Rowat, Peter
Institute for Neural Computation, University of California, San Diego

GRADED SYNAPTIC TRANSMISSION WITH A WIDE TRANSFER FUNCTION CAN GENERATE SYNCHRONOUS OSCILLATIONS IN A PAIR OF MUTUAL EXCITATORY CELLS, OR OUT-OF-PHASE OSCILLATIONS IN A RECIPROCAL INHIBITORY PAIR OF CELLS

In central pattern generators, graded synaptic transmission is widespread and reciprocal inhibition between pairs of cells is common. When the cells are not endogenous bursters, "escape" and "release" are two mechanisms that can generate out-of-phase oscillations (Wang and Rinzel 1992). These mechanisms assume the synaptic transfer function (STF) for graded transmission is narrow - i.e. a step function - and require the threshold for graded transmission to be high or low but not in an intermediate range. If the transfer function for graded transmission is wide, then out-of-phase oscillations can be generated by another mechanism, "synaptic transfer feedback", that will drive oscillations for a much wider range of threshold values, including values in the intermediate range. In the case of reciprocal excitatory synapses, if the STF is narrow then oscillations can only occur if the thresholds of the two synapses are significantly different. However, if the STF is wide, oscillations can be driven by a related form of synaptic transfer feedback and the thresholds can be identical in each cell. In many places where graded transmission occurs, the STF is wide enough to support oscillations by synaptic transfer feedback. Thus this oscillatory mechanism may be more widespread than either release or escape.