Burst Amplitude Research Articles

Role of the Kölliker-Fuse/parabrachial complex in the generation of postinspiratory vagal and sympathetic nerve activities and their recruitment by hypoxemic stimuli in the rat.

In the rat, the activity of laryngeal adductor muscles, the crural diaphragm, and sympathetic vasomotor neurons is entrained to the postinspiratory (post-I) phase of the respiratory cycle, a mechanism thought to enhance cardiorespiratory efficiency. The identity of the central neurons responsible for transmitting respiratory activity to these outputs remains unresolved. Here we explore the contribution of the Kölliker-Fuse/parabrachial nuclei (KF-PBN) in the generation of post-I activity in vagal and sympathetic outputs under steady-state conditions and during acute hypoxemia, a condition that potently recruits post-I activity. In artificially ventilated, vagotomized, and urethane-anesthetized rats, bilateral KF-PBN inhibition by microinjection of the GABAA receptor agonist isoguvacine evoked stereotypical responses on respiratory pattern, characterized by a reduction in phrenic nerve burst amplitude, a modest lengthening of inspiratory time, and an increase in breath-to-breath variability, while post-I vagal nerve activity was abolished and post-I sympathetic nerve activity diminished. During acute hypoxemia, KF-PBN inhibition attenuated tachypneic responses and completely abolished post-I vagal activity while preserving respiratory-sympathetic coupling. Furthermore, KF-PBN inhibition disrupted the decline in respiratory frequency that normally follows resumption of oxygenation. These findings suggest that the KF-PBN is a critical hub for the distribution of post-I activities to vagal and sympathetic outputs and is an important contributor to the dynamic adjustments to respiratory patterns that occur in response to acute hypoxia. Although KF-PBN appears essential for post-I vagal activity, it only partially contributes to post-I sympathetic nerve activity, suggesting the contribution of multiple neural pathways to respiratory-sympathetic coupling.NEW & NOTEWORTHY Inhibition of neurons in the pontine Kölliker-Fuse/parabrachial complex (KF-PBN) differentially inhibited postinspiratory (post-I) activity in vagal and sympathetic outputs. The strong recruitment of post-I vagal activity that occurs in response to hypoxemia is selectively abolished by KF-PBN inhibition. This suggests that 1) post-I activity in vagal and sympathetic outputs may be generated by partially independent mechanisms and 2) neurons in the KF-PBN are a preeminent source of drive for the generation of eupneic post-I activity.

Abnormal beta bursts of depression in the orbitofrontal cortex and its relationship with clinical symptoms

BackgroundRecent researches have reported that frequency-specific patterns of neural activity contain not only rhythmically sustained oscillations but also transient-bursts of isolated events. The aim of this study was to investigated the correlation between beta burst and depression in order to explore depressive disease and the neurological underpinnings of disease-related symptoms. MethodsWe collected resting-state MEG recordings from 30 depressive patients and a matched 40 healthy controls. A Hidden Markov Model (HMM) was applied on source-space time courses for 78 cortical regions of the AAL atlas and the temporal characteristics of beta burst from the matched HMM states were captured. Group differences were evaluated on these beta burst characteristics after permutation tests and, for the depressive group, associations between burst characteristics and clinical symptom severity were determined using Spearman correlation coefficients. ResultsAt a threshold of p=0.05corrected, burst characteristics revealed significant differences between depression patients and controls at the group level, including increased burst amplitude in frontal lobe, decreased burst duration in occipital regions, increased burst rate and decreased burst interval time in some brain regions. Furthermore, burst amplitude in the orbitofrontal cortex (OFC) was positively related to the severity of sleep disturbance and burst rate in the OFC was negatively related to the severity of anxiety in depression patients. ConclusionsThe findings highlight OFC may be a targeted area responsible for the anxiety and sleep disturbance symptom by abnormal beta burst in depressive patients and beta burst characteristics of OFC might serve as a neuro-marker for the depression.

Canard explosions in turbulent thermo-fluid systems.

A sudden transition to a state of high-amplitude periodic oscillations is catastrophic in a thermo-fluid system. Conventionally, upon varying the control parameter, a sudden transition is observed as an abrupt jump in the amplitude of the fluctuations in these systems. In contrast, we present an experimental discovery of a canard explosion in a turbulent reactive flow system where we observe a continuous bifurcation with a rapid rise in the amplitude of the fluctuations within a narrow range of control parameters. The observed transition is facilitated via a state of bursting, consisting of the epochs of large amplitude periodic oscillations amidst the epochs of low-amplitude periodic oscillations. The amplitude of the bursts is higher than the amplitude of the bursts of an intermittency state in a conventional gradual transition, as reported in turbulent reactive flow systems. During the bursting state, we observe that temperature fluctuations of the exhaust gas vary at a slower time scale in correlation with the amplitude envelope of the bursts. We also present a phenomenological model for thermoacoustic systems to describe the observed canard explosion. Using the model, we explain that the large amplitude bursts occur due to the slow-fast dynamics at the bifurcation regime of the canard explosion.

Endomorphin-2 (Endo2) and substance P (SubP) co-application attenuates SubP-induced excitation and alters frequency plasticity in neonatal rat in vitro preparations

Substance P (SubP) and endomorphin-2 (Endo2) are co-localized presynaptically in vesicles of neurons adjacent to inspiratory rhythm-generating pre-Botzinger Complex (preBotC) neurons but the effects of co-released SubP and Endo2 on respiratory motor control are not known. To address this question, SubP alone or a combination of SubP and Endo2 (SubP/Endo2) were bath-applied in a sustained (15-min) or intermittent (5-min application, 5-min washout, x3) pattern at 10–100 nM to neonatal rat brainstem-spinal cord preparations. During neuropeptide application, SubP/Endo2 co-applications generally attenuated SubP-induced increases in burst frequency and decreases in burst amplitude. With respect to frequency plasticity (long-lasting increase in burst frequency 60 min post-neuropeptide application), SubP-induced frequency plasticity was increased with sustained SubP/Endo2 co-applications at 20 and 100 nM. Intermittent SubP/Endo2 co-applications tended to decrease the level of frequency plasticity induced by intermittent SubP alone applications. SubP/Endo2 co-applications revealed potentially new functions for neurokinin-1 (NK1R) and mu-opioid (MOR) receptors on respiratory rhythm-generating medullary neurons.

Comparison of rhythmic jaw muscle activities induced by electrical stimulations of the corticobulbar tract during rapid eye movement sleep with those during wakefulness and non-rapid eye movement sleep in freely moving Guinea pigs

ObjectiveRhythmic jaw muscle activities (RJMAs) occur during rapid eye movement (REM) sleep in humans and animals even though motoneurons are inhibited. The present study compared the characteristics of jaw muscle activities induced by electrical microstimulations of the corticobulbar tract (CT) during REM sleep with those during wakefulness and non-REM sleep. MethodsEleven guinea pigs were surgically prepared for polygraphic recordings with the implantation of a stimulating electrode. Long- and short-train repetitive electrical microstimulations were applied to the CT under freely moving conditions. The response rate, latency, burst amplitude, and cycle length in the digastric muscle were calculated and cortical and cardiac activities were quantified. ResultsLong-train microstimulations induced RJMAs in the digastric muscle followed by masseter muscle activity during wakefulness and non-REM sleep and only induced rhythmic digastric muscle activity during REM sleep. The response rate of RJMAs and the burst amplitude of digastric muscles were significantly lower during REM sleep than during wakefulness and non-REM sleep. However, response latency did not significantly differ between REM sleep and wakefulness. Transient cortical and cardiac changes were associated with RJMAs induced during non-REM sleep, but not during REM sleep. Short-train microstimulations induced a short-latency digastric response, the amplitude of which was significantly lower during REM sleep than during non-REM sleep and wakefulness. ConclusionsThese results suggest that the masticatory CPG was activated by electrical CT stimulations independently of the motoneuron inhibitory system during REM sleep.

Inhibition of muscle sympathetic nerve activity in premenopausal women: responses to sudden sensory stimuli predict responses to mental stress.

Muscle sympathetic nerve responses to sudden sensory stimuli have been elucidated in several studies on young healthy men, showing reproducible interindividual differences ranging from varying degrees of inhibition to no significant change, with very few subjects showing significant excitation. These individual response patterns have been shown to predict the neural response to mental stress and coupled blood pressure responses. The aim of this study was to investigate whether premenopausal healthy women show similar neural and blood pressure responses. Muscle sympathetic nerve recordings from the peroneal nerve were performed in 34 healthy women (mean age 27 ± 8 yr) during sudden sensory stimuli (electrical stimuli to a finger) and 3 min of mental stress (forced arithmetics). After sensory stimuli, 18 women showed varying degrees of inhibition of muscle sympathetic nerve activity (burst amplitude mean reduction 60%, range 34-100%). The remaining 16 showed no inhibition (mean 5%, range -31 to 28%; one subject exhibiting excitation). During 3 min of mental stress, the normalized change in burst incidence for muscle sympathetic nerve activity correlated with the percentage change of muscle sympathetic nerve activity induced by the sensory stimulation protocol (r = 0.64, P = 0.0042). In contrast to men, the neural responses did not predict changes in blood pressure. Thus, premenopausal females show a similar range of individual differences in defense-related muscle sympathetic neural responses as men, but no associated differences in blood pressure responses. Whether these patterns are unchanged after menopause remains to be investigated.NEW & NOTEWORTHY Muscle sympathetic neural responses to sudden sensory stimuli in premenopausal women showed interindividual differences and the distribution of sympathetic responses was similar to that previously found in men. Despite this similarity, the associated differences in transient blood pressure responses seen in men were not found in women. The increased risk of developing hypertension in postmenopausal women warrants an investigation of whether these response patterns are altered after menopause.

Dead or Alive? How Bursty Star Formation and Patchy Dust Can Cause Temporary Quiescence in High-redshift Galaxies

The recent discovery of a galaxy at z = 7.3 with undetected optical emission lines and a blue UV-to-optical continuum ratio in JWST spectroscopy is surprising and needs to be explained physically. Here, we explore two possibilities that could cause such a seemingly quiescent ∼5 × 108 M ⊙ galaxy in the early Universe: (i) stochastic variations in the star formation history (SFH) and (ii) the effect of spatially varying dust attenuation on the measured line and continuum emission properties. Both scenarios can play out at the same time to amplify the effect. A stochastic star formation model (similar to realistic SFHs from hydrodynamical simulations of similar-mass galaxies) can create such observed properties if star formation is fast-varying with a correlation time of <150 Myr given a reasonable burst amplitude of ∼0.6 dex. The total time spent in this state is less than 20 Myr, and the likelihood of such a state to occur over 500 Myr at z = 7 is ∼50% (consistent with current observations). On the other hand, we show that a spectrum with blue UV continuum and lack of emission lines can be reproduced by a blue+red composite spectrum. The UV continuum is emitted from dust-free density-bounded H ii regions (blue component), while the red component is a dust-obscured starburst with weakened emission lines due to strong differential dust attenuation between stellar and nebular emission. Future resolving far-infrared observations with the Atacama Large Millimeter/submillimeter Array will shed light on the latter scenario.

High-gamma and beta bursts in the Left Supramarginal Gyrus can accurately differentiate verbal memory states and performance.

The left supramarginal gyrus (LSMG) may mediate attention to memory, and gauge memory state and performance. We performed a secondary analysis of 142 verbal delayed free recall experiments, in patients with medically-refractory epilepsy with electrode contacts implanted in the LSMG. In 14 of 142 experiments (in 14 of 113 patients), the cross-validated convolutional neural networks (CNNs) that used 1-dimensional(1-D) pairs of convolved high-gamma and beta tensors, derived from the LSMG recordings, could label recalled words with an area under the receiver operating curve (AUROC) of greater than 60% [range: 60-90%]. These 14 patients were distinguished by: 1) higher amplitudes of high-gamma bursts; 2) distinct electrode placement within the LSMG; and 3) superior performance compared with a CNN that used a 1-D tensor of the broadband recordings in the LSMG. In a pilot study of 7 of these patients, we also cross-validated CNNs using paired 1-D convolved high-gamma and beta tensors, from the LSMG, to: a) distinguish word encoding epochs from free recall epochs [AUC 0.6-1]; and distinguish better performance from poor performance during delayed free recall [AUC 0.5-0.86]. These experiments show that bursts of high-gamma and beta generated in the LSMG are biomarkers of verbal memory state and performance.

Unified bursting strategies in ectopic and endogenous even-skipped expression patterns.

Transcription often occurs in bursts as gene promoters switch stochastically between active and inactive states. Enhancers can dictate transcriptional activity in animal development through the modulation of burst frequency, duration, or amplitude. Previous studies observed that different enhancers can achieve a wide range of transcriptional outputs through the same strategies of bursting control. For example, despite responding to different transcription factors, all even-skipped enhancers increase transcription by upregulating burst frequency and amplitude while burst duration remains largely constant. These shared bursting strategies suggest that a unified molecular mechanism constraints how enhancers modulate transcriptional output. Alternatively, different enhancers could have converged on the same bursting control strategy because of natural selection favoring one of these particular strategies. To distinguish between these two scenarios, we compared transcriptional bursting between endogenous and ectopic gene expression patterns. Because enhancers act under different regulatory inputs in ectopic patterns, dissimilar bursting control strategies between endogenous and ectopic patterns would suggest that enhancers adapted their bursting strategies to their trans-regulatory environment. Here, we generated ectopic even-skipped transcription patterns in fruit fly embryos and discovered that bursting strategies remain consistent in endogenous and ectopic even-skipped expression. These results provide evidence for a unified molecular mechanism shaping even-skipped bursting strategies and serve as a starting point to uncover the realm of strategies employed by other enhancers.

Orexin receptor 2 agonist activates diaphragm and genioglossus muscle through stimulating inspiratory neurons in the pre-Bötzinger complex, and phrenic and hypoglossal motoneurons in rodents.

Orexin-mediated stimulation of orexin receptors 1/2 (OX[1/2]R) may stimulate the diaphragm and genioglossus muscle via activation of inspiratory neurons in the pre-Bötzinger complex, which are critical for the generation of inspiratory rhythm, and phrenic and hypoglossal motoneurons. Herein, we assessed the effects of OX2R-selective agonists TAK-925 (danavorexton) and OX-201 on respiratory function. In in vitro electrophysiologic analyses using rat medullary slices, danavorexton and OX-201 showed tendency and significant effect, respectively, in increasing the frequency of inspiratory synaptic currents of inspiratory neurons in the pre-Bötzinger complex. In rat medullary slices, both danavorexton and OX-201 significantly increased the frequency of inspiratory synaptic currents of hypoglossal motoneurons. Danavorexton and OX-201 also showed significant effect and tendency, respectively, in increasing the frequency of burst activity recorded from the cervical (C3-C5) ventral root, which contains axons of phrenic motoneurons, in in vitro electrophysiologic analyses from rat isolated brainstem-spinal cord preparations. Electromyogram recordings revealed that intravenous administration of OX-201 increased burst frequency of the diaphragm and burst amplitude of the genioglossus muscle in isoflurane- and urethane-anesthetized rats, respectively. In whole-body plethysmography analyses, oral administration of OX-201 increased respiratory activity in free-moving mice. Overall, these results suggest that OX2R-selective agonists enhance respiratory function via activation of the diaphragm and genioglossus muscle through stimulation of inspiratory neurons in the pre-Bötzinger complex, and phrenic and hypoglossal motoneurons. OX2R-selective agonists could be promising drugs for various conditions with respiratory dysfunction.

The interactive effects of posture and biological sex on the control of muscle sympathetic nerve activity during rhythmic handgrip exercise.

Body posture and biological sex exhibit independent effects on the sympathetic neural responses to dynamic exercise. However, the neural mechanisms (e.g., baroreflex) by which posture impacts sympathetic outflow during rhythmic muscular contractions, and whether biological sex affects posture-mediated changes in efferent sympathetic nerve traffic during exercise, remain unknown. Thus, we tested the hypotheses that increases in muscle sympathetic nerve activity (MSNA) would be greater during upright compared with supine rhythmic handgrip (RHG) exercise, and that females would demonstrate smaller increases in MSNA during upright RHG exercise than males. Twenty young (30 [6] yr; means [SD]) individuals (9 males, 11 females) underwent 6 min of supine and upright (head-up tilt 45°) RHG exercise at 40% maximal voluntary contraction with continuous measurements of MSNA (microneurography), blood pressure (photoplethysmography), and heart rate (electrocardiogram). In the pooled group, absolute MSNA burst frequency (P < 0.001), amplitude (P = 0.009), and total MSNA (P < 0.001) were higher during upright compared with supine RHG exercise. However, body posture did not impact the peak change in MSNA during RHG exercise (range: P = 0.063-0.495). Spontaneous sympathetic baroreflex gain decreased from rest to RHG exercise (P = 0.006) and was not impacted by posture (P = 0.347). During upright RHG exercise, males demonstrated larger increases in MSNA burst amplitude (P = 0.002) and total MSNA (P = 0.001) compared with females, which coincided with greater reductions in sympathetic baroreflex gain among males (P = 0.004). Collectively, these data indicate that acute attenuation of baroreflex-mediated sympathoinhibition permits increases in MSNA during RHG exercise and that males exhibit a greater reserve for efferent sympathetic neural recruitment during orthostasis than females.NEW & NOTEWORTHY The impact of posture and sex on cardiovascular control during rhythmic handgrip (RHG) exercise is unknown. We show that increases in muscle sympathetic nerve activity (MSNA) during RHG are partly mediated by a reduction in sympathetic baroreflex gain. In addition, males demonstrate larger increases in total MSNA during upright RHG than females. These data indicate that the baroreflex partly mediates increases in MSNA during RHG and that males have a greater sympathetic vasoconstrictor reserve than females.

Inhibitory Subpopulations in preBötzinger Complex Play Distinct Roles in Modulating Inspiratory Rhythm and Pattern.

Inhibitory neurons embedded within mammalian neural circuits shape breathing, walking, and other rhythmic motor behaviors. At the core of the neural circuit controlling breathing is the preBötzinger Complex (preBötC), where GABAergic (GAD1/2+) and glycinergic (GlyT2+) neurons are functionally and anatomically intercalated among glutamatergic Dbx1-derived (Dbx1+) neurons that generate rhythmic inspiratory drive. The roles of these preBötC inhibitory neurons in breathing remain unclear. We first characterized the spatial distribution of molecularly defined preBötC inhibitory subpopulations in male and female neonatal double reporter mice expressing either tdTomato or EGFP in GlyT2+, GAD1+, or GAD2+ neurons. We found that the majority of preBötC inhibitory neurons expressed both GlyT2 and GAD2 while a much smaller subpopulation also expressed GAD1. To determine the functional role of these subpopulations, we used holographic photostimulation, a patterned illumination technique, in rhythmically active medullary slices from neonatal Dbx1tdTomato;GlyT2EGFP and Dbx1tdTomato;GAD1EGFP double reporter mice of either sex. Stimulation of 4 or 8 preBötC GlyT2+ neurons during endogenous rhythm prolonged the interburst interval in a phase-dependent manner and increased the latency to burst initiation when bursts were evoked by stimulation of Dbx1+ neurons. In contrast, stimulation of 4 or 8 preBötC GAD1+ neurons did not affect interburst interval or latency to burst initiation. Instead, photoactivation of GAD1+ neurons during the inspiratory burst prolonged endogenous and evoked burst duration and decreased evoked burst amplitude. We conclude that GlyT2+/GAD2+ neurons modulate breathing rhythm by delaying burst initiation while a smaller GAD1+ subpopulation shapes inspiratory patterning by altering burst duration and amplitude.

Ganglionic blockade modulates sympathetic neural discharge and neurocirculatory regulation in humans

This study investigated the impact of integrated muscle sympathetic nerve activity (MSNA) discharge patterns on human neurocirculatory regulation. In 13 healthy females (42 ± 15 years), the transduction of integrated MSNA (peroneal microneurography) into mean arterial pressure (MAP; arterial catheter) was studied during an intravenous infusion of a nicotinic ganglionic antagonist (trimethaphan camsylate, 1-7 mg/min). Neurovascular transduction (signal averaging) was studied based on the overall response, burst sequence (singlet, doublet, and triplet+), and burst amplitude (binned into tertials: small, medium, and large bursts). Data (mean ± SD) are reported for a 10-minute baseline (BSL), the one-minute period at the midpoint of the trimethaphan infusion with integrated MSNA bursts (TM-Mid), and the last minute of trimethaphan infusion with integrated MSNA bursts (TM-Last). During BSL, the MAP transduction responses were greatest for triplets+ (singlets: 0.9 ± 0.2 mmHg, doublets: 2.0 ± 0.6 mmHg, triplet+: 2.6 ± 0.9 mmHg; P &lt; 0.01) and large bursts (small: 1.0 ± 0.3 mmHg, medium: 1.7 ± 0.5 mmHg, large: 2.2 ± 0.7 mmHg; P &lt; 0.01). Trimethaphan infusion reduced integrated MSNA burst frequency resulting in a greater proportion of singlets (BSL: 45 ± 18 %, TM-Mid: 75 ± 23 %, TM-Last: 94 ± 20 %; P &lt; 0.01), a lower proportion of doublets, and a lower proportion of triplets+ (BSL: 23 ± 19 %, TM-Mid: 9 ± 18 %, TM-Last: 0 ± 0 %; P &lt; 0.01). Trimethaphan infusion reduced integrated MSNA burst amplitude resulting in a greater proportion of small bursts (BSL: 33 ± 0.2 %, TM-Mid: 60 ± 26 %, TM-Last: 78 ± 37 %; P &lt; 0.01), a lower proportion of medium bursts, and a lower proportion of large bursts (BSL: 34 ± 1 %, TM-Mid: 17 ± 26 %, TM-Last: 1 ± 5 %; P &lt; 0.01). Trimethaphan-mediated changes in MSNA burst frequency and amplitude were associated with reduced overall MAP transduction responses (BSL: 1.6 ± 0.5 mmHg, TM-Mid: 0.5 ± 0.2 mmHg, TM-Last: 0.3 ± 0.3 mmHg; P &lt; 0.01). Linear regression analyses demonstrated that the trimethaphan-mediated reduction in the proportion of large bursts ( β = 0.02 ± 0.008 mmHg/%, R2 = 0.13, P = 0.03) more strongly affected sympathetic neurovascular transduction responses than reductions in the proportion of triplet+ burst sequences (P = 0.91). These findings suggest that time varying MSNA discharge patterns, particularly variations in burst amplitude, support human neurocirculatory regulation. This work was supported by the National Institutes of Health and the Natural Sciences and Engineering Research Council of Canada. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Crosstalk Inhibition Between 5-HT2A and Adenosine 2A Receptor-Induced Phrenic Motor Facilitation

Episodic spinal serotonin receptor activation elicits phrenic motor facilitation (pMF), a form of respiratory motor plasticity. Although both intermittent 5-HT2 and 5-HT7 receptor activation elicit pMF, they do so via distinct cellular mechanisms known as the Q (5-HT2A/B) and S (5-HT7) pathways. The Q and S pathways interact via powerful crosstalk inhibition; thus, concurrent activation of both receptor subtypes diminishes/abolishes pMF. At least some of the molecules giving rise to mutually inhibitory interactions between 5-HT2 and 5-HT7 receptors have been identified. Although episodic spinal adenosine 2A (A2A) receptor activation also elicits pMF via the S pathway, we do not know: 1) if 5-HT2 and A2A receptors interact via similar crosstalk inhibition, nor 2) if they do so via the same signaling mechanisms. Thus, we tested the hypothesis that concurrent 5-HT2 and A2A receptor activation diminishes pMF via crosstalk inhibition. Selective 5-HT2A (DOI) and A2A receptor agonists (CGS21680) were delivered to the C4 intrathecal space (3, 6 μl injections, 5-min intervals) in urethane anesthetized, artificially ventilated, vagotomized and paralyzed Sprague Dawley rats. Integrated phrenic nerve burst activity was measured before (baseline), during and 90 minutes post-drug injection. Spinal 5-HT2A and A2A receptor activation both increased phrenic nerve burst amplitude when delivered alone (i.e., pMF); however, pMF was no longer apparent with concurrent receptor activation. The magnitude of pMF, expressed as a % change in phrenic burst amplitude from baseline to 90-min post-injection, was significantly lower with concurrent receptor activation (5-HT2A + A2A= 15 ± 7.7%; n=5) versus 5-HT2A (84 ± 12%; n=5, p=0.0047) and A2A (88 ± 16%; n=5, p=0.0085) alone. Thus, 5-HT2A and A2A receptors interact via crosstalk inhibition similar to 5-HT2 and 5-HT7 receptors. However, the mechanism underlying this crosstalk inhibition remains unknown. NIH HL148030. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A NOVEL METHOD FOR THE ANALYSIS OF RENAL SYMPATHETIC NERVE ACTIVITY FROM MULTI-FIBER NERVE RECORDINGS

Objective: Measurement of renal sympathetic nerve activity (RSNA) via bipolar electrodes from multi-fiber preparations in various species has been used for decades in the context of autonomic regulation research. Traditionally, raw neurograms are usually integrated over short time intervals and this approach works perfectly for the analysis of dynamic RSNA changes due to acute intervention. However, comparability of baseline activities between groups is limited. We present a novel analysis method, based on the raw neurogram sampled at rate of 25 kHz. Design and method: For RSNA-burst analysis a software based programmable algorithm was used. Continuous activities longer than three single spikes (i.e., &gt;8ms) were defined as bursts, followed by silent periods with some single spikes. Approximately 10.000 bursts/rat were analyzed and burst amplitude, burst duration, burst area (i.e., duration integral), as well as the burst frequencies were analyzed. Results: In rats with myocardial infarction (n=11) we found no difference in integrated baseline RSNA as compared to controls ((n=10). However, the new method revealed higher higher burst rate per cardiac cycle [CC] (2.65 ± 0.39 vs. 1.61 ± 0.38 bursts/CC; P&lt;0.001) and burst frequency (15.09 ± 2.42 vs. 8.52 ±1.54 Hz; P&lt;0.001) compared to healthy controls, indicating increased RSNA. Conclusions: Our new method of RSNA baseline analysis was able to detect subtle differences between groups of animals that could not be detected by the traditional method of integrated RSNA analysis. Furthermore, this method has the potential to give further insights into RNSA patterns and synchronization to afferent regulatory input form the kidney itself or other organs.

Chemogenetic phrenic motoneuron activation enables increased tidal volume

Reduced output of the phrenic neuromuscular system and the resultant respiratory insuffciency occurs in many neuromuscular disorders. We hypothesized that expressing an excitatory DREADD (designer receptors exclusively activated by designer drugs) in phrenic motoneurons would enable DREADD-ligand induced increases in inspiratory tidal volume in awake, freely behaving rats. ChAT-Cre rats (n= 9; female n= 3) underwent bilateral injections of a Cre-dependent viral construct, AAV9-hSyn-DIO-hM3D(Gq)-mCherry (titer: 2.07x1012 vg/mL) into the mid-cervical (C4) ventral horn (1 μl injected per side). The combination of focal AAV injection and Cre-dependent expression was expected to drive hM3D(Gq) expression primarily in phrenic motoneurons, which are ChAT-positive and located in the C3-C5 ventral horn. Whole-body plethysmography was used to measure breathing frequency, tidal volume, and minute ventilation before and after intravenous delivery of a DREADD ligand, JHU37160 (J60), or saline (sham). Delivery of the ligand produced an increase in inspiratory tidal volume compared to saline infusion (two-way RM ANOVA, p= 0.037). Respiratory rate was similar between the two conditions (p= 0.582). Two weeks after plethysmography recordings, rats were urethane anesthetized and phrenic nerve electrical activity was directly recorded using suction electrodes. This procedure was done to directly assess the impact of intravenous delivery of the DREADD ligand on phrenic motoneuron output. The J60 ligand caused a rapid, sustained, and bilateral increase in phrenic nerve efferent burst amplitude (one-way RM ANOVA, p&lt; 0.001), whereas saline injection had no impact. The increase in phrenic burst amplitude lasted up to 100 minutes, at which point the experiment was stopped. We conclude that expression of an excitatory DREADD in phrenic motoneurons enables DREADD ligand induced increases in tidal volume in the awake, unrestrained rat. The phrenic nerve recordings verify that this response very likely reflects activation of phrenic motoneurons. Funding: R01HD052682-14 (DDF), R01HL153140-04 (DDF), University of Florida Graduate Fellowship (ESB). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Biological Sex Modestly Influences the Impact of Long Duration Bed Rest on Human Sympathetic Neurocirculatory Regulation

Our understanding regarding the impact of simulated microgravity on sympathetic neurocirculatory regulation, and the modulatory effects of biological sex, remain incomplete. Through retrospective analysis of two long-duration bed rest trials, this study investigated the impact of 60 days of -6° head-down bed rest (HDBR) on the transduction of integrated muscle sympathetic nerve activity (MSNA; peroneal microneurography) into mean arterial pressure (MAP; Finometer) in healthy females ( n = 12, 25-40 years) and males ( n = 13, 21-42 years). Signal averaging quantified sympathetic transduction for 12 cardiac cycles (ECG) following integrated MSNA bursts. The transduction of integrated MSNA bursting patterns was studied based on the overall response, temporal burst firing patterns (singlet, doublet, and triplet+), and burst amplitude (binned into quartiles: Q1-Q4). Data are reported as mean (SD) for a 5-minute baseline period pre-HDBR and post-HDBR. Statistical analysis included mixed-effect analyses with post-hoc t-tests. In the pooled analyses, HDBR reduced the overall MAP transduction response to integrated MSNA bursts (pre-HDBR: 1.4 ± 0.5 mmHg, post-HDBR: 1.1 ± 0.4 mmHg; P = 0.003). This stemmed from attenuated MAP transduction responses to small- and medium-sized bursts (i.e., Q1-Q3) but there was no effect of HDBR on the largest bursts (i.e., Q4: pre-HDBR: 2.2 ± 0.9 mmHg, post-HDBR: 2.1 ± 0.9 mmHg; P = 0.59). HDBR did not affect the transduction response to singlets (P = 0.23), but HDBR reduced the MAP transduction responses to doublets and triplets+ (both P &lt; 0.03). HDBR did not affect the reduction in MAP during non-bursting periods (pre-HDBR: -0.5 ± 0.2 mmHg, post-HDBR: -0.4 ± 0.2 mmHg; P = 0.17). When stratifying the analyses by sex, we observed that HDBR reduced the overall MAP transduction response to integrated MSNA bursts more so in males (P &lt; 0.01) than females (P = 0.14). Conversely, HDBR did not affect the MAP reductions following non-bursting periods in males (P = 0.53), but in females the reduction in MAP following non-bursting periods was less after HDBR, particularly for cardiac cycles 5 to 7 (pre-HDBR: -0.8 ± 0.5 mmHg, post-HDBR: -0.5 ± 0.3 mmHg; P = 0.03). These data suggest that 60 days of HDBR attenuates sympathetic neurocirculatory regulation during baseline conditions, with a modest influence of biological sex. This work was supported by the Canadian Space Agency, Centre National d'Etudes Spatiales, European Space Agency, National Aeronautics and Space Administration, Institute of Aerospace Medicine of the German Aerospace Center (DLR), Fond Européen de Développement Régional (FEDER) and the Natural Sciences and Engineering Research Council of Canada (NSERC). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Effect of Sex on Sympatho-inhibitors and Non-inhibitor Phenotypes during Acute Hyperoxia

Acute hyperoxia (i.e., breathing air consisting of 100% oxygen, O2) reduces muscle sympathetic nerve activity (MSNA), positioning hyperoxia as a potential anti-hypertensive therapeutic. However, the link between hyperoxia and MSNA has not been established in females. We tested the hypothesis that males would exhibit greater reductions in MSNA during hyperoxia than females. We tested healthy females (n=18, 27±5yr, body mass index [BMI] 23±3kg/m2) and males (n=13, 27±5yr, 25±3kg/m2) of similar age (P=0.99) and BMI (P=0.08). Integrated MSNA, blood pressure, and end-tidal O2 (ETO2) and CO2 (ETCO2) were measured during normal room air breathing (BSL; 3-min) and hyperoxic breathing (100% O2; 3-min). Integrated MSNA was quantified as burst frequency (BF; bursts/min), amplitude (BA; a.u.), and total MSNA (a.u.); blood pressure was quantified as mean arterial pressure (MAP). Baseline MSNA BF was not different between females and males (24±7 vs 23±8 bursts/min, respectively, P=0.68); MAP was lower in females than males (85±7 vs 93±7 mmHg; p&lt;0.01). Hyperoxia increased ETO2 (effect of cond: p&lt;0.01) and reduced ETCO2 (effect of cond: p&lt;0.01) in a manner similar between sexes for ETO2 (sex*cond: P=0.56) whereas ETCO2 decreased more in females than males (sex*cond: P=0.01). Overall, hyperoxia evoked reductions in MSNA BF (effect of cond: P=0.02) but not BA (effect of cond: P=0.80) or total MSNA (effect of cond: P=0.26). Nadir MSNA responses during hyperoxia unveiled sex differences insofar as total MSNA was reduced consistently only in males (sex*cond: P=0.04); within the females we observed the presence of sympatho-inhibitors and non-inhibitors. Whereas female and male inhibitors reduced total MSNA via substantial reductions in BF and non-significant reductions in BA, female non-inhibitors demonstrated limited reductions in BF (P=0.11 vs inhibitors) coupled with increases in BA (p&lt;0.01 vs inhibitors), resulting in no net change in total MSNA (p&lt;0.01 vs inhibitors). Overall, these findings indicate sex differences exist in the sympathetic response to hyperoxia, in marked variability in the female sympathetic response to acute hyperoxia. The Women and Children's Health Research Institute. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Contribution of Ih to Postnatal Maturation of Muscarinic Modulation of Inspiratory Bursting at Hypoglossal Motoneurons in Neonatal Mice

Activation of hypoglossal motoneurons (XII MNs) contributes to stiffening of the upper airway during inspiration. The magnitude of this excitation is decreased during sleep, likely due to a combination of withdrawal of noradrenaline and acetylcholine release at XII MNs. Acetylcholine acts at muscarinic acetylcholine receptors (mAChRs) and surprisingly mAChR activation has an excitatory effect on inspiratory bursting in neonatal preparations, which becomes inhibitory in adult preparations. mAChRs modulate several ion channels and characterizing muscarinic effect changes at the XII nucleus will help to explain the mechanism of the inhibitory shift over postnatal maturation. The hyperpolarization activated cyclic nucleotide gated (HCN) channel is positively modulated by mAChRs. HCN channels give rise to Ih, a mixed cation current activated at hyperpolarized membrane potentials that contribute to membrane depolarization. Ihincreases dramatically with postnatal maturation in XII MNs. Thus, we hypothesize that 1) the effects of muscarinic modulation of Ih increases with postnatal maturation, and 2) that muscarinic activation of Ih contributes to the net inhibitory component of muscarinic modulation of inspiratory bursting at XII motoneurons. To test our hypotheses, we used the rhythmic medullary slice preparation to test the functional effects of muscarinic modulation of Ih on inspiratory bursting in neonatal CD1 mice (postnatal day, P0-P4) in combination with pharmacological block of Ih with ZD7288 (25 μM, 150s). Local application of muscarine (100μM, 30s) in the XII motor nucleus increased inspiratory burst amplitude (189 ± 58% of baseline, n = 9). Contrary to our hypothesis, there was no statistically significant difference between inspiratory burst amplitude elicited by muscarine in the presence of ZD7288 (192 ± 47% of baseline, n = 9) versus with the aCSF vehicle control (174 ± 43% of baseline, p = 0.098). We next tested a higher ZD7288 concentration (100 μM) and longer application times (150s, 330s) in neonatal preparations. Preliminary data (n=2) indicate that ZD7288 may increase muscarinic potentiation of inspiratory burst amplitude at XII MNs (muscarinic potentiation (100μM, 30s): control — 112 ±65 % of baseline, aCSF vehicle control - 131 ± 38% of baseline; ZD7288 100μM, 150s - 148 ± 44% of baseline; ZD7288 100μM, 330s - 107 ± 72% of baseline). Future research will elucidate whether the Ih contribution to muscarinic modulation of inspiratory bursting increases with postnatal maturation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Characterization of HCN channel subtypes at hypoglossal motoneurons throughout postnatal maturation in mice

The inspiratory phase of breathing includes a stiffening of the upper airway to decrease airway resistance and is mediated by excitatory motor output from hypoglossal motoneurons (XII MNs). This excitation decreases from wakefulness to sleep. This decrease in excitation is in large part due to increasing acetylcholine levels, which activate muscarinic acetylcholine receptors (mAChRs) that have a net inhibitory effect in adult preparations. By contrast, activation of mAChRs in neonatal rodent preparations has a net effect of potentiating inspiratory burst amplitude. Therefore, characterizing changes in muscarinic effects at XII MNs across postnatal maturation will help elucidate the mechanism underlying the shift from muscarinic excitation to inhibition. mAChRs modulate several effector ion channels including the hyperpolarization activated cyclic nucleotide gated (HCN) channel. HCN channels give rise to I h, a mixed cation current activated at hyperpolarized membrane potentials. I h additionally shows upregulation at XII MNs with postnatal maturation. Since there are four HCN subtypes (HCN1-4), the reported changes in I h may be caused by changes in HCN channel subtype levels. HCN1 and HCN2 are most prominent in adult XII MNs, whereas the expression of HCN1-4 in neonates is unknown. Thus, the purpose of this research is to characterize changes in HCN gene and channel expression levels at XII MNs across postnatal maturation. We hypothesis that both HCN1 and HCN2 subtypes will increase with postnatal maturation, and that HCN2 has higher levels than HCN1. To test this hypothesis, we used neuroanatomical techniques to evaluate changes in expression patterns of the four HCN proteins at the XII nuclei across postnatal maturation in CD-1 mice. We performed double-labeled immunofluorescence experiments against HCN1 and HCN2 and co-labeled with choline acetyltransferase (ChAT) on 20μm transverse brainstem slices across six postnatal age groups under identical conditions: P0-P1, P4-P6, P9-P10, P12-P14, P17-P19, and adult. Images of the XII nuclei were collected using a confocal microscope. ImageJ was used to determine the average XII MN HCN subtype intensity across postnatal maturation. Preliminary data suggest that HCN1 (n=2) channels undergo a decrease in expression at P17-19 before a final increase in adulthood (P0-1= 97-100%, P4-6= 92-100%, P9-10= 85-95%, P12-14= 77-97%, P17-19= 61-67%, adult= 71-82%). By contrast, preliminary data suggest that HCN2 (n=2) expression intensity remained relatively consistent with a decrease in labeling intensity at P4-6 (P0-1= 97-100%, P4-6=62-84%, P9-10= 45-95%, P12-14= 67-90%, P17-19= 50-93%, adult= 75-100%). These modest changes in labeling intensity of HCN channel subtypes may not contribute to the observed shift of mAChR modulation at XII MNs from excitation to inhibition with postnatal maturation. Biomedical Sciences, College of Graduate Studies; Department of Physiology, College of Graduate Studies, Midwestern University; NIH/NHLBI Funding: R15HL148870. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.