Event:

One characteristic of sensory systems that is essential for the animals to correctly assess dynamic environmental information is their capacity to build a spatial sensory map in the central nervous system. The accurate assembly of neural maps requires that developing neurons solve a qualitative problem for synaptic specificity, as well as a quantitative problem to define the number of their synaptic partners. Synaptic specificity often relies on a sequence of dichotomous choices and is largely genetically programmed, but how neurons establish a reproducible projections is less well understood. In fishes, the axonal projections from the mechanosensory lateral line organize a somatotopic neural map. The lateral line provides hydrodynamic information for intricate behaviors such as navigation and prey detection. It also mediates fast startle reactions triggered by the Mauthner cell. However, it is not known how the lateralis neural map is built to sub-serve these contrasting behaviors. I will show evidence that birth order diversifies lateralis afferent neurons in the zebrafish. Early- and late-born lateralis afferents diverge along the main axes of the animal’s hindbrain to synapse with hundreds of second-order targets. However, early-born afferents projecting from primary neuromasts also assemble a separate map by converging on the lateral dendrite of the Mauthner cell, whereas projections from secondary neuromasts never make physical contact with the Mauthner. Neuronal diversity and map topology occur normally in animals permanently deprived of mechanosensory activity. I will discuss how neuronal birth order may govern the assembly of these neural sub-maps, whose combination is likely to govern appropriate behavioral reactions to the sensory context.