Epsilon Open Archive

Abstract

The mushroom bodies are paired, high-order neuropils in the insect brain involved in complex functions such as learning and memory, sensory integration, context recognition and olfactory processing. This thesis explores the structure of the mushroom bodies in the noctuid moth Spodoptera littoralis using neuroanatomical staining methods, immunocytochemistry and electron microscopy, and investigates how the intrinsic neurons of the mushroom body, the Kenyon cells, respond to olfactory stimulation of the antennae using whole-cell patch clamp technique. The mushroom body in S. littoralis contains about 4,000 Kenyon cells, and consists of a calyx, pedunculus and two lobes, one medial and one vertical. The calyx houses dendritic branches of Kenyon cells and the pedunculus and lobes contain the axons and terminals of these neurons respectively. The calyx is doubled and concentrically divided into a broad peripheral zone, which receives input from antennal lobe projection neurons, and a narrow inner zone, which receives yet unidentified input. The lobes are parsed into three longitudinal divisions, which contain a separate subset of Kenyon cells each. The Kenyon cells are divided into three morphological classes, I-III. Class I Kenyon cells have widely branching spiny dendritic arborisations in both zones of the calyx and occupy the two most posterior subdivisions of the lobes called α/β and α´/β´. Class II Kenyon cells have narrow clawed dendritic trees in the calyx and invade the most anterior division in the lobes, called γ. Class III Kenyon cells have clawed, diffusely branching dendrites in the calyx and provide a separate system of axons and terminal branches, partly detached from the rest of the mushroom body, called the Y tract and lobelets. Kenyon cells within the classes display differential labeling with antisera against neuroactive substances. Kenyon cells make synaptic contact with one another and with other neuron types in the mushroom body. Extrinsic inhibitory and putative modulatory neurons were identified. Whole-cell patch clamp recordings revealed that Kenyon cells exhibit broadly tuned subthreshold activation by odor stimulation and a few cells responded with action potentials to specific biologically relevant odor combinations.