Neural and smooth muscle development in the chicken gizzard

The development of the autonomic ganglia of Auerbach's plexus and gizzard smooth muscle was studied in chicken embryos. Nervous system and smooth-muscle-specific antibodies were employed in immunofluorescence stainings on tissue sections to investigate the temporal and spatial frame of neural and muscular differentiation in relation to each other. Subserosal clusters of neural cells were clearly demonstrable at embryonic day 5 (ED5), the earliest stage analysed, with the monoclonal antibody El (SGIII-1). Fine nerve fibres (ED6) and, later, large axon bundles projecting from subserosal neuron clusters towards the lumen were followed and found to reach the luminal border by ED11. Already in early development the area of the future laminar tendons on the ventral and dorsal surface of the gizzard was devoid of neuroblasts, and nerve fibres were not extending to the muscle-tendon borderline until ED16. Double stainings with antibodies to smooth muscle myosin (SMM) and El revealed that SMM expression, taken as an indicator for muscle differentiation, followed neural growth. It was first detectable in close apposition to the differentiating neuroblasts in the caudal and cranial portion of the gizzard at ED6. With further development, myosin expression proceeded inward towards the lumen in a wave which followed the ingrowth of E1-positive nerve fibres from the prospective Auerbach plexus. Neuromuscular differentiation deviated from this pattern in the lateral tendon area where nerve growth was delayed and myosin expression preceeded the arrival of E1-positive nerve fibres. The findings suggest that the gizzard could serve as a model system for the analysis of potential early nervous system imprints on smooth premuscle mesenchyme differentiation.     

REGIONAL CHANGES IN CEREBRAL GABA CONCENTRATION AND CONVULSIONS PRODUCED BY d AND BY l-ALLYLGLYCINE

Abstract— The convulsant action of allylglycine (2-amino-4-pentenoic acid) is due to the metabolic conversion of allylglycine to 2-keto-4-pentenoic acid, a more potent glutamic acid decarboxylase inhibitor and more potent convulsant than the parent compound. We report regional changes in cerebral GABA concentration in rats after administration of d - and l -allylglycine. d -Allylglycine (3.75 mmol/kg) induced convulsions in 95–115 min, characterised by repeated clonic limb movements and rapid rotation around the head to tail axis. GABA concentrations were only reduced in cerebellum and ponsmedulla during the pre and post-convulsive periods. The localised reduction of GABA concentration is consistent with the enzymic conversion of d -allylglycine to 2-keto-4-pentenoic acid catalysed by cerebral d -amino acid oxidase, an enzyme known to be localised to the hind brain and spinal cord. l -allylglycine (1.2mmol/kg i.p.) induced convulsions in 65 -90 min, characterised by violent running followed by tonic flexion and extension. During the pre-convulsive period, GABA concentrations were reduced in all brain areas studied except the globus pallidus and ventral midbrain. The widespread decreases in GABA concentration suggest that the enzyme(s) which catalyse the conversion of l -allylglycine to 2-keto-4-pentenoic acid are widely distributed within the brain.     

C-glycosylflavone accumulation in Sandoz 6706-treated barley seedlings is a photocontrolled response

Sandoz 6706 pretreatment of white light grown barley seedlings causes a 60% increase in saponarin (6-C-glucosyl-7-O-glucosylapigenin) but a 300% increase in lutonarin (3′-hydroxysaponarin). Norflurazon has little effect on saponarin levels but is almost as effective as Sandoz 6706 in enhancing lutonarin net synthesis. Barley roots contain saponarin and lutonarin only after herbicide treatment. Mung bean seedlings respond to Sandoz 6706 by accumulating higher levels of rutin and delphinidin 3-glucoside. The results are discussed in relation to the site of action of the herbicides, the High Energy photoresponse, and control of flavonoid 3′-hydroxylation.     

THE KINETICS OF CONTACT INHIBITION IN MAMMALIAN CELLS

To elucidate the process of contact inhibition in mammalian cells, we investigated the kinetics of growth arrest in [³H]thymidine labelled embryonic chinese hamster (Cricetulus griseus L.) cells after the addition of various concentrations of unlabelled cells. It was observed that after the contact inhibition concentration had been reached, the cells grew undisturbed for one more generation. In the following 24 hr the concentration fell back to the level at the beginning of the experiment and stayed there.     

Acyl chain conformational ordering in 1,2 dipalmitoylphosphatidylethanolamine. Integration of FT-IR and 2H NMR results.

The extent of trans-gauche isomerization at the 4 and 4' positions of the acyl chains of fully hydrated 4,4,4',4'-d4 1,2-dipalmitoylphosphatidylethanolamine (4-d4 DPPE) bilayers was quantitatively evaluated from the infrared (IR) intensity of the CD2 rocking modes. About 20% gauche conformers were observed at 72 degrees C (above Tm), while at 23 degrees C, well below Tm, about 4% were noted. The order parameter SC-D was determined from 2H nuclear magnetic resonance (NMR) quadrupolar splittings. SC-D is the product of a segmental order parameter (S gamma), which depends on conformational order, and a chain order parameter (S alpha) which depends on slower motions such as chain wobble. The IR-determined percentage of gauche forms was converted into a segmental order parameter and factored out of the measured value for SC-D to yield an estimate of S alpha = 0.59 for L alpha phase DPPE. A comparison with S alpha for 1,2-dipalmitoylphosphatidylcholine (DPPC) suggests that increased wobble is responsible for enhanced motional averaging of the quadrupolar splittings in the latter at a similar reduced temperature. The extent of conformational disordering [at the 4(4') position] is essentially unchanged between the two molecules. The current study demonstrates the advantage of integrating quantitative IR with 2H NMR data, for elucidation of the contributions of the individual motions that average the NMR quadrupolar splittings.     

Early electrochemical events in lectin-lymphocyte interaction

Concanavalin A, at extremely low concentrations, will produce significant increases in the electrophoretic mobility of murine splenic T lymphocytes. It has been established that the alteration in cellular surface charge is mediated by a factor produced by those lymphocytes that have reacted directly with con A. We originally conjectured that the mobility change might be the consequence of an alteration in the distribution of the charged moieties of membrane glycoproteins. The results of experiments conducted at low temperature raise some questions about this mechanism. Further experiments have been performed to establish the nature of the physicochemical alterations in the peripheral zone of the factor-stimulated lymphocytes that are manifest as changes in cellular surface charge. The results of these studies indicate that, subsequent to the interaction of T lymphocytes with con A, there is a reduction in the number of positively charged amino groups effective at the electrophoretic surface of the cells.     

Ribonucleotide reductase: A structural study of the dimeric iron site

The iron-containing B2 subunit of ribonucleotide reductase from Escherichia coli has been investigated by Raman spectroscopy. Both the tyrosyl radical-containing native protein and the radical-free protein exhibit a resonance-enhanced Raman band at 500 cm^?1. This band is assigned to an Fe-O vibrational mode arising from an oxygen-containing ligand. The failure to observe any tyrosinate ring modes makes it unlikely that ribonucleotide reductase is an iron-tyrosinate protein and rules out tyrosinate oxygen as a ligand. It is proposed that the 500 cm^?1 band in ribonucleotide reductase is analogous to the 510 cm^?1 Fe-O vibrational mode of methemerythrin and arises from an oxo- or carboxylate-bridge between the antiferromagnetically-coupled Fe(III) ions.