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Biomedical subjects

G Geiger

Publications and source records attributed to G Geiger.

At least 55 records · Page 3Linked to original sources
PubMed1983

Neuronal organization in fly optic lobes altered by laser ablations early in development or by mutations of the eye.

The role of afferent and efferent connections in the differentiation of optic lobe interneurons was investigated by using laser ablations of neuronal precursors in the brain of Musca domestica and analysis of two eye mutants of the same species. The first mutant, split eye, had no connections between the retina and the optic lobes. In this case the optic lobes were drastically reduced in volume and the neural organization within the neuropil regions was altered. The other mutant, spindle, had reduced retinae that innervated reduced optic lobes with a normal-appearing orderly arrangement of neurons. In addition disordered neuropil, composed of identified visual interneurons, was found that had no afferent innervation. Three main types of alterations resulting from laser ablations were analyzed. These ablations removed entire neuropil regions or parts of these: (1) removal of the first optic neuropil region (the lamina) resulting in receptor axons projecting directly to the second neuropil (the medulla) and sprouting of medulla neurons toward the receptor layer; (2) removal of one part of the third optic neuropil (the lobula plate) and severe alteration of the other part (the lobula) resulting in sprouting of lobula neurons into the medulla neuropil; and (3) removal of the entire optic lobe resulting in reduction of the volume of the lateral midbrain and photoreceptor axons forming a tangle beneath the retina. Our findings confirm that afferent retinal input is essential for normal differentiation and maintenance of many optic lobe interneurons. Furthermore, it was seen that a normal columnar organization of the neuropils and the dendritic patterns of visual interneurons are dependent on afferent inputs. A common response to removal of inputs was a reorganization of axonal and dendritic projections.

Animals↗
PubMed1983

Differentiation of fly visual interneurons after laser ablation of their central targets early in development.

To test the differentiation of visual interneurons that had their targets removed before axogenesis, we ablated neuronal precursors in brains of first instar fly larvae by using a laser microsurgery unit. We describe ablations that resulted in the elimination of the third neuropil region (the lobula complex) of the optic lobes. Neural differentiation in the more peripheral second and first neuropil regions (the medulla and the lamina) was thus studied in the absence of the lobula complex. It was found that the medulla neuropil differentiated with normal columnar and layered organization. The neuropil, however, folded along its central surface. The only connection between the medulla and more central neuropil (the midbrain) was via a bundle of axons (the Cuccati bundle) present also in the normal optic lobes. Some types of neurons that normally connect the medulla and the lobula complex could be identified. These appeared to end in a disorganized neuropil mass in the center of the folded medulla. The differentiation of the lamina neuropil also appeared normal in flies with the lobula complex eliminated and the medulla folded. Also, in optic lobes where the medulla was severely disorganized and/or reduced due to laser ablations, the lamina neuropil appeared more or less normal. The results suggest that lamina and medulla nerve cells can differentiate and develop normal neuropil patterns in absence of their appropriate targets.

Animals↗
PubMed1983

[Extra-anatomic bypass in injuries of the subclavian artery].

11 cases of subclavian vessel injuries are reported. The problems of operative approach are discussed. Two out of 11 cases have been operated on by extraanatomical bypass from the common carotid artery to the subclavian or axillary artery. There resulted no problems by temporarily clamping the common carotid artery, no postoperative carotid steal syndrome was seen. In our opinion carotid-subclavian bypass - well known as standard procedure in chronical disease of the proximal subclavian artery - can also be applied in case of acute trauma of the subclavian artery. Thus the direct riskfull approach for these often polytraumatized patients can be avoided.

Adult↗
PubMed1980

[Leading symptom: esophageal varices hemorrhage in a young man].

Indicating sign: Esophageal hemorrhages in adolescence. Congenital hepatic fibrosis and infantile polycystic disease of the kidneys. A 17-year-old patient with hypersplenism and signs of portal hypertension came to clinical treatment after an esophageal hemorrhage. Rare syndrome of congenital hepatic fibrosis with portal hypertension and splenomegaly, with infantile polycystic disease of the kidneys and aneurysms of the splenic artery was recognizable by means of ultrasound, laparoscopy and angiography. Therapeutically splenorenal shunt and splenectomy were carried out.

Adolescent↗
PubMed1980

[Morphological evaluation of joint-crossing expanded PTFE prosthesis (author's transl)].

Ten expanded polytetrafluoroethylene (PTFE) vascular grafts were implanted in dogs crossing the joint, performed as iliofemoral bypass. After 1, 3, 6, and 9 months the grafts were studied by light microscopy, scanning, and transmission electron microscopy. There was a good patency of all straight prostheses. The pre- and postkink areas showed thrombosis leading to stenosis. After 9 months endothelium was spread over all other parts of the luminal surface, including the kink area. Intramurally there was a focal ingrowth of fibroblastic cells with the characteristics of myocytes.

Animals↗
PubMed1978

[Pericardial tamponade, an acute emergency during transvenous cardiac pacemaker implantation (author's transl)].

Three cases of right ventricular perforation and acute pericardial tamponade during transvenous pacemaker implantation and one case of chronic electrode penetration are reported. Successful repair was achieved via pericardiotomy in all cases with acute tamponade. Fragility of the myocardium in the elderly is considered to be the major reason for this complication which may occur despite the use of flexible electrodes and correct surgical technique. The relatively small intervention of inferior pericardiotomy appears to be the therapy of choice in case of tamponade. This approach should be feasible when transvenous pacemakers are implanted. Immediate availability of general anesthesia and postoperative intensive care appears to be manatory.

Acute Disease↗
PubMed1975

The Müller-Lyer figure and the fly.

In the Müller-Lyer illusion two horizontal line segments of equal length are perceived by humans as unequal. The gaze of a fly presented with Müller-Lyer figures corresponds to human eye movements and human (illusionary) evaluations of the segment lengths. It is suggested that a theory similar to the phenomenological theory which accounts for the fly's gaze may account for the human eye's movement during an observation of Müller-Lyer figures.

Animals↗