Preferential expression of cellular retinoic acid binding protein in a subpopulation of neural cells in the developing mouse embryo

The cellular retinoic acid binding protein is thought to be involved in the retinoic-acid-mediated signal transduction pathway. We have isolated the mouse cellular retinoic acid binding protein cDNA from an embryonal-carcinoma-derived cell line by using differential cDNA cloning strategies. In situ hybridization on sections of mouse embryos of various developmental stages indicated that the cellular retinoic acid binding protein gene, which we localized on mouse chromosome 9, is preferentially expressed in a subpopulation of neurectodermal cells. This restricted expression pattern suggests an important role for cellular retinoic acid binding protein in murine neurogenesis.     

Probable loss of tolerance and simulation of autoimmunization in induced chimeras in doves

Chimeras were induced in doves (Streptopelia) by making parabionts of embryonating eggs that carried genes for erythrocyte antigens, which were readily identified. The parabiotic pairs were chosen so that new antigenic specificities would appear if somatic cell mating took place. However, no evidence of somatic cell mating was noted. Erythrocytic chimerism was no longer. detectable in some birds after varying periods of time. In a few others tolerance was presumably lost, since their plasma contained antibodies against cellular antigens that either were present, or had been present, in the bird's circulation.     

Atrial granules in the dog heart after cardiac denervation

Summary Because the increase in sodium excretion during left atrial distension in conscious dogs is abolished after chronic cardiac denervation, we have investigated whether this is a result of the disappearance of specific atrial granules. Electron microscopy and light-microscopical and ultrastructural immunohistochemistry of canine atria show that atrial granules displaying immunoreactivity for cardiac hormones of the cardiodilatin/atrial natriuretic polypeptide (CDD/ANP) family are still present in denervated left and right atria, although reduced in quantity. It is concluded that the atrial-induced natriuresis is not only related to the existence of specific atrial granules. The functional link between atrial-induced natriuresis provoked by atrial distension and the release of atrial polypeptide hormones remains uncertain because the denervated heart can secrete CDD although the diuretic-natriuretic effect is altered.     

A new approach to biochemical evaluation of brain dopamine metabolism

1. Dopaminergic neurotransmission in brain is receiving increased attention because of its known involvement in Parkinson's disease and new methods for the treatment of this disorder and because of hypotheses relating several psychiatric disorders to abnormalities in brain dopaminergic systems. 2. Chemical assessment of brain dopamine metabolism has been attempted by measuring levels of its major metabolite, homovanillic acid (HVA), in cerebrospinal fluid, plasma, or urine. Because HVA is derived in part from dopamine formed in noradrenergic neurons, plasma levels and urinary excretion rates of HVA do not adequately reflect solely metabolism of brain dopamine. 3. Using debrisoquin, the peripheral contributions of HVA to plasma or urinary HVA can be diminished, but the extent of residual HVA formation in noradrenergic neurons is unknown. By measuring the levels of methoxy-hydroxyphenylglycol (MHPG) in plasma or of urinary norepinephrine metabolites (total MHPG in monkeys; the sum of total MHPG and vanillyl mandelic acid (VMA) in humans) along with HVA, it is possible to estimate the degree of impairment by debrisoquin of HVA formation from noradrenergic neuronal dopamine and thereby better assess brain dopamine metabolism. 4. This method was applied to a monkey before and after destruction of the nigrostriatal pathway by the administration of MPTP.     

Distribution of the Glucose-1,6-Bisphosphate System in Brain and Retina

The distribution of glucose-1,6-bisphosphate (G16P2) synthase was measured in more than 70 regions of mouse brain, and nine layers of monkey retina. Activities in gray areas varied as much as 10-fold, in a hierarchical manner, from highest in telencephalon, especially the limbic system, to lowest in cerebellum, medulla, and spinal cord. The synthase levels were significantly correlated among different regions with G16P2 itself, as well as with previously published levels of a brain specific IMP-dependent G16P2 phosphatase. In contrast, neither G16P2 nor either its synthase or phosphatase correlated positively with phosphoglucomutase, and in all regions the G16P2 levels greatly exceeded requirements for activation of this mutase. This strengthens the view that G16P2 has some function besides serving as coenzyme for phosphoglucomutase. However, attempts to correlate the "G16P2 system," as defined by the three coordinately related elements, synthase, phosphatase, and G16P2, with other enzymes of carbohydrate metabolism, or with regional data of Sokoloff et al. [J. Neurochem. 28, 897-916 (1977)] for glucose consumption, were unsuccessful. This leaves open the possibility that brain G16P2 might serve as a phosphate donor for specific nonmetabolic effector proteins.     

D-periodic distribution of collagen type IX along cartilage fibrils

It has recently become apparent that collagen fibrils may be composed of more than one kind of macromolecule. To explore this possibility, we developed a procedure to purify fibril fragments from 17-d embryonic chicken sternal cartilage. The fibril population obtained shows, after negative staining, a uniformity in the banding pattern and diameter similar to the fibrils in situ. Pepsin digestion of this fibril preparation releases collagen types II, IX, and XI in the proportion of 8:1:1. Rotary shadowing of the fibrils reveals a d-periodic distribution of 35-40-nm long projections, each capped with a globular domain, which resemble in form and dimensions the aminoterminal globular and collagenous domains, NC4 and COL3, of type IX collagen. The monoclonal antibody (4D6) specific for an epitope close to the amino terminal of the COL3 domain of type IX collagen bound to these projections, thus confirming their identity. Type IX collagen is therefore distributed in a regular d-periodic arrangement along cartilage fibrils, with the chondroitin sulfate chain of type IX collagen in intimate contact with the fibril.     

Sorbitol Gum in Xerostomics: The Effects on Dental Plaque pH and Salivary Flow Rates1

Adequate salivary flow is important for patient comfort and maintenance of oral health. Xerostomia, or dry mouth, is a common clinical complaint. Masticatory and gustatory activity can stimulate salivary flow from functional salivary tissue and the use of sugarless mints and gums have been recommended to individuals who complain of xerostomia, but there are minimum clinical data. A clinical study assessing the effect on salivary flow rates and dental plaque pH of a sorbitol-sweetened chewing gum in subjects with the complaint of xerostomia was conducted. The chewing of the gum in this present study stimulated salivary flow in the subjects with xerostomia. Statistically significant stimulated whole mouth and parotid salivary flow rate increases were found when compared to unstimulated whole mouth and parotid salivary flow rates. Chewing of the sorbitol-sweetened gum also effectively reduced the drop in pH seen following the exposure to a fermentable carbohydrate. The findings of this present study indicate that chewing of a sorbitol-sweetened gum may be of benefit to patients with the complaint of xerostomia.     

A comparison of net and gross rates of oxygen production as a function of light intensity in some natural plankton populations and in a Synechococcus culture

In vitrorates of gross and net oxygen production were measuredas a function of light intensity in some plankton communitiescollected from Bedford Basin, Nova Scotia, and in a monoclonalculture of Synechococcus. The rate of gross oxygen productionwas measured by a technique in which the stable oxygen isotope,¹⁸O, serves as a photosynthetic tracer Net oxygen productionwas measured by automated Winkler technique. The rate of communityrespiration in the light was then determined by the differencebetween gross and net rates of oxygen production. In the naturalpopulations examined, neither gross nor net oxygen productionrates were significantly inhibited at the highest light intensitymeasured (500–800 µE m^–2 s^–1) In a samplein which the dark respiration rate was small relative to themaximal rate of production [P_max;sensu Platt et al (1980) JMar. Res., 38, 687–701] the rates of ‘light’respiration were 3 times greater. In two other communities,with high rates of dark respiration relative to P_maxthe ratesof ‘light’ respiration were closer to rates of darkrespiration. In the Synechococcus clone, both gross and netoxygen production rates were inhibited at high light intensities.Rates of ‘light’ respiration were found to varyas a function of light intensity. The greatest rates of respirationwere measured in samples incubated at light intensities thatwere just saturating (100 µE m^–2 s^–1). Therates of ¹⁴C production were also measured as a function oflight intensity The photosynthetic quotients, based on ¹⁴C productionrates and gross oxygen production rates, average 1 9