Implantable Radiotelemetry Research Articles

Abstract P426: Reduced Nfatc1 Expression Results in Enhanced Pressure Natriuresis and Resistance to Salt-Sensitive Hypertension

Background: Nuclear factor of activated T cells-cytoplasmic 1 (NFATc1) has recently been shown to have a non-canonical role in chronic kidney disease in humans by a trans-ethnic meta-analysis of genome-wide associate studies (GWAS). Follow-up studies in a salt-sensitive mouse model showed that Nfatc1 mRNA expression was suppressed in the kidneys when animals were fed a high-salt diet. Here, we further explore the link between NFATc1 and salt-sensitive (SS) hypertension. Methods: Adult male wild-type (WT) and heterozygous Nfatc1 knockout (Het) mice (2-5 months of age) on the SS 129S6 background were started on standard chow (0.8% NaCl, NSD) and then switched to a high-salt diet (6% NaCl, HSD). Systolic blood pressure (SBP) was measured by either tail cuff manometry with at least 2 weeks of training or implantable radiotelemetry transmitters with at least 2 weeks of post-surgical recovery. Immediately before and for 2-3 days after the change in diet, 24 h urine was collected using metabolic cages, and urinary sodium was measured by flame photometry. Sigmoid pressure-natriuresis curves were generated and the Hill slope was compared between genotypes. Results: WT mice showed a significant increase in SBP between NSD and after 3 weeks on HSD (127.8±9.9 vs 143.4±8.9, p = 0.0089, n = 9). In contrast, Het mice had no change in SBP (125.8±8.7 mmHg vs. 125.7±10.6 mmHg, p = 1.0, n = 9). During the initial switch to the HSD, SBP was not significantly different between WT and Het mice (133.2±2.9 vs. 134.4±3.0, p = 0.45, n = 7/group). However, WT mice had a shallower pressure-natriuresis curve (Hill slope of 0.58 vs. 0.93, 7 mice/group, 25/26 data points). Conclusion: Our data illustrates that decreasing Nfatc1 expression in a mouse model is protective against SS hypertension. While acute increases in SBP in response to HSD remained in Het mice, sodium excretion was increased and SBP remained unchanged after 3 weeks, indicating that NFATc1 has the potential to be a therapeutic target against SS hypertension.

Realtime monitoring of thrombus formation in vivo using a self-reporting vascular access graft

BackgroundChronic kidney disease (CKD) affects 10% of the global population costing over a hundred billion dollars per annum and leading to increased risk of cardiovascular disease. Many patients with CKD require regular haemodialyses. Synthetic arteriovenous grafts (AVG) are increasingly used to provide rapid vascular connection for dialysis. Initially, they have excellent patency rates but are critically limited by neointimal hyperplasia at the venous anastomosis, which drives subsequent thrombosis, graft failure and death.MethodsHere, we describe a system in which electrical impedance spectroscopy sensors are incorporated circumferentially into the wall of a synthetic arteriovenous graft. This is combined with an implantable radiotelemetry system for data transmission outside the patient. The system was tested using monolayers of endothelial and smooth muscle cells as well as swine blood and clots with explanted human carotid artery plaques. Sensor testing was then performed in vitro and the device was implanted in vivo in female swine.ResultsThe device can wirelessly report the accumulation of biological material, both cells and blood. Differences are also detected when comparing controls with pathological atheroma. In swine differences between blockage formation in a graft were remotely obtained and wireless reported.ConclusionsCombining electrical impedance spectroscopy and an implantable radiotelemetry system enables graft surveillance. This has the potential to be used for early detection of venous stenosis and blood clot formation in real-time in vivo. In principle, the concept could apply to other cardiovascular diseases and vascular implantable devices.

Calcitonin gene-related peptide protects from soluble fms-like tyrosine kinase-1-induced vascular dysfunction in a preeclampsia mouse model.

Introduction: Preeclampsia (PE) is a hypertensive disorder during pregnancy associated with elevated levels of soluble FMS-like tyrosine kinase (sFLT-1) and increased vascular sensitivity to angiotensin II (ATII). Calcitonin gene-related peptide (CALCA) is a potent vasodilator that inhibits the ATII-induced increase in blood pressure and protects against ATII-induced increases in oxidative stress through a mitochondrial-dependent pathway in male mice. In rodent pregnancy, CALCA facilitates pregnancy-induced vascular adaptation. Most of the vascular effects of CALCA are mediated by vascular smooth muscle cells (VSMCs). We recently reported that CALCA treatment inhibits sFLT-1-induced decreases in cAMP synthesis in omental artery smooth muscle cells (OASMCs) isolated from pregnant women and has relaxant effects in omental arteries (OAs) isolated from pregnant women with preeclamptic (PE) pregnancies. The current study was designed to assess the effects of sFLT-1 on mitochondrial bioenergetics in OASMCs isolated from pregnant women in the presence or absence of CALCA and assess the development of vascular dysfunction in sFLT-1 using a mouse model of PE pregnancy. Methods: OASMCs were isolated from pregnant women to assess the effects of sFLT-1 on mitochondrial bioenergetics and oxidative stress using the Seahorse assay and quantitative PCR. Pregnant mice overexpressing sFLT-1 via adenoviral delivery were used to assess the effects of CALCA infusion on the sFLT-1-induced increase in blood pressure, ATII hypersensitivity, fetal growth restriction, and the elevated albumin-creatinine ratio. Systemic blood pressure was recorded in conscious, freely moving mice using implantable radio telemetry devices. Results: CALCA inhibited the following sFLT-1-induced effects: 1) increased oxidative stress and the decreased oxygen consumption rate (OCR) in response to maximal respiration and ATP synthesis; 2) increases in the expression of mitochondrial enzyme complexes in OASMCs; 3) increased mitochondrial fragmentation in OASMCs; 4) decreased expression of mitophagy-associated PINK1 and DRAM1 mRNA expression in OASMCs; and 5) increased blood pressure, ATII hypersensitivity, fetal growth restriction, and the albumin-creatinine ratio in sFLT-1-overexpressing pregnant mice. Conclusion: CALCA inhibits sFLT-1-induced alterations in mitochondrial bioenergetics in vascular smooth muscle cells and development of maternal vascular dysfunction in a mouse model of PE.

Lipocalin‐2 deficiency prevents hypertension in dietary obese mice

Objectives Lipocalin-2 is a pro-inflammatory adipokine up-regulated in obese animals and human subjects. Mice without lipocalin-2 (LKO) are protected from dietary or genetic obesity-induced metabolic dysfunctions and vascular abnormalities. The present study aimed to investigate the role of lipocalin-2 and the mechanisms underlying its actions in dietary obesity-induced hypertension. Methods Wild-type (WT) and LKO, as well as mice with tissue-specific deletion of lipocalin-2 were subjected to 20-weeks high-fat diet treatment. Blood pressure was monitored with implantable radio telemetry. Wire myography was performed to evaluate the vascular responses in mesenteric arteries without or with the attached perivascular adipose tissue (PVAT). Enzyme-linked immunosorbent assay (ELISA), Western blotting and quantitative PCR were performed to measure the levels of angiotensin peptides and angiotensin-converting enzymes. Results Deletion of LCN2 alleles prevented the development of hypertension induced by dietary obesity. Lipocalin-2 deficiency inhibited obesity-associated arterial remodeling and promoted the anti-contractile function of PVAT. The data demonstrated that lipocalin-2 was involved in the local production of angiotensin peptides via modulating the expression of angiotensin-converting enzymes. Conclusion Lipocalin-2 plays a causal role in blood pressure elevation. The source of the pathological form of lipocalin-2 contributing to obesity-induced hypertension needs to be further investigated.

Enhanced hippocampal type II theta activity AND altered theta architecture in mice lacking the Cav3.2 T-type voltage-gated calcium channel

T-type Ca2+ channels are assumed to contribute to hippocampal theta oscillations. We used implantable video-EEG radiotelemetry and qPCR to unravel the role of Cav3.2 Ca2+ channels in hippocampal theta genesis. Frequency analysis of spontaneous long-term recordings in controls and Cav3.2−/− mice revealed robust increase in relative power in the theta (4–8 Hz) and theta-alpha (4–12 Hz) ranges, which was most prominent during the inactive stages of the dark cycles. Urethane injection experiments also showed enhanced type II theta activity and altered theta architecture following Cav3.2 ablation. Next, gene candidates from hippocampal transcriptome analysis of control and Cav3.2−/− mice were evaluated using qPCR. Dynein light chain Tctex-Type 1 (Dynlt1b) was significantly reduced in Cav3.2−/− mice. Furthermore, a significant reduction of GABA A receptor δ subunits and GABA B1 receptor subunits was observed in the septohippocampal GABAergic system. Our results demonstrate that ablation of Cav3.2 significantly alters type II theta activity and theta architecture. Transcriptional changes in synaptic transporter proteins and GABA receptors might be functionally linked to the electrophysiological phenotype.

Intra-Subject Variability and Diurnal Cycle of Ocular Perfusion Pressure as Characterized by Continuous Telemetry in Nonhuman Primates.

PurposeTo characterize ocular perfusion pressure (OPP) fluctuations with continuous telemetry over 24-hour periods across multiple days in nonhuman primates (NHPs) to test the hypotheses that OPP differs among NHPs and that the diurnal cycle of OPP is characterized by low OPP during sleep.MethodsWe have developed and validated two implantable radiotelemetry systems that allow continuous measurement of intraocular pressure (IOP), arterial blood pressure (BP), and OPP up to 500 Hz. OPP was measured unilaterally in 12 male NHPs for periods of 38 to 412 days. IOP transducers were calibrated directly via anterior chamber manometry, and OPP was calculated continuously as central retinal artery BP minus IOP. OPP data were corrected for signal drift between calibrations and averaged hourly.ResultsOPP varied widely among animals, with daily averages ranging from ∼47 to 65 mm Hg. In eight of 12 NHPs, OPP was significantly lower during sleep compared to waking hours. In three animals, the diurnal cycle was reversed and OPP was significantly higher during sleep (P < 0.05), and one NHP showed no diurnal cycle. Day-to-day OPP variability within NHPs was the largest source of overall OPP variability, even larger than the differences between NHPs. Average daily OPP showed an unexplained ∼32-day cyclic pattern in most NHPs.ConclusionsAverage OPP varied widely and exhibited differing diurnal cycles in NHPs, a finding that matches those of prior patient studies and indicates that OPP studies in the NHP model are appropriate. Infrequent snapshot measurements of either IOP or BP are insufficient to capture true IOP, BP, and OPP and their fluctuations.

Gastric smooth muscle cells manifest an abnormal phenotype in Parkinson's disease rats with gastric dysmotility.

Gastroparesis is a common symptom in Parkinson's disease (PD) and whether any change occurs in gastric smooth muscle cells (SMCs) of PD patients is unclear. We previously reported that rats with bilateral substantia nigra lesions induced by 6-hydroxydopamine (6-OHDA), referred to as 6-OHDA rats, manifest typical gastroparesis. In the present study, we further investigate the underlying mechanism. By means of an organ bath system and an implantable radiotelemetry system, both a weakened contractile force of gastric circular smooth muscle and gastric myoelectric activity were detected in the 6-OHDA rats and phasic and tonic contractions elicited by carbachol or high concentration of potassium were significantly reduced in gastric circular muscle strips. A thickened smooth muscle layer was observed under a light microscope and an ultrastructure of hypertrophic SMCs, with increased caveolae and decreased dense bodies, was observed under transmission electron microscope. Furthermore, the mRNA and protein expression levels of contractile markers (myosin light chain 20, myosin heavy chain 11 and α-smooth muscle actin) and the transcription factor serum response factor (SRF) were significantly decreased, while the TNFα and IL-1β content was increased in the 6-OHDA rats. These results suggest that the decreased contractile force in 6-OHDA rats may be associated with the phenotypic abnormality observed in SMCs, which is due to downregulated contractile proteins induced by decreased SRF expression in the inflammatory muscular microenvironment.

Combination cannabinoid and opioid receptor antagonists improves metabolic outcomes in obese mice

The CB1 receptor antagonist, rimonabant, causes weight loss but also produces undesirable psychiatric side effects. We investigated using a combination of rimonabant with the opioid receptor antagonists naloxone and norBNI to treat the metabolic sequelae of long-term high fat diet feeding in mice. This combination has previously been shown to have positive effects on both weight loss and mood related behaviour. Diet-induced obese mice were treated chronically with either low dose rimonabant (1 mg/kg) or the combination of rimonabant, naloxone and norBNI (rim nal BNI). After 6 days of treatment, glucose and insulin tolerance tests were performed and body composition analysed using DEXA. Changes in BAT thermogenesis were assessed using implantable radio telemetry probes. Behavioural responses to acute rimonabant or rim nal BNI were examined in the forced swim test and elevated plus maze. Separately, we assessed shifts in Fos immunoreactivity in response to rimonabant or rim nal BNI. Rim nal BNI was significantly better than rimonabant treatment alone at reducing body weight and food intake. In addition, it improved fasting blood glucose and fat mass. Acute low dose rimonabant did not alter behaviour in either the forced swim test or elevated plus maze. Combination rim nal BNI reversed the behavioural effects of high dose (10 mg/kg) rimonabant in obese mice. Rim nal BNI altered Rimonabant-induced Fos in a number of nuclei, with particular shifts in expression in the central and basolateral amygdala, and insular cortex. This study demonstrates that the combination of rimonabant, naloxone and norBNI is effective at producing weight loss over a sustained period of time without altering performance in standardised mouse behaviour tests. Fos expression patterns offer insight into the neuroanatomical substrates subserving these physiological and behavioural changes. These results indicate that CB1-targeted drugs for weight loss may still be feasible.

Mixed linage kinase 3 functions as a cGMP-dependent protein kinase I alpha substrate and regulates blood pressure and cardiac remodeling in vivo

Protein kinase G I alpha (PKGIα) counteracts hypertension and pathologic cardiac remodeling. These effects require the PKGIα leucine zipper (LZ) protein binding domain. However, PKGIα LZ-binding substrates mediating these effects remain incompletely understood. We previously demonstrated that Mixed Lineage Kinase 3 (MLK3) binds the PKGIα LZ domain in the heart. In the present study we hypothesized that MLK3 functions as a PKGIα substrate and cardiovascular effector. We observed that recombinant MLK3 precipitated with affinity purified PKGIα but not with LZ mutant PKGIα. When PKGIα was precipitated with RP-cGMP beads, which inhibit PKG kinase activity, we observed decreased PKGIα-MLK3 co-precipitation, supporting a requirement of PKGIα kinase activity for MLK3-PKGIa interaction. PKGIα phosphorylated MLK3 in vitro as assayed by Western blot. We next analysed mice with genetic deletion of MLK3. In the baseline state, MLK3-/- mice display normal cardiac function as assessed by echocardiography and invasive cardiac hemodynamics. MLK3-/- mice develop cardiac hypertrophy by 3 months of age (heart weight/tibia length 64.4 ± 1.9 mg/cm WT, 73.6 ± 2.1 mg/cm MLK3-/-; p<0.001; n=11 WT, 14 MLK3-/-). Compared with WT littermates, anesthetized MLK3-/- mice have elevated blood pressure (BP) (94.3 ± 2.1 mmHg WT, 109.3 ± 2.5 mmHg MLK3-/-; p<0.001). Conscious male MLK3-/- mice monitored continuously with implantable arterial radiotelemetry (10-12 weeks of age) had overt hypertension compared with WT littermates (Systolic BP: WT 121.5 ± 2.0 mmHg, MLK3-/- 161.6 ± 5.1 mmHg; p<0.01; Diastolic BP: WT 87.0 ± 2.9 mmHg, MLK3-/- 114.5 ± 2.7 mmHg; p<0.001; n=4 WT, 3 MLK3-/-). We observed no difference in baseline heart rate between genotypes. Chronic administration of hydralazine (250 mg/L) normalized BP in MLK3-/- mice, but did not completely inhibit cardiac hypertrophy. Further, in response to LV pressure overload by transaortic constriction (TAC), which equalized left ventricular (LV) systolic pressure between genotypes, MLK3-/- mice had increased LV hypertrophy (LV/Tibia length) as well as elevated LV end diastolic pressure, and worsening of LV ejection fraction, preload recruitable stroke work, and other LV systolic and diastolic indices (n=8-10), indicating advanced cardiac dysfunction. Together, our findings identify MLK3 as a direct PKGI substrate, and reveal that deletion of MLK3 leads to hypertension and pathologic cardiac hypertrophy. These findings support a model in which, in response to activation by PKGIα, MLK3 inhibits hypertension and cardiac hypertrophy. We conclude that identifying novel PKGIα LZ substrates, like MLK3, may reveal new candidate therapeutic targets for hypertension and heart failure.

3-Iodothyroacetic acid lacks thermoregulatory and cardiovascular effects in vivo.

3-Iodothyronamine (3-T1 AM) is an endogenous thyroid hormone derivative reported to induce strong hypothermia and bradycardia within minutes upon injection in rodents. Although 3-T1 AM is rapidly converted to several other metabolites in vivo, these strong pharmacological responses were solely attributed to 3-T1 AM, leaving potential contributions of downstream products untested. We therefore examined the cardiometabolic effects of 3-iodothyroacetic acid (TA1 ), the main degradation product of 3-T1 AM. We used a sensitive implantable radiotelemetry system in C57/Bl6J mice to study the effects of TA1 on body temperature and heart rate, as well as other metabolic parameters. Interestingly, despite using pharmacological TA1 doses, we observed no effects on heart rate or body temperature after a single TA1 injection (50 mg·kg(-1) , i.p.) compared to sham-injected controls. Repeated administration of TA1 (5 mg·kg(-1) , i.p. for 7 days) likewise did not alter body weight, food and water intake, heart rate, blood pressure, brown adipose tissue (BAT) thermogenesis or body temperature. Moreover, mRNA expression of tissue specific genes in heart, kidney, liver, BAT and lung was also not altered by TA1 compared to sham-injected controls. Our data therefore conclusively demonstrate that TA1 does not contribute to the cardiovascular or thermoregulatory effects observed after 3-T1 AM administration in mice, suggesting that the oxidative deamination constitutes an important deactivation mechanism for 3-T1 AM with possible implications for cardiovascular and thermoregulatory functions.

Deamidated lipocalin-2 induces endothelial dysfunction and hypertension in dietary obese mice.

BackgroundLipocalin‐2 is a proinflammatory adipokine upregulated in obese humans and animals. A pathogenic role of lipocalin‐2 in hypertension has been suggested. Mice lacking lipocalin‐2 are protected from dietary obesity‐induced cardiovascular dysfunctions. Administration of lipocalin‐2 causes abnormal vasodilator responses in mice on a high‐fat diet (HFD).Methods and ResultsWild‐type and lipocalin‐2 knockout mice were fed with standard chow or HFD. Immunoassays were performed for evaluating the circulating and tissue contents of lipocalin‐2. The relaxation and contraction of arteries were studied using a wire myograph. Blood pressure was monitored with implantable radio telemetry. Dietary obesity promoted the accumulation of lipocalin‐2 protein in blood and arteries. Deficiency of this adipokine protected mice from dietary obesity‐induced elevation of blood pressure. Mass spectrometry analysis revealed that human and murine lipocalin‐2 were modified by polyamination. Polyaminated lipocalin‐2 was rapidly cleared from the circulation. Adipose tissue was a major site for lipocalin‐2 deamidation. The circulating levels and the arterial accumulation of deamidated lipocalin‐2 were significantly enhanced by treatment with linoleic acid (18:2n−6), which bound to lipocalin‐2 with high affinity and prevented its interactions with matrix metalloproteinase 9 (MMP9). Combined administration of linoleic acid with lipocalin‐2 caused vascular inflammation and endothelial dysfunction and raised the blood pressure of mice receiving standard chow. A human lipocalin‐2 mutant with cysteine 87 replaced by alanine (C87A) contained less polyamines and exhibited a reduced capacity to form heterodimeric complexes with MMP9. After treatment, C87A remained in the circulation for a prolonged period of time and evoked endothelial dysfunction in the absence of linoleic acid.ConclusionsPolyamination facilitates the clearance of lipocalin‐2, whereas the accumulation of deamidated lipocalin‐2 in arteries causes vascular inflammation, endothelial dysfunction, and hypertension.

Measurement of right ventricular pressure by telemetry in conscious moving rabbits

Implantable radiotelemetry methodology has been used to continuously monitor pulmonary hemodynamics including right ventricular pressure (RVP) or pulmonary arterial pressure (PAP) in conscious, untethered and freely moving animals such as mice and rats. The use of implantable radiotelemetry to monitor RVP or PAP has never previously been described in rabbits. The aim of the present study was to use implantable radiotelemetry to continuously monitor RVP in conscious adult rabbits. Telemetry transmitters were implanted in 44 adult male New Zealand rabbits using a trans-diaphragm approach for the catheter placement. RVP, heart rate (HR) and activity were monitored every 15 min for 20 s. Body mass was recorded once a week. A total of 39 (88%) rabbits were successfully implanted. Thirty rabbits survived the surgical procedure resulting in an overall survival rate of 73%. RVP, HR and activity were long-term monitored in 17 rabbits for an average period of 103 ± 15 days. Weekly body mass follow-up showed that implantable radiotelemetry did not impair the normal development of the animal. Twenty-four-hour period monitoring of RVP, HR and activity showed concomitant changes in RVP, HR and activity according to the dark/light cycle applied to the rabbits. To conclude, implantable radiotelemetry methodology can be safely used to continuously monitor RVP in conscious rabbits.

Effect of Ambient Temperature on the Thermoregulatory and Locomotor Stimulant Effects of 4-Methylmethcathinone in Wistar and Sprague-Dawley Rats

The drug 4-methylmethcathinone (4-MMC; aka, mephedrone, MMCAT, “plant food”, “bath salts”) is a recent addition to the list of popular recreational psychomotor-stimulant compounds. Relatively little information about this drug is available in the scientific literature, but popular media reports have driven recent drug control actions in the UK and several US States. Online user reports of subjective similarity to 3,4-methylenedioxymethamphetamine (MDMA, “Ecstasy”) prompted the current investigation of the thermoregulatory and locomotor effects of 4-MMC. Male Wistar and Sprague-Dawley rats were monitored after subcutaneous administration of 4-MMC (1–10 mg/kg ) using an implantable radiotelemetry system under conditions of low (23°C) and high (27°C) ambient temperature. A reliable reduction of body temperature was produced by 4-MMC in Wistar rats at 23°C or 27°C with only minimal effect in Sprague-Dawley rats. Increased locomotor activity was observed after 4-MMC administration in both strains with significantly more activity produced in the Sprague-Dawley strain. The 10 mg/kg s.c. dose evoked greater increase in extracellular serotonin, compared with dopamine, in the nucleus accumbens. Follow-up studies confirmed that the degree of locomotor stimulation produced by 10 mg/kg 4-MMC was nearly identical to that produced by 1 mg/kg d-methamphetamine in each strain. Furthermore, hypothermia produced by the serotonin 1A/7 receptor agonist 8-hydroxy-N,N-dipropyl-2-aminotetralin (8-OH-DPAT) was similar in each strain. These results show that the cathinone analog 4-MMC exhibits thermoregulatory and locomotor properties that are distinct from those established for methamphetamine or MDMA in prior work, despite recent evidence of neuropharmacological similarity with MDMA.

Changes in ambient temperature differentially alter the thermoregulatory, cardiac and locomotor stimulant effects of 4-methylmethcathinone (mephedrone)

BackgroundThe substituted cathinone compound known as mephedrone (4-methylmethcathinone; 4-MMC) has become popular with recreational users of psychomotor-stimulant compounds. Only recently have the first preclinical studies provided information about this drug in the scientific literature; nevertheless, media reports have led to drug control actions in the UK and across several US states. Rodent studies indicate that 4-MMC exhibits neuropharmacological similarity to 3,4-methylenedioxymethamphetamine (MDMA) and prompt investigation of the thermoregulatory, cardiac and locomotor effects of 4-MMC. This study focuses on the role of ambient temperature, which has been shown to shift the effects of MDMA from hyperthermic to hypothermic. MethodsMale Sprague-Dawley rats were monitored after subcutaneous administration of 4-MMC (1.0–5.6mg/kg) using an implantable radiotelemetry system under conditions of low (20°C) and high (30°C) ambient temperature. ResultsA pharmacokinetic study found a Tmax of 0.25h and a Cmax of 1206ng/ml after 5.6mg/kg 4-MMC. A dose-dependent reduction of body temperature was produced by 4-MMC at 20°C but there was no temperature change at 30°C. Increased locomotor activity was observed after 4-MMC administration under both ambient temperatures, however, significantly more activity was observed at 30°C. Heart rate was slowed by 1.0 and 5.6mg/kg 4-MMC at 20°C, and was slower in the 30°C vs. 20°C condition across all treatments. ConclusionThese results show that the cathinone analog 4-MMC exhibits in vivo thermoregulatory properties that are distinct from those produced by MDMA.

Adaptations of the Autonomous Nervous System Controlling Heart Rate Are Impaired by a Mutant Thyroid Hormone Receptor-α1

Thyroid hormone has profound direct effects on cardiac function, but the hormonal interactions with the autonomic control of heart rate are unclear. Because thyroid hormone receptor (TR)-alpha1 has been implicated in the autonomic control of brown adipose energy metabolism, it might also play an important role in the central autonomic control of heart rate. Thus, we aimed to analyze the role of TRalpha1 signaling in the autonomic control of heart rate using an implantable radio telemetry system. We identified that mice expressing the mutant TRalpha1R384C (TRalpha1+m mice) displayed a mild bradycardia, which becomes more pronounced during night activity or on stress and is accompanied by a reduced expression of nucleotide-gated potassium channel 2 mRNA in the heart. Pharmacological blockage with scopolamine and the beta-adrenergic receptor antagonist timolol revealed that the autonomic control of cardiac activity was similar to that in wild-type mice at room temperature. However, at thermoneutrality, in which the regulation of heart rate switches from sympathetic to parasympathetic in wild-type mice, TRalpha1+m mice maintained sympathetic stimulation and failed to activate parasympathetic signaling. Our findings demonstrate a novel role for TRalpha1 in the adaptation of cardiac activity by the autonomic nervous system and suggest that human patients with a similar mutation in TRalpha1 might exhibit a deficit in cardiac adaptation to stress or physical activity and an increased sensitivity to beta-blockers.

Telemetric intracardiac ECG dramatically improves interval detection and reduces artifact when compared to a subcutaneous lead placement in freely‐moving dogs

Implantable radio-telemetry is a commonly used technology for monitoring electrocardiogram (ECG) signals in conscious, freely-moving animals. Traditionally, biopotential leads from a transmitter are placed subcutaneously in a lead II orientation through a simple surgical procedure. Although a wealth of valuable information can be obtained using this technique, it can be subject to muscle noise and morphology changes resulting from animal activity. ECG signals acquired from within the heart greatly minimize movement artifact and provide consistent morphology, high-amplitude waveforms ideal for interval detection. This study compares the subcutaneous ECG to intracardiac ECG data acquired telemetrically from unrestrained beagle dogs. The intracardiac ECG signal was obtained by using a bipolar pacing lead (Oscor Inc., Palm Harbor, FL) which was inserted into the right jugular vein and advanced into the right ventricle. The pacing lead was interfaced to a telemetry transmitter (Data Sciences International (DSI), St. Paul, MN) using a custom connector. The intracardiac ECG yielded relatively noise free waveforms with signal to noise ratios superior to subcutaneous ECG electrodes with signal quality maintained even during periods of high activity which, in the subcutaneous ECG signal, typically resulted in significant artifact. The percentage of waveforms that could be measured by automated ECG interval analysis software was significantly greater than via subcutaneous ECG electrodes. Intracardiac ECG combined with other parameters such as blood pressure and body temperature has proven to be an in-valuable tool for chronic cardiovascular evaluation.

Measurement of cortical and hippocampal epileptiform activity in freely moving rats by means of implantable radiotelemetry

Implanted radiotelemetry has been used for the measurement of cortical electroencephalogram (EEG), locomotor activity, body temperature and cardiovascular parameters. This technique allows high quality data acquisition from freely moving animals with no complications of externalised apparatus. This paper focuses on the methodology for short and long-term monitoring of epileptiform activity by simultaneous cortical EEG, hippocampal (HC) EEG and electromyogram (EMG) in rats. The circadian rhythm of temperature (CRT) was monitored after surgery to estimate the need for post surgical recovery of animals. Different placements of EMG electrodes were assessed in order to minimise artefacts and increase sensitivity. The occurrence of epileptiform ictal and interictal activity following an acute injection of either 40 mg/kg pentylenetetrazole (PTZ) or 13.8 mg/kg kainic acid (KA) was investigated. The occurrence of spontaneous seizures was also monitored 5–8 weeks after administration of KA. The present study demonstrated a sensitive method for monitoring cortical EEG, hippocampal EEG and EMG short and long-term by implantable radiotelemetry in freely moving rats.

Measurement of cortical and hippocampal epileptiform activity in freely moving rats by means of implantable radiotelemetry

Implanted radiotelemetry has been used for the measurement of cortical electroencephalogram (EEG), locomotor activity, body temperature and cardiovascular parameters. This technique allows high quality data acquisition from freely moving animals with no complications of externalised apparatus. This paper focuses on the methodology for short and long-term monitoring of epileptiform activity by simultaneous cortical EEG, hippocampal (HC) EEG and electromyogram (EMG) in rats. The circadian rhythm of temperature (CRT) was monitored after surgery to estimate the need for post surgical recovery of animals. Different placements of EMG electrodes were assessed in order to minimise artefacts and increase sensitivity. The occurrence of epileptiform ictal and interictal activity following an acute injection of either 40 mg/kg pentylenetetrazole (PTZ) or 13.8 mg/kg kainic acid (KA) was investigated. The occurrence of spontaneous seizures was also monitored 5–8 weeks after administration of KA. The present study demonstrated a sensitive method for monitoring cortical EEG, hippocampal EEG and EMG short and long-term by implantable radiotelemetry in freely moving rats.

Investigation of the sleep electrocorticogram of the common marmoset ( Callithrix jacchus) using radiotelemetry

Objective: To evaluate the use of a totally implantable radiotelemetry system for recording the sleep electrocorticogram (ECoG) of a small new world primate, the common marmoset ( Callithrix jacchus) without restraint during data collection. Methods: Under anaesthesia a telemetry transmitter, which allowed the recording of a single ECoG channel, was implanted intraperitoneally. This system allowed ECoG data to be recorded overnight from animals living in pairs within their habitual laboratory environment over a period of 12 months. Data were subsequently scored using modified Rechtschaffen and Kales criteria (A manual of standardized terminology, techniques and scoring system for sleep stages of human subjects. Los Angeles, UCLA Brain Information Service/Brain Research Institute, 1968) into stages of waking, light sleep, deep sleep and probable rapid eye movement sleep (pREM). Concurrent video recording was used to assist in the categorising of pREM. Results: Results showed that, as in man, the marmoset exhibits sleep cycles with stages alternating between non-REM (deep sleep and light sleep) and pREM sleep throughout the night. In common with other non-human primates the duration of each of the sleep stages was relatively short and punctuated with frequent waking. Conclusions: These data suggest that sleep in marmosets housed under laboratory conditions (a) can be recorded without restraint and (b) has potential to be used as a model for human sleep.

A telemetry system for the study of spontaneous cardiac arrhythmias.

The characteristics of spontaneous cardiac arrhythmias leading to sudden cardiac death are largely unknown. To study arrhythmias in animal models, an eight-channel implantable radio telemetry system has been developed to record continuously cardiac electrograms over a period of weeks to months, with maintenance restricted to changing batteries. The inputs are connected in a unipolar manner. Each channel has a gain of fifty and is AC coupled, band limited to 0.07-260 Hz. The signals are digitized with 12 bits resolution at 1000 samples/s. The amplifiers, analog-to-digital converter, and control logic are packaged in an implantable unit. An umbilical cable is passed through the skin to an external backpack unit for power and data transmission. A custom serial interface card, a PC/104 form factor 25-MHz 80386-based single-board computer with a PCMCIA wireless local area network (WLAN) card, and battery power supply make up the backpack. Data are read into the parallel port of the computer, buffered, then transmitted over the WLAN to the laboratory network where it can be analyzed and archived. Approximately 12 h of 14,000 bytes/s data can be collected with each set of batteries. The system is suitable for continuous monitoring of animal models of spontaneous arrhythmias and sudden cardiac death.