Biology subjects

Pickering, A. E.

Publications and source records attributed to Pickering, A. E..

17 recordsLinked to original sources

bioRxiv2026

Contribution of Wide Dynamic Range neuronal activation to somatosensory evoked potentials supports use as biomarker of spinal nociceptive processing

Identifying objective translational biomarkers of spinal nociceptive processing is important to accelerate analgesic development. The primary negative component (N1) of spinal somatosensory evoked potentials (SEPs) has been proposed as such a biomarker. However, the cellular substrates of the N1 potential (evoked by innocuous electrical stimulation) and their relevance to nociceptive processing have not been directly demonstrated. Here, we employed a 64-channel multielectrode recording approach in the dorsal horn of anaesthetised Wistar rats to functionally characterise the neuronal populations activated during the generation of spinal SEPs and determine how their activity is modulated by tapentadol. Single units were classified based on their responses to mechanical stimulation of the hindpaw, and their electrically evoked responses to sciatic nerve stimulation. Of 59 well-isolated units, 47 (80%) were classified as wide dynamic range (WDR) neurons and 12 (20%) as low-threshold mechanoreceptive (LTMR) neurons, spatially distributed across spinal laminae III-V. Tapentadol (10 mg/kg, intraperitoneal (i.p)) selectively attenuated the mechanically- and electrically-evoked activity of WDR neurons without affecting LTMR responses. This WDR-inhibition was largely reversed by naloxone (0.25 mg/kg, i.p) but not by atipamezole (1 mg/kg, i.p), identifying a predominant opioid receptor-mediated mechanism of inhibition in the naive state. The magnitude of WDR inhibition by tapentadol correlated with the degree of reduction of the N1 amplitude. These findings establish activity in WDR neurons as a core component of the N1 potential, supporting the use of spinal SEPs as a translational biomarker of analgesic target engagement within the dorsal horn. SummaryMultielectrode recordings identify inhibition of WDR neurons as the mechanism by which tapentadol modulates spinal SEPs, supporting use as a biomarker of spinal nociceptive processing.

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bioRxiv2026

A mechanically stable neural probe for percutaneous high-resolution, multichannel recordings in peripheral nerves

The development of neural probes has enabled a deeper understanding and improved treatment for neurological disorders. Microneurography is currently the gold standard for assessing the electrophysiological signature of pain mechanisms in the human peripheral nervous system. However, its clinical utility is limited by the low recording yield and signal-to-noise ratio of single-electrode probes. To overcome these limitations, we developed mechanically robust, multi-electrode probes designed for acute percutaneous insertion and recording in peripheral nerves. The electrical and mechanical stability of these probes was confirmed through repeated insertions in artificial human skin and rat peripheral nerves. In addition, ex vivo and in vivo experiments demonstrated enhanced functional performance, with multi-site recordings enabling the isolation of single-fiber activity. Importantly, our probes can be operated analogously to conventional microneurography needles while substantially increasing the information yield, providing enhanced capabilities for minimally invasive peripheral nerve assessment.

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bioRxiv2025

Preclinical assay of the effects of lacosamide, pregabalin and tapentadol on the rat N1 spinal somatosensory evoked potential.

The high failure rate in translating novel analgesics into the clinic has highlighted the need for more translatable biomarkers of analgesic efficacy. The N13 component of spinal somatosensory evoked potential (SEP) has been proposed as a biomarker of spinal nociceptive processing in humans, but it is not known whether this can be back translated into rodents. Tapentadol, lacosamide and pregabalin were used as pharmacological probes to assess the sensitivity of spinal SEPs to drug action. In anaesthetised, naive rats (n=44), a multielectrode silicon probe was inserted into the L4 spinal cord to record SEPs from the dorsal horn following electrical stimulation of the sciatic nerve. At baseline, the N1 component (rodent equivalent of the human N13) had an amplitude of 1.33 {+/-} 0.07mV at a latency of 4.6 {+/-} 0.2ms following low-intensity stimulation, with an intensity-dependent amplitude increase into the noxious range. The N1 amplitude was significantly reduced by 10mg/Kg tapentadol (40.2 {+/-} 12.5 % vs vehicle 96.2 {+/-} 8.0 %) and 30mg/Kg lacosamide (46.3 {+/-} 20.9 % lacosamide vs vehicle 115 {+/-} 5.9 %) at 60 minutes after intraperitoneal administration. Tapentadol also reduced the N1 amplitude in the noxious range. Lacosamide increased the stimulus current required to evoke the half maximal N1 response (EC50), without reducing the maximum N1 amplitude in the noxious range. Pregabalin (at any dose up to 30mg/kg) did not modulate the N1 amplitude. These results show the spinal N1 is differentially modulated in a way that reflects distinct mechanisms of drug action consistent with it being a translatable biomarker of analgesic efficacy.

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bioRxiv2025

Synthetic torpor in the rat recapitulates key deatures of torpor and protects the heart from ischaemia-reperfusion injury

During times of environmental stress, many animals enter torpor: a reversible protective physiological state typically characterised by reductions in core temperature, heart rate and oxygen consumption. Species that naturally enter this hypothermic and hypometabolic state are tolerant of ischaemia-reperfusion injury. Consequently, there is a growing interest in utilizing aspects of torpor for clinical applications, such as protection from stroke or myocardial infarction. It is currently unknown, however, whether a torpor-like state is protective in animals that do not naturally enter torpor. Using viral vector-mediated chemogenetic activation of the medial preoptic area of the hypothalamus, we induced synthetic torpor in the rat, a species that does not naturally enter torpor. We demonstrate this state is cardioprotective in an ex vivo ischaemia-reperfusion injury model with an ~40% reduction in infarct size. Synthetic torpor-induced cardioprotection of the normothermic, isolated heart is not dependent on prior hypothermia in vivo. Phosphoproteomic analysis of cardiac tissue indicates the protective effects of synthetic torpor may be mediated by parallel activation of cell survival and stress tolerance pathways and inhibition of cell death pathways. These findings provide important insights into the mechanisms of organ protective effects of synthetic torpor states with implications for future clinical translation in humans.

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bioRxiv2024

Food-entrainment of circadian timekeeping in the dorsal vagal complex

The dorsal vagal complex (DVC) is a multi-component brainstem satiety centre which has gained attention as a key target of anti-obesity pharmacotherapies. Our recent studies revealed its circadian timekeeping properties, with molecular and electrophysiological 24h rhythms persisting independently of the primary hypothalamic clock. However, the factors entraining these brainstem oscillators, and the downstream transcriptional targets of the DVC molecular clock remain unclear. Here, using fluorescent in situ hybridisation, we demonstrate core clock gene expression in inhibitory and excitatory neuronal populations of the DVC, as well as in its output cholinergic vagal neurons. We further reveal that the molecular clock is associated with rhythmic expression of numerous neurotransmitter receptor genes in the DVC in vivo, with the phase of both clock and clock-controlled gene expression tightly regulated by meal timing. These findings uncover food-entrained circadian rhythms in the DVC and have important implications for clinical studies targeting brainstem satiety mechanisms.

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bioRxiv2024

Diversity of ancestral brainstem noradrenergic neurons across species and multiple biological factors

The brainstem cell group, locus coeruleus (LC), is present across vertebrates and influences cardiorespiratory, metabolic, immune, and cognitive functions by activating in two putatively distinct firing patterns. Yet, the degree to which the LC firing rates and patterns are homogenous across species has never been assessed due to inherently limited sample sizes. To remedy this, we pooled cross-species data from 20 laboratories to show that firing rates differ across species and are modulated by sex, age, and type of in vitro or in vivo preparation. Contrary to the prevailing dual-mode firing pattern schema, we observed patterns spread across a low-dimensional manifold, with subregions enriched for specific biological factors and neurodegenerative disease models. Our findings show considerable diversity in an ancestral vertebrate neuromodulatory system.

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bioRxiv2022

Noradrenergic cross-modular reciprocal inhibition within the Locus Coeruleus.

The Locus Coeruleus (LC) is the primary noradrenergic nucleus in the brain with widespread projections driving changes in cognitive state and animal behaviour. The LC is composed of multiple "modules" with specific efferent target domains enabling discretional neuromodulation. LC neuronal activity releases noradrenaline within the nucleus as a local feedback mechanism, but it is not known how this influences modular output. We address this question using whole-cell recordings and calcium imaging in rat pontine slices in combination with LC neuronal ensemble modelling to assess the influence of local noradrenaline release on cross-modular interactions. Electrophysiological recordings of LC neurons from rats transduced with the optogenetic actuator ChR2 showed auto-inhibition and lateral inhibition (of surrounding non-transduced neurons). This inhibition was strongly frequency dependent and was mediated by noradrenaline acting on alpha2-adrenceptors (2R). To allow calcium-imaging of LC neuronal ensembles a Canine-Adenoviral vector strategy was developed using the PRS promoter to drive selective expression GCaMP6s. Calcium imaging allowed resolution of both increases and decreases in LC activity (to TTX / clonidine or high potassium). Selective chemogenetic-activation of subsets of LC neurons (expressing the ionotropic actuator PSAM) revealed both a direct excitation (after application of PSEM308, 3-30{micro}M) and an 2R-mediated inhibition of neighbouring LC cells (non-transduced). Differential retrograde targeting of PSAM or GCaMP6s to specific LC modules showed the presence of strong, reciprocal cross-modular inhibition (shown for the LC-olfactory bulb vs LC bulbospinal modules) and a subsequent rebound activity inversion. This represents a preferential, targeted, cross-modular, lateral inhibition within the LC rather than a non-specific surround inhibition. Computational modelling showed the emergence of lateral inhibition and biphasic responses to modular activation when 2R signalling and noradrenergic reuptake saturation were included. This interaction may facilitate recruitment of neuronal ensembles by coherent inputs and represents a bottom-up differential contrast-enhancement mechanism within the LC to produce a modality specific focus.

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bioRxiv2021

Neurons in the dorsomedial hypothalamus promote, prolong, and deepen torpor

Torpor is a naturally occurring, hypometabolic, hypothermic state engaged by a wide range of animals in response to imbalance between the supply and demand for nutrients. Recent work has identified some of the key neuronal populations involved in daily torpor induction in mice, in particular projections from the preoptic area of the hypothalamus (POA) to the dorsomedial hypothalamus (DMH). The DMH plays a role in thermoregulation, control of energy expenditure, and circadian rhythms, making it well positioned to contribute to the expression of torpor. We used activity dependent genetic TRAPing techniques to target DMH neurons that were active during natural torpor bouts in female mice. Chemogenetic reactivation of torpor-TRAPed DMH neurons in calorie-restricted mice promoted torpor, resulting in longer and deeper torpor bouts. Chemogenetic inhibition of torpor-TRAPed DMH neurons did not block torpor entry, suggesting a modulatory role for the DMH in the control of torpor. This work adds to the evidence that the POA and the DMH form part of a circuit within the mouse hypothalamus that controls entry into daily torpor. SignificanceDaily heterotherms such as mice employ torpor to cope with environments in which the supply of metabolic fuel is not sufficient for the maintenance of normothermia. Daily torpor involves reductions in body temperature, as well as active suppression of heart rate and metabolism. How the central nervous system controls this profound deviation from normal homeostasis is not known, but a projection from the preoptic area to the dorsomedial hypothalamus has recently been implicated. We demonstrate that the dorsomedial hypothalamus contains neurons that are active during torpor. Activity in these neurons promotes torpor entry and maintenance, but their activation alone does not appear to be sufficient for torpor entry.

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bioRxiv2021

Trial by trial, machine learning approach identifies temporally discrete Aδ- and C-fibre mediated laser evoked potentials that predict pain behaviour in rats.

Laser evoked potentials (LEPs) - the EEG response to temporally-discrete thermal stimuli - are commonly used in experimental pain studies in humans. Such stimuli selectively activate nociceptors and produce EEG features which correlate with pain intensity. The rodent LEP has been proposed to be a translational biomarker of nociception and pain, however its validity has been questioned because of reported differences in the classes of nociceptive fibres mediating the response. Here we use a machine learning, trial by trial analysis approach on wavelet-denoised LEPs generated by stimulation of the plantar hindpaw of rats. The LEP amplitude was more strongly related to behavioural response than to laser stimulus energy. A simple decision tree classifier using LEP features was able to predict behavioural responses with 73% accuracy. An examination of the features used by the classifier showed that mutually exclusive short and long latency LEP peaks were clearly seen in single-trial data, yet were not evident in grand average data pooled from multiple trials. This bimodal distribution of LEP latencies was mirrored in the paw withdrawal latencies which were preceded and predicted by the LEP responses. The proportion of short latency events was increased after intradermal application of high dose capsaicin (to defunctionalise TRPV1 expressing nociceptors), suggesting they were mediated by A{delta}-fibres (specifically AMH-I). These findings demonstrate that both C- and A{delta}-fibres contribute to rodent LEPs and concomitant behavioural responses, providing a real-time assay of specific fibre function in conscious animals. Single-trial analysis approaches can improve the utility of LEPs as a translatable biomarker of pain.

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bioRxiv2021

Simultaneous Brain, Brainstem and Spinal Cord pharmacological-fMRI reveals multilevel opioidergic roles in attentional analgesia in humans

Pain perception is decreased by shifting attentional focus away from a threatening event. This attentional analgesia engages parallel descending control pathways from anterior cingulate (ACC) to locus coeruleus, and ACC to periaqueductal grey (PAG) - rostral ventromedial medulla (RVM), indicating possible roles for noradrenergic or opioidergic neuromodulators. To determine which pathway modulates nociceptive activity in humans we used simultaneous whole brain-spinal cord pharmacological-fMRI (N=39) across three sessions. Noxious thermal forearm stimulation generated somatotopic-activation of dorsal horn (DH, C6 segment) whose activity mirrored attentional pain modulation. Activity in an adjacent cluster reported the interaction between task and noxious stimulus. Effective connectivity analysis revealed that ACC recruits PAG and RVM to modulate spinal cord activity. Blocking endogenous opioids with Naltrexone impairs attentional analgesia and disrupts RVM-DH and ACC-PAG connectivity. Noradrenergic augmentation with Reboxetine did not alter attentional analgesia. Cognitive pain modulation is mediated by opioidergic ACC-PAG-RVM descending control which supresses spinal nociceptive activity.

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bioRxiv2020

Loss of cortical control over the descending pain modulatory system determines the development of the neuropathic pain state in rats

The loss of descending inhibitory control is thought critical to the development of chronic pain but what causes this loss in function is not well understood. We have investigated the dynamic contribution of prelimbic cortical neuronal projections to the periaqueductal grey (PrL-P) to the development of neuropathic pain in rats using combined opto- and chemo-genetic approaches. We found PrL-P neurons to exert a tonic inhibitory control on thermal withdrawal thresholds in uninjured animals. Following nerve injury, ongoing activity in PrL-P neurons masked latent hypersensitivity and improved affective state. However, this function is lost as the development of sensory hypersensitivity emerges. Despite this loss of tonic control, opto-activation of PrL-P neurons at late post-injury timepoints could restore the anti-allodynic effects by inhibition of spinal nociceptive processing. We suggest that the loss of cortical drive to the descending pain modulatory system underpins the expression of neuropathic sensitisation after nerve injury.

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bioRxiv2020

Parallel cortical-brainstem pathways to attentional analgesia

Pain perception is diminished when attention is diverted. Our previous human fMRI study, using a 2x2 factorial design with thermal stimuli and concurrent visual attention task, linked the brainstem triad of locus coeruleus (LC), rostroventromedial medulla (RVM) and periaqueductal grey (PAG) to attentional analgesia. This study was repeated with a larger cohort, replicating our earlier findings. Pain intensity was encoded by the RVM, whilst activity in the contralateral LC correlated with the magnitude of attentional analgesia. Psycho-Physiological Interaction analysis informed subsequent Dynamic Causal Modelling and identified two parallel paths between forebrain and the brainstem regions involved in analgesia. These cortico-brainstem connections were modulated by attentional demand: a bidirectional anterior cingulate cortex (ACC) - right-LC loop, and a top-down influence of task on ACC-PAG-RVM. Under conditions of competing attentional demands the ACC recruits discrete brainstem circuits to modulate nociceptive input.

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bioRxiv2019

Corticotrophin-Releasing Hormone neurons of Barrington’s nucleus: Probabilistic, spinally-gated control of bladder pressure and micturition

Micturition, the co-ordinated process of expulsion of urine from the bladder, requires precise control of bladder and urethral sphincter via parasympathetic, sympathetic and somatic motoneurons. In adult mammals this involves a spinobulbospinal control circuit incorporating Barringtons nucleus in the pons (Barr). The largest Barr cell population is comprised of pontospinal glutamatergic neurons that express corticotrophin-releasing hormone. There is evidence that BarrCRH neurons can generate bladder contractions but it is unknown whether they act as a simple switch or a high-fidelity pre-parasympathetic motor drive and whether their activation can actually trigger voids. Combined opto- and chemo-genetic manipulations along with recordings in mice shows that BarrCRH neurons provide a probabilistic drive that generates co-ordinated voids or non-voiding contractions depending on the phase of the micturition cycle. These findings inform a new inferential model of micturition and emphasise the importance of the state of the spinal gating circuit in the generation of voiding.

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bioRxiv2019

Regulation of food intake by astrocytes in the brainstem dorsal vagal complex

Food intake is controlled by the coordinated action of numerous brain regions but a complete understanding remains elusive. Of these brain regions the brainstem dorsal vagal complex (DVC) is the first site for integration of visceral synaptic and hormonal cues that act to inhibit food intake. The DVC consists of three nuclei: the nucleus of the solitary tract (NTS), area postrema (AP) and dorsal motor nucleus of the vagus (DMX). Targeted chemogenetic activation of appetite-responsive NTS neuronal populations causes short term decreases in food intake. Astrocytes are a class of glial cell which provide metabolic and structural support to neurons and play an active role in modulating neurotransmission. Within the hypothalamic arcuate nucleus (ARC) astrocytes are regulated by both positive and negative energy balance and express receptors for hormones that influence satiety and hunger. Chemogenetic activation of these ARC astrocytes alters food intake. Since NTS astrocytes respond to vagal stimulation, we hypothesised that they may be involved in mediating satiety. Here we show that NTS astrocytes show plastic alterations in morphology following excess food consumption and that chemogenetic activation of DVC astrocytes causes a decrease in food intake, by recruiting an appetite-inhibiting circuit, without producing aversion. These findings are the first using genetically-targeted manipulation of DVC astrocytes to demonstrate their role in the brains regulation of food intake.

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bioRxiv2019

Locus-coeruleus norepinephrine activity gates sensory-evoked awakenings from sleep

A defining feature of sleep is reduced responsiveness to external stimuli, but the mechanisms gating sensory-evoked arousal remain unclear. We hypothesized that reduced locus-coeruleus norepinephrine (LC-NE) activity during sleep mediates unresponsiveness, and its action promotes sensory-evoked awakenings. We tested this using electrophysiological, behavioral, pharmacological, and optogenetic techniques alongside auditory stimulation in freely behaving rats. We found that systemic reduction of NE signaling lowered probability of sound-evoked awakenings (SEAs). The level of tonic LC activity during sleep anticipated SEAs. Optogenetic LC activation promoted arousal as evident in sleep-wake transitions, EEG desynchronization, and pupil dilation. Importantly, liminal LC excitation before sound presentation increased SEA probability. Optogenetic LC silencing using a soma-targeted anion-conducting channelrhodopsin (stGtACR2) suppressed LC spiking and constricted pupils. Brief periods of LC opto-silencing reduced the probability of SEAs. Thus, LC-NE activity determines the likelihood of sensory-evoked awakenings and its reduction during sleep constitutes a key factor mediating behavioral unresponsiveness.

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bioRxiv2018

Locus Coeruleus tracking of prediction errors optimises cognitive flexibility: an Active Inference model.

The locus coeruleus (LC) in the pons is the major source of noradrenaline (NA) in the brain. Two modes of LC firing have been associated with distinct cognitive states: changes in tonic rates of firing are correlated with global levels of arousal and behavioural flexibility, whilst phasic LC responses are evoked by salient stimuli. Here, we unify these two modes of firing by modelling the response of the LC as a correlate of a prediction error when inferring states for action planning under Active Inference (AI).\n\nWe simulate a classic Go/No-go reward learning task and a three-arm foraging task and show that, if LC activity is considered to reflect the magnitude of high level state-action prediction errors, then both tonic and phasic modes of firing are emergent features of belief updating. We also demonstrate that when contingencies change, AI agents can update their internal models more quickly by feeding back this state-action prediction error - reflected in LC firing and noradrenaline release - to optimise learning rate, enabling large adjustments over short timescales. We propose that such prediction errors are mediated by cortico-LC connections, whilst ascending input from LC to cortex modulates belief updating in anterior cingulate cortex (ACC).\n\nIn short, we characterise the LC/ NA system within a general theory of brain function. In doing so, we show that contrasting, behaviour-dependent firing patterns are an emergent property of the LCs crucial role in translating prediction errors into an optimal mediation between plasticity and stability.\n\nAuthor SummaryThe brain uses sensory information to build internal models and make predictions about the world. When errors of prediction occur, models must be updated to ensure desired outcomes are still achieved. Neuromodulator chemicals provide a possible pathway for triggering such changes in brain state. One such neuromodulator, noradrenaline, originates predominantly from a cluster of neurons in the brainstem - the locus coeruleus (LC) - and plays a key role in behaviour, for instance, in determining the balance between exploiting or exploring the environment.\n\nHere we use Active Inference (AI), a mathematical model of perception and action, to formally describe LC function. We propose that LC activity is triggered by errors in prediction and that the subsequent release of noradrenaline alters the rate of learning about the environment. Biologically, this describes an LC-cortex feedback loop promoting behavioural flexibility in times of uncertainty. We model LC output as a simulated animal performs two tasks known to elicit archetypal responses. We find that experimentally observed phasic and tonic patterns of LC activity emerge naturally, and that modulation of learning rates improves task performance. This provides a simple, unified computational account of noradrenergic computational function within a general model of behaviour.

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bioRxiv2017

Engagement of spinal- vs prefrontal-projecting locus coeruleus neurons parses analgesia from aversion & anxiety in rats

The locus coeruleus (LC) projects throughout the brain and spinal cord and is the major source of central noradrenaline. It remains unclear whether the LC acts functionally as a single global effector or as discrete modules. Specifically, while spinal-projections from LC neurons can exert analgesic actions, it is not known whether they can act independently of ascending LC projections. Using viral vectors taken up at axon terminals, we expressed chemogenetic actuators selectively in LC neurons with spinal (LC:SC) or prefrontal cortex (LC:PFC) projections. Activation of the LC:SC module produced robust, lateralised analgesia while activation of LC:PFC produced aversion. In a neuropathic pain model, LC:SC activation reduced hind-limb sensitization and induced conditioned place preference. By contrast, activation of LC:PFC exacerbated spontaneous pain, produced aversion and increased anxiety-like behaviour. This independent, contrasting modulation of pain-related behaviours mediated by distinct noradrenergic modules provides evidence for a discrete functional organisation of the LC.

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