(A, C) Dark-field photomicrographs of sections through the caudate putamen hybridized with oligonucleotides specific for IRK1 (A) and IRK2 (C). Bright-field high-power photomicrographs in B and Ddemonstrate expression of IRK1 in most cells except the large neurons (B), whereas IRK2 mRNA is expressed predominantly by this population of large cells (D). Scale bars: A, C, 150 μm; B, D, 15 μm.