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The number of morphological synapses between neurons does not predict the strength of their physiological synaptic interactions: A study of dendrites in the nematode Ascaris suum
Author(s) -
Angstadt James D.,
Donmoyer Judith E.,
Stretton Antony O.W.
Publication year - 2001
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.1116
Subject(s) - inhibitory postsynaptic potential , excitatory postsynaptic potential , neuroscience , biology , motor neuron , neuron , neurotransmission , synapse , synaptic plasticity , electrophysiology , anatomy , spinal cord , biochemistry , receptor
Previous electrophysiological and anatomical studies of Ascaris suum motor neurons demonstrated a strong correlation between functional interactions and the presence of anatomically defined synapses. However, one example of a physiologically robust synaptic connection was encountered for which no anatomical evidence of direct chemical synapses was found. This involved synaptic transmission from an identified excitatory motor neuron to its inhibitory partner. In this study, pressure injection of horseradish peroxidase or nickel lysine into inhibitory motor neurons revealed numerous spines projecting from the main neuronal process toward the neuromuscular surface that then branched and extended fine, longitudinal processes up to 130 μm in length. Subsequent examination of nickel lysine‐injected spines by electron microscopy revealed numerous chemical synapses, including for the first time direct inputs from the excitatory neuron. However, the numbers of synapses from this motor neuron were very small relative to inputs from other identified cells. Thus, direct synapses are unlikely to explain the robust nature of this physiological interaction. J. Comp. Neurol. 432:512–527, 2001. © 2001 Wiley‐Liss, Inc.