(A) Diagram of experimental setup with tdTomato (tdT+) unipolar brush cells (UBCs) in whole-cell current clamp configuration. FR was measured during baseline period, followed by application of Drd1 agonist SKF81297 (500 µM) with 300-ms long puffs from a proximally located pipette. (B) Membrane voltage traces from an example cell which increased its firing rate (FR) in response to SKF81297 application. (C, D) Group comparison, mean FRs during the baseline period, and application of SKF81297 (n = 13 cells, paired Wilcoxon signed rank test, p=0.02, *p<0.05). (E-G) Changes in firing rate (ΔFR) in E, resting membrane potential (ΔmV) in F, and input resistance (ΔRin) in G after drug application. Comparisons are between three independent datasets. SKF81297: puff application of Drd1 agonist. Antagonist: SKF81297 was applied in the presence of Drd1 blockers 1 µM SKF83566, 1 µM SCH39166, and 1 µM SCH23390. Artificial cerebrospinal fluid (ACSF): puff application ACSF (Kruskal-Wallis test, FR p=0.0044, Vm p=0.0024, Rin p=0.02; Dunn’s multiple comparison test, *p<0.05, **p<0.01). (H) Schematic of experimental setup. Voltage clamp recordings of tdT+ UBCs, paired with stimulation of mossy fiber inputs to evoke NMDA receptor mediated currents (intertrial interval [ITI], 5 s), in the presence of blockers for AMPA, GABA, and glycine receptors (1 µM NBQX, 1 µM gabazine, and 1 µM strychnine). (I) Sample traces show an increase in NMDAR current amplitudes during the application of SKF81297. (J) Trace of normalized peak amplitude of NMDAR currents across cells (n = 10 cells). Shaded region, ± SEM. (K) Summary plot of average evoked N-Methyl-D-aspartate receptor (NMDAR) current amplitudes before and after application of 10 µM SKF81297 (n = 10 cells, paired t-test, p=0.0251). (L) Top: Schematic of two-photon MNI-L-glutamate uncaging experiments. TdT+ UBCs were voltage clamped and imaged using a two-photon laser scanning microscope. Laser pulses (725 nm) directed near the dendritic brush (25 mW, 1 ms, 60 s ITI) were used to evoke NMDAR mediated currents. Bottom: Example current trace. (M) Two-photon imaging Z-projection of a tdT+ UBC. Arrows represent separate uncaging site locations. Scale bar, 10 µm. (N) NMDAR current amplitudes in ACSF vs 10 µM SKF81297 (unpaired t-test, p=0.0068, **p<0.01). Each data point is the average amplitude of NMDAR currents evoked by glutamate uncaging from one cell (ACSF n = 14 cells, SKF81297 n = 13 cells). (O) Cumulative distribution of uncaging-evoked NMDAR current peak amplitudes for ACSF (14 cells, 466 individual trials) and SKF81297 (13 cells, 349 individual trials) groups.