Journal of Neurophysiology, Vol 61, Issue 2 382-390, Copyright © 1989 by APS
Effects of baclofen on transient neurons in the mudpuppy retina: electrogenic and network actions
S. H. Bai and M. M. Slaughter
Department of Biophysical Sciences, School of Medicine, State University of New York, Buffalo 14214.
1. Baclofen increases transient light responses of amacrine and ganglion
cells despite acting as a classical inhibitory transmitter to both
hyperpolarize and shunt these cells. 2. This effect seems to occur at the
level of the inner retina and appears not to be due to an additional input
from bipolar cells. 3. In some transient cells baclofen increases the total
amplitude of the light response but does not change the peak potential of
the light evoked EPSP. In these cells, the baclofen-induced enhancement can
be accounted for by an increase in driving force of the excitatory
postsynaptic potential (EPSP) resulting from the hyperpolarization. 4.
However, in other cells the peak of the light response after baclofen
application is greater, which cannot be accounted for by a change in
driving force. This effect of baclofen can be mimicked by a blockers of
gamma-aminobutyric acid (GABA) and glycine, suggesting that in these cells
baclofen's enhancement is due in part to network effects resulting in a
removal of sustained inhibition. 5. Therefore, the paradoxical effect of an
inhibitory transmitter producing an enhancement of synaptic responses seems
due to at least two mechanisms. 6. The results indicate that some transient
cells receive significant tonic inhibition which limits their response
amplitude in a push-pull type mechanism, but other cells are not under this
inhibitory control process.
