Single Doses of Acrylamide Reduce Retrograde Transport Velocity

Abstract: Single doses of acrylamide (0–1.3 mmol/kg) produced a dose-dependent decrease in the transport of ¹²⁵I-tetanus toxin to the perikarya of sensory neurons in dorsal root ganglia and motor neurons in ventral spinal cord. Acrylamide was a more potent inhibitor of retrograde transport in sensory axons than in motor axons. Substantially greater doses of N,N '-methylene-bis-acryl-amide, a reportedly non-neurotoxic analog of acrylamide, were required to alter the axonal transport of ¹²⁵I-tetanus toxin. Velocity of retrograde transport was assessed by determining the position of the leading edge of transported¹²⁵I-tetanus toxin at times following single doses of acrylamide. Acrylamide reduced the velocity of ¹²⁵I-tetanus toxin transport in a dose-dependent manner by up to 75%. No change in neuronal uptake of ¹²⁵I-tet-anus toxin was detected. It is concluded that single doses of acrylamide produce profound alterations in retrograde transport which precede the appearance of structural changes in affected nerve fibers.     

The stability of the yeast plasmid pJDB248 depends on growth rate of the culture

Summary The stability of the plasmid pJDB 248 has been measured in theS. cerevisiae strain S150-2B growing in a chemostat under conditions of glucose limitation. It was found that reducing the growth rate of the culture led to a more rapid loss of the plasmid from the cells.     

Plasma alpha natriuretic peptide in cardiac impairment.

Regional plasma alpha human atrial natriuretic peptide concentrations were measured, and their relation to intracardiac pressures assessed, in an unselected series of 45 patients undergoing diagnostic cardiac catheterisation. Arteriovenous gradients in plasma concentrations of alpha human atrial natriuretic peptide were consistent with its cardiac secretion and its clearance by the liver and kidneys. Plasma concentrations of the peptide in the pulmonary artery, aorta, and superior vena cava correlated closely with the mean right atrial and pulmonary arterial pressures, and similar, though weaker, positive relations were seen with the left ventricular end diastolic and pulmonary artery wedge pressures. Concentrations of both atrial natriuretic peptide and renin showed significant inverse relations with serum sodium concentrations. Plasma concentrations of alpha human atrial natriuretic peptide are an additional objective indicator of the severity of haemodynamic compromise in patients with cardiac impairment.     

Response of end bud cells from immature rat mammary gland to hormones when cultured in collagen gel

End buds from 4- to 5-week-old rat mammary glands were isolated and cultured within a rat tail tendon collagen gel matrix. Media containing equine serum or porcine serum and cholera toxin promoted growth, but not the production of casein or thioesterase II, nor did they induce a state of differentiation as assessed by cell ultrastructure. Medium supplemented with only 5% porcine serum, insulin and cholera toxin did not support growth or differentiation. However, when prolactin, estradiol, progesterone and hydrocortisone were added to this medium, growth was stimulated greatly and a differentiated state was induced as assessed by the production of casein and thioesterase and by the appearance of a highly secretory ultrastructure.     

The pH dependence of hydrogen exchange in proteins

The static accessibility modified discrete charge model for electrostatic interactions in proteins is extended to the prediction of the pH dependence of hydrogen exchange reactions. The exchange rate profiles of buried amide protons are shown to follow the calculated pH dependence of the electrostatic component of protein stability. Rate profiles are calculated for individual buried amide protons in ribonuclease S and bovine pancreatic trypsin inhibitor. The electrostatic free energy of stabilization of the protein and the energy required to bring the catalytic ion to an exchange site are expressed as an apparent, pH-dependent contribution to the activation energy. Changes in the electrostatic stabilization of the proteins affect the calculated exchange rate for buried amide protons by more than 1000, while local field effects raise or lower the predicted exchange rates by less than 100. The pH dependence of exchangeable protons at the protein surface, such as the C-2 imidazole protons, is shown to follow the estimated energy required to introduce the catalytic ion at the exchange site. These calculations are discussed in terms of current models for proton exchange which incorporate the dynamic nature of the structure to explain exchange data from the interior of a protein.     

Neutral and Acid Sphingomyelinases of Rat Brain: Somatotopographical Distribution and Activity Following Experimental Manipulation of the Dopaminergic System In Vivo

The activities of neutral, magnesium-stimulated, and acid sphingomyelinases were measured in five regions of rat brain. Neutral enzyme activity was 2-3-fold higher in striatum than in parietal cortex and 13-fold higher than in cerebral white matter. Acid sphingomyelinase activity was more evenly distributed throughout these regions. Striatal neutral sphingomyelinase activity was not affected by treatment of rats with reserpine or haloperidol and was reduced (16%) by 6-hydroxydopamine. Striatal acid sphingomyelinase was unaffected by reserpine and 6-hydroxydopamine, and was increased (17%) by haloperidol. We conclude that neutral, magnesium-stimulated sphingomyelinase activity differs in various regions of rat brain and is particularly enriched in the corpus striatum. However, it appears to be a constitutive component of tissue rather than a readily modulated regulatory element of the catecholaminergic system.     

The use of thioesterase II as a rat mammary epithelial cell-specific marker

The avidin-biotin-peroxidase complex immunoperoxidase technique was employed to determine the intercellular distribution of thioesterase II in rat mammary glands. This enzyme is responsible for shifting the product specificity of the fatty-acid synthetase enzyme complex from long to medium chain fatty acids. Thioesterase II was found exclusively in the cells lining the lumen of the ductal and alveolar structures in glands from mature virgin (150 days old) and pregnant rats. The ductal cell staining intensity was considerably less than that of the alveolar cells in the mature virgin rat glands. No immunoreactive thioesterase II was found in the stromal, adipose, vascular, or myoepithelial components of the gland in the developmental stages examined. In the glands from immature virgin rats (40-45 days old) thioesterase II was again found only in the epithelial cells lining the lumen of the ductal and end-bud structures although this layer was usually more than one cell thick. Quantitative determination of thioesterase II activity in cytosol preparations revealed similar levels in mammary fragments from enzymatically-dissociated glands obtained from mature virgins and in end buds derived from immature virgins, but somewhat higher levels in mammary structures derived from late-pregnant animals. These immunohistological and biochemical results demonstrate thioesterase II's usefulness as a mammary epithelial cell-specific marker.