Relative loss of the striatal striosome compartment, defined by calbindin-D28k immunostaining, following developmental hypoxic-ischemic injury.

The striatum is especially vulnerable to hypoxic-ischemic injury, both in adulthood and during development. Striatal injury is likely to play a major role in the chronic abnormalities of motor control which occur as a consequence of developmental hypoxia-ischemia. Previous studies have shown that two striatal neuron phenotypes, cholinergic and NADPH-diaphorase-positive, are resistant to developmental hypoxia-ischemia, but little is otherwise known of patterns of vulnerability among other striatal neurons. In particular, there has been no data available about patterns of vulnerability within the major striatal neuron group, the medium-sized neurons. Since a major anatomical and functional organization of these neurons is in their localization to either the striosome or the matrix compartments, we have examined the effect of developmental hypoxia-ischemia on these compartments using a quantitative morphologic analysis of immunostaining for the calcium-binding protein calbindin-D28k. We have found that there is a predominant loss of the striosome compartment; in the presence of a mean loss of 33% of total striatal area, there was a 49% decrease in striosomal area. There was also a 41% reduction in the number of striosomes, and a small (14%) but significant decrease in the mean area of individual striosomes. The striosome loss was uniform in the rostrocaudal dimension. At a cellular level, the density of calbindin-positive neurons, expressed as number per unit area, was preserved. While there are several possible explanations for the selective loss of the striosome compartment, one hypothesis is that the lower level of calbindin within these neurons makes them more vulnerable to increases in intracellular calcium, which has been postulated to play a role in hypoxic-ischemic injury. The predominant loss of the striosome compartment following hypoxic-ischemic injury may lead to an imbalance with the functionally distinct matrix system. Such an imbalance may contribute to the abnormalities of motor control observed after this form of injury.