Autoradiographic localization of high affinity uptake sites for 3H-D-aspartate in the rat olfactory bulb

In order to reveal excitatory amino acid-ergic neuronal connections in the rat olfactory bulb, uptake sites for the tritiated D-aspartic acid were analyzed by high resolution autoradiography. Light microscopy revealed both cellular and terminal-like uptake. Based on electron microscopy, overwhelming majority of the cellular uptake was assigned to glial cells. A fairly high number of labelled terminals appeared in the surroundings of the mitral cell somata, within the deepest portion of the external plexiform layer, in the internal plexiform layer and in the outer half of the granule cell layer. Labelled terminals synapsed onto likely granule cell dendrites or spines, at asymmetric membrane thickenings. These results suggest that, although the output neurons may not utilize glutamic or aspartic acid as their transmitters, these amino acids may, however, contribute to the bulbar neurotransmission, as mediator substances of a subgroup of centrifugal fibers to the olfactory bulb.     

Nucleoside triphosphate pyrophosphatase of rabbit matrix vesicles, a mechanism for the generation of inorganic pyrophosphate in epiphyseal cartilage

Inorganic pyrophosphate (PPi) may be important in the regulation of mineralisation but its origin in epiphyseal cartilage is ill-defined. Nucleoside triphosphate pyrophosphatase is one potential source, as this enzyme catalyses the formation of PPi from nucleoside triphosphates. This enzyme has been identified in matrix vesicles derived from rabbit epiphyseal cartilage and a method developed to measure the activity using ATP as substrate in intact matrix vesicles under relatively physiological conditions. The enzyme had a high affinity for ATP (Km less than 10 microM) and was also active towards GTP, CTP and UTP. Disruption of the matrix vesicle membrane by sonication failed to alter the activity. Treatment of sonicated matrix vesicles with Triton X-100 increased the activity which may indicate a direct effect of the detergent on the enzyme. Activity towards ATP was inhibited substantially by ADP and AMP and by another potential substrate beta,gamma-methyleneadenosine 5'-triphosphate. Dichloromethylene bisphosphonate, an analogue of the product PPi, inhibited the activity to a lesser extent. Two other potential substrates, NADP+ and thymidine 5'-monophosphate p-nitrophenyl ester were only weakly inhibitory as was 1-hydroxyethylidene 1,1-bisphosphonate. These results imply that nucleoside triphosphates are the substrates in vivo and the inhibitory effects of ADP and AMP suggest mechanisms whereby this activity could be regulated.     

Cultured fetal rat pituitaries kept in synthetic medium are able to initiate synthesis of trophic hormones

Summary An immunohistochemical study was performed to determine the capacity of early fetal pituitaries to differentiate into specific hormone-synthesizing tissue in the absence of any influence from the central nervous system. Rathke's pouches from rats were removed from their juxtadiencephalic position on day 11 and 12 of gestation and maintained for 2–7 days in a chemically defined culture medium (M 199) without antibiotics and serum supplementation. The immunocytochemical observations provided evidence for the differentiation of ACTH-, TSH-gb-, LH-gb-, FSH-gb-, GH- and PRL-synthesizing cells in the isolated organ cultured from 11 to 12-day-old pituitary primordia. The appearance of specific hormone-synthesizing cells in vitro displayed a delay of 1.5–2 days compared to the day of appearance in vivo, however, the sequential order of developmental events occurred as observed in vivo. The present results suggest that endocrine or neuroendocrine signals are not required for the expression of specific secretory functions of fetal pituitaries, at least at an age of 11–12 days.     

Competition in the gradostat: the role of the communication rate

In this paper we study a mathematical model of competition between two species of microorganisms for a single limiting nutrient in a laboratory device called a gradostat. A gradostat consists of several (we consider only two) chemostats (CSTR's) connected together so that material can flow between the vessels in such a way that a nutrient gradient is established. Our model is a slightly modified version of one considered recently by Jäger et al. [3], in that the rate of exchange of material between the two vessels (the communication rate) is allowed to differ from the dilution rate. The outcome of competition turns out to be surprisingly sensitive to variation of the communication rate. We identify several coexistence regimes in parameter space and describe a method for obtaining operating diagrams for given pairs of competing microorganisms.Research supported in part by NSF Grant DMS 8521605     

Nicotinic Agonists Regulate α-Bungarotoxin Binding Sites of TE671 Human Medulloblastoma Cells

The TE671 human medulloblastoma cell line expresses a variety of characteristics of human neurons. Among these characteristics is the expression of membrane-bound high-affinity binding sites for alpha-bungarotoxin, which is a potent antagonist of functional nicotinic acetylcholine receptors on these cells. These toxin binding sites represent a class of nicotinic receptor isotypes present in mammalian brain. Treatment of TE671 cells during proliferative growth phase with nicotine or carbamylcholine, but not with muscarine or d-tubocurarine, induced up to a five-fold increase in the density of radiolabeled toxin binding sites in crude membrane fractions. This effect was blocked by co-incubation with the nicotinic antagonists d-tubocurarine and decamethonium, but not by mecamylamine or by muscarinic antagonists. Following a 10-13 h lag phase upon removal of agonist, recovery of the up-regulated sites to control values occurred within an additional 10-20 h. These studies indicate that the expression of functional nicotinic acetylcholine receptors on TE671 cells is subject to regulation by nicotinic agonists. Studies of the murine CNS have consistently indicated nicotine-induced up-regulation of nicotinic acetylcholine receptors, thereby supporting the identification of the toxin binding site on these cells as the functional nicotinic receptor. Although a mechanism for this effect is not apparent, nicotine-induced receptor blockade does not appear to be involved.     

Determining the basic characteristics of aerosols suitable for studies of deposition in the respiratory tract

Studies of aerosol particle deposition in the respiratory tract requires experimental inhalation of artificial model aerosols. The paper formulates some of the most important requirements for the properties of such aerosols. Several suitable fractions were prepared as part of a research project dealing with the use of microporous polymers for diagnostic purposes. 5 fractions of the polymer designated G-gel 60 with the particle size as stated by the manufacturer, ranging from 3 to 7 micron were evaluated using a 16-channel particle dispersity analyzer HIAC/ROYCO MT 3210 with the sensor 1200 and operated by a microprocessor, the equipment being coupled to an APPLE IIe computer. G-gel 60 particles introduced into the aerosol were characterized by the parameters CMAD, MMAD and sg both numerically and graphically. The measurement procedure was found to be very sensitive with respect to all fractions in evaluating the subtile differences between different lot numbers of the aerosol. G-gel 60 fractions characterized both numerically and graphically were compared with the known aerosols from paraffin oil and atmospheric air. The equipment MT 3210 enables prompt determination of the percentages of aerosol particles distribution by size class. The authors conclude that the procedure, both in its numerical and graphical versions, is particularly suitable for the diagnosis of aerosol particles deposition in the respiratory tract, offering a new application for HIAC/ROYCO in the field of medicine. In evaluating atmospheric aerosol in exhaled air, the number of particles was found to be below that in inhaled air, the difference being dependent on the choice of investigation methods. Percentual distribution of deposited particles following one minute ventilation proved to be at its maximum, as regards atmospheric aerosol, in the 0.30-0.50 micron range. The deposition curve was similar to already published curves, being characterized by an S-shaped pattern with maximum deposition in the greater size classes. An analysis of inhaled, exhaled and deposited aerosol suggested that deposited aerosol is more polydisperse and has particles of greater sizes than inhaled aerosol. Investigation of the effect of apnoe on deposition indicated that deposition increased as a function of apnoeic pause.     

Tyrosine and tryptophan modification monitored by ultraviolet resonance Raman spectroscopy

Nitration of tyrosine with tetranitromethane shifts the tyrosine absorption spectrum and abolishes its 200 nm-excited resonance Raman spectrum. There is no detectable resonance Raman contribution from either reactants or products. Likewise, modification of tryptophan with 2-hydroxy-5-nitrobenzyl bromide (HNBB) shifts its absorption spectrum and abolishes its 218 nm-excited resonance Raman spectrum. In this case resonance Raman bands due to HNBB are seen, but are readily distinguishable from the tryptophan spectrum, can be computer-subtracted. When stellacyanin was treated with tetranitromethane the UV resonance Raman spectrum was greatly attenuated; quantitation of the 850 cm-1 tyrosine band intensity gave a value of 4.3 tyrosines modified out of the seven present in stellacyanin, in good agreement with an estimate of 4.7 from the absorption spectrum. For cytochrome c, the resonance Raman spectrum indicates that two out of the four tyrosines are modified by tetranitromethane treatment, consistent with the crystal structure, which shows two buried tyrosines and two at the protein surface. Treatment of stellacyanin with HNBB gave a reduction in the tryptophan spectrum, excited at 218 nm, consistent with one of the three tryptophans being modified. These modification procedures should be useful in distinguishing spectra of buried tyrosine and tryptophan residues from those at the surface.     

Aerosol particle deposition in human lungs

The pneumoconiosis developing after inhalation of air-borne dusts in the work place depends on the relation between the value of particle deposition in the respiratory tract and the rate of particle clearance from sites of their deposition. For testing the deposition in humans an aerosol of paraffin oil was given to a cohort of healthy persons. The characteristic parameters of the aerosol had been defined. The concentration of particles in 5 channels were measured in both the inhaled and exhaled air samples using the particle counter ROYCO 225. The deposition fraction was calculated from the relation of particle amount in expired air to the amount in inhaled air in each distribution class. In this preliminary report the results comparable with the prediction mathematical curve are discussed.     

Further data on the origin of gonadotropin releasing hormone in the median eminence of the rat hypothalamus

Gonadotropin releasing hormone (GnRH) content of the two halves of the median eminence of the rat hypothalamus was determined by radioimmunoassay three weeks after three different unilateral knife cuts around the preoptic area. A unilateral cut in front or above the area caused a more than 25% decrease in the GnRH content of the two halves of the median eminence. A cut lateral to the preoptic region had only a slight effect similar to that observed after sham operations. The data suggest that probably more than 50% of the rat median eminence GnRH derives from outside the preoptic-suprachiasmatic region. The GnRH fibres projecting to the median eminence but arising from outside the preoptic region, probably mainly from GnRH perikarya in the limbs of the diagonal band of Broca and septum, enter this area partly from rostral and partly from above, but not from lateral direction. partly from rostral and partly from above, but not from lateral direction. Several of these fibres probably cross before terminating in the median eminence.