title: Patterns of synaptic contact upon individually labeled large cells of the dorsal lateral geniculate nucleus of the cat.
abstract: Four large geniculate cells that were densely filled with horseradish peroxidase have been studied in detail, at first light microscopically, to define the shape and distribution of the dendritic arbors, and then electron microscopically, to define the pattern of synaptic contacts upon their surfaces. Three of the cells had the morphological characteristics of a class 1 cell, and one cell was intermediate between class 1 and 2. All of these cells had few of the characteristic grape-like appendages, thought to receive retinal input within synaptic glomeruli. Retinal afferents were mainly distributed around proximal juxtasomatic dendritic segments and dendritic branch points. Some retinal afferents made simple axodendritic contacts, while others formed a part of a synaptic glomerulus. None of the retinal afferents forming synapses near the perikaryon were involved in glomeruli. Within the glomeruli involving class 1 cells, retinal terminals can relate both to dendritic segments, particularly near branch points, as well as to dendritic appendages. The few singly placed grape-like appendages were always contacted by retinal afferents, but not necessarily in a glomerular arrangement. Terminals interpreted as cortico-geniculate were seen most commonly upon peripheral dendritic segments, while those containing pleomorphic vesicles (F) were distributed more or less evenly over all parts of the dendritic and perikaryal surface. The perikaryon itself was contacted by F-type terminals but was not contacted by retino-geniculate or cortico-geniculate terminals. A class of slender axonal terminal, containing round synaptic vesicles and few or no mitochondria, was found contacting two of the four perikarya, but the origin of these slender axons is unknown. It is concluded that the surfaces of geniculate class 1 cells can be separated into several functionally distinct zones on the basis of the synaptic contacts they receive.
mesh_terms: D000818:Animals; D001370:Axonal Transport; D002415:Cats; D003712:Dendrites / Q000502:physiology / Q000648:ultrastructure; D005829:Geniculate Bodies / Q000502:physiology* / Q000648:ultrastructure; D006735:Horseradish Peroxidase; D008854:Microscopy, Electron; D009474:Neurons / Q000502:physiology*; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D006735:Horseradish Peroxidase