Increased heart rate variability in mice overexpressing the Cu/Zn superoxide dismutase

Cu/Zn superoxide dismutase (SOD1) is implicated in various pathological conditions including Down's syndrome, neurodegenerative diseases, and afflictions of the autonomic nervous system (ANS). To assess the SOD1 contribution to ANS dysfunction, especially its influence on cardiac regulation, we studied the heart rate variability (HRV) and cardiac arrhythmias in conscious 12-month-old male and female transgenic mice for the human SOD1 gene (TghSOD1). TghSOD1 mice presented heart rate reduction as compared with control FVB/N individuals. All HRV parameters reflecting parasympathetic activity were increased in TghSOD1. Pharmacological studies confirmed that the parasympathetic tone was exacerbated and the sympathetic pathway was functional in TghSOD1 mice. A high frequency of atrioventricular block and premature ventricular contractions was observed in TghSOD1. By biochemical assays we found that SOD1 activities were multiplied by 9 and 4 respectively in the heart and brainstem of transgenic mice. A twofold decrease in cholinesterase activity was observed in the heart but not in the brainstem. We demonstrate that SOD1 overexpression induces an ANS dysfunction by an exacerbated vagal tone that may be related to impaired cardiac activity of the cholinesterases and may explain the high occurrence of arrhythmias.     

Heart rate dynamics in iNOS knockout mice

Nitric oxide has both an inhibitory and excitatory role in the regulation of pre-ganglionic sympathetic neurons, involving the iNOS and nNOS systems respectively. The aim of the present study was to examine cardiovascular autonomic activity in iNOS knockout mice using spectral analysis of heart rate variability (HRV), and to determine the role of iNOS in altered HRV in endotoxaemia. Electrocardiograms were recorded in anaesthetised mice, and the R-R intervals digitized for spectral analysis of HRV and cardiac rhythm regularity using sample entropy analysis. The basal heart rate was higher in iNOS knockout mice compared with controls (465+/-8 vs 415+/-13 beat/min P<0.05), with a significant increase in the low frequency power of HRV spectra in iNOS knockout mice compared with controls (49.4+/-4.3 vs 33.8+/-5.6 normalized units, P<0.05), consistent with increased cardiac sympathetic activity. Endotoxaemia is known to decrease HRV, but the role of iNOS is unknown. LPS (20 mg/kg i.p) increased basal heart rate in both wild type and iNOS knockout mice, but caused a depression of HRV and sample entropy in both groups. Studies in isolated beating atria showed that the changes of HRV under basal or post-LPS conditions disappeared in vitro, suggesting that the autonomic system is responsible for altered HRV. We conclude that disruption of iNOS gene leads to an increase in the low frequency power of HRV consistent with increased cardiac sympathetic activity. These data also demonstrate that LPS-induced decrease of HRV is independent of iNOS.     

Genetic selection on a behavioural fear trait is associated with changes in heart rate variability in quail

This study investigated whether genetic selection on a divergent behavioural trait of fearfulness (tonic immobility duration) was related to changes in the nervous control of the heart. Quail selected for either long or short tonic immobility (LTI or STI, respectively) duration was compared with an unselected control line (CTI). The autonomic control of the heart was assessed by heart rate variability analysis and pharmacological blockades. Quail were surgically fitted with a telemetric device. Heart rate before injection did not differ between the three lines. The vagal-sympathetic effect (VSE) at rest differed significantly from 1 in CTI and STI quail, suggesting that parasympathetic activity was dominant. In LTI quail, VSE did not differ from 1, suggesting a balance between parasympathetic and sympathetic activities. The intrinsic heart rate reached after the successive injections of propranolol and atropine did not differ between lines and was higher than the heart rate at rest in STI, which was in line with results of VSE at rest. After atropine injection, the sympathetic activity indicated by the low-frequency power was lower in CTI than in the two selected quail. After propranolol injection, the parasympathetic activity indicated by the root of the mean squares of successive differences and the high-frequency power was higher in STI than in CTI and LTI quail. Selection on tonic immobility duration thus appears to be associated with changes in the sympathovagal control of the heart, which may influence behavioural responses to stressful situations.     

Autonomic control of heart rate in the neonatal rhesus monkey

Autonomic control of resting heart rate was assessed using atropine and propranolol in 20 neonatal (2 to 3 weeks old) male Rhesus monkeys. After release from restraint for placement of a venous catheter, the average heart rate significantly decreased from 220 +/- 7 beats/min to 181 +/- 6 beats/min within 15 minutes and remained stable for the 2 hours. Autonomic control of resting heart rate is mediated through both divisions of the autonomic nervous system with the sympathetic system having a dominant influence. This is in contrast to the adult Rhesus, where the parasympathetic nervous system controls resting heart rate.     

Nerve fibers in the gut and pancreas of the rat displaying neuropeptide-Y immunoreactivity

Summary Immunoreactive neuropeptide Y (NPY) was demonstrated in neuronal elements in the gut and pancreas of the rat. Immunoreactive endocrine cells could not be detected. The occurrence of NPY containing nerve-cell bodies in the submucosal and myenteric ganglia indicates an intrinsic origin of the NPY fibers. However, an additional extrinsic supply of NPY fibers is suggested by the finding that abdominal sympathectomy caused the disappearance of some NPY fibers, notably those around blood vessels. The distribution of NPY fibers in all layers of the gut wall suggests multiple functions of NPY, including a role in the regulation of intramural neuronal activities, smooth muscle tone, and local blood flow.     

Separate neurochemical classes of sympathetic postganglionic neurons project to the left ventricle of the rat heart

The sympathetic innervation of the rat heart was investigated by retrograde neuronal tracing and multiple label immunohistochemistry. Injections of Fast Blue made into the left ventricular wall labelled sympathetic neurons that were located along the medial border of both the left and right stellate ganglia. Cardiac projecting sympathetic postganglionic neurons could be grouped into one of four neurochemical populations, characterised by their content of calbindin and/or neuropeptide Y (NPY). The subpopulations of neurons contained immunoreactivity to both calbindin and NPY, immunoreactivity to calbindin only, immunoreactivity to NPY only and no immunoreactivity to calbindin or NPY. Sympathetic postganglionic neurons were also labelled in vitro with rhodamine dextran applied to the cut end of a cardiac nerve. The same neurochemical subpopulations of sympathetic neurons were identified by using this technique but in different proportions to those labelled from the left ventricle. Preganglionic terminals that were immunoreactive for another calcium-binding protein, calretinin, preferentially surrounded retrogradely labelled neurons that were immunoreactive for both calbindin and NPY. The separate sympathetic pathways projecting to the rat heart may control different cardiac functions.     

Development of neuropeptide Y and tyrosine hydroxylase immunoreactive innervation in postnatal rat heart

Neuropeptide Y (NPY), immunoreactive (IR), and tyrosine hydroxylase (TH)-IR nerve fibers were scarce at birth in rat heart, but increased rapidly during the first 2 postnatal weeks, reaching approximately adult levels by the third week. The sequence of development was: interatrial septum and atrial wall, free ventricular wall starting from the epicardium, and finally the atrial appendages and interventricular septum. In ventricles and atrial appendages both fiber types developed similarly. In interatrial septum and atrial walls more NPY-IR than TH-IR fibers were evident, and NPY-IR, but not TH-IR, neurons were detected in intrinsic ganglia. Doublelabel immunohistochemistry provided further evidence that NPY is located in ventricular and atrial noradrenergic nerves, but is also located in nonnoradrenergic nerves in atria.     

Expression of freezing and fear‐potentiated startle during sustained fear in mice

Fear‐potentiated acoustic startle paradigms have been used to investigate phasic and sustained components of conditioned fear in rats and humans. This study describes a novel training protocol to assess phasic and sustained fear in freely behaving C57BL/6J mice, using freezing and/or fear‐potentiated startle as measures of fear, thereby, if needed, allowing in vivo application of various techniques, such as optogenetics, electrophysiology and pharmacological intervention, in freely behaving animals. An auditory Pavlovian fear conditioning paradigm, with pseudo‐randomized conditioned–unconditioned stimulus presentations at various durations, is combined with repetitive brief auditory white noise burst presentations during fear memory retrieval 24 h after fear conditioning. Major findings are that (1) a motion sensitive platform built on mechano‐electrical transducers enables measurement of startle responses in freely behaving mice, (2) absence or presence of startle stimuli during retrieval as well as unpredictability of a given threat determine phasic and sustained fear response profiles and (3) both freezing and startle responses indicate phasic and sustained components of behavioral fear, with sustained freezing reflecting unpredictability of conditioned stimulus (CS)/unconditioned stimulus (US) pairings. This paradigm and available genetically modified mouse lines will pave the way for investigation of the molecular and neural mechanisms relating to the transition from phasic to sustained fear.     

Autonomic nervous control of blood pressure and heart rate during hypoxia in the cod,Gadus morhua

Summary The autonomic nervous and possible adrenergic humoral control of blood pressure and heart rate during hypoxia was investigated in Atlantic cod. The oxygen tension in the water was reduced to 4.0–5.3 kPa (i.e.. P_wO₂=30–40 mmHg), and the fish responded with an immediate increase in ventral and dorsal aortic blood pressure (P _va P _da), as well as a slowly developing bradycardia. The plasma concentrations of circulating catecholamines increased during hypoxia with a peak in the plasma level of noradrenaline occurring before the peak for adrenaline. Bretylium was used as a chemical tool to differentiate between neuronal and humoral adrenergic control of blood pressure and heart rate (f _H) during hypoxia. The increase in P _va and P _da in response to hypoxia was strongly reduced in bretylium-treated cod, which suggests that adrenergic nerves are responsible for hypoxic hypertension. In addition, a small contribution by circulating catecholamines to the adrenergic tonus affecting P _va during hypoxia was suggested by the decrease in P _va induced by injection of the -adrenoceptor antagonist phentolamine. The cholinergic and the adrenergic tonus affecting heart rate were estimated by injections of atropine and the -adrenoceptor antagonist sotalol. The experiments demonstrate an increased cholicholinergic as well as adrenergic tonus on the heart during hypoxia.     

Effect of chronic psychogenic stress exposure on enkephalin neuronal activity and expression in the rat hypothalamic paraventricular nucleus

This study tested the hypothesis that the activation pattern of enkephalinergic (ENKergic) neurons within the paraventricular nucleus of the hypothalamus (PVH) in response to psychogenic stress is identical whether in response to repeated exposure to the same stress (homotypic; immobilization) or to a novel stress (heterotypic; air jet puff). Rats were assigned to either acute or chronic immobilization stress paradigms (90 min/day for 1 or 10 days, respectively). The chronic group was then subjected to an additional 90-min session of either heterotypic or homotypic stress. A single 90-min stress session (immobilization or air jet) increased PVH-ENK heteronuclear (hn) RNA expression. In chronically stressed rats, exposure to an additional stress session (whether homotypic or heterotypic) continued to stimulate ENK hnRNA expression. Acute immobilization caused a marked increase in the numbers of Fos-immunoreactive and Fos-ENK double-labeled cells in the dorsal and ventral medial parvicellular, and lateral parvicellular subdivisions of the PVH. Chronic immobilization caused an attenuated Fos response ( approximately 66%) to subsequent immobilization. In contrast, chronic immobilization did not impair ENKergic neuron activation within the PVH following homotypic or heterotypic stress. These results indicate that within the PVH, chronic psychogenic stress markedly attenuates the Fos response, whereas ENKergic neurons resist habituation, principally within the ventral neuroendocrine portion of the nucleus. This suggests an increase in ENK effect during chronic stress exposure. Homotypic (immobilization) and heterotypic (air jet) psychogenic stressors produce similar responses, including Fos, ENK-Fos, and ENK hnRNA, within each subdivision of the PVH, suggesting similar processing for painless neurogenic stimuli.     

Thermal sensitivity of heart rate and insensitivity of blood pressure in the Antarctic nototheniid fish <Emphasis Type="Italic">Pagothenia borchgrevinki</Emphasis>

The Antarctic notothenioids are among the most stenothermal of fishes, well adapted to their stable, cold and icy environment. The current study set out to investigate the thermal sensitivity/insensitivity of heart rate and ventral aortic blood pressure of the Antarctic nototheniid fish Pagothenia borchgrevinki over a range of temperatures. The heart rate increased rapidly from –1 to 6°C (Q₁₀=2.0–3.3), but was relatively insensitive to temperature above the ~6°C lethal limit of the species (Q₁₀=1.2). The increase in heart rate from –1 to 6°C was the result of a 45% increase in excitatory adrenergic tone, masking a 37% increase in inhibitory cholinergic tone. Ventral aortic pressure was regulated well above the lethal limit, up to at least 10°C. With the return of the fish to environmental temperatures, the heart rate rapidly decreased back to control levels, while ventral aortic pressure increased and remained elevated for over an hour following a 6°C exposure.     

Fractal dynamics in circadian cardiac time series of corticotropin-releasing factor receptor subtype-2 deficient mice

Non-linear fractal analysis of circadian 24 hr heartbeat interval time series was performed in corticotropin releasing factor receptor-subtype 2 (CRFR2) deficient mice. We hypothesized that, as a result of its central as well as its peripheral expression, CRFR2 would mediate or interfere with the circadian rhythmicity. The dynamical properties of cardiac interbeat intervals were expected to be different between CRFR2 (+/+) and CRFR2 (–/–) mice when studied over an extended circadian 24 hr cycle. The dynamics of neurocardiac control were found to remain remarkably stable throughout the circadian cycle. In disagreement with the initial hypothesis, the dynamical properties underlying the cardiac control process were common to both CRFR2 (+/+) and CRFR2 (–/–) mice suggesting that control of heart rate does not rely on the elaborate interaction of the CRFR2-sensor and its intrinsic feedback arrangement. Lack of expression of CRFR2 would not compromise cardiac control and its dynamical output or is subserved by other, unknown mechanisms. Functional integrity of CRFR2 would not constitute an indispensable requirement of physiologic cardiac control. The circadian rhythm of heart rate is generated centrally and is independent of expression of CRFR2. While `normal' strain C57BL/6N mice exhibit a circadian dark/light cycle of heart rate, absence of circadian fluctuations in transgenic CRFR2-mice (both +/+ and –/–) and `normal' strain C57BL/6J mice points at the importance of other deficiencies that may be related to a common genetic background. Mutant mice that share a common 129SvJ- or C57BL/6J-derived genetic background may not present an optimal model for physiological studies of cardiovascular control.     

Molecular classification of scrapie strains in mice using gene expression profiling

Transmissible spongiform encephalopathy strains demonstrate specific prion characteristics, each with specific incubation times, and strain-specific patterns of deposition of the misfolded isoform of prion, PrPSc, in the brains of infected individuals. Different biochemical properties, including glycosylation profiles and the degree of proteinase resistance, have been shown to be strain-specific. However, no relationship between these properties and the phenotypic differences in the subsequent diseases has as yet been determined. Here we explore the utility of gene expression profiles to identify differences in the host response to different strains of prion agent. We identify 114 genes that exhibit significantly different levels of expression in mice infected with three strains of scrapie. These genes represent a pool of genes involved in a strain-specific response to prion disease. We have identified the most discriminatory genes from this list utilizing a wrapper-based feature selection algorithm with external cross-validation.     

Kinetics of heart rate and catecholamines during exercise in humans The effect of heart denervation

To elucidate the role of factors other than the nervous system in heart rate (f _c) control during exercise, the kinetics off _c and plasma catecholamine concentrations were studied in ten heart transplant recipients during and after 10-min cycle ergometer exercise at 50 W. Thef _c did not increase at the beginning of the exercise for about 60 s. Then in the eight subjects who completed the exercise it increased following an exponential kinetic with a mean time constant of 210 (SEM 22) s. The two other subjects were exhausted after 5 and 8 min of exercise during whichf _c increased linearly. At the cessation of the exercise,f _c remained unchanged for about 50 s and then decreased exponentially with a time constant which was unchanged from that at the beginning of exercise. In the group of eight subjects plasma noradrenaline concentration ([NA]) increased after 30 s to a mean value above resting of 547 (SEM 124) pg · ml^–1, showing a tendency to a plateau, while adrenaline concentration ([A]) did not increase significantly. In the two subjects who became exhausted an almost linear increase in [NA] occurred up to about 1,300 pg · ml^–1 coupled with a significant increase in [A]. During recovery an immediate decrease in [NA] was observed towards resting values. The values of thef _c increase above resting levels determined at the time of blood collection were linearly related with [NA] increments both at the beginning and end of exercise with a similar slope, i.e. about 2.5 beats · min^–1 per 100 pg · ml^–1 of [NA] change. These findings would seem to suggest that in the absence of heart innervation the increase inf _c depends on plasma [NA].     

Variations in heart rate and rhythm of harbor seal pups during rehabilitation

Heart rate and rhythm is regulated by the autonomic nervous system, which matures during the first months of life. Little is known about heart rate and rhythm development and potential arrhythmias in seal pups during rehabilitation in seal centers. Using an iPhone ECG device, 1 min ECGs were obtained from harbor seal pups admitted to a seal rehabilitation facility. ECGs were taken from 55 seals after admission, 53 seals after 14 d, and 52 seals prior to release. From 24 seal pups additional ECGs were taken daily for the first week of rehabilitation. At admission sinus rhythm with a median heart rate of 148 complexes per minute was detected, prior to release sinus bradycardia or sinus arrhythmia with a median heart rate of 104 complexes minute was present. P wave morphology was highly variable and single supra‐ and ventricular premature complexes were recorded in individual animals. The first 14 d were characterized by highly variable heart rates and rhythms, including episodes of sinus tachycardia and 2nd degree atrioventricular blocks. The reduction in heart rates and development of a regular heart rhythm during rehabilitation suggest adaptation to the unfamiliar environment, resolution of disease, and/or maturation of the autonomic nervous system.     

Maternal deprivation affects the neuromuscular protein profile of the rat colon in response to an acute stressor later in life

Early life stress as neonatal maternal deprivation (MD) predisposes rats to alter gut functions in response to acute psychological stressors in adulthood, mimicking features of irritable bowel syndrome (IBS). We applied proteomics to investigate whether MD permanently changes the protein profile of the external colonic neuromuscular layer that may condition the molecular response to an acute stressor later in life.

Male rat pups were separated 3 h/day from their mothers during the perinatal period and further submitted to water avoidance (WA) stress during adulthood. Proteins were extracted from the myenteric plexus-longitudinal muscle of control (C), WA and MD + WA rat colon, separated on 2D gels, and identified by mass spectrometry. MD amplified the WA-induced protein changes involved in muscle contractile function, suggesting that stress accumulation along life imbalances the muscle tone towards hypercontractility. Our results also propose a stress dependent regulation of gluconeogenesis. Secretogranin II – the secretoneurin precursor – was induced by MD. The presence of secretoneurin in myenteric ganglia may partially explain the stress-mediated modulation of gastrointestinal motility and/or mucosal inflammation previously described in MD rats.

In conclusion, our findings suggest that neonatal stress alters the responses to acute stress in adulthood in intestinal smooth muscle and enteric neurons.     

Diverse human aldolase C gene promoter regions are required to direct specific LacZ expression in the hippocampus and Purkinje cells of transgenic mice

Aldolase C is selectively expressed in the hippocampus and Purkinje cells in adult mammalian brain. The gene promoter regions governing cell-specific aldolase C expression are obscure. We show that aldolase C messenger expression in the hippocampus is restricted to CA3 neurons. The human distal promoter region (-200/-1200 bp) is essential for beta-galactosidase (beta-gal) expression in CA3 neurons and drives high stripe-like beta-gal expression in Purkinje cells. The 200 bp proximal promoter region is sufficient to drive low brain-specific and stripe-like beta-gal expression in Purkinje cells. Thus, the human aldolase C gene sequences studied drive endogenous-like expression in the brain.