A Microscopic Survey of Olfactory Neurons in Insect Brains

Abstract

The tobacco hawkmoth, Manduca sexta, is a model organism that has been used to understand how animal's olfactory systems process information. The neural circuits in its primary olfactory center, the AL, are analogous in many ways to the olfactory bulb in vertebrate species. In moths, individual neurons comprising the olfactory circuits in different synaptic centers are highly diverse and interconnected in very complicated ways, and thus are difficult to analyze. To overcome this problem, my project took "survey-like" approach to determine what types of individual neurons are connected to a specific largely unexplored higher olfactory center, the lateral horn. This region is targeted by all projection neurons-output neurons-of the AL. A particular region within the lateral horn (delta region) in male moths receives input from projection neurons that process information about conspecific female sex pheromone of this species. It remains unclear how many types of neurons innervate this region. An electroporation technique was used to probe this question using dissected male moths and passing a current through a dye-filled electrode. This technique allows the dye to be injected into the neurites in the vicinity of the electrode tip and travel through the inner network.