Monday, May 14, 2007

Synaptic communication in the visual cortex

The traditional view of pyramidal neurons, which are excitatory, is that they can only excite their downstream target cells. A new study of the mouse visual cortex shows that cortical pyramidal neurons can elicit an inhibitory synaptic current in another neighboring pyramidal neuron.

This very complex study was performed by the Komatsu Group (mouse over the Neuroscience Department) at the Research Institute of Environmental Medicine at Nagoya University and reported in Science 4 May 2007: Vol. 316. no. 5825, pp. 758 - 761 in the article Specialized Inhibitory Synaptic Actions Between Nearby Neocortical Pyramidal Neurons. It appears to build on earlier research by Callaway at the Salk Institute for Biological Studies (see Nature Neuroscience  3, 701 - 707).

This inhibition may play a crucial role in the regulation of the cortical output signal. According to traditional views, pyramidal neurons receive inhibitory inputs via action potentials initiated in inhibitory interneurons after integration of synaptic inputs to their somatodendritic domain. Thus, synaptic transmission from inhibitory nerve terminals to layer-2/3 pyramidal cells is driven by two distinct signaling pathways:

  1. via an integration of feedforward and feedback signals in inhibitory interneurons, and
  2. more directly via output signals of nearby pyramidal cells

The presence of interpyramidal inhibition suggests that the functional influence of inhibitory neurons can be far greater than might be predicted by their relatively small numbers. Understanding what this important role is, will take quit a lot more research.

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