Journal of Neuroscience, Vol 4, 1904-1911, Copyright © 1984 by Society for Neuroscience
The action of cholinergic agonists on the squid stellate ganglion giant synapse
EF Stanley
Although the giant synapse in the squid stellate ganglion has served as a
model in the understanding of the ionic and electrical changes that occur
during the release of transmitter from nerve terminals, little is known
about the pharmacology of this synapse or the identity of its
neurotransmitter. In the present study, the suggestion that acetylcholine
(ACh) is the excitatory transmitter at this synapse was tested by exploring
the actions of cholinergic agents on the pre- and postsynaptic giant axons
and on the excitatory postsynaptic potential (EPSP). A novel arterial
perfusion technique that circumvents the diffusion barrier from the bathing
medium to the synapse has been used to demonstrate a depolarizing action of
ACh and its agonist carbachol on the post- but not the presynaptic axon.
The cholinergic receptors are distinct from receptors activated by amino
acids, such as glutamate, have a reversal potential of about -48 mV, are
anion- permeable, and desensitize without blocking the EPSP. It is
concluded that these receptors are involved in an inhibitory input onto the
postsynaptic giant axon and, therefore, that ACh is most probably not the
transmitter at the squid giant synapse.