Diversity of K+ Currents in identified central neurons of the insect olfactory system
Final Report Abstract
The detection, conduction and processing of olfactory information requires complex neuronal circuits. In insects the antennal lobe is the first synaptic relay and processing station in the olfactory pathway, and is considered the functional analog of the vertebrate olfactory bulb. In the antennal lobe a diverse population of central neurons helps to process, structure, and spatially represent olfactory information. Local interneurons form synaptic connections exclusively in the antennal lobe, while a primary task of the projection neurons is the transfer of pre-processed olfactory information from the antennal lobe to higher order centres. In this context our long term goal is to understand how neuron type specific sets of ionic currents shape the specific intrinsic electrophysiological properties and synaptic properties of the different neuron types. Towards this aim we here characterized cell type specific voltage and Ca2+ activated K+ currents, and ligand gated post synaptic currents in distinct types of antennal lobe neurons and analysed their influence on the physiological properties of these neurons. Transient voltage activated K+ current (IA), for example, exhibited marked cell type specific differences in voltage dependence of steady-state activation and inactivation, and differences in inactivation kinetics during sustained depolarization. Pharmacological experiments revealed that IA in all neuron types was partially blocked by α-dendrotoxin and phrixotoxin-2, which are considered blockers with specificity for shaker and shal type channels, respectively. These findings suggest that IA in each cell type is a mixed current generated by channels of both families. The functional role of IA was analysed in occlusion experiments under current-clamp, in which portions of IA were blocked by α-dendrotoxin or phrixotoxin-2. These experiments showed that and how IA contributes significantly to the intrinsic electrophysiological properties such as the action potential waveform and membrane excitability. On the synaptic level this is the first study that directly showed dual fast- and slowinhibitory action of local interneurons, which was predicted to be key in shaping complex odour responses in the insect antennal lobe. We also provided the first direct characterization of rapid postsynaptic currents coincident with presynaptic spikes between antennal lobe neurons.
Publications
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(2012) Towards a Single cell-based analysis of neuropeptide expression in Periplaneta americana antennal lobe neurons. J Comp. Neurol. 520, 694-716
Neupert S, Fusca D, Schachtner J, Kloppenburg P, Predel R
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(2013) Choline acetyltransferase-like immunoreactivity in a physiologically distinct subtype of olfactory nonspiking local interneurons in the cockroach (Periplaneta americana). J Comp Neurol. 521, 3556-69
Fusca D, Husch A, Baumann A, Kloppenburg P
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(2014) Neural coding: sparse but on time. Curr. Biol. 24, 957-959
Kloppenburg P, Nawrot MP
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(2014). Rapid and slow chemical synaptic interactions of cholinergic projection neurons and GABAergic local interneurons in the insect antennal lobe. J. Neurosci. 34, 13039-13046
Warren, B. and Kloppenburg, P.
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(2015). Colocalization of allatotropin and tachykinin-related peptides with classical transmitters in physiologically distinct subtypes of olfactory local interneurons in the cockroach (Periplaneta americana). J. Comp. Neurol. 523, 1569-1586
Fusca, D., Schachtner, J., and Kloppenburg, P.
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(2016). Properties and physiological function of Ca2+-dependent K+ currents in uniglomerular olfactory projection neurons. J. Neurophysiol. 115, 2330-2340
Bradler, C., Warren, B., Bardos, V., Schleicher, S., Klein, A., Kloppenburg, P.
