Whole cell and cell-attached recordings were performed on LHb slices using a patch amplifier (Multiclamp 700B) under infrared-differential interference contrast microscopy. Data acquisition and analysis were carried out using DigiData 1440A, pClamp 10 (molecular devices, Union City, CA), Clampfit and Mini Analysis 6.0.3 (Synaptosoft Inc.). Signals were filtered at 3 kHz and digitized at 10 kHz. The recording ACSF was the same as the cutting solution except that it was ascorbic acid-free. Spontaneous activity was monitored using cell-attached voltage-clamp recordings of action potentials (APs) at
I = 0 pA for 5 minutes. Number of APs was counted over 5 min and spike frequency was calculated. Neuronal excitability recordings in response to depolarization were performed in whole-cell current-clamp mode. The patch pipettes (3–6 MΩ) were filled with 130 mM K-gluconate, 15 mM KCl, 4 mM ATP-Na+, 0.3 mM GTP-Na+, 1 mM EGTA, and 5 mM HEPES (pH adjusted to 7.28 with KOH, osmolarity adjusted to 275–280 mOsm). LHb neurons were given increasingly depolarizing current steps at +10pA intervals ranging from +10pA to +100pA, allowing us to measure AP generation in response to membrane depolarization (5 sec duration). Current injections were separated by a 20s interstimulus interval and neurons were kept at −65 mV with manual direct current injection between pulses. Synaptic transmission blockade was achieved by adding 6,7-dinitroquinoxaline-2,3-dione (DNQX; 10 µM), picrotoxin (100µM) and APV (50 µM) to block AMPA, GABA
A and NMDA receptor-mediated synaptic transmission, respectively. The number of APs induced by depolarization at each intensity was counted and averaged for each experimental group.
Because AHP amplitude increases with increasing number of APs, we measured AP threshold, mAHP and fAHP amplitudes at the current step that was sufficient to generate the first AP/s (58 (
link)). AP threshold was measured at the beginning of the upward rise of the AP. mAHP was measured as the difference between AP threshold and the peak negative membrane potential at the end of the current step. fAHPs were calculated as the difference between AP threshold and the peak negative potential following the AP (
Figure 1E). Resting membrane potential (RMP) was assessed at the beginning of the recording by quickly switching to
I=0. Input resistance (Rin) was determined by injecting a small (50 pA) hyperpolarizing current pulse (5s) and calculated by dividing the steady-state voltage response by the current pulse amplitude. Reported AP half width, AP peak amplitude were obtained from measurements of AP characteristics in Clampfit.
Whole-cell recordings of GABA
AR-mediated mIPSCs were isolated in ACSF perfused with DNQX; 10 µM, strychnine (1 µM) and tetrodotoxin (TTX, 1 µM). The patch pipettes (3–6 MΩ) were filled with 125 mM KCl, 2.8 mM NaCl, 2 mM MgCl
2, 2 mM ATP-Na
+, 0.3 mM GTP-Na
+, 0.6 mM EGTA, and 10 mM HEPES (pH adjusted to 7.28 with KOH, osmolarity adjusted to 275–280 mOsm). AMPAR-mediated mEPSCs were isolated in ACSF perfused with picrotoxin (100µM), D-APV (50µM) and TTX (1 µM). Patch pipettes for mEPSC recordings were filled with 117 mM Cs-gluconate, 2.8 mM NaCl, 5 mM MgCl
2, 2 mM ATP-Na
+, 0.3 mM GTP-Na
+, 0.6 mM EGTA, and 20 mM HEPES (pH adjusted to 7.28 with CsOH, osmolarity adjusted to 275–280 mOsm). For both mIPSCs and mEPSCs, LHb neurons were voltage-clamped at −70 mV and recorded over 10 sweeps, each lasting 50 seconds.
EPSCs were evoked with a stimulating electrode placed in the stria medullaris. Evoked EPSCs were recorded in ACSF perfusion containing picrotoxin (100µM) while the cell was voltage-clamped at +40 mV. Internal solution for patch pipettes was similar to that used for mEPSC recordings (Cs-gluconate-based) but also included intracellular spermine (10µM). AMPAR-mediated currents were isolated with D-APV (50 µM), a selective NMDA receptor antagonist. Isolated AMPAR-mediated currents were then subtracted from the combined EPSC to provide the NMDA receptor-mediated current and thus, the AMPA/NMDA ratio. AMPAR EPSCs were also recorded at holding potentials ranging from −65 to +40 mV in the presence of picrotoxin (100µM), APV (50 µM) and intracellular spermine (10 µM) included in Cs-gluconate-based internal. Normalized current-voltage (I–V) curves were then generated by dividing the AMPAR EPSC peak amplitudes by the mean of AMPAR EPSC peak amplitude recorded at −65 mV. AMPAR EPSC rectification was determined by dividing peak AMPAR EPSCs amplitudes recorded at −65 mV by those recorded at +40 mV.
The excitatory and inhibitory balance (EPSC/IPSC, E/I ratio,) was recorded with a Cs-gluconate-based internal solution similar to mEPSC recordings. Evoked EPSCs and IPSCs from LHb neurons were recorded in the same neuron in drug-free ASCF using a stimulating electrode placed in the stria medullaris. EPSCs were recorded at the reversal potential for GABA
A IPSCs (−55 mV), and IPSCs were recorded at the reversal potential for EPSCs (+10 mV) in the same LHb neuron. The E/I ratio was then calculated as EPSC/IPSC amplitude ratio by dividing the average peak amplitude of 10 consecutive sweeps of EPSCs or IPSCs from the same recording. The cell input resistance and series resistance were monitored through all the experiments and if these values changed by more than 10%, data were not included.
Antalarmin, CYPPA, 1-EBIO, WIN 55,212-2 and AM251 were prepared as stock solution in DMSO and were diluted (1:10000) to final concentration in ACSF of 1µM, 10µM, 300mM, 2µM, and 10µM, respectively. Stock solutions for apamin, rat CRF, iberiotoxin, and Antisauvagine-30 were prepared in distilled water and diluted (1:1000) to final concentration in ACSF of 100nM, 250nM, 100nM, and 25nM, respectively. The intra-pipette concentrations of BAPTA, GDPβs and PKI(6–22) were 30mM, 300µM, and 10µM, respectively. In some of our control interleaved experiments, AP recordings were continued for an hour without addition of drugs and no significant changes were observed over time. For all drug experiments, a baseline depolarization-induced AP recording/ mIPSC/mEPSC was recorded in each neuron, and then the appropriate drug was added to the slice by the perfusate and AP generation in response to depolarizing current steps was again tested 25–30 min after. For apamin and CYPPA experiments, a second baseline with apamin or CYPPA was obtained before the addition of CRF and AP generation was re-evaluated 25–30min after CRF application. CRF wash-out experiments in
Supplementary figures were performed following 15min of bath application of CRF and the recordings continued at least for 90 min after the initiation of wash out of CRF.
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