Assigning potential neurotransmitters and neuromodulators to identified local interneurons of the antennal lobe
Final Report Abstract
The ability to detect, process and perceive complex odours is a significant evolutionary advantage. Complex neural circuits have evolved to accomplish this task with remarkable efficiency. We consider a detailed knowledge about the circuit’s component neurons’ functional and morphological properties as essential to understand how olfactory networks process information. In this context, the insect olfactory system, with its many functional and structural similarities to the vertebrate olfactory system, has served as an excellent model to investigate general mechanisms of olfactory information processing. In the insect antennal lobe different types of local interneurons mediate complex excitatory and inhibitory interactions between the glomerular pathways to structure the spatio-temporal representation of odours. Mass spectrometric and immunohistochemical studies have shown that in local interneurons classical neurotransmitters are likely to colocalize with a variety of substances that can potentially act as co-transmitters or neuromodulators. In the antennal lobe of the cockroach P. Americana, GABA has been identified as the potential inhibitory transmitter of spiking type I local interneurons, whereas acetylcholine is most likely the excitatory transmitter of non-spiking type IIa1 local interneurons. This study used whole-cell patch clamp recordings combined with single cell labelling and immunohistochemistry to test if the GABAergic type I local interneurons and the cholinergic type IIa1 local interneurons express allatotropin and tachykinin-related neuropeptides (TKRPs). These are two of the most abundant types of peptides in the insect antennal lobe. GABA-like - and choline acetyltransferase-like immunoreactivity (-lir) were used as markers for GABAergic and cholinergic neurons, respectively. ~50% of the GABA-lir spiking type I local interneurons were allatotropin-lir, and ~40% of these neurons were TKRP-lir. About 20 % of non-spiking choline acethyltransferase-lir type IIa1 local interneurons were TKRP-lir. Our results suggest that in subpopulations of GABAergic and cholinergic local interneurons, allatotropin and TKRPs might act as co-transmitters or neuromodulators. To unequivocally assign neurotransmitters, co-transmitters and neuromodulators to identified classes of antennal lobe neurons is an important step to deepen our understanding of information processing in the insect olfactory system.
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, Susanne; Fusca, Debora; Schachtner, Joachim; Kloppenburg, Peter & Predel, Reinhard
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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, Debora; Husch, Andreas; Baumann, Arnd & Kloppenburg, Peter
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(2014) Neural coding: sparse but on time. Curr. Biol. 24, 957-959
Kloppenburg, Peter & Nawrot, Martin Paul
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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, Ben & Kloppenburg, Peter
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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, Debora; Schachtner, Joachim & Kloppenburg, Peter
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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, Cathleen; Warren, Ben; Bardos, Viktor; Schleicher, Sabine; Klein, Andreas & Kloppenburg, Peter
