The mature striatum is divided into a labyrinthine system of striosomes embedded in a surrounding matrix compartment. We pulse-labeled striosomal cells (S cells) and matrix cells (M cells) in cats with 3H-thymidine and followed their distributions during fetal and postnatal development. We identified three maturational phases in S-cell distributions. The early phase (sampled at embryonic day [E]27–E35 following E24-E28 3H-thymidine) was characterized by a transient medial accumulation of synchronously generated S cells within the caudate nucleus adjoining the ganglionic eminence, potentially a waiting compartment. Band-like arrangements of synchronously generated S cells then formed beyond this medial band. During the second phase (sampled at E38–E45), the loosely banded S-cell distributions were transformed into clustered arrangements typical of developing striosomes. In the third phase (sampled from E52 into the postnatal period), these developed into the typical mature striosomal architecture. At adulthood, gentle mediolateral birthdate-gradients in S cells were still evident, but M cells, produced over mid to late prenatal ages, became broadly distributed, without apparent gradients or banding arrangements. These findings suggest that the maturational histories of the striosomal and matrix neurons are influenced by their generation times and local environments, and that future S cells have transient, nonstriosomal distributions prior to their aggregation into striosomal clusters, including a putative waiting compartment. Further, the eventual patterning of the striosomal compartment reflects outside-in, band-like gradient patterns of settling of synchronously generated S cells, patterns that could be related both to neural processing in the mature striatum and to patterns of vulnerability of striatal neurons. J. Comp. Neurol. 523:943–962, 2015. © 2014 Wiley Periodicals, Inc.
Using pulse labeling with 3H-thymidine during embryonic development in cats, the authors traced the settling patterns of future striosomal cells and matrix cells during fetal development and into adulthood. They find that striosomal cells, born early, have transient quasi-banded arrangements before forming clustered arrangements typical of postnatal striatum.