Quantitative analysis of olfactory receptor neuron projections in the antennal lobe of the malaria mosquito, Anopheles gambiae

Mosquitoes are highly dependent on the olfactory sense to find their hosts. How olfactory information concerning host odors is represented and processed in the brain to elicit olfactory guided behavior is not known. We present an exploratory analysis of central projections of olfactory receptor neurons originating from antennal and maxillary palp sensilla known to be involved in the detection of host odors in the malaria mosquito, Anopheles gambiae. We developed computational neuroanatomic methods to determine quantitatively the positions of olfactory receptor neuron terminal arborizations and compare them between brains. These quantitative analyses suggested the existence of five nonoverlapping projection zones within the antennal lobe, with one zone receiving exclusive input from maxillary palp sensilla and two zones each receiving exclusive input from trichoid or grooved-peg antennal sensilla. Projection patterns were not found to depend significantly on the odorants used during the staining procedure. The separate zones receiving input from different sensillum types seemed to represent a functional segregation because olfactory receptor neurons present in the different sensilla differed in their response profiles. (C) 2004 Wiley-Liss, Inc.