The effect of autonomic manipulation on heart rate variability in dogs

Beat‐to‐beat variation of heart rate is reflective of autonomic balance and has been used to assess pain and stress in human beings. The purpose of this investigation was to pharmacologically manipulate the autonomic nervous system and to determine the effect of these manipulations on heart rate variability (HRV) in dogs. Four adult male hound dogs (27 ± 1 kg) were used in the investigation. Each dog was given five treatments: Parasympathetic blockade (glycopyrrolate; 0.01 mg kg^–1 IV and 0.01 mg kg^–1 IM), parasympathetic stimulation (phenylephrine; 0.005 mg kg^–1 IV + 0.05 mg kg^–1hour^–1), sympathetic blockade (propranolol; 0.11 mg kg^–1 IV), sympathetic stimulation propranolol; 0.01 μg kg^–1 minute^–1), and saline control. At least 48 hours were allowed between treatments. ECG recordings were obtained using an ambulatory ECG monitor. A 5‐minutes period of continuous recording obtained ~30 minutes after initiation of drug administration was used for data analysis. Changes in HRV were evaluated by time and frequency‐domain analysis. The standard deviation of normal R‐R intervals (SDNN), as well as the standard deviation of successive differences in RR intervals (SDSD) were assessed for each treatment. Low frequency (LFP; 0.05–0.15 Hz), high frequency (HFP; 0.15–0.35 Hz), and total (TP; 0.017–0.5 Hz) spectral power were also determined. The LFP:HFP ratio was also evaluated. A two‐way anova with a Tukey's test was used to detect differences (p < 0.05). Administration of glycopyrrolate or isoproterenol increased HR and decreased SDNN and SDSD below control levels. Phenylephrine or propranolol administration were without effect. LFP was diminished by glycopyrrolate and isoproterenol, but was unaffected by phenylephrine and propranolol. HFP, TP, and LFP:HFP were unaffected by treatment. Both branches of the autonomic nervous system influence SDNN and LFP. SDSD, in contrast, is altered primarily by parasympathetic activity. Thus, it appears that parasympathetic activity modulates HRV in the resting dog, as either withdrawal of parasympathetic influence or accentuated sympathetic activity led to significant changes in these measures of HRV. Conversely, augmentation of parasympathetic activity or withdrawal of sympathetic tone minimally affected HRV.     

Stratospheric Mean Ages and Transport Rates from Observations of Carbon Dioxide and Nitrous Oxide

Measurements of stratospheric carbon dioxide (CO2) and nitrous oxide (N2O) concentrations were analyzed to investigate stratospheric transport rates. Temporal variations in tropospheric CO2 were observed to propagate into the stratosphere, showing that tropospheric air enters the lower tropical stratosphere continuously, ascends, and is transported rapidly (in less than 1 month) to both hemispheres. The mean age A of stratospheric air determined from CO2 data is approximately 5 years in the mid-stratosphere. The mean age is mathematically equivalent to a conserved tracer analogous to exhaust from stratospheric aircraft. Comparison of values for A from models and observations indicates that current model simulations likely underestimate pollutant concentrations from proposed stratospheric aircraft by 25 to 100 percent.     

Relationships among Puberty,Muscle and Fat,and Liveweight Gain during Mating in Young Female Sheep

Greater depths of muscle are associated with better reproductive performance in ewe lambs, but, in adult ewes, reproductive performance also seems to vary with liveweight gain during the mating period. Therefore, in a large field study with Merino ewe lambs, we tested whether the relationships among eye muscle depth (EMD), fat depth (FAT) and reproductive performance depend on liveweight gain during the mating period. We selected lambs with a wide range in phenotypic values for depths of eye muscle (EMD) and fat (FAT) and assigned them to dietary treatments designed to achieve low (LOW, n = 244) or high (HIGH, n = 237) rates of liveweight gain during a 28‐day mating period. The LOW treatment maintained live weight, whereas the HIGH treatment gained 179 ± 3.8 g/day (p < 0.001). From those ewe lambs that attained puberty, first oestrus was detected at live weight 37.8 ± 0.2 kg and age 232 days. The proportion of ewes that attained puberty increased with EMD (p < 0.01). Ewes from the HIGH treatment were more fertile (pregnant ewes per 100 ewes exposed to rams) and had a higher reproductive rate (foetuses in utero per 100 ewes exposed to rams; p < 0.001) than those from the LOW treatment. Fertility and reproductive rate were positively correlated with weight gain during mating as well as live weight at the start of mating, FAT and EMD (p < 0.05 to <0.001). We conclude that faster growth, due to either extra nutrition during mating or higher phenotypic potential for fat and muscle, will increase reproductive performance in ewe lambs mated at 8 months of age.     

Ultrasound Confirmation of Ovulation in Mares: A Normal Corpus Luteum or a Haemorrhagic Anovulatory Follicle?

The most common pathological anovulatory condition that occurs spontaneously during the breeding season in the mare is the haemorrhagic anovulatory follicle (HAF). A relatively high proportion of mares, soon after ovulation, develop a corpus haemorrhagicum (CH) with a central lacuna. This type of corpora lutea may resemble an HAF, which may complicate the accurate diagnosis of ovulation. The main objective of this study was to compare the ultrasound data of mares examined frequently with HAFs and CHs to elucidate whether it is possible to distinguish them from each other. A total of 135 ovulating mares were classified according to the morphology of the corpus luteum (CL) in mares with: a solid CL, a CH with small or with large central cavities. Ultrasound characteristics of the development of 11 HAF and 13 CHs with a large central cavity were compared. The pre‐ovulatory follicular diameter of ovulatory mares was significantly correlated with the diameter of CH with large central cavities. The percentage of mares with post‐ovulatory areas eligible to be mistaken with a CH was <25%. Although a predictive diagnosis of an HAF/CH can be made on the basis of several ultrasonographic endpoints, the only parameter that allows a definitive diagnosis is the thickness of the luteal border. This is <3 mm in HAFs in contrast to >5 mm in CHs. However, this only applies when the unidentified structure has non‐organized contents.     

Effects of initial and extended exposure to an endophyte-infected tall fescue seed diet on faecal and urinary excretion of ergovaline and lysergic acid in mature geldings

Abstract

AIM: To determine the amount of ergovaline and lysergic acid retained or excreted by geldings fed endophyte-infected seed containing known concentrations of these alkaloids, and the effects of exposure time on clinical expression of toxicosis.

METHODS: Mature geldings (n=10) received diets containing either endophyte-free (E-) or endophyte-infected (E+) tall fescue seed during three experimental phases. The first phase (Days ?14 to ?1) was an adaptation phase, to allow all horses to adapt to a diet containing E- tall fescue seed. The second (Days 0 to 3) was the initial exposure phase to E+ tall fescue seed, used for the delivery of ergovaline and lysergic acid at 0.5 and 0.3 mg/kg of diet, respectively, to test the initial effects of exposure on routes and amounts of elimination of alkaloid. During this phase, half the geldings were exposed to an E+ diet while the rest served as controls by remaining on the E- diet. Once assigned to treatments, geldings remained on the same diet through the third phase (Days 4 to 21), which served as the extended exposure phase. Total outputs of faeces and urine were collected within each phase, to determine retention of ergovaline and lysergic acid and nutrient digestibility. Serum was collected weekly and analysed for activities of enzymes and concentrations of prolactin. Bodyweights (BW) and rectal temperatures were recorded weekly.

RESULTS: BW, rectal temperature, enzyme activities and concentrations of prolactin in serum, and nutrient digestibility were not affected by treatment. Total intake of ergovaline by geldings on the E+ diet was 3.5 and 3.6 (SE 0.20) mg/day, and 2.1 and 2.3 (SE 0.11) mg/day were not accounted for in initial and extended phases, respectively. Lysergic acid was excreted in the urine (4.0 and 4.9 (SE 0.97) mg/day) and faeces (2.5 and 2.7 (SE 0.35) mg/day) at greater amounts than that consumed (2.0 and 1.9 (SE 0.09) mg/day) during the initial and extended exposure phases, respectively. Animals exposed to E+ seed for a period of 20 days appeared to excrete more (1.5 vs 1.2 mg/day; SE 0.08; p=0.03) ergovaline in the faeces than those exposed for only 4 days.

CONCLUSIONS: Exposure time to the ergot alkaloids had a limited effect on the route of elimination or the amounts of ergovaline or lysergic acid excreted by horses. The primary alkaloid excreted was lysergic acid, and urine was the major route of elimination. These data will aid future research to improve animals′ tolerance to toxic endophyte-infected tall fescue.     

The effect of anesthesia and surgery on heart rate variability in dogs

Heart rate variability (HRV) may be useful for objective assessment of stress and pain in animals. The objective of this study was to describe the effect of anesthesia and surgery on HRV in dogs. We hypothesized that surgery would decrease HRV to a greater degree and for a longer duration than anesthesia alone. Four healthy male dogs (29 ± 2 kg) were instrumented for ambulatory ECG monitoring. Continuous ECG data was obtained for 1 day prior to, and 6 days following anesthesia alone (ANES) or anesthesia plus unilateral stifle arthrotomy (ANSX). The anesthetic protocol included xylazine (0.5 mg kg^–1 IM), morphine (0.5 mg kg^–1 IM), atropine (0.04 mg kg^–1 IM), thiopental (10 mg kg^–1 IV) and isoflurane in oxygen. A single dose of morphine (0.5 mg kg^–1 IM) was administered at extubation. Time domain analysis of HRV was performed on 5 minutes epochs of artefact‐ and arrhythmia‐free ECG data obtained at 12 noon and 12 midnight on each of the seven experimental days. Mean RR interval, standard deviation of normal R‐R intervals (SDNN), and the standard deviation of successive differences in RR intervals (SDSD) were compared to baseline for ANES and ANSX. Pain scores obtained during the day were also evaluated. Significance was set at p < 0.01. There were no differences between groups for any baseline data. Mean RR interval did not differ from baseline on days 1–6 in ANES or ANSX. SDNN and SDSD values at noon were not different from baseline on days 1–6 in ANES or ANSX. At midnight on days 1 and 2, SDNN was significantly decreased from baseline in ANSX, and on day 1 a significant difference between groups existed. ANSX values of SDSD at midnight were significantly decreased from baseline and ANES on day 1. Pain scores for ANSX were significantly greater than baseline on days 1–3, and different from ANES on days 1–5. These results suggest that HRV is decreased following anesthesia plus surgery, and that changes in HRV may be associated with pain.     

Association of stomatal frequency and morphology in Lycopersicon species with resistance to Xanthomonas campestris pv. vesicatoria

Study of the stomata and leaf epidermis of eight Lycopersicon species has revealed a relationship between frequency of stomata, stomatal size and some morphological leaf characteristics, and resistance to bacterial leaf spot caused by Xanthomonas campestris pv. vesicatoria. Significant correlations were found between the stomatal frequency in both adaxial and abaxial leaf epidermis and the number of bacterial lesions per leaf area ( r = 0.70 and 0.68, respectively) and the frequency of stomata in both adaxial and abaxial epidermis and disease incidence (percentage of diseased plants) ( r =0.87 and 0.80, respectively) for all the Lycopersicon species and one hybrid tested. A correlation was also found between disease incidence and number of bacterial lesions per leaf area ( r = 0.85). The length and width of stomata were correlated with frequency of stomata in adaxial and abaxial epidermis ( r = 0.85, 0.75, 0.89 and 0.90, respectively). The stomatal width was correlated with the number of bacterial lesions per cm² ( r =0.82; P = 0.0065). Scanning electron microscopic studies of the leaf surface and stomata indicated that other morphological features such as the raised stomatal complex in L. hirsutum and persistent, hydrophobic waxy coating of the epidermis in L. peruvianum may also be relevant in disease response.     

Quantifying Transport Between the Tropical and Mid-Latitude Lower Stratosphere

Airborne in situ observations of molecules with a wide range of lifetimes (methane, nitrous oxide, reactive nitrogen, ozone, chlorinated halocarbons, and halon-1211), used in a tropical tracer model, show that mid-latitude air is entrained into the tropical lower stratosphere within about 13.5 months; transport is faster in the reverse direction. Because exchange with the tropics is slower than global photochemical models generally assume, ozone at mid-latitudes appears to be more sensitive to elevated levels of industrial chlorine than is currently predicted. Nevertheless, about 45 percent of air in the tropical ascent region at 21 kilometers is of mid-latitude origin, implying that emissions from supersonic aircraft could reach the middle stratosphere.