Structural basis of developmental plasticity in the corticostriatal system

Previous studies have shown that in developing monkey corticostriatal fibres terminate around striatal cytoarchitectonic compartments--cell islands, showing transfiguration around 105th embryonic day (E105) of gestation. In the present study we have analyzed these striatal cytoarchitectonic islands and acetylcholinesterase (AChE) rich patches in the developing human brain considering them as structural indicators of the development of the corticostriatal pathways. Postmortal brain tissue of 27 fetuses and prematurely born infants, ranging from 11-34 postovulatory weeks (POW) whose deaths were attributed to non neurological causes, were processed by Nissl method, AChE histochemistry and imunocytochemical technique (synaptophysin). All specimens are part of the Zagreb Neuroembryological Collection. Initial AChE patches, presumably corresponding to the dopaminergic islands, were seen as early as 10 POW whereas cytoarchitectonical cell islands were not observed until 14 POW The main developmental change occurs between 20-24 POW when AChE negative cell poor zones develop around cell islands. This transient AChE pattern of striatal organization reaches its peak around 28 POW being most prominent along lateral border of putamen. In one case of periventricular hemorrhagic lesion with premortem survival period we have found reorganization of AChE patches in the putamen which indicates structural plasticity of corticostriatal pathways. In conclusion we propose that cell poor zones serve as waiting compartments for growing corticostriatal fibers which approach striatum through subcallosal bundle and external capsule. The period of the existence of striatal compartments (14-30 POW) is a sensitive period for structural plasticity and vulnerability after periventricular lesions.