Perfusion with cGMP analogue adapts the action potential response of pheromone-sensitive sensilla trichoidea of the hawkmoth Manduca sextain a daytime-dependent manner

Abstract

SUMMARY Pheromone-dependent mate search is under strict circadian control in different moth species. But it remains unknown whether daytime-dependent changes in pheromone sensitivity already occur at the periphery in male moths. Because adapting pheromone stimuli cause rises of cyclic guanosine monophosphate (cGMP) in pheromone-sensitive trichoid sensilla of the night-active hawkmoth Manduca sexta, we wanted to determine whether cGMP decreases pheromone-sensitivity of olfactory receptor neurons in a daytime-dependent manner. Long-term tip recordings from trichoid sensilla were performed at the early day (ZT 1-4), when many moths are still active, and at the middle of the day (ZT 8-11), when moths are resting. A non-adapting pheromone-stimulation protocol combined with perfusion of the sensillum lymph with the membrane-permeable cGMP analogue 8bcGMP adapted the action potential response but not the sensillar potential. Perfusion with 8bcGMP decreased the initial action potential frequency, decreased the numbers of action potentials elicited in the first 100 ms of the pheromone response and attenuated the reduction of action potential amplitude. Furthermore, the decrease in 8bcGMP-dependent action potential frequency was stronger in recordings made at ZT 8-11 than at ZT 1-4. In the control recordings during the course of the day the pheromone responses became increasingly tonic and less phasic. At ZT 8-11 only, this daytime-dependent effect was further enhanced by 8bcGMP application. Thus we hypothesize that during the moths' resting phase,elevated cGMP levels underlie a daytime-dependent decrease in pheromone sensitivity and a decline in the temporal resolution of pheromone pulses.

Deterrence of feeding in Rhodnius prolixus (Hemiptera: Reduviidae) after treatment of antennae with a nitric oxide donor

“…Electrophysiological studies show that nucleotide-activated currents in cultured ORNs of M. sexta are directly activated by cAMP and cGMP (Krannich & Stengl, 2008); and that a cGMP analog adapted the action potential response of pheromonesensitive sensilla trichoidea of M. sexta in a daytime-dependent manner (Flecke et al, 2006).…”

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

“…The animals were kept under long-day photoperiod conditions (L:D 17h:7h) at 24-27°C and 40-60% relative humidity. The preparation, recording conditions and digitization have been described previously (Flecke et al, 2006). Since light sources with an emission frequency above 600nm do not function as a zeitgeber (Pittendrigh et al, 1970) and to avoid light-dependent phase shifts, red light emitting LEDs with a narrow frequency spectrum were used for illumination of the preparation and the set-up during the scotophase (Kingbright LKR 530100, Kingbright Electronics, Issum, Germany).…”

“…The second messenger 8bcAMP at a concentration of 10 mmol l -1 or 100 mmol l -1 was applied by perfusion over the recording electrode as described previously (Flecke et al, 2006). Therefore, altered sensillum lymph Ringer solutions were employed.…”

“…8bcAMP perfusion started at the beginning of the recordings. The high 8bcAMP concentration of 10 mmol l -1 used in most of the recordings was necessary to obtain significant diffusion during the first hour of the recordings and is equal to the concentration of 8-bromo 3Ј,5Ј-cyclic guanosine monophosphate employed in an earlier study (Flecke et al, 2006). In a subset of recordings the biogenic amine OA (1mmoll -1 ) was applied in the same way (Flecke and Stengl, 2009).…”

“…The osmolarity was adjusted to 475 mosmol l -1 for sensillum lymph Ringer solution and to 450mosmoll -1 for the haemolymph Ringer solution using mannitol. Details of the pheromone stimulation have been given previously (Flecke et al, 2006). Stimuli with doses of 10 or 1 mg of synthetic BAL [(E,Z)-10,12-hexadecadienal], generously provided by T. Christensen (University of Arizona, Tucson, AZ, USA) and J. Krieger (University of Hohenheim, Stuttgart, Germany), were applied in a non-adapting stimulation protocol (stimulus duration: 50 ms) in intervals of 5 min for 180 min of the recording duration.…”