The Effect of Netrin on Visually Guided Behavior
Mentor:Susana Cohen-Cory, Professor, Neurobiology and Behavior School of Biological Sciences, University of California, Irvine
Netrin-1 plays multiple roles in development. In axon guidance, netrin-1 acts as an attractive or repulsive guidance due depending on the receptors expressed on the axons. Previous work has shown that acute global treatment of netrin-1 to the optic tectum of Xenopus laevis tadpoles results in acute changes to the retinotecal circuit. Specifically, dendrites of the tectal neurons grow away from the retinal axon, suggesting that the connectivity between dendrites and axons is altered. This experiment looked at the changes in the function of the retinotectal circuit, that accompany morphology changes due to netrin-1 treatment. To determine functional changes in the retinotectal circuit, we used Xenopus laevis tadpoles, at stage 45 and 49, in a visually based avoidance task. We compared the ability of untreated tadpoles to avoid a moving black dot on a white background; to tadpoles that were injected with 14 ng of netrin-1 to the optic tectum and those injected with equal volumes of vehicle solution. Each tadpole was subjected to 2.5 minute trials at 2, 4, and 24 hours post injection, the tadpole was tasked with avoiding one dot every 30 seconds. Dividing the number of dots avoided by the total dots we calculated the percent avoided. We found that in general the stage 45 animals had a higher percent avoidance rate than the stage 49 animals for the first trial. For the stage 45 animals, the netrin injected group had a lower percent avoided rate than the untreated group at 2 hours. For stage 49 animals, the netrin injected group had a higher percent avoidance than the untreated group for the first trial. Our results indicate that disrupting normal netrin signaling alters visual responses as the retinotectal circuit matures, and this may affect the emergence of complex behaviors.