Nucleus Of The Solitary Tract Research Articles

An NTS-CeA projection modulates depression-like behaviors in a mouse model of chronic pain

Depressive symptoms comorbid with chronic pain are a common health problem, but the underlying neural circuit mechanisms remain elusive. Here, we identify a glutamatergic projection from the nucleus of the solitary tract (NTS) to the central nucleus of the amygdala (CeA) that mediates depression-like behaviors in a chemotherapy-induced neuropathic pain model. Inhibition or ablation of the glutamatergic NTS neurons alleviates depressive but not hypersensitive behaviors in these mice. The projected neurons form excitatory synapses with somatostatin-expressing neurons in the CeA. Silencing the NTS-CeA projection alleviates depressive but not hypersensitive behaviors, whereas activating the proection promotes depressive behaviors. In addition, in naïve mice, activation of the NTS-CeA projection induces obvious depressive behaviors that can be blocked by silencing the CeA somatostatin-expressing neurons. Together, we reveal a modulatory role of the NTS and its glutamatergic projection to the CeA circuit in modulating depression-like behaviors comorbid to chronic pain.

The development of a novel antioxidant-based antiemetic drug to improve quality of life during anticancer therapy

Anticancer agents can effectively treat several types of cancers but are often limited in clinical settings due to various adverse effects. In particular, nausea and vomiting are serious side effects that markedly reduce the patients' quality of life. Accordingly, the development of novel antiemetic drugs that lack side effects is crucial, given that most conventional antiemetic drugs are known to possess side effects. In addition, reactive oxygen species generated by anticancer agents are involved in nausea and vomiting; hence, appropriate antioxidants might also be effective toward nausea and vomiting.Silicon (Si)-based agents can abundantly generate antioxidant hydrogen in the intestine. Therefore, we assessed whether Si-based agents could be effective against nausea associated with anticancer agents in cisplatin-injected mice. We observed numerous neurons expressing c-Fos protein, a neuronal activity marker, in the nausea-associated regions of the dorsal medulla (area postrema, nuclei of the solitary tract, and dorsal vagal nuclei) 24 h after cisplatin injection. Conversely, mice fed a diet containing 2.5% Si-based agents showed a reduction in c-Fos-positive neurons.These findings revealed that the Si-based agent alleviated cisplatin-induced nausea. Si-based agents demonstrate potent antioxidant effects by producing hydrogen, which has no known side effects and will be a safer antiemetic agent and greatly help improve the quality of life of patients undergoing anticancer drug treatment.

The Neural Code for Taste in the Nucleus of the Solitary Tract of Rats with Obesity Following Roux-En-Y Gastric Bypass Surgery.

Previous work has shown that taste responses in the nucleus tractus solitarius (NTS; the first central relay for gustation) are blunted in rats with diet-induced obesity (DIO). Here, we studied whether these effects could be reversed by Roux-en-Y gastric bypass (RYGB) surgery, an effective treatment for obesity. Rats were fed a high energy diet (60% kcal fat; HED) both before and after undergoing RYGB. Electrophysiological responses from NTS cells in unrestrained rats were recorded as they licked tastants from a lick spout. Sweet, salty, and umami tastes, as well as their naturalistic counterparts, were presented. Results were compared with those of lean rats from a previous study. As with DIO rats, NTS cells in RYGB rats were more narrowly tuned, showed weaker responses, and less lick coherence than those in lean rats. Both DIO and RYGB rats licked at a slower rate than lean rats and paused more often during a lick bout. However, unlike DIO rats, the proportion of taste cells in RYGB rats was similar to that in lean rats. Our data show that, despite being maintained on a HED after surgery, RYGB can induce a partial recovery of the deficits seen in the NTS of DIO rats.

Vertebral artery dissection induced lateral medullary syndrome characterized with severe bradycardia: a case report and review of the literature

Lateral medullary syndrome is the most common type of brainstem infarction. Lateral medullary syndrome results in damage to the corresponding cranial nerve nuclei and the nucleus tractus solitarius, with vertigo, ipsilateral ataxia, crossed sensory disturbances, Horner's sign, bulbar palsy, and other underlying symptoms or signs. However, cases with cardiac arrhythmia and other autonomic dysfunctions as the primary manifestations are less common. Clinically, sudden death occasionally occurs in patients with lateral medullary syndrome, which may be associated with severe cardiac arrhythmia. These patients may suffer in life-threatening arrhythmia and even cardiac arrest, and vital signs should be closely monitored to prevent sudden death. In younger patients, vertebral artery dissection is the most common cause. Here, we present a case of lateral medullary syndrome caused by vertebral artery dissection with severe bradycardia. The patient was a 49-year-old man who was admitted with "sudden onset of numbness in the left limbs and right side of the face for 1 hour". Electrocardiogram (ECG) monitoring showed a repeated heart rate decrease to as low as 23 beats/min, followed by a gradual increase in heart rate to 35-55 beats/min after 2-3 seconds. Head magnetic resonance imaging (MRI) examination revealed right dorsolateral cerebral infarction of the medulla oblongata. Digital subtraction angiography (DSA) revealed a right vertebral artery dissecting aneurysm. We performed an emergency placement of a temporary pacemaker, followed by conservative treatment with platelet aggregation inhibitors, vascular softening agents and improved collateral circulation. Elective spring coil embolization of the vertebral artery dissecting aneurysm and stent implantation were performed. At outpatient follow-up, the patient had a good prognosis. Clinical management of patients with lateral medullary syndrome should be prioritized, with close cardiac monitoring at the early stages of observation and pacemaker placement and tracheal intubation as required to prevent adverse events.

Distinct effects of orexin A on spontaneous and evoked synaptic currents in the rat nucleus tractus solitarius

Orexins are produced in hypothalamic areas and orexin-containing neurons are distributed in widespread areas of the central nervous system. Orexins regulate several physiological functions such as arousal, food intake and autonomic control. The presence of orexin-containing neuron terminals and orexin receptors has been confirmed in the nucleus tractus solitarius (NTS), which receives primary afferent fibers from peripheral organs including baroreceptors. However, the neuronal effects of orexin-1 receptor (OX1R) activation were not examined. Here, we aimed to determine the effects of OX1R activation on excitatory synaptic transmission. OX1R activation increased the frequency of spontaneous excitatory synaptic currents (sEPSCs). This effect was blocked by the prior application of L-NAME. In contrast, the amplitude of evoked excitatory postsynaptic currents (eEPSCs) was suppressed by OX1R activation, and this effect was prevented by a cannabinoid receptor 1 blocker, AM251, but not by the pretreatment with L-NAME. Altogether, these results suggest that OX1R activation increases sEPSCs frequency by stimulating NO production, whereas it inhibits eEPSCs by releasing endocannabinoids in the NTS. Thus, OX1R activation had distinct effects on spontaneous and evoked excitatory synaptic transmissions in the NTS.

Organisation of enkephalin inputs and outputs of the central nucleus of the amygdala in mice

The central nucleus of the amygdala (CeA) is a key hub integrating sensory inputs and modulating behavioural outputs. The CeA is a complex structure with discrete subdivisions, high peptidergic heterogeneity and broad CNS afferent and efferent projections. While several neuropeptide systems within the CeA have been examined in detail, less is known about CeA preproenkephalin (ppENK) cells. Here, we used a recently developed transgenic Penk-Cre mouse line to advance our understanding of the efferent and afferent connectivity of ppENK in the CeA. First, to determine the fidelity of Cre expression in Penk-Cre transgenic mice, we conducted RNAscope in the CeA of Penk-Cre mice. Our analysis revealed that 96.6 % of CeA Cre+ neurons co-expressed pENK mRNA, and 99.7 % of CeA pENK+ neurons co-expressed Cre mRNA, indicating faithful recapitulation of Cre expression in CeA ppENK-expressing cells, supporting the fidelity of the Penk-Cre reporter mouse. Anterograde tracing of CeAPenk cells showed strong efferent projections to the extended amygdala, midbrain and hindbrain PBN and NTS. Retrograde tracing of Penk afferents to the CeA were more restricted, with primary innervation originating within the amygdala complex and bed nucleus of the stria terminalis, and minor innervation from the parabrachial nucleus and nucleus of the solitary tract. Together, our data provide a comprehensive map of ENKergic efferent and afferent connectivity of the CeA in Penk-Cre mice. Further, we highlight both the utility and limitations of the Penk-Cre mice to study the function of CeA, PBN and NTS ppENK cells.

Cardiovascular baroreflex circuit moonlights in sleep control

Sleep disturbances are strongly associated with cardiovascular diseases. Baroreflex, a basic cardiovascular regulation mechanism, is modulated by sleep-wake states. Here, we show that neurons at key stages of baroreflex pathways also promote sleep. Using activity-dependent genetic labeling, we tagged neurons in the nucleus of the solitary tract (NST) activated by blood pressure elevation and confirmed their barosensitivity with optrode recording and calcium imaging. Chemogenetic or optogenetic activation of these neurons promoted non-REM sleep in addition to decreasing blood pressure and heart rate. GABAergic neurons in the caudal ventrolateral medulla (CVLM)-a downstream target of the NST for vasomotor baroreflex-also promote non-REM sleep, partly by inhibiting the sympathoexcitatory and wake-promoting adrenergic neurons in the rostral ventrolateral medulla (RVLM). Cholinergic neurons in the nucleus ambiguous-a target of the NST for cardiac baroreflex-promoted non-REM sleep as well. Thus, key components of the cardiovascular baroreflex circuit are also integral to sleep-wake brain-state regulation.

Inhibition of Water-Evoked Swallowing During Noxious Mechanical Stimulation of Tongue in Anesthetized Rats.

Dysphagia is sometimes accompanied by pain. Because orofacial structures subserve mastication and swallowing, orofacial pain might impair both functions. Tongue biting can occur not only accidentally while eating but also in some pathological conditions. However, it remains unclear whether noxious mechanical stimulation of the tongue affects swallowing. To explore this question, we evaluated the effects of lingual pinch stimulation on the initiation of swallowing evoked by distilled water (DW) infusion with a flow rate of 5.0µL/s for 20s into the pharyngolaryngeal region in anesthetized rats. The swallowing reflex was identified by electromyographic (EMG) bursts in the suprahyoid muscles which include the anterior belly of the digastric muscle, mylohyoid and geniohyoid muscles, and laryngeal elevation by visual inspection. The number of DW-evoked swallows during pinch stimulation was significantly smaller than that in a control condition or during pressure stimulation. The onset latency of the first swallow during pinch stimulation was significantly longer than that in the control condition. DW-evoked swallowing was almost abolished following bilateral transection of the superior laryngeal nerve (SLN) compared with the control condition, suggesting that the SLN plays a crucial role in the initiation of DW-evoked swallowing. Finally, electrophysiological data indicated that some SLN-responsive neurons in the nucleus tractus solitarii (nTS) exhibited delayed latency from a single SLN stimulation during lingual pinch stimulation. These results suggest that noxious mechanical stimulation of the tongue inhibits the initiation of swallowing and modulates neuronal activity in the nTS.

Sleep architecture and sleep-disordered breathing in fatal insomnia

Study objectivesFatal insomnia (FI) is a rare prion disease severely affecting sleep architecture. Breathing during sleep has not been systematically assessed. Our aim was to characterize the sleep architecture, respiratory patterns, and neuropathologic findings in FI. MethodsEleven consecutive FI patients (ten familial, one sporadic) were examined with video-polysomnography (vPSG) between 2002 and 2017. Wake/sleep stages and respiration were evaluated using a modified scoring system. Postmortem neuropathology was assessed in seven patients. ResultsMedian age at onset was 48 years and survival after vPSG was 1 year. All patients had different combinations of breathing disturbances including increased respiratory rate variability (RRV; n = 7), stridor (n = 9), central sleep apnea (CSA) (n = 5), hiccup (n = 6), catathrenia (n = 7), and other expiratory sounds (n = 10). RRV in NREM sleep correlated with ambiguous and solitary nuclei degeneration (r = 0.9, p = 0.008) and reduced survival (r = −0.7, p = 0.037). Two new stages, Subwake1 and Subwake2, present in all patients, were characterized. NREM sleep (conventional or undifferentiated) was identifiable in ten patients but reduced in duration in eight. REM sleep occurred in short segments in nine patients, and their reduced duration correlated with medullary raphe nuclei degeneration (r = −0.9, p = 0.005). Seven patients had REM without atonia. Three vPSG patterns were identified: agitated, with aperiodic, manipulative, and finalistic movements (n = 4); quiet-apneic, with CSA (n = 4); and quiet-non-apneic (n = 3). ConclusionsFI patients show frequent breathing alterations, associated with respiratory nuclei damage, and, in addition to NREM sleep distortion, have severe impairment of REM sleep, related with raphe nuclei degeneration. Brainstem impairment is crucial in FI.

Brainstem ADCYAP1+ neurons control multiple aspects of sickness behaviour

Infections induce a set of pleiotropic responses in animals, including anorexia, adipsia, lethargy and changes in temperature, collectively termed sickness behaviours1. Although these responses have been shown to be adaptive, the underlying neural mechanisms have not been elucidated2–4. Here we use of a set of unbiased methodologies to show that a specific subpopulation of neurons in the brainstem can control the diverse responses to a bacterial endotoxin (lipopolysaccharide (LPS)) that potently induces sickness behaviour. Whole-brain activity mapping revealed that subsets of neurons in the nucleus of the solitary tract (NTS) and the area postrema (AP) acutely express FOS after LPS treatment, and we found that subsequent reactivation of these specific neurons in FOS2A-iCreERT2 (also known as TRAP2) mice replicates the behavioural and thermal component of sickness. In addition, inhibition of LPS-activated neurons diminished all of the behavioural responses to LPS. Single-nucleus RNA sequencing of the NTS–AP was used to identify LPS-activated neural populations, and we found that activation of ADCYAP1+ neurons in the NTS–AP fully recapitulates the responses elicited by LPS. Furthermore, inhibition of these neurons significantly diminished the anorexia, adipsia and locomotor cessation seen after LPS injection. Together these studies map the pleiotropic effects of LPS to a neural population that is both necessary and sufficient for canonical elements of the sickness response, thus establishing a critical link between the brain and the response to infection.

Taste Impairments in a Parkinson’s Disease Model Featuring Intranasal Rotenone Administration in Mice

Background:Taste impairments are often accompanied by olfactory impairments in the early stage of Parkinson’s disease (PD). The development of animal models is required to elucidate the mechanisms underlying taste impairments in PD.Objective:This study was conducted to clarify whether the intranasal administration of rotenone causes taste impairments prior to motor deficits in mice.Methods:Rotenone was administrated to the right nose of mice once a day for 1 or 4 week(s). In the 1-week group, taste, olfactory, and motor function was assessed before and after a 1-week recovery period following the rotenone administration. Motor function was also continuously examined in the 4-weeks group from 0 to 5 weeks. After a behavioral test, the number of catecholamine neurons (CA-Nos) was counted in the regions responsible for taste, olfactory, and motor function.Results:taste and olfactory impairments were simultaneously observed without locomotor impairments in the 1-week group. The CA-Nos was significantly reduced in the olfactory bulb and nucleus of the solitary tract. In the 4-week group, locomotor impairments were observed from the third week, and a significant reduction in the CA-Nos was observed in the substantia nigra (SN) and ventral tegmental area (VTA) at the fifth week along with the weight loss.Conclusion:The intranasal administration of rotenone caused chemosensory and motor impairments in an administration time-period dependent manner. Since chemosensory impairments were expressed prior to the locomotor impairments followed by SN/VTA CA neurons loss, this rotenone administration model may contribute to the clarification of the prodromal symptoms of PD.

Ticking and talking in the brainstem satiety centre: Circadian timekeeping and interactions in the diet-sensitive clock of the dorsal vagal complex.

The dorsal vagal complex (DVC) is a key hub for integrating blood-borne, central, and vagal ascending signals that convey important information on metabolic and homeostatic state. Research implicates the DVC in the termination of food intake and the transition to satiety, and consequently it is considered a brainstem satiety centre. In natural and laboratory settings, animals have distinct times of the day or circadian phases at which they prefer to eat, but if and how circadian signals affect DVC activity is not well understood. Here, we evaluate how intrinsic circadian signals regulate molecular and cellular activity in the area postrema (AP), nucleus of the solitary tract (NTS), and dorsal motor nucleus of the vagus (DMV) of the DVC. The hierarchy and potential interactions among these oscillators and their response to changes in diet are considered a simple framework in which to model these oscillators and their interactions is suggested. We propose possible functions of the DVC in the circadian control of feeding behaviour and speculate on future research directions including the translational value of knowledge of intrinsic circadian timekeeping the brainstem.

TRPV1: A Common Denominator Mediating Antinociceptive and Antiemetic Effects of Cannabinoids.

The most common medicinal claims for cannabis are relief from chronic pain, stimulation of appetite, and as an antiemetic. However, the mechanisms by which cannabis reduces pain and prevents nausea and vomiting are not fully understood. Among more than 450 constituents in cannabis, the most abundant cannabinoids are Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD). Cannabinoids either directly or indirectly modulate ion channel function. Transient receptor potential vanilloid 1 (TRPV1) is an ion channel responsible for mediating several modalities of pain, and it is expressed in both the peripheral and the central pain pathways. Activation of TRPV1 in sensory neurons mediates nociception in the ascending pain pathway, while activation of TRPV1 in the central descending pain pathway, which involves the rostral ventral medulla (RVM) and the periaqueductal gray (PAG), mediates antinociception. TRPV1 channels are thought to be implicated in neuropathic/spontaneous pain perception in the setting of impaired descending antinociceptive control. Activation of TRPV1 also can cause the release of calcitonin gene-related peptide (CGRP) and other neuropeptides/neurotransmitters from the peripheral and central nerve terminals, including the vagal nerve terminal innervating the gut that forms central synapses at the nucleus tractus solitarius (NTS). One of the adverse effects of chronic cannabis use is the paradoxical cannabis-induced hyperemesis syndrome (HES), which is becoming more common, perhaps due to the wider availability of cannabis-containing products and the chronic use of products containing higher levels of cannabinoids. Although, the mechanism of HES is unknown, the effective treatment options include hot-water hydrotherapy and the topical application of capsaicin, both activate TRPV1 channels and may involve the vagal-NTS and area postrema (AP) nausea and vomiting pathway. In this review, we will delineate the activation of TRPV1 by cannabinoids and their role in the antinociceptive/nociceptive and antiemetic/emetic effects involving the peripheral, spinal, and supraspinal structures.

Brain Insulin Receptor Antagonism Augments The Blood Pressure Response To Activation Of The Exercise Pressor Reflex

Type 2 diabetes mellitus (T2DM) results in abnormal control of blood pressure (BP). However, the underlying mechanisms remain to be elucidated. The transport of insulin into the central nervous system is decreased in T2DM. The resultant central hypoinsulinemia reduces neuronal excitability. The nucleus tractus solitarius (NTS) is a key central integration site for incoming signals from peripheral sensory neurons including input from working skeletal muscle and arterial baroreceptors. Working skeletal muscle activates primary sensory fibers and evokes the exercise pressor reflex (EPR) to reflexively increase BP, a response modulated by the baroreflex. Central hypoinsulinemia in T2DM may influence how neurons in the NTS process this sensory information during exercise affecting BP responsiveness. PURPOSE: To determine whether acute antagonism of insulin receptors in the NTS alters EPR function in baro-intact and barodenervated rats. METHODS: L4 and L5 ventral roots were electrically stimulated in healthy decerebrated male Sprague-Dawley rats to evoke hindlimb muscle contraction and EPR activation in intact and sino-aortic barodenervated rats. Mean arterial pressure (MAP) responses to activation of the EPR were assessed before and 30 min following NTS microinjections of the insulin receptor antagonist, GSK1838705 (100uM), or vehicle, dimethyl sulfoxide (DMSO). RESULTS: In baro-intact rats, contraction-induced changes in MAP were significantly greater following GSK1838705 (Pre, 16 ± 10 mmHg vs. Post, 23 + 13 mmHg, n = 11, p < 0.01) but not DMSO (Pre, 15 ± 8 mmHg vs. Post, 15 + 8 mmHg, n = 9). In barodenervated rats, neither GSK1838705 (Pre, 27 ± 16 mmHg vs. Post, 28 ± 21 mmHg, n = 8) nor DMSO (Pre, 34 ± 17 mmHg vs. Post, 30 ± 27 mmHg, n = 9) affected the MAP response to contraction. CONCLUSIONS: The findings demonstrate that central insulin receptor antagonism augments the BP response to EPR activation, which is abolished by barodenervation. The findings also suggest that insulin in the NTS maintains the capacity to buffer EPR-mediated increases in BP via baroreflex-mediated mechanisms. Alterations in this buffering capacity due to the central hypoinsulinemia in T2DM could account, in part, for the exaggerated pressor response to exercise in this disease. Supported by NIH-NHLBI, Lawson & Rogers Lacy Research Fund.

Vagus nerve stimulation increases stomach-brain coupling via a vagal afferent pathway

BackgroundMaintaining energy homeostasis is vital and supported by vagal signaling between digestive organs and the brain. Previous research has established a gastric network in the brain that is phase synchronized with the rhythm of the stomach, but tools to perturb its function were lacking. ObjectiveTo evaluate whether stomach-brain coupling can be acutely increased by non-invasively stimulating vagal afferent projections to the brain. MethodsUsing a single-blind randomized crossover design, we investigated the effect of acute right-sided transcutaneous auricular vagus nerve stimulation (taVNS) versus sham stimulation on stomach-brain coupling. ResultsIn line with preclinical research, taVNS increased stomach-brain coupling in the nucleus of the solitary tract (NTS) and the midbrain while boosting coupling across the brain. Crucially, in the cortex, taVNS-induced changes in coupling occurred primarily in transmodal regions and were associated with changes in hunger ratings as indicators of the subjective metabolic state. ConclusionstaVNS increases stomach-brain coupling via an NTS-midbrain pathway that signals gut-induced reward, indicating that communication between the brain and the body is effectively modulated by vago-vagal signaling. Such insights may help us better understand the role of vagal afferents in orchestrating the recruitment of the gastric network which could pave the way for novel neuromodulatory treatments.

Abstract P064: Anatomical Substrate For Leptin Control Of Central Autonomic Network Regulating Cardiovascular And Metabolic Functions

Leptin, a hormone secreted by adipose tissue, is a critical signal influencing energy balance and blood pressure through modulation of the autonomic nervous system. However, the anatomical substrates for leptin regulation of the central autonomic network underlying cardiovascular and metabolic functions remains unknown. Here, we used a retrograde pseudorabies virus encoding a green fluorescent protein (PRV-GFP) in mice expressing a red fluorescent (td-Tomato) in leptin receptor (LepR) neurons to map the LepR neurons that project polysynaptically to the kidneys, the left lobe of the liver, or the interscapular brown adipose tissue (iBAT). The animals were sacrificed at 5-, 6-, or 7-days post-PRV injection, the brain imaged using confocal microscopy, and co-localization quantified. We identified approximately 100 nuclei containing LepR neurons and more than 60 nuclei expressing GFP after PRV-GFP inoculation of the kidney, liver, or iBAT. Interestingly, 42 nuclei that express LepR neurons (tdTomato) also express GFP after PRV-GFP inoculation of either kidney, liver, or iBAT. Of these shared nuclei, we observed co-expression of tdTomato and GFP in only a few nuclei. After inoculation of PRV-GFP into kidneys, 25% of GFP expressing neurons in the preoptic (PO) nucleus co-localized with tdTomato while 3% co-localization was noted in the lateral hypothalamus (LH), and 1% in the nucleus of the solitary tract (nTS). For the liver, 35% co-localization was observed in the PO and 2.5% in the LH. For the iBAT, 20% co-localization was seen in the PO, 1.5% in the LH, and 8% in the nTS. Co-localization was also observed in other areas such as the septal nucleus, arcuate nucleus, dorsal and ventral medial hypothalamus, periaqueductal gray, and ventral tegmental area. In summary, LepR neurons projecting to the kidney, liver, or iBAT are present in specific regions such as the preoptic nuclei, some hypothalamic areas, and the nTS with the level of co-localization dependent on the organ. Our data suggest that although LepR neurons are distributed throughout the brain, those associated with the autonomic networks controlling cardiovascular and metabolic functions reside in specific regions of the brain.

Emx1-Cre Is Expressed in Peripheral Autonomic Ganglia That Regulate Central Cardiorespiratory Functions.

The Emx1-IRES-Cre transgenic mouse is commonly used to direct genetic recombination in forebrain excitatory neurons. However, the original study reported that Emx1-Cre is also expressed embryonically in peripheral autonomic ganglia, which could potentially affect the interpretation of targeted circuitry contributing to systemic phenotypes. Here, we report that Emx1-Cre is expressed in the afferent vagus nerve system involved in autonomic cardiorespiratory regulatory pathways. Our imaging studies revealed expression of Emx1-Cre driven tdtomato fluorescence in the afferent vagus nerve innervating the dorsal medulla of brainstem, cell bodies in the nodose ganglion, and their potential target structures at the carotid bifurcation such as the carotid sinus and the superior cervical ganglion (SCG). Photostimulation of the afferent terminals in the nucleus tractus solitarius (NTS) in vitro using Emx1-Cre driven ChR2 reliably evoked EPSCs in the postsynaptic neurons with electrophysiological characteristics consistent with the vagus afferent nerves. In addition, optogenetic stimulation targeting the Emx1-Cre expressing structures identified in this study, such as vagus nerve, carotid bifurcation, and the dorsal medulla surface transiently depressed cardiorespiratory rate in urethane anesthetized mice in vivo. Together, our study demonstrates that Emx1-IRES-Cre is expressed in the key peripheral autonomic nerve system and can modulate cardiorespiratory function independently of forebrain expression. These results raise caution when interpreting systemic phenotypes of Emx1-IRES-Cre conditional recombinant mice, and also suggest the utility of this line to investigate modulators of the afferent vagal system.

Characteristics and Impact of the rNST GABA Network on Neural and Behavioral Taste Responses.

The rostral nucleus of the solitary tract (rNST), the initial CNS site for processing gustatory information, is comprised of two major cell types, glutamatergic excitatory and GABAergic inhibitory neurons. Although many investigators have described taste responses of rNST neurons, the phenotypes of these cells were unknown. To directly compare the response characteristics of both inhibitory and noninhibitory neurons, we recorded from mice expressing Channelrhodopsin-2 (ChR2) under the control of GAD65, a synthetic enzyme for GABA. We observed that chemosensitive profiles of GABAergic taste neurons (G+TASTE) were similar to non-GABA taste neurons (G-TASTE) but had much lower response rates. We further observed a novel subpopulation of GABA cells located more ventrally in the nucleus that were unresponsive to taste stimulation (G+UNR), suggesting pathways for inhibition initiated by centrifugal sources. This preparation also allowed us to determine how optogenetic activation of the rNST GABA network impacted the taste responses of G-TASTE neurons. Activating rNST inhibitory circuitry suppressed gustatory responses of G-TASTE neurons across all qualities and chemosensitive types of neurons. Although the tuning curves of identified G-TASTE were modestly sharpened, the overall shape of response profiles and the ensemble pattern remained highly stable. These neurophysiological effects were consistent with the behavioral consequences of activating GAD65-expressing inhibitory neurons using DREADDs. In a brief-access licking task, concentration-response curves to both palatable (sucrose, maltrin) and unpalatable (quinine) stimuli were shifted to the right when GABA neurons were activated. Thus, the rNST GABAergic network is poised to modulate taste intensity across the qualitative and hedonic spectrum.

Abstract 051: Exploiting Angiotensin Sensitive Vagal Afferents To Understand And Alleviate Hypertension: A Closed Loop System For Blood Pressure Control

Cardiovascular homeostasis is maintained by neural signals arising from arterial baroreceptors (BRs) that apprise the brain of vascular stretch. Here, we test the overall hypothesis that angiotensin-II (AngII) type 1a receptor expressing neurons within the nodose ganglia (NDG AT1aR ) serve as BR that undergo plasticity during chronic elevations in BP. We found that NDG AT1aR receive input from the aortic arch, project to the caudal nucleus of the solitary tract (cNTS), and synthesize Piezo-1/-2. AT1aR-GCaMP6s mice were used to determine whether NDG AT1aR couple their firing to elevated BP. Two-photon intravital imaging revealed that phenylephrine (PE; i.v.) increased GCaMP6s fluorescence within NDG AT1aR (ΔF/F max = 0.65±0.05*, Time ΔF/Fmax = 92s) and this response was delayed in mice given DOCA-salt (Time ΔF/Fmax = 124s) or chronic AngII (Time ΔF/Fmax = 155s). To determine if optical perturbation of NDG AT1aR affects the baroreflex, expression of excitatory channelrhodpsin2 (ChR2) or inhibitory halorhodopsin (Halo) was directed to AT1aR cells. Optical excitation of NDG AT1aR at their axon terminals in the cNTS elicited frequency-dependent decreases in BP (ΔSBP @ 0.5, 1, 2, 3 Hz = -6.74±3.42 # , -9.75±2.33 # , -23.24±4.39 # , -25.27±4.38 # ) and HR (ΔHR @ 0.5, 1, 2, 3 Hz = -7.81±3.14 # , -14.86±3.22 # , -23.39±5.02 # , -23.66±4.13 # ). Conversely, optical inhibition of NDG AT1aR at axon terminals in the cNTS blunted pressor responses to PE (ΔHR PE(Min) = -36.15±5.31, ΔHR PE+Light(Min) = -23.11±3.33 + ). ChR2-expressing mice were then subjected to DOCA-salt. Optical excitation elicited hypotensive (ΔSBP Min = -21.11±4.05 + ) and bradycardic (ΔHR Min = -235.6±46.69 + ) responses; however, the duration of these effects was altered. We developed a closed loop system to target NDG AT1aR at axon terminals in the cNTS of ChR2-expressing mice to determine if these neurons can be exploited to alleviate hypertension. Mice were subjected to acute and chronic stimuli to elevate BP and stimulated by the system until BP returned below threshold. Collectively, these studies reveal the structure and function of NDG AT1aR and suggest that such neurons may be exploited to discern and relieve hypertension. ( p &lt; 0.05, * time by treatment, # time by frequency, or + time by light interaction)

A brainstem map for visceral sensations

The nervous system uses various coding strategies to process sensory inputs. For example, the olfactory system uses large receptor repertoires and is wired to recognize diverse odours, whereas the visual system provides high acuity of object position, form and movement1–5. Compared to external sensory systems, principles that underlie sensory processing by the interoceptive nervous system remain poorly defined. Here we developed a two-photon calcium imaging preparation to understand internal organ representations in the nucleus of the solitary tract (NTS), a sensory gateway in the brainstem that receives vagal and other inputs from the body. Focusing on gut and upper airway stimuli, we observed that individual NTS neurons are tuned to detect signals from particular organs and are topographically organized on the basis of body position. Moreover, some mechanosensory and chemosensory inputs from the same organ converge centrally. Sensory inputs engage specific NTS domains with defined locations, each containing heterogeneous cell types. Spatial representations of different organs are further sharpened in the NTS beyond what is achieved by vagal axon sorting alone, as blockade of brainstem inhibition broadens neural tuning and disorganizes visceral representations. These findings reveal basic organizational features used by the brain to process interoceptive inputs.