Ultraviolettes Licht und Entstehung der Hautkrebse

Ohne Zusammenfassung     

Regionally defective colonization of the terminal bowel by the precursors of enteric neurons in lethal spotted mutant mice

In order to gain insight into the process of colonization of the bowel by the neural crest-derived precursors of enteric neurons, the development of the enteric nervous system was examined in lethal spotted mutant mice, a strain in which a segment of bowel is congenitally aganglionic. In addition, nerve fibers within the ganglionic and aganglionic zones of the gut of adult mutant mice were investigated with respect to their content of acetylcholinesterase, immunoreactive substance P, vasoactive intestinal polypeptide and serotonin, and their ability to take up [³Hserotonin. In both the fetal gut of developing mutant mice and in the mature bowel of adult animals abnormalities were limited to the terminal 2 mm of colon. The enteric nervous system in the proximal alimentary tract was indistinguishable from that of control animals for all of the parameters examined. In the terminal bowel, the normal plexiform pattern of the innervation and ganglion cell bodies were replaced by a coarse reticulum of nerve fibers that stained for acetylcholineserase and were continuous with extrinsic nerves running between the colon and the pelvic plexus. These coarse nerve bundles contained greatly reduced numbers of fibers that displayed substance P- and vasoactive intestinal polypeptide-like immunoreactivity, but a serotonergic innervation was totally missing from the aganglionic bowel. During development, acetylcholineserase and uptake of [³Hserotonin appeared in neural elements in the foregut of mutant mice on the 12th day of embryonic life (E12), about the same time these markers appeared in the forgut in normal mice. By day E14, neurons expressing one or the other marker were recognizable as far distally as about 2 mm from the anus. The appearance of neurons in segments of gut grown for 2 weeks as expiants in culture was used as an assay for the presence of neuronal progenitor cells in the segments of fetal bowel at the time of explantation. Both acetyl- cholinesterase activity and uptake of [³Hserotonin developed in neuronsin vitro in expiants of proximal bowel between days E10 and E17. At all times, however, the terminal 2mm of mutant but not normal fetal gut gave rise to aneuronal cultures. In some mutant mice rare, small, ectopically-situated pelvic ganglia were found just outside aganglionic segments of fetal colon. Uptake of [³Hserotonin, normally a marker for intrinsic enteric neurites, was found in these ganglia.The experiments suppport the hypothesis that the terminal 2 mm of the gut in lethal spotted mutant mice is intrinsically abnormal and thus cannot be colonized by the precursors of enteric neurons. The defect seems to be specific in that both cells and processes of intrinsic enteric neurons, including all serotonergic and most peptidergic neurites, seem to be excluded from the abnormal region while extrinsic nerve fibers, including sympathetic and sensory axons, are able to enter the aganglionic zones. Since examination of neural progenitor cells has failed to reveal a significant proximo-distal displacement of these cells through the enteric tube during development of the murine bowel, a defect in the migration of precursor cells down the alimentary tract to the terminal gut seems unlikely to be substantially involved in the pathogenesis of aganglionosis. This conclusion is supported by the normal enteric nervous system in proximal regions of the mutant gut and the presence of enteric type neurons outside of, but at the same level as the aganglionic region.     

Ketamine protects hippocampal neurons from anoxia in vitro

Ketamine, a dissociative, general anesthetic, blocks the excitation produced by activating one class of excitatory amino acid receptors, the N-methyl-D-aspartate receptor in the rat. We have found that ketamine can protect hippocampal neurons in culture and slice from anoxia. When added to cultures immediately prior to anoxic exposure, ketamine prevented the neuronal destruction seen after a day of anoxia. Neurons appeared undamaged and had normal resting and action potentials. Adenosine triphosphate levels in ketamine-protected anoxic cultures were approximately two-thirds of normal controls. Ketamine also prevented the irreversible loss of the population spike seen in hippocampal slices after prolonged perfusion with anoxic buffer. These results suggest that ketamine may have therapeutic potential in preventing anoxic damage from stroke in man.     

Urothelial cell DNA adducts in rubber workers

Workers employed in the rubber industry appear to have a significant excess cancer risk in a variety of sites, including cancer of the urinary bladder. In this cross-sectional study, we investigated the occurrence of DNA adducts in exfoliated bladder cells of currently exposed, nonsmoking rubber workers (n = 52) and their relationship with occupational exposure estimates and acetylation phenotype (NAT2). Four DNA adducts were identified, with the proportion of positive samples (e.g., DNA samples with quantifiable levels of a specific DNA adduct) ranging from 3.8 to 79%. The highest proportion of positive samples and the highest relative adduct labeling levels were in workers involved in the production functions "mixing" and "curing," areas with potential for substantial exposure to a wide range of chemical compounds used in rubber manufacturing (P < 0.05 for adducts 2 and/or 3, compared to all other departments). No statistically significant relationships were found between identified DNA adducts and urinary mutagenicity or personal inhalable and dermal exposure estimates. Interestingly, subjects with a fast NAT2 acetylation phenotype tended to have higher levels of DNA adducts. This study suggests that rubber workers engaged in mixing and curing may be exposed to compounds that can form DNA adducts in urothelial cells. Larger studies among rubber workers should be conducted to study in more detail the potential carcinogenicity of exposures encountered in these work areas.     

Research approaches in health manpower development. Some alternatives

Traditional scientific research approaches have contributed only minimally to the resolution of problems related to the educational aspects of health manpower development. It has been suggested that this lack of impact has been due mainly to the incompatibility of the traditional approaches with the phenomena of concern--naturally occurring educational, human, and social events. The problem has been addressed in considerable detail in the literature that relates to the more general view of education, and the alternative research approaches described in this article are derived from this broader-based literature.     

Early results and follow-up of balloon angioplasty for branch pulmonary artery stenoses

Two hundred eighteen balloon angioplasty procedures were performed in 135 patients with branch pulmonary artery stenoses from June 1984 to February 1989. Arteries were dilated in patients with tetralogy of Fallot (n = 49), tetralogy of Fallot/pulmonary atresia (n = 64), isolated peripheral pulmonary artery stenoses (n = 58) and "other" lesions (the majority had truncus arteriosus or single ventricle and surgically induced pulmonary artery stenoses (n = 47). Mean age at dilation was 6.6 +/- 6.3 years (range 1 month to 38.5 years). The mean diameter of the lesion increased from 3.8 +/- 1.7 to 5.5 +/- 2.1 mm with dilation (p = 0.001). The overall success rate was 58% (127 of 218 dilations), assessed by the following criteria: an increase greater than or equal to 50% of predilation diameter, an increase greater than 20% in flow to the affected lung or a decrease greater than 20% in systolic right ventricular to aortic pressure ratio. Success did not correlate with patient age. Mean balloon to artery ratio was higher in successful (4.2) than in failed (3.0) angioplasty procedures (p = 0.0001). There were four early deaths: two of the patients had pulmonary artery rupture with angioplasty performed less than 1 month after pulmonary artery surgery. An aneurysm occurred in 11 arteries and transient pulmonary edema in four patients. At angiography performed a mean of 10 months (range 1 to 54) after dilation, the mean diameter of 57 arteries was unchanged (5.5 versus 5.4 mm). However, 5 of 32 initially successfully dilated vessels had returned to predilation size as a result of restenosis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Discovery of novel peptidic dopamine transporter ligands by screening a positional scanning combinatorial hexapeptide library.

The acute reinforcing effects of cocaine are thought by some to result from cocaine binding to the dopamine (DA) transporter, which inhibits DA uptake and increases synaptic DA levels in the mesolimbic system. Other data suggest that neurotransmitters other than DA contribute to cocaine reinforcement and addiction. These considerations illustrate the need to have additional research tools with which to test the "DA hypothesis." One strategy is to identify drugs which bind to the DA transporter (DAT ligands) but which do not inhibit DA uptake as effectively as cocaine. The purpose of the present study was to identify members of a novel structural class of DAT ligands and to characterize their interactions at the DA transporter. A positional scanning hexapeptide D-amino acid library was screened for inhibition of [(125)I]RTI-55 binding to rat caudate DA transporters. Based on the results, 12 peptides were synthesized. All 12 peptides inhibited [(125)I]RTI-55 binding to DA transporters with IC(50) values, which ranged from 1.8 microM to 12 microM. The two most potent peptides (TPI-669-1 and TPI-669-4) were prepared in larger quantities and were characterized further for activity at the DAT and 5-HT transporter. Both peptides inhibited DA and 5-HT uptake and transporter binding with IC(50)/K(i) values in the low micromolar range. In vivo microdialysis studies demonstrated that both peptides increase extracellular DA and 5-HT in the nucleus accumbens of rats. These data demonstrate that peptides can function as inhibitors of biogenic amine transport. Future work will focus on developing more potent and selective peptides. Published 1999 Wiley-Liss, Inc.     

Opioid peptide receptor studies, 11: involvement of Tyr148, Trp318 and His319 of the rat mu-opioid receptor in binding of mu-selective ligands

Previous data obtained with the cloned rat mu opioid receptor demonstrated that the "super-potent" opiates, ohmefentanyl (RTI-4614-4) and its four enantiomers, differ in binding affinity, potency, efficacy, and intrinsic efficacy. Molecular modeling (Tang et al., 1996) of fentanyl derivatives binding to the mu receptor suggests that Asp147, Tyr148, Trp318, and His319 are important residues for binding. According to this model, Asp147 interacts with the positively charged opiate agonist to form potent electrostatic and hydrogen-bonding interactions. In this study, the role of weak electrostatic and hydrogen-bonding "pi-pi" interactions of the O atom of the carbonyl group and the phenyl ring structures of RTI-4614-4 and its four enantiomers with residues Tyr148, Trp318, and His319 were explored via site-directed mutagenesis. Tyr148 (in transmembrane helix 3 {TMH3}), Trp318 (TMH7), and His319 (TMH7) were individually replaced with phenylalanine or alanine. Receptors transiently expressed in COS-7 cells were labeled with [125I]IOXY according to published procedures. Mutation of Tyr148 to phenylalanine reduced the binding affinities of some mu-selective agonists (2-7 fold) but did not alter the affinities of DAMGO, naloxone, and the non-selective opiates etorphine and buprenorphine. In contrast, this mutation significantly increased the binding affinities (decreased the Kd values) of [D-Ala2,D-Leu5]enkephalin, IOXY, and dermorphin. Mutation of Trp318 decreased opioid receptor binding to almost undetectable levels. Substitution of alanine for His319 significantly reduced binding affinities for the opioid ligands tested (1.3- to 48-fold), but did not alter the affinities of naloxone and bremazocine. These results indicate the importance of Tyrl48 and His319 for the binding of fentanyl derivatives to the mu receptor. Functional studies using the mutant receptors will provide additional insight into the mechanism of action of RTI-4614-4 and its four enantiomers.