An IRES-lacZ and a neo cassette replaced a 115 bp section of sequence encoding amino acids 74 to 112. Brain expression of lacZ, as revealed by X-gal staining, is heterogeneous, being greatest in the brainstem, midbrain, diencephalon and cerebellum and low in forebrain regions; in the spinal cord, expression is restricted to the gray matter. (J:100127)