Antennal olfactory receptors

Differential sensory sensitivity. The insect s perception of plant odours differs essentially from their discrimination of non-volatile taste substances, as phytophagous insects may already perceive the odour at some distance from the plant. In adult phytophagous insects the antennae bear a large number of olfactory sensilla in order to detect the minute concentrations of the leaf odour components in the air downwind from a plant. The overall sensitivity of the antennal olfactory receptor system can be measured by making use of the electroantennogram technique (17). An electroantennogram (EAG) is the change in potential between the tip of an antenna and its base, in response to stimulation by an odour component. Such an EAG reflects the receptor potentials of the olfactory receptor cell population in the antenna. 

The antennal olfactory receptor system in several phytophagous insects is very sensitive in the detection of the green odour components. In the Colorado beetle Leptinotarsa decemlineata, the threshold of response for trans-2-hexen-1-ol is circa 10b molecules per ml of air (17). In comparison, at 760 mm Hg and 20 C, 1 ml of air contains about 1019 molecules. The insects tested i.e., the migratory locust Locusta migratoria, the carrot fly Psila rosae (18), the cereal aphid Sitobion avenae (19), the Colorado beetle L. decemlineata (17), Leptinotarsa... 

The sensitivity of the antennal olfactory receptor system differs even between Colorado beetle populations (see Figure 5). The beetles of the field population in Wageningen are relatively more sensitive for cis-3-hexenyl acetate when tested than those of the laboratory stock culture. Beetles of the Utah population are relatively less sensitive for trans-2-hexen-1-ol and trans-2-hexenal than the individuals of the field population in Wageningen, and those insects obtained from the laboratory stock culture. The functional significance of these differences for the geographic variation in host plant range of this insect species needs further elucidation (21,22). 

Figure 4. Sensitivity spectrum of the antennal olfactory receptor system in several phytophagous insect species to the green odor components. BAG amplitudes in response to the iruiividual components are visualized in the areas of circles. Data were derived from Refs. 18 (a), 19 (b), 17 (c), and 20 (d).

Schafer, R. and Sanchez, T. V. (1976). The nature and development of sex attractant specificity in cockroaches of the genus Periplaneta. II. Juvenile hormone regulates sexual dimorphism in the distribution of antennal olfactory receptors. Journal of Experimental Zoology 198 323-336. 

Selzer, R. (1981). The processing of a complex food odor by antennal olfactory receptors of Periplaneta americana. Journal of Comparative Physiology A 144 509-519. 

On the specificities of antennal olfactory receptor cells of Periplaneta americana. Chemical Senses 8 375-395. 

Shields V. D. C. and Hildebrand J. G. (2001) Responses of a population of antennal olfactory receptor cells in the female moth Manduca sexta to plant-associated volatile organic compounds. J. Comp. Physiol. A 186, 1135-1151. 

Cmjar R. M., Scalera G., Liscia A., Angioy A. M., Bigiani A., Pietra P. and Tomassini Barbarossa I. (1989) Morphology and EAG mapping of the antennal olfactory receptors in Dacus olea. Entomol. Exp. Appl. 51, 77-85. 

Fujimora K., Yokohari F. and Tateda H. (1991) Classification of antennal olfactory receptors of the cockroach Periplaneta americana L. Zool. Sci. (Tokyo) 8, 243-255. 

Hansson, B.S., Ochieng, S.A., Grosmaitre, X., Anton, S., Njagi, P.G.N. Physiological responses and central nervous projections of antennal olfactory receptor neurons in the adult desert locust, Schistocerca gregaria (Orthoptera Acrididae). J. Comp. Physiol. A 179, 157-167 (1996)... 

Payne and Dickens (357) have described a technique to elucidate the specificity of the receptor system of the southern pine beetle, D. frontalis. The technique employs the differential adaptation of the antennal olfactory receptors to various test compounds either the single unit recording technique or the electroantennogram (EAG) technique is used. It is designed to determine whether different compounds are recognized by the same receptor site and is based on the exposure of the antennal preparation to one compound until the site is completely adapted, followed by exposure to a test compound. It is claimed that failure to show a response to a test compound after adaptation to another indicates that all the chemorecognition sites for the test compound are occupied by the first compound. As it had been shown that the receptors for both bicyclic ketals and host terpenes respond with equal intensites (358), Dickens and Payne (321) calculated the percent of the acceptors (receptor sites) capable of interacting with the various compounds tested. 

Fig-1 Schematic view of the overall olfactory processing in insects. Pheromones and other semiochemicals are detected by specialized sensilla on the antennae, where the chemical signal is transduced into nervous activity. The olfactory receptor neurons in the semiochemi-cal-detecting sensilla are connected directly to the antennal lobe. Here the semiochemical-derived electrical signals are processed and sent out (through projection neurons) to the protocerebrum. Olfactory information is then integrated with other stimulus modalities, a decision is made, and the motor system is told what to do... 

Potential PBPs (OS-E and OS-F) U02545, U02546 identified on the third antennal segment of adult males (McKenna etal. 1994) PBP-related proteins found in different subsets of olfactory sensilla (Pikielny etal. 1994) First insect olfactory receptors (of unknown odorant selectivity) identified on the maxillary palp (Clyne etal. 1999)... 

Hansson B. S., Almaas T. J. and Anton S. (1995) Chemical communication in heliothine moths. V. Antennal lobe projection patterns of pheromone-detecting olfactory receptor neurons in the male Heliothis virescens (Lepidoptera Noctuidae). J. Comp. Physiol. A 177, 535-543. 

The sex attractants of Bombyx and Porthetria (and probably those of most Lepidoptera as well as of insects of other orders) are received by olfactory receptors of the male antennae 38), Removal of one male antenna does not prevent detection of the sex scent, but complete removal of both antennae results in loss of such reception. Schneider and coworkers 35, 36) have taken advantage of this antennal reception in developing an electrophysiological method for the bioassay of insect sex attractants which is approximately 1000 times more sensitive than any known behavioral method. They found that stimulation of the sensory cells in the male antenna by exposure to the female sex scent set up a local electrical potential (receptor potential) %hose amplitude is dependent upon the intensity of the stimulant. The... 

Alioto TS, Ngai J (2005) The odorant receptor repertoire of teleost fish. BMC Genomics 6 173 Anton S et al (2003) Central projections of olfactory receptor neurons from single antennal and palpal sensilla in mosquitoes. Arthropod Struct Dev 32 319-327 Bartelt RJ et al (1985) cis-Vaccenyl acetate as an aggregation pheromone in Drosophila mela-nogaster. J Chem Ecol 11 1747-1756... 

S.A. Ochieng, P. Anderson and B.S. Hansson, Antennal lohe projection patterns of olfactory receptor neurons involved in sex pheromone detection in Spodoptera httorahs (Lepidoptera Nocmidae), Tissue Cell. 27 (1995) 221-232. 

B.S. Hansson, Antennal lobe projection patterns of pheromone-specific olfactory receptor neurons in moths, in Insect pheromone research new directions, R.T. Carde, A.K. Minks (eds.), Chapman Hall New York, (1997), pp. 164-183. 

Steinbrecht, R.A. Zur Morphometric der Antenne des Seidenspinners, Bombyx mori L. Zahl und Verteilung der Riechsensillen (Insecta, Lepidoptera). Z Morph Tiere 66, 93-126 (1970) Steinbrecht, R.A., Kasang, G. Capture and conveyance of odour molecules in an insect olfactory receptor. In Schneider, D. (ed.) Olfaction and Taste IV, Stuttgart, Wissensch Verlags-ges, pp. 193-199 (1972)... 

It should be mentioned that data on cockroach antennal (U3) and maxillar palp (jtU) olfactory sensilla show that different receptor cells display consistently different sensitivities towards the same ranges of n-alcohols (e.g. so called pentano and heptanol receptors). Additionally, the existence of vertebrate olfactory receptor cells which display different sensitivities for the same alcohols can be concluded from single-unit adaptation and cross adaptation studies ( ). Although the effects could be due to different protein receptor species, they can also be explained on the basis of different lipid compositions in the receptor cells in question. 

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