The development of a patchy organization of the rat striatum.

The rat striatum can be divided into patch and matrix compartments. Patches, as marked by high opiate receptor binding, first emerge perinatally from a dense, diffuse field of striatal opiate binding. Our quantitative analysis revealed that the patch compartment formed its peak proportion of the total striatal area at postnatal day 7. After this time, patches occupied a smaller proportion of the striatum, reflecting the fact that the number of patches and mean area per patch reached near adult levels during the first postnatal week, yet the volume of the striatum as a whole continued to increase for several weeks postnatally. Results from transplant and early postnatal lesion experiments suggested that connections between the striatum and other brain areas are important for the formation and/or maintenance of the patch and matrix compartments. Transplants of embryonic striatum to cavities in the cortex of young adult hosts developed diffuse opiate receptor binding but not dopamine receptor binding. Significantly, the opiate receptor binding seen in the transplants was never organized into the dense patches normally seen in the adult striatum. In a few transplants areas of relatively higher opiate receptor binding occurred in areas of relatively low neuronal cell density, as is seen in early normal development, but the dense adult patches never developed. Coronal diencephalic hemisections, but not decortications, in the early postnatal period produced drastic shrinkage of the striatum and, more importantly, a large decrease in opiate receptor patches when expressed as a proportion of total striatal area. Neuronal connections with more caudal brain structures may play a role in the final differentiation and maintenance of the striatal compartments.