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Shawn Lockeryが分子生物学会生化学会合同年会(BMB2007)で来日


東京大学Global COEセミナー

演者 Shawn R. Lockery
(Institute of Neuroscience&s_comma; University of Oregon&s_comma; USA)
日時 平成19年12月18日(火) 10:00~12:00
場所 理学部旧1号館4階450号室

タイトル "Neuronal and theoretical analysis of spatial
orientation behavior in C. elegans."

Regulation of locomotion is the final common path for
orientation to taste&s_comma; smell&s_comma; oxygen&s_comma; temperature&s_comma; and other
ecologically significant stimuli in C. elegans. Locomotory
state (forward vs. reverse) is thought to be controlled by a
network of forward and reverse command neurons in two
reciprocally connected pools&s_comma; but how this network functions
is poorly understood. We propose a model in which the
network acts as a stochastic&s_comma; bi-stable switch. The model
makes three simple assumptions: (a) forward command neurons
act as a single unit&s_comma; as do reverse command neurons; (b)
unit activation switches stochastically between two states:
OFF and ON; (c) the stochastic processes underlying the
state changes of the forward and reverse units are
uncorrelated. The model predicts that forward and reverse
locomotion&s_comma; and also the transitions between them&s_comma; are
punctuated by brief pauses in which crawling speed drops to
zero. It further predicts that there are two pause states
(i.e. both units off or both units on). Using a new
tracking system that records velocity with a precision of
±19 um/sec at a rate of 30 samples/sec&s_comma; we detected frequent
episodes of near-zero speed which we interpret as the
predicted pause states. The dwell-time distribution for
pauses has two exponential components consistent with the
existence of at least two pause states. Mean dwell times of
these states are 10 and 100 ms. We are currently developing
methods to determine the rate constants for transitions
between the forward&s_comma; reverse&s_comma; and pause states.
Mathematically&s_comma; the rate constants strongly constrain the
signs and strengths of synaptic connections among command
neurons in the model offering&s_comma; thereby&s_comma; a means of inferring
neuronal connectivity from behavior. We are testing this
idea by determining how the rate constants are altered by
chronic depolarization and hyperpolarization of command
neurons&s_comma; ablations&s_comma; and feeding state.

世話人 東大・理・生化 飯野雄一(iino@biochem.s.u-
tokyo.ac.jp&s_comma; 03-5841-3034)