Fig. 7. Acute suppression of SST interneuron activity in Cg1/M2 occludes the behavioral effects of ketamine.
a Timeline for experiments involving use of Cre-dependent expression of designer receptors exclusively activated by designer drugs (DREADD) in SST-IRES-Cre animals. b Fraction of time spent freezing during CS+ and trace period, subtracted by that during CS− and trace period on the testing day. For hM4D(Gi) + Vehicle condition, ketamine (10 mg/kg) treatment caused an impairment in freezing compared to saline (saline: 44 ± 7%, ketamine: 4 ± 2%, mean ± s.e.m.; P = 2 × 10−4, Wilcoxon rank-sum test; n = 10 animals for saline and 9 for ketamine). For hM4D(Gi) + CNO condition, there was impairment in freezing in saline-treated animals with no further difference relative to ketamine-treated (10 mg/kg) animals (saline: 5 ± 2%, ketamine: 3 ± 2%, mean ± s.e.m.; P = 0.78, Wilcoxon rank-sum test; n = 9 animals for saline and 10 for ketamine). There was no effect of CNO on ketamine-induced (10 mg/kg) impairment as tested in the mCherry + CNO condition (saline: 39 ± 5%, ketamine: 1.5 ± 1%, mean ± s.e.m.; P = 2 × 10−4, Wilcoxon rank-sum test; n = 10 animals each for saline and ketamine). c Pre-pulse inhibition as a measure of sensorimotor gating. For hM4D(Gi) + Vehicle condition, a two-way within-subjects ANOVA with pre-pulse intensity (3, 6, and 9 dB) and drug (saline, ketamine (40 mg/kg)) as within-subjects factors found significant main effects of pre-pulse intensity (F(2,30) = 30.6, P = 6 × 10−7) and drug (F(1,15) = 21.9, P = 3 × 10−4), and a significant interaction (F(2,30) = 4.0, P = 0.03). Post-hoc Tukey-Kramer’s tests for saline vs. ketamine were significant at 3 dB (22 ± 4%, 6 ± 4%, mean ± s.e.m., P = 0.01), at 6 dB (42 ± 6%, 12 ± 5%, mean ± s.e.m., P = 1 × 10−4), at 9 dB (51 ± 5%, 23 ± 6%, mean ± s.e.m., P = 0.002). n = 16 animals each for saline and ketamine. For hM4D(Gi) + CNO condition, a two-way within-subjects ANOVA found a significant main effect of pre-pulse intensity (F(2,26) = 11.9, P = 2 × 10−4) but a non-significant main effect of drug (F(1,13) = 4.1 P = 0.06) and interaction (F(2,26) = 1.2, P = 0.3). Post-hoc Tukey-Kramer’s tests for saline vs. ketamine were not significant at 3 dB (−14 ± 8%, 1 ± 4%, mean ± s.e.m., P = 0.06), at 6 dB (8 ± 3%, 10 ± 6%, mean ± s.e.m., P = 0.71), at 9 dB (17 ± 5%, 26 ± 4%, mean ± s.e.m., P = 0.16). n = 14 animals each for saline and ketamine. For mCherry + CNO condition, a two-way within-subjects ANOVA found significant main effects of pre-pulse intensity (F(2,28) = 30.4, P = 9 × 10−8) and drug (F(1,14) = 56.0, P = 3 × 10−5), and a non-significant interaction (F(2,28) = 0.5, P = 0.62. Post-hoc Tukey-Kramer’s tests for saline vs. ketamine were significant at 3 dB (27 ± 4%, −3 ± 5%, mean ± s.e.m., P = 5 × 10−4), at 6 dB (49 ± 4%, 12 ± 5%, mean ± s.e.m., P = 1 × 10−5), at 9 dB (58 ± 5%, 24 ± 7%, mean ± s.e.m., P = 1 × 10−5). n = 16 animals each for saline and ketamine. *P < 0.05; **P < 0.01; ***P < 0.001; n.s., not significant.