OLFACTORY SENSORY NEURON AND OLFACTORY BULB RESPONSES TO NOVEL PUTATIVE PHEROMONE COMPONENTS AND COMBINATIONS IN THE SEA LAMPREY (Petromyzon marinus)

The olfactory system of fishes mediates a wide array of behaviours including migration and spawning. These olfactory-mediated behaviours are elicited by chemical mixtures known as pheromones, released by a conspecific with the intent of communicating to a conspecific. Olfactory sensory neurons expressing the complementary odour receptor for an odorant will bind it, initiating an intracellular cascade resulting in the depolarization of the cell and propagation of sensory information toward brain structures known as olfactory bulbs. While generalist olfactory sensory neurons (OSNs) have been observed in insects, some OSNs in the main olfactory epithelium of mammals as well as fish express odour receptors that show high specificity for a single odorant or structurally similar odorants. Although the male sea lamprey (Petromyzon marinus) sex pheromone components 3 keto-petromyzonol sulfate (3kPZS) and 3,12-diketo-4,6-petromyzonene-24-sulfate (DKPES) stimulate responses at the level of the olfactory epithelium, only 3kPZS and a DKPES/3kPZS mixture has elicited a behavioural response from ovulating females. Thus, it was hypothesized that the OSNs of the sea lamprey respond to a single pheromone odorant, and the objective of my thesis was to determine the cellular response specificity of sea lamprey OSNs and to characterize neural responses from the olfactory bulb, the location of the first order synapses and associated interneurons. We used calcium imaging to investigate the specificity of odorant responses by individual OSNs to amino acid and pheromone odorants and found that sea lamprey OSNs showed high specificity in responding to single amino acids and pheromone odorants. At the level of the olfactory bulb, the local field potential detection thresholds for several pheromone odorants were determined and several previously untested single pheromone odorants were found to stimulate responses from the dorsal bulbar region. This study characterises, for the first time in the sea lamprey, the specificity of individual OSN responses to pheromone odorants and describes the olfactory responses to 4 newly elucidated putative sea lamprey pheromone odorants that were found to elicit responses from both the olfactory epithelium and olfactory bulb