Prenatal Development of Parvalbumin Immunoreactivity in the Human Striate Cortex

In human primary visual cortex, parvalbumin (PV) is expressedby Cajal-Retzius cells in layer I by 20 weeks of gestation (20W),but its immunoreactivity is mostly lost by term. PV immunoreactivityin layers II–VI mainly develops later, from 26 to 34W,following an approximately ‘inside-outside’ sequencein a series of bands. PV-positive perikarya appear in layerV by 20W, but only in small numbers. They increase in numberand staining intensity by 26W. By 30W a band of densely labelledsomata and neuropil occupies layers IVC–VI. By 34W a second,less dense, band of cell bodies and neuropil appears in IVBand IVC