Pool size estimations for dense-core vesicles in mammalian CNS neurons.

Claudia M Persoon,Swati Arora,Joris P Nassal,Jan Rt Van Weering,Alessandro Moro,Natalia Dominguez,Jurjen H Broeke,Matthijs Verhage,Ruud F Toonen,Margherita Farina

doi:10.15252/embj.201899672

Abstract

Neuropeptides are essential signaling molecules transported and secreted by dense‐core vesicles (DCVs), but the number of DCVs available for secretion, their subcellular distribution, and release probability are unknown. Here, we quantified DCV pool sizes in three types of mammalian CNS neurons in vitro and in vivo. Super‐resolution and electron microscopy reveal a total pool of 1,400–18,000 DCVs, correlating with neurite length. Excitatory hippocampal and inhibitory striatal neurons in vitro have a similar DCV density, and thalamo‐cortical axons in vivo have a slightly higher density. Synapses contain on average two to three DCVs, at the periphery of synaptic vesicle clusters. DCVs distribute equally in axons and dendrites, but the vast majority (80%) of DCV fusion events occur at axons. The release probability of DCVs is 1–6%, depending on the stimulation. Thus, mammalian CNS neurons contain a large pool of DCVs of which only a small fraction can fuse, preferentially at axons.

Highlights

Regulated secretion of chemical signals in the nervous system occurs principally from two organelles, synaptic vesicles and densecore vesicles (DCVs)
Estimations of synaptic vesicle pool sizes in cultured hippocampal neurons show a total population of 100–200 synaptic vesicles per bouton, containing a fast ready releasable pool (RRP) of approximately five vesicles that are immediately available for secretion upon stimulation, which can be resupplied by a recycling pool of 10–20 vesicles (Neher, 2015; Rizzoli & Betz, 2005; FernandezAlfonso & Ryan, 2006)
For hippocampal as well as striatal neurons, the number of chromogranin B (ChgB) puncta per neuron correlated with neurite length (Fig 1K)

Summary

Introduction

Regulated secretion of chemical signals in the nervous system occurs principally from two organelles, synaptic vesicles and densecore vesicles (DCVs). Synaptic vesicles release neurotransmitters at synapses, whereas neuronal DCVs transport and secrete neuropeptides and neurotrophins that regulate brain development, neurogenesis, and synaptic plasticity (Park & Poo, 2013; van den Pol, 2012; Zaben & Gray, 2013; Pang et al, 2004; Malva et al, 2012). We have previously shown that cultured mouse hippocampal neurons and human induced pluripotent stem cell (iPSC)-derived neurons release approximately 10–100 DCVs upon repetitive stimulation (Arora et al, 2017; Farina et al, 2015; van de Bospoort et al, 2012; Emperador Melero et al, 2017). The number of DCVs present in mammalian neurons and probability of their release upon stimulation are currently unknown

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