Figure 4.

A–B′, Representative traces from electrophysiological recordings of D1 (A) and D2 (A′) striatal MSNs at 250 pA (A, A′) or 450 pA (B, B′) of current. C, No differences were observed in the frequency of action potential firing or rheobase (C, inset) in D1 MSNs of mice that expressed the HIV-1 Tat transgene (Tat⁺) or their control counterparts (Tat⁻). C′, However, MSNs in Tat⁺ mice demonstrated a significantly reduced frequency of action potentials while stimulating at 200–350 pA and a significantly greater frequency of action potentials at 450 pA in D2 MSNs compared with Tat⁻ MSNs. D2 MSN rheobase values were significantly greater in Tat⁺ compared with Tat⁻, mice (C′, inset). *Significant difference from Tat⁻ following a significant interaction of genotype and stimulus current (pA) intensity, p < 0.05.