Studies Of Cells Within Three Chemosensory Structures In The Sea Lamprey (Petromyzon marinus)

Chemosensory systems play an important role in any organism collecting and processing information to regulate behaviours such as feeding, homing, avoidance and reproduction. In this thesis, I investigated the cells within the olfactory system and the diffuse chemosensory system of the sea lamprey. Calcium imaging of olfactory epithelial cellular responses to the polyamine odorants spermine and spermidine showed that separate cells responded to these odorants. The secondary goal of this thesis was focused on the loading of cells in the accessory olfactory organ (AOO) with neural activity indicators to examine the odorant response profiles of these cells. Multiple in vivo and electroporation dye loading strategies were attempted, with no successful loading of these cells. Investigating the AOO is still critical as it may provide insight into the importance of having more than one olfactory pathway. The third goal of this study was to investigate the location of nerve fibers on dermal papillae that contain solitary chemosensory cells (SCCs) of the diffuse chemosensory system. The findings show that nerve fibres entered the dermal papillae and, in many cases, were seen adjacent to SCCs in oral larval papillae and in nasal, gill and fin papillae following metamorphosis and in adults. This finding indicates that SCCs communicate with nerve fibers located in the cutaneous dermal papillae and that these fibers may be involved in processing sensory information that stimulates specific behavioural responses. Overall, this thesis examines the function of specific cells associated with lamprey chemosensory systems which may provide insight to appropriate behavioural responses necessary for survival and reproduction

Understanding lamprey reproduction by examining olfactory sensory neurons.

The sea lamprey is an invasive jawless fish species in the Great Lakes. Its voracious appetite for salmon and whitefish led to the collapse of fisheries in Lake Erie during the past century. Currently, sea lamprey populations are controlled by vigilant management strategies. One target is the disruption of lamprey spawning migration and reproduction. Both are guided by pheromones, odorants released by other lampreys. Lampreys have distinct behavioural responses to specific pheromones. The polyamine, spermine, stimulates reproductive behaviour, but spermidine (which has fewer hydrocarbons and amine groups less than spermine) does not stimulate a behavioural response. My study investigates if olfactory sensory neurons are narrowly tuned to spermine and spermidine or if these cells are broadly tuned (as we see in rodents and humans). Calcium imaging was used to observe the cellular responses to odorants. I observed that spermine and spermidine elicit a one-cell one-odorant response profile in sea lamprey olfactory sensory neurons. The concentration threshold for the cellular responses to spermine was lower than for spermidine. This study supports the idea of odorant fidelity to specific olfactory sensory neurons in the sea lamprey. The odorant activation of single olfactory sensory neurons by an odorant may contribute to the specific responses to specific lamprey pheromones. This knowledge of cellular activity behind sea lamprey biology contributes to ongoing research utilizing pheromone communication to disrupt sea lamprey reproduction

Vampires of the Great Lakes: Neural Responses of Dermal Papillae to Bile Acid Metabolites

The sea lamprey (Petromyzon marinus) is an ancient vertebrate that is an invasive species to the Great Lakes which potentially can cause \u3e$6,000,000,000 damages to the fishing industry. Chemicals in the external environment are detected by the senses of smell and taste, as well as by specialized receptor cells called solitary chemosensory cells (SCCs) where they are connected to nerve fibers. In aquatic vertebrates, SCCs are located on the skin and are hypothesized to play a role in searching for food and predator avoidance. SCCs are located on the dermal papillae (nipple-like structure) of the mouth, nose, gills and fins of this animal, however, the function of these cells is still unknown. The water collected from thawed dead trout is a potent stimulus for neural responses in the dermal papillae. It is not known which molecules within this thawed dead trout water stimulate this chemosensory response. In this study synthetic analogues of bile acids isolated from dead trout water were tested for chemosensory potency through multi-unit electrophysiological recordings. We found stimulatory chemosensory responses in all skin regions of the sea lamprey to dead trout water and varying response profiles to the synthetic analogues of bile acids. Knowledge of specific molecules that stimulate SCC nerve fibers in the sea lamprey will contribute to an understanding of the functional role of the SCC system in the sea lamprey and vertebrates at large. Finally, this study contributes to the safeguarding the Great Lakes by managing sea lamprey populations through chemical attraction or avoidance strategies