Research Interests

The research being carried out in my laboratory deals with the developmental neurobiology of the visual system. Currently, three broad issues are being pursued. First, we are interested in the formation of On and Off pathways which signal increments and decrements of light. It is commonly the case, that connections in the brain concerned with coding different features of the sensory world are separated into distinct domains. On/Off retinal pathways represent a prime example of such an organization at a very early level of the neuroaxis. The three cell types involved in this organization (On and Off cone bipolar cells which stratify onto the segregated dendrites of On and Off ganglion cells as well as the processes of cholinergic amacrine cells) have been all well-characterized in the mature retina. Consequently, this system serves as an excellent model for our developmental studies. In the past, we have shown that glutamate-mediated activity is essential for the stratification of On and Off dendrites of retinal ganglion cells. More recently, we demonstrated a highly specific ingrowth pattern of On and Off bipolar cell axons. Remarkably, ganglion cells, the major target of these retinal interneurons were found not to be essential for normal segregation of bipolar cell axons. Currently, we are exploring the involvement of cholinergic amacrine cells in this process. This has motivated us to construct a novel method for immunolesioning cholinergic neurons. 

A second major focus is the ontogeny of functional properties in retinal ganglion cells. This work mainly involves making whole-cell patch clamp recordings from ganglion cells in embryonic and postnatal retinas. The main goal here is to determine when and how different classes of retinal ganglion cells attain their mature extrinsic as well as intrinsic response properties. For instance, recently we showed that early in development, when the dendrites of ganglion cells are still in a multistratified state, these neurons respond briskly both to the onset and the offset of light. This means that individual ganglion cells are innervated by both On as well as Off cone bipolar cells before these inputs attain their mature segregated state.

A third focus is the formation of specific retinal projection patterns. This work has become increasingly focused on the molecular cues that might underlie the highly precise patterns of projections exhibited by retinal neurons. In particular, we are currently using microarray technologies to identify genes expressed by different classes of retinal ganglion cells that could be responsible for guiding these neurons to make either a crossed or uncrossed projections at the optic chiasm.