Sensilla olfactory receptor neuron

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... 

Fig. 1 Olfactory organ of insects. Insects have two types of olfactory organ antenna and maxillary palp. Antennae and maxillary palps both bear numerous sensilla. An individual sensillum houses between one and four dendrites of olfactory receptor neurons, a Morphology of the olfactory organ of the adult silkmoth. b Morphology of the olfactory organ of silkmoth larvae...

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... 

Upon returning to our home base we analyzed the more detailed structure of the olfactory organs of B. latro. The aesthetascs could be divided into at least two types, where one is more prevalent towards the tip of the antenna, and displays what might be a terminal pore. The placement and the possible pore could indicate a function in taste perception. The major part of the aesthetascs was uniformly scale-like without terminal pore. In fact, no pores at all could be observed, not even the minute cuticular pores observed in almost all insect olfactory sensilla. We have so far not been able to elucidate how molecules in gas phase enter the inside of the B. latro aesthetascs. Each hair was shown to contain a very large number of olfactory receptor neurons, not only similar to what has been found in other crustaceans, but also in e.g., honeybees and locusts (Hansson et al. 1996 Ochieng et al. 1998). 

Fig. 12.2 Chemosensors of spiny lobsters, (a) Chemosensors are found on all appendages and body surfaces, (b, c) The antennules are covered with different types of chemosensilla, including several in the aesthetasc tuft aesthetasc sensilla (a), guard sensilla (gs), companion sensilla (cs), asymmetric sensilla (as) and those outside the tuft setuled sensilla (ss), hooded sensilla (hs), plumose (ps), and simple sensilla (ms). The aesthetascs however are the only sensilla that house exclusively chemoreceptors (the others also contain mechanoreceptors). The aesthetascs contain olfactory receptor neurons that mediate responses to intraspecific signals and cues. Reproduced from Steullet et al. (2001) with permission from The Journal of Experimental Biology...

Figure 3.2 (See color insert.) Schematic overview of insect antennal structures and possible modes of elec-trophysioiogicai measurements. Antennae are adorned with many sensillum types, each housing olfactory receptor neuron (ORNs) of various sensitivities as defined by the olfactory receptors they express. Approximate summated responses from many/all sensilla can be recorded in the fonn of voltage deflections, termed electroantennogram (right), or individual ORN responses can be measured by penetrating a single sensillum (bottom).

Largely, the insect detectors for pheromones and other semiochemicals are arrays of hair-like sensilla distributed over the surface of the antennae and palps. In some species, such as scarab beetles [3, 4] and the honeybee [5], semiochemicals are received by olfactory plates. The more ubiquitous hair-like sensilla typically consist of hollow cuticular hairs (10-400 pm long, 1-5 pm thick) innervated by one or several olfactory receptor cells (neurons) and three auxiliary cells [6]. 

The sensitivity and selectivity of olfaction and contact chemosensation are due (1) in the brain, to the existence of a neuronal network of neurons tuned to a specific chemical stimulus, and (2) in the periphery, to the existence of olfactory/ chemosensory receptor neurons housed in sensory microorgans called sensilla. The sensilla can best be viewed as simple cuticular porous extrusions that increase the surface that captures airborne odorants or chemicals dissolved in water droplets. They contain the receptive olfactory or chemosensory structures (Schneider, 1969). The olfactory sensilla are most numerous on the antennae and mediate the reception of sex pheromones and plant volatiles, as well as other odorants. Low volatility pheromones may also be detected by contact chemoreceptors on... 

Insect chemosensory organs have been differentially developed for taste and olfactory sensing. The contact and the distant chemosensory sensilla are responsible for nonvolatile and volatile chemical reception, respectively. The CHCs with long carbon chains are non-volatile, and therefore thought to be received by taste sensilla (Ebbs and Amrein, 2007). However, because of their insolubility in water, it was very difficult to obtain response recordings to them from taste sensilla. Success was recently obtained, however, in Drosophila melanogaster, where a male-specific CHC as a sex-pheromone inhibiting male-male courtship was found to stimulate the bitter taste receptor neuron within the... 

Generally, the taste sensillum contains only small numbers of receptor neurons for fundamental tastes. Hence, the taste sensillum might not be suitable for perception of CHC pheromones that contain many components. For such multi-component pheromone perception, olfactory sensilla with many receptor neurons might be more suitable, even though CHC contact pheromones are non-volatile in most cases. 

Fig. 3.1. Antenna of the male satumiid moth Antheraea polyphemus. Upper panel Schematic view of the antenna. Each antennal stem segment has four side branches. Lower panel Two antennal segments enlarged with different types of sensilla. The numerous, long olfactory hairs contain two or three receptor neurons responding to two or three components of the female pheromone.

Cate HS, Gleeson RA, Derby CD (1999) Activity-dependent labeling of the olfactory organ of blue crabs suggests that pheromone-sensitive and food-odor sensitive receptor neurons are packaged together in aesthetasc sensilla. Chem Senses 24 559... 

The olfactory receptor cells in insects are usually found on the antennae (Schneider, 1964). These primary sensory ceUs receive the information from the odor signals and transfer it via their own axons to the second order neurons in the antennal lobe (Fig. 2.1). The receiving part of the receptor cell is located within the olfactory organ or sensilla, whose outer structure can be seen on the... 

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