Markers of Oxidative Stress in Dogs with Myxomatous Mitral Valve Disease are Influenced by Sex, Neuter Status, and Serum Cholesterol Concentration

Background

Cardiovascular disease has been associated with oxidative stress, which has been suggested to contribute to myocardial remodeling in human patients. Little is known about the relationship between myxomatous mitral valve disease (MMVD) and oxidative stress in dogs.

Objective

To determine whether clinical stage of MMVD is associated with changes in the plasma concentrations of certain markers of oxidative stress in clinically healthy dogs and dogs with MMVD.

Animals

Seventy five privately owned dogs: 59 cavalier King Charles Spaniels (CKCS) with different severities of MMVD and 16 dogs of different breeds with clinical signs of congestive heart failure (CHF) caused by MMVD.

Methods

Markers of oxidative stress including malondialdehyde (MDA), oxidized low‐density lipoprotein (oxLDL), and vitamin E (α‐tocopherol and γ‐tocopherol) were measured in plasma and their association with clinical stage of MMVD was assessed by regression analyses.

Results

Plasma oxLDL concentration was significantly lower in female dogs compared with males (P = .01). Significantly higher plasma γ‐tocopherol concentrations were found in neutered (P = .003) dogs. Vitamin E (α‐tocopherol [P = .0004] and γ‐tocopherol [P = .003]) was associated with body condition score (BCS), but the association disappeared when cholesterol was included in the analyses. All markers of oxidative stress (MDA, oxLDL, and vitamin E) were positively associated with serum cholesterol concentration (P ≤ .04), but none were associated with clinical stage of MMVD.

Conclusions

In conclusion, markers of oxidative stress are associated with sex, BCS, neuter status, and cholesterol. The results cannot confirm a relationship between oxidative stress and clinical stage of the disease in dogs with MMVD.

Effect of Body Weight on Echocardiographic Measurements in 19,866 Pure-Bred Cats with or without Heart Disease

BACKGROUND

Echocardiography is a cost-efficient method to screen cats for presence of heart disease. Current reference intervals for feline cardiac dimensions do not account for body weight (BW).

OBJECTIVE

To study the effect of BW on heart rate (HR), aortic (Ao), left atrial (LA) and ventricular (LV) linear dimensions in cats, and to calculate 95% prediction intervals for these variables in normal adult pure-bred cats.

ANIMALS

19 866 pure-bred cats.

METHODS

Clinical data from heart screens conducted between 1999 and 2014 were included. Associations between BW, HR, and cardiac dimensions were assessed using univariate linear models and allometric scaling, including all cats, and only those considered normal, respectively. Prediction intervals were created using 95% confidence intervals obtained from regression curves.

RESULTS

Associations between BW and echocardiographic dimensions were best described by allometric scaling, and all dimensions increased with increasing BW (all P<0.001). Strongest associations were found between BW and Ao, LV end diastolic, LA dimensions, and thickness of LV free wall. Weak linear associations were found between BW and HR and left atrial to aortic ratio (LA:Ao), for which HR decreased with increasing BW (P<0.001), and LA:Ao increased with increasing BW (P<0.001). Marginal differences were found for prediction formulas and prediction intervals when the dataset included all cats versus only those considered normal.

CONCLUSIONS AND IMPORTANCE

BW had a clinically relevant effect on echocardiographic dimensions in cats, and BW based 95% prediction intervals may help in screening cats for heart disease.

Serotonin markers show altered transcription levels in an experimental pig model of mitral regurgitation

Serotonin (5-hydroxytryptamine, 5-HT) signalling is implicated in the pathogenesis of myxomatous mitral valve disease (MMVD) through 5-HT1B receptor (R), 5-HT2AR and 5-HT2BR-induced myxomatous pathology. Based on increased tryptophan hydroxylase-1 (TPH-1) and decreased serotonin re-uptake transporter (SERT) in MMVD-affected valves, increased valvular 5-HT synthesis and decreased clearance have been suggested. It remains unknown how haemodynamic changes associated with mitral regurgitation (MR) affect 5-HT markers in the mitral valve, myocardium and circulation. Twenty-eight pigs underwent surgically induced MR or sham-operation, resulting in three MR groups: control (CON, n = 12), mild MR (mMR, n = 10) and severe MR (sMR, n = 6). The gene expression levels of 5-HT1BR, 5-HT2AR, 5-HT2BR, SERT and TPH-1 were analysed using quantitative PCR (qPCR) in the mitral valve (MV), anterior papillary muscle (AP) and left ventricle (LV). MV 5-HT2BR was also analysed with immunohistochemistry (IHC) in relation to histological lesions and valvular myofibroblasts. All 5-HTR mRNAs were up-regulated in MV compared to AP and LV (P <0.01). In contrast, SERT and TPH-1 were up-regulated in AP and LV compared to MV (P <0.05). In MV, mRNA levels were increased for 5-HT2BR (P = 0.02) and decreased for SERT (P = 0.03) in sMR vs. CON. There were no group differences in 5-HT2BR staining (IHC) but co-localisation was found with α-SMA-positive cells in 91% of all valves and with 33% of histological lesions. In LV, 5-HT1BR mRNA levels were increased in sMR vs. CON (P = 0.01). In conclusion, these data suggest that MR may affect mRNA expression of valvular 5-HT2BR and SERT, and left ventricular 5-HT1BR in some pigs.

Matrix metalloproteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs) and transforming growth factor-β (TGF-β) in advanced canine myxomatous mitral valve disease

This study investigated mitral valve and myocardial protein and gene expression of matrix metalloproteinases (MMPs), their tissue inhibitors (TIMPs) and transforming growth factor-β (TGF-β) and plasma MMP and TGF-β concentrations in age-matched dog groups euthanized due to either advanced myxomatous mitral valve disease (MMVD) or other reasons. Furthermore, echocardiographic data and lumen/area ratio were correlated with tissue and plasma levels of MMPs, TIMPs and TGF-βs. Mitral valve and myocardial gene expression of MMP2, MMP14, TGF-β1 and TGF-β2 were increased and plasma MMP9 was decreased in advanced MMVD dogs. Myocardial gene expression of TIMP2 and TIMP3 were increased in advanced MMVD. All affected markers correlated to echocardiographic parameters. Significantly narrowed lumen/area ratio was associated with increased myocardial expression of MMP2, MMP14, TIMP2 and TIMP3. No differences in tissue protein expression were recorded. MMP2, MMP14, TIMP2, TIMP3, TGF-β1 and TGF-β2 appear to play a local role in the development of advanced MMVD.

Biopterin status in dogs with myxomatous mitral valve disease is associated with disease severity and cardiovascular risk factors

BACKGROUND

Endothelial dysfunction (ED) has been suggested to be associated with myxomatous mitral valve disease (MMVD) in dogs. Tetrahydrobiopterin (BH4) is an important cofactor for production of the endothelium-derived vasodilator nitric oxide (NO). Under conditions of oxidative stress, BH4 is oxidized to the biologically inactive form dihydrobiopterin (BH2). Thus, plasma concentrations of BH2 and BH4 may reflect ED and oxidative stress.

OBJECTIVE

To determine plasma concentrations of BH2 and BH4 in dogs with different degrees of MMVD.

ANIMALS

Eighty-four privately owned dogs grouped according to ACVIM guidelines (37 healthy control dogs including 13 Beagles and 24 Cavalier King Charles Spaniels [CKCSs], 33 CKCSs with MMVD of differing severity including 18 CKCSs [group B1] and 15 CKCSs [group B2], and 14 dogs of different breeds with clinical signs of congestive heart failure [CHF] because of MMVD [group C]).

METHODS

Dogs underwent clinical examination including echocardiography. Plasma concentrations of BH2 and BH4 were measured using high-performance liquid chromatography with fluorescence detection.

RESULTS

Higher plasma BH4 and BH2 concentrations were found with dogs in CHF compared with all other groups (control, B1 and B2; P ≤ .001). Females had higher concentrations of BH4 and BH4/BH2 (P ≤ .0003). BH4/BH2 was found to decrease with age (P < .0001). Cardiovascular risk factors in humans such as passive smoking (P ≤ .01) and increased body weight (P ≤ .009) were associated with lower BH4 concentrations.

CONCLUSIONS AND CLINICAL IMPORTANCE

Age, sex, body weight, passive smoking, and cardiac status are associated with plasma biopterin concentration in dogs. Additional studies should clarify the clinical implications of the findings.

Holter monitoring of small breed dogs with advanced myxomatous mitral valve disease with and without a history of syncope

Background

Syncope is a transient loss of consciousness occasionally occurring in dogs with advanced myxomatous mitral valve disease (MMVD).

Objective

(1) To study ECG changes during syncopal episodes in dogs with advanced MMVD and (2) to compare the occurrence of arrhythmias and changes in heart rate variability (HRV) between dogs with advanced MMVD with and without a history of syncope.

Animals

Forty‐three privately owned dogs (<15 kg) with advanced MMVD: 21 with and 22 without a history of syncope.

Methods

Prospective study with dogs recruited for an evaluation including history, physical examination, echocardiography, and arrhythmia and HRV analysis performed on 24‐hour Holter recordings.

Results

A syncopal episode was observed during Holter monitoring in 4 dogs: 3 dogs had sinus rhythm and 1 dog had sinus arrest followed by escape rhythm. An arrhythmia variable representing sinus arrhythmia was significantly lower in dogs with a history of syncope than in those without (P = .008). Eight of 26 HRV variables were significantly different between dogs with and without a history of syncope.

Conclusions and Clinical Importance

Compared with dogs without a history of syncope, dogs with advanced MMVD and a history of syncope did not have a higher occurrence of arrhythmias, but had less sinus arrhythmia, and had changes in HRV variables representing decreased overall HRV, decreased parasympathetic, and increased sympathetic modulation of heart rate.

Comparative study of the neurotrophic effects elicited by VEGF-B and GDNF in preclinical in vivo models of Parkinson's disease

Vascular endothelial growth factor B (VEGF-B) has recently been shown to be a promising novel neuroprotective agent for several neurodegenerative conditions. In the current study we extended previous work on neuroprotective potential for Parkinson's disease (PD) by testing an expanded dose range of VEGF-B (1 and 10 μg) and directly comparing both neuroprotective and neurorestorative effects of VEGF-B in progressive unilateral 6-hydroxydopamine (6-OHDA) PD models to a single dose of glial cell line-derived neurotrophic factor (GDNF, 10 μg), that has been established by several groups as a standard in both preclinical PD models. In the amphetamine-induced rotational tests the treatment with 1 and 10 μg VEGF-B resulted in significantly improved motor function of 6-OHDA-lesioned rats compared to vehicle-treated 6-OHDA-lesioned rats in the neuroprotection paradigm. Both doses of VEGF-B caused an increase in tyrosine hydroxylase (TH)-positive cell and fiber count in the substantia nigra (SN) and striatum in the neuroprotective experiment. The effect size was comparable to the effects seen with GDNF. In the neurorestoration paradigm, VEGF-B injection had no significant effect in either the behavioral or the immunohistochemical analyses, whereas GDNF injection significantly improved the amphetamine-induced rotational behavior and reduced TH-positive neuronal cell loss in the SN. We also present a strong positive correlation (p=1.9e-50) of the expression of VEGF-B with nuclear-encoded mitochondrial genes involved in fatty acid metabolism in rat midbrain, pointing to the mitochondria as a site of action of VEGF-B. GDNF showed a positive correlation with nuclear-encoded mitochondrial genes that was not nearly as strong (p=0.018). VEGF-B counteracted rotenone-induced reduction of (a) fatty acid transport protein 1 and 4 levels and (b) both Akt protein and phosphorylation levels in SH-SY5Y cells. We further verified VEGF-B expression in the human SN pars compacta of healthy controls and PD patients, in neuronal cells that show co-expression with neuromelanin. These results have demonstrated that VEGF-B has potential as a neuroprotective agent for PD therapy and should be further investigated.

Left ventricular twist and circumferential strain in dogs with myxomatous mitral valve disease

BACKGROUND

During the cardiac cycle, the ventricle undergoes a twisting motion because of the oblique orientation of the left ventricular (LV) myofibers. This can be quantified by speckle-tracking echocardiography (STE). In mitral regurgitation (MR) in humans, the short axis deformation has been suggested as being pivotal to LV function. Decreased and delayed LV twist has been described in experimental MR, but has not been studied in myxomatous mitral valve disease (MMVD).

HYPOTHESES

(1) Magnitude (CSt) and rate (CSRs) of systolic circumferential deformation decrease before the onset of congestive heart failure (CHF); (2) magnitude and rate of LV twist decrease, and onset of untwist is delayed, with increasing MMVD severity.

ANIMALS

A total of 97 privately owned small- to medium-sized dogs.

METHODS

Severity of MMVD was assessed by echocardiography and presence of clinical signs of CHF. Magnitude and rate of LV twist and circumferential deformation were evaluated by STE.

RESULTS

Dogs with CHF receiving treatment had increased CSt, CSRs, early diastolic untwisting rate, and delayed onset of untwist compared to dogs with minimal MMVD and increased systolic twist compared to dogs with mild MMVD (all P < .01). CSt and time to onset of untwist increased with echocardiographic variables of MR severity (all P < .002). CSRs and several LV twist variables decreased with increasing systolic LV internal diameter (all P < .01).

CONCLUSIONS AND CLINICAL IMPORTANCE

No STE-derived variable was decreased before onset of CHF. In dogs with CHF receiving treatment, the delayed onset of relaxation might indicate LV dysfunction and the hyperdynamic CSt and LV twist reflect compensatory mechanisms.

Radial and longitudinal strain and strain rate assessed by speckle-tracking echocardiography in dogs with myxomatous mitral valve disease

BACKGROUND

Assessment of left ventricular (LV) function using conventional echocardiographic methods is difficult in mitral regurgitation (MR) owing to altered hemodynamic loading conditions. Newer methods such as speckle-tracking echocardiography (STE) provide assessment of LV strain (St) and strain rates (SR).

HYPOTHESES

Global St and SR are 1) decreased in dogs with clinical signs of congestive heart failure (CHF) due to myxomatous mitral valve disease (MMVD) compared with clinically healthy dogs, and are 2) associated with conventional echocardiographic indices of MMVD severity.

ANIMALS

The study subjects were 93 privately owned dogs with different MMVD severities.

METHODS

Prospectively recruited dogs were grouped according to MMVD severity based on echocardiographic evaluation of MR and presence of clinical signs. Global radial and longitudinal St, SR, and indices of LV dyssynchrony were assessed.

RESULTS

On group-wise comparisons, dogs with CHF had increased global longitudinal St, global longitudinal and radial SR in systole (SRs), and early diastole (SRe) compared with dogs with no or minimal MR (all P < .04). On multiple regression analyses, these global STE variables increased with degree of MR, but associations with left atrial-to-aortic root ratio (LA/Ao) were best described by second-order polynomial equations. Thus, curvilinear relationships were found for LA/Ao and longitudinal St, SRs, and SRe (all P < .002) and radial St and SRe (all P < .001).

CONCLUSIONS AND CLINICAL IMPORTANCE

Assessed by STE, LV function appeared to be augmented in moderate-to-severe disease. However, at CHF stages with greatly enlarged atria, a decrease to levels comparable to dogs with no or minimal MR was observed.

Advanced electrocardiographic parameters change with severity of mitral regurgitation in Cavalier King Charles Spaniels in sinus rhythm

BACKGROUND

Multiple advanced resting ECG (A-ECG) techniques have improved the diagnostic or prognostic value of ECG in detecting human cardiac diseases even before onset of clinical signs or changes in conventional ECG.

OBJECTIVE

To determine which A-ECG parameters, derived from 12-lead A-ECG recordings, change with severity of mitral regurgitation (MR) caused by myxomatous mitral valve disease (MMVD) in Cavalier King Charles Spaniels (CKCSs) in sinus rhythm.

ANIMALS

Seventy-six privately owned CKCSs.

METHODS

Dogs were prospectively divided into 5 groups according to the degree of MR (estimated by color Doppler mapping as the percentage of the left atrial area affected by the MR jet) and presence of clinical signs. High fidelity approximately 5-minute 12-lead ECG recordings were evaluated using custom software to calculate multiple conventional and A-ECG parameters.

RESULTS

Nineteen of 76 ECG parameters were significantly different (P < .05) across the 5 dog groups. A 4-parameter model that incorporated results from 1 parameter of heart rate variability, 2 parameters of QT variability, and 1 parameter of QRS amplitude was identified that explained 82.4% of the variance with a correlation coefficient (R) of 0.60 (P < .01). When age or murmur grade was included in the statistical model the prediction value further increased the R to 0.74 and 0.85 (P < .01), respectively.

CONCLUSION

In CKCSs with sinus rhythm, 4 selected A-ECG parameters further improve prediction of MR jet severity beyond age and murmur grade, although the predictive increment in this study probably is not sufficient to warrant utilization in clinical veterinary practice.

Heart rate, heart rate variability, and arrhythmias in dogs with myxomatous mitral valve disease

BACKGROUND

Autonomic modulation of heart rhythm is thought to influence the pathophysiology of myxomatous mitral valve disease (MMVD).

HYPOTHESES

(1) Holter-derived variables reflecting autonomic modulation of heart rhythm change with MMVD severity in Cavalier King Charles Spaniels (CKCS); (2) Holter-derived variables can identify MMVD severity in CKCS; and (3) Holter-derived variables in CKCS in congestive heart failure (CHF) secondary to MMVD differ from those in dogs of other breeds in CHF.

ANIMALS

Ninety privately owned dogs: 70 CKCS with variable MMVD severity and 20 non-CKCS in CHF secondary to MMVD.

METHODS

Dogs were prospectively recruited and divided into 5 MMVD severity groups based on history, breed, and physical and echocardiographic examination findings. Holter-derived variables included heart rate variability (HRV), heart rate (HR), and arrhythmia evaluated from 24-hour Holter recordings.

RESULTS

In CKCS, 18 of 26 HRV (all P < .0002) and 3 of 9 arrhythmia (all P < .0004) variables decreased with increasing MMVD, whereas minimum and mean HR (all P < .0001) increased with increasing MMVD severity. An arrhythmia variable representing sinus arrhythmia ("premature normals") (P < .0001) and the HRV variable triangular index (TI) (P < .0001) could distinguish CKCS with moderate or severe mitral regurgitation from CKCS in CHF in specific intervals. Among dogs in CHF, Holter-derived variables did not differ among breeds.

CONCLUSIONS AND CLINICAL IMPORTANCE

In CKCS, Holter-derived variables changed with MMVD severity. "Premature normals" and TI showed diagnostic potential. Breed differences were not seen among dogs in CHF secondary to MMVD.

Herpes folliculitis: clinical, histopathological, and molecular pathologic observations

BACKGROUND

Herpes folliculitis is a rare manifestation of herpes virus infection and it is often misdiagnosed. Diagnostic criteria are not well established, only 24 patients being reported in the literature. Recently it has been suggested that herpetic folliculitis is more common in infections with varicella zoster (VZV) than in those with herpes simplex viruses (HSV-1 and -2).

OBJECTIVES

To refine diagnostic criteria for folliculitis caused by VZV, HSV-1 and HSV-2, and to study whether follicular involvement enables morphological differentiation between VZV and HSV infections.

PATIENTS AND METHODS

Twenty-one patients with herpetic infection of follicular epithelium were assessed clinically and histopathologically. Polymerase chain reaction (PCR) studies for specific DNA of herpes viruses were performed on paraffin-embedded biopsy specimens.

RESULTS

In 17 of our cases PCR was positive for VZV, four were positive for HSV-1, none for HSV-2. The clinical presentation of herpes folliculitis often lacked vesicles or pustules (14/21). Histopathological features were often devoid of ballooning (12/21), multinucleated giant cells (12/21) and keratinocytes with steel grey nuclei (15/21). The most consistent findings were lymphocytic folliculitis and perifolliculitis (20/21) and necrotic keratinocytes in follicular epithelium (12/21). In zoster, but not in varicella eruption or HSV infections, follicular involvement was unaccompanied by marked changes in the epidermal surface.

CONCLUSIONS

In biopsy specimens taken from herpes virus infections, involvement of follicular units is more commonly encountered in VZV infections compared with HSV infections. Early in the course, herpes folliculitis presents as lymphocytic folliculitis devoid of epithelial changes considered to be diagnostic of herpes virus infections. Exclusive involvement of follicles is rather typical of zoster.

Intramyocardial arterial narrowing in dogs with subaortic stenosis

Earlier studies have described intramyocardial arterial narrowing based on hyperplasia and hypertrophy of the vessel wall in dogs with subaortic stenosis (SAS). In theory, such changes might increase the risk of sudden death, as they seem to do in heart disease in other species. This retrospective pathological study describes and quantifies intramyocardial arterial narrowing in 44 dogs with naturally occurring SAS and in eight control dogs. The majority of the dogs with SAS died suddenly (n=27); nine had died or been euthanased with signs of heart failure and eight were euthanased without clinical signs. Dogs with SAS had significantly narrower intramyocardial arteries (P<0.001) and more myocardial fibrosis (P<0.001) than control dogs. Male dogs and those with more severe hypertrophy had more vessel narrowing (P=0.02 and P=0.02, respectively), whereas dogs with dilated hearts had slightly less pronounced arterial thickening (P=0.01). Arterial narrowing was not related to age, but fibrosis increased with age (P=0.047). Dogs that died suddenly did not have a greater number of arterial changes than other dogs with SAS. This study suggests that most dogs with SAS have intramyocardial arterial narrowing and that the risk of dying suddenly is not significantly related to the overall degree of vessel obliteration.

Effect of thyroid hormone supplementation on survival of euthyroid dogs with congestive heart failure due to systolic myocardial dysfunction: a double-blind, placebo-controlled trial

Nineteen euthyroid dogs of 12 breeds with echocardiographic signs of dilated cardiomyopathy (DCM) and radiographic and clinical signs of congestive heart failure (CHF) were evaluated in a randomised, double-blind, and placebo-controlled study. The dogs received either thyroxine or placebo as an adjunct to digoxin, furosemide and propranolol. The group assignment of individual dogs and serum concentrations of thyroid hormones remained unknown to owners and investigators during the entire study period. Dogs were evaluated clinically and with electrocardiography (ECG), thoracic radiography, echocardiography and measurement of total thyroxine (tT4) and thyroid stimulating hormone (TSH) before beginning of the trial, and then one week, 2 months, 6 months and yearly after initial examination, and, when applicable, at the time of euthanasia. End-point of the study was euthanasia (n = 17) due to severe congestive heart failure or sudden death (n = 2). Survival times ranged from 17 to 1030 days (median 187 days) in the placebo group, and from 18 to 1000 days (median 73 days) in the treatment group. There was no statistically significant difference in survival times between the treatment group and the placebo group (p = 0.46). Post mortem and histopathologic examinations revealed the attenuated wavy fiber type of DCM in 11 dogs, and myocardial infarcts, arteriosclerosis and chronic valvular disease in one dog. In conclusion, there was a wide range in survival times of dogs treated with digoxin, furosemide and propranolol. Adding thyroid hormones to the treatment did not significantly influence survival.

Developmental regulation of the A-type potassium-channel current in hippocampal neurons: role of the Kvbeta 1.1 subunit

The rapidly inactivating A-type K+ current (IA) is prominent in hippocampal neurons; and the speed of its inactivation may regulate electrical excitability. The auxiliary K+ channel subunit Kvbeta 1.1 confers fast inactivation to Shaker-related channels and is postulated to affect IA. Whole-cell patch clamp recordings of rat hippocampal pyramidal neurons in primary culture showed a developmental decrease in the time constant of inactivation (tau(in)) of voltage-gated K+ currents: 17.9+/-1.5 ms in young neurons (5-7 days in vitro; n=53, mean+/-S.E.M.); 9.9+/-1.0 ms in mature neurons (12-15 days in vitro; n=72, mean+/-S.E.M., P<0.01). During the same developmental time, the level of Kvbeta 1.1 transcript increased more than two-fold in vitro and in vivo, determined by semi-quantitative reverse transcriptase-polymerase chain reaction for hippocampus. The hypothesis that up-regulation of Kvbeta 1.1 led to the changes in tau(in) was tested in vitro, using antisense knockdown. Kvbeta 1.1-specific antisense DNA was introduced with a modified herpes virus co-expressing enhanced green fluorescent protein and knockdown of Kvbeta 1.1 was verified by immunocytochemistry. Following transduction with the antisense virus, mature neurons reverted to tau(in) values characteristic of young neurons: 18.3+/-2.4 ms (n=20). The effect of antisense knockdown on electrical excitability was tested using current-clamp protocols to induce repetitive firing. Treatment with the antisense virus increased the interspike interval over a range of membrane depolarization (baseline membrane potential=-40 to +20 mV). This effect was most pronounced at -40 mV, where the ISI of the first pair of action potentials was nearly doubled. These data indicate that Kvbeta 1.1 contributes to the developmental control of IA in hippocampal neurons and that the magnitude of effect is sufficient to regulate electrical excitability. Viral-mediated antisense knockdown of Kvbeta 1.1 is capable of decreasing the electrical excitability of post-mitotic hippocampal neurons, suggesting this approach has applicability to gene therapy of neurological diseases associated with hyperexcitability.

Viral vector-mediated expression of K+ channels regulates electrical excitability in skeletal muscle

Modification of K+ currents by exogenous gene expression may lead to therapeutic interventions in skeletal muscle diseases characterized by alterations in electrical excitability. In order to study the specific effects of increasing outward K+ currents, we expressed a modified voltage-dependent K+ channel in primary cultured rat skeletal muscle cells. The rat Kv1.4 channel was expressed as an N-terminal fusion protein containing a bioluminescent marker (green fluorescent protein). Transgene expression was carried out using the helper-dependent herpes simplex 1 amplicon system. Transduced myoballs, identified using fluorescein optics and studied electrophysiologically with single-cell patch clamp, exhibited a greater than two-fold increase in K+ conductance by 20-30 h after infection. This increase in K+ current led to a decrease in membrane resistance and a 10-fold increase in the current threshold for action potential generation. Electrical hyperexcitability induced by the Na+ channel toxin anemone toxin II (1 microM) was effectively counteracted by overexpression of Kv1.4 at 30-32 h after transduction. Thus, virally induced overexpression of a voltage-gated K+ channel in skeletal muscle has a powerful effect in reducing electrical excitability.

Ischaemic heart disease in the dog: a review of 65 cases

Sixty-five dogs are reviewed with histopathologically confirmed intramural arteriosclerosis. Clinical data (clinical signs, electrocardiographic findings and ultrasound parameters) on these animals were collected from nine small animal clinics in Sweden: 16 dogs had died suddenly, with few or no previous clinical signs; 13 dogs died or were euthanased during or shortly after general anaesthesia or sedation; 30 dogs developed acute (14) or chronic (16) congestive heart failure; and six dogs died or were euthanased for causes unrelated to cardiac disease. Electrocardiography of 23 of the dogs revealed several types of arrhythmias, with atrial fibrillation and sinus tachycardia being most commonly detected. Ultrasonographic examinations of 24 dogs found a relatively high number (19) with decreased indices of contractility. Dogs that had died suddenly and in relation to general anaesthesia or sedation had a higher incidence (25 of 29) of purely arteriosclerotic changes in the myocardial vessels, whereas just over half the dogs with congestive heart failure (16 of 30) had other concomitant heart lesions (in most cases endocardiosis). The incidence of myocardial infarcts was high (51 of 65 cases). It is postulated that arteriosclerosis in the dog may be an important reason for sudden death and death during general anaesthesia. Coronary arterial disease should also be a consideration in the clinical evaluation of dilated cardiomyopathy and may contribute to the decreased myocardial contractility when it is present in dogs with mitral regurgitation.

The middle ear bioelectronic microphone for a totally implantable cochlear hearing device for profound and total hearing loss

BACKGROUND

A bioelectronic middle ear microphone (BMEM) has been developed in a laboratory bench model and successfully tested in fresh human temporal bones. A transducer actually has been bench-tested in our laboratory; it was implanted in chronic animal experiments (cats) as well as in humans for a period of 1 year as a driver of a semi-implantable electromagnetic middle ear hearing device (IDE, FDA approved). This BMEM is the result of the use of this same electromagnetic transducer used in a reverse mode. The applicability of the BMEM is for the development of a totally implantable cochlear implant using the eardrum as a diaphragm that transmits vibrations to a magnet cemented to the ossicles. This BMEM is to be powered by a lithium-ion implantable, rechargeable battery.

MATERIALS AND METHODS

To test the efficacy of this BMEM, the experiment was divided into two parts: (1) bench model, and (2) fresh human temporal bones, using an air-core electromagnetic (EM) coil and a ferrite core EM coil for comparison.

RESULTS

In the bench model, the average displacement at 3 kHz was 0.95 microns (peak) for 4 V p-p and 1.65 microns (peak) for 10 V p-p. At 5 kHz, the measurements were somewhat higher. In fresh human temporal bones, with sound source in the ear canal (60 dB HL and 90 dB HL), the result was better with the magnet implanted on the head of the malleus with the incus removed. The ferrite core EM coil with the magnet implanted on the malleus with the incus removed was compared with the air-core EM coil. At 60 dB HL, the ferrite core EM coil yielded more than four times the amplitude of the EM coil. At 90 dB HL, the ferrite core EM coil produced more than five times the amplitude compared with the air-core coil.

CONCLUSION

This BMEM using an EM ferrite coil and a permanent magnet on the head of the malleus is more efficient when compared with an EM air-core coil. This BMEM may be applicable to the construction of a totally implantable cochlear implant. Further research is necessary to integrate this BMEM with the other components of the design concept of the totally implantable cochlear implant.

Expression of Niemann-Pick type C transcript in rodent cerebellum in vivo and in vitro

This study assesses the developmental expression of the Niemann-Pick type C mRNA in vivo and in vitro in rat cerebellum. NPC is an autosomal recessive neurovisceral lipid storage disease associated with an alteration in cholesterol trafficking. In the mouse model of NPC and in the early onset form of human NPC, Purkinje neurons are among the first neurological targets, suffering stunted growth during postnatal development and dying, leading to ataxia. Recently, the genes responsible for human (NPC1) and mouse (Npc1) NPC disease have been cloned. Based on a highly homologous domain, we designed primers to look for levels of Npc1 mRNA with a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) approach using cyclophilin as an internal standard. Total RNA was isolated from various postnatal developmental stages of the rat cerebellum as template for the analyses. Npc1 transcripts were observed at postnatal day 0 and at later stages of development, both in vivo and in vitro from primary cerebellar cultures. To identify the location of Npc1 inside the cerebellum, we performed immunostaining with an anti-Npc1 antibody in primary rat cerebellar cultures identifying reactive Purkinje neurons by double-labeling with the Purkinje specific marker calbindin and sub-populations of glial cells. In summary, Npc1 is expressed in rat cerebellum in vivo and in vitro and is expressed during early postnatal development as well as in the adult cerebellum. Since Npc1 is expressed at similar levels throughout development, the vulnerability of Purkinje neurons to this disease is likely to involve disruption of an interaction with other developmentally-regulated proteins.

Differential expression of three classes of voltage-gated Ca(2+) channels during maturation of the rat cerebellum in vitro

Voltage-gated Ca(2+) channels provide a mode of Ca(2+) influx that is essential for intracellular signaling in many cells. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to assess the relative amounts of mRNAs encoding three classes of Ca(2+) channels (alpha1A, alpha1B and alpha1E) during development, in cultures established from prenatal rat cerebellar cortex. Ca(2+) channel transcript levels were standardized to a constitutive marker (cyclophilin). For all three classes of Ca(2+) channels, transcript levels were highest at early stages (4-10 days in vitro) and declined with age. This developmental pattern was differentially regulated by a depolarizing agent, tetraethylammonium chloride (TEA, 1 mM). Chronic depolarization yielded a significant elevation in transcript levels for alpha1B (N-type) and alpha1E (R-type) Ca(2+) channels during neuronal maturation (10-21 days in vitro), but dramatically suppressed transcript levels for the alpha1A (P-type) Ca(2+) channel at all stages of development. The effects of TEA on alpha1A, alpha1B and alpha1E transcript levels were mimicked by increasing external K(+) (from 5 to 10 mM). The regulatory effects of depolarization on transcript levels were dependent on extracellular Ca(2+) for alpha1E but not for alpha1A. For alpha1B, transcript levels depended on extracellular Ca(2+) only for increased K(+) as the depolarizing stimulus, but not for TEA. These results suggest that levels of Ca(2+) channel transcripts in rat cerebellum are developmentally regulated in vitro and can be influenced differentially by transmembrane signaling via chronic depolarization and Ca(2+) entry. Dynamic regulation of Ca(2+) channel expression may be relevant to the different functional roles of Ca(2+) channels and their regional localization within neurons.

Auscultation in mild mitral regurgitation in dogs: observer variation, effects of physical maneuvers, and agreement with color Doppler echocardiography and phonocardiography

Observer variation in diagnosing mild mitral regurgitation in dogs by cardiac auscultation was assessed by having 6 veterinarians with different levels of experience examine 57 Cavalier King Charles Spaniels. Comparisons with color Doppler echocardiography and phonocardiography were made, and the effects of 2 physical maneuvers on the auscultatory findings were evaluated. Using mildly diseased dogs, interobserver agreement in diagnosing the presence or absence of left-sided murmurs ranged from 63% to 88%. The agreement with phonocardiography (range, 53-91%) increased with the amount of observer experience. The 2 most experienced observers could discern soft ejection murmurs from regurgitant murmurs and were able to diagnose 89% of the dogs with regurgitant jets larger than 30% of the left atrial area. In general, less experienced observers diagnosed most jets larger than 50%. In many dogs with small jets, no murmur was found by auscultation and phonocardiography. The audibility of mild regurgitation was significantly reduced in dogs that were difficult to auscultate. Early systolic murmurs were typical of mild regurgitation, whereas holosystolic murmurs typified severe regurgitation. In a few dogs, late systolic murmurs alternated with holosystolic murmurs. Systolic clicks were found phonocardiographically in 18 dogs with mild to moderate regurgitation, but the audibility apparently was low. In many mildly affected dogs, physical maneuvers increased murmur intensity. Thus, some form of dynamic auscultation might facilitate the diagnosis of mild regurgitation. Auscultatory findings in mild regurgitation appear to depend on observer experience, circulatory status, and how difficult the dog is to auscultate.

An endogenous inactivating inward-rectifying potassium current in oocytes of Xenopus laevis

An endogenous inward-rectifying K+ current is described, which is present in native oocytes of some Xenopus laevis donors. Experiments were performed using defolliculated oocytes from donor frogs obtained from two different suppliers. In all oocytes from animals from one source, an inward-rectifying K+ current could be elicited with negative pulses from a holding potential of -20 mV in external solutions with a high K+ concentration. Increasing external K+ concentrations increased the amplitude of this current and shifted the reversal potential towards more positive potentials. In 118 mM KCl, the inward-rectifying K+ current partially inactivated between -20 and -80 mV and completely inactivated at more negative membrane potentials; 50% steady-state inactivation occurred near -50 mV. The time course of inactivation of the inward-rectifying current could be well fitted with two exponentials. The slow time constant had values of about 500 ms and was voltage independent. In contrast, the fast time constant and the time to reach the peak inward current decreased with more negative membrane potentials. Ba2+, Cs+, quinine (all 5 mM) and 50 mM tetraethylammonium partially blocked the inward-rectifying K+ current, whereas 10 mM 4-aminopyridine was without blocking effect. The oxidant chloramine-T blocked the inward-rectifying K+ current without slowing its inactivation.

Cloning, functional expression and mRNA distribution of an inwardly rectifying potassium channel protein

In GH3/B6 cells at least two different inward K+ currents are observed that are regulated by thyrotropin-releasing hormone and somatostatin, respectively. Using a polymerase chain reaction based approach a cDNA was isolated and functionally expressed in human embryonic kidney cells that encodes an inward rectifier K+ channel, rIRK3, with a predicted molecular mass of 49.7 kDa. Corresponding transcripts of 2.6 kb have been detected in rat brain, pituitary and GH3/B6 cells. In situ hybridization revealed that rIRK3 mRNA is distributed throughout the brain and occurs predominantly in the piriform cortex, indusium griseum, supraoptic nucleus, facial nucleus and cerebellar Purkinje cells.

Contactless semi-implantable electromagnetic middle ear device for the treatment of sensorineural hearing loss. Short-term and long-term animal experiments

A contactless electromagnetic hearing device has been designed following basic science experiments, improvement of electronics, and precision micromechanics. Different prototypes have been developed and tested in the laboratory, fresh human temporal bones, and acute and chronic animal experimentation. A conductive hearing loss model was first developed in the cat using samarium cobalt as the target magnet. Later, a highly efficient electromagnetic air-core coil was selected to vibrate a neodymium iron boron magnet cemented to the body of the incus and tested in acute and chronic experiments using the cat as the model. In this group of animals, the ossicular chain was left intact. There was no failure of the target magnet, driving coil, or implanted electronics. The only problem encountered in this evaluation was a malfunction of the receiving antenna that had to be redesigned and retrofitted into the implanted units. This system would be suitable for the treatment of moderate to severe sensorineural hearing loss. Planning to begin human clinical trials is ongoing.

A contactless electromagnetic implantable middle ear device for sensorineural hearing loss

Following basic science experiments, improvement of precision micromechanics and electronics design, and development of different prototypes, a contactless electromagnetic hearing device has been successfully implanted in cats (acute experiments). Chronic animal experiments using the cat as well as the rabbit are ongoing to test the components of the device. A highly efficient air core coil is used to vibrate a neodymium-iron-boron magnet cemented to the body of the incus. The parts of the system, including implanted electronics (hybrid circuit, solid state), are laser welded and hermetically sealed. The system allows for the generation of enough force which vibrates the magnet implanted on the incus. It would be suitable for the treatment of moderate to severe sensorineural hearing loss.