acase@tulane.edu

acase@tulane.edu

The fine structure and the terminations of the retinal and cortical afferents of the pretectal nucleus of the optic tract in the cat were examined. Data concerning cell size reveal a Gaussian distribution of cells and statistical analyses and histograms indicate there are no subpopulations or laminations of neurons. The parenchyma of the nucleus of the optic tract is separated by numerous myelinated fascicles into synaptic islands. These islands vary in size and may contain perikarya. Within some of the larger synaptic islands, somata are frequently found in close apposition. Electron microscopic examination of these paired somata has identified areas that appear to be adhesion placques rather than chemical or electrical synapses The terminals within the nucleus are divided into five classes based upon their synaptic vesicles, size, and mitochondrial characteristics. These terminal types are: (1) the RLP, (2) RLD, (3) RSD, (4) PD(,1), and (5) PD(,2) profiles. Additionally, type I and type II glomeruli are identified. Type I glomeruli are observed in clusters and are composed of central RLP profiles forming synapses with peripherally placed dendrites of small and medium diameter and PD profiles. Type II glomeruli have central dendrites commonly in contact with RLD and RLP profiles. Serial synaptic complexes with PD(,2) profiles as their intermediate components are also observed After placing injections of HRP into one eye or unilaterally transecting the optic nerve, retinal terminals are identified as only RLP profiles and are observed either as central axons within Type I glomeruli or as extraglomerular profiles After placing injections of HRP into the visual cortex, corticopretectal projections are identified as both RSD and RLD terminals. RSD profiles are found terminating on small and medium diameter dendrites whereas RLD terminals form asymmetric synapses on dendrites of medium and large diameter Double marker experiments involving the simultaneous unilateral transection of the optic nerve and placement of HRP within the visual cortex were performed. Only two examples of degenerating retinal profiles and HRP labelled cortical terminals in contact with the same neuron were observed. Nevertheless, on the basis of these data it is suggested that neurons in the retina and visual cortex do synapse on the same neurons in the nucleus of the optic tract. Functional considerations of the microcircuitry are also presented / acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

After a saline flush containing 1 ml of 1% NaNO(,2), a vasodilator, 42 female normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) from 3 to 24 months of age were sacrificed by an intracardiac perfusion of 3% glutaraldehyde in 0.1M phosphate buffer, pH 7.3. Proximal portions of the left coronary arteries, jejunal branches of the superior mesenteric arteries which gave rise to the terminal mesenteric arcades, and 3-5 mm thick cross-sectional slices of the jejunum were isolated, postfixed in 1% OsO(,4) for 1 hr, dehydrated in ethanols and embedded in Epon 812. Mean systolic blood pressure was always significantly different between WKY and SHR; it increased steadily with age in SHR (144 to 209 mm Hg) and decreased steadily in WKY (121 to 89 mm Hg). Mean relative ventricular weight was always higher in SHR compared to WKY and increased with age (0.46 to 0.74% body weight in SHR and 0.40 to 0.41% body weight in WKY). Significant differences in this parameter were observed at 1 and 2 years of age between WKY and SHR. Mean medial thickness/lumen diameter ratio (measured with a calibrated ocular micrometer) in jejunal arterioles was always significantly higher in SHR compared to WKY (p < 0.0005). This ratio showed no significant changes with age in WKY, but in SHR it increased significantly from 3 months to 1 year and then decreased significantly from 1 year to 2 years. The ratio increase in SHR was associated with a significant increase in medial thickness; the ratio decrease was associated with a significant increase in lumen diameter In the coronary arteries, lipofuscin-like inclusions in smooth muscle cells (SMC) developed with age. Compared to WKY, organelles were increased in SHR endothelial cells, SMC and fibroblasts at all ages. Compared to WKY and increasing with age, the following alterations were observed in SHR. Endothelial Weibel-Palade bodies increased and SMC processes extended into the subendothelial space. Orcein stain suggested active synthesis of elastin by SMC. SMC developed membranous whorls (as did fibroblasts in the adventitia), cell invaginations, cell processes and nuclear lobulation. SMC degenerative alterations included loss of myofilaments, focal cytoplasmic necrosis, necrotic cells with pyknotic nuclei, and formation of cell debris. Collagen, basement membrane-like material (determined with silver methenamine) and debris accumulated in the extracellular space. Fibroblast-like cells were noted in the media. Medial degenerative alterations were most prominent at the medio-adventitial junction in the younger animals and progressed toward the intima with increasing age in SHR. A non-elastic homogeneous substance with intimate relation to debris was noted in the adventitia of aged SHR Similar ultrastructural alterations were noted in SHR mesenteric arteries, although the changes were, in general, not as extensive as in coronary arteries. Fine structural degenerative alterations were not observed in SHR jejunal arterioles These observations indicate that structural alterations in the cardiovascular system of SHR progress with increasing age and that significant differences (qualitative and quantitative) in various parameters of vascular structure are observed between WKY and SHR, even in advanced age / acase@tulane.edu

acase@tulane.edu

The cyclic nucleotides, cAMP and cGMP, have been implicated as modulators of a wide variety of intracellular processes, including regulation of the cell cycle. This study was designed to monitor the levels of cAMP and cGMP at hourly intervals during the cell cycle in the syncytial plasmodium of Physarum polycephalum, and to assay the cell-cycle related activity of cAMP- and cGMP-dependent phosphodiesterase in isolated nuclei, whole-cell plasmodial homogenates, and subcellular fractions of the organism. Cyclic nucleotides were extracted in perchloric acid, washed with diethyl ether, and after removing polysaccharides with 95% ethanol, were dried and assayed by radioimmunoassay, following succinylation, using a commercially available kit. In addition to whole-cell homogenates, and sonicated isolated nuclei, the other fractions used in the phosphodiesterase assays were the supernatant and resuspended precipitate (particulate) resulting from a 10 minute, 20,000 g centrifugation of the whole-cell preparation. The phosphodiesterase activities of the various samples were assayed in an incubation mixture consisting of 50mM Tris-Hcl (pH 7.5) and 1.67mM MgCl(,2). All cell-cycle related assays, except those using isolated nuclei, were run at two final substrate concentrations, 1 x 10('-3)M and 1 x 10('-5)M for cAMP-dependent phosphodiesterase activity, and 5 x 10('-4)M and 1 x 10('-5)M for cGMP-dependent phosphodiesterase activity. Nuclear samples were assayed only at the higher substrate concentrations. Following incubation, all samples were reacted with snake venom nucleotidase to convert the generated 5' nucleotides to nucleosides. The nucleosides were separated from the cyclic nucleotide substrate (containing tracer amounts of tritiated substrate) either with fluoridated anion exchange resin, or anion exchange resin-loaded paper. Phosphodiesterase activity was calculated in terms of picomoles of cyclic nucleotide hydrolyzed per minute of incubation per milligram of protein. This study has demonstrated the presence of both cAMP- and cGMP-dependent phosphodiesterase in the isolated nuclei of Physarum polycephalum. In addition it has shown that with one exception the cAMP- and cGMP-dependent phosphodiesterase activity in all of the fractions fluctuates throughout the cell cycle. The whole-cell homogenate using 5 x 10('-4)M cGMP as substrate did not reveal cell-cycle related fluctuation. Kinetic data are also presented which indicate the presence of multiple phosphodiesterase activity in both the whole cell and particulate fractions for the cGMP-dependent enzyme, and in the particulate fraction for the cAMP-dependent enzyme. The derived Km values indicate that the substrate affinities of the phosphodiesterases are similar to those found previously in numerous mammalian cell studies. This study showed that cyclic nucleotides fluctuate to a significant degree during the cell cycle. No pattern was generated that was suggestive of a cause-effect relationship between the cyclic nucleotides and the cell cycle / acase@tulane.edu

acase@tulane.edu

acase@tulane.edu