Somatosensory and visual correlation in the optic tectum of a python, Python regius: a horseradish peroxidase and Golgi study

Abstract

In snakes with infrared receptors the optic tectum receives infrared input in addition to visual and general somatosensory inputs. In order to observe their rectal termination patterns in ball pythons, Python regius, we injected horseradish peroxidase (HRP) into the nucleus of the lateral descending trigeminal tract (LTTD) which mediates infrared information, the optic nerve, and the nucleus of the trigeminal descending tract (TTD) which relays general somatosensory information. Fibers from LTTD were found in layers 5–13 of the contralateral optic tectum, and were especially dense in layers 7a–8. Optic nerve fibers terminated in layers 7a–13 of the contralateral tectum, and mainly in layers 12–13. TTD fibers were few, and could be seen in only the rostral half of the contralateral tectum. These fibers were found in layers 5–7b, but mainly in layers 6–7a. Among various types of neurons stained by the Golgi-Cox method, we focused on six types of neurons whose dendritic arborization overlapped with the distribution of the terminals of these sensory afferents described above. It is possible that these different sensory modalities converge on a single neuron of the various types.