Response characteristics of an identified, sexually dimorphic olfactory glomerulus

Partitioning of synaptic neuropil into glomeruli is a common feature of pri mary olfactory centers in most animal species. The functional significance of glomeruli, however, is not yet well understood. The present study is par t of our effort to test the hypothesis that each glomerulus is a functional unit dedicated to processing information about a particular odorant or att ribute of odor molecules and that the glomerular array constitutes a map of "odor space." We investigated the physiological and morphological features of uniglomerular projection neurons (PNs) associated with an identified gl omerulus in each antennal lobe of the female sphinx moth, Manduca sexta. Th is "lateral large female glomerulus" (latLFG) is sexually dimorphic and the refore may play a female-specific role, such as processing of information a bout one or more odorants important for orientation of a female to host pla nts for oviposition. Together with the medial LFG (medLFG), the latLFG resi des outside the array of spheroidal ordinary glomeruli, near the entrance o f the antennal (olfactory) nerve. Each LFG is innervated by four to five PN s. Using intracellular recording and staining, we examined the responses of latLFG-PNs to odorants that represent major classes of volatiles released by host plants of M. sexta. All latLFG-PNs were excited when the ipsilatera l antenna was stimulated with low concentrations of the monoterpenoid linal ool. Dose-response analysis showed that neither other monoterpenoids nor re presentatives of other classes of host plant volatiles were similarly stimu latory to latLFG-PNs. These findings are consistent with the idea that each glomerulus has a characteristic, limited molecular receptive range.