[1] UNIV PENN, SCH DENT MED, DEPT BIOCHEM, PHILADELPHIA, PA 19104 USA
[2] UNIV PENN, MONELL CHEM SENSES CTR, PHILADELPHIA, PA 19104 USA
[3] VET AFFAIRS MED CTR, PHILADELPHIA, PA 19104 USA
[4] FLORIDA STATE UNIV, DEPT PSYCHOL, TALLAHASSEE, FL 32306 USA
[5] SUNTORY LTD, INST FUNDAMENTAL RES, OSAKA 618, JAPAN
[6] UNIV STUTTGART HOHENHEIM, DEPT ZOOPHYSIOL, W-7000 STUTTGART 70, GERMANY