Effects of neurotransmitters and guidance cues on neuronal growth cone guidance via receptor-mediated pathways

Elisabeth E Garland, Purdue University

Abstract

Growth cones are motile structures located at the tips of axons and guide axons to their proper target locations during development. Soluble and membrane-bound cues induce growth cone guidance by changing the dynamics of the actin and microtubule cytoskeleton. Neurotransmitters, including serotonin (5-HT) have been established as soluble guidance cues. This project has focused on determining the effects neurotransmitters and guidance cues on bag cell and sensory neuron growth cones from the marine mollusk, Aplysia californica. This is an excellent model system to study growth cone responses to 5-HT and concurrent changes in the cytoskeleton because Aplysia growth cones express multiple 5-HT receptors, are large (up to 100 μm in diameter), and are suitable for high-resolution time-lapse imaging. We found that bath application of 5-HT inhibits growth cone protrusion and causes F-actin redistribution in sensory neuron growth cones. These effects are likely caused by second messenger signaling pathways downstream of G protein-coupled 5-HT receptors, which could activate different protein kinases. Pharmacological studies suggest that these effects of 5-HT do not appear to be mediated by the second messenger, cAMP. It remains to be determined which specific kinase signaling pathways downstream of 5-HT receptors cause growth cone responses to 5-HT. Inputs from PKA, PKC, and MAPK pathways alone do not appear to mediate this response, but interactions between these pathways, as well as calcium signaling pathways are likely involved. In studies of guidance cues, we found that Slit2 applied in a bath format causes significant inhibition of growth cone protrusion in bag cell neurons. Both 5-HT and Slit2 are therefore useful for studies of growth cone guidance in the Aplysia system and can be used as control molecules for future experiments. These findings will provide insight into mechanisms of axonal guidance by neurotransmitters and guidance cues during both neuronal development and regeneration.

Degree

M.S.

Advisors

Watts, Purdue University.

Subject Area

Neurosciences|Cellular biology|Pharmacology

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