“Strong” and “weak” synaptic differentiation in the crayfish opener muscle: Structural correlates
作者:
C. K. Govind,
J. Pearce,
J. M. Wojtowicz,
H. L. Atwood,
期刊:
Synapse
(WILEY Available online 1994)
卷期:
Volume 16,
issue 1
页码: 45-58
ISSN:0887-4476
年代: 1994
DOI:10.1002/syn.890160106
出版商: Wiley Subscription Services, Inc., A Wiley Company
关键词: Synapse;Ultrastructure;Postsynaptic potentials;Active zone;Synaptic differentiation;Freeze‐fracture
数据来源: WILEY
摘要:
AbstractThe single excitor motoneuron to the limb opener muscle in the crayfish Procambarus clarkii provides multiterminal innervation to individual muscle fibers. At low impulse frequencies, these neuromuscular synapses generate a threefold larger junctional potential in fibers of the proximal region of the muscle compared to those in the central region. Focal extracellular recording from synapse‐bearing “boutons” showed more quantal release at low frequencies in the proximal region. Structural correlates for the physiological differences were sought. Fluorescence microscopy of surface innervation stained with a vital fluorescent dye, 4‐Di‐2‐Asp, showed that density of innervation was not greater in the proximal region and thus could not account for the overall differences in synaptic strength. Freeze fracture studies showed that the intramembrane organization of excitatory synapses and their active zones was qualitatively similar in proximal and central sites. Serial section electron microscopy of several innervation sites in proximal and central regions showed homogeneity in number and size of synapses. However, presynaptic dense bars (at release sites, or active zones) were longer and occurred at a higher density in proximal than in central synapses. The differences in number and length of presynaptic dense bars correlate positively with the differences in synaptic strength represented by junctional potential amplitudes and quantal contents of individual surface recording sites. Since many individual proximal synapses have multiple dense bars, co‐operativity among these may serve to enhance transmitter output. It is concluded that occurrence of dense bars is a significant pre synaptic correlate of synaptic strength in this neuron. © 1994 W
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