Tectal activation of premotor and motor networks during feeding in salamanders.

In salamanders, three separate pathways, a crossed and two uncrossed ones, extend from the tectum mesencephali to the brain stem and spinal cord. These pathways arise from different types of tectal neurons; their dendrites arborize in different layers of retinal afferents and, thus, receive different types of retinal information. Collaterals of descending axons extend in regions, where motoneurons and interneurons related to prey capture are situated. The response properties of tectal neurons, interneurons and motoneurons related to prey capture were revealed by intracellular recording with subsequent dye (biocytin) injection. Most tectal neurons exhibit long latencies after optic-nerve stimulation, which indicates a complex processing of visual information inside the tectum. Our data show that no one-way connection exists between the tectum and motor nuclei; rather, these centres, together with a number of interneurons, exhibit a complex interaction during feeding.