SENSITIVE PERIODS OF OLFACTORY IMPRINTING IN LAKE STURGEON

RATIONALE: Lake sturgeon population rehabilitation is a top priority in the Great Lakes Basin. A broad concern from management, production and research groups to current rehabilitation programs is whether sturgeon stocking compromises sensory imprinting in their early life stages, which affects their migration and reproduction activities when they are mature (Zollweg et al. 2002). Studies show that sensory imprinting profoundly affects lifelong neural wiring and behavior of animals. In salmon, its homeward migration is guided by an imprinted olfactory memory of their natal streams. We hypothesize that there is a sensitive period for sturgeon olfactory imprinting in their early life stages. Olfactory imprinting is a process of formation of an unconditioned long-term memory to exposed odors, which eventually leads to long-lasting changes in the animal’s behavior upon encountering the olfactory cues later on. Formation of long-term memory must involve molecular biological and/or anatomical changes of neurons that may be detected by various cellular and molecular biology approaches. Determination of sensitive period of olfactory imprinting allows us to make strategic plans on how and when to stock sturgeon, a critical step for establishment of self-sustaining lake sturgeon population. The study will also establish research procedures for examination of olfactory imprinting in other native fish species in the Great Lakes.

OBJECTIVES: The olfactory system is critically important for fish feeding, migration and reproduction, and olfactory imprinting may profoundly shape these behaviors. We hypothesize that the sensitive period of olfactory imprinting is a period of high neural proliferation in the olfactory cortical center and memory formation center in the telencephalon, and a period of relatively high thyroid hormone activity in the telencephalon. The beginning of this period is associated with increased levels of Otx2 and parvalbumin in the telencephalon, and the ending of this period is linked to reduced expression of NMDA receptor regulatory subunits. Studying molecular biological and morphological changes in the telencephalon allow us to narrow down the sensitive period of olfactory imprinting.

METHODS: To delineate the sensitive period of olfactory imprinting, we have determined various life stages to be examined based on our previous data. We have obtained sturgeon samples from hatcheries. These samples will be used for experiments outlined below. First, 50 ug of total RNA of the telencephalon will be sequenced to obtain genetic information using 454 sequencing technology. We will trace changes of gene expression levels in the telencephalon at various life stages using real time quantitative PCR and determine distribution patterns and levels of proteins associated to the sensitive period using the immunohistochemistry method. The mRNAs and proteins to be examined include: thyroid hormone receptors, deiodinases, NMDA receptor subunit NR2A and NR2B, parvalbumin, proliferating cell nuclear antigen, and cyclin dependent kinase 5. Experiments will be repeated multiple times. Statistical method ANOVA will be used in data analysis.

RELEVANCE TO PROGRAM: Delisting sturgeon from the endangered species and making it economically viable is a Great Lakes Basin wide effort. Olfactory imprinting profoundly influences fish behavior including migration and reproduction. Our work will allow us to avoid interfering nature olfactory imprinting process and manipulate olfactory imprinting process for the benefits of restoration of native species. These efforts allow us to effectively provide prescriptions for restoration of self-sustaining population of native species in the Great Lakes.

DELIVERABLES/PRODUCTS: We will provide detail data to demonstrate the time window of olfactory imprinting. This technical report can be immediately applied to lake sturgeon management. The genetic information of lake sturgeon will be organized and made available to the Great Lakes communities. The results will be published in peer reviewed research journals. The information will also be disseminated through workshops, teaching, seminars and scientific meetings.