TITLE:

NMDA RECEPTORS AND THE COMPUTATIONAL PRIMITIVES OF NEURONS

DATE:

Friday, February 6th, 2009

TIME:

3:30 PM

LOCATION:

GMCS 214

SPEAKER:

Patrick Shoemaker, Ph.D., Senior Scientist, Tanner Research, Inc.

ABSTRACT:

I discuss the neural computational primitives that are afforded by the class of common excitatory synaptic receptors identified with the agonist N-methyl-D-aspartate (NMDA). The macroscopic current-voltage relationship of the ion channels activated by NMDA receptors is non-monotonic due to blockade of the channels by extracellular magnesium, effective mainly at membrane potentials below about -25mV Â relative to the extracellular space. The negative conductance of NMDA receptor channels in this region, in combination with other membrane conductances (both inherent and synaptically activated) can give rise to two phenomena of computational significance: amplification and bistability. These clearly have possible roles in signal processing and short-term memory in the nervous system. In addition, the nonlinear current-voltage relation of the class of inward-rectifying potassium channels Kir3 is well-suited to promoting these phenomena in concert with the NMDA conductance. I show that amplification and bistability can be localized in dendrites, the long, thin input structures of neurons; bifurcation from monostable to bistable dynamic regimes occurs not just with the degree of activation of the relevant channels, but also with the electrical length of a cable-like dendrite. The recently described association of GABA-B synaptic receptors with Kir3 channels suggests that these computationally significant phenomena can be evoked and regulated as a function of synaptic input to a neuron.

HOST:

Jose Castillo

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