Activity-dependent development of neuronal circuits The topic of this session is "activity-dependent neuronal circuit development". The developmental mechanisms of mammalian neuronal circuits have been extensively studied in the visual system, in which the retinal ganglion neurons project to the dorsal lateral geniculate nucleus (dLGN) in the thalamus and superior colliculus, then dLGN neurons project to the layer 4 of the primary visual cortex. In matured brain, termini of axons originated from left and right eyes occupy separated regions in the dLGN and superior colliculus. In some animals such as cat, ferret and monkey, termini of thalamocortical axons representing the left and right eyes also occupy separated regions in layer 4 of the primary visual cortex. During early stages of circuit formation, molecular cues and their receptors in the target regions and axons, respectively, play major roles in guiding axons toward the correct targets such as the dLGN, superior colliculus, and primary visual cortex. After eye opening, neuronal activity induced by vision have drastic effects for the refinement of thalamocortical connectivity. However, the roles of early neuronal activity for circuit refinement before eye opening, such as initial establishment of two-eye segregation in the primary visual cortex, dLGN and superior colliculus, remain largely controversial. In the paper, the authors addressed this question by focusing on two-eye segregation of retinogeniculate axonal termini in dLGN. Although experiments in this paper are simple, it may be difficult for you to understand what they argue if you are not familiar with the field. To understand the background (history of the field) better, reading a review by Crowley, J.C. and Katz, L.C. (see below) may help. In the session, we will not go into the detail of the data. Instead, we would like to discuss what are the authors’ ultimate goal and what they achieved and did not achieve in the current work. I recommend you to have knowledge of basic anatomy of mammalian visual system in advance. Crowley, J.C. and Katz, L.C. |