Neuronal birth order identifies a dimorphic sensorineural map.

Area of Science:

• Neuroscience
• Developmental Biology
• Sensory Systems

Background:

• The brain forms topographic maps from sensory input, like the somatotopic map of the fish lateral line.
• The lateral line system is crucial for fish behaviors including navigation, prey detection, and startle responses mediated by the Mauthner cell.
• How the lateral line neural map develops to support these diverse functions remains unclear.

Purpose of the Study:

• To investigate how the lateralis neural map is assembled in zebrafish.
• To determine the role of neuronal birth order in shaping sensory maps.
• To understand the relationship between map formation and behavioral output.

Main Methods:

• Tracing axonal projections of early- and late-born lateralis afferent neurons in zebrafish.
• Analyzing the synaptic targets of these neurons, including the Mauthner cell.
• Assessing map development in zebrafish deprived of mechanosensory activity.

Main Results:

• Early- and late-born lateralis afferent neurons diverge in the hindbrain, synapsing with distinct second-order targets.
• Early-born afferents from primary neuromasts form a separate map converging on the Mauthner cell.
• Secondary neuromast projections do not contact the Mauthner cell, and map development proceeds normally without mechanosensory input.

Conclusions:

• Neuronal birth order is a key factor in diversifying lateralis afferent neurons and assembling distinct neural submaps.
• The combination of these submaps likely dictates appropriate behavioral responses based on sensory context.
• Neural map assembly is largely independent of ongoing sensory experience.