RT Journal Article
SR Electronic
T1 The Connection from Cortical Area V1 to V5: A Light and Electron Microscopic Study
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 10525
OP 10540
DO 10.1523/JNEUROSCI.18-24-10525.1998
VO 18
IS 24
A1 John C. Anderson
A1 Tom Binzegger
A1 Kevan A. C. Martin
A1 K. S. Rockland
YR 1998
UL http://www.jneurosci.org/content/18/24/10525.abstract
AB Area V5 (middle temporal) in the superior temporal sulcus of macaque receives a direct projection from the primary visual cortex (V1). By injecting anterograde tracers (biotinylated dextran andPhaseolus vulgaris lectin) into V1, we have examined the synaptic boutons that they form in V5 in the electron microscope. Nearly 80% of the target cells in V5 were spiny (excitatory). The boutons formed asymmetric (Gray’s type 1) synapses with spines (54%), dendrites (33%), and somata (13%). All somatic targets and some (26%) of the target dendritic shafts showed features characteristic of smooth (inhibitory) cells. Each bouton formed, on average, 1.7 synapses. The larger boutons formed multiple synapses with the same neuron and completely enveloped the entire spine head. On most dendritic shafts and all somata the postsynaptic density en face was disk-shaped but in about half the cases the reconstructed postsynaptic densities of synapses on spines appeared as complete or partial annuli. Even in the zones of densest innervation only 3% of the asymmetric synapses were formed by the labeled boutons. Although the V1 projection forms only a small minority of synapses in V5, its affect could be considerably amplified by local circuits in V5, in a way analogous to the amplification of the small thalamic input to area V1.