Quantitative morphology and synaptology of cerebellar glomeruli in the rat

Abstract

Computer-assisted stereological and quantitative morphological approaches were used to analyse cerebellar glomeruli of the "simple type" in serial ultrathin sections. It was found that, of the total volume (110-200 micron3) of the glomeruli studied, 53% was occupied by granule cell dendrites, 34% by mossy terminal and 13% by Golgi axons. None of the four analysed glomeruli contained Golgi cell dendrites. The mossy terminals that were studied received, on the average, 53 granule cell dendrites. All of the dendrites originated from different granule cells and all made synaptic contacts with mossy terminal. However only about 60% of granule cell dendrites made synapses with Golgi axons. The surface of the mossy terminals occupied by synaptic junctions, was found to be 5.4-5.5%. Each granule cell dendrite emitted 3-5 terminal protrusions ("dendritic digits"). Each digit receives one or more synaptic contact from either the mossy terminal (67% of all digits), or from Golgi axon varicosities (25%). Only about 8% of all digits were contacted synaptically by both types of axonal terminals. All of the dendritic digits that were observed made synaptic connections. Each digit was, on the average, connected by symmetric attachment plaques to 4 neighbouring digits. Three-dimensional reconstructions of mossy terminal and some of contacting granule cell dendrites demonstrated that the dendrites curved around the central mossy terminal and were much longer than expected from earlier Golgi-impregnation studies. In addition to mossy terminals and Golgi axons, an axon terminal of small calibre that contained large, empty, spheroid vesicles were occasionally observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Synaptic Release Generates a Tonic GABAAReceptor-Mediated Conductance That Modulates Burst Precision in Thalamic Relay Neurons

“…Although both cerebellar granule neurons and thalamic relay neurons have been shown to express ␦ subunits, the anatomical location of these receptors, relative to the release sites, could be quite different. For example, the glomerular arrangement in cerebellar granule neurons is such that multiple granule cells project their dendrites into a single glomerulus (Jakab and Hamori, 1988). Therefore, dendritic ␦-GABA A Rs could .…”

GABA Transporter Deficiency Causes Tremor, Ataxia, Nervousness, and Increased GABA-Induced Tonic Conductance in Cerebellum

“…The cerebellar glomerulus, like the basket cell-Purkinje cell pinceau synapse and the chandelier cell-pyramidal cell cartridge of cortex, is a highly organized synaptic structure that contains many synaptic contacts produced by just a few presynaptic inhibitory axons (Jakab and Hamori, 1988) and features a dense level of GAT1 expression (Chiu et al, 2002). The dramatically prolonged granule cell IPSC waveforms in mGAT1 KO mice are certainly consistent with the idea that GAT1 plays a more important role in clearing GABA after multivesicular release in structures such as the glomerulus, where diffusion is limited (Nielsen et al, 2004).…”

Tonic Activation of GABAB Receptors Reduces Release Probability at Inhibitory Connections in the Cerebellar Glomerulus

“…The consistency of quantal parameter estimates was presumably enhanced by the availability of single quantum properties extracted from independent minis measurements, by the secure identification of minimal eIPSCs through a comparison with sIPSCs and by the selection of transmission failures through the indirect eIPSC component. The multiquantal nature of neurotransmission is supported by the expectation-maximization (EM) observation that Golgi cell axon terminals make multiple contacts containing several synaptic vesicles on different dendritic digits on the same granule cell dendrite (Hámori and Somogy 1983;Hámori and Szentagothai 1966;Jakab and Hámori 1988). Additional EM analysis may be useful to estimate the number of morphologically identified active zones and postsynaptic receptor density.…”