Designing a norepinephrine optical tracer for imaging individual noradrenergic synapses and their activity in vivo

Matthew Dunn,Yekaterina Kovalyova,Samuel Clark,Dalibor Sames,David Sulzer,Richard J Karpowicz,Eric R Kandel,Adam Henke,Kimberly A Kempadoo

doi:10.1038/s41467-018-05075-x

Abstract

Norepinephrine is a monoamine neurotransmitter with a wide repertoire of physiological roles in the peripheral and central nervous systems. There are, however, no experimental means to study functional properties of individual noradrenergic synapses in the brain. Development of new approaches for imaging synaptic neurotransmission is of fundamental importance to study specific synaptic changes that occur during learning, behavior, and pathological processes. Here, we introduce fluorescent false neurotransmitter 270 (FFN270), a fluorescent tracer of norepinephrine. As a fluorescent substrate of the norepinephrine and vesicular monoamine transporters, FFN270 labels noradrenergic neurons and their synaptic vesicles, and enables imaging synaptic vesicle content release from specific axonal sites in living rodents. Combining FFN270 imaging and optogenetic stimulation, we find heterogeneous release properties of noradrenergic synapses in the somatosensory cortex, including low and high releasing populations. Through systemic amphetamine administration, we observe rapid release of cortical noradrenergic vesicular content, providing insight into the drug’s effect.

Highlights

Norepinephrine is a monoamine neurotransmitter with a wide repertoire of physiological roles in the peripheral and central nervous systems
The introduction of fluorescent false neurotransmitter 270 (FFN270), the first fluorescent false neurotransmitter (FFN) developed to label noradrenergic synapses, has to our knowledge, provided the first tool to image the primary function of synaptic transmission— synaptic vesicle exocytosis—in the central nervous system (CNS) in vivo
This finding is in accordance with our recent study using FFN200, which demonstrated that a portion of dopaminergic puncta in the striatum do not release significant amounts of FFN200 and are functionally “silent”, and is consistent with a new study indicating that only a fraction of DA synapses possesses presynaptic scaffolding proteins that enable synaptic vesicle fusion[63]

Summary

Introduction

Norepinephrine is a monoamine neurotransmitter with a wide repertoire of physiological roles in the peripheral and central nervous systems. There are, no experimental means to study functional properties of individual noradrenergic synapses in the brain. Development of new approaches for imaging synaptic neurotransmission is of fundamental importance to study specific synaptic changes that occur during learning, behavior, and pathological processes. As a fluorescent substrate of the norepinephrine and vesicular monoamine transporters, FFN270 labels noradrenergic neurons and their synaptic vesicles, and enables imaging synaptic vesicle content release from specific axonal sites in living rodents. The NE system plays numerous physiological roles, including brain-wide regulation of neurovascular coupling and cerebrospinal fluid flux[6], and local effects such as modulation of cortical and hippocampal neuronal circuitry[7]. To determine how behavior and sensory input alter specific synapses, novel tools to measure neurotransmission at individual synapses in vivo must be developed

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Conclusion