Nuclear derivatives and axonal projections originating from rhombomere 4 in the mouse hindbrain.
The r4-derived territory is located in the pontine region of the brainstem, forming a wedge-shaped
slice that broadens from the choroidal roof to the ventral midline. R4-derived neuronal populations
migrate radially inside and tangentially outside this rhombomere, forming nuclei of the sensorimotor
auditory, vestibular, trigeminal and reticular systems. R4-derived fibre tracts contribute to the
lateral lemniscus, the trigeminothalamic tracts, the medial tegmental tract and the medial forebrain
bundle, which variously project to the midbrain, thalamus, hypothalamus and telencephalon. Other
tracts such as the trigeminocerebellar and vestibulocerebellar tracts reach the cerebellum, while
the medial and lateral vestibulospinal tracts, and the reticulospinal and trigeminal oro-spinal
tracts extend into the spinal cord. Many r4-derived fibres are crossed, they decussate to the
contralateral side traversing the midline through the cerebellar, collicular and intercollicular
commissures, as well as the supraoptic decussation. Moreover, some fibres enter into the posterior
and anterior commissures and some terminals reach the septum. Overall, this study provides an
overview of all r4 neuronal populations and axonal tracts from their embryonic origin to the adult
final location and target.