A quantitative study of synaptic interconnections in the dorsal lateral geniculate nucleus of the cat

Close to one half of the synapses occur in „encapsulated synaptic zones,“ where grapelike dendritic appendages are related mainly to intrageniculate and retinogeniculate axons, and about half lie in “interstitial zones, “ where corticogeniculate and some intrageno-axonal axons contact distal dendrite segments.

Abstract

2,700 synaptic contacts have been classified according to criteria described in an accompanying paper and the results summarized in tabular form. Only about 20% of the synaptic contacts in laminae A and A1 are formed by axons identifiable as retinogeniculate fibers. About 1/4 of these retinogeniculate synapses are axo-axonal. Approximately 45% of the contacts in these laminae are formed by axons tentatively identifiable as corticogeniculate fibers; about 35% by presumed intrageniculate fibers. Close to one half of the synapses occur in "encapsulated synaptic zones," where grapelike dendritic appendages are related mainly to intrageniculate and retinogeniculate axons, and about half lie in "interstitial zones," where corticogeniculate and some intrageniculate axons contact distal dendritic segments. Regions of the nucleus receiving from peripheral parts of the retina have relatively more corticogeniculate synapses, and have fewer intrageniculate synapses in the encapsulated zones than do regions receiving from the central parts of the retina. Most of the tissue in lamina B resembles the interstitial zones of laminae A and A1 and over 2/3 of the contacts in lamina B may prove to be corticogeniculate. The retinogeniculate fibers in this lamina are associated with relatively few other axons in simple, small encapsulated zones.