Cynthia Nyquist-Battie

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

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

Maternal ethanol consumption: Effect on skeletal muscle development in guinea pig offspring

The effect of ethanol on developing skeletal muscle was analyzed by examining the gastrocnemius muscle from newborn guinea pigs, exposed to ethanol during the second half of gestation. Electron microscopy revealed vacuolated sarcoplasmic reticula, enlarged lipid droplets, decreased glycogen and mitochondrial abnormalities in the skeletal muscle samples from the ethanol-exposed newborn guinea pigs. None of these abnormalities were seen in the newborn controls who were born to dams which consumed the same amount of calories as the ethanol-treated dams. The ethanol-associated abnormalities, seen in this study, are similar to those seen in ultrastructural examination of skeletal muscle from chronic alcoholics.

Regional distribution of the molecular forms of acetylcholinesterase in adult rat heart.

Acetylcholinesterase (AChE), the enzyme that degrades acetylcholine, exists as multiple molecular forms that differ in their quaternary structure and mode of attachment to the cell surface. The distribution of the individual molecular forms of AChE in various cardiac regions with distinct anatomical characteristics was investigated. The results confirmed those of others by showing that the total pool of cardiac AChE had a nonuniform distribution in heart that paralleled the distribution of choline acetyltransferase. The rank order of this distribution was right a trial appendage >interatrial septum > left atrial appendage=right ventricle=interventricular septum > left ventricle. Velocity sedimentation in sucrose gradients of extracts from selected cardiac areas showed that four molecular forms were present in all areas but that the proportions of these forms differed as a function of area. The right and left ventricular walls, the apical portion of the Interventricular septum, and the left atrial appendage contained G, and G4 (globular) AChE in near-equal proportions, but in the basal portion of interventricular septum, the contribution of G4 AChE was greater than that of G1 AChE. The right atrial appendage and the interatrial septum had the largest amount of activity attributable to G4 AChE and the lowest amount attributable to G1 AChE. In all cardiac regions, A12 (asymmetric) AChE comprised 8–10% of the total AChE pool. The results of this research show that the composition of the globular AChE pool varies in heart as a function of region and that cardiac regions that have the highest AChE activity and that contain parasympathetic ganglia and nodal areas have different pools of globular AChE molecules than other areas. In addition, it appears that there is a uniform proportion of A12 AChE in all areas of rat heart.

Acetylcholine levels, choline acetyltransferase and acetylcholinesterase molecular forms during thyroxine-induced cardiac hypertrophy.

The effects of left ventricular hypertrophy induced by hyperthyroidism on three biochemical markers of parasympathetic innervation were investigated. In response to subcutaneous injections of thyroxine (400 micrograms/kg; T4) for 6 days, the left ventricle, but not the right, developed significant hypertrophy (20%). In the enlarged left ventricle, acetylcholine (ACh) content and choline acetyltransferase (ChAT) activity per chamber were elevated approx. 25-30%, although no change in these two markers was evident when the data were expressed per unit wet weight. Immunoblot analysis showed that the relative abundance of ChAT protein increased in the hypertrophied left ventricle in correlation with the increased ChAT activity. No changes in ACh content, ChAT activity and ChAT relative abundance were evident in the right ventricle of T4-treated animals. Although hyperthyroidism did not alter AChE specific activity (per unit wet weight) in the left ventricle, the percent activities of the individual AChE globular forms were affected in this chamber. Specifically, T4-treatment reduced the percent activity of globular (G)4 AChE by 20% and increased that of the combined G1 and G2 AChE pool by 15%. Interestingly, in the hypertrophied left ventricle total AChE activity in its extracellular or functionally-relevant pool was reduced due to a loss of G4 AChE activity. These results show that a compensatory increase in parasympathetic innervation can occur during hyperthyroid-induced left ventricular hypertrophy. However, the reduced activity of the functionally-relevant AChE pool suggests that the clearance of ACh after release may be slowed in the hypertrophied left ventricle.

Acetylcholinesterase molecular forms in muscle and non-muscle cells of rat heart

Experiments were performed to determine the cellular associations of the molecular forms of acetylcholinesterase (AChE) in adult rat heart. For this purpose, a cardiac muscle and a non-muscle fraction were isolated from rat heart ventricles after perfusion with collagenase and hyaluronidase, extracts of these fractions were subjected to ultracentrifugation on linear density gradients of sucrose (5-20%), and fractions of these gradients were analyzed for AChE activity. The results show that only globular AChE molecular forms were present in isolated cardiac muscle cells. Globular AChE forms were also present in the non-muscle cells fraction but in different proportions. The proportions of globular AChE forms plus the high specific activity of choline acetyltransferase in the non-muscle cell fraction suggest that this fraction contains cholinergic nerve fragments. The results of this study also show that asymmetric AChE is released during the perfusion of heart with the digestive enzymes, which suggests that asymmetric AChE is bound to the extracellular matrix of heart.

Changes in the expression of acetylcholinesterase molecular forms during rat heart development

The development of the molecular forms of acetylcholinesterase was studied in rat heart during the perinatal period. In this study, the activity of acetylcholinesterase increased both per unit wet weight and per unit protein from post‐conception day 14 to day 42. Additionally, the activity of atrial acetylcholinesterase per unit wet weight increased more rapidly after birth than that of ventricular acetylcholinesterase. The percent contribution of the various molecular forms to the total acetylcholinesterase pool in heart changed dramatically from the fetal to the neonatal period. This switch primarily consisted of a decrease in the ratio of the asymmetric to globular forms. Thus, the specific activity of globular forms increased while that of the asymmetric forms remained relatively stable. When the atria and ventricles were examined separately at 19 days post‐conception, the percent contribution of the individual molecular forms in the two cardiac areas was different. The atria contained a pool of acetylcholinesterase forms similar to postnatal heart while the ventricles contained a pool of acetylcholinesterase forms with a lower globular to asymmetric ratio. Finally, this study showed that greater than half of the acetylcholinesterase pool was inhibited by incubating hearts from fetal rats with echothiopate iodide, suggesting that a large portion of acetylcholinesterase catalytic sites are externalized in fetal heart.

Differential effects of high salt intake on neuropeptide Y and adrenergic markers in hearts of Dahl rats.

Adrenergic markers and neuropeptide Y (NPY) were examined in Dahl NaCl-sensitive and -resistant outbred male rats, fed either 0.35% or 8% NaCl diets for 8 weeks. The high salt diet caused left ventricular hypertrophy in sensitive rats but not in the resistant strain. Norepinephrine stores were not affected by high salt intake, but tyrosine hydroxylase, and dopamine beta-hydroxylase were elevated in the salt-induced hypertrophied left ventricle in conjunction with increased levels of nerve growth factor and p75 neurotrophin receptor. In contrast, high salt intake reduced ventricular neuropeptide Y in both Dahl salt-resistant and -sensitive rats.

Reduced levels of globular and asymmetric forms of acetylcholinesterase in rat left ventricle with pressure overload hypertrophy

The aim of the present work was to determine the effect of abdominal aortic stenosis on molecular forms of acetylcholinesterase (AChE) in rat heart. Pressure-overload, left ventricular hypertrophy was produced in male Sprague-Dawley rats by suprarenal abdominal aortic constriction. After two weeks the relative heart weight was increased over 20% compared to sham-surgical controls, mostly due to left ventricular enlargement. Aortic constriction reduced AChE activity per wet weight and per unit protein by 25-30% in the left ventricle and interventricular septum, but not in the other chambers. However, total AChE activity per chamber was normal in the left ventricle and interventricular septum, but was elevated in the atria. The molecular forms of AChE were separated in linear sucrose gradients and their specific activities were calculated from the resulting percent activities and total AChE activities. This data showed that although aortic constriction had no effect on ratios of the various forms, it did reduce the specific activities of globular and asymmetric forms in the left ventricle and interventricular septum. The reduced AChE activity suggests that slower rates of ACh hydrolysis occur in the left ventricle in pressure-overload hypertrophy.

Changes in Acetylcholinesterase Molecular Form Expression during Rat Heart Development

Acetylcholinesterase ( AChE) is a glycoprotein with multiple molecular forms that can be divided into two classes.’ Asymmetric forms (A) contain catalytic subunits covalently bound to a collagen-helical peptide. The second class is termed globular( G) and consists of molecules that lack collagen tails. Globular forms exist as monomers (GI), dimers (G2), and tetramers (G.,) of the catalytic subunits. A and G forms of AChE are present in all chambers of rat heart, although most areas of the atria exhibit higher AChE-specific activities than the ventri~les.2~~ AChE is present in fetal rat heart before the onset of functional innervation.” To determine if the expression of AChE changes during the establishment of cholinergic innervation, a study of AChE molecular forms in developing rat heart was conducted.

Cardiac Acetylcholinesterase Molecular Forms and Choline Acetyltransferase in the Dahl (Salt-Sensitive) Hypertensive Strain of Rats: A Regional Study

A regional study of acetylcholinesterase (AChE) molecular forms and choline acetyltransferase (ChAT) in the hearts of Dahl-salt sensitive (DS) and salt resistant (DR) rats was performed in animals administered either 8% or 0.35% dietary NaCl. Atria isolated from DS rats, regardless of dietary NaCl intake, had lower activities of all of the AChE molecular forms and ChAT when compared to their dietary-matched DR controls. In the ventricles, the activities of AChE molecular forms and ChAT were lower in DS rats compared to dietary-matched DR rats only when 8% NaCl diets were administered. The percent contribution of each of the molecular forms to the total AChE pool was not affected by animal strain or diet.