Figure 2. Sex-specific alteration of membrane excitability of NAc core MSNs after withdrawal from long-access methamphetamine self-administration. A1, Representative traces of action potentials in response to depolarizing step current injections (350, 450, and 550 pA) in MSNs from saline male (Sal-M; upper panel) or saline female (Sal-F; lower panel) rats. A2, Mean current–voltage (I–V) relationship of MSNs. Average number of action potentials triggered by incremental depolarizing step currents (0–600 pA, Δ50 pA, 500-ms duration) in Sal-M rats (23 cells, 6 rats) and Sal-F rats (34 cells, 8 rats). MSNs from females showed a significantly higher excitability at current injections from 300 to 550 pA than males. * indicates significant main effects of injected current (p < 0.0001) and sex (p < 0.01), and a significant injected current × sex interaction (p < 0.0001); post hoc Bonferroni’s multiple comparisons at 300 pA, p < 0.01; 350 pA, p < 0.001; 400–450 pA, p < 0.0001; 500 pA, p < 0.01; and 550 pA, p < 0.05. B1, Representative traces. B2, Spike threshold was higher in Sal-M rats (20 cells, 6 rats) compared with Sal-F rats (36 cells, 8 rats; two-tailed unpaired t test **p < 0.01). C1, Representative traces of ramp current injection (500 pA/2 s)-induced firing in MSNs. C2, The rheobase current measured by using a ramp current injection in saline rats and each methamphetamine group. A bigger average rheobase current in MSNs from Sal-M rats was observed compared with Sal-F rats. MSNs from the male methamphetamine (Meth-M) WD30–75 group showed lower rheobase currents compared with Sal-M rats with no differences between Sal-M and Meth-M WD100–135. The rheobase currents of MSNs from female methamphetamine rats (Meth-F) were similar in all Meth groups compared with saline controls (Tukey’s test, **p < 0.01, ***p < 0.001; Sal-M, 24 cells, 6 rats; Meth-M WD30–75, 29 cells, 8 rats; Meth-M WD100–135, 22 cells, 6 rats; Sal-F, 19 cells, 6 rats; Meth-F WD30–75, 28 cells, 7 rats; Meth-F WD100–135, 14 cells, 5 rats). D, Average resting membrane potential of MSNs was similar in each group (Tukey’s test, p > 0.05; Sal-M, 25 cells, 6 rats; Meth-M WD30–75, 29 cells, 8 rats; Meth-M WD100–135, 21 cells, 6 rats; Sal-F, 19 cells, 6 rats; Meth-F WD30–75, 28 cells, 7 rats; Meth-F WD100–135, 14 cells, 5 rats). E1, Representative membrane voltage traces in response to subthreshold current injections. E2, Mean I–V relationships following incremental subthreshold current injections (step current injections, –150 to 25 pA/Δ25 pA, 1 s). F, Average input membrane resistance (Rm) of MSNs recorded from saline, Meth WD30–75 and Meth WD100–135 groups in males and females was similar (Tukey’s test, p > 0.05; Sal-M, 21 cells, 6 rats; Meth-M WD30–75, 32 cells, 8 rats; Meth-M WD100–135, 22 cells, 6 rats; Sal-F, 34 cells, 8 rats; Meth-F WD30–75, 33 cells, 8 rats; Meth-F WD100–135, 16 cells, 6 rats). G1, Representative traces of action potentials evoked by 0-, 200-, 400-pA current steps. G2, Mean number of action potentials in response to depolarizing current injections (step, 0–600 pA/Δ50 pA, 0.5 s) in males. Meth-M WD30–75 rats showed increased action potentials at 300–500 pA, whereas Meth-M WD100–135 rats showed increased action potentials at 500 pA compared with Sal-M rats. * indicates significant main effects of injected current (p < 0.0001) and group (p < 0.01), and a significant injected current × group (p < 0.0001); post hoc Tukey’s multiple comparisons, Sal-M versus Meth-M WD30–75: at 300 pA, p < 0.05; 350 pA, p < 0.001; 400 pA, p < 0.0001; 450 pA, p < 0.001; and 500 pA, p < 0.05; Sal-M versus Meth-M WD100–135: at 500 pA, p < 0.05; Sal-M, 22 cells, 6 rats; Meth-M WD30–75, 31 cells, 8 rats; Meth-M WD100–135, 16 cells, 7 rats. H1, Representative traces of action potentials evoked by 0-, 200-, 400-pA current steps. H2, Mean number of action potentials in response to depolarizing currents injected (step, 0–600 pA/Δ50 pA, 0.5 s) in females. No difference was observed between saline and methamphetamine groups (post hoc Tukey’s multiple comparisons p > 0.05; Sal-F, 34 cells, 8 rats; Meth-F WD30–75, 28 cells, 7 rats; Meth-F WD100–135, 15 cells, 6 rats). Data are presented as mean ± SEM.