Ca²⁺ permeability of kainate receptors switches off during late embryonic and early postnatal development. A, The number of DRG neurons showing high Ca²⁺ permeability decreases with age. Eachsymbol represents a ratio of peak Ca²⁺ response normalized to the areaunder the curve of KA-induced current, as demonstrated in the inset. Each symbol represents one DRG neuron. Day 0 represents the day of birth (totaln = 32). B, The E18 and neonate (P0–P2) animals show a larger current amplitude than do older animals. The average amplitudes of KA-induced currents are binned into three age groups: E18 (n = 5), P0–P2 (n= 16), and P3–P6 (n = 9). Singleand doubleasterisks indicate significant differences (based on Student's t test) between P3–P6 and P0–P2 groups (p < 0.05) and between P3–P6 and E18 groups (p < 0.05), respectively. There was no significant difference between E18 and P0–P2 groups. C, The developmental change inI–V relationship is shown. Each X symbolrepresents the rectification index from one DRG neuron. The rectification index is expressed as the ratio of conductance at +60 and −60 mV. D, The averages of the rectification indices at different ages are shown (gray bars, scale onlefty-axis) along with the average Ca²⁺ permeabilities, calculated from the domoate-induced currents and Ca²⁺ responses (as inA; white bars, scale onrighty-axis). The singleasterisks indicate significant differences (based on Student's t test) between P0–P1 and P7 groups (p < 0.05). The error bars indicate the SEM.