The authors stained sections of adult human brains with an antibody for proliferating cell nuclear antigen (PCNA), which is expressed in dividing cells. They identified a Nissl-positive structure containing a stream of PCNA-positive cells that, starting in the SVZ, followed a caudal and ventral path (which they named the descending limb of the stream), wrapping itself around the rostral side of the caudate nucleus. From the bottom of the caudate the stream turned rostrally and ventrally (and was named the rostral limb of the RMS) towards the anterior olfactory cortex, where it entered the olfactory tract and eventually the olfactory bulb. 90% of the PCNA-positive cells were found in the descending limb of the human RMS, whereas the rostral limb only contained 10%, indicating that more proliferation took place early in the RMS and that, as in the rodent RMS, cells may start differentiating as they approach the olfactory tract.
To assess whether the cells forming the RMS were indeed migratory, the authors stained sections for polysialylated neural cell adhesion molecule (PSA–NCAM), which is expressed by migrating neurons. PSA–NCAM-positive cells were found throughout the RMS. Furthermore, βIII-tubulin, a marker of immature neurons, colocalized with PSA–NCAM in cells in the SVZ, olfactory tract and olfactory bulb. Electron microscopy confirmed that the SVZ cells resembled the migratory cells found in the rodent SVZ. Together, these data indicate that the human brain contains an RMS consisting of migrating neuroblasts.
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