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Calretinin positive neurons form an excitatory amplifier network in the spinal cord dorsal horn.

ABSTRACT: Nociceptive information is relayed through the spinal cord dorsal horn, a critical area in sensory processing. The neuronal circuits in this region that underpin sensory perception must be clarified to better understand how dysfunction can lead to pathological pain. This study used an optogenetic approach to selectively activate spinal interneurons that express the calcium-binding protein calretinin (CR). We show that these interneurons form an interconnected network that can initiate and sustain enhanced excitatory signaling, and directly relay signals to lamina I projection neurons. Photoactivation of CR interneurons in vivo resulted in a significant nocifensive behavior that was morphine sensitive, caused a conditioned place aversion, and was enhanced by spared nerve injury. Furthermore, halorhodopsin-mediated inhibition of these interneurons elevated sensory thresholds. Our results suggest that dorsal horn circuits that involve excitatory CR neurons are important for the generation and amplification of pain and identify these interneurons as a future analgesic target.

SUBMITTER: Smith KM

PROVIDER: S-EPMC6908433 | biostudies-literature | 2019 Nov

REPOSITORIES: biostudies-literature

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Calretinin positive neurons form an excitatory amplifier network in the spinal cord dorsal horn.

Smith Kelly M KM Browne Tyler J TJ Davis Olivia C OC Coyle A A Boyle Kieran A KA Watanabe Masahiko M Dickinson Sally A SA Iredale Jacqueline A JA Gradwell Mark A MA Jobling Phillip P Callister Robert J RJ Dayas Christopher V CV Hughes David I DI Graham Brett A BA

eLife 20191112

Nociceptive information is relayed through the spinal cord dorsal horn, a critical area in sensory processing. The neuronal circuits in this region that underpin sensory perception must be clarified to better understand how dysfunction can lead to pathological pain. This study used an optogenetic approach to selectively activate spinal interneurons that express the calcium-binding protein calretinin (CR). We show that these interneurons form an interconnected network that can initiate and sustai ...[more]

PMID: 31713514

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Project description:The superficial dorsal horn (SDH) of the spinal cord represents the first site of integration between innocuous and noxious somatosensory stimuli. According to gate control theory, diverse populations of excitatory and inhibitory interneurons within the SDH are activated by distinct sensory afferents, and their interplay determines the net nociceptive output projecting to higher pain centers. Although specific SDH cell types are ill defined, numerous classifications schemes find that excitatory and inhibitory neurons fundamentally differ in their morphology, electrophysiology, neuropeptides, and pain-associated plasticity; yet little is known about how these neurons respond over a range of natural innocuous and noxious stimuli. To address this question, we applied an in vivo imaging approach in male mice where the genetically encoded calcium indicator GCaMP6s was expressed either in vGluT2-positive excitatory or vIAAT-positive inhibitory neurons. We found that inhibitory neurons were markedly more sensitive to innocuous touch than excitatory neurons but still responded dynamically over a wide range of noxious mechanical stimuli. Inhibitory neurons were also less sensitive to thermal stimuli than their excitatory counterparts. In a capsaicin model of acute pain sensitization, the responses of excitatory neurons were significantly potentiated to innocuous and noxious mechanical stimuli, whereas inhibitory neural responses were only depressed to noxious stimuli. These in vivo findings show that excitatory and inhibitory SDH neurons diverge considerably in their somatosensory responses and plasticity, as postulated by gate control theory.SIGNIFICANCE STATEMENT Gate control theory posits that opposing spinal excitatory and inhibitory neurons, differently tuned across somatosensory modalities, determine the net nociceptive output to higher pain centers. Little is known about how natural stimuli activate these two neural populations. This study applied an in vivo calcium imaging approach to genetically target these neurons and contrast their responses over a range of innocuous and noxious mechanical and thermal stimuli. Compared with excitatory neurons, we found that inhibitory neurons are more sensitive to innocuous touch and far less sensitive to thermal stimuli. An acute model of pain also revealed that these subtypes undergo divergent mechanosensory plasticity. Our data provide important and novel insights for gate-control inspired models of pain processing.

Dataset Information

Calretinin positive neurons form an excitatory amplifier network in the spinal cord dorsal horn.

Publications

Calretinin positive neurons form an excitatory amplifier network in the spinal cord dorsal horn.

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