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

Abstract

SUMMARYOctopamine causes time-dependent disadaptation of pheromone-sensitive olfactory receptor neurons (ORNs) of Manduca sexta. Because the majority of insect octopamine receptors are positively coupled to adenylyl cyclases we examined whether cyclic adenosine monophosphate (cAMP) mimics octopamine-dependent modulation of pheromone transduction in a time-dependent manner. Long-term tip recordings of single trichoid sensilla of Manduca sexta were performed during three zeitgeber times (ZTs, ZT 0=lights on), while stimulating the sensilla with two doses of the main pheromone component bombykal in a non-adapting protocol. The membrane-permeable cAMP analogue 8bcAMP increased the normalized sensillar potential amplitude in a time-and bombykal dose-dependent way. At the higher bombykal dose only, the applied 8bcAMP antagonized an endogenous decrease in the mean sensillar potential amplitude at ZT 1-4 and ZT 8-11 when ORNs were adapted but not at ZT 22-1, when ORNs were sensitized. In contrast to octopamine, 8bcAMP did not consistently affect the initial pheromone-dependent action potential frequency, the phasic/tonic response pattern, or the time-dependent shift to lower mean action potential frequencies at ZT 8-11. Furthermore, 8bcAMP increased the spontaneous action potential frequency time dependently, but differently from octopamine. In conclusion, our results show that cAMP only partly mimics the octopamine-dependent disadaptation of olfactory receptor neurons during photophase, apparently due to another missing octopamine-dependent synergistic factor such as defined intracellular calcium levels. Supplementary material available online at

Pheromone Transduction in Moths

“…In addition, octopamine increased the spontaneous activity of the pheromone-sensitive ORNs. This increase was only partly mimicked by cAMP-rises (Figure 2; Flecke and Stengl, 2009; Flecke et al, 2010). Possibly, cAMP increased the open probability of the leaky OR/COR ion channel complex as reported in the fruitfly (Wicher et al, 2008).…”

“…In different moth species octopamine improves pheromone source location daytime-dependently in behavioral studies (Linn Jr. and Roelofs, 1986). Octopamine disadapts ORNs and renders pheromone responses more phasic, apparently via a cAMP-dependent transduction cascade and an additional possibly Ca 2+ -dependent cascade in tip recordings of intact trichoid sensilla (Pophof, 2000, 2002; Flecke and Stengl, 2009; Flecke et al, 2010). In addition, octopamine increased the spontaneous activity of the pheromone-sensitive ORNs.…”

No Evidence for Ionotropic Pheromone Transduction in the Hawkmoth Manduca sexta

“…sexta , raised from egg in the rearing facilities of the University of Kassel as described previously [30]. Animals were entrained to a 17:7h light:dark cycle with Zeitgebertime (ZT) 0 light on and ZT 17 light off.…”

Biogenic Amines in Insect Antennae

“…Later, OA modulation of olfactory sensitivity in the antenna of M. sexta was found to be linked to the circadian rhythmicity in pheromone reception through cAMP-dependent disadaptation in receptor cells (Flecke and Stengl, 2009; Flecke et al, 2010; Stengl, 2010). The antennal OA receptor cloned in the M. sexta shares high sequence similarity with other insect α-adrenergic-like OA receptors and increases both cAMP and Ca 2+ intracellular concentration in response to an agonist (Dacks et al, 2006).…”

“…The cross-talk between their signaling pathways and the intracellular biochemical machinery in antennal tissues is attracting attention of researchers (Flecke and Stengl, 2009; Flecke et al, 2010; Chen and Luetje, 2014), but is not studied in detail.…”