Phagocytic activity of the stellate cells in the anuran pars intermedia

Summary In an attempt to study further the stellate cell and its functions, the ultrastructure of this cell type in the neurointermediate lobe of the bullfrog, Rana catesbeiana, was examined in both organ and dissociated-cell culture. The cytoplasmic activity of stellate cells from neurointermediate lobes incubated 3 1/2 or 5 1/2 h was greater than that of those in vivo. Mitochondria and bundles of cytoplasmic filaments were numerous, in addition to prominent, well-developed Golgi complexes with associated vesicles. The most striking ultrastructural feature was the presence of phagocytic vacuoles that contain cellular debris. The stellate cells were seen to form cytoplasmic processes that phagocytosed this extracellular debris identifiable as belonging to the secretory cells of the pars intermedia. The stellate cells from the dissociated-cell preparations were also seen to contain debris within phagocytic vacuoles. In those neurointermediate lobes transplanted for 3 1/2 to 4 days into the anterior chamber of the eye, the stellate cells demonstrated similar phagocytic ability, but the phagocytic vacuoles contained material that seemed to be at a later stage of degradation. In all three of these conditions, the stellate cells were not seen to release this cellular debris nor were they seen to undergo cell division. These glial-like stellate cells of the pars intermedia acted as macrophages in all three of these experiments. There is now, therefore, a need to determine under what conditions, if any, these stellate cells function in vivo as macrophages.Supported by NSF Program for Small College Faculty Engaged in Research at Larger Institutions and Department of Energy — Associated Western Universities Faculty Participation Program. The authors thank Dr. W. Ferris and Dr. J. Berliner for the use of the electron microscopy facilities at the University of Arizona and Nuclear Medicine Laboratory, UCLA, respectively. Warm thanks are due to Ms. Ruth Cole for technical assistance     

Ultrastructure of the dogfish adenohypophysis

Summary Granular hormone-producing cells and agranular cells (stellate cells, including giant and pericavitary cells) were electron microscopically studied in the hypophysis of the small spotted dogfish (Scyllium canicula) up to several months after hatching. Comparisons of results obtained in embryos, newly hatched fish and adults show an increase of the mean granule diameter in the four major endocrine cell types. Small granule cells which are present in all lobes are especially numerous in the ventral lobe. The structures observed in certain cavity boundary cells suggest a role in resorption and transport.     

Permeability of the amphibian pars intermedia to peroxidase injected intravascularly

To study the penetration of protein from the blood into and through the pars intermedia of anurans, the electron-dense tracer, horseradish peroxidase (HRP), was injected into the vascular system of the frog, Rana pipiens. Pinocytotic vesicles were seen along plasma membranes of the stellate cells abutting the pericapillary spaces between the pars intermedia and pars nervosa. The HRP was seen within both the pericapillary spaces and these pinocytotic vesicles. In addition, the HRP was very prominent in the extracellular spaces between adjacent stellate and/or MSH cells and around nerve endings and thus, appeared to move from the vascular spaces and into the interior of the pars intermedia. Therefore, the poorly vascularized pars intermedia may have such a route for transfer of materials throughout the gland.     

TGFbeta1 autocrine growth control in isolated pancreatic fibroblastoid cells/stellate cells in vitro

TGFβ1 is a multifunctional factor, controlling cellular growth and extracellular matrix production. Deletion of the TGFβ1 gene in mice results in multiple inflammatory reactions. Targeted overexpression of TGFβ1 in pancreatic islet cells leads to fibrosis of the exocrine pancreas in transgenic mice. In pancreatic fibrosis interstitial fibroblasts are primary candidates for production and deposition of extracellular matrix. Still, little is known about regulation of these cells during development of pancreatic disease. We established primary cell lines of pancreatic fibroblastoid/stellate cells (PFC) from rat pancreas. Investigation of rPFCs in vitro shows TGFβ1 expression by RT-PCR analysis. Mature TGFβ1 was detected in culture supernatants by immunoassay. Rat PFCs in culture possess both receptors TGFβ receptor type I, and type II, necessary for TGFβ1 signal transduction. Inhibition of TGFβ1 activity by means of neutralizing antibodies interferes with an autocrine loop and results in a 2-fold stimulation of cell growth. So far, pancreatic fibroblastoid/stellate cells in vitro were known as a target of TGFβ1 action, but not as a source of TGFβ1. Our data indicate TGFβ1 activity in rat pancreas extends beyond regulation of matrix production, but appears to be important in growth control of pancreatic fibroblastoid cells.     

Wt1 and retinoic acid signaling are essential for stellate cell development and liver morphogenesis

Previous studies of knock-out mouse embryos have shown that the Wilms’ tumor suppressor gene (Wt1) is indispensable for the development of kidneys, gonads, heart, adrenals and spleen. Using OPT (Optical Projection Tomography) we have found a new role for Wt1 in mouse liver development. In the absence of Wt1, the liver is reduced in size, and shows lobing abnormalities. In normal embryos, coelomic cells expressing Wt1, GATA-4, RALDH2 and RXRα delaminate from the surface of the liver, intermingle with the hepatoblasts and incorporate to the sinusoidal walls. Some of these cells express desmin, suggesting a contribution to the stellate cell population. Other cells, keeping high levels of RXRα immunoreactivity, are negative for stellate or smooth muscle cell markers. However, coelomic cells lining the liver of Wt1-null embryos show decreased or absent RALDH2 expression, the population of cells expressing high levels of RXRα is much reduced and the proliferation of hepatoblasts and RXRα-positive cells is significantly decreased. On the other hand, the expression of smooth muscle cell specific α-actin increases throughout the liver, suggesting an accelerated and probably anomalous differentiation of stellate cell progenitors. We describe a similar retardation of liver growth in RXRα-null mice as well as in chick embryos after inhibition of retinoic acid synthesis. We propose that Wt1 expression in cells delaminating from the coelomic epithelium is essential for the expansion of the progenitor population of liver stellate cells and for liver morphogenesis. Mechanistically, at least part of this effect is mediated via the retinoic acid signaling pathway.     

Immunohistochemical analyses of cell–cell interactions during hepatic organoid formation from fetal mouse liver cells cultured in vitro

Cell–cell interactions among cell types constituting the fetal liver such as hepatoblasts, stellate cells and endothelial cells lead to functional lobule development. The present study was undertaken to investigate hepatic histogenesis in the primary culture of E12.5 mouse livers, including cell–cell and cell–matrix interactions. Fetal livers were dispersed with protease treatment and cultured for 5 days. Cellular adhesion of each hepatic cell type, gene expression and extracellular matrix deposition were analyzed by immunohistochemistry and immunoblotting. Immunohistochemical analysis demonstrated that the primary culture of fetal liver cells contained at least hepatoblasts, mesenchymal cells, endothelial cells, hemopoietic cells and Kupffer cells. Although hepatoblasts, mesenchymal cells, and endothelial cells aggregated separately in the initial step, they then formed a spheroid together, adhering to the glass slide, which led to the formation of flattened hepatic organoids. Hepatoblasts more preferentially adhered to mesenchymal cells than endothelial cells. Several extracellular matrix depositions were seen in aggregates consisting of at least hepatoblasts and mesenchymal cells within 12 h, but were poor in those lacking hepatoblasts. These data show that the primary culture of fetal liver cells contains most cell types constituting fetal livers, and may be useful for studying cell–cell interactions during liver development.     

Regeneration of Cholinesterases in the Stellate and Normal and Denervated Superior Cervical Ganglia of the Cat Following Inactivation by Sarin

Abstract: Experiments were designed to test the hypothesis that ganglionic butyrylcholinesterase (BuChE) is derived from acetylcholinesterase (AChE). At 5 to 8 days following preganglionic denervation of the right superior cervical ganglion (SCG), cats were given sarin, 2.0 μmol/kg, i.v. At intervals of 1 h and 1, 2, 3, 6, 11, and 22 days later, they were killed, and the AChE and BuChE contents of both SCG and both stellate ganglia (StG) were assayed. The regeneration of AChE in the normal ganglia occurred in two phases: an initial rapid phase, to 25-40% of control activity in 1 day, and a slow phase, to approximately 70% of control activity in 22 days. BuChE reached approximately 85% of control activity in normal SCG and StG at 22 days. In the denervated SCG, AChE activity reached a maximum of approximately 17% of normal at 1 day, the value prior to the administration of sarin, and did not increase appreciably above this subsequently. BuChE activity in the denervated SCG reached approximately 50% of normal ganglia at 22 days. At each interval, its activity approached 55% of that of the contralateral normal SCG, the value found in the denervated SCG prior to the administration of sarin. Hence, the regeneration of BuChE appears to be independent of the presence of AChE in the neuropil. The origin of ganglionic BuChE remains obscure.     

Biochemical activity and multiple locations of particulate guanylate cyclase in Rhyacophila dorsalis acutidens (Insecta: Trichoptera) provide insights into the cGMP signalling pathway in Malpighian tubules

In insect renal physiology, cGMP and cAMP have important regulatory roles. In Drosophila melanogaster, considered a good model for molecular physiology studies, and in other insects, cGMP and cAMP act as signalling molecules in the Malpighian tubules (MTs).However, many questions related to cyclic nucleotide functions are unsolved in principal cells (PC) and stellate cells (SC), the two cell types that compose the MT. In PC, despite the large body of information available on soluble guanylate cyclase (sGC) in the cGMP pathway, the functional circuit of particulate guanylate cyclase (pGC) remains obscure. In SC, on the other side, the synthesis and physiological role of the cGMP are still unknown. Our biochemical data regarding the presence of cyclic nucleotides in the MTs of Rhyacophila dorsalis acutidens revealed a cGMP level above the 50%, in comparison with the cAMP. The specific activity values for the membrane-bound guanylate cyclase were also recorded, implying that, besides the sGC, pGC is a physiologically relevant source of cGMP in MTs. Cytochemical studies showed ultrastructurally that there was a great deal of pGC on the basolateral membranes of both the principal and stellate cells. In addition, pGC was also detected in the contact zone between the two cell types and in the apical microvillar region of the stellate cells bordering the tubule lumen. The pGC signal is so well represented in PC and, unexpectedly in SC of MTs, that it is possible to hypothesize the existence of still uncharacterized physiological processes regulated by the pGC-cGMP system.     

星状神经节电刺激建立交感神经介导的急性房颤犬模型

目的建立交感神经张力异常介导的急性房颤动物模型的方法学。方法将16只随意来源犬分为三组：对照组（n=4）,右侧星状神经节（aSG）组（n=6）和左侧星状神经节（LSG）组（n=6）,测定心房和肺静脉不同部位的房颤诱发率、房颤持续时间。结果RSG刺激显著增加右心房（RA）的房颤诱发率和持续时间（P〈0．05）,LSG刺激显著增加左心房（LA）、左上肺静脉（LSPV）、左下肺静脉（LIPV）的房颤诱发率和持续时间（P〈0．05）;与刺激时相比,RSG切除显著降低RA的房颤诱发率和持续时间（P〈0．05）;LSG切除显著降低LA、LSPV、LIPV的房颤诱发率和持续时间（P〈0．05）。结论星状神经节电刺激同时快速心房起搏6h可成功建立交感神经介导的急性房颤犬模型,星状神经节电刺激使心房和肺静脉部位的房颤诱发率显著升高,房颤持续时间显著延长,去星状神经节支配可减少房颤的发生和维持。