Presynaptic calcium signalling in cerebellar mossy fibres

Abstract

Whole-cell recordings were obtained from mossy fibre terminals in adult turtles in order to characterize the basic membrane properties. Calcium imaging of presynaptic calcium signals was carried out in order to analyse calcium dynamics and presynaptic GABA B inhibition. A tetrodotoxin (TTX)-sensitive fast Na + spike faithfully followed repetitive depolarizing pulses with little change in spike duration or amplitude, while a strong outward rectification dominated responses to long-lasting depolarizations. High-threshold calcium spikes were uncovered following addition of potassium channel blockers. Calcium imaging using Calcium-Green dextran revealed a stimulus-evoked all-or-none TTX-sensitive calcium signal in simple and complex rosettes. All compartments of a complex rosette were activated during electrical activation of the mossy fibre, while individual simple and complex rosettes along an axon appeared to be isolated from one another in terms of calcium signalling. CGP55845 application showed that GABA B receptors mediated presynaptic inhibition of the calcium signal over the entire firing frequency range of mossy fibres. A paired-pulse depression of the calcium signal lasting more than 1 s affected burst firing in mossy fibres; this paired-pulse depression was reduced by GABA B antagonists. While our results indicated that a presynaptic rosette electrophysiologically functioned as a unit, topical GABA application showed that calcium signals in the branches of complex rosettes could be modulated locally, suggesting that cerebellar glomeruli may be dynamically sub-compartmentalized due to ongoing inhibition mediated by Golgi cells. This could provide a fine-grained control of mossy fibre-granule cell information transfer and synaptic plasticity within a mossy fibre rosette.

Coding Odor Identity and Odor Value in Awake Rodents

“…This phase shift is suggested to result from inhibition in the OB that selectively delays mitral cell activity. These results indicate that mitral and tufted cells might be encoding different type of information about the odors, idea that is supported by the fact that mitral and tufted cells project differentially to the anterior PC and olfactory tubercle, respectively (Igarashi et al, 2012, Nagayama et al, 2010). …”

“…Olfactory signals processed by these local circuits are modified and transferred to the piriform cortex and other subcortical regions (Shepherd et al, 2004, Nagayama et al, 2010, Wachowiak and Shipley, 2006, Linster and Cleland, 2009). Therefore, MT activity ultimately represents olfactory information in the OB.…”

“…This kind of sniff coupled gamma oscillation from different cell types is also dependent on brain states: both fast and slow gamma oscillations can be induced during awake state, while both oscillations failed to induce during slow wave and rapid-eye-movement sleep. Interestingly the axons from mitral and tufted cells differ largely in their main targeting of piriform cortex as opposed to the olfactory tubercle (Nagayama et al, 2010). …”

Fusion Competent Synaptic Vesicles Persist upon Active Zone Disruption and Loss of Vesicle Docking

“…5I, J). In both conditions, release saturated above 5 mM [Ca 2+ ] ex , likely because Ca 2+ influx itself saturates at 5 mM (Ariel and Ryan, 2010). When we expressed these data normalized to the largest response (Fig.…”

The Contribution of Extrasynaptic Signaling to Cerebellar Information Processing

“…Metabotropic GABA B Rs on MF axons are not activated by baseline GoC activity, but can be recruited with higher frequency GoC stimulation (16). Spillover activation of GABA B Rs decreased MF glutamate release through local control of terminal Ca 2+ influx, such that release may even be modulated on a sub-glomerular scale (31). GABA spillover also plays a significant role in the direct inhibition of GCs through dendritic GABA A Rs.…”