Firing profiles of lamina II neurons recorded in rat spinal cord slices. A: In the current clamp configuration of the whole-cell patch clamp, four distinct firing profiles were recorded in lamina II neurons in response to incremental depolarizing currents steps of 900 ms every 20 s. They are referred to as repetitive (R), phasic (P), delayed (D) and single spike (S). Typical repetitive firing profile is characterized by the tonic generation of action potentials during the depolarization. The phasic profile is characterized by a strong accommodation leading to a plateau. The delayed firing profile exhibits a time-dependent silent phase before bursting. Lastly, a small proportion of lamina II neurons displays only a single spike (sometimes two) at the beginning of the depolarization. Stars show characteristic firing profile at longer time-scale. Dashed lines represent -60 mV. As shown on the right diagram, no correlation could be found between the firing profile and the location of the recorded neuron. B: Biocytin revelation (images) and reconstruction (drawings) of recorded cells illustrating the large variety of morphology of lamina II neurons. In our hands, no correlation was observed between a specific morphology and the firing pattern.