Olfactory transduction is thought to be mediated by a G protein-coupled increase in intracellular adenosine 3',5'-monophosphate (cAMP) that triggers the opening of cAMP-gated cation channels and results in depolarization of the plasma membrane of olfactory neurons. In olfactory neurons isolated from the channel catfish, Ictalurus punctatus, stimulation with olfactory stimuli (amino acids) elicits an influx of calcium that leads to a rapid increase in intracellular calcium. In addition, in a reconstitution assay a plasma membrane calcium channel has been identified that is gated by inositol-1,4,5-trisphosphate (IP3), which could mediate this calcium influx. Together with previous studies indicating that stimulation with olfactory stimuli leads to stimulation of phosphoinositide turnover in olfactory cilia, these data suggest that an influx of calcium triggered by odor stimulation of phosphoinositide turnover may be an alternate or additional mechanism of olfactory transduction.

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Four behavioral experiments conducted in both the laboratory and the field provide evidence that adult sea lamprey (Petromyzon marinus) select spawning rivers based on the odor of larvae that they contain and that bile acids released by the larvae are part of this pheromonal odor. First, when tested in a recirculating maze, migratory adult lamprey spent more time in water scented with larvae. However, when fully mature, adults lost their responsiveness to larvae and preferred instead the odor of mature individuals. Second, when tested in a flowing stream, migratory adults swam upstream more actively when the water was scented with larvae. Third, when migratory adults were tested in a laboratory maze containing still water, they exhibited enhanced swimming activity in the presence of a 0.1 nM concentration of the two unique bile acids released by larvae and detected by adult lamprey. Fourth, when adults were exposed to this bile acid mixture within flowing waters, they actively swam into it. Taken together, these data suggest that adult lamprey use a bile acid based larval pheromone to help them locate spawning rivers and that responsiveness to this cue is influenced by current flow, maturity, and time of day. Although the precise identity and function of the larval pheromone remain to be fully elucidated, we believe that this cue will ultimately prove useful as an attractant in sea lamprey control.

The results of recent preference tests indicate that both male and female landlocked sea lampreys (Petromyzon marinus), after reaching a specific stage of sexual maturation, release pheromones which attract conspecifics of the opposite sex. In addition, sexually immature males, captured at the beginning of a spawning migration, exhibit a preference for water in which sea lamprey larvae have been held, suggesting that chemical signals, originating from populations of sea lamprey larvae in a river, may aid migrating adults in selecting a suitable spawning stream. The possible influence of a number of environmental and physiological factors on pheromone communication in sea lampreys is discussed. Synthetic pheromones have been utilized in insect pest management programs as lures for mass-trapping one or both sexes and for disrupting normal pheromone communication. Similar strategies may be applicable in an integrated program of sea lamprey population management.Key words: pheromones, reproduction, spawning migration, sea lampreys, population management, preference behavior

Background: In gnathostomes, chemosensory receptors (CR) expressed in olfactory epithelia are encoded by evolutionarily dynamic gene families encoding odorant receptors (OR), trace amineassociated receptors (TAAR), V1Rs and V2Rs. A limited number of OR-like sequences have been found in invertebrate chordate genomes. Whether these gene families arose in basal or advanced vertebrates has not been resolved because these families have not been examined systematically in agnathan genomes.

The cyclic lipodepsipeptide, syringomycin E, when incorporated into planar lipid bilayer membranes, forms two types of channels (small and large) that are different in conductance by a factor of sixfold. To discriminate between a cluster organization-type channel structure and other possible different structures for the two channel types, their ionic selectivity and pore size were determined. Pore size was assessed using water-soluble polymers. Ion selectivity was found to be essentially the same for both the small and large channels. Their reversal (zero current) potentials with the sign corresponding to anionic selectivity did not differ by more than 3 mV at a twofold electrolyte gradient across the bilayer. Reduction in the single-channel conductance induced by poly(ethylene glycol)s of different molecular weights demonstrated that the aqueous pore sizes of the small and large channels did not differ by more than 2% and were close to 1 nm. Based on their virtually identical selectivity and size, we conclude that large syringomycin E channels are clusters of small ones exhibiting synchronous opening and closing.

A B S T R A C T The electrical properties of olfactory receptor neurons, enzymaticallydissociated from the channel catfish (Ictalurus punctatus), were studied using the whole-cell patch-damp technique. Six voltage-dependent ionic currents were isolated. Transient inward currents (0.1-1.7 nA) were observed in response to depolarizing voltage steps from a holding potential of -80 mV in all neurons examined. They activated between -70 and -50 mV and were blocked by addition of 1 v.M tetrodotoxin (TYX) to the bath or by replacing Na + in the bath with N-methyl-D-glucamine and were classified as Na + currents. Sustained inward currents, observed in most neurons examined when Na + inward currents were blocked with ~ and outward currents were blocked by replacing K + in the pipette solution with Cs ÷ and by addition of 10 mM Ba 2÷ to the bath, activated between -40 and -30 mV, reached a peak at 0 mV, and were blocked by 5 p~M nimodipine. These currents were classified as L-type Ca 2÷ currents. Large, slowly activating outward currents that were blocked by simultaneous replacement of K ÷ in the pipette with Cs ÷ and addition of Ba 2÷ to the bath were observed in all olfactory neurons examined. The outward K ÷ currents activated over approximately the same range as the Na ÷ currents (-60 to -50 mV), but the Na ÷ currents were larger at the normal resting potential of the neurons (-45 _ 11 mV, mean _ SD, n --52). Four different types of K ÷ currents could be differentiated: a Ca2+-activated K ÷ current, a transient K ÷ current, a delayed rectifier K + current, and an inward rectifier K + current. Spontaneous action potentials of varying amplitude were sometimes observed in the cell-attached recording configuration. Action potentials were not observed in whole-cell recordings with normal internal solution (K ÷ = 100 mM) in the pipette, but frequently appeared when K ÷ was reduced to 85 mM. These observations suggest that the membrane potential and action potential amplitude of catfish olfactory neurons are significantly affected by the activity of single channels due to the high input resistance (6.6 -+ 5.2 G~, n = 20) and low membrane capacitance (2.1 -+ 1.1 pF, n = 46) of the cells. Stimulation of voltage-clamped receptor neurons with a mixture of amino acids (100 tzM each of L-arginine, L-alanine, and L-norleucine with or without L-glutamate), which act at independent classes of receptor sites, elicited receptor currents that were heterogeneous in terms of voltage and ion dependence, time course, reversal potential, and sensitivity to drugs, and appeared to result from at least two different processes. These different types of receptor cell responses to odorant amino acids may reflect activation of different transduction pathways.

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