UC San Diego

A characteristic feature of developing neural circuits is that they exhibit spontaneous, patterned activity. The effects of this activity have been well characterized in the developing visual system, where the spontaneous activity, called retinal waves, is known to be important in the establishment of retinotopic and eye-specific maps. However, there has been little focus on the issue of cell autonomous effects of spontaneous activity. Retinal waves, like other forms of spontaneous activity in the spinal cord and hippocampus, are characterized at the single neuron level by periodic increases in intracellular calcium concentration with a periodicity on the order of a minute. One likely mechanism by which neurons can "decode" these slow oscillations is through activation of second messenger cascades that either influence transcriptional activity or drive post-translational modifications. Recently, genetically encoded, fluorescent reporters have been developed that allow imaging of second messenger pathways other than calcium, such as the cAMP/PKA pathway. This dissertation focuses on the use of these FRET-based, reporters of the cAMP/PKA pathway to study the activity of second messenger cascades during retinal waves. In chapter 1, recent advances in efficacy and utility of genetically encoded, fluorescent indicators of the cAMP/PKA pathway are described. In chapter 2, we report the spontaneous activation of the cAMP/PKA pathway in retinal ganglion cells (RGCs). Spontaneous activation of the cAMP/PKA pathway is dependent on, and maintains a temporally consistent relationship with retinal waves and is dependent on calcium influx. Chapter 3 describes the mechanism by which calcium influx leads to an increase in PKA activity, specifically focusing on the role of calcium activated adenylate cyclases and phosphodiesterases. We present evidence that multiple adenylate cyclases underlie the calcium-induced PKA activation in RGCs. Chapter 4 concludes with a model of the cAMP/PKA pathway in retinal ganglion cells and discussion of the possible function of periodic PKA transients in the development of visual circuits