Mice were decapitated under deep anesthesia and slices were prepared in ice-cold cutting solution (85 mM NaCl, 75 mM sucrose, 2.5 mM KCl, 25 mM glucose, 1.25 mM NaH2PO4, 4 mM MgCl2, 0.5 mM CaCl2, and 24 mM NaHCO3) using a VT1200S vibratome (Leica). Slices were incubated at 35 °C for ~30 min and then kept at room temperature until use. During recordings the slices are kept at 35 °C in continuously perfused with artificial cerebrospinal fluid (126 mM NaCl, 2.5 mM KCl, 26 mM NaHCO3, 2 mM CaCl2, 2 mM MgCl2, 1.25 mM NaH2PO4, and 10 mM glucose, saturated with carbogen,) Fluorescently labeled MRR neurons were visualized in an upright microscope (Eclipse FN-1; Nikon) with epifluorescent illumination (Lambda FLED @ 530 nm; Sutter Instrument) combined with a CMOS camera (DaVinci 1k, RedShirtImaging). The neurons were patched with thin-wall borosilicate pipettes (pipette resistance: 3.69±0.09 MΩ, BF150-117-10, Sutter Instrument) filled with small amount (~1 µl) of intracellular solution containing 133.5 mM K-gluconate, 1.8 mM NaCl, 1.7 mM MgCl2, 0.05 mM EGTA, 10 mM HEPES, 2 mM Mg-ATP, 0.4 mM Na2-GTP, 10 mM phosphocreatine, and 8 mM biocytin (pH 7.25;  290-300 mOsm). Pipette capacitance and the bridge balance were carefully compensated in all current clamp recordings. For the RNA harvesting, the recordings were made using a HEKA EPC800 amplifier (HEKA Elektronik) digitized with a Digidata1440A A/D converter (Molecular Devices). The data acquisition was controlled by the pClamp10 software package. After patching the identified neurons, we measured the basic electrophysiological parameters of the cells including the resting membrane potential, the spontaneous synaptic activity, and the firing pattern. The length of the recording session was limited to 5 min from the break-in. The cytosol together with the nucleus was extracted from the neuron by the application of small negative pressure to the pipette. The tip of the quickly removed pipette was gently pushed into a microtube containing ice cold reaction buffer (lysis buffer with RNase inhibitor, Takara SMART-Seq HT PLUS Kit). The sample containing tubes was spun briefly and snap-frozen on dry ice. To suppress RNase contamination, the workplace including parts of the experimental setup was cleaned each day before the start of the sample collection with RNase AWAY (Thermo Fisher). Sample collection: After electrophysiological recordings, the cells' cytosol was aspirated via the same recording glass pipette that used for recording, and using a positive pressure, expelled into microtubes containing 1 µl of 1x lysis buffer with RNase inhibitor (SMART-Seq HT PLUS Kit, Takara). The samples were immediately frozen on dry ice and stored at -80°C until further processing. cDNA and library preparation for next-generation sequencing: Single-cell mRNA processing was performed using the SMART-Seq HT PLUS Kit (Takara) and according to manufacturer's protocol. In brief, samples were reverse transcribed to cDNA, amplified, and purified with AMPure XP beads (Beckman Coulter). The quantity and the quality of the purified cDNA was assessed using Fragment Analyzer (Advanced Analytical). Subsequently, the cDNA was fragmented and adapters including indices for cell identification were added to the fragments. The quality and quantity were again assessed using Fragment Analyzer. For library preparation, the single cell samples with unique index adapters were pooled in equal amounts. The sequencing was performed on a NovaSeq 6000 (Illumina) instrument using 150 bp paired end configuration and a full SP-flowcell. Processing of sequencing data: After sequencing, raw reads were de-multiplexed with Illumina's bcl2fastq2 (v2.20).