(a) Streptavidin (568 nm) labelling of record Lpar1-EGFP SPNs in mouse S1BF at P2. (b) Superimposed electrophysiology traces recorded from one of the cells shown in (a) in response to hyperpolarising and depolarising threshold current injection. (c) Maximum firing frequency for the same cell; scale bar is the same for (b) and (c). (d–i) Summary data for 103 cells grouped according to age: P1–2 (n = 22); P3–4 (n = 27); P5–6 (n = 24); P7–8 (n = 30). The range of passive membrane properties recorded included (d) resting membrane potential (RMP) (mV); (e) Input resistance (RIN) (GΩ); (f) membrane time constant (tau) (ms). Active properties included (g) current injection required for threshold spike (rheobase) (mV); (h) spike amplitude (mV); (i) maximum firing frequency (Hz). We observed a statistically significant difference between age groups for RIN (ANOVA, F = 21.17, p<0.001), decay time constant (Kruskal–Wallis test, KW = 37.75, p<0.001), rheobase (Kruskal–Wallis test, KW = 15.74, p<0.01), spike amplitude (ANOVA, F = 22.05, p<0.001), and maximum firing frequency (Kruskal–Wallis test, KW = 43.15, p<0.001), whereas no statistical significant difference was observed for resting membrane potential (ANOVA, F = 1.74, p>0.05). Significant multiple comparisons of note are indicted in the relevant panels: *0.01<p<0.05; **p<0.01.