Cell type-specific mechanisms of voltage-dependent spike frequency modulation in the insect olfactory system.

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Central nervous systems consist of multiple neuronal circuits that ensure the efficient execution of many different tasks. These networks' task-specific functional and computational features are governed by the intrinsic cellular properties and the synaptic connections between the networks' component neurons. Typically, the neurons of these circuits have highly specialized physiological and morphological phenotypes. Prominent examples of defined, task-specific, high-performance neuronal circuits are the primary olfactory systems that have evolved in arthropods and vertebrates. These circuits share similar architectures and processing principles across phyla.Based on extensive studies, there is a general understanding of how olfactory information is processed and how the neurons in the insect antennal lobe, the functional equivalent of the vertebrate olfactory bulb, respond to odors. Nevertheless, while it is evident that the neurons' odor responses are determined by their synaptic input and intrinsic electrophysiological properties, surprisingly little is known about their cell type-specific intrinsic properties and how they shape odor responses in the different neurons. However, since the properties of the component neurons ultimately determine the function of the network, defining the cell type-specific electrophysiological phenotypes is the basis for realistic (computational) models and the prerequisite for a truly mechanistic understanding of olfactory information processing.Accordingly, the project aims to define cell type-specific functional phenotypes and identify the main ionic currents that mediate them. The focus is on 2 neuron types that play a crucial role in the insect olfactory system, the inhibitory GABAergic multiglomerular local interneurons, and the excitatory cholinergic uniglomerular projection neurons. In this context, we also address whether the conserved circuit organization observed between insect species is associated with similar intrinsic electrophysiological properties and ionic mechanisms. For this purpose, the studies are performed comparatively on two evolutionarily distant insect species, the hemimetabolous cockroach P. americana and the holometabolous fruit fly D. melanogaster.