Synaptic Organization of VGLUT3 Expressing Low-Threshold Mechanosensitive C Fiber Terminals in the Rodent Spinal Cord

Larsson, Max; Broman, Jonas

doi:10.1523/eneuro.0007-19.2019

Cited by 25 publications

(22 citation statements)

References 75 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We identified 8 Homer-associated VGLUT3 contacts onto a single GRP-eGFP cell from each of two GRP::eGFP mice with the electron microscope. We found that, as reported recently 38 , the VGLUT3 boutons corresponded to central axons of synaptic glomeruli, which were presynaptic to several dendritic profiles and were postsynaptic to profiles that resembled peripheral axons ( Fig. 7k-m).…”

Section: Results Egfp Expression In the Grp::egfp Mouse Is Restrictedsupporting

confidence: 87%

Expression of green fluorescent protein defines a specific population of lamina II excitatory interneurons in the GRP::eGFP mouse

Bell

Gutièrrez‐Mecinas

Stevenson

et al. 2020

Sci Rep

View full text Add to dashboard Cite

Dorsal horn excitatory interneurons that express gastrin-releasing peptide (GRP) are part of the circuit for pruritogen-evoked itch. They have been extensively studied in a transgenic line in which enhanced green fluorescent protein (eGFP) is expressed under control of the Grp gene. The GRP-eGFP cells are separate from several other neurochemically-defined excitatory interneuron populations, and correspond to a class previously defined as transient central cells. However, mRNA for GRP is widely distributed among excitatory interneurons in superficial dorsal horn. Here we show that although Grp mRNA is present in several transcriptomically-defined populations, eGFP is restricted to a discrete subset of cells in the GRP::eGFP mouse, some of which express the neuromedin receptor 2 and likely belong to a cluster defined as Glut8. We show that these cells receive much of their excitatory synaptic input from MrgA3/MrgD-expressing nociceptive/pruritoceptive afferents and C-low threshold mechanoreceptors. Although the cells were not innervated by pruritoceptors expressing brain natriuretic peptide (BNP) most of them contained mRNA for NPR1, the receptor for BNP. In contrast, these cells received only ~ 10% of their excitatory input from other interneurons. These findings demonstrate that the GRP-eGFP cells constitute a discrete population of excitatory interneurons with a characteristic pattern of synaptic input. Neuronal circuits in the spinal dorsal horn process somatosensory information, which is then transmitted to the brain by projection cells. The vast majority of dorsal horn neurons are interneurons, and these can be assigned to two main classes: excitatory and inhibitory cells 1,2. Nociceptive and pruritoceptive primary afferents terminate in the superficial dorsal horn (SDH; laminae I-II), and ~ 75% of neurons in this region are excitatory interneurons 2. Recent studies have shown that these cells can be assigned to several largely non-overlapping populations, based on the expression of different neuropeptides 3-6 , and these are thought to have distinct roles in pain and itch. There is compelling evidence that gastrin-releasing peptide (GRP) and its receptor (GRPR) play a key role in itch. Intrathecal administration of GRP evokes scratching, while GRPR antagonists reduce scratching in response to pruritogens 7-11. In addition, mice lacking GRPR, or those in which GRPR-expressing dorsal horn neurons are ablated, show reduced responses in several itch models 7,8,12,13. Excitatory interneurons within the SDH provide a source of GRP 7,14-16 , and several studies have investigated the role of these cells by using BAC transgenic mouse lines from the GENSAT project 17 in which either enhanced green fluorescent protein (eGFP) 7,14,15,18-20 or Cre recombinase 18-21 is expressed under control of the Grp promoter

show abstract

Section: Results Egfp Expression In the Grp::egfp Mouse Is Restrictedsupporting

confidence: 87%

Expression of green fluorescent protein defines a specific population of lamina II excitatory interneurons in the GRP::eGFP mouse

Bell

Gutièrrez‐Mecinas

Stevenson

et al. 2020

Sci Rep

View full text Add to dashboard Cite

show abstract

“…Spinal VGLUT1 synapses are associated with low threshold mechanoreceptive afferents and descending corticospinal inputs, while VGLUT2 synapses are predominantly derived from intrinsic spinal interneurons, with some additional expression amongst high-threshold nociceptive afferents and some descending rubrospinal and vestibulospinal inputs 27,28,43,46,80 . Our structural analyses reveal that VGLUT1 boutons were larger than VGLUT2 boutons, and often contacted multiple distinct PSDs, indicative of Type II glomeruli that are widely reported in the dorsal horn laminae III-IV and associated with both VGLUT1 and VGLUT3 expression 29,81,82 . Additionally, we now show that the PSDs associated with VGLUT1 are typically larger and contain a greater number of PSD95 NCs than those associated with VGLUT2, which would tentatively suggest that VGLUT1 synapses form stronger connections 72,73 .…”

Section: Discussionmentioning

confidence: 68%

“…characterising and differentiating spinal synaptic inputs have largely focussed either on synapses solely onto motor neurons [22][23][24][25] or synapses within pain and sensory processing circuitry of the dorsal horn [26][27][28][29] . While the current literature offers in-depth information on subsets of synapses within the spinal cord, a comprehensive and comparative microscopy-based survey of excitatory synapses throughout the spinal cord, i.e.…”

mentioning

confidence: 99%

Nanostructural Diversity of Synapses in the Mammalian Spinal Cord

Broadhead

Bonthron

Arcinas

et al. 2020

Sci Rep

View full text Add to dashboard Cite

functionally distinct synapses exhibit diverse and complex organisation at molecular and nanoscale levels. Synaptic diversity may be dependent on developmental stage, anatomical locus and the neural circuit within which synapses reside. Furthermore, astrocytes, which align with pre and postsynaptic structures to form 'tripartite synapses', can modulate neural circuits and impact on synaptic organisation. In this study, we aimed to determine which factors impact the diversity of excitatory synapses throughout the lumbar spinal cord. We used PSD95-eGFP mice, to visualise excitatory postsynaptic densities (pSDs) using high-resolution and super-resolution microscopy. We reveal a detailed and quantitative map of the features of excitatory synapses in the lumbar spinal cord, detailing synaptic diversity that is dependent on developmental stage, anatomical region and whether associated with VGLUT1 or VGLUT2 terminals. We report that PSDs are nanostructurally distinct between spinal laminae and across age groups. PSDs receiving VGLUT1 inputs also show enhanced nanostructural complexity compared with those receiving VGLUT2 inputs, suggesting pathway-specific diversity. Finally, we show that PSDs exhibit greater nanostructural complexity when part of tripartite synapses, and we provide evidence that astrocytic activation enhances PSD95 expression. Taken together, these results provide novel insights into the regulation and diversification of synapses across functionally distinct spinal regions and advance our general understanding of the 'rules' governing synaptic nanostructural organisation. Neuronal synapses show considerable structural, molecular and functional diversity throughout the nervous system. Their morphology, molecular composition and nanostructural organisation determines synaptic strength and function 1,2 , and must therefore be finely tuned to the circuits within which they operate 3. Synapse morphology may be determined by a number of factors, such as the type of neuron, the anatomical location, the activity state of the network, and development and ageing 4-9. In order to understand the basic logic of different neural circuits, it is pertinent to study the principles of synaptic morphology that underlie the function of neural circuits. Such information may help produce a set of basic 'rules' governing synaptic structure and therefore function. Key scaffolding proteins such as PSD95, one of the most abundantly expressed proteins from the Dlg family, form the core molecular architecture of the synapse 10-13. At a molecular level, PSD95 interacts with a host of different signalling enzymes and neurotransmitter receptors within the postsynaptic density (PSD) to form PSD95-dependent super-complexes (~1.5MDa in weight) 14-17. These super-complexes are heterogeneously distributed within the PSD, forming protein-enriched domains known as nanoclusters (NCs, ~140 nm diameter) 4,5,18,19 , which align with presynaptic release sites to form trans-synaptic nanocolumns 1. Visualising PSD95 enables us to determine the na...

show abstract

“…These projection neurons are, however, wide dynamic range and also respond to noxious stimuli (Andrew 2010). Furthermore, C-LTMR terminals in dorsal horn lamina IIi that connect to lamina I projection neurons (Lu and Perl 2003, Maxwell et al 2007, Lu et al 2013) do so via an interneuronal relay subject to complex regulation (Larsson and Broman 2019). Other recent evidence suggests that rodent C-LTMR afferents access the dorsal column pathway (Abraira et al 2017) via the interneuronal rich dorsal horn zone that receives synapses from myelinated and unmyelinated low threshold mechanosensitive receptor subtypes (Li et al 2011, Abraira and Ginty 2013, Abraira et al 2017).…”

Section: Discussionmentioning

confidence: 99%

“…Spinal inputs to this thalamic relay derive, almost exclusively, from projection cells in dorsal horn lamina I via the spinothalamic tract (Craig and Zhang 2006). The central terminals of C-low threshold mechanosensitive receptor (C-LTMR) afferents, the animal equivalent of C-tactile afferents, arborise in laminae II/IIIi of the spinal cord dorsal horn (Light and Perl 1979, Sugiura 1996, Li et al 2011, Abraira and Ginty 2013, Larsson and Broman 2019). Lamina II cells activated by C-LTMR afferents arborise in lamina I (Lu and Perl 2005, Maxwell et al 2007, Lu et al 2013) where they can contact projection neurons (Lu et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Spinal signaling of C-fiber mediated pleasant touch in humans

Sharma

Marley

Olausson

et al. 2019

Preprint

View full text Add to dashboard Cite

1 C-tactile afferents form a distinct channel that encodes pleasant tactile stimulation. Prevailing 2 views indicate they project, as with other unmyelinated afferents, in lamina I-spinothalamic 3 pathways. However, we found that spinothalamic ablation in humans, whilst profoundly im-4 pairing pain, temperature and itch, had no effect on pleasant touch perception. Only discrimi-5 native touch deficits were seen. These findings preclude privileged C-tactile-lamina I-spinotha-6 lamic projections and imply integrated hedonic and discriminative spinal processing from the 7 body. 8 9 17 vates contralateral posterior insula cortex (Olausson et al. 2002, Olausson, Cole, Vallbo, et al. 2008), 18 a region considered a gateway for sensory systems to emotional cortical areas (Craig 2008), but not 19 somatosensory areas S1 and S2 (Olausson et al. 2002, Olausson, Cole, Vallbo, et al. 2008). In addi-20 tion, patients with ischaemic stroke affecting the posterior contralateral opercular-insular cortex 21 demonstrate impairments in the perception of C-tactile optimal touch (Kirsch et al. 2019). Conversely, 22 posterior insula activation is not modulated by C-tactile optimal stimulation in individuals with con-23 genital C-fiber denervation (Morrison et al. 2011). C-tactile mediated affective touch pathways are, 24 therefore, proposed to diverge from the Aβ low threshold mechanoreceptor afferent dorsal col-25 umn/medial-lemniscal discriminative touch stream and form a distinct coding channel projecting pri-26 marily to emotional rather than classical somatosensory cortical regions (Craig 2002, Morrison, 27 Löken, and Olausson 2010, McGlone, Wessberg, and Olausson 2014). 10 11 1 Figure 1. Anterolateral cordotomy induces marked deficits in canonical Lamina I spinothalamic 2 tract modalities.3 Myelogram (a) and schematic (b) showing the anterolateral cordotomy procedure. Following dual 4 puncture contrast is injected to document the position of the dentate ligament. Radiofrequency lesions 5 are given through the cordotomy probe within the anterolateral funiculus. Dot plots showing changes 6 in pre-cordotomy to post-cordotomy thermal detection and pain thresholds are shown in (c) and (d) 7 respectively. Data are presented as median and interquartile range. Significant differences (Related-8

show abstract

Synaptic Organization of VGLUT3 Expressing Low-Threshold Mechanosensitive C Fiber Terminals in the Rodent Spinal Cord

Abstract: Visual Abstract

Cited by 25 publications

References 75 publications

Expression of green fluorescent protein defines a specific population of lamina II excitatory interneurons in the GRP::eGFP mouse

Expression of green fluorescent protein defines a specific population of lamina II excitatory interneurons in the GRP::eGFP mouse

Nanostructural Diversity of Synapses in the Mammalian Spinal Cord

Spinal signaling of C-fiber mediated pleasant touch in humans

Contact Info

Product

Resources

About