Do subplate neurons comprise a transient population of cells in developingneocortex of rats?

Studies were undertaken to determine whether neurons of the subplate layer represent; a transient or stable population of cells in developing neocorte x of rat;. The first set of studies sought to determine the fraction of sub plate neurons that is lost during early postnatal development. The optical dissector method was used to analyze fluorescently stained material in anim als the age of postnatal day 0 (P0) to P40. These results demonstrate a red uction of slightly less than half of the total number of subplate neurons f rom PO to P40. Counts of labeled cells in littermates at varied ages after [H-3]thymidine or BRDU treatment on gestational day 14 (G14 - birthdate of occipital subplate neurons) or G18 (birthdate of layers III-TV neurons) dem onstrate loss of approximately 50% of neurons in the subplate layer between P0 and P40, somewhat greater than the loss of neurons from cortical layers III-TV. The second set of studies investigated whether subplate neurons di splay cellular atrophy during postnatal development. Analysis of subplate n eurons injected intracellularly with Lucifer yellow in fixed slice preparat ions indicates no reduction in soma size, number of dendrites, or extent of dendritic fields of subplate neurons taken from animals age P0 to P60. The third set of studies investigated whether functional markers of subplate n eurons are reduced during postnatal development. Analysis of tissue stained histochemically for cytochrome oxidase or acetylcholinesterase, or stained immunocytochemically for GABA, somatostatin, or neuropeptide Y, demonstrat e a remarkable loss of expression of staining patterns from late gestationa l ages to P20. These data demonstrate that, although subplate neurons seem not to be a transient population of cells in the usual sense of being elimi nated by cell death or structural atrophy, the loss of histochemical and im munocytochemical markers indicates that they may be a functionally transien t population of cells. J. Comp. Neurol. 426: 632-650, 2000. (C) 2000 Wiley- Liss, Inc.