The development of the amphibian trochlear nucleus. An HRP study

The quantitative and qualitative development of the trochlear nucleus of salamanders and frogs was studied using horseradish peroxidase (HRP) as a retrograde marker. A higher number of labelled motoneurons significantly declined in later larval stages, presumably by cell death, as in birds and mammals. In agreement with this assumption, HRP-filled apoptotic cells were found in larvae. Many more labelled trochlear motoneurons were found in adult than in larval amphibians, and [3H]thymidine labelling showed postlarval cell production in the area of the trochlear nucleus. Data are discussed in the context of cell death and ongoing cell proliferation.