Input-output and discharge properties of neurons are shaped by both passive and active electrophysiological membrane properties. Whole-cell patch clamp recordings in lamina I-III neurons in an isolated preparation of the whole spinal cord of juvenile rats with attached dorsal roots and dorsal root ganglia was used to further define which of these properties provides the most impactful classification strategy. A total of 95 neurons were recorded in segment L5 and were classified based on the responses to L4 dorsal root stimulation. The results showed that high threshold and silent neurons had higher membrane resistance and more negative resting membrane potential than low threshold or wide dynamic range neurons. Rheobase in low threshold and wide dynamic range neurons was significantly lower than that of high threshold or silent neurons. Four types of firing patterns were identified in response to depolarizing current injections. Low threshold cells most frequently showed a phasic firing pattern characterized by a short initial burst of action potentials, single-spiking or irregular firing bursts at the onset of a depolarizing pulse. High threshold and wide dynamic range neurons were characterized by tonic firing with trains of spikes occurring at regular intervals throughout the current pulse. The majority of silent neurons displayed a delayed onset of firing in response to current injection. These results indicate that passive membrane properties of spinal neurons are tuned to optimize the responses to particular subsets of afferent stimuli.
- patch clamp
- dorsal root
- anatomical class
- Copyright © 2016, Journal of Neurophysiology