THE OLFACTORY SYSTEM OF MIGRATORY ADULT SEA LAMPREY (PETROMYZON-MARINUS) IS SPECIFICALLY AND ACUTELY SENSITIVE TO UNIQUE BILE-ACIDS RELEASED BY CONSPECIFIC LARVAE

Larval sea lamprey inhabit freshwater streams and migrate to oceans or lakes to feed after a radical metamorphosis; subsequently, mature adu lts return to streams to spawn. Previous observations suggested that l amprey utilize the odor of conspecific larvae to select streams for sp awning. Here we report biochemical and electrophysiological evidence t hat this odor is comprised of two unique bile acids released by larvae . High performance liquid chromatography and mass spectrometry demonst rated that larval sea lamprey produce and release two unique bile acid s, allocholic acid (ACA) and petromyzonol sulfate (PS). Electro-olfact ogram (EGG) recording also demonstrated that the olfactory system of m igratory adult sea lamprey is acutely and specifically sensitive to AC A and PS; detection thresholds for these compounds were similar to 10( -12) M. ACA and PS were the most potent of 38 bile acids tested and cr oss-adaptation experiments suggested that adult sea lamprey have speci fic olfactory receptor sites associated with independent signal transd uction pathways for these bile acids. These receptor sites specificall y recognize the key substituents of ACA and PS such as a 5 alpha-hydro gen, three axial hydroxyls, and a C-24 sulfate ester or carboxyl. In c onclusion, the unique lamprey bile acids, ACA and PS, are potent and s pecific stimulants of the adult olfactory system, strongly supporting the hypothesis that these unique bile acids function as migratory pher omones in lamprey.