Inhibitory synaptic currents in stellate cells of rat cerebellar slices.

Abstract

1. In thin cerebellar slices of rats aged 14-21 days, voltage-gated currents, synaptic currents and GABA responses were studied with the tight-seal whole-cell recording technique from stellate cells (8-9 micrograms soma diameter) located in the outer two-thirds of the molecular layer. 2. In symmetrical Cl- conditions, stellate cells voltage-clamped at -60 mV showed spontaneous inhibitory postsynaptic currents (IPSCs). As were the GABAA responses of the same cells, the IPSCs were blocked by bicuculline. The frequency of occurrence of IPSCs ranged from 0.2 to 1.9 events per second (21 cells). The mean amplitude of the events ranged from 61 to 226 pA (mean +/- S.E.M.: 132 +/- 11; n = 21). 3. The temporal course of IPSCs was characterized by a rapid rise (mean +/- S.E.M. of the time to peak: 1.1 +/- 0.1 ms, n = 7) and a slow decay. The decay phase was described by a double exponential function with time constants of 8.7 +/- 0.6 ms, and 40.9 +/- 3.7 ms respectively (means +/- S.E.M.; n = 7). 4. A minor fraction (15 to 20%) of the spontaneous synaptic events recorded in control saline had a faster onset than that of the IPSCs and decayed with a rapid mono-exponential decay (time constant of 1.0-1.3 ms). These were excitatory postsynaptic currents (EPSCs) unaffected by bicuculline and blocked by the glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). 5. Bath application of TTX (0.5-1 microM), which blocked voltage-gated Na+ currents in stellate cells, induced a variable decrease in the frequency of IPSCs (mean +/- S.E.M. of the frequency ratio in TTX over control: 0.47 +/- 0.09; n = 12). However, the toxin had no significant effect either on the mean amplitude or on the kinetics of the IPSCs. The mean amplitude of the miniature IPSCs was 141 +/- 13 pA (mean +/- S.E.M.; n = 22). 6. In TTX-containing solutions, the frequency of the IPSCs was unaffected when Ca2+ currents were eliminated either by removal of extracellular Ca2+ and addition of EGTA, or by addition of Cd2+. Miniature IPSCs of 200-300 pA were still observed. 7. In symmetrical Cl- conditions, local application of GABA to stellate cells induced an inward current and an increase in membrane noise. Responses to prolonged applications of GABA showed desensitization in both whole-cell mode and somatic outside-out patches. The chord conductance estimated from recording single GABA channel events in somatic outside-out patches was 28 pS.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular and synaptic organization of GABAA receptors in the cerebellum: Effects of targeted subunit gene deletions

“…In addition, PC also carry extrasynaptic GABA A receptors diffusely distributed on the cell surface and are modulated by tonic inhibition, notably due to GABA release from basket cells (25). Similar, high frequency and high amplitude sIPSCs have been well characterized also in stellate cells (26,27), underscoring the major role played by postsynaptic GABA A receptors in the molecular layer.…”

Impact of single-site axonal GABAergic synaptic events on cerebellar interneuron activity

“…Our immunolabeling results show that a significant number of varicosities are localized close to the soma and may therefore influence the membrane potential (Vm) in the axon initial segment (AIS) substantially. This, together with the fact that MLIs have a high input resistance (Midtgaard, 1992;Llano and Gerschenfeld, 1993), made us hypothesize that single axonal synaptic events, although filtered, may strongly influence neuronal firing (as was shown previously for somatodendritic glutamatergic events; Carter and Regehr, 2002). A first indication that this is indeed the case appeared when performing the experiments in Fig.…”

“…4 D) predicts a nonfiltered (in situ) amplitude of 100 pA. In equivalent experimental conditions, Llano and Gerschenfeld (1993) reported somatodendritic GABAergic postsynaptic currents ranging between 61 and 226 pA. Assuming a singlechannel conductance of 30 pS for GABA A Rs (Bormann et al, 1987), and considering the range of values found for the autoR conductances (1-5 nS), we estimate that each presynaptic varicosity is endowed with 33-167 channels.…”

Readily releasable pool of synaptic vesicles measured at single synaptic contacts

“…To study quantal release and the RRP directly, we identified individual synaptic connections and measured quantal events evoked postsynaptically by presynaptic calcium uncaging with localized laser light. Inhibitory synapses among cerebellar molecular layer interneurons (MLIs; stellate and basket cells) were used because they make only a few synaptic contacts on their postsynaptic partner and because each connection exhibits a large quantal size, on the order of 200 pA at resting potential under symmetrical Cl − conditions (3,19,20). Our strategy was to establish a recording from a synaptically connected pair of MLIs and to find the synaptic contacts between the two neurons.…”