Quantitative distribution of descending tectal efferent cells in salamanders.

In salamanders of the species Salamandra salamandra, Pleurodeles waltl, and Plethodon jordani, tectal efferent neurons projecting to the bulbar reticular formation show a stereotyped distribution as revealed by the horseradish peroxidase (HRP) method. The density of these cells increases toward caudal tectal levels reaching its maximum at the isthmic region. Neurons with ipsilaterally descending axons constitute 60-87% and are concentrated in the dorsomedial and ventrolateral sector of the tectal hemisphere, with only few neurons in the intermediate part. The contralaterally descending neurons are concentrated in the lateral sector. This pattern is assumed to reflect a motor map in the coordinates of the salamander neck muscle system.