A targeting vector was designed to insert an internal ribosome entry site (IRES), the ChR2(H134R)-EYFP fusion gene, and a self-excising neo cassette, ACNF, downstream of the olfactory receptor 160 gene. The neo cassette is excised. Only olfactory sensory neurons (OSN) expressing this specific odorant receptor, M72, express ChR2(H134R)-EYFP, rendering them light sensitive.