Identification of different antennal-lobe neuron categories;: a morphological and physiological study of second order neurons in the primary olfactory brain centre of the moth Heliothis virescens

Abstract

Olfaction is the sense of smell, first mediated by specialized sensory cells in the sensilla hair covering the moth antennae, projecting to the primary olfactory centre the antennal lobe. From this first synaptic level the secondary neuronal fibers follow one of the three antennal lobe tracts to higher olfactory neuropils called the calyces and the lateral horn. The antennal lobe is also innervated by local interneurons and centrifugal neurons. Moths are preferred objects of olfactory research due to their highly sensitive and species-specific olfactory systems. Their ability to process and compute plant odour information, on the other hand, is still fairly unknown. This despite the many odour specific olfactory sensory neurons classified. The present study aimed to identify individual antennal-lobe neurons physiologically and morphologically in the moth Heliothis virescens. The insects were stimulated with identified primary plant odorants and multicomponent blends, in addition to known pheromone components, during intracellular recordings from second order neurons in the antennal lobe. Then, staining of the neurons was attempted and successfully stained neurons were characterized. The categories of antennal lobe neurons comprise diverse morphological and physiological properties and all three types are represented in this thesis. The results of this thesis show a varied antennal lobe neuron population concerning both the morphology and the physiologic characteristics. Both confirming the known morphologic characteristics but also revealing exceptions previously not described in H. virescens specially or in moth in general. Also, no differences were found between the physiological properties of neurons following the three antennal lobe tracts. Of special interest is the centrifugal neuron presented in this thesis with appurtenant interesting physiological and morphological data, previously not been identified in H. virescens.