Adaptation in pheromone-sensitive trichoid sensilla of the hawkmoth Manduca sexta

Abstract

While the transduction cascade of pheromone-sensitive olfactory receptor neurons (ORNs) in insects has been thoroughly investigated in vitro (Breer et al., 1988Boekhoff et al., 1990Boekhoff et al., , 1993Stengl et al., 1992;Stengl, 1993Stengl, , 1994Wegener et al., 1993Wegener et al., , 1997, little is known about olfactory adaptation and the mechanisms involved. Adaptation is a universal characteristic of receptor cells of all sensory modalities (Burkhardt, 1961). There are different definitions for the term 'adaptation' but implicit in any definition is a decrease in sensitivity due to the influence of a previous (conditioning) stimulus (Zack, 1979).Moths distinguish pheromone mixtures according to the concentration ratios of the different pheromone components. Thus, differentiation of pheromone concentrations is very crucial for recognition of prospective mates. Turbulences and wind velocities determine the structure of the pheromone filaments that stimulate the antenna of a flying moth. Thus, adapting and non-adapting pheromone stimuli of variable concentrations and stimulus durations reach different parts of the antenna at various time intervals. It is still unknown how the moth can recognize relevant pheromone ratios in various states of adaptation. In our study of pheromone-sensitive ORNs, we examine how adapting pheromone stimuli affect the encoding of different pheromone concentrations (quantity coding) in the intact moth. We distinguish the rapidly (within seconds to minutes) reversible reduction of sensitivity due to prior stimulation (short-term adaptation) from the decline in excitation, as seen during a phasic-tonic response to a stimulus of long duration (desensitization; Zufall and Leinders-Zufall, 2000). Thus, we compare quantity coding in response to short (50·ms) and long (1000·ms) pheromone stimuli, as possibly encountered during flight to the calling female. We do not examine the more slowly occurring (within several minutes to hours) reduction of sensitivity due to In extracellular tip recordings from long trichoid sensilla of male Manduca sexta moths, we studied dose-response relationships in response to bombykal stimuli of two different durations in the adapted and the non-adapted state. Bombykal-responsive cells could be distinguished from non-bombykal-sensitive cells in each trichoid sensillum because the bombykal-responsive cell always generated the action potentials of larger initial amplitude. The bombykal cell, which was recorded at a defined location within a distal flagellar annulus, can resolve at least four log 10-units of pheromone concentrations but is apparently unable to encode all stimulus durations tested. Parameters of the amplitudemodulated sensillar potential and the frequencymodulated action potential responses were examined in different states of adaptation. Evidence is presented for the existence of several mechanisms of adaptation, which affect distinct steps of the transduction cascade. After adapting pheromone stimuli, the sensillar potential rises to a lower ampl...

Modeling and Regression Analysis of Semiochemical Dose–Response Curves of Insect Antennal Reception and Behavior

“…It is apparent from many studies that dose-response curves of electroantennographic (EAG) voltages or neuronal spike frequencies, as well as bioassays in the laboratory, are plotted with a logarithmic scale on the x-axis (e.g., Al Abassi et al 2000; Anderson et al 1993;Byers 1983;Delorme and Payne 1990;Dickens et al 1997;Dolzer et al 2003;Gemeno et al 2003;Hilbur et al 2001;Moore 1981;Preiss and Priesner 1988;Schal et al 1990;. The plots of data points of increasing dosages usually are connected by straight lines, probably because the curvilinear relationships were poorly understood and complicated to plot.…”

Olfactory coding in Drosophila larvae investigated by cross-adaptation

“…This approach, known as cross-adaptation, has been employed in studies of chemosensation in a range of organisms, including bacteria (Gestwicki and Kiessling, 2002), lobsters (Daniel et al, 1994), mice (Kelliher et al, 2003), frogs (Takeuchi et al, 2003), houseflies (Kelling et al, 2002), C. elegans (Colbert and Bargmann, 1995), Manduca sexta (Dolzer et al, 2003) and Drosophila adults (de Bruyne et al, 1999) and larvae (Cobb and Domain, 2000).…”

Perfusion with cAMP analogue affects pheromone-sensitive trichoid sensilla of the hawkmothManduca sextain a time-dependent manner

“…The pheromone responses and the spontaneous activity were evaluated with Clampfit 8 (Molecular Devices, Sunnyvale, CA, USA) and the Microsoft Excel Add-in XtraCell (Dolzer, 2002). All analyses were performed using the direct-current-coupled signal.…”

“…Several directly or indirectly cAMP-dependent ion channels are known in ORNs of M. sexta (Stengl et al, 1999;Dolzer, 2002;Krannich and Stengl, 2008). An apparently directly cAMPdependent non-specific cation channel and a cAMP-dependent Ca 2+ channel were identified in M. sexta , next to other cyclic nucleotide-sensitive cation and potassium channels (Dolzer, 2002;Dolzer et al, 2008).…”