皮質抑制性ニューロンと局所回路

抄録

Activities of cortical pyramidal cells are regulated by GABAergic nonpyramidal cells with temporally and spatially differentiated inhibitotry wiring. Cortical inhibitory synapses were believed to make synaptic contacts mainly on soma and/or proximal dendrites of pyramidal cells, however the latest our finding shows approximately 1/3 of axon terminals of cortical nonpyramidal cells, such as double bouquet cell, Martinotti cell and neurogliaform cell, make synaptic contact on spine head, which also receive an asymmetrical input, called double innervated (DI) spine. From morphological point of view, the inhibitory synapse on DI spine probably has a vetoed function to the asymmetrical excitatory input. We studied morphological properties of the double innervated spines using vesicular glutamate transporters (VGLUTs) positive terminals, which show complementary distribution in cortex, VGLUT1 positive terminals were mostly originated from cortical pyramidal cells and VGLUT2 positive terminals mostly from thalamic projection neurons. This complementary localizations permitted to study an origin of the excitatory terminals on the DI spines. We observed 291 VGLUT1 innervated and 442 VGLUT2 innervated spine heads and found the target of these inhibitory synapses were almost exclusively DI spines received VGLUT2 positive excitatory synapse. Forty four (9.6%) out of 442 spine heads innervated by VGLUT2 positive synapses received symmetrical synaptic input and only 2 (0.7%) out of 291 VGLUT1 innervated DI spines were found. These results indicated that part of thalamo-cortical efferent fibers were vetoed by inhibitory synapse selectively at spine head. [J Physiol Sci. 2006;56 Suppl:S33]