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Distribution, laminar location, and morphology of tectal neurons projecting to the isthmo‐optic nucleus and the nucleus isthmi, pars parvocellularis in the pigeon ( Columba livia ) and chick ( Gallus domesticus ): A retrograde labelling study
Author(s) -
Woodson Walter,
Reiner Anton,
Anderson Keith,
Karten Harvey J.
Publication year - 1991
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.903050310
Subject(s) - biology , tectum , nucleus , axoplasmic transport , horseradish peroxidase , anatomy , neuroscience , midbrain , central nervous system , biochemistry , enzyme
Retrograde transport of Phaseolus vulgaris leucoagglutinin (PHA‐L), fluorogold, fast blue, rhodamine labelled microspheres, and horseradish peroxidase (HRP) was employed to study the distribution, laminar location within the optic tectum, and morphology of tectal cells projecting upon the isthmo‐optic nucleus (ION) and the nucleus isthmi, pars parvocellularis (Ipc), in the pigeon and chick. Following injections into the ION, all retrograde markers labelled tecto‐ION neurons and their dendrites in the ipsilateral tectum. The cells were located within a relatively narrow band at the border between layers 9 and 10 of the stratum griseum et fibrosum superficial (SGFS). Retrogradely labelled neuronal somata were different in both dendritic branching and shape; however, tecto‐ION neurons generally possessed non‐spiny radially oriented and multi‐branched dendrites. The apical processes extended into the retino‐recipient layers (2–7) of the SGFS and basal dendrites extended into layers 12–14 of the SGFS. Positive neuronal somata were observed throughout the rostro‐caudal extent of the optic tectum. The average distance between adjacent tecto‐ION neurons varied from one region to another. Specifically, retro‐gradely labelled cells were more numerous in the caudal, lateral, and ventral tectum, and less numerous at rostro‐dorsal levels. Approximately 12,000 tecto‐ION neurons were labelled within the ipsilateral optic tectum following either PHA‐L or fluorescent dye injections. While the regional distribution of tecto‐Ipc neurons was not examined, the morphology indicated that the cells had a single radially oriented dendritic process. Therefore, the apical dendrites are more restricted than those of tecto‐ION cells. Moreover, the dendrites were spiny and arborized within layers 3, 5, and 9 of the ipsilateral optic tectum. The axon of tecto‐Ipc cells arise from the apical process as a shepherd's crook and descend into the deep layers of the optic tectum. These results indicate that (1) tecto‐ION and tecto‐Ipc neurons are possibly monosynaptically activated by retinal input, (2) tecto‐ION neurons are heterogeneous in morphology, and (3) there is a differential distribution of the tecto‐ION neurons throughout the rostro‐caudal extent of the optic tectum, suggesting a greater representation of the caudo‐ventral portion of the optic tectum within the ION. The discussion primarily concerns the organization of the retino‐tecto‐ION‐retinal circuit in light of the distribution and morphology of tecto‐ION neurons within the optic tectum.