Quantitative analysis of sex-pheromone coding in the antennal lobe of the moth Agrotis ipsilon: a tool to study network plasticity

Abstract

To find a mating partner, moths rely on pheromone communication. Released in very low amounts, female sex pheromones are used by males to identify and localize females. Depending on the physiological state (i.e. age, reproductive state), the olfactory system of the males of the noctuid moth Agrotis ipsilon is 'switched on or off'. To understand the neural basis of this behavioural plasticity, we performed a detailed characterization of the qualitative, quantitative and temporal aspects of pheromone coding in the primary centre of integration of pheromonal information, the macroglomerular complex (MGC) of the antennal lobe. MGC neurons were intracellularly recorded and stained in sexually mature virgin males. When stimulating antennae of males with the three main components of the female pheromone blend, most of the neurons showed a biphasic excitatory-inhibitory response. Although they showed different preferences, 80% of the neurons responded at least to the main pheromone component (Z-7-dodecenyl acetate). Six stained neurons responding to this component had their dendrites in the largest MGC glomerulus. Changes in the stimulus intensity and duration affected the excitatory phase but not the inhibitory phase properties. The stimulus intensity was shown to be encoded in the firing frequency, the number of spikes and the latency of the excitatory phase, whereas the stimulus duration only changed its duration. We conclude that the inhibitory input provided by local interneurons following the excitatory phase might not contribute directly to the encoding of stimulus characteristics. The data presented will serve as a basis for comparison with those of immature and mated males.

Brief predator sound exposure elicits behavioral and neuronal long-term sensitization in the olfactory system of an insect

“…2A), and 101 MGC neurons in 50 naive males serving as control. The observed responses of MGC neurons exhibited the same characteristics as in a previous study (22) and response patterns were rather uniform and highly similar to response patterns of projection neurons in other noctuid moths (34). The response threshold, i.e., the lowest concentration that elicited an odor response exceeding the hexane response by at least 10% (Materials and Methods) was established for all neurons investigated.…”

Plant odour stimuli reshape pheromonal representation in neurons of the antennal lobe macroglomerular complex of a male moth

“…All stimuli diluted in hexane were used after a minimum evaporation time of 30min. We used 1ng of the blend prepared as in Jarriault et al (Jarriault et al, 2009), 100g of heptanal and a mixture of both as stimuli. These doses of the pheromone and heptanal had previously been shown to elicit clear responses in ORNs and AL neurons (Barrozo et al, 2010;Barrozo et al, 2011).…”

“…These doses of the pheromone and heptanal had previously been shown to elicit clear responses in ORNs and AL neurons (Barrozo et al, 2010;Barrozo et al, 2011). Stimulation was controlled by a CS55 stimulation device (Syntech, Kirchzarten, Germany) with air flow compensation, as described earlier (Jarriault et al, 2009). Briefly, a continuous air flow of 0.3ms -1 was blown over the antenna during the whole experiment.…”

Modelling the signal delivered by a population of first-order neurons in a moth olfactory system

“…Their small number explains that they are rarely found in the recorded samples (the ratio of sample size to number of pheromone-sensitive ORNs is only about 1‰). However, they are essential to explain the responses of the projection neurons (PNs) to which the ORNs are connected in the MGC because the average PN has much lower threshold and shorter latency than the average ORN (Jarriault et al, 2009). These properties of PNs can be explained only if they selectively react to the ORNs with the lowest thresholds and shortest latencies (Grémiaux et al, in preparation).…”