Geniculocortical synapses involving apical dendrites of layer V pyramidal cells in area 17 of the albino rat visual cortex: a combined Golgi/EM study.
Using the combined Golgi/EM technique (Fairén et al. 1977) we have investigated whether apical dendrites of layer V pyramidal cells with different diameters receive different numbers of geniculocortical synapses. An electrolytic lesion was made in the lateral geniculate nucleus (LGN) of albino rats. After a survival time of two days degenerating boutons of LGN afferents onto visual cortex (area 17) were identified by electron microscopy. Postsynaptic layer V pyramidal cells marked by Golgi impregnation were studied. The location of nine identified pyramids was determined by light microscopy. The diameter of the apical dendrites - ranging from 0.9 to 2.5 mum - was measured on electron micrographs. The dendrites of eight out of the nine pyramids make synaptic contacts with geniculocortical afferents in layer IV and lower layer III. The degenerative geniculocortical terminals were mostly of the electron dense type; one times the electron lucent type was observed. These axon terminals synapse mainly with asymmetrical synaptic junctions on spines. Occasionally synaptic contacts were found on dendritic shafts. Most degenerating synapses are localized on the pyramidal cell with the thinnest apical dendrite. There was also an other thin apical dendrite, which did not receive any degenerating bouton. All out of one apical dendrites of different size are involved in geniculocortical synapses without giving any preference to dendrites of a defined diameter.
D000818:Animals; D001369:Axons / Q000648:ultrastructure; D003712:Dendrites / Q000648:ultrastructure*; D005829:Geniculate Bodies / Q000033:anatomy & histology*; D008854:Microscopy, Electron; D009410:Nerve Degeneration; D051381:Rats; D011919:Rats, Inbred Strains; D013569:Synapses / Q000648:ultrastructure*; D014793:Visual Cortex / Q000033:anatomy & histology*; D014795:Visual Pathways / Q000033:anatomy & histology