Figure 12.

Adult lamina I projection neurons exhibit greater action potential discharge in response to sensory input when preceded by neonatal tissue damage. A, Example of a spino-parabrachial neuron that discharged a single action potential (AP) from its resting membrane potential regardless of the intensity of dorsal root stimulation. B, Other projection neurons responded to increasing primary afferent stimulation with a progressive increase in the number of postsynaptic APs. C, D, Neonatal hindpaw incision led to a significant leftward shift in the stimulus–response function in both the single-spiking (p = 0.004; two-way ANOVA; C), and repetitive-firing (p < 0.0001; two-way ANOVA; D) subtypes of adult lamina I projection neurons.