Figure 3. Activation of PSAM⁴-GlyR depolarizes D1-MSNs and does not inhibit firing.

(A) In PSAM⁴-GlyR⁺ neurons, activation of PSAM⁴-GlyR with uPSEM⁷⁹² (10 and 50 nM) significantly depolarized the membrane potential (V_m) compared to control (non-PSAM⁴-GlyR) neurons, measured in current-clamp (two-way ANOVA with Sidak’s multiple comparisons test). (B) Representative traces of current-clamp recordings from a control (top) or PSAM⁴-GlyR⁺ neuron (bottom). Action potential firing was evoked by somatic current injection (250 pA, 2 s) in aCSF (left) and 50 nM uPSEM⁷⁹² (right). Dashed line is −80 mV. (C) Distribution of firing response of PSAM⁴-GlyR⁺ neurons after 10 or 50 nM uPSEM⁷⁹² application. In 10 nM uPSEM⁷⁹², 14/14 neurons continued to fire with current injection. In 50 nM, 9/16 neurons fired with current injection (induced firing), 1/16 fired spontaneously without a current injection (spont. firing), and 6/16 went into depolarization block (DP block). (D) Representative traces of current-clamp recordings from a PSAM⁴-GlyR⁺ neuron that went into depolarization block with uPSEM⁷⁹². Response to somatic current injection (250 pA, 2 s) in aCSF (gray) and after uPSEM⁷⁹² application (black). The membrane potential in uPSEM⁷⁹² was more depolarized than the potential where the neuron entered depolarization block in aCSF. Dashed line is −80 mV. (E) Plot of change in the minimum current needed to induce firing (approximate rheobase: ~rb) induced by uPSEM⁷⁹² (10 and 50 nM) in control (gray) and PSAM⁴-GlyR⁺ (black) in cells that continued to fire (10/16). No significant change of ~rb was observed. (F) Plot of number of action potentials (APs) fired versus injected current in control neurons in aCSF (open) and in uPSEM⁷⁹² (closed). No significant difference was observed. (G) Plot of AP firing frequency versus injected current in control neurons in aCSF (open) and in uPSEM⁷⁹² (closed). No significant difference was observed. (H) Plot of number of APs fired versus injected current in PSAM⁴-GlyR⁺ neurons in aCSF (open) and in uPSEM⁷⁹² (closed). No significant difference was observed. (I) Plot of AP firing frequency versus injected current in PSAM⁴-GlyR⁺ neurons in aCSF (open) and in uPSEM⁷⁹² (closed). No significant difference was observed. Line and error bars represent means ± SEM, * indicates statistical significance, ns denotes not significant.