Fig. 4.

ChAT interneurons can be activated by cocaine in slice and required for cocaine conditioning in vivo. (A) The frequency of spontaneous action potentials in a ChAT neuron increased 10 min after bath application of cocaine (5 μM). ACSF, artificial cerebrospinal fluid. (B) Firing rate over time for this ChAT neuron. Horizontal gray bar, application of cocaine; vertical dotted line, 10 min after cocaine application, the time point illustrated in detail in (A) and (C). (C) Population data illustrating the cocaine-induced increase in firing in ChAT neurons, comparing the baseline firing rate (averaged over the 2.5 min before cocaine application) with the rate after cocaine infusion (averaged between 10 and 12.5 min after onset of cocaine application; gray bars, cells receiving cocaine; white bars, control cells receiving only ACSF; P < 0.005, paired two-tailed t test for cocaine-treated group before versus after cocaine; P < 0.05 unpaired two-tailed t test comparing cocaine versus control cells after cocaine or vehicle). (D) Schematic illustration of a bilateral cannula system with double fibers inserted to illuminate the medial portion of the NAc. (Left inset) Endpoint of cannula track for all mice used in (H). (Right inset) eYFP expression in NAc of a ChAT∷Cre⁺ mouse injected with Cre-dependent eNpHR3.0-eYFP. (E) Conditioning paradigm for cocaine CPP (H). Mice were conditioned with ip cocaine (20 mg/kg), along with ChAT cell inhibition with eNpHR3.0 (wavelength: 590 nm). (F) Tracking data from representative ChAT∷Cre⁺ and ChAT∷Cre⁻ mice on the testing day after cocaine conditioning (day 3). On the previous day (day 2), the mice had received cocaine and light in one left chamber, whereas in the other they received saline. The ChAT∷Cre⁻ mouse (but not the ChAT∷Cre⁺ mouse) exhibited a preference for the conditioned chamber. (G) (Left) Fold change in time in conditioned chamber during day 3 versus day 1 of cocaine CPP (conditioning with cocaine and light). Comparison of ChAT∷Cre⁺ and ChAT∷Cre⁻ littermates; in both cases injected with Cre-dependent eNpHR3.0 (n = 10 ChAT∷Cre⁺, n = 12 ChAT∷Cre⁻; P < 0.01 for two-tailed t test; three cohorts). (Right) Fold change in time in conditioned chamber during day 3 versus day 1 for conditioning with light alone (no cocaine; n = 9 ChAT∷Cre⁺, n = 7 ChAT∷Cre; P > 0.05 for two-tailed t test; three cohorts). Error bars indicate SEM. n.s., not significant. (H) Velocity of virus-injected (Cre-dependent eNpHR3.0) and photostimulated ChAT∷Cre⁺ and ChAT∷Cre⁻ mice in the open field (n = 10 ChAT∷Cre⁺, n = 10 ChAT∷Cre⁻; P > 0.05 for two-tailed t test; three cohorts). (I) Same as (H) for track length in open field (n = 10 ChAT∷Cre⁺, n = 10 ChAT∷Cre⁻; P > 0.05 for two-tailed t test; three cohorts). (J) Same as (H) for time in center of open field (n = 10 ChAT∷Cre⁺, n = 10 ChAT∷Cre; P > 0.05 for two-tailed t test; three cohorts). (A to J) *P < 0.05; **P < 0.01; ***P < 0.005.