Journal of Neuroscience, Vol 9, 784-797, Copyright © 1989 by Society for Neuroscience
The effects of postsynaptic levels of cyclic AMP on excitatory and inhibitory responses of an identified central neuron
LR Wolszon and DS Faber
Department of Biophysical Sciences, State University of New York, Buffalo 14214.
The effects of cAMP on Mauthner (M-) cell excitatory and inhibitory
responses were studied in vivo. Cyclic AMP was iontophoresed into the M-
cell lateral dendrite, after which we monitored the changes in cellular
responsiveness to stimulation of 2 classes of identified presynaptic cells:
(1) excitatory fibers from the posterior branch of the ipsilateral eighth
cranial nerve and (2) inhibitory interneurons activated by the M-cell
collateral and commissural networks. We found that postsynaptic injections
of cAMP increased the magnitudes of the electrically and chemically
mediated EPSPs from the eighth nerve and enhanced M-cell inhibitory
responses as well. Furthermore, cAMP augmented paired-pulse facilitation of
both types of excitatory potentials. No effects on input conductance,
resting membrane potential, or presynaptic spike width were observed. All
effects were mimicked by aminophylline, a cAMP-dependent phosphodiesterase
inhibitor but not by 5'-AMP, the cAMP breakdown product. These results
provide evidence for second-messenger modulation in vivo of electrotonic
and chemical synaptic potentials at mixed synapses. In addition, they
provide the first evidence for cAMP modification of a glycinergic
receptor-channel complex. Preliminary results from some of these
experiments have been reported previously (Wolszon and Faber, 1986).