Tuning of membrane properties regulates subliminal synapses in dorsal horn neurons of intact rats.

Functional plasticity in receptive field properties underlies the mechanism whereby spinal dorsal horn neurons encode changes in pain sensitivity following peripheral injury. Activation of "silent" or subliminal excitatory synapses was hypothesized to account for this injury-induced neural plasticity. To better characterize the mechanisms governing subliminal inputs, we adapted whole-cell patch clamp to the study of dorsal horn neurons in intact, anesthetized rats. In this report we show that the membrane properties of spinal cells correlate to functional class defined by action potential responses to cutaneous stimuli. In addition, we report the discovery of a novel "silent" population of neurons with solely subliminal excitatory inputs at rest that can be activated by membrane depolarization. Finally, an induced change in baseline membrane potential to a level nearer that of a different functional class results in a corresponding change in the responses to cutaneous stimuli of a given cell to that of the new functional class. In summary our findings suggest that biophysical membrane properties are key factors determining the functional profile of spinal neurons. The rapid change of such properties may regulate the function of silent synapses in spinal neurons and underlie rapid development of neural plasticity. Copyright 2002 Elsevier Science (USA).