Direct evidence of H7N7 avian influenza virus mutation from low to high virulence on a single poultry premises during an outbreak in free range chickens in the UK, 2008

H5 and H7 subtypes of low pathogenicity avian influenza viruses (LPAIVs) have the potential to evolve into highly pathogenic avian influenza viruses (HPAIVs), causing high mortality in galliforme poultry with substantial economic losses for the poultry industry. This study provides direct evidence of H7N7 LPAIV mutation to HPAIV on a single poultry premises during an outbreak that occurred in June 2008 in free range laying hens in Oxfordshire, UK. We report the first detection of a rare di-basic cleavage site (CS) motif (PEIPKKRGLF), unique to galliformes, that has previously been associated with a LPAIV phenotype. Three distinct HPAIV CS sequences (PEIPKRKKRGLF, PEIPKKKKRGLF and PEIPKKKKKKRGLF) were identified in the infected sheds suggesting molecular evolution at the outbreak premises. Further evidence for H7N7 LPAIV preceding mutation to HPAIV was derived by examining clinical signs, epidemiological descriptions and analysing laboratory results on the timing and proportions of seroconversion and virus shedding at each infected shed on the premises. In addition to describing how the outbreak was diagnosed and managed via statutory laboratory testing, phylogenetic analysis revealed reassortant events during 2006-2008 that suggested likely incursion of a wild bird origin LPAIV precursor to the H7N7 HPAIV outbreak. Identifying a precursor LPAIV is important for understanding the molecular changes and mechanisms involved in the emergence of HPAIV. This information can lead to understanding how and why only some H7 LPAIVs appear to readily mutate to HPAIV.

Characterization of divergent and atypical canine coronaviruses from Sweden

Field canine coronaviruses (CCVs) identified during a series of outbreaks of gastroenteritis in Swedish dogs were subjected to genetic analysis involving the open reading frame 1b (ORF1b) and the membrane (M) and spike (S) protein genes. Four field viruses originating from the Stockholm region presented identical sequences and segregated separately from other CCVs characterized so far and from GOT/05, the variant recovered in Western Sweden. A recombinant origin of the fifth virus identified in the Stockholm region is suggested. In addition, the five viruses originating from the same geographical area displayed atypical 5′ S gene sequences.

Identification of Sensitive and Specific Avian Influenza Polymerase Chain Reaction Methods Through Blind Ring Trials Organized in the European Union

Many different polymerase chain reaction (PCR) protocols have been used for detection and characterization of avian influenza (AI) virus isolates, mainly in research settings. Blind ring trials were conducted to determine the most sensitive and specific AI PCR protocols from a group of six European Union (EU) laboratories. In part 1 of the ring trial the laboratories used their own methods to test a panel of 10 reconstituted anonymized clinical specimens, and the best methods were selected as recommended protocols for part 2, in which 16 RNA specimens were tested. Both panels contained H5, H7, other AI subtypes, and non-AI avian pathogens. Outcomes included verification of 1) generic AI identification by highly sensitive and specific M-gene real-time PCR, and 2) conventional PCRs that were effective for detection and identification of H5 and H7 viruses. The latter included virus pathotyping by amplicon sequencing. The use of recommended protocols resulted in improved results among all six laboratories in part 2, reflecting increased sensitivity and specificity. This included improved H5/H7 identification and pathotyping observed among all laboratories in part 2. Details of these PCR methods are provided. In summary, this study has contributed to the harmonization of AI PCR protocols in EU laboratories and influenced AI laboratory contingency planning following the first European reports of H5N1 highly pathogenic AI during autumn 2005.

SYBR Green real-time reverse transcription-polymerase chain reaction assay for the generic detection of coronaviruses

Coronaviruses are etiologic agents of respiratory and enteric diseases in humans and in animals. In this study, a one-step real-time reverse transcription-polymerase chain reaction (RT-PCR) assay based on SYBR Green chemistry and degenerate primers was developed for the generic detection of coronaviruses. The primers, designed in the open reading frame 1b, enabled the detection of 32 animal coronaviruses including strains of canine coronavirus, feline coronavirus, transmissible gastroenteritis virus (TGEV), bovine coronavirus (BCoV), murine hepatitis virus (MHV) and infectious bronchitis virus (IBV). A specific amplification was also observed with the human coronaviruses (HCoV) HCoV-NL63, HCoV-OC43, HCoV-229E and severe acute respiratory syndrome coronavirus (SARS-CoV). The real-time RT-PCR detected down to 10 cRNA copies from TGEV, BCoV, SARS-CoV and IBV. In addition, the assay exhibited a high sensitivity and specificity on clinical samples from different animal species. The developed assay represents a potential tool for laboratory diagnostics and for detecting still uncharacterized coronaviruses.

Development of a real-time PCR assay based on primer-probe energy transfer for the detection of swine vesicular disease virus

A real-time PCR assay based on primer-probe energy transfer (PriProET) was developed to detect swine vesicular disease virus (SVDV). Specificity tests of SVDV and heterologous virus showed specific amplification of SVDV strains only. The amplification plot for the closely related Coxsackievirus B5 remained negative. The sensitivity of assay was five copies of viral genome equivalents. A key point of the assay is tolerance toward mutations in the probe region. Melting curve analysis directly after PCR, with determination of probe melting point, confirmed specific hybridisation of the SVDV strains. Eight of twenty SVDV strains tested, revealed shifted melting points that indicated mutations in the probe region. All predicted mutations were confirmed by nucleotide sequencing. With the PriProET system there is a chance to identify phylogenetically divergent strains of SVDV, which may appear negative in other probe-based real-time PCR assays. At the same time, any difference in melting points may provide an indication of divergence in the probe region. The high sensitivity, specificity, and tolerance toward mutations in the probe region of the SVDV PriProET assay may improve the early and rapid detection of a wide range of SVDV strains, allowing reduced turnaround time and the use of high-throughput, automated technology.

Electrocardiographic characterization of stress-induced myocardial infarction in atherosclerotic mice

AIM

We have previously shown that mental and hypoxic stress can trigger the development of myocardial infarction (MI) in atherosclerotic apoE(-/-) x LDLR(-/-) mice. The purpose of the present study was to characterize the interval between stress and MI and determine whether electrophysiological changes precede the precipitation of an infarct by assessing telemetry recordings of the electrocardiogram.

METHODS

Isoflurane anaesthetized apoE(-/-) x LDLR(-/-) (n = 16) and C57BL/6J (n = 8) mice were exposed to systemic hypoxia by reducing the inhaled oxygen concentration to 10% for 10 min. Mental stress was induced in eight conscious apoE(-/-) x LDLR(-/-) and eight C57BL/6J mice by blowing air into the cage. Physiological parameters were recorded every 30 min for 2-6 days by implanted transmitters.

RESULTS

During stress all mice developed transient ischaemic STU-area changes, which returned to normal at the end of stress. During the recovery phase (6 days) 50% (4/8) of the mentally stressed apoE(-/-) x LDLR(-/-) mice developed increased STU-area variability (P < 0.05) followed by dramatic STU-area elevations and spontaneous death at approximately 12-24 h. In hypoxia-exposed apoE(-/-) x LDLR(-/-) mice 56% (9/16) developed MI as determined by elevated serum levels of the infarction marker troponin T which correlated with increased variability in the STU-area (P < 0.05).

CONCLUSION

This is the first mouse model showing that increased STU-area variability is indicative of MI development in atherosclerotic mice following ischaemic stress. Furthermore, our findings suggest a two-phase pathway for the infarction development: an initial phase comprising a transient ischaemic response which triggers a delayed second phase of ischaemia and MI.

Experimental Infection of Cows with Bovine Viral Diarrhoea Virus in Early Pregnancy - Findings in Serum and Foetal Fluids

Nineteen pregnant cows were experimentally infected with bovine viral diarrhoea virus (BVDV) between day 74 and 81 of pregnancy. All cows became infected and developed serum antibodies. Sixteen of the cows delivered persistently infected (PI) offspring, whereas the remaining three gave birth to calves with detectable serum antibodies and free from BVDV. The 16 cows with PI foetuses developed higher levels of antibodies in serum during pregnancy than did their three peers carrying non-PI calves. Multivariate analysis showed that the antibody levels in these two groups of cows were significantly different from day 135 of pregnancy. Foetal fluid was successfully collected from 18 of the 19 infected cows and from five uninfected control cows between 10 and 24 days before delivery by use of a percutaneous, blind puncture technique. No negative effects were observed in the cows or their offspring. BVDV was isolated and detected with an immunoperoxidase test in foetal fluid from 13 of the 16 cows carrying PI foetuses, and from 15 of the cows when a quantitative fluorescent polymerase chain reaction (PCR) technique was used. The negative sample in the PCR assay was positive for BVDV antibodies. The number of viral copies per microlitre in foetal fluids varied between 103 and 1080 in the positive samples. All samples taken from the cows carrying non-PI foetuses were negative for BVDV in both assays. In this experiment, examination of either serum or foetal fluids could identify the cows carrying a PI foetus. Examination of serum for BVDV antibodies was a reliable indicator of a PI foetus if the serum was collected during the last 2 months of pregnancy. For examination of foetal fluids, both viral and serological analyses should be performed. For viral analysis, PCR should be the test of choice. High levels of BVDV antibodies in conjunction with a negative result in the PCR may be indicative of a false-negative virus result. Further experience with the method of collection of foetal fluids is necessary for evaluation of its safety. Investigation of pregnant cows in order to discover a PI offspring before it is born could be a useful tool in control and eradication of BVDV.

Cyclic fluctuations in the cardiac performance of the isolated Langendorff-perfused mouse heart: pyruvate abolishes the fluctuations and has an anti-ischaemic effect

During the development of a Langendorff preparation of isolated mouse hearts, hitherto undescribed cyclic fluctuations in left ventricular pressure and coronary flow were independently observed in three laboratories. Isolated mouse hearts were perfused with crystalloid glucose-containing Krebs-Hensleit buffer in a constant pressure model, and left ventricular pressures were measured via an intraventricular balloon catheter. After acquiring technical skill in preparing the mouse hearts, the perfusionists observed that fluctuations in cardiac performance with a cycle period lasting 5-10 min occurred shortly after initiation of perfusion. Each fluctuation cycle consisted of a phase of increase and a phase of decrease. Synchronized with the fluctuations in left ventricular pressure, increases and decreases in dP/dt max took place. Analogous fluctuations in coronary flow occurred, with onset 1-2 min later than changes in left ventricular systolic pressure. In some preparations a gradual ST-segment elevation was seen on the electrocardiogram during the systolic pressure increase phase. The amplitude of the fluctuations could be augmented by increasing the perfusion pressure, and reduced, but not abolished, by lowering the pressure. Changes in buffer calcium, magnesium, or sodium concentration did not alter the fluctuations, nor did any change of anaesthetics, mouse strain, or left ventricular drainage. Altering the perfusion mode from constant pressure to constant flow did not prevent the occurrence of the cyclic fluctuations. The hearts became stable and the fluctuations disappeared when the buffer was supplemented with 2 mm pyruvate. In the present study, pyruvate given throughout stabilization and reperfusion also markedly attenuated the ischaemic insult, as evidenced by the delayed ischaemic contracture and a reduced magnitude of ischaemic contracture. A cardioprotective effect was only visible at early reperfusion, did not affect the final functional recovery. In conclusion, a phenomenon of cyclic fluctuations in left ventricular pressure followed by fluctuations in coronary flow was observed in isolated mouse hearts. These could be abolished by adding 2 mm pyruvate to the perfusion buffer. Pyruvate in the buffer also markedly attenuated the post-ischaemic deterioration of cardiac performance seen in this mouse model.

Ablation of TRalpha2 and a concomitant overexpression of alpha1 yields a mixed hypo- and hyperthyroid phenotype in mice

Thyroid hormone governs a diverse repertoire of physiological functions through receptors encoded in the receptor genes alpha and beta, which each generate variant proteins. In mammals, the alpha gene generates, in addition to the normal receptor TRalpha1, a non-hormone-binding variant TRalpha2 whose exact function is unclear. Here, we present the phenotype associated with the targeted ablation of TRalpha2 expression. Selective ablation of TRalpha2 resulted in an inevitable, concomitant overexpression of TRalpha1. Both TRalpha2 +/- and -/- mice show a complex phenotype with low levels of free T3 and free T4, and have inappropriately normal levels of TSH. The thyroid glands exhibit mild morphological signs of dysfunction and respond poorly to TSH, suggesting that the genetic changes affect the ability of the gland to release thyroid hormones. However, the phenotype of the mutant mice also has features of hyperthyroidism, including decreased body weight, elevated heart rate, and a raised body temperature. Furthermore, TRalpha2-/- and TRalpha2+/- mice are obese and exhibit skeletal alterations, associated with a late-onset growth retardation. The results thus suggest that the overexpression of TRalpha1 and the concomitant decrease in TRalpha2 expression lead to a mixed hyper- and hypothyroid phenotype, dependent on the tissue studied. The phenotypes suggest that the balance of TRalpha1:TRalpha2 expressed from the TRalpha gene provides an additional level of tuning the control of growth and homeostasis in mammalian species.

Molecular diagnosis of animal diseases: some experiences over the past decade

The experiences of a veterinary research and diagnostic laboratory are summarized on the development and application of the PCR to diagnose a wide range of viral diseases in animals. The group started the routine diagnostic application of the PCR as early as 1988 and today a total of 35 nested PCR assays are in routine use for the detection of 15 DNA and 20 RNA viruses. Special tools and laboratory practice were applied to avoid false-positive results, while false-negatives are avoided by internal controls (mimics). At present, the classical nested PCR methods are being replaced by real-time TaqMan and molecular beacon assays and the multiplex real-time PCR detection of viruses is also under development. By direct sequencing of the PCR products, phylogeny studies are performed and molecular epizootiology results are provided for rapid and exact identification of virus variants. Molecular epizootiology also contributes to trace the routes of virus spreading on large geographic areas. Recently, large efforts have been made to follow the recommendations of Office International des Epizooties for the standardization and international harmonization of the molecular diagnostic assays.

Vascular endothelial growth factor-B-deficient mice display an atrial conduction defect

BACKGROUND

Vascular endothelial growth factors (VEGFs) and their receptors are essential regulators of vasculogenesis and angiogenesis in both embryos and adults. One of the factors with a still unknown physiological function is VEGF-B, which is expressed in many tissues, including the heart.

METHODS AND RESULTS

Mice carrying a targeted deletion in the VEGF-B gene were developed. In VEGF-B(-/-) animals, no gross abnormalities were observed in organs that normally show high expression of VEGF-B, such as the heart, muscle, and kidney. Analysis of heart function by ECG showed that adult VEGF-B(-/-) mice have an atrial conduction abnormality characterized by a prolonged PQ interval. VEGF- or basic fibroblast growth factor-induced corneal angiogenesis was similar in normal and VEGF-B(-/-) mice.

CONCLUSIONS

VEGF-B seems to be required for normal heart function in adult animals but is not required for proper development of the cardiovascular system either during development or for angiogenesis in adults.

Contraction and intracellular Ca(2+) handling in isolated skeletal muscle of rats with congestive heart failure

A decreased exercise tolerance is a common symptom in patients with congestive heart failure (CHF). This decrease has been suggested to be partly due to altered skeletal muscle function. Therefore, we have studied contractile function and cytoplasmic free Ca(2+) concentration ([Ca(2+)](i), measured with the fluorescent dye indo 1) in isolated muscles from rats in which CHF was induced by ligation of the left coronary artery. The results show no major changes of the contractile function and [Ca(2+)](i) handling in unfatigued intact fast-twitch fibers isolated from flexor digitorum brevis muscles of CHF rats, but these fibers were markedly more susceptible to damage during microdissection. Furthermore, CHF fibers displayed a marked increase of baseline [Ca(2+)](i) during fatigue. Isolated slow-twitch soleus muscles of CHF rats displayed slower twitch contraction and tetanic relaxation than did muscles from sham-operated rats; the slowing of relaxation became more pronounced during fatigue in CHF muscles. Immunoblot analyses of sarcoplasmic reticulum proteins and sarcolemma Na(+),K(+)-ATPase showed no difference in flexor digitorum brevis muscles of sham-operated versus CHF rats. In conclusion, functional impairments can be observed in limb muscle isolated from rats with CHF. These impairments seem to mainly involve structures surrounding the muscle cells and sarcoplasmic reticulum Ca(2+) pumps, the dysfunction of which becomes obvious during fatigue.

Activation of inducible nitric oxide synthase/nitric oxide by curli fibers leads to a fall in blood pressure during systemic Escherichia coli infection in mice

Septic shock, a major cause of death, is characterized by a pathophysiologic increased production of nitric oxide (NO), which leads to vasodilation and myocardial toxicity. Septic Escherichia coli frequently express proteinaceous curli fibers. In this study, curliated E. coli induced high levels of NO by directly inducing type 2 nitric oxide synthase (NOS2) both in vitro and in vivo. More severe hypotension and higher plasma nitrite/nitrate levels were seen in wild type mice systemically infected with curliated E. coli than in animals infected with E. coli mutants that lacked curli proteins. Blood pressure remained stable in NOS2-deficient mice with curliated bacteria. Increased heart rates, transient hypothermia, and loss of gross activity were seen in all mice, regardless of curli expression. Study results suggest that expression of curli fibers by E. coli activates the NO/NOS2 arm of the innate immune system, which leads to a significant fall in blood pressure.

Reduced antinociception and plasma extravasation in mice lacking a neuropeptide Y receptor

Neuropeptide Y (NPY) is believed to exert antinociceptive actions by inhibiting the release of substance P and other 'pain neurotransmitters' in the spinal cord dorsal horn. However, the physiological significance and potential therapeutic value of NPY remain obscure. It is also unclear which receptor subtype(s) are involved. To identify a possible physiological role for the NPY Y1 receptor in pain transmission, we generated NPY Y1 receptor null mutant (Y1-/-) mice by homologous recombination techniques. Here we show that Y1-/- mice develop hyperalgesia to acute thermal, cutaneous and visceral chemical pain, and exhibit mechanical hypersensitivity. Neuropathic pain is increased, and the mice show a complete absence of the pharmacological analgesic effects of NPY. In the periphery, Y1 receptor activation is sufficient and required for substance P release and the subsequent development of neurogenic inflammation and plasma leakage. We conclude that the Y1 receptor is required for central physiological and pharmacological NPY-induced analgesia and that its activation is both sufficient and required for the release of substance P and initiation of neurogenic inflammation.

Running and cocaine both upregulate dynorphin mRNA in medial caudate putamen

Physical activities such as long-distance running can be habit forming and associated with a sense of well-being to a degree that justifies comparison with drug-induced addictive behaviours. To understand molecular similarities and dissimilarities controlling these behaviours in humans we compared the effects of running in running wheels to the effects of chronic cocaine or morphine administration on mRNA levels in brain reward pathways in the inbred Fischer and Lewis rat strains. These strains are both inbred from the Sprague-Dawley strain; Lewis rats display a higher preference towards addictive drugs and running than do Fischer rats. After chronic cocaine or running a similar increase of dynorphin mRNA in medial caudate putamen was found in the Lewis rat, suggesting common neuronal adaptations in this brain region to both cocaine and running. Fischer and Lewis rats both responded to cocaine with increased dynorphin mRNA levels in medial caudate putamen. However, only Lewis rats increased dynorphin mRNA after running, possibly reflecting the much higher degree of running by the Lewis strain as compared to the Fischer strain. Moreover, the running-induced upregulation of dynorphin mRNA was blocked by the opioid receptor antagonist naloxone. We suggest that running increases dynorphin mRNA by a mechanism that involves endogenous opioids. The voluntary wheel-running model in rats might be used to study natural reward and compulsive behaviours and possibly also to screen candidate drugs for treatment of compulsive disorders.

Isometric force and endurance in soleus muscle of thyroid hormone receptor-alpha(1)- or -beta-deficient mice

The specific role of each subtype of thyroid hormone receptor (TR) on skeletal muscle function is unclear. We have therefore studied kinetics of isometric twitches and tetani as well as fatigue resistance in isolated soleus muscles of R-alpha(1)- or -beta-deficient mice. The results show 20-40% longer contraction and relaxation times of twitches and tetani in soleus muscles from TR-alpha(1)-deficient mice compared with their wild-type controls. TR-beta-deficient mice, which have high thyroid hormone levels, were less fatigue resistant than their wild-type controls, but contraction and relaxation times were not different. Western blot analyses showed a reduced concentration of the fast-type sarcoplasmic reticulum Ca(2+)-ATPase (SERCa1) in TR-alpha(1)-deficient mice, but no changes were observed in TR-beta-deficient mice compared with their respective controls. We conclude that in skeletal muscle, both TR-alpha(1) and TR-beta are required to get a normal thyroid hormone response.

Enhancement of natural immunity seen after voluntary exercise in rats. Role of central opioid receptors

Chronic voluntary exercise in wheels for 5 weeks in spontaneously hypertensive rats (SHR) augments in vivo natural killer (NK) cell cytotoxicity. Endogenous beta-endorphin is increased in cerebrospinal fluid after voluntary exercise in rats and we have recently shown that beta-endorphin administered i.c.v. augments NK cell mediated cytotoxicity in vivo in a similar way as chronic voluntary exercise. We have now further investigated the involvement of central opioid systems in the exercise-induced augmentation in natural immunity. Exercise consisted of voluntary running in wheels for 5 weeks. In vivo cytotoxicity was measured as clearance of injected 51Cr-labeled YAC-1 lymphoma cells from the lungs. The clearance of YAC-1 cells in vivo was significantly increased in runners as compared to sedentary controls. Selective delta, kappa, or mu-opioid receptor antagonists were administered i.c.v. with osmotic minipumps during the last 6 days of the 5 weeks of running. The delta-receptor antagonist naltrindole (40-50 microg/day) significantly but not completely inhibited the enhanced NK-cell cytotoxicity seen after 5 weeks of exercise. Neither the kappa-receptor antagonist nor-BNI or the mu-receptor antagonist beta-FNA influenced the augmentation in NK cell cytotoxicity. Nor-BNI per se significantly augments in vivo cytotoxicity, indicating some inhibiting effect on natural immunity that could be mediated through the kappa-opioid receptor. Our data suggest the involvement of central delta-opioid receptors in the enhancement of natural cytotoxicity seen after chronic voluntary exercise.

The effect of a neuropeptide Y antagonist, BIBP 3226, on short-term arterial pressure control in conscious unrestrained rats with congestive heart failure

The effects of a neuropeptide Y (NPY) Y1-receptor antagonist (BIBP 3226) on mean arterial pressure (MAP) and heart rate were investigated in conscious unrestrained rats with chronic congestive heart failure. The rats were randomly assigned to 2 groups, and received either BIBP 3226 or its inactive enantiomer (BIBP 3435) as an intravenous infusion (6 mg/kg/h for 1.5 h, respectively). Before, during and after the infusion, rats were stressed with a jet of air and received a bolus injection of NPY (2 nmol/kg iv.). There was no difference between the 2 groups in resting MAP and heart rate before, during or after infusion (BIBP 3226 vs. BIBP 3435). The effects of exogenous NPY on MAP were significantly attenuated in BIBP 3226 group during and 1 h after the infusion (p<0.05). The tissue NPY levels in heart, adrenal gland and kidney in heart failure rats were not different from those in sham-operated rats. The results suggest that Y1-receptor mechanisms are of minor importance in the short-term control of basal MAP and heart rate in conscious unrestrained rats with congestive heart failure.

Somatic nerve stimulation and cholera-induced net fluid secretion in the small intestine of the rat: evidence for an opioid effect

The effects of somatic nerve stimulation on cholera toxin induced secretion was investigated in vivo in anaesthetised rats. Small intestinal secretion was induced with cholera toxin and measured by a gravimetric technique. Afferent stimulation (pulse frequency within train; 100 Hz; train duration: 50 ms; train frequency: 3 Hz) of the sciatic nerve over 30 min significantly reduced the net fluid secretion both during (P < 0.05) and after cessation of the stimulation (P < 0.01). The greatest effect was obtained immediately after the termination of the nerve stimulation when the secretion was reversed to net fluid absorption. The opioid receptor antagonist naloxone (10 mg kg(-1) i.v.) administrated during the stimulation, significantly inhibited the antisecretory effect seen after the stimulation, thus no significant difference was seen between the control period and the periods after cessation of the stimulation. The opioid receptor antagonist naloxone methiodide (10 mg kg(-1) i.v.), which does not cross the blood-brain barrier, partly inhibited the antisecretory effects but not with the same magnitude as naloxone, thus the net fluid secretion was still significantly inhibited after the stimulation (P < 0.05). We conclude that afferent stimulation of the sciatic nerve strongly inhibits the cholera toxin induced secretion in the small intestine. This inhibition involves primarily a central opioid mechanism and to a lesser extent peripheral opioid mechanism.

Deprived of habitual running, rats downregulate BDNF and TrkB messages in the brain

To study possible effects of physical training on the expression of neurotrophic factors and their receptors in the brain, we used a rat strain (spontaneously hypertensive rat, SHR), known to spontaneously run up to 20 km/night. We show that such long-distance running affects the brain-derived neurotrophic factor (BDNF) and TrkB system in hippocampus, and in particular that abrupt deprivation of habitual running leads to long-lasting decreases of BDNF/TrkB expression in hippocampus. Quantitative in situ hybridization demonstrates that running increases the expression of mRNA coding for BDNF and its high affinity receptor TrkB in hippocampus in a running length dependent manner. In addition, we show that an abrupt interruption of prolonged spontaneous exercise decrease expression of mRNA encoding BDNF and TrkB in certain hippocampal areas and that this decrease lasts at least 10 days. This down-regulation was most prominent in medial cornu ammonis 3 (CA3M). Several other trophic factors and receptors were investigated, including NGF, NT3, GDNF, trkC and p75. For these other probes investigated, no robust changes in mRNA expression were noted. Areas examined included sensorimotor cortex and hippocampus. For RET, p75, NT3, TrkB and BDNF we also examined the spinal cord without detecting any robust changes. We conclude that spontaneous running as well as its abrupt termination, leads to area-specific and trophic factor-specific changes in hippocampus.

Addiction-prone Lewis but not Fischer rats develop compulsive running that coincides with downregulation of nerve growth factor inducible-B and neuron-derived orphan receptor 1

We have examined the effects of chronic voluntary running for 30 d on the levels of nerve growth factor inducilble-B (NGFI-B) and neuron-derived orphan receptor 1 (NOR1) mRNAs in Fischer and Lewis rats. The aim was to compare the addiction-prone Lewis rat strain to the Fischer strain in a plausible model for natural reward. The Lewis strain ran markedly more than the Fischer strain, as indicated by the length of running per day when given free access to running wheels. Both strains progressively increased their amount of daily running. By day 14, Lewis rats had reached a maximal level corresponding to 10 km/d, which slowly decreased to approximately 8 km/d. Fischer rats ran considerably less, averaging approximately 1. 5 km/d by day 30. After 30 d of running, levels of mRNA encoding NGFI-B and Nor1 were decreased in cerebral cortex in Lewis but not Fischer rats. The downregulation of NGFI-B mRNA in Lewis rats could not be attenuated by the opioid receptor antagonist naloxone. Instead, naloxone by itself downregulated NGFI-B in striatum and cerebral cortex in both strains. In contrast, naloxone had no effect on Nor1 mRNA levels, although the running-induced downregulation of Nor1 was, in most cases, attenuated by naloxone. Data from the present study suggest that the same genetic factors contributing to the drug addiction-prone behavior of Lewis rats also control the excessive running behavior and that this coincides with downregulation of transcription factors of the NGFI-B family.

Myocardial infarction mediated by endothelin receptor signaling in hypercholesterolemic mice

Myocardial infarction is linked to atherosclerosis, yet the sequence leading from silent coronary atherosclerosis to acute myocardial infarction has remained unclear. Here we show that hypercholesterolemic apolipoprotein E-/- low density lipoprotein receptor-/- mice develop not only coronary atherosclerosis but also myocardial infarction. Exposure of mice to mental stress or hypoxia led to acute ischemia, which, in a large proportion of the mice, was followed by electrocardiographic changes, leakage of troponin T, and loss of dehydrogenase from the myocardium, all indicative of acute myocardial infarction. Apoptotic death of cardiomyocytes was followed by inflammation and fibrosis in the heart. All these pathological changes could be prevented by a blocker of the endothelin type A receptor. Thus, stress elicits myocardial infarction through endothelin receptor signaling in coronary atherosclerosis caused by hypercholesterolemia.

Cardiovascular phenotype and temperature control in mice lacking thyroid hormone receptor-beta or both alpha1 and beta

We have used a telemetry system to record heart rate, body temperature, electrocardiogram (ECG), and locomotor activity in awake, freely moving mice lacking thyroid hormone receptor (TR)-beta or TR-alpha1 and -beta (TR-alpha1/beta). The TR-alpha1/beta-deficient mice had a reduced heart rate compared with wild-type controls. The TR-beta-deficient mice showed an elevated heart rate, which, however, was unresponsive to thyroid hormone treatment regardless of hormonal serum levels. ECG revealed that the TR-beta-deficient mice had a shortened Q-Tend time in contrast to the TR-alpha1/beta-deficient mice, which exhibited prolonged P-Q and Q-Tend times. Mental or pharmacological stimulation of the sympathetic nervous system resulted in a parallel increase in heart rate in all animals. A single injection of a nonselective beta-adrenergic-receptor blocker resulted in a parallel decrease in all mice. The TR-alpha1/beta-deficient mice also had a 0.4 degrees C lower body temperature than controls, whereas no difference was observed in locomotor activity between the different strains of mice. Our present and previous results support the hypothesis that TR-alpha1 has a major role in determining heart rate under baseline conditions and body temperature and that TR-beta mediates a hormone-induced increase in heart rate.

Dilated cardiomyopathy and atrioventricular conduction blocks induced by heart-specific inactivation of mitochondrial DNA gene expression

Mutations of mitochondrial DNA (mtDNA) cause several well-recognized human genetic syndromes with deficient oxidative phosphorylation and may also have a role in ageing and acquired diseases of old age. We report here that hallmarks of mtDNA mutation disorders can be reproduced in the mouse using a conditional mutation strategy to manipulate the expression of the gene encoding mitochondrial transcription factor A (Tfam, previously named mtTFA), which regulates transcription and replication of mtDNA. Using a loxP-flanked Tfam allele (TfamloxP) in combination with a cre-recombinase transgene under control of the muscle creatinine kinase promoter, we have disrupted Tfam in heart and muscle. Mutant animals develop a mosaic cardiac-specific progressive respiratory chain deficiency, dilated cardiomyopathy, atrioventricular heart conduction blocks and die at 2-4 weeks of age. This animal model reproduces biochemical, morphological and physiological features of the dilated cardiomyopathy of Kearns-Sayre syndrome. Furthermore, our findings provide genetic evidence that the respiratory chain is critical for normal heart function.

Hyper-responsiveness of adrenal sympathetic nerve activity in spontaneously hypertensive rats to ganglionic blockade, mental stress and neuronglucopenia

Previous investigations indicate that the spontaneously hypertensive rat (SHR) has elevated sympathetic tone at rest. The present study aimed to determine whether SHR has exaggerated sympatho-adrenal activation in response to various sympathetic stimuli. The mean blood pressure (MBP), heart rate (HR) and preganglionic adrenal sympathetic nerve activity (SNA) were recorded from conscious, unrestrained SHR and from its normotensive control, the Wistar-Kyoto rat (WKY) (n=7, respectively).Ganglionic blockade (trimethaphan, 5 mg/kg) reduced MBP identically in both groups of rats. It did not change HR in SHR, but increased HR significantly in WKY (P<0.05). The adrenal SNA increased in both groups, but the magnitude of the increase was more than threefold greater in SHR (P<0.05). Mental stress caused by air-jet induced significantly greater tachycardia (threefold) and sympatho-adrenal activation (tenfold) in SHR than in WKY rats. In SHR the inhibition of glycolysis (2-deoxy-d-glucose, 500 mg/kg) also produced a profound activation of adrenal SNA (sevenfold) and the increased adrenal SNA was not paralleled by an increased HR. We conclude that a variety of sympathetic stimuli, including ganglionic blockade, mental stress and neuronglucopenia, cause exaggerated activation of preganglionic adrenal SNA in SHR compared with WKY, indicating that adrenal SNA in SHR is hyper-responsive.

Evidence that decreased heart rate in thyroid hormone receptor-alpha1-deficient mice is an intrinsic defect

Using a telemetry system with implantable transmitters, we recorded heart rate, electrocardiogram (ECG), body temperature, and locomotor activity continuously in awake, freely moving mice deficient in the thyroid hormone receptor-alpha1 (TRalpha1). We have previously reported that the TRalpha1-deficient mice have a 20% lower mean heart rate and a 0.5 degrees C lower body temperature compared with wild-type control animals. In this study we found that when 3,5, 3'-triiodothyronine (T3) was given once a day, there was a parallel increase in heart rate (occurring 1 day later in the TRalpha1-deficient mice than in controls) and body temperature. Analysis of single-lead ECG revealed a prolonged QRS and Q-Tend time in the TRalpha1-deficient mice, which was shortened after T3 treatment. Monophasic action potential durations, measured in hearts from anesthetized mice at 90% of repolarization, were significantly prolonged in TRalpha1-deficient mice. Air-jet stress and a single injection of an anticholinergic agent induced a parallel increase, and a beta-adrenergic receptor blocker induced a decrease in heart rate in both groups. There was no difference in beta-adrenergic receptor density. The results indicate that the TRalpha1-deficient mice have a specific defect in intrinsic heart rate regulation.

Triglyceride-based microemulsion for intravenous administration of sparingly soluble substances

A pharmaceutically acceptable microemulsion system composed of a medium-chain triglyceride (MCT), soybean phosphatidylcholine and poly(ethylene glycol)(660)-12-hydroxystearate (12-HSA-EO15) as amphiphiles, and poly(ethylene glycol) 400 (PEG 400) and ethanol as cosolvents is presented and characterized in terms of phase behavior, microstructure, solubilization capacity and in vivo effects after intravenous administration to conscious rats. At a total concentration of 11.9 wt % of soybean phosphatidylcholine and 12-HSA-EO15, a microemulsion region was formed over a wide range of alpha, where alpha is the weight fraction of MCT/(MCT + water + PEG 400 + ethanol). The microstructure of the microemulsion was of a bicontinuous nature even at high oil concentrations. The mean droplet diameter of the oil-in-water emulsion formed after dilution of microemulsions prepared at different alpha within the one-phase region was between 60 and 200 nm. It was concluded that it is possible to administer up to 0.5 mL/kg of the microemulsion (alpha = 0.5) without producing any significant effect on acid-base balance, blood gases, plasma electrolytes, mean arterial blood pressure (MAP), heart rate (HR), and PQ time (the time between depolarization of atrium and chamber). At a dose of 1.5 mL/kg, a temporary increase in MAP, a decrease in HR, and a prolongation of the PQ time were observed.

Increase in nitric oxide formation after chronic voluntary exercise in spontaneously hypertensive rats

The effect of chronic voluntary exercise on the plasma level of nitrate, a major stable metabolite of nitric oxide (NO) was studied in spontaneously hypertensive rats (SHR). Exercise consisted of spontaneous running in wheels for 3-35 days. Blood samples were collected after 3, 7, 14, 21 and 35 days of exercise and all samples were drawn after the running wheel had been locked during the preceding 12 h. The plasma nitrate level was significantly (P < 0.05) elevated in SHR after 35 days of exercise. Surprisingly after 7 days of exercise a significant (P < 0.001) decrease in the nitrate level in plasma was noted. Further research is needed to elucidate this biphasic change in nitrate seen in this study. The elevated level of plasma nitrate seen after 35 days of voluntary exercise was still present up to 36 h after termination of exercise. We conclude that exercise training in SHR elicits an enhanced formation of NO.

Abnormal heart rate and body temperature in mice lacking thyroid hormone receptor alpha 1

Thyroid hormone, acting through several nuclear hormone receptors, plays important roles in thermogenesis, lipogenesis and maturation of the neonatal brain. The receptor specificity for mediating these effects is largely unknown, and to determine this we developed mice lacking the thyroid hormone receptor TR alpha 1. The mice have an average heart rate 20% lower than that of control animals, both under normal conditions and after thyroid hormone stimulation. Electrocardiograms show that the mice also have prolonged QRS- and QTend-durations. The mice have a body temperature 0.5 degrees C lower than normal and exhibit a mild hypothyroidism, whereas their overall behavior and reproduction are normal. The results identify specific and important roles for TR alpha 1 in regulation of tightly controlled physiological functions, such as cardiac pacemaking, ventricular repolarisation and control of body temperature.

Neuropeptide Y Y1 receptor antagonist (BIBP 3226) attenuates stress evoked tachycardia in conscious spontaneously hypertensive rats

The effects of a novel neuropeptide Y (NPY) Y1 receptor antagonist on resting mean blood pressure (MBP) and heart rate (HR) were observed in conscious spontaneously hypertensive rats (SHR). The interference of the antagonist with cardiovascular responses to mental stress and administration of exogenous NPY were also investigated. SHR were randomly received either the NPY Y1 receptor antagonist (BIBP 3226; n = 11) or its inactive enantiomer (BIBP 3435; n = 11) as an infusion (6 mg/kg/h for 1.5 hours). Before, during, and after the infusion, rats were first stressed with a jet of air and then given a bolus injection of exogenous NPY (2 nmol/kg). There was no statistically significant difference of resting MBP and HR between the antagonist and enantiomer groups before, during, or after infusion. The stress-induced maximum increase in HR was significantly reduced during antagonist infusion (P < 0.05). The effects of exogenous NPY on both MBP and HR were significantly attenuated by antagonist infusion (P < 0.05, respectively), and the effect lasted at least 1 hour after the end of the infusion. Plasma catecholamine levels in response to stress were not significantly different between the two groups. The results suggest that endogenous NPY Y1-receptor mechanisms may be of minor importance in short-term regulation of MBP and HR in conscious adult SHR, but may be involved in the response to mental stress.

Effects of calcium antagonist felodipine on renal sympathetic nerve activity in rats with congestive heart failure

In order to assess the effects of dihydropyridine calcium antagonist on sympathetic nerve activity (SNA) in experimental chronic heart failure (CHF), felodipine was given to rats with CHF induced by coronary artery ligation. Anesthetized CHF (n = 7) and sham-operated (n = 9) rats were injected with a bolus dose of felodipine (20 microg/kg) and then infused with felodipine (30 microg/kg/h) for 3 hours. Control CHF rats (n = 8) were given vehicle in the same way. After felodipine treatment, mean blood pressure (MBP) rapidly decreased to 75-85 mmHg, and there was a reflex tachycardia and reflex activation of renal SNA. The heart rate (HR) had returned to baseline level after 3 hours of continuous felodipine infusion, and the SNA returned to baseline level after 2 hours of infusion. At the end of the experiment, renal SNA was 65.4 +/- 11.5% of the baseline level in CHF rats receiving felodipine (P < 0.05) and 94.1 +/- 22.8% in CHF rats receiving vehicle (P > 0.05), but there was no statistical difference between the two groups. Arterial baroreceptor sensitivity (assessed by phenylephrine infusion), which was impaired in CHF rats (-2.7 +/- 0.2 SNA%/mmHg in all CHF rats together vs. -3.6 +/- 0.4 in sham-operated rats, P < 0.5) did not differ significantly from that in sham-operated rats during felodipine infusion (-3.2 +/- 0.4 in felodipine-treated CHF rats vs. -3.7 +/- 0.6 in sham-operated rats) but deteriorated without felodipine treatment (-2.1 +/- 0.3 in CHF rats receiving vehicle, P < 0.05). The biphasic renal SNA response during felodipine infusion suggests that felodipine does not cause persistent sympathetic activation and relatively improves baroreceptor sensitivity in CHF rats.

Effects of hydralazine on renal sympathetic nerve activity in normal and congestive heart failure rats

We investigated the effects of hydralazine on renal sympathetic nerve activity in anaesthetized heart failure rats. Sham-operated rats (group 1) received 0.5 mg kg-1 of hydralazine as bolus and were then infused with 0.3-0.5 mg kg-1 h-1 for 3 h intravenously. Heart failure rats received either the same regime (group 2) as group 1, or the same volume of vehicle (group 3). Heart failure rats exhibited lower mean blood pressure (P < 0.05) and elevated renal sympathetic nerve activity (P < 0.01) in the basal state. In group 2, the mean blood pressure decreased 26% after 30 min of hydralazine administration and remained lower for 3 h, with unchanged renal sympathetic nerve activity. In group 1, the mean blood pressure decreased 36%, and the heart rate and renal sympathetic nerve activity were significantly inhibited. Bilateral vagotomy did not alter renal sympathetic nerve response to hydralazine, but resulted in tachycardia. The results indicate that hydralazine, despite its profound hypotensive effect, did not activate renal sympathetic nerve activity in heart failure rats and inhibited renal sympathetic nerve activity in sham-operated rats. This inhibition was not mediated through the vagal nerve.

Duration and mechanisms of the increased natural cytotoxicity seen after chronic voluntary exercise in rats

We have recently shown that in vivo natural cytotoxicity is enhanced after chronic exercise in spontaneously hypertensive rats (SHRs). In the present report, we have studied the duration of this augmentation and some possible mechanisms involved. Exercise consisted of voluntary running for 4-5 weeks, with the running distance ranging from 2.7-15.6 km day(-1) during the last week of running. In vivo cytotoxicity was measured as clearance of injected 51Cr-labelled YAC-1 lymphoma cells from the lungs. The in vivo natural cytotoxicity was increased in running SHRs, and also in SHRs that had their running wheel locked for 24 and 48 h prior to the experiment, and was still present after 96 h. The enhancement of in vivo cytotoxicity after 5 weeks of exercise was abolished after an acute injection of the beta-adrenergic receptor antagonist timolol (0.5 mg kg(-1) i.v.), indicating that catecholamines are involved in this augmentation. Interestingly, 24 h after the last exercise bout, the increased natural cytotoxicity could be blocked by timolol. The opioid receptor antagonist naloxone given subcutaneously for 7 days by osmotic pumps (6 mg kg(-1) h(-1)) could not reverse the increased in vivo cytotoxicity seen in the running SHRs, suggesting that opioid receptor mechanisms are not involved, or at least not the naloxone-sensitive mu-receptor. Natural immunity was not influenced by the histamine H2 receptor antagonist ranitidine, either in controls or in runners, indicating that the natural killer cell-regulatory effect of histamine is not present in SHRs and does not seem to be involved in the exercise-induced changes in natural immune function. We conclude that the augmentation of in vivo natural cytotoxicity after voluntary chronic exercise in rats is long-lasting and that the augmentation is partly mediated by beta-adrenergic receptors.

The effects of triiodothyronine (T3) on heart rate, temperature and ECG measured with telemetry in freely moving mice

We have set up a telemetry system and recorded heart rate, electrocardiogram (ECG), body temperature and the locomotor activity in awake freely moving mice. The telemetry system (DATA Sciences, St Paul, MN, USA) comprises a transmitter implanted in the peritoneal cavity and a receiver (RA1010) placed underneath the home cage. The signal from the transmitter includes the electrical activity of the heart and the body temperature. The results show that four days after the surgical procedure the mice have recovered and regained a clear circadian rhythm. The heart rate varied under baseline conditions between 432 and 618 beats min-1 and the body temperature between 35.1 and 37.7 degrees C (based on 60 min mean values). A clear time correlation between heart rate, body temperature and locomotor activity was found. As an evaluation of the method we injected T3 s.c. during a period of 4 days. Further, we were interested in whether it was possible to measure an integrated physiological response to T3 and further investigate the time course for the effect. After one day of treatment with triiodothyronine there was a significant increase in body temperature and locomotor activity. The increase in heart rate was seen after 2 days. The ECG recording revealed a significantly shortened QTend- and QRS-time. No significant difference in the PQ-time was found. This method may be of great importance in studies of genetically manipulated mice.

Effects of 1,1-dimethylguanidine administration on blood pressure, heart rate and renal sympathetic nerve activity in normotensive and spontaneously hypertensive rats

1,1-dimethylguanidine (DMG) is an endogenous nitric oxide (NO) synthesis inhibitor. This study investigates the effects of exogenous DMG administration, in anaesthetized spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Mean blood pressure (MBP), heart rate (HR) and renal sympathetic nerve activity (SNA) were recorded in 12- to 14-week old, anaesthetized SHR and WKY. Each rat received increasing bolus injections of DMG intravenously (1.03, 2.05, 6.39, 20.45 and 51.15 mg kg-1). In separate experiments, SHR received L-arginine or D-arginine in a dose of 300 mg kg-1 followed by DMG at 6.39 mg kg-1. Thirty minutes later they received the same doses of the respective arginines followed by DMG at 20.45 mg kg-1 DMG induced dose-dependant increases in MBP in SHR and WKY. In SHR, HR increased with increasing doses of DMG (except at the near-toxic doses of 51.15 mg kg-1), whereas in WKY HR decreased with increasing doses of DMG. The net change of renal SNA ranged from -5 +/- 3 to -55 +/- 12% in SHR and from -6 +/- 8 to -66 +/- 8% in WKY. Pre-treatment with L-arginine in SHR partly inhibited the pressor effect and attenuated the inhibition of renal SNA induced by DMG, but had little effect on HR. Thus the administration of NO inhibitor DMG could alter cardiovascular function and sympathetic nerve activity, and subsequently resulted in tachycardia in SHR and bradycardia in WKY.

Natural immunity and chronic exercise in rats. The involvement of the spleen and the splenic nerves

We have previously shown that voluntary running for 4-5 weeks in the spontaneously hypertensive rat (SHR) significantly increased in natural cytotoxic mechanism in vivo, measured as clearance of 51Cr YAC-1 lymphoma cells from the lungs. In the present study, we have studied the possible role of the spleen and the splenic nerves in this augmentation. The SHR were randomly allocated to either a voluntary exercise group or a sedentary control group. After four weeks of exercise the runners and sedentary control SHR were further assigned to one of four groups: 1) no surgery, 2) sham operation, 3) splenic nerve section and 4) splenectomy. Splenectomy drastically reduced in vivo cytotoxicity in both runners and sedentary controls, but in vivo cytotoxicity of splenectomized voluntary runners was significantly higher than that of splenectomized sedentary control animals. Selective denervation of the spleen did not affect the in vivo cytotoxicity. These results indicate that the enhanced in vivo natural cytotoxic mechanism following voluntary chronic exercise in SHR is partly dependent on intact splenic function. However, this enhancement does not seem to be mediated by the splenic sympathetic nerves.

Voluntary chronic exercise augments in vivo natural immunity in rats

The effect of chronic voluntary exercise on the immune response was studied in spontaneously hypertensive rats. Exercise consisted of voluntary running in wheels for 5 wk, and the mean running distance was 4.2 km/24 h. In vivo cytotoxicity was measured as clearance of injected 51Cr-labeled YAC-1 lymphoma cells from the lungs. The clearance of YAC-1 cells in vivo was significantly increased in runners compared with sedentary controls (P < 0.001). The total number of mononuclear cells in the spleen was significantly decreased in runners compared with controls. Analysis of splenic lymphocyte phenotypes revealed a significantly increased fraction of OX52+/CD5- natural killer cells in runners compared with sedentary controls. In contrast to changes in natural immunity, immunoglobulins G and M levels in serum, the antibody response to antigen in vivo, and the proliferation of splenic T cells in vitro were unchanged. Our data suggest that chronic voluntary exercise augments natural cytotoxicity mechanisms in vivo, whereas splenic T-cell proliferation and the antibody-mediated immune response remain unchanged.

Chronic intracerebroventricular administration of beta-endorphin augments natural killer cell cytotoxicity in rats

We have studied the effect of chronic intracerebroventricular (i.c.v.) infusion of different opioid peptides on natural killer (NK) cell mediated cytotoxicity in vivo in the spontaneously hypertensive rat (SHR). The in vivo NK cell activity was measured as the clearance of 51Cr-labelled YAC-l lymphoma cells from the lung tissues. Further, the phenotype of lymphocytes in spleen and peripheral blood was analysed by flow cytometry (FACS). All opioid drugs were administered i.c.v. for 6 days with osmotic minipumps releasing 1.0 microliter/h. beta-Endorphin (10 or 20 micrograms/rat per day) significantly increased NK cell cytotoxicity in vivo. The opioid receptor antagonist naloxone (10 mg/kg, i.p.) given immediately before the injection of YAC-lymphoma cells, completely abolished the effects of i.c.v. administered beta-endorphin. Corresponding doses of beta-endorphin administered subcutaneously (s.c.) with minipumps for 6 days did not significantly affect NK cell cytotoxicity. Neither Leu- or Met-enkephalin (20 micrograms/rat per day) nor dynorphin (20 micrograms/rat per day) administered i.c.v. had any significant effects on NK cell activity. In beta-endorphin treated SHR, the percentage of cells with NK cell phenotype (OX52+/CD5-) in peripheral blood was not significantly different from that of controls, while the percentage of cells with T cell phenotype (CD5+/OX52-) was significantly decreased. The percentage of splenic NK cells (OX52+/CD5-) and T cells (CD5+/OX52-) was also unchanged by beta-endorphin treatment i.c.v. These results suggest that of the opioid peptides administered i.c.v., only beta-endorphin augments in vivo NK cell mediated cytotoxicity. We thus conclude that these effects most probably are centrally and opioid receptor mediated effects, since beta-endorphin in the same dose administered peripherally does not influence in vivo NK cell cytotoxicity.

Characteristics of renal sympathetic nerve activity in experimental congestive heart failure in the rat

Recently emerging evidence has indicated that efferent renal sympathetic nerve activity (RSNA) is increased in congestive heart failure (CHF). In the present study the cyclic activity of the renal nerve in the normal and CHF rat was studied. An ischaemic myocardial lesion resulting in CHF was induced by left coronary artery ligation. Sham-operated rats subjected to thoracotomy served as normal controls. Renal sympathetic nerve activity was recorded under chloralose anaesthesia. The neural cycle activity was significantly higher in CHF (47 +/- 3%) compared with sham-operated rats (34 +/- 3%, P < 0.005). Baroreceptor control of RSNA was significantly attenuated in CHF compared with normal control rats (P < 0.005). In response to noxious thermal stimulation by 48 degrees C water immersion of the tail tip, the increase of RSNA was significantly higher in CHF compared with sham-operated rats. A stepwise 15% blood volume expansion over 5 min which induced no alterations of blood pressure or heart rate (HR) resulted in a gradual decrease of RSNA in control rats by approximately 25% at the end of the volume expansion procedure. In CHF rats however, there was no significant change in RSNA during volume expansion. It is concluded that in CHF rats: (1) efferent RSNA is increased; (2) baroreceptor control of RSNA is decreased; (3) RSNA in response to cutaneous thermal noxious stimulation is exaggerated; and (4) RSNA inhibition by cardiopulmonary receptors is blunted.

Effects of long-lasting voluntary running on the cerebral levels of dopamine, serotonin and their metabolites in the spontaneously hypertensive rat

The brain regional dopamine (DA) and serotonin (5-HT) levels and turnover were studied in the spontaneously hypertensive rat (SHR), following voluntary, long-lasting (7 weeks) wheel-running exercise. Groups of rats were sacrificed 1-2 h, 23-24 h or 47-48 h after termination of the last running session, and the cerebral tissue levels of 5-HT, 5-HIAA, DA and DOPAC were determined and compared to corresponding levels obtained in sedentary controls. In the exercised animals, there was a selective decrease in the limbic forebrain levels of DOPAC in the immediate post-exercise period (1-2 h), while the DA turnover (DOPAC/DA ratio) was not altered. In addition, the 5-HT and 5-HIAA levels in the serotoninergic nerve terminal limbic forebrain and the 5-HT turnover (5-HIAA/5-HT ratio) in the cell body-containing brain stem areas were decreased in the immediate post-exercise period. No significant changes in the DA, DOPAC, 5-HT or 5-HIAA levels, nor in the DA and 5-HT turnover, were obtained in the remainder of the brain regions analyzed, regardless of time after termination of running. Taken together, the present study indicates that voluntary exercise in the SHR gives rise to differentiated regional effects on brain DA and 5-HT levels and turnover, thus supporting the view that changes in central monoaminergic activity are involved in the functional effects of long-term exercise. Interestingly, the psychomotor-associated limbic forebrain areas appeared particularly susceptible.

Evidence for an adrenergic innervation of the adrenal cortical blood vessels in rats

The aim of this study was to investigate the blood flow in the adrenal cortex of the rat. Relative changes in the adrenal cortical blood flow were continuously measured by Laser Doppler flowmetry in 33 chloralose-anaesthetized artificially ventilated rats during electrical stimulation (1 ms, 5 V) of the left great splanchnic nerve (LGSN), which conveys both pre- and post-ganglionic nerve fibres to the adrenal gland. Laser Doppler flux (LDF) was decreased and regional resistance (RR) was increased by augmenting nerve stimulation at increasingly higher frequencies (2, 4, 8, 20 and 40 Hz). The decrease in LDF, when compared to pre-drug stimulations at 4 Hz was partially or totally inhibited by the adrenergic blocking agents trimethaphan (TRIM), guanethidine (GUA) and alpha 1-blockade with prazosin (PRAZ). Furthermore, both the decrease in LDF and the increase in RR were either completely or partially blocked by stimulation at 40 Hz after TRIM-treatment and GUA-treatment. It is concluded that the adrenal cortex in the rat is innervated by post-ganglionic adrenergic nerve fibres, which are involved in the regulation of blood flow in the adrenal cortex.

Global forebrain ischaemia in the rat: controlled reduction of cerebral blood flow by hypobaric hypotension and two-vessel occlusion

We developed and characterized a model of global forebrain ischaemia in rats, permitting control of CBF at any desired ischaemic level with minimum surgery and without anticoagulation. Both common carotid arteries are occluded temporarily and systemic arterial pressure is lowered by pooling venous blood by lower body negative pressure with a cheap suction device. By measuring rCBF continuously (laser-Doppler-flowmetry) and regulating systemic arterial pressure, the model was used to automatically control cortical rCBF at predetermined ischaemic levels at 50, 30, 15, and 5% of normal rCBF (n = 5). When both common carotid arteries were occluded and systemic arterial pressure was lowered to 55 mmHg with hypobaric hypotension (n = 5), cortical CBF always fell to less than 5% of normal rCBF (n = 5). Prompt recirculation was achieved after reopening of the carotid arteries and return to normobaric body pressure. Hypobaric hypotension with bilateral common carotid occlusion requires only carotid surgery and measurement of systemic arterial pressure; it produces global forebrain ischaemia without anticoagulation as a true step function type insult. If rCBF is measured continuously, the model can be used to control ischaemic CBF to predetermined values.

Cerebrospinal fluid dynorphin-converting enzyme activity is increased by voluntary exercise in the spontaneously hypertensive rat

The activity in cerebrospinal fluid (CSF) of dynorphin-converting enzyme (DCE) has been studied after voluntary exercise in the spontaneously hypertensive (SH) rat. The exercise consisted of spontaneous running in wheels for 4-5 weeks and the average running distance during the last two weeks was 4.0 km/24h. CSF samples were obtained under anaesthesia from the cisterna magna after penetration of the atlanto-occipital membrane. DCE transforms the members of the dynorphin family of opioid peptides into Leu-enkephalin-Arg6. In the present investigation a radioimmunoassay was used for quantitation of Leu-enkephalin-Arg6 release from dynorphin A1-17 and dynorphin B1-13. The rats that were running had a DCE activity (vs. both substrates) in CSF that was approximately 6-12 times higher than in animals not given the running opportunity. A statistically significant correlation between the two prodynorphin-derived substrate peptides was found in terms of DCE activity. We therefore propose that a single enzyme activity may be responsible for the hydrolysis of dynorphin B1-13 and dynorphin A1-17. Furthermore, a significant correlation was also found between running activity and DCE activity 12-14 h before the CSF was withdrawn. Besides measurement of DCE activity by radioimmunoassay, the formation of Leu-enkephalin-Arg6 was identified by reversed-phase micro-column liquid chromatography and plasma desorption mass spectrometry. The experiment shows that voluntary exercise affects opioid peptidergic mechanisms.

Effects of clonidine on renal sympathetic nerve activity, natriuresis and diuresis in chronic congestive heart failure rats

The differential effects of the alpha-2 adrenergic agonist, clonidine, on blood pressure, renal sympathetic nerve activity (RSNA) and renal responses were investigated in conscious as well as anesthetized congestive heart failure (CHF) rats and normal control animals. After the stepwise increments of i.v. clonidine infusion (5, 15 and 30 micrograms/hr for 1 hr), mean arterial pressure gradually decreased in CHF, but increased significantly in the control animals at the higher doses. Urinary volume, sodium and potassium excretions were significantly higher in the normal control animals after the clonidine 30-micrograms/hr infusion compared with the CHF rats. There were almost immediate decreases in RSNA in both the CHF and control groups. Although the control animals reduced RSNA to about 5%, the CHF rats retained 36.5% of their respective control values after clonidine administration. Base-line plasma immunoreactive atrial natriuretic peptide were increased 7-fold in the CHF rats compared to controls. After clonidine, immunoreactive atrial natriuretic peptide increased more than 3-fold in the normal rats, whereas no changes were observed in the CHF group. Our data show that clonidine decreases RSNA in CHF and that the natriuretic and that diuretic effects of an alpha-2 receptor agonist are blunted in experimental CHF. Furthermore, the different mean arterial pressure response in the CHF and control groups at higher doses of clonidine may suggest down-regulation of the vascular alpha-2 adrenergic receptor in CHF.

Differential responses in post- and pre-ganglionic adrenal sympathetic nerve activity and renal sympathetic nerve activity after injection of 2-deoxy-D-glucose and insulin in rats

The aim of the study was to compare pre-ganglionic adrenal nerve activity (pre-aSNA) to post-ganglionic adrenal nerve activity (post-aSNA) in rats after administration of 2-deoxy-D-glucose (2-DG, 500 mg kg-1, i.v.), which mimicks a central hypoglycaemia or to the response in pre-aSNA and post-aSNA to hypoglycaemia after injection of insulin (5U). Renal postganglionic sympathetic nerve recordings (rSNA) in a separate group was used as a reference. Adrenal or renal multifibre nerve activity was recorded in chloralose-anaesthetized Wistar-rats. Trimethaphan, a short-lasting ganglionic blocker, was administered i.v. (10 mg kg-1) in order to test for pre- or post-aSNA in the adrenal nerves. The adrenal nerves was considered to contain predominantly post or preganglionic fibres, respectively if the nerve activity in the adrenal nerve decreased (post-aSNA) or increased (pre-aSNA). In contrast, all renal nerves showed almost a pure postganglionic activity. Post-aSNA responded with a tendency to increase after the 2-DG injection. The highest value (percentage change from control) 5 min after injection was 12 +/- 9%. The pre-aSNA increased with values of 99 +/- 52% at 3 min and 86 +/- 31% at 5 min (percentage change from control). The activity in the rSNA was only slightly decreased after the injection of 2-DG when compared to pre-drug control activity. There was a significant difference between the pre-aSNA vs. post-aSNA at 1 min (P less than 0.05), 3 min (P less than 0.01) and 5 min (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Reflex changes in post- and preganglionic sympathetic adrenal nerve activity and postganglionic sympathetic renal nerve activity upon arterial baroreceptor activation and during severe haemorrhage in the rat

The aim of the study was to compare pre- (pre-aSNA) and postganglionic adrenal sympathetic nerve activity (post-aSNA) and postganglionic renal sympathetic nerve activity (rSNA) in rats during arterial baroreceptor activation and haemorrhage. Adrenal multifibre nerve activity was recorded in chloralose-anaesthetized Wistar rats. To test for pre-aSNA or post-aSNA in adrenal nerves, a ganglionic blocker, trimethaphan (10 mg kg-1), was administered i.v. If the nerve activity in the adrenal nerve decreased or increased the nerve was considered to contain predominantly post- or preganglionic fibres, respectively. In contrast, the renal nerves exhibit an almost pure postganglionic activity. Baroreceptor activity was tested by activation of baroreceptors, with an alpha-receptor agonist, phenylephrine, which was slowly infused (0.5-2 micrograms kg-1 min-1), and to deactivate the baroreceptors the rats were bled down to 50 mmHg for 8 min. The experiments showed that all tested nerve types were baroreceptor dependent. There were no significant differences between the slopes relating nerve activity inhibition to increase in blood pressure (infusion of phenylephrine). During maximal inhibition there was a difference between the rSNA and pre-aSNA, 87 +/- 4%, n = 6, and 68 +/- 6%, n = 10 (P less than 0.01) of the control value, respectively. The maximal inhibition of post-aSNA was 80 +/- 3%, n = 7, of the control value. During haemorrhage there was a difference between the nerve populations. Pre-aSNA responded with a marked increase within 1.5 min (159 +/- 29% of control, n = 7) and was then maintained at that level until retransfusion.(ABSTRACT TRUNCATED AT 250 WORDS)