Figure 5.

Basal muscarinic tone suppresses the excitability of D₂ MSNs but is insufficient to explain the physiological dichotomy. a, b, Sample current-clamp recordings from wild-type and M₁R −/− D₂ spiny neurons. c, d, F–I relationships of D₁ and D₂ wild-type and M₁R −/− MSNs. Note the decrease in firing in the D₂ MSN population from M₁R −/− mice. e, f, I–V relationships of wild-type versus M₁R −/− D₁ MSNs and wild-type (wt) versus D₂ MSNs. g, h, Peak current measured at −150 mV does not differ in the D₁ MSNs. (D₁ MSN wt: median, −1836 pA, n = 35; D₁ MSN M₁R −/−: median, −2045 pA, n = 14). M₁R −/− D₂ MSNs show increased inward currents in the absence of M₁R tone (D₂ MSN wt: median, −1159 pA, n = 31; D₂ MSN M₁R −/−: median, −1298 pA, n = 14; p < 0.05). *Statistical significance.