Development of layer I and the subplate in the rat neocortex

Exp Neurol. 1990 Jan;107(1):48-62. doi: 10.1016/0014-4886(90)90062-w.


Development of layer I and the subplate of the rat neocortex was examined with [3H]thymidine autoradiography. The experimental animals used for neurogenesis were the offspring of pregnant females injected with [3H]thymidine on 2 consecutive days: Embryonic Day (E) 13-E14, E14-E15, . . . E21-E22, respectively. On Postnatal Day 5, the proportion of layer I and subplate cells originating during 24-h periods were quantified at three anteroposterior levels. Presumptive Cajal-Retzius cells (large horizontal cells) are generated mainly on E14 and subplate cells on E14 and E15 ("outside-in" gradient). Both populations are generated earlier than cells in the cortical plate, which has an "inside-out" gradient. The subplate also has a ventrolateral/older to dorsomedial/younger neurogenetic gradient. The small- to medium-sized horizontal cells in layer I have an extensive period of neurogenesis with an "outside-in" gradient. To study morphogenesis, pregnant females were given single injections of [3H]-thymidine during gestation and embryos were removed in successive 24-h intervals (sequential-survival). On E15 and E16, cells accumulate outside the neuroepithelium in the primordial plexiform layer with older presumptive Cajal-Retzius cells superficial and younger presumptive subplate cells deep. The Cajal-Retzius cells permanently settle superficially among a first system of extracellular channels that appears on E14. Before reaching their final settling sites, subplate cells form the incipient cortical plate in the ventrolateral neocortex on E16. On E17, a seocnd system of extracellular channels appears below the cortical plate. On E18 and E19, subplate cells leave the cortical plate and permanently settle among the deep extracellular channels in a separate layer.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Animals, Newborn / growth & development*
  • Autoradiography
  • Cerebral Cortex / cytology
  • Cerebral Cortex / embryology*
  • Cerebral Cortex / growth & development
  • Embryonic and Fetal Development
  • Rats
  • Rats, Inbred Strains
  • Thymidine


  • Thymidine