Structure-Function relationship of identified insect olfactory projection neurones
Final Report Abstract
The ability to detect, process and perceive complex odors is a significant evolutionary advantage. Complex neural circuits have evolved to accomplish this task with remarkable efficiency. We consider a detailed knowledge about the functional and morphological properties of the circuit's component neurons 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. The olfactory receptor neurons, each expressing a single functional receptor gene, send their axons to the antennal lobe, where they collate by receptor type and converge into specific glomeruli. In the glomeruli they form synapses with projection neurons (PNs) and local interneurons (LNs). The PNs relay information to higher order neuropiles including the lateral lobe of the protocerebrum and the mushroom bodies, in which they provide synaptic input to the Kenyon cells. The LNs mediate complex inhibitory and excitatory interactions between glomeruli to restructure the olfactory representation in the AL, which ultimately shapes the tuning profile of PNs. As olfactory information is processed and travels along the central olfactory pathways its representation is significantly altered. Using electrophysiological recordings combined with morphological and immunohistochemical examinations, this study analyzed in detail the relationship between function, intrinsic electrophysiological properties and morphology of the central olfactory neurons. For example: We characterized different types of neurons with distinctive physiological properties: 1) PNs and type I LNs that generated Na+ driven action potentials upon odor stimulation and 2) type II LNs, in which odor stimulation evoked depolarizations, but no Na+ driven action potentials. Type II LNs did not express voltage dependent transient Na+ currents and accordingly would not trigger transmitter release by Na+ driven action potentials. The distinct intrinsic firing properties were reflected in functional parameters of their voltage-activated Ca2+ currents (ICa). Consistent with graded synaptic release, we found a shift in the voltage for half-maximal activation of ICa to more hyperpolarized membrane potentials in the type II LNs. These marked physiological differences imply consequences for their computational capacity, synaptic output kinetics, and thus their function in the olfactory circuit.
Publications
- Functional parameters of voltage-activated Ca2+ currents from olfactory interneurons in the antennal lobe of Periplaneta americana. J Neurophysiol 99: 320-332, 2008
Husch A, Hess S, and Kloppenburg P
- Calcium current diversity in physiologically different local interneuron types of the antennal lobe. J Neurosci 29: 716-726, 2009
Husch A, Paehler M, Fusca D, Paeger L, and Kloppenburg P
- Distinct electrophysiological properties in subtypes of nonspiking olfactory local interneurons correlate with their cell type-specific Ca2+ current profiles. J Neurophysiol 102: 2834- 2845, 2009
Husch A, Paehler M, Fusca D, Paeger L, and Kloppenburg P
- Intrinsic membrane properties and inhibitory synaptic input of kenyon cells as mechanisms for sparse coding? J Neurophysiol 102: 1538- 1550, 2009
Demmer H and Kloppenburg P
