Cajal-Retzius neurons in developing monkey neocortex show immunoreactivity for calcium binding proteins.

Immunoreactivity for two calcium binding proteins, 28 kDa calbindin and parvalbumin, was used to label cells morphologically identical to Cajal-Retzius neurons in the developing visual, prefrontal, sensory-motor and temporal cortex of Old World monkeys. At all fetal ages examined (E110-E155), Cajal-Retzius neurons throughout the cortex were immunoreactive for calbindin as well as being acetylcholinesterase positive. Between E130 and E150, the calbindin-immunoreactive Cajal-Retzius cells in the visual cortex, and a few in other cortical areas, also showed parvalbumin immunoreactivity. A reduced population of immunoreactive Cajal-Retzius cells was detected at birth, and none could be visualized by immunocytochemistry or histochemistry at later postnatal ages. Calbindin and parvalbumin immunoreactivity represents a potentially useful marker for this developmentally regulated population of neurons, and the varied expression of the two proteins suggests that Cajal-Retzius neurons may represent a neurochemically heterogeneous cell population.