T. Kadota et al., SYNAPTIC SPINULES ATTENDANT ON POSTTETANIC POTENTIATION IN CAT SYMPATHETIC-GANGLION, Proceedings of the Japan Academy. Series B Physical and biological sciences, 72(3), 1996, pp. 48-51
A synaptic spinule formed on the postsynaptic membrane in the cat supe
rior cervical ganglion (SCG) in vivo was electron microscopically stud
ied, When the preganglionic nerve fiber was tetanically stimulated at
10 Hz for more than 10 seconds, a post-tetanic potentiation (PTP) was
electrophysiologically detected and maintained up to 30 min. Concurren
tly with PTP, a small process, termed as synaptic spinule, was generat
ed as a small projection standing out from the postsynaptic dendritic
membrane with a straightly extended contour. The spinule produced a br
eak at about a middle point of the postsynaptic density (PSD) and divi
ded it into two parts forming a perforated synapse. Then, the spinule
increased in size, invaginated into the cytoplasm of the nerve termina
l, and subdivided the presynaptic terminal bag into two compartments.
Each of the compartments retained a morphology of an active synaptic s
ite with a cluster of synaptic vesicles associated with a presynaptic
active zone standing opposite to the one part of the subdivided PSD. T
he longer the tetanic stimulation in period, the more the synapses wit
h the spinule increased in number. In addition to this, a few spinules
(multiple type of spinule) were often formed after the stimulation of
1 min and more than two compartments were generated in a single nerve
ending. The present observations have suggested that the synaptic spi
nule is a morphological representation of the ''synaptic plasticity''
which is electrophysiologically displayed as the PTP in cat SCG in viv
o.