Automated and rapid self-report of nociception in transgenic mice

Abstract

there are currently no rapid, operant pain behaviors in rodents that use a self-report to directly engage higher-order brain circuitry. We have developed a pain detection assay consisting of a lick behavior in response to optogenetic activation of predominantly nociceptive peripheral afferent nerve fibers in head-restrained transgenic mice expressing ChR2 in TRPV1 containing neurons. TRPV1-ChR2-EYFP mice (n = 5) were trained to provide lick reports to the detection of light-evoked nociceptive stimulation to the hind paw. Using simultaneous video recording, we demonstrate that the learned lick behavior may prove more pertinent in investigating brain driven pain processes than the reflex behavior. Within sessions, the response bias of transgenic mice changed with respect to lick behavior but not reflex behavior. Furthermore, response similarity between the lick and reflex behaviors diverged near perceptual threshold. our nociceptive lick-report detection assay will enable a host of investigations into the millisecond, single cell, neural dynamics underlying pain processing in the central nervous system of awake behaving animals. The importance of the brain in nociception has been theorized since Descartes' Treatise of Man 1. Melzack and Wall, whose gate control theory highlights the role of the spinal cord in pain processing, acknowledged the need for the myriad, interconnected brain areas to synthesize the perception of pain 2. Advances in human neural recording technologies have allowed scientists to test theories describing how brain circuits map onto pain 3. Human functional MRI (fMRI) has shown that perceived pain correlates with activation of primary somatosensory cortices, anterior cingulate cortex, and other brain regions implicated in the discriminatory and affective components of pain 4,5. Electroencephalography (EEG) and magnetoencephalography (MEG) have implicated the regulation of specific oscillatory components, for example alpha oscillations in the sensorimotor cortex, in pain perception 6. While techniques such as fMRI, EEG, and MEG paint a macroscopic picture of brain dynamics, these techniques cannot achieve the cellular or temporal resolution necessary for elucidating the neural circuits underlying pain perception. Genetic manipulations 7 and in vivo neural recordings in rodents are foundational in this respect as they afford the granularity required to characterize neural circuit activity and therapeutic outcomes 8-10. Unfortunately, the inability to compare behavioral outputs between animal and human studies presents a significant barrier for clinical translation of experimental results. Pain in humans is primarily measured using verbal self-reports, such as the visual analogue scale 11 , while pain in rodents is inferred from behavioral signals of discomfort, such as reflex behaviors 11,12. Reflex behaviors, like the hind paw withdrawal, are used to characterize evoked pain. Although reflex behaviors have been shown to positively correlate with self-reports of pain in humans 13 , decerebrated ...

TRPV1-lineage somatosensory fibers communicate with taste neurons in the mouse parabrachial nucleus

“…Excitation of TRPV1-lineage primary neurons represents a broad stimulus for somatosensory pathways that is functionally significant. TRPV1-lineage afferents comprise small diameter Ad-and Cfibers that express peptidergic and nonpeptidergic nociceptive markers and project to superficial lamina in the dorsal horn of the spinal cord and Vc (Cavanaugh et al, 2011a;Mishra et al, 2011;Browne et al, 2017;Black et al, 2020), which relay to the PB area (Jasmin et al, 1997). Silencing TRPV1-lineage afferents in mice causes deficits in thermosensory, algesic-related, and pruritoceptive responses while excitation induces nocifensive behaviors (Mishra et al, 2011;Park et al, 2015;Browne et al, 2017).…”

“…We focused on trigeminal fibers marked by the capsaicin receptor: the transient receptor potential (TRP) ion channel TRP vanilloid 1 (TRPV1). Optogenetic stimulation of TRPV1-lineage afferents engages primary nociceptive neurons involved with protective thermosensory and nocifensive behaviors (Cavanaugh et al, 2011a;Mishra et al, 2011;Stemkowski et al, 2016;Browne et al, 2017;Black et al, 2020). We hypothesized that TRPV1-lineage fibers communicate with taste-active PB cells through a synaptic relay in the dorsal Vc, which projects to PB gustatory neurons (Li and Lemon, 2019).…”

TRPV1-Lineage Somatosensory Fibers Communicate with Taste Neurons in the Mouse Parabrachial Nucleus

“…We focused on trigeminal fibers marked by the capsaicin receptor: the transient receptor potential (TRP) ion channel TRP vanilloid 1 (TRPV1). Optogenetic stimulation of TRPV1-lineage afferents engages primary nociceptive neurons involved with protective thermosensory and nocifensive behaviors (Cavanaugh et al, 2011a;Mishra et al, 2011;Stemkowski et al, 2016;Browne et al, 2017;Black et al, 2020). TRPV1-lineage fibers populate the spinal trigeminal tract (Cavanaugh et al, 2011a;Mishra et al, 2011), which supplies Vc neurons with orofacial sensory input (Capra and Dessem, 1992).…”

TailTimer: A device for automating data collection in the rodent tail immersion assay

“…For this reason, chemical stimulation is inadequate for studying acute pain. Similarly, different types of nociceptive stimuli are known to recruit distinct circuitry and induce pain with more-or-less specificity [ 1 – 3 ]. For instance, assays utilizing mechanical stimuli (e.g., von Frey) may activate innocuous afferents that could confound the observed pain response [ 2 , 3 ].…”

“…Similarly, different types of nociceptive stimuli are known to recruit distinct circuitry and induce pain with more-or-less specificity [ 1 – 3 ]. For instance, assays utilizing mechanical stimuli (e.g., von Frey) may activate innocuous afferents that could confound the observed pain response [ 2 , 3 ]. Thermal stimulation, however, models a naturally-encountered stimulus, and its ability to induce pain with a relatively high degree of specificity contributes to its wide utilization throughout pain research [ 1 ].…”