Biology subjects

Mastitskaya, S.

Publications and source records attributed to Mastitskaya, S..

7 recordsLinked to original sources

bioRxiv2025

Relaxation of cardiac pericytes by GLP-1 activating KATP channels mediates remote ischaemic preconditioning cardioprotection

Failure to reperfuse the coronary microvasculature ("no-reflow") affects up to 50% of patients after unblocking a coronary artery that caused ischaemia and acute myocardial infarction. No-reflow is associated with reduced left ventricular ejection fraction, increased infarct size and death. We have established that no-reflow results from cardiac pericytes constricting coronary capillaries, and that pharmacologically relaxing pericytes reduces no-reflow. Remote ischaemic preconditioning, by briefly making a limb ischaemic, protects against cardiac ischaemic injury, and we have shown this is mediated by release of the gut hormone glucagon-like peptide 1 (GLP-1). We now demonstrate that, by releasing GLP-1, remote ischaemic preconditioning reduces pericyte-mediated coronary capillary constriction and no-reflow, and that the dilating effect of GLP-1 on coronary capillaries is abolished by block or genetic deletion of pericyte KATP channels. These results define a brain-gut-heart pathway mediating remote ischaemic cardioprotection, and suggest pharmacological therapies to reduce ischaemia-induced coronary no-reflow and improve post-infarct recovery.

physiology↗

bioRxiv2024

Anatomical and functional organization of cardiac fibers in the porcine cervical vagus nerve allows spatially selective efferent neuromodulation

Cardiac disease progression reflects the dynamic interaction between adversely remodeled neurohumoral control systems and an abnormal cardiac substrate. Vagal nerve stimulation (VNS) is an attractive neuromodulatory option to dampen this dynamic interaction; however, it is limited by off-target effects. Spatially-selective VNS (sVNS) offers a promising solution to induce cardioprotection while mitigating off-target effects by specifically targeting pre-ganglionic parasympathetic efferent cardiac fibers. This approach also has the potential to enhance therapeutic outcomes by eliminating time-consuming titration required for optimal VNS. Recent studies have demonstrated the independent modulation of breathing rate, heart rate, and laryngeal contraction through sVNS. However, the spatial organization of afferent and efferent cardiac-related fibers within the vagus nerve remains unexplored. By using trial-and-error sVNS in vivo in combination with ex vivo micro-computed tomography fascicle tracing, we show the significant spatial separation of cardiac afferent and efferent fibers (179{+/-}55{degrees} SD microCT, p<0.05 and 200{+/-}137{degrees} SD, p<0.05 sVNS - degrees of separation across a cross-section of nerve) at the mid-cervical level. We also show that cardiac afferent fibers are located in proximity to pulmonary fibers consistent with recent findings of cardiopulmonary convergent neurons and circuits. We demonstrate the ability of sVNS to selectively elicit desired scalable heart rate decrease without stimulating afferent-related reflexes. By elucidating the spatial organization of cardiac-related fibers within the vagus nerve, our findings pave the way for more targeted neuromodulation, thereby reducing off-target effects and eliminating the need for titration. This, in turn, will enhance the precision and efficacy of VNS therapy in treating cardiac pathology, allowing for improved therapeutic efficacy. Condensed AbstractSpatially-selective vagus nerve stimulation (sVNS) presents a promising approach for addressing chronic heart disease with enhanced precision. Our study reveals significant spatial separation between cardiac afferent and efferent fibers in the vagus nerve, particularly at the mid-cervical level. Utilizing trial-and-error sVNS in vivo and micro-computed tomography fascicle tracing, we demonstrate the potential for targeted neuromodulation, achieving therapeutic effects like scalable heart rate decrease without stimulating afferent-related reflexes. This spatial understanding opens avenues for more effective VNS therapy, minimizing off-target effects and eliminating the need for titration, thereby expediting therapeutic outcomes in myocardial infarction and related conditions. TweetWith functional and structural imaging, we found organization of vagal efferent & afferent cardiac regions. We can selectively activate only cardiac efferents to achieve bradycardia; desired to reduce the effects of sympathetic overactivation associated with heart disease #VNS #Cardiac #VagusNerve Key PointsO_LISpatially-selective vagus nerve stimulation (sVNS) presents a promising approach for addressing chronic heart disease with enhanced precision. C_LIO_LIOur study reveals significant spatial separation between cardiac afferent and efferent fibers in the vagus nerve, particularly at the mid-cervical level. C_LIO_LIUtilizing trial-and-error sVNS in vivo and micro-computed tomography fascicle tracing, we demonstrate the potential for targeted neuromodulation, achieving therapeutic effects like scalable heart rate decrease without stimulating afferent-related reflexes. C_LIO_LIThis spatial understanding opens avenues for more effective VNS therapy, minimizing off-target effects and eliminating the need for titration, thereby expediting therapeutic outcomes in myocardial infarction and related conditions. C_LI

neuroscience↗

bioRxiv2023

Human vagus nerve fascicular anatomy: a microCT segmentation and histological study

BackgroundPrevious research has revealed the logical mapping of fascicles in both human somatic and pig vagus nerves, but the organization of fascicles within the human vagus nerve remains largely unknown. Understanding its fascicular arrangement would significantly advance our knowledge of the autonomic nervous system and facilitate studies and application of selective vagus nerve stimulation to avoid off-target effects. The purpose of this study was to trace the thoracic branches of human vagus nerves, investigate their fascicular organization, and analyze the nerves histologically and morphologically. MethodsBoth left and right vagus nerves were dissected from human cadavers, preserving the cardiac, recurrent laryngeal, and pulmonary branches. The nerves were prepared, scanned using microCT, and the fascicles segmented and traced from their branching points. Histology and immunohistochemistry were performed for morphological analysis and validation of the microCT segmentation. The data was then analyzed and compared between nerves. ResultsThe organization of the cardiac, pulmonary, and recurrent laryngeal fascicles was observed for a short distance from their entry point into the nerves. Initially, left vagus nerves showed merging of cardiac and pulmonary fascicles, while the recurrent laryngeal fascicles remained separate. In right vagus nerves, the cardiac fascicles merged with both pulmonary and recurrent laryngeal fascicles. MicroCT imaging limitations prevented visualization and tracing of fiber organization within merged fascicles. Immunohistochemistry and morphological analysis revealed that right vagus nerves were larger and had more fascicles than the left and fascicle counts varied along the nerve, indicating anastomoses. The superior cardiac branch was separate from other fascicles near the VNS cuff placement. ConclusionsIt is possible that organ-specific fibers may still retain some spatial organization despite most fascicles being merged at cervical level. However, fiber tracing and in vivo studies could provide valuable information beyond microCT to resolve this further. The separate superior cardiac fascicles offer potential for targeted neuromodulation of the heart, benefiting conditions like myocardial infarction, heart failure, and atrial fibrillation. Overall, the study provides insights into the morphology and anatomy of human vagus nerves. Our findings thereby contribute to the development of selective vagus nerve stimulation strategies for more precise autonomic regulation.

neuroscience↗

bioRxiv2022

Organotopic organisation of the cervical vagus nerve

Despite detailed characterization of fascicular organization of somatic nerves, the functional anatomy of fascicles evident in human and large mammal cervical vagus nerve is unknown. The vagus nerve is a prime target for intervention in the field of electroceuticals due to its extensive distribution to the heart, larynx, lungs, and abdominal viscera. However, current practice of the approved vagus nerve stimulation (VNS) technique is to stimulate the entire nerve. This produces indiscriminate stimulation of non-targeted effectors and undesired side effects. Selective neuromodulation is now a possibility with a spatially-selective vagal nerve cuff. However, this requires the knowledge of the fascicular organization at the level of cuff placement to inform selectivity of only the desired target organ or function. We imaged function over milliseconds with fast neural electrical impedance tomography and selective stimulation, and found consistent spatially separated regions within the nerve correlating with the three fascicular groups of interest, suggesting organotopy. This was independently verified with structural imaging by tracing anatomical connections from the end organ with microCT and the development of an anatomical map of the vagus nerve. This confirmed organotopic organization. Here we show, for the first time, localized fascicles in the porcine cervical vagus nerve which map to cardiac, pulmonary and recurrent laryngeal function (N=4). These findings pave the way for improved outcomes in VNS as unwanted side effects could be reduced by targeted selective stimulation of identified organ-specific fascicles and the extension of this technique clinically beyond the currently approved disorders to treat heart failure, chronic inflammatory disorders and more.

neuroscience↗

bioRxiv2019

MicroCT optimisation for imaging fascicular anatomy in peripheral nerves

Vagus nerve stimulation (VNS) is a promising therapy for treatment of various conditions resistant to standard therapeutics. However, due to the lack of understanding of the fascicular organisation of the vagus nerve, VNS leads to unwanted off-target effects. Micro-computed tomography (microCT) can be used to trace fascicles from periphery and image fascicular anatomy. In this work we optimised the microCT protocol of the rat sciatic and subsequent pig vagus nerves.\n\nAfter differential staining, the optimal staining time was selected and scanning parameters were altered in subsequent scans. Scans were reconstructed, visualised in ImageJ and fascicles segmented with a custom algorithm in Matlab to determine ultimate parameters for tracking of the nerve. Successful segmentation for tracking of individual fascicles was achieved after 24 hours and 120 hours of staining with Lugols solution (1% total iodine) for rat sciatic and pig vagus nerves, respectively, and the following scanning parameters: 4 {micro}m voxel size, 35 kVp energy, 114 {micro}A current, 4 W power, 0.25 fps in 4 s exposure time, 3176 projections and a molybdenum target.\n\nThe optimised microCT protocol allows for segmentation and tracking of the fascicles within the nerve. This will be used to scan the full length of the pig, and possibly, the human vagus nerves. The resulting segmentation map of the functional anatomical organisation of the vagus nerve will enable selective VNS ultimately allowing for the avoidance of the off-target effects and improving its therapeutic efficacy.

neuroscience↗

bioRxiv2019

Astrocytes modulate baroreceptor reflex sensitivity at the level of the nucleus of the solitary tract

Astrocytes play an important role in cardiovascular reflex integration at the level of the nucleus tractus solitarii (NTS). Existing reports from brainstem slice preparations suggest that astrocytes here respond to input from the solitary tract by increasing intracellular calcium. However, the physiological significance of this neuron-astrocyte signaling in vivo remains unknown. Here, we report that stimulation of the vagus nerve in an anesthetized rat induced rapid [Ca2+]i increases in astrocytes transduced to express calcium sensor GCaMP6. The receptors involved were determined using brainstem-derived astroglial cell cultures were loaded with [Ca2+] indicator Fura-2. 5-HT (10 {micro}M) caused robust increases in [Ca2+]i, and pharmacological interrogation revealed the expression of functional 5-HT2A receptors. This observation was confirmed in vivo: intravenous administration of ketanserin decreased the magnitude of [Ca2+]i responses, induced by vagal afferent simulation, by [~]50%. However, the response was completely blocked by topical application of the AMPA receptor antagonist CNQX alone. To investigate the role of astrocyte-neuron communication, the vesicular release in the NTS astrocytes was blocked by virally driven expression of a dominant-negative SNARE protein in vivo. This increased baroreflex sensitivity in awake animals, which was also observed in anesthetized animals after topical application of the P2Y1 receptor antagonist MDS-2500 to the NTS. We hypothesize that NTS astrocytes respond to incoming afferent release of glutamate and this response is modulated by 5-HT originating from vagal afferents or other sources. ATP is then released, which acts on inhibitory interneurons via P2Y1 receptors and thus modulates the expression of cardiovascular reflexes.\n\nSignificance statementCardiorespiratory nuclei in the brainstem integrate cardiovascular sensory information to optimise tissue perfusion and blood gas concentrations. We describe experimental evidence that NTS astrocytes participate in setting the baroreflex sensitivity by release of ATP acting on P2Y1 receptors on inhibitory interneurons. Activation of astrocytes is partly under control of 5-HT co-released with glutamate from vagal afferents, which allows modulation of autonomic response to high frequency/duration of afferent stimulation by monitoring extra-synaptic 5-HT acting on glial 5-HT2A receptors. This could represent a signaling pathway that is activated under pathological conditions and is responsible for baroreflex impairment in conditions that result in astrogliosis, for example from systemic inflammatory response or chronic hypoxia/hypercapnia.

neuroscience↗

bioRxiv2019

Circadian control of intrinsic heart rate via a sinus node clock and the pacemaker channel

In the human, there is a circadian rhythm in the resting heart rate and it is higher during the day in preparation for physical activity. Conversely, slow heart rhythms (bradyarrhythmias) occur primarily at night. Although the lower heart rate at night is widely assumed to be neural in origin (the result of high vagal tone), the objective of the study was to test whether there is an intrinsic change in heart rate driven by a local circadian clock. In the mouse, there was a circadian rhythm in the heart rate in vivo in the conscious telemetrized animal, but there was also a circadian rhythm in the intrinsic heart rate in denervated preparations: the Langendorff-perfused heart and isolated sinus node. In the sinus node, experiments (qPCR and bioluminescence recordings in mice with a Per1 luciferase reporter) revealed functioning canonical clock genes, e.g. Bmal1 and Per1. We identified a circadian rhythm in the expression of key ion channels, notably the pacemaker channel Hcn4 (mRNA and protein) and the corresponding ionic current (funny current, measured by whole cell patch clamp in isolated sinus node cells). Block of funny current in the isolated sinus node abolished the circadian rhythm in the intrinsic heart rate. Incapacitating the local clock (by cardiac-specific knockout of Bmal1) abolished the normal circadian rhythm of Hcn4, funny current and the intrinsic heart rate. Chromatin immunoprecipitation demonstrated that Hcn4 is a transcriptional target of BMAL1 establishing a pathway by which the local clock can regulate heart rate. In conclusion, there is a circadian rhythm in the intrinsic heart rate as a result of a local circadian clock in the sinus node that drives rhythmic expression of Hcn4. The data reveal a novel regulator of heart rate and mechanistic insight into the occurrence of bradyarrhythmias at night.

physiology↗