The Journal of Neuroscience, March 1, 2002, 22(5):1895-1904
Combinatorial and Cross-Fiber Averaging Transform Muscle
Electrical Responses with a Large Stochastic Component into
Deterministic Contractions
Neil J.
Hoover1,
Adam
L.
Weaver1,
Patricia I.
Harness2, and
Scott L.
Hooper1
1 Neuroscience Program, Department of Biological
Sciences, Irvine Hall, Ohio University, Athens, Ohio 45701, and
2 Neuroscience Doctoral Program, University of California
Davis, Davis, California 95616
Pyloric muscles of the stomatogastric neuromuscular system of the
lobster Panulirus interruptus produce highly deterministic (range, less than ±6% of mean amplitude) contractions in response to
motor nerve stimulation with unchanging spike bursts containing physiological (5-10) spike numbers. Intracellular recordings of extrajunctional potentials (EJPs) evoked in these muscles by motor nerve stimulation revealed a large, apparently stochastic amplitude variation (range, ±36% of mean amplitude). These observations raised
the question of how do electrical responses with a large amplitude
variation give rise to deterministic muscle output? We show here that
this question is likely resolved by (1) combinatorial averaging within
individual muscle fibers of the multiple EJPs that occur in motor
neuron bursts, and (2) averaging across muscle fibers whose electrical
responses are uncorrelated. Synapses with high inherent variability are
also present in vertebrate CNSs. Combinatorial averaging in
multispike inputs would also reduce variation in postsynaptic response
at these synapses. The data reported here provide further support that
bursting presynaptic activity could make such synapses functionally
deterministic as well.
Key words:
synaptic variation; stomatogastric system; lobster; Panulirus interruptus; neuromuscular transform; stochastic; excitatory junctional potential
Copyright © 2002 Society for Neuroscience 0270-6474/02/2251895-10$05.00/0
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