Z. Vidnyanszky et J. Hamori, QUANTITATIVE ELECTRON-MICROSCOPIC ANALYSIS OF SYNAPTIC INPUT FROM CORTICAL AREA-17 AND AREA-18 TO THE DORSAL LATERAL GENICULATE-NUCLEUS IN CATS, Journal of comparative neurology, 349(2), 1994, pp. 259-268
Cortical feedback is the largest extraretinal projection to the latera
l geniculate nucleus. This input is thought to modulate the transfer o
f visual information in a state-dependent manner. The quantitative dis
tribution and synaptology of axon terminals arising from different cor
tical areas is still an unsolved question. To address this problem, th
e synaptic termination pattern of corticogeniculate axons from cortica
l areas 17 and 18 entering the lateral geniculate nucleus of the cat w
as examined. The Phaseolus vulgaris leucoagglutinin anterograde tract
tracing method was used for the labeling of corticogeniculate terminal
s. Postsynaptic targets were characterized by postembedding gamma-amin
obutyric acid (GABA) immunocytochemistry. In both laminae A and Al, la
beled corticogeniculate axons from area 17 established synaptic contac
ts with GABA-immunopositive, interneuronal dendritic profiles more fre
quently (17.5% of all axons) than did labeled axon terminals from area
18 (7% of axons). Conversely, 76% of labeled corticogeniculate axons
from area 17, as opposed to 87% of labeled axons from area 18, termina
ted on GABA-immunonegative relay cell dendrites. Furthermore, the mean
diameter of GABA-negative relay cell dendrites postsynaptic to labele
d axons from area 17 was significantly smaller than the diameter of re
lay cell dendrites synapsing with labeled terminals from area 18. Thes
e results indicate that the corticogeniculate axons from cortical area
s 17 and 18 exhibit different synaptic termination patterns in the dor
sal lateral geniculate nucleus of the cat, suggesting that these two p
rojections may subserve different functions in visual information proc
essing. (C) 1994 Wiley-Liss, Inc.