Summary
The isthmic nucleus (IN) of the frog brain forms a linkage, relaying visual information from one tectum to the other. It receives afferent input from the tectum of the same side and projects bilaterally to both tecta. The ultrastructural features of the tecto-isthmic synaptic connections were studied in young postmetamorphic Xenopus frogs.
Most synaptic profiles in the isthmic nucleus have spheroidal vesicles and an asymmetric zone of apposition. Frequently, synaptic glomeruli consisting of up to 8 terminal boutons surrounding a shaft dendrite were observed. The syanptic density in the rostral IN was slightly higher than in the middle or caudal portions.
Partial deafferentation by transection of the tectoisthmic pathway or total deafferentation by removal of the tectum was followed by a widespread degeneration of terminals in the ipsilateral IN. In the former case, the density of synapses in the IN decreased initially by about 64%, and then increased by 30 days after operation to about 50% of the normal synaptic density. After tectal removal, all the terminal boutons in the isthmic neuropil degenerated by 3 days after operation. These studies, along with recent findings, indicate that most, if not all, of the afferent fibres to IN are of tectal origin.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Adams JC (1981) Heavy metal intensification of DAB-based HRP reaction product. J Histochem Cytochem 29:775
Beazley LD, Keating MJ, Gaze RM (1972) The appearance during development of responses in the optic tectum following visual stimulation of the ipsilateral eye in Xenopus laevis. Vision Res 12:407–410
Dann JF, Beazley LD (1982) The development of connexions between the isthmic nucleus and the tectum in Xenopus and Limnodynastes tadpoles. Neurosci Lett 33:107–113
Gaze RM, Keating MJ, Székely G, Beazley LD (1970) Binocular interaction in the formation of specific intertectal neuronal connexions. Proc R Soc Lond (B) 175:107–147
Glasser S, Ingle D (1978) The nucleus isthmus as a relay station in the ipsilateral visual projection to the frog's optic tectum. Brain Res 159:214–218
Grobstein P, Comer C (1983) The nucleus isthmi as an intertectal relay for the ipsilateral oculotectal projection in the frog, Rana pipiens. J Comp Neurol 217:54–74
Grobstein P, Comer C, Hollyday M, Archer SM (1978) A crossed isthmotectal projection in Rana pipiens and its involvement in the ipsilateral visuotectal projection. Brain Res 156:117–123
Gruberg ER, Lettvin JY (1980) Anatomy and physiology of a binocular system in the frog Rana pipiens. Brain Res 192:313–325
Gruberg ER, Udin SB (1978) Topographic projections between the nucleus isthmi and the tectum of the frog Rana pipiens. J Comp Neurol 179:489–500
Khalil SH, Lázár Gy (1977) Nucleus isthmi of the frog: Structure and tecto-isthmic projection. Acta Morphol Acad Sci Hung 25:51–59
Larsell O (1924) The nucleus isthmi of the frog. J Comp Neurol 36:309–322
Levine RL (1980) An autoradiographic study of the retinal projection in Xenopus laevis with comparisons to Rana. J Comp Neurol 189:1–29
Peters A, Palay SL, Webster H deF (1976) Fine structure of the nervous system: The neurons and supporting cells. WB Saunders, Philadelphia
Straznicky C, McCart R (1987) The effects of tectal lesion on the survival of isthmic neurons in Xenopus. Develop 101 (in press)
Tay D, Straznicky C (1980) The development of the nucleus isthmi in Xenopus: An autoradiographic study. Neurosci Lett 16:313–318
Tóth P, Lázár Gy, Görcs T (1980) Retinal projections in the adult Xenopus laevis: A study with cobalt filling technique. Acta Morphol Acad Sci Hung 28:365–374
Udin SB, Fisher MD (1985) The development of the nucleus isthmi in Xenopus laevis. 1. Cell genesis and the formation of connections with the tectum. J Comp Neurol 232:25–35
Udin SB, Keating MJ (1981) Plasticity in a central nervous pathway in Xenopus: Anatomical changes in the isthmotectal projection after larval eye rotation. J Comp Neurol 203:575–594
Udin SB, Keating MJ, Dawes EA, Grant S, Deakin JFW (1985) Intertectal neuronal plasticity in Xenopus laevis: Persistence despite catecholamine depletion. Dev Brain Res 19:81–88
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
McCart, R., Straznicky, C. The ultrastructural organization of the isthmic nucleus in Xenopus. Anat Embryol 177, 325–330 (1988). https://doi.org/10.1007/BF00315840
Issue Date:
DOI: https://doi.org/10.1007/BF00315840