Spontaneous spiking activity in morphologically characterized neuron categories

Individual neurons can be characterized by their electrophysiological activity. Such characterizations have helped researchers investigate the functioning of individual neurons and neural networks consisting of distinct neuron categories. In the primary olfactory center of the insect brain, the antennal lobe, electrophysiological characterizations have in large part focused on the alterations in activity during odor stimulation. In comparison, the background on which neural responses occur, i.e. the spontaneous activity, has been sparsely described. Attempts to identify neuron categories in the antennal lobe, using physiological parameters of spontaneous spiking activity, has only been performed in one study. It demonstrated that physiology can indeed be used to predict morphology. In this thesis, in vivo intracellular recording and staining, combined with confocal microscopy, was performed in the noctuid moth Helicoverpa armigera to gather physiological and neuroanatomical data on two types of antennal lobe neurons; local interneurons and projection neurons. The main purpose of the study is to investigate whether these two morphologically different neuron categories can be identified by their spontaneous spiking patterns. The results approved that the spontaneous activity could be used as an indicator to identify neuron category without morphological classification, and the correct classification rate is up to 76%. In addition, we investigated whether sub-categories of projection neurons could be identified. However, identified clusters had no significant association with morphological features, neither dendritic arborizations, nor confinement to antennal lobe tract. Moreover, this thesis includes novel findings on projection neuron morphology. As many as three neurons confined to the recently discovered transverse antennal lobe tract were identified here.