Using vagus nerve stimulation (VNS), we sought to determine the contribution of vagal afferents to efferent control of cardiac function. In anesthetized dogs, the right and left cervical vagosympathetic trunks were stimulated in the intact state, following ipsilateral or contralateral vagus nerve transection (VNTx), and then following bilateral VNTx. Stimulations were performed at currents from 0.25 to 4.0 mA, frequencies from 2 to 30 Hz, and a 500-μs pulse width. Right or left VNS evoked significantly greater current-and frequency-dependent suppression of chronotropic, inotropic, and lusitropic function subsequent to sequential VNTx. Bradycardia threshold was defined as the current first required for a 5% decrease in heart rate. The threshold for the right vs. left vagus-induced bradycardia in the intact state (2.91 ± 0.18 and 3.47 ± 0.20 mA, respectively) decreased significantly with right VNTx (1.69 ± 0.17 mA for right and 3.04 ± 0.27 mA for left) and decreased further following bilateral VNTx (1.29 ± 0.16 mA for right and 1.74 ± 0.19 mA for left). Similar effects were observed following left VNTx. The thresholds for afferent-mediated effects on cardiac parameters were 0.62 ± 0.04 and 0.65 ± 0.06 mA with right and left VNS, respectively, and were reflected primarily as augmentation. Afferent-mediated tachycardias were maintained following β-blockade but were eliminated by VNTx. The increased effectiveness and decrease in bradycardia threshold with sequential VNTx suggest that 1) vagal afferents inhibit centrally mediated parasympathetic efferent outflow and 2) the ipsilateral and contralateral vagi exert a substantial buffering capacity. The intact threshold reflects the interaction between multiple levels of the cardiac neural hierarchy.

Background Autonomic regulation therapy involving either vagus nerve stimulation (VNS) or spinal cord stimulation (SCS) represents emerging bioelectronic therapies for heart disease. The objective of this study was to determine if VNS and/or SCS modulate primary cardiac afferent sensory transduction of the ischemic myocardium. Methods Using extracellular recordings in 19 anesthetized canines, of 88 neurons evaluated, 36 ventricular-related nodose ganglia sensory neurons were identified by their functional activity responses to epicardial touch, chemical activation of their sensory neurites (epicardial veratridine) and great vessel (descending aorta or inferior vena cava) occlusion. Neural responses to 1 min left anterior descending (LAD) coronary artery occlusion (CAO) were then evaluated. These interventions were then studied following either: i) SCS [T1-T3 spinal level; 50 Hz, 90% motor threshold] or ii) cervical VNS [15–20 Hz; 1.2 × threshold]. Results LAD occlusion activated 66% of identified nodose ventricular sensory neurons (0.33 ± 0.08–0.79 ± 0.20 Hz; baseline to CAO; p < 0.002). Basal activity of cardiac-related nodose neurons was differentially reduced by VNS (0.31 ± 0.11 to 0.05 ± 0.02 Hz; p < 0.05) as compared to SCS (0.36 ± 0.12 to 0.28 ± 0.14, p = 0.59), with their activity response to transient LAD CAO being suppressed by either SCS (0.85 ± 0.39–0.11 ± 0.04 Hz; p < 0.03) or VNS (0.75 ± 0.27–0.12 ± 0.05 Hz; p < 0.04). VNS did not alter evoked neural responses of cardiac-related nodose neurons to great vessel occlusion. Conclusions Both VNS and SCS obtund ventricular ischemia induced enhancement of nodose afferent neuronal inputs to the medulla.

Key points: The evoked cardiac response to bipolar cervical vagus nerve stimulation (VNS) reflects a dynamic interaction between afferent mediated decreases in central parasympathetic drive and suppressive effects evoked by direct stimulation of parasympathetic efferent axons to the heart. The neural fulcrum is defined as the operating point, based on frequency–amplitude–pulse width, where a null heart rate response is reproducibly evoked during the on-phase of VNS. Cardiac control, based on the principal of the neural fulcrum, can be elicited from either vagus. Beta-receptor blockade does not alter the tachycardia phase to low intensity VNS, but can increase the bradycardia to higher intensity VNS. While muscarinic cholinergic blockade prevented the VNS-induced bradycardia, clinically relevant doses of ACE inhibitors, beta-blockade and the funny channel blocker ivabradine did not alter the VNS chronotropic response. While there are qualitative differences in VNS heart control between awake and anaesthetized states, the physiological expression of the neural fulcrum is maintained. Abstract: Vagus nerve stimulation (VNS) is an emerging therapy for treatment of chronic heart failure and remains a standard of therapy in patients with treatment-resistant epilepsy. The objective of this work was to characterize heart rate (HR) responses (HRRs) during the active phase of chronic VNS over a wide range of stimulation parameters in order to define optimal protocols for bidirectional bioelectronic control of the heart. In normal canines, bipolar electrodes were chronically implanted on the cervical vagosympathetic trunk bilaterally with anode cephalad to cathode (n = 8, ‘cardiac’ configuration) or with electrode positions reversed (n = 8, ‘epilepsy’ configuration). In awake state, HRRs were determined for each combination of pulse frequency (2–20 Hz), intensity (0–3.5 mA) and pulse widths (130–750 μs) over 14 months. At low intensities and higher frequency VNS, HR increased during the VNS active phase owing to afferent modulation of parasympathetic central drive. When functional effects of afferent and efferent fibre activation were balanced, a null HRR was evoked (defined as ‘neural fulcrum’) during which HRR ≈ 0. As intensity increased further, HR was reduced during the active phase of VNS. While qualitatively similar, VNS delivered in the epilepsy configuration resulted in more pronounced HR acceleration and reduced HR deceleration during VNS. At termination, under anaesthesia, transection of the vagi rostral to the stimulation site eliminated the augmenting response to VNS and enhanced the parasympathetic efferent-mediated suppressing effect on electrical and mechanical function of the heart. In conclusion, VNS activates central then peripheral aspects of the cardiac nervous system. VNS control over cardiac function is maintained during chronic therapy.

Vagus nerve stimulation (VNS) currently treats patients with drug-resistant epilepsy, depression, and heart failure. The mild intensities used in chronic VNS suggest that primary visceral afferents and central nervous system activation are involved. Here, we measured the activity of neurons in the nucleus of the solitary tract (NTS) in anesthetized rats using clinically styled VNS. Our chief findings indicate that VNS at threshold bradycardic intensity activated NTS neuron discharge in one-third of NTS neurons. This VNS directly activated only myelinated vagal afferents projecting to second-order NTS neurons. Most VNS-induced activity in NTS, however, was unsynchronized to vagal stimuli. Thus, VNS activated unsynchronized activity in NTS neurons that were second order to vagal afferent C-fibers as well as higher-order NTS neurons only polysynaptically activated by the vagus. Overall, cardiovascular-sensitive and -insen-sitive NTS neurons were similarly activated by VNS: 3/4 neurons with monosynaptic vagal A-fiber afferents, 6/42 neurons with monosynaptic vagal C-fiber afferents, and 16/21 polysynaptic NTS neurons. Provocatively, vagal A-fibers indirectly activated C-fiber neurons during VNS. Elevated spontaneous spiking was quantitatively much higher than synchronized activity and extended well into the periods of nonstimulation. Surprisingly, many polysynaptic NTS neurons responded to half the bradycardic intensity used in clinical studies, indicating that a subset of myelinated vagal afferents is sufficient to evoke VNS indirect activation. Our study uncovered a myelinated vagal afferent drive that indirectly activates NTS neurons and thus central pathways beyond NTS and support reconsideration of brain contributions of vagal afferents underpinning of therapeutic impacts. NEW & NOTEWORTHY Acute vagus nerve stimulation elevated activity in neurons located in the medial nucleus of the solitary tract. Such stimuli directly activated only myelinated vagal afferents but indirectly activated a subpopulation of second- and higher-order neurons, suggesting that afferent mechanisms and central neuron activation may be responsible for vagus nerve stimulation efficacy.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20755号 / 医博第4285号 / 新制||医||1024(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 伊佐 正, 教授 宮本 享, 教授 井上 治久 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

No description available.

Our objective was to determine whether chronic vagus nerve stimulation (VNS) mitigates pressure overload (PO)-induced remodeling of the cardioneural interface. Guinea pigs (n = 48) were randomized to right or left cervical vagus (RCV or LCV) implant. After 2 wk, chronic left ventricular PO was induced by partial (15–20%) aortic constriction. Of the 31 animals surviving PO induction, 10 were randomized to RCV VNS, 9 to LCV VNS, and 12 to sham VNS. VNS was delivered at 20 Hz and 1.14 ± 0.03 mA at a 22% duty cycle. VNS commenced 10 days after PO induction and was maintained for 40 days. Time-matched controls (n = 9) were evaluated concurrently. Echocardiograms were obtained before and 50 days after PO. At termination, intracellular current-clamp recordings of intrinsic cardiac (IC) neurons were studied in vitro to determine effects of therapy on soma characteristics. Ventricular cardiomyocyte sizes were assessed with histology along with immunoblot analysis of selected proteins in myocardial tissue extracts. In sham-treated animals, PO increased cardiac output (34%, P < 0.004), as well as systolic (114%, P < 0.04) and diastolic (49%, P < 0.002) left ventricular volumes, a hemodynamic response prevented by VNS. PO-induced enhancements of IC synaptic efficacy and muscarinic sensitivity of IC neurons were mitigated by chronic VNS. Increased myocyte size, which doubled in PO (P < 0.05), was mitigated by RCV. PO hypertrophic myocardium displayed decreased glycogen synthase (GS) protein levels and accumulation of the phosphorylated (inactive) form of GS. These PO-induced changes in GS were moderated by left VNS. Chronic VNS targets IC neurons accompanying PO to obtund associated adverse cardiomyocyte remodeling.

This paper aims to determine whether chronic vagus nerve stimulation (VNS) mitigates myocardial infarction (MI)-induced remodeling of the intrinsic cardiac nervous system (ICNS), along with the cardiac tissue it regulates. Guinea pigs underwent VNS implantation on the right cervical vagus. Two weeks later, MI was produced by ligating the ventral descending coronary artery. VNS stimulation started 7 days post-MI (20 Hz, 0.9 ± 0.2 mA, 14 s on, 48 s off; VNS-MI, n = 7) and was compared with time-matched MI animals with sham VNS (MI n = 7) vs. untreated controls (n = 8). Echocardiograms were performed before and at 90 days post-MI. At termination, IC neuronal intracellular voltage recordings were obtained from whole-mount neuronal plexuses. MI increased left ventricular end systolic volume (LVESV) 30% (P = 0.027) and reduced LV ejection fraction (LVEF) 6.5% (P < 0.001) at 90 days post-MI compared with baseline. In the VNS-MI group, LVESV and LVEF did not differ from baseline. IC neurons showed depolarization of resting membrane potentials and increased input resistance in MI compared with VNS-MI and sham controls (P < 0.05). Neuronal excitability and sensitivity to norepinephrine increased in MI and VNS-MI groups compared with controls (P < 0.05). Synaptic efficacy, as determined by evoked responses to stimulating input axons, was reduced in VNS-MI compared with MI or controls (P < 0.05). VNS induced changes in myocytes, consistent with enhanced glycogenolysis, and blunted the MI-induced increase in the proapoptotic Bcl-2-associated X protein (P < 0.05). VNS mitigates MI-induced remodeling of the ICNS, correspondingly preserving ventricular function via both neural and cardiomyocyte-dependent actions.

La dépression est une pathologie grave qui, malgré de multiples stratégies thérapeutiques, demeure résistante chez un tiers des patients. Les techniques de stimulation cérébrale sont devenues une alternative intéressante pour les patients résistants à diverses pharmacothérapies. La stimulation du nerf vague (SNV) a ainsi fait preuve de son efficacité en clinique et a récemment été approuvée comme traitement additif pour la dépression résistante. Cependant, les mécanismes d’action de la SNV en rapport avec la dépression n’ont été que peu étudiés. Cette thèse a donc eu comme premier objectif de caractériser l’impact de la SNV sur les différents systèmes monoaminergiques impliqués dans la pathophysiologie de la dépression, à savoir la sérotonine (5-HT), la noradrénaline (NA) et la dopamine (DA), grâce à l’utilisation de techniques électrophysiologiques et de la microdialyse in vivo chez le rat. Des études précliniques avaient déjà révélé qu’une heure de SNV augmente le taux de décharge des neurones NA du locus coeruleus, et que 14 jours de stimulation sont nécessaires pour observer un effet comparable sur les neurones 5-HT. Notre travail a démontré que la SNV modifie aussi le mode de décharge des neurones NA qui présente davantage de bouffées, influençant ainsi la libération terminale de NA, qui est significativement augmentée dans le cortex préfrontal et l’hippocampe après 14 jours. L’augmentation de la neurotransmission NA s’est également manifestée par une élévation de l’activation tonique des récepteurs postsynaptiques α2-adrénergiques de l’hippocampe. Après lésion des neurones NA, nous avons montré que l’effet de la SNV sur les neurones 5-HT était indirect, et médié par le système NA, via l’activation des récepteurs α1-adrénergiques présents sur les neurones du raphé. Aussi, tel que les antidépresseurs classiques, la SNV augmente l’activation tonique des hétérorécepteurs pyramidaux 5-HT1A, dont on connait le rôle clé dans la réponse thérapeutique aux antidépresseurs. Par ailleurs, nous avons constaté que malgré une diminution de l’activité électrique des neurones DA de l’aire tegmentale ventrale, la SNV induit une augmentation de la DA extracellulaire dans le cortex préfrontal et particulièrement dans le noyau accumbens, lequel joue un rôle important dans les comportements de récompense et l’hédonie. Un deuxième objectif a été de caractériser les paramètres optimaux de SNV agissant sur la dépression, en utilisant comme indicateur le taux de décharge des neurones 5-HT. Des modalités de stimulation moins intenses se sont avérées aussi efficaces que les stimulations standards pour augmenter l’activité électrique des neurones 5-HT. Ces nouveaux paramètres de stimulation pourraient s’avérer bénéfiques en clinique, chez des patients ayant déjà répondu à la SNV. Ils pourraient minimiser les effets secondaires reliés aux périodes de stimulation et améliorer ainsi la qualité de vie des patients. Ainsi, ces travaux de thèse ont caractérisé l’influence de la SNV sur les trois systèmes monoaminergiques, laquelle s’avère en partie distincte de celle des antidépresseurs classiques tout en contribuant à son efficacité en clinique. D’autre part, les modalités de stimulation que nous avons définies seraient intéressantes à tester chez des patients recevant la SNV, car elles devraient contribuer à l’amélioration des bénéfices cliniques de cette thérapie. / Depression is a severe psychiatric disorder, in which a third of patients do not achieve remission, despite the wide variety of therapeutic strategies that are currently available. Brain stimulation has emerged as a promising alternative therapy in cases of treatment resistance. Vagus nerve stimulation (VNS) has shown promise in treating resistant-depressed patients, and it has been approved as an adjunctive treatment for resistant depression. However, the mechanism of action by which VNS exerts its antidepressant effects has remained elusive. The first goal of this thesis was therefore to characterize the impact of VNS on monoaminergic systems known to be implicated in the pathophysiology of depression such as serotonin (5-HT), norepinephrine (NE) and dopamine (DA), by means of electrophysiologic techniques and microdialysis in the rat brain. Previous research has indicated that one hour of VNS increased the basal firing activity of locus coeruleus NE neurons and, secondarily, that of 5-HT neurons, but only after 14 days of stimulation. Our work demonstrated that VNS also modified the firing pattern of NE neurons towards a bursting mode of discharge. This mode of firing was shown to lead to enhanced NE release in the prefrontal cortex and hippocampus after 14 days. Increased NE neurotransmission was also evidenced by enhanced tonic activation of postsynaptic α2-adrenoceptors in the hippocampus. Selective lesioning of NE neurons was then used to demonstrate that the effects of VNS on the 5-HT system were indirect, and mediated by the activation of α1-adrenoceptors located on the dorsal raphe 5-HT neurons. Similar to classical antidepressants, VNS also enhanced the tonic activation of pyramidal 5-HT1A heteroreceptors, which are known to play a key role in the antidepressant response. We also found that in spite of a diminished firing activity of ventral tegmental area DA neurons after VNS, extracellular DA levels were significantly elevated in the prefrontal cortex, and particularly in the nucleus accumbens which plays an important role in reward behavior and hedonia. A second objective was to characterize the optimal VNS parameters to treat depression using the firing activity of 5-HT neurons as an indicator. It was found that less stimulation was as effective as the standard levels to increase 5-HT neurons firing rate. These novel parameters could be helpful for clinical application in VNS responsive patients, to potentially minimize and/or even prevent stimulation-related side effects, thus improving their quality of life. In brief, these studies reveal an influence of VNS on all three central monoamine systems, which differs in part from that of classical antidepressants while contributing to the clinical efficacy of this approach. It will also be interesting to determine whether the proposed lower stimulation parameters are as effective in providing antidepressant response in patients receiving VNS, which should contribute to improve the clinical benefits of that therapy.

La dépression est une pathologie grave qui, malgré de multiples stratégies thérapeutiques, demeure résistante chez un tiers des patients. Les techniques de stimulation cérébrale sont devenues une alternative intéressante pour les patients résistants à diverses pharmacothérapies. La stimulation du nerf vague (SNV) a ainsi fait preuve de son efficacité en clinique et a récemment été approuvée comme traitement additif pour la dépression résistante. Cependant, les mécanismes d’action de la SNV en rapport avec la dépression n’ont été que peu étudiés. Cette thèse a donc eu comme premier objectif de caractériser l’impact de la SNV sur les différents systèmes monoaminergiques impliqués dans la pathophysiologie de la dépression, à savoir la sérotonine (5-HT), la noradrénaline (NA) et la dopamine (DA), grâce à l’utilisation de techniques électrophysiologiques et de la microdialyse in vivo chez le rat. Des études précliniques avaient déjà révélé qu’une heure de SNV augmente le taux de décharge des neurones NA du locus coeruleus, et que 14 jours de stimulation sont nécessaires pour observer un effet comparable sur les neurones 5-HT. Notre travail a démontré que la SNV modifie aussi le mode de décharge des neurones NA qui présente davantage de bouffées, influençant ainsi la libération terminale de NA, qui est significativement augmentée dans le cortex préfrontal et l’hippocampe après 14 jours. L’augmentation de la neurotransmission NA s’est également manifestée par une élévation de l’activation tonique des récepteurs postsynaptiques α2-adrénergiques de l’hippocampe. Après lésion des neurones NA, nous avons montré que l’effet de la SNV sur les neurones 5-HT était indirect, et médié par le système NA, via l’activation des récepteurs α1-adrénergiques présents sur les neurones du raphé. Aussi, tel que les antidépresseurs classiques, la SNV augmente l’activation tonique des hétérorécepteurs pyramidaux 5-HT1A, dont on connait le rôle clé dans la réponse thérapeutique aux antidépresseurs. Par ailleurs, nous avons constaté que malgré une diminution de l’activité électrique des neurones DA de l’aire tegmentale ventrale, la SNV induit une augmentation de la DA extracellulaire dans le cortex préfrontal et particulièrement dans le noyau accumbens, lequel joue un rôle important dans les comportements de récompense et l’hédonie. Un deuxième objectif a été de caractériser les paramètres optimaux de SNV agissant sur la dépression, en utilisant comme indicateur le taux de décharge des neurones 5-HT. Des modalités de stimulation moins intenses se sont avérées aussi efficaces que les stimulations standards pour augmenter l’activité électrique des neurones 5-HT. Ces nouveaux paramètres de stimulation pourraient s’avérer bénéfiques en clinique, chez des patients ayant déjà répondu à la SNV. Ils pourraient minimiser les effets secondaires reliés aux périodes de stimulation et améliorer ainsi la qualité de vie des patients. Ainsi, ces travaux de thèse ont caractérisé l’influence de la SNV sur les trois systèmes monoaminergiques, laquelle s’avère en partie distincte de celle des antidépresseurs classiques tout en contribuant à son efficacité en clinique. D’autre part, les modalités de stimulation que nous avons définies seraient intéressantes à tester chez des patients recevant la SNV, car elles devraient contribuer à l’amélioration des bénéfices cliniques de cette thérapie. / Depression is a severe psychiatric disorder, in which a third of patients do not achieve remission, despite the wide variety of therapeutic strategies that are currently available. Brain stimulation has emerged as a promising alternative therapy in cases of treatment resistance. Vagus nerve stimulation (VNS) has shown promise in treating resistant-depressed patients, and it has been approved as an adjunctive treatment for resistant depression. However, the mechanism of action by which VNS exerts its antidepressant effects has remained elusive. The first goal of this thesis was therefore to characterize the impact of VNS on monoaminergic systems known to be implicated in the pathophysiology of depression such as serotonin (5-HT), norepinephrine (NE) and dopamine (DA), by means of electrophysiologic techniques and microdialysis in the rat brain. Previous research has indicated that one hour of VNS increased the basal firing activity of locus coeruleus NE neurons and, secondarily, that of 5-HT neurons, but only after 14 days of stimulation. Our work demonstrated that VNS also modified the firing pattern of NE neurons towards a bursting mode of discharge. This mode of firing was shown to lead to enhanced NE release in the prefrontal cortex and hippocampus after 14 days. Increased NE neurotransmission was also evidenced by enhanced tonic activation of postsynaptic α2-adrenoceptors in the hippocampus. Selective lesioning of NE neurons was then used to demonstrate that the effects of VNS on the 5-HT system were indirect, and mediated by the activation of α1-adrenoceptors located on the dorsal raphe 5-HT neurons. Similar to classical antidepressants, VNS also enhanced the tonic activation of pyramidal 5-HT1A heteroreceptors, which are known to play a key role in the antidepressant response. We also found that in spite of a diminished firing activity of ventral tegmental area DA neurons after VNS, extracellular DA levels were significantly elevated in the prefrontal cortex, and particularly in the nucleus accumbens which plays an important role in reward behavior and hedonia. A second objective was to characterize the optimal VNS parameters to treat depression using the firing activity of 5-HT neurons as an indicator. It was found that less stimulation was as effective as the standard levels to increase 5-HT neurons firing rate. These novel parameters could be helpful for clinical application in VNS responsive patients, to potentially minimize and/or even prevent stimulation-related side effects, thus improving their quality of life. In brief, these studies reveal an influence of VNS on all three central monoamine systems, which differs in part from that of classical antidepressants while contributing to the clinical efficacy of this approach. It will also be interesting to determine whether the proposed lower stimulation parameters are as effective in providing antidepressant response in patients receiving VNS, which should contribute to improve the clinical benefits of that therapy.