IPSC Kinetics at Identified GABAergic and Mixed GABAergic and Glycinergic Synapses onto Cerebellar Golgi Cells

Abstract

In the rat cerebellum, Golgi cells receive serotonin-evoked inputs from Lugaro cells (L-IPSCs), in addition to spontaneous inhibitory inputs (S-IPSCs). In the present study, we analyze the pharmacology of these IPSCs and show that S-IPSCs are purely GABAergic events occurring at basket and stellate cell synapses, whereas L-IPSCs are mediated by GABA and glycine. Corelease of the two transmitters at Lugaro cell synapses is suggested by the fact that both GABA A and glycine receptors open during individual L-IPSCs. Double immunocytochemical stainings demonstrate that GABAergic and glycinergic markers are coexpressed in Lugaro cell axonal varicosities, together with the mixed vesicular inhibitory amino acid transporter. Lugaro cell varicosities are found apposed to glycine receptor (GlyR) clusters that are localized on Golgi cell dendrites and participate in postsynaptic complexes containing GABA A receptors (GABA A Rs) and the anchoring protein gephyrin. GABA A R and GlyR/gephyrin appear to form segregated clusters within individual postsynaptic loci. Basket and stellate cell varicosities do not face GlyR clusters. For the first time the characteristics of GABA and glycine cotransmission are compared with those of GABAergic transmission at identified inhibitory synapses converging onto the same postsynaptic neuron. The ratio of the decay times of L-IPSCs and of S-IPSCs is a constant value among Golgi cells. This indicates that, despite a high cell-to-cell variability of the overall IPSC decay kinetics, postsynaptic Golgi cells coregulate the kinetics of their two main inhibitory inputs. The glycinergic component of L-IPSCs is responsible for their slower decay, suggesting that glycinergic transmission plays a role in tuning the IPSC kinetics in neuronal networks.

Besides Purkinje cells and granule neurons: an appraisal of the cell biology of the interneurons of the cerebellar cortex

“…On their way, these longer axons may even course through the white matter (Laine and Axelrad 1996). As direct targets of Lugaro cells, basket and stellate cells have been identiWed only by morphological means (Laine and Axelrad 1998), whereas the projections of Lugaro cells onto Golgi (Dieudonne and Dumoulin 2000;Dumoulin et al 2001;Dieudonne 1995) and Purkinje cells (Dean et al 2003) have been analyzed functionally. It has been estimated that one Lugaro cell projects to more than 100 Golgi cells (Dieudonne and Dumoulin 2000); comparable numerical estimates for the Lugaro to Purkinje cell, or Lugaro to basket/ stellate cell projections are not available.…”

“…Whereas the Lugaro cell input to Golgi cells has mixed GABAergic and glycinergic components (Dumoulin et al 2001), their input to (juvenile; analyzed at postnatal day 14 in the rat) Purkinje cells is mediated only by GABA A receptors (Dean et al 2003). (Adult) Purkinje cells do express glycine receptors (Triller et al 1987), though these are rather sparsely localized on main dendritic shafts.…”

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

“…The specificity of transmission in their postsynaptic targets is ensured by the differential expression of receptors. Thus, spontaneous IPSCs in granule cells are mediated selectively by GABA A receptors (39), whereas Golgi cells, Lugaro cells, unipolar brush cells, and possibly other interneurons exhibit either glycinergic or mixed glycinergic/GABAergic currents ( Figure 1) (42,43). At least in Golgi cells, GABA A and glycine receptors can co-exist within a given postsynaptic site (42).…”

Pharmacological Characterization of Glycine-Gated Chloride Currents Recorded in Rat Hippocampal Slices

“…Omission of the primary antibody served as a negative control to ensure the specificity of labeling. The specificity of this antibody has been thoroughly characterized to confirm its selectively for GlyR subunits (Pfeiffer et al 1984) and has been extensively used in anatomical localization studies (e.g., Dumoulin et al 2001;Tsen et al 2000). Stained cells were observed with a confocal laser-scanning microscope equipped with appropriate filters.…”

“…Elegant electrophysiological recordings from motoneurons in spinal cord and brain stem slices show that miniature IPSCs are mediated by the activation of both receptors, demonstrating cotransmission of these two inhibitory neurotransmitters (Jonas et al 1998;O'Brien and Berger 1999). A recent study in cerebellar slices has also demonstrated GABA and glycine co-release at synapses onto Golgi cells (Dumoulin et al 2001). However, in recordings from identified lamina I neurons in spinal cord slices, it appears that although glycine and GABA are coreleased, GABA A Rs seem to be located extrasynaptically because the GABA A Rmediated component of the synaptic current is observed only following large but not minimally evoked monosynaptic IPSCs (Chery and de Koninck 1999).…”