Conscious Rabbits Research Articles

Non-invasive blood pressure measurement in conscious rabbits: A comparison of Doppler ultrasonic and oscillometric devices.

This study aimed to compare Doppler (the most commonly used technique for non-invasive indirect blood pressure [NIBP] measurement in rabbits) and oscillometric devices for NIBP measurements in conscious rabbits. Blood pressure (BP) measurements were obtained for49 conscious rabbits using the Doppler and oscillometric devices. Each measurement was repeated in triplicate. Three rabbits were excluded from the study because it was not possible to obtain BP measurements using the oscillometric device. The American College of Veterinary Internal Medicine (ACVIM) guidelines were followed to compare the results obtained with the two devices. A total of 164 systolic BP measurements were obtained with the Doppler device and 182 were obtained with the oscillometric technique. The mean of the three values obtained for each animal with each device was used for statistical analysis. The analysis demonstrated a poor level of agreement between the measurements obtained with the two devices. Oscillometric devices rely on built-in software algorithms to perform calculations and produce their measurements. However, the oscillometric devices currently available only have the software for dogs and cats installed. Therefore, these conclusions should be revised when a device with software specifically for rabbits is commercialised. This study indicates that oscillometric devices should not be used as a substitute for the Doppler technique when measuring BP in rabbits.

Hemorrhage Magnitude Correlates with Sympathetic Vasomotion in Conscious Rabbits

Each year, over 1.8 million people die from hemorrhagic shock, and the median time from onset to death is only two hours, making early recognition and prompt action the cornerstone of management. The sympathetic nervous system is the most rapid physiological hemodynamic compensatory mechanism, and we have developed a novel measure of sympathetic vascular control called sympathetic vasomotion which could serve as an early marker of hemorrhage. We performed unilateral renal denervation on six rabbits and instrumented these rabbits with bilateral renal flow probes and arterial pressure telemeters to allow for measurement of sympathetic vasomotion. After a two-week recovery period, the rabbits then underwent controlled blood withdrawal via an auricular arterial catheter. The differences in admittance gain and phase shift occurrence between the innervated and denervated kidneys increased significantly before any other hemodynamic changes. Over the first 15 minutes of hemorrhage, the differences in admittance gain and phase shift correlated with hemorrhage magnitude (r = 0.69 and 0.63, respectively), whereas the differences in coherence did not. The sum of the admittance gain and phase shift differences showed a slightly higher correlation with hemorrhage magnitude (r = 0.71). This data suggests that some features of sympathetic vasomotion may be useful as a biomarker for diagnosing early-stage normotensive hemorrhage and assessing treatment response. Further studies are needed to evaluate the utility of sympathetic nervous system monitoring in clinical contexts. Supported by NIH P01 HL62222 and NIH F30 HL118974. 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.

Existence of Quantum Pharmacology in Sartans: Evidence in Isolated Rabbit Iliac Arteries.

Quantum pharmacology introduces theoretical models to describe the possibility of ultra-high dilutions to produce biological effects, which may help to explain the placebo effect observed in hypertensive clinical trials. To determine this within physiology and to evaluate novel ARBs, we tested the ability of known angiotensin II receptor blockers (ARBs) (candesartan and telmisartan) used to treat hypertension and other cardiovascular diseases, as well as novel ARBs (benzimidazole-N-biphenyl tetrazole (ACC519T), benzimidazole-bis-N,N'-biphenyl tetrazole (ACC519T(2)) and 4-butyl-N,N0-bis[[20-2Htetrazol-5-yl)biphenyl-4-yl]methyl)imidazolium bromide (BV6(K+)2), and nirmatrelvir (the active ingredient in Paxlovid) to modulate vascular contraction in iliac rings from healthy male New Zealand White rabbits in responses to various vasopressors (angiotensin A, angiotensin II and phenylephrine). Additionally, the hemodynamic effect of ACC519T and telmisartan on mean arterial pressure in conscious rabbits was determined, while the ex vivo ability of BV6(K+)2 to activate angiotensin-converting enzyme-2 (ACE2) was also investigated. We show that commercially available and novel ARBs can modulate contraction responses at ultra-high dilutions to different vasopressors. ACC519T produced a dose-dependent reduction in rabbit mean arterial pressure while BV6(K+)2 significantly increased ACE2 metabolism. The ability of ARBs to inhibit contraction responses even at ultra-low concentrations provides evidence of the existence of quantum pharmacology. Furthermore, the ability of ACC519T and BV6(K+)2 to modulate blood pressure and ACE2 activity, respectively, indicates their therapeutic potential against hypertension.

Taipan Natriuretic Peptides Are Potent and Selective Agonists for the Natriuretic Peptide Receptor A.

Cardiovascular ailments are a major cause of mortality where over 1.3 billion people suffer from hypertension leading to heart-disease related deaths. Snake venoms possess a broad repertoire of natriuretic peptides with therapeutic potential for treating hypertension, congestive heart failure, and related cardiovascular disease. We now describe several taipan (Oxyuranus microlepidotus) natriuretic peptides TNPa-e which stimulated cGMP production through the natriuretic peptide receptor A (NPR-A) with higher potencies for the rat NPR-A (rNPR-A) over human NPR-A (hNPR-A). TNPc and TNPd were the most potent, demonstrating 100- and 560-fold selectivity for rNPR-A over hNPR-A. In vivo studies found that TNPc decreased diastolic and systolic blood pressure (BP) and increased heart rate (HR) in conscious normotensive rabbits, to a level that was similar to that of human atrial natriuretic peptide (hANP). TNPc also enhanced the bradycardia due to cardiac afferent stimulation (Bezold-Jarisch reflex). This indicated that TNPc possesses the ability to lower blood pressure and facilitate cardiac vagal afferent reflexes but unlike hANP does not produce tachycardia. The 3-dimensional structure of TNPc was well defined within the pharmacophoric disulfide ring, displaying two turn-like regions (RMSD = 1.15 Å). Further, its much greater biological stability together with its selectivity and potency will enhance its usefulness as a biological tool.

Low-level tragus stimulation improves autoantibody-induced hyperadrenergic postural tachycardia syndrome in rabbits

Recent studies have demonstrated that antiadrenergic autoantibodies are involved in the pathophysiology of postural orthostatic tachycardia syndrome (POTS). The purpose of this study was to test the hypothesis that transcutaneous low-level tragus stimulation (LLTS) ameliorates autoantibody-induced autonomic dysfunction and inflammation in a rabbit model of autoimmune POTS. Six New Zealand white rabbits were co-immunized with peptides from the α1-adrenergic and β1-adrenergic receptors to produce sympathomimetic antibodies. The tilt test was performed on conscious rabbits before immunization, 6 weeks after immunization, and 10 weeks after immunization with 4-week daily LLTS treatment. Each rabbit served as its own control. An enhanced postural heart rate increase in the absence of significant change in blood pressure was observed in immunized rabbits, confirming our previous report. Power spectral analysis of heart rate variability during the tilt test showed a predominance of sympathetic over parasympathetic activity in immunized rabbits as reflected by markedly increased low-frequency power, decreased high-frequency power, and increased low-to-high-frequency ratio. Serum inflammatory cytokines were also significantly increased in immunized rabbits. LLTS suppressed the postural tachycardia, improved the sympathovagal balance with increased acetylcholine secretion, and attenuated the inflammatory cytokine expression. Antibody production and activity were confirmed with invitro assays, and no antibody suppression by LLTS was found in this short-term study. LLTS improves cardiac autonomic imbalance and inflammation in a rabbit model of autoantibody-induced hyperadrenergic POTS, suggesting that LLTS may be used as a novel neuromodulation therapy for POTS.

Abstract 14182: A Missense Mutation in Ryanodine Receptor 2 Leads to Structural Remodeling of the Heart and Cardiac Arrhythmia in a Rabbit Model

Ryanodine receptor 2 (RyR2) is the Ca 2+ release channel of sarcoplasmic reticulum that provides the majority of Ca 2+ necessary for contractions of the heart. RyR2 mutations are linked to catecholaminergic polymorphic ventricular tachycardia (CPVT), an inherited arrhythmogenic disorder with normal heart structure. There are reports suggesting that RyR2 mutations can also lead to structural heart disease, notably arrhythmogenic right ventricular cardiomyopathy (ARVC); however, additional research is required to support this association. We generated a rabbit model carrying the missense mutation RyR2-V2475F, linked to CPVT in humans. Heterozygous (V2475F +/- ) rabbits show a CPVT-like syndrome and display arrhythmia under pharmacological stress. Homozygotes (V2475F +/+ ) show a stronger phenotype, with 37% of the animals (13/35) experiencing sudden death at 22.5±3.8 weeks old during regular housing. Remarkably, gross examination of V2475F +/+ hearts showed significant structural remodeling, characterized by fibrous infiltrations and thinning of the right ventricle with or without left ventricle involvement. This phenotype is reminiscent of ARVC. Lead II ECG obtained in conscious rabbits by telemetry showed that V2475F +/+ animals have significant bradycardia (144.6±11.1 bpm) with prolonged QT interval (QTc: 180.4±8.2 ms, n=6) compared to WT (HR: 224.9±4.2 bpm, p=0.04; QTc: 157.4±5.3 ms, p=0.02, n=5). After subcutaneous injection of 0.5 mg/kg of isoproterenol, WT rabbits showed the expected positive chronotropic response (HR, 367±10 bpm, n=3) while V2475F +/+ animals developed bouts of ventricular tachycardia. Mild emotional stress applied by transporting the animal around the laboratory, also induced ventricular arrhythmia in 100% (5/5) V2475F +/+ rabbits, while WT littermates were unaffected. RyR2-V2475F expressed in a rabbit model triggers remarkably different phenotypes based on the zygosity of the animals, ranging from a purely arrhythmogenic syndrome (CPVT) in V2475F +/- animals to severe structural disease compatible with ARVC in V2475F +/+ rabbits. The RyR2-V2475F rabbit model is therefore an excellent model to dissect the intersection of arrhythmic and structural phenotypes due to RyR2 dysfunction.

Carotid Baroreceptor Magnetic Activation and Beat-to-Beat Blood Pressure Variability, Implications to Treat Abrupt Blood Pressure Elevation in Labile Hypertension.

Mounting evidence suggests enhanced blood pressure (BP) variability (BPV) independent role in cardiovascular (CV) damage. The goal was to estimate the effect of the carotid baroreceptor (CB) magnetic stimulation on sudden high BP elevation. Mean femoral arterial BP (MAP), heart rate (HR), baroreflex sensitivity (BRS), and ear lobe skin microcirculatory blood flow, by microphotoelectric plethysmography (MPPG), were simultaneously recorded in conscious rabbits sedated by pentobarbital intravenous (i.v.) infusion (5 mg/kg/h) after 40 min CB exposure to 350 mT static magnetic field (SMF), by Nd2 -Fe14 -B magnets (n = 14), or sham magnets exposure (n = 14). BRS was assessed from HR and MAP responses to abrupt hypotension induced by i.v. bolus injections of nitroprusside (Ni) and abrupt MAP elevation (MAPAE ) by i.v. bolus of phenylephrine (Ph). Beat-to-beat BPV was estimated by MAP standard deviation. SMF CB exposure significantly increased BRSNi (74.5 ± 17.8%, P < 0.001) and microcirculation (23.8% ± 11.0%, P = 0.039); decreased MAP (-5.7 ± 1.7%, P < 0.014) and phenylephrine-induced MAPAE (-19.1%, P = 0.043). MAPAE positively correlated with resting MAP (r = 0.342, P = 0.0383) and MAP SD (r = 0.383, P = 0.0194), and inversely with BRSPh (r = -0.47, P = 0.0156). SMF CB exposure enhanced the nitroprusside, which acts by releasing nitric oxide (NO), vasodilatory effect. This indicates arterial baroreflex to improve vessel sensitivity to NO, which is a new physiology with BP buffering effect. A positive correlation of MAP SD to phenylephrine BP ramps suggests a causal relationship and BPV prognostic significance to forecast abrupt BP elevation. Mechano/baroreceptor magneto-sensing property proposed to be the basic physiology by which SMFs boost CV autonomic regulation with potential implementation in high CV risk labile arterial hypertensive disease. © 2022 Bioelectromagnetics Society.

Brain activity studied with magnetic resonance imaging in awake rabbits.

We reviewed fMRI experiments from our previous work in conscious rabbits, an experimental preparation that is advantageous for measuring brain activation that is free of anesthetic modulation and which can address questions in a variety of areas in sensory, cognitive, and pharmacological neuroscience research. Rabbits do not struggle or move for several hours while sitting with their heads restrained inside the horizontal bore of a magnet. This greatly reduces movement artifacts in magnetic resonance (MR) images in comparison to other experimental animals such as rodents, cats, and monkeys. We have been able to acquire high-resolution anatomic as well as functional images that are free of movement artifacts during several hours of restraint. Results from conscious rabbit fMRI studies with whisker stimulation are provided to illustrate the feasibility of this conscious animal model for functional MRI and the reproducibility of data gained with it.

A study of standard values of two-dimensional, M-mode and doppler echocardiography in conscious small domestic rabbits

A study of standard values of two-dimensional, M-mode and doppler echocardiography in conscious small domestic rabbits

Effect of preemptive topical application of lidocaine or prilocaine–lidocaine on successful catheterization of ear veins in New Zealand White rabbits

ObjectiveTo compare 5% lidocaine ointment applied for 10 minutes before intravenous (IV) catheterization to a eutectic mixture of local anesthetics (2.5% lidocaine and 2.5% prilocaine; EMLA) cream applied for 10 or 60 minutes prior and a water-based placebo for 60 minutes for successful marginal ear IV catheterization in rabbits. Study designRandomized, blinded, complete crossover, controlled trial. AnimalsA total of 10 intact male, New Zealand White rabbits aged 4 months. MethodsAfter application of one of the treatments on the marginal ear vein, an operator unaware of the treatment attempted IV catheter placement. Successful IV catheterization was considered as a catheter inserted at the first attempt, safely secured, with appropriate patency. Generalized linear mixed models were developed to identify relevant predictors of successful catheter placement. ResultsEars that had EMLA cream applied 60 minutes before the catheterization attempt had more than 10 times the odds of successful catheter placement [odds ratio (OR)=10.75; 95% confidence interval (CI), 1.92–60.16; p < 0.008] compared with placebo. Both the application of EMLA cream or lidocaine ointment 10 minutes before the catheterization attempt resulted in approximately three times the odds of successful catheter placement compared with placebo, but were not statistically significant. Conclusions and clinical relevanceApplication of EMLA cream on the marginal ear vein 60 minutes before catheterization increases the chance of successful IV catheter placement in conscious rabbits.

Transcutaneous vagus nerve stimulation attenuates autoantibody-mediated cardiovagal dysfunction and inflammation in a rabbit model of postural tachycardia syndrome.

Previous studies demonstrated M2 muscarinic acetylcholine receptor-activating autoantibodies (M2R-AAb) were present in some patients with postural tachycardia syndrome (POTS). This study examines how these autoantibodies might contribute to the pathophysiology of POTS, and whether low-level tragus stimulation (LLTS) can ameliorate autoantibody-mediated autonomic dysregulation in the rabbit. Five New Zealand white rabbits were immunized with a M2R second extracellular loop peptide to produce cholinomimetic M2R-AAb. Tilt test and infusion studies were performed on conscious rabbits before immunization, 6weeks after immunization, and 8weeks after immunization with 2-week daily LLTS treatment. Each rabbit served as its own control. Compared to preimmune state, an enhanced heart rate increase and decreased parasympathetic activity upon tilting were observed in immunized rabbits. Furthermore, these rabbits demonstrated an attenuated heart rate-slowing response to infusion of the M2R orthosteric agonist arecaidine propargyl ester (APE), suggesting an inhibitory allosteric effect of M2R-AAb. There was also a significant increase in serum inflammatory cytokines in immunized rabbits. LLTS treatment suppressed the postural tachycardia, improved the sympathovagal balance with increased acetylcholine secretion, reduced the levels of inflammatory cytokines, and reversed the attenuated heart rate response to APE in immunized rabbits. No suppression of M2R-AAb expression by LLTS was found during this short-term study period. Receptor-modulating activity of M2R-AAb produced in immunized rabbits was confirmed with in vitro bioassay. Autoantibody inhibition of cholinergic ligand activity may be involved in the development of cardiovagal dysfunction and inflammation associated with POTS, both of which can be improved by vagal stimulation.

Abstract 13994: Single-Dose Intervention With Rapamycin at Reperfusion Preserves Cardiac Function Through Attenuation of Inflammation and Increased Cardiomyocyte Proliferation in Diabetic Rabbit- Role of Hippo Pathway

Background: Rapamycin (RAPA, mTOR inhibitor) given at reperfusion protects diabetic rabbit hearts against ischemia/reperfusion (I/R) injury by reducing infarct size and apoptosis. We hypothesized that RAPA administration may preserve post-ischemic cardiac function through decreased inflammation and increased cardiomyocyte proliferation with regulation of YAP- the effector of Hippo pathway). Methods and Results: Diabetes (DM) was induced by administration of alloxan monohydrate (125 mg/kg, i.v.) in New Zealand rabbits (n=12; body weight≈3 kg, 4-month-old). Four weeks after alloxan treatments, conscious diabetic rabbits (maintaining blood glucose&gt;250 mg/dL) were subjected to 45 min of ischemia and 10 days of reperfusion (R) by inflating/deflating previously implanted hydraulic balloon occluder. RAPA (0.25 mg/kg, i.v.) or DMSO (vehicle) was infused 5 min before onset of R. Post-I/R cardiac function in diabetic rabbit, assessed by echocardiography, showed significant improvement of ejection fraction (EF, Fig. A ). Left ventricular fibrosis ( Fig. B , evaluated by picrosirius red staining) was attenuated following treatment of RAPA in diabetic rabbits. Immunofluorescence staining revealed the attenuation of post-I/R inflammasome formation with RAPA treatment as shown by reduced ASC aggregation (apoptosis speck-like protein with a caspase recruitment domain) in cardiomyocytes ( Fig. C ). RAPA suppressed the phosphorylation of YAP in cytosol of cardiomyocytes ( Fig. D ). Proliferation markers, Ki-67 positive and phospho-Aurora B Kinase positive cells indicated cardiomyocytes were in G2-M phase in RAPA-treated diabetic rabbits after I/R injury ( Fig. E ). Conclusion: RAPA treatment at reperfusion preserves cardiac function and improves cardiomyocyte proliferation with attenuation of inflammation and possibly regulation of Hippo pathway following I/R injury in diabetes.

Renal Deafferentation Prevents Progression of Hypertension and Changes to Sympathetic Reflexes in a Rabbit Model of Chronic Kidney Disease.

[Figure: see text].

Intraocular Pressure-Lowering Effects of Trabeculectomy Versus MicroShunt Insertion in Rabbit Eyes

PurposeTo compare the surgical results of PRESERFLO MicroShunt (MicroShunt) insertion and trabeculectomy in rabbit eyes.MethodsTrabeculectomy or MicroShunt insertion was performed on the eyes of Japanese white rabbits. Intraocular pressure (IOP) was measured on conscious rabbits using a rebound tonometer for up to 12 weeks after surgery. Filtering bleb appearance was evaluated. Scarring in the filtering bleb was assessed by immunohistochemical analyses. The change in mRNA expression in the conjunctiva was evaluated using RNA sequence analyses.ResultsThe preoperative IOP of the operative eye did not differ significantly between trabeculectomy (11.6 ± 1.0 mmHg, n = 10) and MicroShunt insertion (12.6 ± 1.3 mmHg, n = 10). In both groups, the IOP of the operative eye was significantly lower than that of the contralateral eye at one day postoperatively, which continued until 12 weeks after surgery. The peak differences in IOP were −8.4 ± 3.0 (trabeculectomy) and −8.1 ± 2.1 mmHg (MicroShunt) at two weeks after surgery; no significant differences were observed in IOP reduction between the groups. Appearance and immunohistochemical analyses of the filtering bleb showed no significant difference between the groups. Moreover, RNA sequence analysis results showed no difference between the groups in mRNA expression fluctuations.ConclusionsPostoperative IOP, bleb appearance, and immunohistochemical analysis results were similar in the trabeculectomy and MicroShunt groups, indicating that MicroShunt insertion is as effective as trabeculectomy in lowering IOP.Translational RelevanceComparison of surgical procedures using animal models has made it possible to predict clinical efficacy and safety.

Renal Sympathetic Denervation Does Not Consistently Affect Renal Input Impedance

The renal sympathetic nerves are important regulators of renal blood flow, and the investigation of renal blood flow markers of sympathetic innervation is important to the field of therapeutic renal denervation. Input impedance analysis is a classic method used to analyze the pressure-flow relationship of a vascular bed at the cardiac frequency and its harmonics, and renal sympathetic nerve activity shows robust cardiac cycle-related synchronization. Thus, we hypothesized that renal sympathetic denervation in two different animal models would result in consistent changes in renal input impedance, making it a potentially useful clinical marker of renal sympathetic innervation. Traditional ensemble-averaged impedance analysis (Figure 1) was performed on renal arterial pressure-flow data from ten conscious rabbits that underwent chronic, surgical renal denervation and nine anesthetized pigs that underwent acute, functional renal denervation via thoracic intrathecal administration of ropivacaine. A novel method in which input impedance was calculated for each beat of the recording, allowing for assessment of beat-to-beat impedance temporal variability, was also used. While acute functional renal denervation increased the impedance modulus in the swine model, no difference was observed in the highly controlled unilaterally denervated rabbit model (Figure 2). Renal denervation decreased beat-to-beat variability of the impedance modulus in both models of renal denervation. Renal denervation increased impedance phase shift variability in rabbits but not in swine. Renal sympathetic denervation does not consistently affect classic measures of input impedance. Beat-to-beat impedance modulus variability was greater in the innervated kidneys of both rabbits and pigs, highlighting the time-varying nature of renal sympathetic outflow which is not captured by traditional impedance analysis. Other pressure-flow analysis methods may be better suited for the identification of renal sympathetic innervation for clinical applications.

MODULATION OF SYMPATHETIC NERVE ACTIVITY BY SGLT2 INHIBITOR EMPAGLIFLOZIN IN DIABETIC RABBITS

Objective: Treatment with the sodium-glucose cotransporter 2 (SGLT2) inhibitor empagliflozin in patients with type-2 diabetes is associated with 38% reduction in cardiovascular mortality. We explored the notion that the mechanisms underlying these benefits may involve an action on the sympathetic nervous system (SNS). Design and method: Diabetes was induced by alloxan in New-Zealand White rabbits. We determined the associated changes in blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA) as well as baroreflex responses to changes in BP and norepinephrine spillover in conscious rabbits. The effects of one-week treatment with empagliflozin were compared to those of another blood glucose-lowering treatment insulin, the proximally-acting natriuretic acetazolamide, the ACE inhibitor perindopril, vehicle treatment and to an untreated diabetic group. Results: Diabetic rabbits were treated with daily insulin to maintain a stable elevation in blood glucose over 4 weeks (20.5 ± 0.4 mM vs 6.5 ± 0.4 mM in controls). BP was 9% greater in diabetic than non-diabetic rabbits (P = 0.02) but there were no differences in RSNA or HR. One-week treatment with empagliflozin (without insulin) lowered blood glucose by 43% but there was no difference in BP, HR or RSNA between these animals and untreated diabetic rabbits or those treated with acetazolamide. However, insulin treatment alone lowered blood glucose similarly to empagliflozin (32%) and increased HR (+10%) while perindopril lowered BP (-9%). In diabetic rabbits there was marked augmentation of the maximum RSNA response to baroreceptor unloading compared to non-diabetic (+69%, P &lt; 0.01). Empagliflozin attenuated the baroreflex by 34% and there was a similar reduction after acetazolamide (-29%, both P &lt; 0.05). Empagliflozin also attenuated the HR baroreflex (-8%) but insulin and perindopril had no effect on either baroreflex. Norepinephrine spillover to plasma was similar in diabetic and non-diabetic rabbits but was elevated after both empagliflozin and acetazolamide (+147% and + 134%, P &lt; 0.05). Conclusions: Empagliflozin normalised the maximal RSNA response to lowering BP, which was exaggerated in diabetic rabbits, without altering BP or resting RSNA. A similar action of the natriuretic acetazolamide suggests that the mechanism underlying the cardiovascular benefits of empagliflozin may involve increased sodium and water excretion.

Multi-system Monitoring for Identification of Seizures, Arrhythmias and Apnea in Conscious Restrained Rabbits.

Patients with ion channelopathies are at a high risk of developing seizures and fatal cardiac arrhythmias. There is a higher prevalence of heart disease and arrhythmias in people with epilepsy (i.e., epileptic heart.) Additionally, cardiac and autonomic disturbances have been reported surrounding seizures. 1:1,000 epilepsy patients/year die of sudden unexpected death in epilepsy (SUDEP). The mechanisms for SUDEP remain incompletely understood. Electroencephalograms (EEG) and electrocardiograms (ECG) are two techniques routinely used in the clinical setting to detect and study the substrates/triggers for seizures and arrhythmias. While many studies and descriptions of this methodology are in rodents, their cardiac electrical activity differs significantly from humans. This article provides a description of a non-invasive method for recording simultaneous video-EEG-ECG-oximetry-capnography in conscious rabbits. As cardiac electrical function is similar in rabbits and humans, rabbits provide an excellent model of translational diagnostic and therapeutic studies. In addition to outlining the methodology for data acquisition, we discuss the analytical approaches for examining neuro-cardiac electrical function and pathology in rabbits. This includes arrhythmia detection, spectral analysis of EEG and a seizure scale developed for restrained rabbits.

Role of Mineralocorticoid and Angiotensin Type 1 Receptors in the Paraventricular Nucleus in Angiotensin-Induced Hypertension.

The hypothalamic paraventricular nucleus (PVN) is an important site where an interaction between circulating angiotensin (Ang) and mineralocorticoid receptor (MR) activity may modify sympathetic nerve activity (SNA) to influence long-term elevation of blood pressure. We examined in conscious Ang II-treated rabbits, the effects on blood pressure and tonic and reflex renal SNA (RSNA) of microinjecting into the PVN either RU28318 to block MR, losartan to block Ang (AT1) receptors or muscimol to inhibit GABAA receptor agonist actions. Male rabbits received a moderate dose of Ang II (24 ng/kg/min subcutaneously) for 3 months (n = 13) or sham treatment (n = 13). At 3 months, blood pressure increased by +19% in the Ang II group compared to 10% in the sham (P = 0.022) but RSNA was similar. RU28318 lowered blood pressure in both Ang II and shams but had a greater effect on RSNA and heart rate in the Ang II-treated group (P < 0.05). Losartan also lowered RSNA, while muscimol produced sympatho-excitation in both groups. In Ang II-treated rabbits, RU28318 attenuated the blood pressure increase following chemoreceptor stimulation but did not affect responses to air jet stress. In contrast losartan and muscimol reduced blood pressure and RSNA responses to both hypoxia and air jet. While neither RU28318 nor losartan changed the RSNA baroreflex, RU28318 augmented the range of the heart rate baroreflex by 10% in Ang II-treated rabbits. Muscimol, however, augmented the RSNA baroreflex by 11% in sham animals and none of the treatments altered baroreflex sensitivity. In conclusion, 3 months of moderate Ang II treatment promotes activation of reflex RSNA principally via MR activation in the PVN, rather than via activation of AT1 receptors. However, the onset of hypertension is independent of both. Interestingly, the sympatho-excitatory effects of muscimol in both groups suggest that overall, the PVN regulates a tonic sympatho-inhibitory influence on blood pressure control.

Long-Term Stable Recording of Single-Neuron Spike Activity in the Amygdala in Conscious Rabbits

The development of current technologies for neurophysiological research has made it possible to observe the activity of large numbers of neurons involved in the operation of distributed neural neurons in the whole brain. An important aspect of such studies is the stability of the signal being recorded, which determines the ability to make recordings from a single cell for prolonged periods. The aim of the present work was to assess the possibility of using chronically implanted multiple microwires for stable recording of the activity of individual neurons in the rabbit brain. Experiments were performed on two adult male European rabbits (Orictolagus cuniculus), in which bundles of microwires were implanted in the amygdala. Experimental data were captured over periods of 72 days in rabbit No. 1 and 964 days in rabbit No. 2. Assessment of neuron signal recording quality showed that the recording device used here made high-quality recordings of the activity of single neurons over long periods. Use of an automated algorithm identified stable recordings of single neurons, which in future will provide for multifaceted investigations of changes in the activity of brain cells with complex behavior.

Comparative study on epidural administration of dexmedetomidine, dexmedetomidine-lidocaine or lidocaine in conscious rabbits.

The aim of this study was to compare the cardiorespiratory, arterial blood gas and antinociceptive effects of dexmedetomidine (D), dexmedetomidine-lidocaine (DL) or lidocaine (L) administered epidurally on conscious rabbits. Eight six-month-old male New Zealand rabbits were randomly distributed into three treatments: D (2.5 μg/kg); DL (2.5 μg/kg; 2 mg/kg); and L (2 mg/kg). The drugs were injected epidurally via a catheter. Cardiorespiratory, arterial blood gas and antinociceptive variables were recorded before administration, 5 and 10 min after drug administration, then every 10 min until the animals presented a positive response to nociceptive stimulation of perineal dermatomes. Two animals had permanent paralysis after DL treatment due to hemorrhage and congestion with neuron necrosis in spinal cord segments. There was a reduction in mean arterial pressure in treatment L at 5 and 10 min, compared with the baseline, and in treatment DL at 10-30 min. Increases in pH were observed in treatment D at 5 and 10 min, and in DL at all the times evaluated, compared with the baseline. No alterations were observed in other blood gas or electrolyte variables. Antinociceptive effects were evaluated in the perineal, sacral and lumbar regions, and were restricted to the perineal region following D and L treatment. The antinociceptive effects following DL were greater than D and L alone in all of the regions. L and D promotes short-term antinociceptive effects for up to 15 min and, when used in combination with D, increased the duration and extent of sensory block by up to 45 min.