In tissues from Crohn's disease patients, the density of interstitial cells of Cajal was reduced throughout the tunica muscularis in comparison to control small intestines. The disturbance of intestinal motility that occurs in patients with Crohn's disease may be a consequence of the loss of or defects in specific populations of interstitial cells of Cajal within the tunica muscularis.
The digestive gland of Pecten muximus consists, as in other lamellibranchs, of numcrous blindcnding tubules which communicatc with the stomach by partially ciliated main ducts and non ciliated secondary ducts. Thc non-ciliated cells of the main ducts arc charactcrizcd by a well developed brush border constituted by high and dcnsc microvilli and a strong pinocytotic activity. Ciliatcd and non ciliatcd cclls havc a very similar fine structure. The digcstivc tubulcs have a large lumen and contain digestive cells at diffcrcnt stagcs of absorption , digestion and excrction, onc part of thc tubules being functional while the other is disintcgrating. Thc dark crypts contain the flagellated secrctory cclls, charactcrizcd by a well developed granular cndoplasmic rcticulum, and the young immature cells which may replacc both thc sccretory and digestive cells. The numerous lipid droplcts occurring in thc digestive duct cells and in the digcstivc cclls rcvcal the lipid storage function of the digestivc gland. Several enzyme activitics involvcd in digestion have been localized in the digcstivc gland. High amylase activity and cellulase and lysozyme activitics have been found in the ducts and in the tubules, whcrcas no protcolytic activity could be detected histochemically. Somc intraccllular peptidases and glycosidases have been localized in thc cclls of the digestive gland, especially in the brush-bordcr cclls of the ducts and in the functional part of the tubules. High alkaline and acid phosphatase activities are displaycd by the duct brush-border cells and the digestive and secretory cclls. These results show the main role of the digestive gland, both in cxtracellular digestion (secretion of thc digcstivc enzymes) and in absorption and intracellular digestion and providc information on the respective functions of thc different cells within these processes.
Aphid counts were made on a maize field over three years (1985)(1986)(1987) in western France. Metopolophium dirhodum Wlk. and Sitobion avenae F. were present from early June. Numbers were maximal in late July and the species disappeared in August. Rhopalosiphum padi L. numbers fluctuated differently each year. In 1985 and 1986 they were very low in the first part of July, then increased appreciably to the end of August, reaching very high levels in September 1985. In 1987, R. pad2 colonised the field from July, it reached a maximum in Au ust, but was no longer abundant in September-October. For all three aphid species there was a goof correlation between weekly counts on maize and corresponding suction trapping of alates. Percentage of maize infected by barley yellow dwarf virus (BYDV) was also recorded over three years. Levels varied between 20-30 YO in 1985 and were 0 % and 1 % in 1986 and 1987 respectively. BYDV infection pathways for maize, together with the role of this crop in the annual cycle of the aphid vector and the virus are discussed.Monique Henry and C. A . Dedvyver Material and methodsObservations were made on a silage maize field (c.v. DEA), 10 km west of Rennes, on the INRA experimental farm at Le Rheu. Aphid samplingAphid population numbers were estimated from field counts between June and the end of September.Counts were made at one to three weekly intervals, on one maize stalk every 10 m over line transects, spaced at 10 m intervals. O n each transect the first plant sampled was selected randomly. The first two counts were made on 50 plants and the others on 10 plants in 1985 and 25 in 1986 and 1987. Species, number and position were recorded for all aphids on the sampled plants. A suction trap at Le Rheu (Rkseau Agraphid, ROBERT and CHOPPIN DE JANVRY 1977), provided ca ture data for alate aphids over the three years. Time was measured in normalised weeks (LEWIS ancfTAvLoR 1967). Estimation of BYDV infection levels on maizePlant samples were collected during each aphid count. In 1985, total leaf material from the plant was sampled, whereas, in 1986 and 1987, only single leaves were sampled. These were taken from the area where virus concentration was highest (HENRY 1987). Samples were stored at -18 "C before assay by ELIZA (Enzyme linked immunosorbent assay).Records of symptoms of reddening similar to that decribed by STONER (1977) were made.In October 1984October , 1986October and 1987, samples were collected in ten maize fields in the Rennes area. Aphid colonisation was recorded for each and one leaf taken from 5 (1984), 10 (1986) or 100 (1987) plants. Leaves were assay by ELISA. ELISA procedureELISA procedure followed the method described by CLARK and ADAMS (1977). One grame (mean) samples were ground in phosphate buffer 0.06M (pH = 7.2) with 1 % added powdered milk (HENRY 1987). This extraction buffer attenuates background apparent with the usual buffer (PBS-T-PVP). The immunoglobulins used (obtained by BIOREBA') react essentially with "PAV-like" strain of BYDV. However, weak reactions...
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