Fig. 1. Schematic diagram of recombinant herpes viruses. The transgene expression cassette is inserted between herpes genes UL36 and UL37. The μ-opioid receptor (μOR) complementary DNA is inserted in either the sense or the antisense orientation relative to the cytomegalovirus (hCMV) immediate early enhancer–promoter. EGFP = enhanced green fluorescent protein; IR = internal repeat; IRES = internal ribosome entry site; L = long; PA = polyadenylation signal; S = short.