Afferent Activity Research Articles

Direct activation of airway sensory C-fibers by SARS-CoV-2 S1 spike protein.

Respiratory viral infection can lead to activation of sensory afferent nerves as indicated by the consequential sore throat, sneezing, coughing, and reflex secretions. In addition to causing troubling symptoms, sensory nerve activation likely accelerates viral spreading. The mechanism how viruses activate sensory nerve terminals during infection is unknown. In this study, we investigate whether coronavirus spike protein activates sensory nerves terminating in the airways. We used isolated vagally-innervated mouse trachea-lung preparation for two-photon microscopy and extracellular electrophysiological recordings. Using two-photon Ca2+ imaging, we evaluated a total number of 786 vagal bronchopulmonary nerves in six experiments. Approximately 49% of the sensory fibers were activated by S1 protein (4 μg/mL intratracheally). Extracellular nerve recording showed the S1 protein evoked action potential discharge in sensory C-fibers; of 39 airway C-fibers (one fiber per mouse), 17 were activated. Additionally, Fura-2 Ca2+ imaging was performed on neurons dissociated from vagal sensory ganglia (n = 254 from 22 mice). The result showed that 63% of neurons responded to S1 protein. SARS-CoV-2 S1 protein can lead to direct activation of sensory C-fiber nerve terminals in the bronchopulmonary tract. Direct activation of C-fibers may contribute to coronavirus symptoms, and amplify viral spreading in a population.

A-kinase anchoring protein 79/150 coordinates α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor sensitization in sensory neurons

Changes in sensory afferent activity contribute to the transition from acute to chronic pain. However, it is unlikely that a single sensory receptor is entirely responsible for persistent pain. It is more probable that extended changes to multiple receptor proteins expressed by afferent neurons support persistent pain. A-Kinase Anchoring Protein 79/150 (AKAP) is an intracellular scaffolding protein expressed in sensory neurons that spatially and temporally coordinates signaling events. Since AKAP scaffolds biochemical modifications of multiple TRP receptors linked to pain phenotypes, we probed for other ionotropic receptors that may be mediated by AKAP and contribute to persistent pain. Here, we identify a role for AKAP modulation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid Receptor (AMPA-R) functionality in sensory neurons. Pharmacological manipulation of distinct AMPA-R subunits significantly reduces persistent mechanical hypersensitivity observed during hyperalgesic priming. Stimulation of both protein kinases C and A (PKC, PKA, respectively) modulate AMPA-R subunit GluR1 and GluR2 phosphorylation and surface expression in an AKAP-dependent manner in primary cultures of DRG neurons. Furthermore, AKAP knock out reduces sensitized AMPA-R responsivity in DRG neurons. Collectively, these data indicate that AKAP scaffolds AMPA-R subunit organization in DRG neurons that may contribute to the transition from acute-to-chronic pain.

The Lateral Parabrachial Nucleus Inputs to the Lateral Hypothalamus Trigger Nocifensive Behaviors

The lateral parabrachial nucleus (LPBN) is known to play a key role in relaying noxious information from the spinal cord to the brain. Different LPBN efferent mediate different aspects of the nocifensive response. However, the function of the LPBN → lateral hypothalamus (LH) circuit in response to noxious stimuli has remained unknown. Here, we show that LPBN → LH circuit is activated by noxious stimuli. Interestingly, either activation or inhibition of this circuit induced analgesia. Optogenetic activation of LPBN afferents in the LH elicited spontaneous jumping and induced place aversion. Optogenetic inhibition inhibited jumping behavior to noxious heat. Ablation of LH glutamatergic neurons could abolish light-evoked analgesia and jumping behavior. Our study revealed a role for the LPBN → LH pathway in nocifensive behaviors.

Spontaneous activity in peripheral sensory nerves: a systematic review.

In the peripheral nervous system, spontaneous activity in sensory neurons is considered to be one of the 2 main drivers of chronic pain states, alongside neuronal sensitization. Despite this, the precise nature and timing of this spontaneous activity in neuropathic pain is not well-established. Here, we have performed a systematic search and data extraction of existing electrophysiological literature to shed light on which fibre types have been shown to maintain spontaneous activity and over what time frame. We examined both in vivo recordings of preclinical models of neuropathic pain, as well as microneurography recordings in humans. Our analyses reveal that there is broad agreement on the presence of spontaneous activity in neuropathic pain conditions, even months after injury or years after onset of neuropathic symptoms in humans. However, because of the highly specialised nature of the electrophysiological methods used to measure spontaneous activity, there is also a high degree of variability and uncertainty around these results. Specifically, there are very few directly controlled experiments, with less directly comparable data between human and animals. Given that spontaneous peripheral neuron activity is considered to be a key mechanistic feature of chronic pain conditions, it may be beneficial to conduct further experiments in this space.

Kv2 channels contribute to neuronal activity within the vagal afferent-nTS reflex arc.

Diversity in the functional expression of ion channels contributes to the unique patterns of activity generated in visceral sensory A-type myelinated neurons versus C-type unmyelinated neurons in response to their natural stimuli. In the present study, Kv2 channels were identified as underlying a previously uncharacterized delayed rectifying potassium current expressed in both A- and C-type nodose ganglion neurons. Kv2.1 and 2.2 appear confined to the soma and initial segment of these sensory neurons; however, neither was identified in their central presynaptic terminals projecting onto relay neurons in the nucleus of the solitary tract (nTS). Kv2.1 and Kv2.2 were also not detected in the peripheral axons and sensory terminals in the aortic arch. Functionally, in nodose neuron somas, Kv2 currents exhibited frequency-dependent current inactivation and contributed to action potential repolarization in C-type neurons but not A-type neurons. Within the nTS, the block of Kv2 currents does not influence afferent presynaptic calcium influx or glutamate release in response to afferent activation, supporting our immunohistochemical observations. On the other hand, Kv2 channels contribute to membrane hyperpolarization and limit action potential discharge rate in second-order neurons. Together, these data demonstrate that Kv2 channels influence neuronal discharge within the vagal afferent-nTS circuit and indicate they may play a significant role in viscerosensory reflex function.NEW & NOTEWORTHY We demonstrate the expression and function of the voltage-gated delayed rectifier potassium channel Kv2 in vagal nodose neurons. Within sensory neurons, Kv2 channels limit the width of the broader C-type but not narrow A-type action potential. Within the nucleus of the solitary tract (nTS), the location of the vagal terminal field, Kv2 does not influence glutamate release. However, Kv2 limits the action potential discharge of nTS relay neurons. These data suggest a critical role for Kv2 in the vagal-nTS reflex arc.

Elevated Serotonin in Mouse Spinal Dorsal Horn Is Pronociceptive.

Serotonergic neurons in the rostral ventral medulla (RVM) contribute to bidirectional control of pain through modulation of spinal and trigeminal nociceptive networks. Deficits in this pathway are believed to contribute to pathologic pain states, but whether changes in serotonergic mechanisms are pro- or antinociceptive is debated. We used a combination of optogenetics and fiber photometry to examine these mechanisms more closely. We find that optogenetic activation of RVM serotonergic afferents in the spinal cord of naive mice produces mechanical hypersensitivity and conditioned place aversion (CPA). Neuropathic pain, produced by chronic constriction injury of the infraorbital nerve (CCI-ION), evoked a tonic increase in serotonin (5HT) concentrations within the spinal trigeminal nucleus caudalis (SpVc), measured with liquid chromatography-tandem mass spectroscopy (LC-MS/MS). By contract, CCI-ION had no effect on the phasic serotonin transients in SpVc, evoked by noxious pinch, and measured with fiber photometry of a serotonin sensor. These findings suggest that serotonin release in the spinal cord is pronociceptive and that an increase in sustained serotonin signaling, rather than phasic or event driven increases, potentiate nociception in models of chronic pain.

Abstract 14951: Input From Renal Afferent Nerves Contributes to Hypertensive Heart Failure With Preserved Systolic Function Through Baroreflex Impairment and Sympathoexcitation

Introduction: Activation of renal afferent nerves, which can be caused by hypertensive renal damage, increases sympathetic output. The nucleus tractus solitarius (NTS) receives the inputs from baroreflex afferent nerves as well as renal afferent nerves. Baroreflex dysfunction leads to increased left ventricular (LV) end-diastolic pressure even in the heart with preserved systolic function. The GABAergic inhibitory system in the NTS blunts the signals from baroreflex afferent nerves, resulting in increased sympathetic output. Hypothesis: Input from renal afferent nerves contributes to hypertensive heart failure with preserved systolic function through baroreflex impairment and sympathoexcitation mediated by increased GABAergic inhibition in the NTS. Methods and Results: Male Dahl salt-sensitive rats with 8% high-salt diet from 7 weeks of age develop hypertensive HFpEF at 19 weeks. These rats underwent sham surgery (Sham), selective afferent renal denervation (ARDN), or additionally dissection of baroreflex afferent nerves (ARDN+BAROX) at 9 weeks. As controls, rats underwent sham surgery with a low-salt diet. The rats were evaluated at 19 weeks. Systolic blood pressure was similarly elevated in the three groups on high-salt diet. Impaired LV diastolic function assessed by echocardiography and pressure-volume loop analysis in Sham was recovered in ARDN group, while systolic function was preserved in all the group. Decreased baroreflex sensitivity and increased sympathetic output in Sham were attenuated in ARDN group. Activity of GABAergic neurons in the NTS evaluated by immunostaining was increased in Sham compared to controls, and was attenuated in ARDN group. All of the changes in ARDN were cancelled in ARDN+BAROX group. Conclusion: Input from renal afferent nerves contributes to hypertensive heart failure with preserved systolic function through baroreflex impairment and sympathoexcitation along with increased GABAergic inhibition in the NTS.

Abstract 17513: Decreased Sensory Neurotransmission Due to Neuronal Mitochondrial Dysfunction Mediates Sex Differences in Vagal Remodeling After Myocardial Infarction

Background: Vagal dysfunction after chronic myocardial infarction (MI) exacerbates heart failure and predisposes to ventricular tachyarrhythmias (VT/VF). VT/VF after MI is more common in males than females. The mechanisms behind these sex differences are unknown. Hypothesis: We hypothesized that differences in autonomic remodeling in the vagal ganglia, which in a healthy state, provide beat-to-beat sensory neurotransmission and modulate efferent cardiac vagal tone, may serve as the mechanisms behind the sex differences in the incidence of VT/VF. Methods: MI was created (left anterior descending artery ligation) in male and female mice expressing channel rhodopsin in glutamatergic vagal neurons (VGlut2-ChR2-EYFP mice). Sham animals underwent thoracotomy only. Two weeks post-MI, heart rate (HR) responses were assessed following in vivo vagal afferent nerve activation via optogenetic stimulation (5 sec duration, 20 Hz, 10 ms and 20 ms stimulations). Ventricular fibrosis was quantified. Mitochondrial oxygen consumption rates (OCR), glutamate levels, and the levels of oxidative stress marker, 4-hydroxy nonenal (4HNE), were measured in the vagal ganglia. Results: Male MI animals demonstrated significantly reduced HR responses to optogenetic stimulation than female MI animals. No sex differences in the degree of ventricular fibrosis was observed. A decrease in glutamate content accompanied by decreased mitochondrial OCR and increased 4HNE levels was observed in the vagal ganglia of male infarcted vs. female infarcted mice, figure. There were no differences in the HR responses, glutamate content, mitochondrial OCR, and 4HNE levels between sham males vs. sham females. Conclusion: This study demonstrates significant sex differences in vagal remodeling post-MI, with decreased efferent vagal tone in males mediated at least in part by reduced vagal afferent glutamatergic signaling associated with impaired neuronal mitochondrial function.

Selective recording of physiologically evoked neural activity in a mixed autonomic nerve using a minimally invasive array.

Real-time closed-loop control of neuromodulation devices requires long-term monitoring of neural activity in the peripheral nervous system. Although many signal extraction methods exist, few are both clinically viable and designed for extracting small signals from fragile peripheral visceral nerves. Here, we report that our minimally invasive recording and analysis technology extracts low to negative signal to noise ratio (SNR) neural activity from a visceral nerve with a high degree of specificity for fiber type and class. Complex activity was recorded from the rat pelvic nerve that was physiologically evoked during controlled bladder filling and voiding, in an extensively characterized in vivo model that provided an excellent test bed to validate our technology. Urethane-anesthetized male rats (n = 12) were implanted with a four-electrode planar array and the bladder instrumented for continuous-flow cystometry, which measures urodynamic function by recording bladder pressure changes during constant infusion of saline. We demonstrated that differential bipolar recordings and cross-correlation analyses extracts afferent and efferent activity, and discriminated between subpopulations of fibers based on conduction velocity. Integrated Aδ afferent fiber activity correlated with bladder pressure during voiding (r2: 0.66 ± 0.06) and was not affected by activating nociceptive afferents with intravesical capsaicin (r2: 0.59 ± 0.14, P = 0.54, and n = 3). Collectively, these results demonstrate our minimally invasive recording and analysis technology is selective in extracting mixed neural activity with low/negative SNR. Furthermore, integrated afferent activity reliably correlates with bladder pressure and is a promising first step in developing closed-loop technology for bladder control.

The Positive Effect of Renal Denervation Persists even Through Regrowth of Afferent Axons Improving Renal Afferent Nerve Activity During High Sodium Intake in Rats

The Positive Effect of Renal Denervation Persists even Through Regrowth of Afferent Axons Improving Renal Afferent Nerve Activity During High Sodium Intake in Rats

How does the lower urinary tract contribute to bladder sensation? ICI-RS 2023.

Bladder sensation is critical for coordinating voluntary micturition to maintain healthy bladder function. Sensations are initiated by the activation of sensory afferents that innervate throughout the bladder wall. However, the physiological complexity that underlies the initiation of bladder sensory signaling in health and disease remains poorly understood. This review summarises the latest knowledge of the mechanisms underlying the generation of bladder sensation and identifies key areas for future research. Experts in bladder sensory signaling reviewed the literature on how the lower urinary tract contributes to bladder sensation and identified key research areas for discussion at the 10th International Consultation on Incontinence-Research Society. The importance of bladder sensory signals in maintaining healthy bladder function is well established. However, better therapeutic management of bladder disorders with exaggerated bladder sensation, including overactive bladder syndrome (OAB) and interstitial cystitis/bladder pain syndrome (IC/BPS) is limited by a lack of knowledge in a number of key research areas including; the contribution of different nerves (pudendal, pelvic, hypogastric) to filling sensations in health and disease; the relative contribution of stretch sensitive (muscular) and stretch-insensitive (mucosal) afferents to bladder sensation in health and disease; the direct and indirect contributions of the muscularis mucosae to bladder contraction and sensation; and the impact of manipulating urothelial release factors on bladder sensation. Disturbances in bladder sensory signaling can have severe consequences for bladder sensation and function including the development of OAB and IC/BPS. Advancing therapeutic treatments for OAB and IC/BPS requires a deeper understanding of the mechanisms underlying the generation of bladder sensation, and key areas for future research have been identified.

Dental Tissue Engineering by Neural Differentiation of Dental Stem Cells and Nano-systems: A Review

Background: Pulpitis is a pulpal inflammation. It generally occurs when there is inflammation within a tooth as a result of anything like grinding or decay. After dental inflammation, microcirculation and sensory nerve activity seem to play the most critical role in reducing inflammation. Therefore, researchers emphasize the study of dental nerve activity, especially in acute clinical problems in inflamed teeth and pulp regeneration. This review aims to investigate the possibility of using dental stem cells to regenerate dental nerves in order to repair dentin-pulp complexes for maintaining and restoring tooth structure and function, which nanosystems can help in this matter. Materials and Methods: In this paper, we review the literature regarding the theory of dental tissue engineering by neural differentiation of dental stem cells and nano-systems, and the comprehensive search on PubMed, Scopus, and Web of Science was conducted up to July 2022. Results: According to recent studies, dental soft and hard tissue healing also includes nerve fibers. A deeper understanding of how dental nerves are implicated in pulpitis may assist endodontic treatment. Stem cell-based treatments may be used to regenerate dental nerves to repair dentin-pulp complexes to maintain and restore tooth structure and function. Conclusion: The emphasis on dental nerve regeneration appears to be a critical stage in fostering spontaneous tooth regeneration as well as a sustainable tooth regeneration method. It is essential to further investigate dental tissue engineering by neural differentiation of dental stem cells.

Efferent involvement in neural adaptation to acoustical stimuli: Insights from otoacoustic emissions

Neural adaptation to sound level statistics has been demonstrated at various levels of the auditory pathway, including the auditory periphery. Adaptation is thought to improve the efficiency of encoding acoustic stimuli using limited neural resources without compromising accuracy. However, the precise mechanisms underlying the statistical learning of an acoustic environment are not fully understood. This includes the potential contribution to the stimulus-specific modulation of afferent auditory nerve activity by the medial olivocochlear reflex (MOCR), an efferent feedback loop linking the brainstem to the cochlear amplifier. We used otoacoustic emissions (OAEs) to investigate evidence of neural adaptation in the MOCR in response to broadband elicitors of fluctuating intensity whose mean levels were either predictable (alternating low [48 dB SPL] and high [66 dB SPL]) or unpredictable (randomly occurring low and high mean levels). Magnitudes and time-courses of the MOCR obtained in normal-hearing ears were compared for differences based on the presence or absence of an acoustically predictable context. Our findings will provide valuable insights into the role of the efferent auditory system in neural adaptation to acoustical stimuli at the auditory periphery.

A multivariate physiological model of vagus nerve signalling during metabolic challenges in anaesthetised rats for diabetes treatment

Objective. This study aims to develop a comprehensive decoding framework to create a multivariate physiological model of vagus nerve transmission that reveals the complex interactions between the nervous and metabolic systems. Approach. Vagus nerve activity was recorded in female Sprague-Dawley rats using gold hook microwires implanted around the left cervical vagus nerve. The rats were divided into three experimental cohorts (intact nerve, ligation nerve for recording afferent activation, and ligation for recording efferent activation) and metabolic challenges were administered to change glucose levels while recording the nerve activity. The decoding methodology involved various techniques, including continuous wavelet transformation, extraction of breathing rate (BR), and correlation of neural metrics with physiological signals. Main results. Decrease in glucose level was consistently negatively correlated with an increase in the firing activity of the intact vagus nerve that was found to be conveyed by both afferent and efferent pathways, with the afferent response being more similar to the one on the intact nerve. A larger variability was observed in the sensory and motor responses to hyperglycaemia. A novel strategy to extract the BR over time based on inter-burst-interval is also presented. The vagus afferent was found to encode breathing information through amplitude and firing rate modulation. Modulations of the signal amplitude were also observed due to changes in heart rate in the intact and efferent recordings, highlighting the parasympathetic control of the heart. Significance. The analytical framework presented in this study provides an integrative understanding that considers the relationship between metabolic, cardiac, and breathing signals and contributes to the development of a multivariable physiological model for the transmission of vagus nerve signals. This work progresses toward the development of closed-loop neuro-metabolic therapeutic systems for diabetes.

Effectiveness of motor and prefrontal cortical areas for brain-controlled functional electrical stimulation neuromodulation

Objective. Brain-computer interface (BCI)-controlled functional electrical stimulation (FES) could excite the central nervous system to enhance upper limb motor recovery. Our current study assessed the effectiveness of motor and prefrontal cortical activity-based BCI-FES to help elucidate the underlying neuromodulation mechanisms of this neurorehabilitation approach. Approach. The primary motor cortex (M1) and prefrontal cortex (PFC) BCI-FES interventions were performed for 25 min on separate days with twelve non-disabled participants. During the interventions, a single electrode from the contralateral M1 or PFC was used to detect event-related desynchronization (ERD) in the calibrated frequency range. If the BCI system detected ERD within 15 s of motor imagery, FES activated wrist extensor muscles. Otherwise, if the BCI system did not detect ERD within 15 s, a subsequent trial was initiated without FES. To evaluate neuromodulation effects, corticospinal excitability was assessed using single-pulse transcranial magnetic stimulation, and cortical excitability was assessed by motor imagery ERD and resting-state functional connectivity before, immediately, 30 min, and 60 min after each intervention. Main results. M1 and PFC BCI-FES interventions had similar success rates of approximately 80%, while the M1 intervention was faster in detecting ERD activity. Consequently, only the M1 intervention effectively elicited corticospinal excitability changes for at least 60 min around the targeted cortical area in the M1, suggesting a degree of spatial localization. However, cortical excitability measures did not indicate changes after either M1 or PFC BCI-FES. Significance. Neural mechanisms underlying the effectiveness of BCI-FES neuromodulation may be attributed to the M1 direct corticospinal projections and/or the closer timing between ERD detection and FES, which likely enhanced Hebbian-like plasticity by synchronizing cortical activation detected by the BCI system with the sensory nerve activation and movement related reafference elicited by FES.

Neuropathic pain; what we know and what we should do about it.

Neuropathic pain can result from injury to, or disease of the nervous system. It is notoriously difficult to treat. Peripheral nerve injury promotes Schwann cell activation and invasion of immunocompetent cells into the site of injury, spinal cord and higher sensory structures such as thalamus and cingulate and sensory cortices. Various cytokines, chemokines, growth factors, monoamines and neuropeptides effect two-way signalling between neurons, glia and immune cells. This promotes sustained hyperexcitability and spontaneous activity in primary afferents that is crucial for onset and persistence of pain as well as misprocessing of sensory information in the spinal cord and supraspinal structures. Much of the current understanding of pain aetiology and identification of drug targets derives from studies of the consequences of peripheral nerve injury in rodent models. Although a vast amount of information has been forthcoming, the translation of this information into the clinical arena has been minimal. Few, if any, major therapeutic approaches have appeared since the mid 1990's. This may reflect failure to recognise differences in pain processing in males vs. females, differences in cellular responses to different types of injury and differences in pain processing in humans vs. animals. Basic science and clinical approaches which seek to bridge this knowledge gap include better assessment of pain in animal models, use of pain models which better emulate human disease, and stratification of human pain phenotypes according to quantitative assessment of signs and symptoms of disease. This can lead to more personalized and effective treatments for individual patients. Significance statement: There is an urgent need to find new treatments for neuropathic pain. Although classical animal models have revealed essential features of pain aetiology such as peripheral and central sensitization and some of the molecular and cellular mechanisms involved, they do not adequately model the multiplicity of disease states or injuries that may bring forth neuropathic pain in the clinic. This review seeks to integrate information from the multiplicity of disciplines that seek to understand neuropathic pain; including immunology, cell biology, electrophysiology and biophysics, anatomy, cell biology, neurology, molecular biology, pharmacology and behavioral science. Beyond this, it underlines ongoing refinements in basic science and clinical practice that will engender improved approaches to pain management.

Inhibitory Gating of Thalamocortical Inputs onto Rat Gustatory Insular Cortex.

In primary gustatory cortex (GC), a subregion of the insular cortex, neurons show anticipatory activity, encode taste identity and palatability, and their activity is related to decision-making. Inactivation of the gustatory thalamus, the parvicellular region of the ventral posteromedial thalamic nucleus (VPMpc), dramatically reduces GC taste responses, consistent with the hypothesis that VPMpc-GC projections carry taste information. Recordings in awake rodents reported that taste-responsive neurons can be found across GC, without segregated spatial mapping, raising the possibility that projections from the taste thalamus may activate GC broadly. In addition, we have shown that cortical inhibition modulates the integration of thalamic and limbic inputs, revealing a potential role for GABA transmission in gating sensory information to GC. Despite this wealth of information at the system level, the synaptic organization of the VPMpc-GC circuit has not been investigated. Here, we used optogenetic activation of VPMpc afferents to GC in acute slice preparations from rats of both sexes to investigate the synaptic properties and organization of VPMpc afferents in GC and their modulation by cortical inhibition. We hypothesized that VPMpc-GC synapses are distributed across GC, but show laminar- and cell-specific properties, conferring computationally flexibility to how taste information is processed. We also found that VPMpc-GC synaptic responses are strongly modulated by the activity regimen of VPMpc afferents, as well as by cortical inhibition activating GABAA and GABAB receptors onto VPMpc terminals. These results provide a novel insight into the complex features of thalamocortical circuits for taste processing.SIGNIFICANCE STATEMENT We report that the input from the primary taste thalamus to the primary gustatory cortex (GC) shows distinct properties compared with primary thalamocortical synapses onto other sensory areas. Ventral posteromedial thalamic nucleus afferents in GC make synapses with excitatory neurons distributed across all cortical layers and display frequency-dependent short-term plasticity to repetitive stimulation; thus, they do not fit the classic distinction between drivers and modulators typical of other sensory thalamocortical circuits. Thalamocortical activation of GC is gated by cortical inhibition, providing local corticothalamic feedback via presynaptic ionotropic and metabotropic GABA receptors. The connectivity and inhibitory control of thalamocortical synapses in GC highlight unique features of the thalamocortical circuit for taste.

Negative Emotions Recruit the Parabrachial Nucleus Efferent to the VTA to Disengage Instrumental Food Seeking.

The parabrachial nucleus (PBN) interfaces between taste and feeding systems and is also an important hub for relaying distress information and threats. Despite that the PBN sends projections to the ventral tegmental area (VTA), a heterogeneous brain region that regulates motivational behaviors, the function of the PBN-to-VTA connection remains elusive. Here, by using male mice in several behavioral paradigms, we discover that VTA-projecting PBN neurons are significantly engaged in contextual fear, restraint or mild stress but not palatable feeding, visceral malaise, or thermal pain. These results suggest that the PBN-to-VTA input may relay negative emotions under threat. Consistent with this notion, optogenetic activation of PBN-to-VTA glutamatergic input results in aversion, which is sufficient to override palatable feeding. Moreover, in a palatable food-reinforced operant task, we demonstrate that transient optogenetic activation of PBN-to-VTA input during food reward retrieval disengages instrumental food-seeking behaviors but spares learned action-outcome association. By using an activity-dependent targeting approach, we show that VTA DA neurons are disengaged by the PBN afferent activation, implicating that VTA non-DA neurons may mediate PBN afferent regulation. We further show that optogenetic activation of VTA neurons functionally recruited by the PBN input results in aversion, dampens palatable feeding, and disengages palatable food self-administration behavior. Finally, we demonstrate that transient activation of VTA glutamatergic, but not GABAergic, neurons recapitulates the negative regulation of the PBN input on food self-administration behavior. Together, we reveal that the PBN-to-VTA input conveys negative affect, likely through VTA glutamatergic neurons, to disengage instrumental food-seeking behaviors.SIGNIFICANCE STATEMENT The PBN receives multiple inputs and thus is well positioned to route information of various modalities to engage different downstream circuits to attend or respond accordingly. We demonstrate that the PBN-to-VTA input conveys negative affect and then triggers adaptive prioritized responses to address pertinent needs by withholding ongoing behaviors, such as palatable food seeking or intake shown in the present study. It has evolutionary significance because preparing to cope with stressful situations or threats takes priority over food seeking to promote survival. Knowing how appropriate adaptive responses are generated will provide new insights into circuitry mechanisms of various coping behaviors to changing environmental stimuli.

KV7 but not dual small and intermediate KCa channel openers inhibit the activation of colonic afferents by noxious stimuli.

In numerous subtypes of central and peripheral neurons, small and intermediate conductance Ca2+-activated K+ (SK and IK, respectively) channels are important regulators of neuronal excitability. Transcripts encoding SK channel subunits, as well as the closely related IK subunit, are coexpressed in the soma of colonic afferent neurons with receptors for the algogenic mediators ATP and bradykinin, P2X3 and B2, highlighting the potential utility of these channels as drug targets for the treatment of abdominal pain in gastrointestinal diseases such as irritable bowel syndrome. Despite this, pretreatment with the dual SK/IK channel opener SKA-31 had no effect on the colonic afferent response to ATP, bradykinin, or noxious ramp distention of the colon. Inhibition of SK or IK channels with apamin or TRAM-34, respectively, yielded no change in spontaneous baseline afferent activity, indicating these channels are not tonically active. In contrast to its lack of effect in electrophysiological experiments, comparable concentrations of SKA-31 abolished ongoing peristaltic activity in the colon ex vivo. Treatment with the KV7 channel opener retigabine blunted the colonic afferent response to all applied stimuli. Our data therefore highlight the potential utility of KV7, but not SK/IK, channel openers as analgesic agents for the treatment of abdominal pain.NEW & NOTEWORTHY Despite marked coexpression of small (Kcnn1, Kcnn2) and intermediate (Kcnn4) conductance calcium-activated potassium channel transcripts with P2X3 (P2rx3) or bradykinin B2 (Bdkrb2) receptors in colonic sensory neurons, pharmacological activation of these channels had no effect on the colonic afferent response to ATP, bradykinin or luminal distension of the colon. This is in contrast to the robust inhibitory effect of the KV7 channel opener, retigabine.

Abstract 057: The Positive Effect Of Renal Denervation Persists Even Through Regrowth Of Afferent Axons Improving Renal Afferent Nerve Activity During High Sodium Intake In Rats

Introduction: Previous work of ours suggests that pathologically decreased sensitivity of renal afferent neurons (reduced number of highly active tonic neurons) due to high salt diet is normalized 1 wk after renal denervation (DNX). Now we tested the hypothesis that normalized sensitivity of renal neurons persists after DNX even through regrowth of afferent axons after 12 wk. This morphological regrowth of afferent nerves 12wk after renal DNX (postDNX) was shown by us previously. Material and methods: 6 male Sprague Dawley (SD) rats were put on high salt diet (HS; 8% NaCl) for 10 days. In another group of 12 rats on high salt diet (HS) left kidneys were denervated (postDNX) 12 weeks prior to examination. Rats on standard diet were used as controls. Harvested dorsal root ganglion neurons (DRG Th11-L2) with renal afferents were investigated in primary neuronal cell culture using current clamp mode to assess action potential generation during current injection and to characterize neurons as tonic highly active and phasic less active neurons. Results: In renal neurons from rats on HS the relation of tonic to phasic neurons shifted towards less active phasic units (62% tonic neurons in controls [n=72 out of 114] vs. 42% [n=37 out of 86] on HS, (p<0.05, z-test)). Denervation of the left kidney in rats on high salt diet (HS-DNX) led to a recovery of afferent renal DRG neurons after 1 wk; (40% tonic neurons [n=32 out of 80] on HS vs. 72% tonic neurons [n=58 out of 81] on HS+DNX)(p<0.05, z-test)). Even 12 weeks after renal denervation this regained electrophysiological property of tonic firing persisted (43% tonic neurons [n=35 out of 82] on HS vs. 69% tonic neurons [n=46 of 67]on HS-postDNX, p<0.05, z-test)). Conclusion: The reduced proportion of highly active tonic neurons increased 1 wk after renal denervation to control levels. Even 12 weeks after renal denervation, this effect of renal denervation persisted, and the sensitivity of renal neurons to electrical stimuli did not change despite high-salt diet. Hence, the positive effects of renal denervation persisted even through the regrowth of renal afferent axons to the kidney.