Trophic transfer efficiency in the Lake Superior food web: assessing the impacts of non-native species.

Ecosystem-based management relies on understanding how perturbations influence ecosystem structure and function (e.g., invasive species, exploitation, abiotic changes). However, data on unimpacted systems are scarce, therefore, we often rely on impacted systems to make inferences about 'natural states.' Among the Laurentian Great Lakes, Lake Superior provides a unique case study to address non-native species impacts because the food web is dominated by native species. Additionally, Lake Superior is both vertically (benthic versus pelagic) and horizontally (nearshore versus offshore) structured by depth, providing an opportunity to compare the function of these sub-food webs. We developed an updated Lake Superior EcoPath model using data from the 2005/2006 lake-wide multi-agency surveys covering multiple trophic levels. We then compared trophic transfer efficiency (TTE) to previously published EcoPath models. Finally, we compared ecosystem function of the 2005/2006 ecosystem to that with non-native linkages removed and compared native versus non-native species-specific approximations of TTE and trophic flow. Lake Superior was relatively efficient (TTE = 0.14) compared to systems reported in a global review (average TTE = 0.09) and the microbial loop was highly efficient (TTE > 0.20). Non-native species represented a very small proportion (<0.01%) of total biomass and were generally more efficient and had higher trophic flow compared to native species. Our results provide valuable insight into the importance of the microbial loop and represent a baseline estimate of non-native species impacts on Lake Superior. Finally, this work is a starting point for further model development to predict future changes in the Lake Superior ecosystem.

Pineal gland: influence on gonads of male rats treated with androgen 3 days after birth.

Either blinding or the injection of 1 milligram of testosterone propionate into male Sprague-Dawley rats, 3 days old, results in testes and accessory organs (seminal vesicles and coagulating glands) that are smaller than normal when the rats are 72 days old. The response to blinding is prevented by removal of the pineal gland, whereas the response to treatment with testosterone is unaffected by pinealectomy. Combination of the two treatments in 3-day- old rats causes testes to be less than one-third their normal size at 72 days of age; pinealectomy in these rats permits the reproductive organs to grow to the same size as those in the androgen-treated animals.

Quantitation of a 55K cellular protein: similar amount and instability in normal and malignant mouse cells.

Quantitative expression of a specific 55,000 (55K)-molecular-weight cellular protein was studied in two groups of mouse embryo fibroblast (clonal) cells originating from two parent clones, one of which possessed high tumorigenicity and the other of which possessed very low tumorigenicity. From the clone with low tumorigenicity, tumor lines and clones were obtained by selecting rare spontaneously transformed highly tumorigenic (mutant) cells. Cells were labeled during exponential growth for 3 h at 37 degrees C, with [35S]methionine, and the cellular 55K protein was immunoprecipitated with a monoclonal antibody and quantitated. There were low and approximately equal amounts of 55K protein in cells (clones) with both low and high tumorigenicity from both groups of cells, and there was no correlation at all between quantitative expression of 55K protein and of cellular tumorigenicity. There was approximately 10- to 20-fold more 55K protein in all simian virus 40-transformed T antigen-positive derivative clones, as shown previously. The T antigen-negative revertant tumor lines and clones obtained by an immunological in vivo selection method had low amounts of 55K protein, similar to the parent cell before simian virus 40 transformation. In all of the T antigen-negative cells, including the highly tumorigenic cells, degradation (turnover?) of the 55K protein was rapid, and a half-life of 15 to 60 min was estimated from pulse-chase experiments. In all of the T antigen-positive cells the 55K protein was stable (half-life greater than 10 h). In primary cells established from the tumors induced by highly tumorigenic cells there was a very low or no detectable amount of the 55K protein. This is in contrast to the primary cells obtained from early murine embryos in which we have reported high amounts of (stable) 55K proteins.

Evaluation of the abnormal sella turcica.

Current neurodiagnostic and endocrine evaluation for pituitary tumors, empty sella syndrome, and parasellar lesions includes new techniques. Multidirectional polytomography of the sella turcica in detecting very small pituitary adenomas is important. Also, the role of computerized axial tomography (CT scanning) in defining size and extent of sellar and parasellar lesions is increasing. There has been a decline in the use of cerebral angiography and pneumoencephalography, especially the latter, in the diagnostic workup of these patients since the introduction of CT scanning.

Observations on the cyclic nucleotide concentrations in human cerebrospinal fluid.

Previous studies have shown that the concentrations of 3', 5' cyclic adenosine monophosphate (cAMP) and 3', 5' cyclic guanosine monophosphate (cGMP) in cerebrospinal fluid (CSF), brain, or both, are increased by melanotropic peptides and catechol amines, and by cholinergic agents. The present study measured the concentrations of cAMP, cGMP, and melanotropic activity in the CSF of normal patients and in 136 subjects with various neurologic diseases. In normal lumbar CSF, concentrations (ave +/- SD) were: cAMP, 21 +/- 8 mM; cGMP, 2.4 +/- 0.5 mM; melanotropic activity, 17 +/- 6 units/100 ml. Concentrations of cAMP, cGMP, and melanotropic activity did not differ significantly (P is less than .05) from normal in the following categories of adult and pediatric patients: back pain due to vertigo of unknown cause; cerebral atrophy; cerebral vascular disease; and brain tumor subdural hematoma not causing increased ventricular pressure. Nine children with retarded psychomotor development caused by diffuse brain disease (infection, trauma, hemorrhage, degenerative process, long-standing hydrocephalus with thinning of the cerebral mantle) had subnormal levels of cAMP and melanotropic activity. These two variables were significantly correlated in the entire series of CSF samples (r=+0.55, P is less than .005). cGMP was elevated in the ventricular fluid of adult and pediatric patients when the ventricular pressure was abnormally elevated. The nucleotide's level rose as high as 50 X normal when ventricular pressure exceeded 300 mm H2O. The concentration of ventricular cGMP was proportional to that of ventricular pressure (r=+0.76, P is less than .005). The correlation was similar regardless of the type of hydrocephalus (congenital or acquired, communicating or obstructive), the age of the patient, or the nature of the underlying disease.

Fluorescence microscopy of etched methacrylate sections improves the study of mitosis in plant cells.

Etched sections of methacrylate infiltrated plant tissue [Gubler (1989) Cell Biol. Int; Rep., 13:137-145; Baskin et al. (1992) Planta, 187:405-413] offer many advantages over the more traditional squash technique of Wick et al. [(1981) J. Cell Biol. 89:685-690] for immunofluorescence microscopic investigation of the plant cytoskeleton, especially during mitosis. These advantages include: (1) unimpeded access of antibody probes, (2) confocal-like imaging without the expense of confocal equipment, (3) maintenance of organ architecture as well as intracellular structure, (4) the ability to independently examine separate focal planes with the same or multiple antibody(s) or other labelling compounds, and (5) the ability to archive unetched sections, polymerized or non-polymerized infiltrated tissue. In this paper examples of staining of various microtubule cytoskeletal and mitotic proteins are shown in a variety of methacrylate embedded plant tissues.

Computed tomography of the buccomasseteric region: 1. Anatomy.

The differential diagnosis to consider in a patient presenting with a buccomasseteric region mass is rather lengthy. Precise preoperative localization of the mass and a determination of its extent and, it is hoped, histology will provide a most useful guide to the head and neck surgeon operating in this anatomically complex region. Part 1 of this article describes the computed tomographic anatomy of this region, while part 2 discusses pathologic changes. The clinical value of computed tomography as an imaging method for this region is emphasized.

Improved detection of cerebral hypoperfusion with internal carotid balloon test occlusion and 99mTc-HMPAO cerebral perfusion SPECT imaging.

A new method that employs a cerebral perfusion imaging agent, 99mTc-HMPAO, is described for identifying those patients who clinically pass an internal carotid artery balloon test occlusion but who then may develop a cerebral infarction after permanent occlusion. Test balloon occlusion of the internal carotid artery was performed in 17 patients, and 99mTc-HMPAO was injected intravenously while the balloon was inflated. The balloon was deflated and removed approximately 15-20 min later, and single-photon emission CT (SPECT) imaging of the brain was performed. In patients with an area of focal hypoperfusion, the 99mTc-HMPAO study was repeated the next day to determine if the hypoperfusion was due to the temporary balloon occlusion or to a preexisting abnormality. All 17 patients had normal neurologic examinations at the time of the balloon test occlusion. Fifteen had symmetric perfusion on the 99mTc-HMPAO SPECT scans. Five of these had permanent internal carotid artery occlusion, and four did not develop a neurologic deficit. One patient developed an ipsilateral watershed infarction after internal carotid artery occlusion during significant intraoperative hypotension. Two patients had ipsilateral regions of hypoperfusion with the test occlusion. Both these patients had repeat nonocclusion 99mTc-HMPAO SPECT studies that were normal. One patient is being followed. The second patient had ipsilateral EEG changes associated with temporary intraoperative occlusion of the internal carotid artery during aneurysm surgery. Although the numbers are relatively small, this study suggests that this protocol may be able to predict a good outcome after permanent carotid artery occlusion as well as to identify patients who are at greater risk for developing cerebral infarction after permanent occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

The bright intervertebral disk: an indirect sign of abnormal spinal bone marrow on T1-weighted MR images.

Two phantoms were constructed and imaged for the purpose of reproducing and understanding the relatively increased signal intensity of intervertebral disks on T1-weighted MR images in three patients with diffuse vertebral metastases. The first phantom simulated a normal spine and showed that the disks and vertebral bodies were of similar intensity. The second phantom simulated an abnormal spine and showed that the disks were brighter than the vertebrae. Prolonged relaxation times from the vertebral bodies as well as manipulation of the window width and level are the factors responsible for the presence of bright disks on T1-weighted images. Variations in the window width and level can accentuate the apparent increase in signal intensity from the disks but not reverse it. Although the presence of bright disks may be subtle, recognition of this sign should raise the possibility of diffuse replacement of normal fatty bone marrow in the vertebrae.

Gadopentetate dimeglumine-enhanced MR imaging in children following surgery for brain tumor: spectrum of meningeal findings.

Gadopentetate dimeglumine-enhanced MR imaging was performed in 51 consecutive postoperative pediatric neurosurgical patients with a diagnosis of brain tumor. These studies were examined retrospectively to determine the spectrum of meningeal findings in this patient population. Patterns of enhancement were correlated with type of surgery, interval since surgery, clinical and CSF findings, and the use of radiation and steroid therapies. Normal postoperative meningeal findings include no meningeal enhancement or mild focal or diffuse dural enhancement. More moderate dural or subdural enhancement may be seen in clinically well children who have postsurgical subdural collections, or who have a remote history of serious meningeal disease (meningitis or subarachnoid hemorrhage). In all six cases in which nodular dural, leptomeningeal, or ependymal enhancement was seen, recurrent local tumor, leptomeningeal metastases, or infection were present. Leptomeningeal tumor or infection should be suspected if such patterns of enhancement are noted. Parameters that did not appear to affect the pattern of meningeal enhancement included type of surgery, interval since surgery, or therapeutic radiation.

MR measurement of intracranial CSF volume in 41 elderly normal volunteers.

A noninvasive nonplanimetric MR protocol was used to measure the total intracranial CSF volume in 41 normal subjects, aged 60-84 years, who were intensively screened to eliminate CNS disease. The protocol entailed application of MR imaging data acquired with a spin-echo sequence in a single thick slice encompassing the head. The results show a strong correlation between increased intracranial CSF volume and increasing age, and a weaker correlation between increased intracranial CSF volume and increasing total intracranial volume. The possibility of employing a CSF volume measurement as a reflection of brain atrophy to help diagnose dementia is discussed.

Duplex Doppler sonography of the carotid artery: false-positive results in an artery contralateral to an artery with marked stenosis.

Anecdotal reports have described a false-positive "jet effect" or velocity increase in the carotid artery contralateral to an artery with significant stenosis or occlusion when using duplex Doppler sonography. In this study, the frequency, significance, and possible reasons for this finding were evaluated by a retrospective comparison of duplex sonography and angiography. Twenty-three patients with unilateral 81-100% carotid artery stenosis who underwent both duplex sonography (16 Acuson, seven Quantum) and angiography were evaluated. In 14 patients, there was an accurate or slight underestimate (less than 20%) of stenosis present in the internal carotid artery contralateral to an artery with tight stenosis/occlusion. In nine, a velocity increase in the internal carotid artery resulted in overestimation (10-80%) of the actual degree of stenosis. In one of these nine patients, real-time images were sufficient to explain the velocity increase on the basis of vessel tortuosity. In one, falsely elevated velocity resulted from inaccurate assignment of the Doppler angle of incidence in a patient in whom real-time visualization of a distal internal carotid lesion was poor. In four of the nine patients, cross filling via the circle of Willis toward the side of greater stenosis occurred. However, seven of 14 patients in whom there was duplex sonography/angiography agreement or slight duplex sonography underestimation also had cross filling. Vertebral artery patency did not correlate well with the presence of a "jet effect."(ABSTRACT TRUNCATED AT 250 WORDS)

Intracranial ganglioglioma: MR, CT, and clinical findings in 18 patients.

Eighteen cases of pathologically proved intracranial gangliogliomas were reviewed to determine their MR, CT, and clinical characteristics. Seventeen patients were evaluated with contrast-enhanced CT and 14 were studied by MR imaging. Eight tumors were predominantly cystic; half of these demonstrated some contrast enhancement, and five contained calcifications. These cystic gangliogliomas were located, in order of decreasing frequency, in the cerebellum, temporal, frontal, and parietal lobes. Ten tumors were solid; eight of these showed contrast enhancement, and only one contained calcifications. Small cysts were present in one solid mass. Solid gangliogliomas occurred preferentially in the temporal lobes. On MR, the findings were nonspecific and reflected the CT findings. In one patient who received gadolinium-DTPA the lesion did not enhance. Clinically, all patients presented with nonfocal long-standing symptoms and all but three were alive an average of 18 months after the initial diagnosis. Pathologists are recognizing ganglioglioma with increasing frequency, and although its radiographic characteristics vary, it should be included in the differential diagnosis when the above-described findings are encountered.

Primary cerebral neuroblastoma: CT and MR findings in 12 cases.

A retrospective CT, MR, and clinical study was performed in 12 patients, five children and seven adults, with histologically proved primary CNS neuroblastoma. The CT and MR appearances of these neoplasia were more variable than generally recognized. Although seven tumors were predominantly intraparenchymal masses with calcification and cyst formation, five were intra- or juxtaventricular. CT was preferable to noncontrast MR both at initial diagnosis and follow-up for identification of calcification, recurrent tumor at surgical sites, and leptomeningeal disease. Noncontrast MR was useful primarily for localization of peri- and intraventricular lesions. We conclude that primary CNS neuroblastoma has a more variable radiographic appearance than is generally recognized, and that an intra- or periventricular epicenter is common.

Large hypothalamic and optic chiasm gliomas in infants: difficulties in distinction.

Hypothalamic and optic chiasm gliomas may be indistinguishable clinically, radiographically, and pathologically. Ten children with giant gliomas of the hypothalamus and optic pathway, all under age 2 years, had masses greater than 3 cm in diameter. Pathologically all proven cases (seven) were cytologically benign fibrillary astrocytomas. Previous authors have recognized the difficulty in distinguishing these lesions; in this series, using previously suggested criteria, masses of optic chiasm could not be differentiated from hypothalamic origins. Likewise, at surgery and autopsy, the origin of these large masses was indeterminate. These tumors were more aggressive, invasive, and less responsive to therapy than the relatively benign orbital and optic nerve gliomas of older children and adults.

Computed tomography of the buccomasseteric region: 2. Pathology.

Part 2 of this article concerns itself with alterations in the normal anatomy (described in part 1) by various disease processes. Ten patients are described with various facial masses. The role of computed tomography in the clinical workup of these patients is stressed.

A prospective comparison of duplex sonography vs angiography of the vertebral arteries.

A prospective blind comparison was completed between duplex sonography and angiography of the vertebral arteries. Thirty-two vertebral arteries were studied for direction of flow, degree of origin plaque or stenosis, Doppler characteristics, and vessel size. The vertebral arteries were reliably identified by imaging their course from the subclavian artery into the transverse foramina and by identifying a Doppler signal similar in waveform to the internal carotid artery. With Doppler, a 90% accuracy was obtained for direction of blood flow. Nonvisualization of origins was primarily due to vessel depth and/or tortuosity. In 12 vessel origins that were well seen with both techniques, angiography and sonography agreed in two-thirds of the cases. In four cases, origin plaque was underestimated with duplex imaging. Interestingly, no Doppler frequency or velocity elevation was identified distal to significant stenoses. One false-positive diagnosis of occlusion occurred with sonography, in which a 99% origin stenosis resulted in no detectable Doppler signal. By comparing sonography with angiography, sonography was shown to be 80% accurate in determining vertebral artery size. Our preliminary results indicate that duplex scanning is a reasonably accurate screening technique for size, patency, and direction of blood flow in the vertebral arteries. Duplex evaluation of the vertebral artery origin was limited by vessel depth, tortuosity, and calcifications.

Diagnosis of cerebral metastases: double-dose delayed CT vs contrast-enhanced MR imaging.

For patients suspected of having cerebral metastases, double-dose delayed CT (DDD-CT) has proved significantly more sensitive than CT scans obtained immediately after administration of a lesser dose of iodinated contrast material. Previous reports confirm the advantages of postcontrast MR imaging over contrast-enhanced CT, but data comparing DDD-CT and contrast-enhanced MR have not been reported. This study describes comparative imaging results in 23 patients who had contrast-enhanced MR imaging to clarify equivocal findings on DDD-CT studies. Contrast-enhanced MR demonstrated more than 67 definite or typical parenchymal metastases. T2-weighted MR revealed more than 40, while DDD-CT revealed only 37 typical metastatic lesions. Three patients had five or fewer lesions on DDD-CT and lesions "too numerous to count" on MR. The frequency of equivocal or unconvincing lesions was similar on DDD-CT (11) and contrast-enhanced MR (10). On T2-weighted images, we noted a substantially higher number of equivocal lesions (19), fewer definite metastases, and a number of definite metastases that had no corresponding lesion on the enhanced studies, confirming the inability of T2-weighted imaging to specifically identify cerebral metastases. In one case, multiple tiny lesions on T2-weighted images were not apparent on DDD-CT scans and were recognized only in retrospect on contrast-enhanced MR images. In this series, MR with enhancement proved superior to DDD-CT for lesion detection, anatomic localization of lesions, and differentiation of solitary vs multiple lesions. Cost-benefit considerations precluded a comparison between the two techniques in all patients suspected of having cerebral metastases.(ABSTRACT TRUNCATED AT 250 WORDS)

Flow-sensitive MR imaging of ventriculoperitoneal shunts: in vitro findings, clinical applications, and pitfalls.

To determine ventriculoperitoneal shunt patency during routine MR imaging of the head, 23 patients were studied with T1-weighted fast-field-echo scans. Without knowledge of the results of previous MR/CT studies or of the patients' clinical history, we reviewed the fast-field-echo studies and divided them according to those judged to have shunt flow (18) and those judged not to have flow (five). Fast-field-echo sequences showed high signal intensity, consistent with CSF flow and shunt patency in 17 medium-pressure systems and one high-pressure system. No signal was seen in five patients with high-pressure valve shunts. Combined clinical evaluation and MR/CT studies showed that three patients had probable shunt malfunction. One patient had true shunt malfunction; and although malfunction was thought to be present in two symptomatic patients, surgical revision showed the shunts to be patent. The possibility of temporary shunt obstruction is postulated to explain the clinical and MR findings in those two cases. The remaining two cases (9% of the patients) had no clinical evidence of shunt malfunction, and the MR findings probably reflected periodic CSF flow. One patient had an intracranial segment that was not connected and showed no flow on MR. No false-positive results (apparent flow in a nonfunctioning shunt) occurred. Using a standard medium-pressure shunt system, we constructed and imaged a phantom, which confirmed our clinical observations. T1-weighted fast-field-echo sequences may be useful in assessing patency of medium-pressure CSF shunt systems.

MR of Leigh's disease (subacute necrotizing encephalomyelopathy).

MR images of three patients with Leigh's disease (subacute necrotizing encephalomyelopathy) were compared with CT findings. In all patients typical lesions in the basal ganglia were identified with both MR and CT. In two patients MR permitted identification of additional lesions not detected with CT. In one patient progression of MR abnormalities over a 4-month period correlated well with clinical deterioration in neurologic status. T2-weighted images with a repetition time (TR) greater than 1950 msec and an echo time (TE) greater than or equal to 60 msec or inversion-recovery images with a 50-msec TE, 1213-msec inversion time, and 3000-msec TR were advantageous in identifying multiple necrotic lesions in the brainstem, deep gray matter, periventricular white matter, and cerebral cortex. In this series MR was more sensitive in detecting and localizing multifocal necrotic lesions of Leigh's disease than CT was, and thus may be a useful diagnostic tool for patients with the appropriate clinical and laboratory abnormalities.