Figure 5.

In vitro classification of monosynaptic primary afferent inputs to adult lamina I projection neurons. EPSCs evoked by dorsal root stimulation that met the criteria for a monosynaptic response (see Materials and Methods) were classified as being mediated by LT A-fibers (blue), HT A-fibers (green), LT C-fibers (pink), or HT C-fibers (data not shown). Each symbol represents a single lamina I projection neuron. A combination of EPSC threshold and EPSC latency (corrected for synaptic delay) was considered to categorize the subtype of primary afferent input to the sampled projection neuron. The stimulus thresholds and axonal conduction velocities used to classify the afferent subtype were calibrated on a daily basis following the recordings of CAPs from the dorsal roots as described earlier. Low-threshold A-fiber inputs could be distinguished from HT A-fiber inputs based on both stimulus intensity and EPSC onset latency, and separated from the low-threshold C-fiber responses based on EPSC latency alone.