Fig. 2. N -methyl-d-aspartate (NMDA), 1,000 μm–evoked maximal current amplitudes in control (CNMDA) and 100 μm morphine–treated (M100NMDA) dorsal horn neurons grouped according to neuronal size. ( A ) Representative traces of 1,000 μm NMDA and 1,000 μm kainate (KA)–evoked current recorded from small (low-capacitance) dorsal horn neurons. ( B ) NMDA, 1,000 μm–evoked maximal current amplitudes normalized to capacitance (Imax/capacitance) in smaller neurons with capacitance of 5.0–22.0 pF. ( C ) Medium neurons with capacitance of 22.1–38.0 pF. ( D ) Large neurons with capacitance of 38.1 pF or greater. In control experiments, 1,000 μm kainate–evoked AMPA receptor mediated responses were also recorded and did not show any differences in Imax/capacitance between various sized dorsal horn neurons that were untreated (CKA) and morphine treated (M100KA). Numbers within the bars indicate the number of dorsal horn neurons from which the data were averaged. (Student t test, * P < 0.05).