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First published online January 12, 2004
Journal of Experimental Biology 207, 633-644 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00784

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Modular organization of the silkmoth antennal lobe macroglomerular complex revealed by voltage-sensitive dye imaging

Hiroyuki Ai^* and Ryohei Kanzaki

Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan

Author for correspondence (e-mail: kanzaki{at}biol.tsukuba.ac.jp)

Accepted 10 November 2003

We succeeded in clarifying the functional synaptic organization of the macroglomerular complex (MGC) of the male silkmoth Bombyx mori by optical recording with a voltage-sensitive dye. Sensory neurons in the antennae send their axons down either the medial nerve (MN) or lateral nerve (LN), depending on whether they are located on the medial or lateral flagella. Pheromone-sensitive fibers in the MN are biased towards the medial MGC, and those in the LN are biased towards the lateral MGC in the antennal lobe. In our optical recording experiments, the postsynaptic activities in the MGC were characterized by pharmacological analysis. Postsynaptic activities in the MGC were separated from sensory activities under Ca²⁺-free conditions, and subsequently the inhibitory postsynaptic activities were separated by applying bicuculline. We found that the inhibitory postsynaptic responses always preceded the postsynaptic responses separated under Ca²⁺-free conditions. Moreover, the excitatory postsynaptic activities were calculated by subtracting the inhibitory potentials from the posysynaptic activities separated under Ca²⁺-free conditions. When the MN was stimulated, the amplitudes of the excitatory postsynaptic activities in the central toroid, the medial toroid and the medial cumulus were selectively higher than those in the other areas. By contrast, when the LN was stimulated, excitatory postsynaptic activities were evoked in areas in both the lateral toroid and the lateral cumulus. The inhibitory postsynaptic activities were equally distributed throughout the whole MGC. These data suggest that there is a modular organization to the MGC such that information from the two main branches of the antenna is segregated to different sub-regions of the MGC glomeruli.

Key words: insect, Bombyx mori, optical recording, postsynaptic response, GABA, topology, brain

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