Submillisecond kinetics and low efficacy of parallel fibre‐Golgi cell synaptic currents in the rat cerebellum

Abstract

The whole‐cell configuration of the patch clamp technique was used to record from Golgi cells in thin slices of the rat cerebellum (P12‐P25). Their active membrane properties and the input that they receive from the parallel fibres were characterized. Most cells were filled with biocytin and morphologically identified by the presence of a large axonal arbor restricted to the granular layer. The morphological parameters of eighteen of the best‐preserved cells were quantified. A slow capacitive current transient, characteristic of the Golgi cell axon, was used to identify Golgi cells whenever their morphology could not be preserved. Golgi cells fire action potentials spontaneously at 3 ± 1.7 Hz (n= 17). Their firing frequency increases linearly with the amplitude of depolarizing current pulses and displays marked adaptation. When hyperpolarized Golgi cells display an anomalous rectification which is blocked by 2 mM CsCl, indicating the presence of an Ih‐like current. Golgi cells receive a spontaneous excitatory input from parallel fibres. This input is composed of small amplitude, mostly monoquantal, EPSCs. Chemical stimulation of granule cells by locally applied kainate evokes tetrodotoxin (TTX)‐dependent events with similar properties. The parallel fibre‐Golgi cell EPSCs have both AMPA and NMDA components. The NMDA component is blocked by 1 mM external magnesium at ‐60 mV and decays with time constants of 31 ± 9 ms and 170 ± 15 ms (at +61 mV in the presence of magnesium). In the presence of 10 μM internal spermine, the AMPA component of the spontaneous EPSCs is markedly slowed (0.96 ± 0.25 ms to 1.86 ± 0.47 ms; n= 4) and reduced in amplitude (49 ± 7 %; n= 4) when depolarizing the cell from ‐70 mV to +61 mV. The decay kinetics of individual AMPA EPSCs were found to be variable, in part because of dendritic filtering. A more detailed analysis reveals that the synaptic AMPA conductances are regulated during development and close faster at days P19‐P25 than at days P13‐P16. These data suggest that the efficacy of the parallel fibre‐Golgi cell input is rather low. This places strong constraints on the conditions in which the inhibitory feedback exerted by the Golgi cell can be operational. The possibility is considered that the Golgi cell‐granule cell circuit shows an oscillatory behaviour. This hypothesis is discussed in relation to the models of Albus and Marr.

Serotonin-Driven Long-Range Inhibitory Connections in the Cerebellar Cortex

“…After bath application of serotonin, the synaptic activity dramatically increased. In Figure 1 B the fast synaptic currents are EPSCs, which can be blocked by AMPA receptor antagonists (Dieudonné, 1998), whereas the synaptic currents with a slower decay are IPSCs, which can be blocked by the combined application of gabazine and strychnine (Dieudonné, 1995). As can be seen in Figure 1 B, serotonin induced a dramatic increase in the frequency of the IPSCs but not the EPSCs.…”

“…Putative L ugaro cells were visually selected by their position next to the Purkinje cell bodies and by the bipolar shape of their soma and proximal dendrites. Although Golgi cells located near the Purkinje cell layer can be mistaken for L ugaro cells, most Golgi cells could be discarded on the basis of their large axonal capacitive transient (Dieudonné, 1998). In all cases the recorded cells were filled with biocytin for later observation of their morphology.…”

“…Spontaneous synaptic currents were detected automatically using the AC S software kindly provided by P. Vincent (Institut des Neurosciences, Paris). All detected events were subjected to visual inspection, and EPSC s were discarded on the basis of their fast decay time course (Dieudonné, 1998). Selected events could then be transferred in a file with the format of clampex files and f urther analyzed using the C lampfit program of the PC lamp6 package.…”

“…Golgi cells were selected for recording both on visual criteria, as previously explained (Dieudonné, 1995), and on the basis of their characteristic passive electrical properties (Dieudonné, 1998). Purkinje cells were visually identified.…”

Immunohistochemical localization of Ih channel subunits, HCN1–4, in the rat brain

“…Relationships between HCN localization and electrophysiological function I h has been identified in numerous cell types in the brain, including neurons in the olfactory bulb (Cadetti and Belluzzi, 2001), neocortex (Berger et al, 2001), hippocampus (Magee, 1999), caudate putamen (Momiyama and Koga, 2001), amygdala (Womble and Moises, 1993), nucleus of accumbens (Uchimura et al, 1990), thalamus (Ludwig et al, 2003), hypothalamus (Kamondi and Reiner, 1991), ventral tegmental area (Jiang et al, 1993), superior colliculus (Saito and Isa, 1999), substantia nigra (Washio et al, 1999), mesencephalic trigeminal nucleus (Khakh and Henderson, 1998), inferior olivary complex , dorsal raphe (Jolas et al, 2000), lateral lemniscus (Fu et al, 1997), area postrema (Funahashi et al, 2002), nucleus of the solitary tract (Iwahori et al, 2002), hypoglossal nucleus (Parkis and Berger, 1997) and cerebellum (Li et al, 1993;Dieudonne, 1998). In the present study, all of these regions showed one or more HCN-LIs.…”