Central projections of the maxillary and antennal nerves in the mosquito Aedes aegypti

In the mosquito Aedes aegypti, CO2-sensitive receptor neurones are located together with two other types of chemoreceptor neurones in club-shaped sensilla basiconica on the most distal segment of the maxillary palps. In order to identify the central target neuropiles of these neurones and to determine whether antennal receptor neurones project into the same area, the palpal and antennal nerves were labelled by anterograde staining with horseradish peroxidase and by experimentally induced degeneration. The different methods revealed a consistent projection pattern. (1) Maxillary afferents project into the suboesophageal ganglion and ascend further into the ipsilateral antennal lobe. There, they terminate within an identified glomerulus of the ventroposterior lobe. (2) Afferents of the antennal flagellum project into all glomeruli of the ipsilateral antennal lobe, with the exception of the glomerulus innervated by the maxillary nerve. The present anatomical findings suggest that primary processing of information about CO2 levels takes place in a defined glomerulus which also receives input from other palpal chemoreceptor neurones.