Physiological Characterization of Protocerebral Neurons in the Olfactory Network of the Moth, Heliothis virescens

Abstract

In the sensory systems of insects, the primary olfactory centre in the antennal lobe has been one of the major areas of interest for the last two decades. Considerable progress has been made in understanding this earlier part of the olfactory network, whereas very little is known about the odour processing of the higher order centres within the protocerebrum. In this study, the olfactory system of the moth Heliothis virescens was employed as a model. Intracellular recordings and stainings of neurons in the higher order olfactory centre in the lateral protocerebrum (LP) were performed during stimulation with identified primary plant odorants and multicomponent blends. Neurons were visualized by scanning with confocal laser microscope and 3-dimensional reconstructions. In order to morphologically identify and characterize neurons in the LP, recontructed neurons were registered into a standard brain atlas that has been developed for this species. Two different analyses were performed on the obtained physiology. First, a cluster analysis revealed clear divitions with respect to different neurons interspike interval (ISI) distributions, thus indicating groups of neurons with different functional properties within the higher order olfactory network. Secondly, a novel method in which to quantify complex temporal response patterns was introduced. A t-test used to compare the quantified reponses to single odorants versus blends showed that the majority of neurons ( ~70%) in the LP responded stronger to multicomponent blends. This indicated a predominant synergistic interaction of plant odours in the higher order olfactory centre of H. virescens.