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Abstract

We used single sensillum recordings to define male Helicoverpa zea
olfactory receptor neuron physiology followed by cobalt staining to
trace the axons to destination glomeruli of the antermal lobe. Receptor
neurons in type A sensilla that respond to the major pheromone
component, (Z)-11-hexadecenal, projected axons to the cumulus of the
macroglomerular complex (MGC). In approximately 40% of these sensilla a
second receptor neuron was stained that projected consistently to a
specific glomerulus residing in a previously unrecognized glomerular
complex with six other glomeruli stationed immediately posterior to the
MGC. Cobalt staining corroborated by calcium imaging showed that
receptor neurons in type C sensilla sensitive to (Z)-9-hexadecenal
projected to the dorsomedial posterior glomerulus of the MGC, whereas
the co-compartmentalized antagonist-sensitive neurons projected to the
dorsomedial anterior glomerulus. We also discovered that the olfactory
receptor neurons in type B sensilla exhibit the same axonal projections
as those in type C sensilla. Thus, it seems that type B sensilla are
anatomically type C with regard to the projection destinations of the
two receptor neurons, but physiologically one of the receptor neurons is
now unresponsive to everything except (Z)-9-tetradecenal, and the other
responds to none of the pheromone-related odorants tested.