Blanka KALINOVA. Bill S. HANSSON
Institute of Organic Chemistry and Biochemistry, Insect
Chemical Ecology Unit,Flemingovo nam. 2, 166 10, Prague. The Czech Republic
Department of Ecology, Lund University, S-223 62 Lund, Sweden
The antennal lobe of the insect brain is the primary processing center of olfactory sensory information. The glomeruli of the antennal lobe are the convergence sites of axons of antennal receptor neurons and antennal lobe interneurons. All synaptic contacts between these two populations of neurons take place within glomeruli. In male M. sexta, the macroglomerular complex (MGC), specialized for primary processing of information about the conspecific female sex-pheromone blend, contains two distinct glomerular compartments. A globular subdivision, the cumulus, is located just at the entrance of the antennal nerve while a ring-like, toroidal subdivision, toroid, is found further away from the antennal nerve entrance. These anatomically distinct subdivisions represent two functionally separate regions of pheromone-information- processing neuropile as revealed in previous studies, when responses to antennal stimulation were recorded intracellularly in the antennal lobes and neuronal arborizations within the MGC were studied by injection of intracellular dye. Projection neurons tuned to the major pheromone component, (E,Z)-10,12-hexedecadienal (bombykal) displayed dendritic arborizations restricted to the toroidal subdivision of the MGC, while neurons responding selectively to antennal stimulation with (E,Z)-11,13-pentadecadienal, a stable mimic of a second essential pheromone component, (E.E,Z)-10,12,14-hexadecatrienal, arborized exclusively in the cumulus (Hansson et al., 1991).
Single, functionally-identified receptor neurons can be stained by cobalt Iysine or horseradish peroxidase presented in the electrode fluid during stimulation with the key stimulus (Hansson et al., 1992; Shanbhag and Singh, 1992). The infused receptor neuron'axons can subsequently be traced to their target area. In the present study, the central projections of bombykal-specific receptor neurons in the male sphinx moth were studied using cobalt Iysine as a marker. Neurons that responded selectively to bombykal projected exclusively into the cumulus part of the MGC. Our preliminary results thus show no correlation between the arborization area of receptor neuron axons and projection neuron dendrites of neurons displaying similar specificity. The lack in overlap between these two neuronal types within the MGC suggests the existence of local interneurons serving as interfaces between receptor and projection neurons.
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