Z. Vidnyanszky et al., LIGHT-MICROSCOPIC AND ELECTRON-MICROSCOPIC ANALYSIS OF SYNAPTIC INPUTFROM CORTICAL AREA-17 TO THE LATERAL POSTERIOR NUCLEUS IN CATS, Experimental Brain Research, 109(1), 1996, pp. 63-70
The morphology and synaptic organization of the corticothalamic (CT) F
ibres from area 17 were studied in the lateral posterior nucleus (LP)
of the thalamus in cats. Injection of the anterograde tracer Phaseolus
vulgaris leucoagglutinin (PHAL) into primary visual cortex labelled a
band of CT fibres in the LP with terminal field confined to its later
al division ''LP1'', PHAL-labelled CT axons in the LP1 gave rise to bo
th en passant and terminal boutons. They usually established several s
ynaptic contacts - often in complex glomerulus-like synaptic arrangeme
nts - with dendritic shafts of large diameter and presynaptic dendrite
s containing pleomorphic vesicles. Postsynaptic targets of the PHAL-la
belled CT boutons were characterized by postembedding gamma-aminobutyr
ic acid (GABA) immunocytochemistry. It appeared that, in the LP1 of th
e cat, almost half (44.5%) of the postsynaptic dendrites to CT boutons
from area 17 belonged to the GABA-immunopositive interneurons and the
majority (41%) of these GABA-immunopositive dendrites were F2 termina
ls. These results indicate that the CT axons from the striate cortex i
n the LP of the cat, in addition to a direct excitatory action, exert
a powerful feed-forward inhibition on the thalamic principal cells.