The projections of chemically identified nerve fibres in canine ileum

Summary The projections of nerve fibres with immunoreactivity for the peptides enkephalin (ENK), gastrin-releasing peptide (GRP), neuropeptide Y (NPY), somatostatin (SOM), substance P (SP) and vasoactive intestinal peptide (VIP) were studied in canine small intestine by analysing the consequences of lesions of intrinsic and extrinsic nerves. Of peptides present in fibres supplying myenteric ganglia, GRP, SOM and VIP were in anally directed nerve pathways, whereas ENK and NPY were in orally directed pathways. Pathways ran for up to about 30 mm. SP fibres ran for short distances in both directions in the myenteric plexus. The circular muscle was supplied with ENK, NPY, SP and VIP fibres arising from the myenteric ganglia, whereas most mucosal SP and VIP fibres were deduced to arise from submucous ganglia. There were projections of fibres reactive for ENK, GRP, SOM, SP and VIP from myenteric ganglia to submucous ganglia. Antibodies to tyrosine hydroxylase were used to locate noradrenaline nerve fibres supplying the intestine; these fibres all disappeared when extrinsic nerves running through the mesentery to the small intestine were cut. It is deduced that there is an ordered pattern of projections of peptide-containing fibres in the canine intestine.     

下丘脑外侧区注射TRH对大鼠胃酸分泌的影响

本文采用连续收集胃腔灌流法,观察下丘脑外侧区(LHA)注射促甲状腺激素释放激素(TRH)对大鼠胃酸分泌的影响,并分析TRH在LHA促进胃酸分泌的作用机制。结果表明:(1)LHA注射TRH(1μg)明显地刺激胃酸分泌;(2)预先向LHA注射酚妥拉明(10μg)、美多心安(5μg)及胃泌素抗体1μl(1:640)并不影响TRH的泌酸作用,如预先向LHA注射阿托品(5μg)则可消除TRH的泌酸效应;(3)垂体摘除及肾上腺切除均不影响TRH的泌酸作用;(4)隔下迷走神经切断后,LHA注入TRH的泌酸效应仍然出现,但持续时间显著缩短;腹腔交感神经节摘除后,TRH仍能促进胃酸分泌,但分泌量少而平稳。以上结果提示:LHA是TRH中枢泌酸效应的有关结构之一,其中枢机制是通过胆碱能M受体中介的,腹腔交感神经节和膈下迷走神经是TRH泌酸效应的传出途径。前者引起的泌酸反应出现较早且引起泌酸高峰,但持续时间短;后者则引起低平的持续分泌。     

Interactions between developmental processes,growth, and food selection in the larvae and juveniles of Rutilus rutilus (L.) (Cyprinidae)

Summary The aim of this study was to assess the effects of developmental events, occurring in fish during the first weeks after hatching, on the quantity and quality of the ingested food and on growth. The investigation was carried out with the larvae and juveniles of Rutilus rutilus, the single cyprinid species occurring in an oligotrophic subalpine lake in Tirol, Austria. Comparison between availability of prey in the water and gut contents suggests that the selection of food by the young fish is strongly influenced by developmental processes. For example, the prevalence of indigestible phytoplankton in the gut of young larvae can be taken as a sign of the not yet fully developed sensory and locomotory capacities of the young fish (El-Fiky et al. 1987). Furthermore, quantitative and qualitative changes in the gut contents correlate strongly with changes in the form and relative length of the gut, but reflect only weakly the availability of prey in the water. In the Seefelder See population of R. rutilus the switch from a phytoplankton to a cladoceran dominated diet is accompanied by an increase in relative growth rate by nearly one order of magnitude (Wieser et al. 1988).     

Limitations on Sphagnum growth and net primary production in the foothills of the Philip Smith Mountains,Alaska

Summary In the foothills of the Philip Smith Mountains, Brooks Range, Alaska, tussock tundra occurs on rolling hills and in valleys that were shaped by Pleistocene glaciations. During the 1986 and 1987 summer seasons, Sphagnum growth and production were determined in water tracks on tundra slopes that acted to channel water flow to the valley bottom stream and in intertrack tundra areas that were relatively homogeneous with respect to downslope drainage. Measurements were made under ambient environmental conditions and on mosses receiving supplemental irrigation in each area. Growth rate for Sphagnum spp. (cm shoot length increase/day) was low and relatively constant in intertrack tundra and highest but quite variable in water tracks. A strong negative correlation was found between Sphagnum spp. growth rate and solar irradiance in the shady environment below Salix canopies in the water tracks. Estimates of net annual dry weight (DW) production for Sphagnum spp. ranged from 0.10 g DW dm^-2 yr^-1 in intertrack tundra vegetation to 1.64 g DW dm^-2 yr^-1 in well-shaded water tracks. Experimental water additions had little effect on growth and production in intertrack tundra and well-developed water tracks, but significantly increased growth in a weakly-developed water track community. Low production over large areas of tundra slopes may occur due to presence of slow growing species resistant to dessication in intertrack tundra as opposed to rapidly growing less compact species within the limited extent of water tracks. We hypothesize that species capable of rapid growth occur also in weakly-developed water tracks, and that these are water-limited more often than plants occurring in well-developed water track situations. Where experienced, high light intensity may additionally limit growth due to photoinhibition.     

Comparison of population dynamics between slow- and fast-growing strains of the rotifer Brachionus calyciflorus pallas in continuous culture

Summary The population dynamics of a slow- and a fast-growing strain of the rotifer Brachionus calyciflorus are compared. Rotifers were grown in steady-states, at various specific growth rates (), in both two-stage chemostat and turbidostat cultures on the green alga Chlorella pyrenoidosa. Population variables, including specific ingestion (I), loss (L) and filtration (F) rates, yield (Y), production (P) and half-saturation coefficient of growth (K _g), were calculated using a growth model based on saturation kinetics. I, L, F and K _g were shown to be higher and Y and P lower for the fast-growing strain. Differences between the two strains with regard to these variables may represent tradeoffs associated with the faster potential growth rate. Steady-state relationships between these values and for the fast-growing strain, however, deviated from model predictions which suggest a possible shift from carbon to non-carbon growth limitation.     

Using growth analysis to interpret competition between a C3 and a C4 annual under ambient and elevated CO2

Summary Detailed growth analysis in conjunction with information on leaf display and nitrogen uptake was used to interpret competition between Abutilon theophrasti, a C₃ annual, and Amaranthus retroflexus, a C₄ annual, under ambient (350 l l^-1) and two levels of elevated (500 and 700 l l^-1) CO₂. Plants were grown both individually and in competition with each other. Competition caused a reduction in growth in both species, but for different reasons. In Abutilon, decreases in leaf area ratio (LAR) were responsible, whereas decreased unit leaf rate (ULR) was involved in the case of Amaranthus. Mean canopy height was lower in Amaranthus than Abutilon which may explain the low ULR of Amaranthus in competition. The decrease in LAR of Abutilon was associated with an increase in root/shoot ratio implying that Abutilon was limited by competition for below ground resources. The root/shoot ratio of Amaranthus actually decreased with competition, and Amaranthus had a much higher rate of nitrogen uptake per unit of root than did Abutilon. These latter results suggest that Amaranthus was better able to compete for below ground resources than Abutilon. Although the growth of both species was reduced by competition, generally speaking, the growth of Amaranthus was reduced to a greater extent than that of Abutilon. Regression analysis suggests that the success of Abutilon in competition was due to its larger starting capital (seed size) which gave it an early advantage over Amaranthus. Elevated CO₂ had a positive effect upon biomass in Amaranthus, and to a lesser extent, Abutilon. These effects were limited to the early part of the experiment in the case of the individually grown plants, however. Only Amaranthus exhibited a significant increase in relative growth rate (RGR). In spite of the transitory effect of CO₂ upon size in individually grown plants, level of CO₂ did effect final biomass of competitively grown plants. Abutilon grown in competition with Amaranthus had a greater final biomass than Amaranthus at ambient CO₂ levels, but this difference disappeared to a large extent at elevated CO₂. The high RGR of Amaranthus at elevated CO₂ levels allowed it to overcome the difference in initial size between the two species.This study was supported by a grant from the US Department of Energy     

Binding and internalization of gold-conjugated somatostatin and growth hormone-releasing hormone in cultured rat somatotropes

Summary The synthetic peptides somatostatin (SRIF) and growth hormone-releasing hormone (GRH) were coupled directly to colloidal gold of different particle sizes. Both conjugates were biologically active in displacing the corresponding radiolabeled hormones from high affinity binding sites in pituitary membranes. Release of growth hormone (GH) from cultured anterior pituitary cells was modulated by both conjugates alone or in combination. Ultrastructural studies were performed with cells incubated at 4° C (2 h) and 37° C (2 min-2 h) with one of the labeled peptides or their combination. Somatotropes were identified by immunostaining with anti-rGH followed by protein A-ferritin, thus obtaining a triple labeling. Both hormone conjugates were internalized in different vesicles in the beginning but accumulated during longer incubation times in the same compartment. The secretory vesicles and the nucleus were not labeled by any hormone conjugate. In contrast to SRIF-gold, the uptake of GRH-gold conjugate decreased with longer incubation times. This effect could be neutralized by simulatenous incubation of the somatotropes with both regulating hormones. Hence, whereas the binding and internalization of SRIF by somatotropes do not seem to be influenced by GRH, the corresponding processes for GRH are stimulated by the presence of SRIF.     

Vasoactive intestinal polypeptide (VIP)- and neuropeptide Y (NPY)-containing nerve fibres in the penile cavernous tissue of green monkeys (Cercopithecus aethiops)

Summary The cavernous body of green monkeys contains many unmyelinated and few myelinated axons. The unmyelinated axons form terminals in the adventitia of the arteries, between trabecular muscle cells, in the interstitium, and close to endothelium cells of the sinuses. All terminals displayed predominantly small clear vesicles and very few large granular vesicles; small granular vesicles were not seen. However, in rabbit penises, terminals with many large granular vesicles are prominent. Immunohistochemistry (PAP technique) showed a dense network of VIP- and NPY-reactive fibres around the arteries and around trabecular muscles. The density of nerve fibres was particularly high around the subendothelial cushions of the helicine arteries. Double staining for NPY and VIP revealed that both peptides were colocalized. Immunocytochemistry (preembedding PAP technique) showed VIP- and NPY-reactivity in terminals with small clear vesicles; the reaction product was bound to the cytoplasmic face of different membrane types. Although the intracellular localization of the reaction product is probably due to artefactual displacement during preparation, the uniformity of the terminals questions the view that large and small granular vesicles in all species characterize peptidergic and noradrenergic terminals, respectively. The essential findings can be summarized as (1) a high degree of uniformity of nerve terminals, (2) colocalization of VIP and NPY, (3) heavy innervation of the subendothelial cushions of the helicine arteries, and (4) possible innervation of endothelial cells.