrix contains diffuse SYN immunoreactivity which gradually becomes as intense as that of the patches. The latter, thus, can no longer be delineated in the 30th week. The results show that fibrous SYN immunolabelling most probably indicating intra-axonal transport of synaptic vesicles can only be observed during the first half of gestation. Moreover, it becomes obvious that the patch compartment can selectively be visualized by anti-SYN until the 28th week. This pattern may correspond to the early dopaminergic innervation from the substantia nigra which is known to reach the developing patches. From the 28th week a transition from patchy to diffuse immunolabelling is seen. The increase in matrix labelling may be due to the occurrence of new neuronal contacts. The changeover from patchy to homogeneous SYN immunolabelling takes place distinctly earlier than changes in the distribution of other neuroactive substances described before.

Alterations in myelin formation in fetal brains of twins.

Insufficient nutrition is known to lead to disturbances in postnatal myelin formation. This study aims to demonstrate that early myelination is altered in human twin pregnancies. Five brains of twins with a symmetric blood supply and three brains of twins with chronic fetal-fetal transfusion syndrome (one hypervolemic acceptor and two hypoxemic donors) were investigated and compared with six brains of singletons. The globus pallidus, where myelination normally starts within the prosencephalon, was studied immunohistochemically using antibodies against myelin basic protein (MBP) and with the aid of electron microscopy. In twins and donors, MBP-immunostained somata of myelin-forming oligodendrocytes were packed densely within the globus pallidus, whereas in singletons and acceptors an intense fibrous immunoreactivity was observed. Electron micrographs revealed noncompacted myelin in twins, whereas in singletons the multilaminar structure of compact myelin was observed. The results demonstrate a distinct qualitative alteration in myelination because of nutritional insufficiency during pregnancy. The lack of MBP-positive fibers (i.e., compact myelin sheaths) may be correlated to impaired maturation of oligodendroglia. The alterations described here may reflect a delayed incorporation of MBP into the processes so that the formation of compact myelin is retarded.