Male-specific, sex pheromone-selective projection neurons in the antennal lobes of the mothManduca sexta

Abstract

A subset of olfactory projection neurons in the brain of male Manduca sexta is described, and their role in sex pheromone information processing is examined. These neurons have extensive arborizations in the macroglomerular complex (MGC), a distinctive and sexually dimorphic area of neuropil in the antennal lobe (AL), to which the axons of two known classes of antennal pheromone receptors project. Each projection neuron sends an axon from the AL into the protocerebrum. Forty-one projection neurons were characterized according to their responses to electrical stimulation of the antennal nerve as well as olfactory stimulation of antennal receptors. All neurons exhibited strong selectivity for female sex pheromones. Other behaviorally relevant odors, such as plant volatiles, had no obvious effect on the activity of these neurons. Two broad physiological categories were found: cells that were excited by stimulation of the ipsilateral antenna with pheromones (29 out of 41), and cells that received a mixed input (inhibition and excitation) from pheromone pathways (12 out of 41). Of the cells in the first category, 13 out of 29 were equally excited in response to stimulation of the antenna with either the principal natural pheromone (bombykal) or a mimic of a second unidentified pheromone ('C-15') and were similarly excited by the natural pheromone blend. The remaining 16 out of 29 cells responded selectively, and in some cases, in a dose-dependent manner, to stimulation of the antenna with bombykal or C-15, but not both. Some of these neurons had dendritic arborizations restricted to only a portion of the MGC neuropil, whereas most had arborizations throughout the MGC. Of the cells in the second category, 9 out of 12 were excited by bombykal, inhibited by C-15, and showed a mixed response to the natural pheromone blend. For the other 3 out of 12 cells, the response polarity was reversed for the two chemically-identified odors. Two additional neurons, which were not tested with olfactory stimuli, were tonically inhibited in response to electrical stimulation of the ipsilateral antennal nerve. These observations suggest that some of the male-specific projection neurons may signal general pheromone-triggered arousal, whereas a smaller number can actively integrate inputs from the two know receptor classes (Bal- and C-15-selective) and may operate as 'mixture detectors' at this level of the olfactory subsystem that processes information about sex pheromones.

Effect of juvenile hormone on the central nervous processing of sex pheromone in an insect

“…The AL was manually desheathed to facilitate microelectrode penetration. A flow system perfused the head cavity with saline (10).…”

Humanitarian Demining Using an Insect Based Chemical Unmanned Aerial Vehicle

“…Approximately 85% of the neurons of the MGC display transient responses correlated with the pheromone signal, but are only able to resolve odor pulses of up to a few Hz (Christensen & Hildebrand 1987;Christensen et al 1993;Lei & Hansson 1999). Surprisingly, this frequency response range is similar to the characteristics of the plume pulsing experiments that show that moths display a faster upwind displacement for pulsed pheromone signals (Murlis & Jones 1981;Murlis 1992).…”

“…The second corner stone of the model is based on the Macro Glomerular Complex (MGC) of the Antennal Lobe (AL) of the moth, a glomerulus that evolved to solely process the pheromone signals (Christensen & Hildebrand 1987;Kanzaki et al 1989;Hansson et al 1991;Christensen et al 1993;Christensen et al 1995). Approximately 85% of the neurons of the MGC display transient responses correlated with the pheromone signal, but are only able to resolve odor pulses of up to a few Hz (Christensen & Hildebrand 1987;Christensen et al 1993;Lei & Hansson 1999).…”

Queen mandibular pheromone: questions that remain to be resolved

“…In moths it is clear that uPNs and mPNs are involved extensively in the processing of sex pheromone signals at the level of the ALs. For example, moth uPNs, although responding predominantly to one component of the sex pheromone blend, are usually more generalist than the ORNs they synapse with (Christensen and Hildebrand 1987;Hansson et al 1994Hansson et al , 1991Jarriault et al 2010Jarriault et al , 2009Mustaparta 1996). In contrast, some PNs in the moth (including some identified as mPNs) respond only when all components of the pheromone blend are presented (Anton et al 1997;Christensen et al 1995;Hansson et al 1994).…”