passages.id: split_4_validation_1378_passage
passages.type: progene_text
passages.text: The neuronal populations were identified with digoxigenin - tagged complementary RNA probes for preproenkephalin ( ENK ) and substance P ( SP ) targeted to striatal projection neurons , and somatostatin ( SOM ) , glutamic acid decarboxylase 67 kD ( GAD ( 67 ) ) , and choline acetyltransferase ( ChAT ) targeted to striatal interneurons .