Journal of Neuroscience, Vol 7, 1769-1779, Copyright © 1987 by Society for Neuroscience
Physiological consequences of a peptide cotransmitter in a crayfish nerve-muscle preparation
CA Bishop, JJ Wine, F Nagy and MR O'Shea
The pentapeptide proctolin is colocalized with a conventional,
conductance-increasing neurotransmitter in 3 of 5 excitatory motoneurons
that innervate a posture-related tonic flexor muscle of the crayfish. It is
released from these neurons in response to nerve impulses. Nanomolar
concentrations of proctolin superfused on the tonic flexor muscle act
postsynaptically to potentiate tension generated by a given level of
depolarization. Proctolin alone has no detectable effect on muscle tension,
nor does it alter the resting membrane potential of the muscle. Proctolin
produces no detectable effect on the EPSPs of the 1 proctolinergic
motoneuron that was examined. Neurally released proctolin can be
selectively depleted from severed motor axons following prolonged,
low-frequency stimulation; EPSPs reflecting conventional transmitter
release are unaltered by this procedure. After proctolin depletion, tension
generated by the motoneuron is greatly reduced. Taken together, these
results indicate that the peptide secondary transmitter in this
neuromuscular preparation is an important contributor to the magnitude of
tension generated by the motoneuron, but since its effect is dependent on
the depolarizing EPSPs of the conventional neurotransmitter, it does not
contribute to the temporal aspects of tension generation. These aspects are
controlled exclusively by the conventional neurotransmitter.
Previous Article | Next Article
