Biomedical subjects
Publications and source records attributed to M Behan.
The ultrastructure of the fat body of Aedes aegypti was followed from emergence through a blood meal. Changes in the volume of protein granules and lipid droplets were also examined. The relationship of these events to the known endocrinology of vitellogenin synthesis in mosquitoes is discussed.
Fatty tissues and tumors have been described as characteristically cyst-like on ultrasound examination, with relatively few internal echoes. The authors offer several examples of lipomatous masses and tissues which are markedly echogenic. In vitro studies suggest that this is an inherent property of body fat and is not due to coexistent fibrous tissue or tumor vascularity. The echogenicity of fat has important implications for diagnostic ultrasound: (a) the presence of fat in tissues and masses may be demonstrated by ultrasound, and (b) because the high-level internal echoes blend with the echo pattern of bowel gas and retroperitoneal fat, lipomatous abdominal masses may easily be overlooked.
The common hepatic and proximal common bile ducts (common duct) lie anteriorly and generally to the right of the portal vein in the porta hepatis. This constant anatomic relationship can be used to demonstrate the common duct and to differentiate it from the portal vein by gray scale ultrasonography. The patient is scanned longitudinally from the right anterior abdominal wall with the ultrasound beam directed posteromedially until two tubular structures are demonstrated in the porta hepatis. The more anterior tubular structure in this projection is the common duct. If the common duct is less than 3 mm in diameter, it may not be clearly delineated. In these cases the absence of common duct dilatation can be inferred. The usefulness of this view for detecting common duct dilatation was evaluated in a series of 101 consecutive cases proven by surgery, autopsy, or cholangiography. The overall accuracy was 96% (four false negative studies; no false positives). We conclude that sonography should be the imaging procedure of choice for suspected extrahepatic biliary obstruction if the serum bilirubin level precludes intravenous cholangiography.
The excretion of ioglycamate in the bile of the rhesus monkey was measured at 5% and at 100% bile diversion following an intravenous bolus injection of ioglycamate. At 100% diversion the bile volume was reduced and the concentration of ioglycamate was increased, but the quantity excreted was unchanged. A similar study using iodipamide reported previously gave the same result. When the ioglycamate was given by intravenous infusion, the effect of 100% bile diversion was quite different. The concentration of ioglycamate in the bile was unchanged by the bile diversion but the excretion was reduced. These results indicate that the transport maximum for the excretion of ioglycamate in bile is not a constant and is reduced by interruption of the enterohepatic circulation of bile salts. The maximum concentration of ioglycamate in bile was constant and was independent of the reduction in bile salt output produced by 100% bile diversion. Following a single bolus injection however, the reduction in bile flow produced by 100% bile diversion increased the biliary concentration of ioglycamate. These results suggest that the excretion of ioglycamate is limited by a maximum concentration rather than a transport maximum. The maximum rate of transport (Tm) is dependent on two factors--the maximum concentration of ioglycamate in the bile and the rate of bile flow. The maximum concentration is achieved by an infusion technique and not by a single bolus injection and this supports the view that an infusion technique should be used for intravenous cholangiography.
Myelolipoma of the adrenal gland is a rare tumor composed of varying proportions of fat and bone marrow elements. In about half of the reported cases with radiologic findings the mass was radiolucent, indicating the presence of fat; the remainder were of soft tissue density or calcified. Arteriography is of limited value in diagnosis, since myelolipomas are typically avascular. With the advent of gray scale ultrasound and computed tomography (CT), fat can be detected in lesions which do not appear radiolucent on radiographs. Two cases of myelolipoma are reported in which ultrasound showed a markedly echogenic mass, an appearance chracteristic of lipomatous tumors. In the second case, the mass was of soft tissue density on radiographs, markedly echogenic on sonogram, and definitively fatty on CT scan. Ultrasound and CT are valuable techniques for making a preoperative diagnosis of this tumor.
The excretion of the biliary contrast medium meglumine ioglycamate into the bile is limited by a hepatic transport maximum system. A minimum plasma concentration, approximately 800-1,000 microgram/ml is required to maintain maximum excretion of contrast medium. Serial measurements of the plasma levels of ioglycamate were made on 21 patients during routine intravenous cholangiography, using different infusion rates. An infusion regimen using 10 mg/kg/min for 15 min, then 60 mg/min is described, which rapidly elevates the plasma concentration to the optimum level and maintains it at, or slightly above this level.
A comparison is presented of the image quality obtained with a 70 mm Ge(Li) detector scanner and with routine techniques based on NaI (Tl) detectors. One hundred and sixty-five pairs of brain scans have been examined for which the patients have been scanned with both Ge(Li) and NaI (Tl) detectors. It is concluded that no major difficulties exist in introducing Ge(Li) scanners and that while a comparison of scans from different instruments is difficult there is evidence that improved diagnostic information may be obtained from scanners with Ge(Li) detectors.
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The value of sonography in the diagnosis of renal masses in a series of 119 consecutive histologically confirmed cases is presented. Sonography correctly identified 92% of the cystic and 90% of the solid renal masses. Causes of incorrect diagnoses included lesions smaller than 2 cm, masses in the left upper pole, diffusely infiltrating urothelial tumors, echogenic fatty lesions (early in our experience), and acute abscesses and hematomas. Angiography in the same series of cases correctly diagnosed 80% of the cystic and 88% of the solid renal masses. Avascular lesions were the main cause for equivocal or incorrect angiographic diagnoses. We conclude that sonography is more definitive than angiography in the diagnosis of avascular masses, while angiography excels when the lesion is vascular or small. Combining the sonographic and angiographic findings allowed accurate diagnosis in over 99% of the cases.
We investigated the effect on prostate carcinoma detection of 12 versus 6 core biopsies at transrectal ultrasound (TRUS), when all biopsies are taken from the lateral peripheral zone. This was a prospective study of 202 consecutive men, ages 51 to 81 years, referred for TRUS-guided biopsy of the prostate gland. All patients had prostate serum antigen levels higher than 4.0 ng/mL and/or abnormal digital rectal examination. In each case three biopsies were taken from the peripheral zones of the right and left lobes of the prostate. Biopsies were taken at the apex, midway between the apex and the base, and at the base. A second set of biopsies was taken from the same regions and analyzed separately. In total, twelve biopsies were taken. Note was subsequently made of additional carcinoma diagnosis increase in Gleason grade, and new diagnoses of carcinoma in the opposite side of the gland diagnosed on the second set of biopsies alone. Seventy-eight of the 202 men (38.6%) had prostatic carcinoma diagnosed on TRUS-guided biopsy. Of these 78 patients, six were diagnosed with malignancy based on the second set of biopsies alone, a 2.9% increase in the 202 patients, representing an increased yield of 8.3% (95% confidence interval, 5.3-28.6%). In nine cases (12.5%; 95% confidence interval, 6.2-22.9%), the Gleason tumor grade was increased on the second set of sextant biopsies; in an additional nine cases, carcinoma was detected in the opposite side of the gland. There were two complications (1%). A 12- versus six-core biopsy strategy for TRUS-guided biopsy of the prostate gland improves detection and histologic grading of prostate carcinoma. The added benefit of additional biopsies was lower in this series than in some prior studies using extensive biopsy protocols.
The mammalian superior colliculus is involved in the transformation of sensory signals into orienting behaviors. Sensory and motor signals are integrated in the colliculus to produce movements of the eyes, head, and neck. While there is a considerable amount of information available on the afferent and efferent connections of the colliculus, almost nothing is known about its intrinsic circuitry, particularly that of its deepest layers. It is likely that intrinsic connections in these deeper layers of the colliculus participate in the sensory-motor transformations leading to orienting movements. In this study, we used the neuroanatomical tracer biocytin to label small groups of neurons in the deeper layers of the cat superior colliculus and examine the distribution of their axons and terminals. We found a broadly distributed network of intrinsic projections throughout the deep layers of the superior colliculus. While the majority of terminals were found in a 1-2 mm radius around the injection site, labeled terminals were found throughout the deep layers of the colliculus up to 5 mm from the injection site. In addition, these injections sometimes labeled terminals in the superficial tectum. Extensive projections were demonstrated by the more superficial injections, but few terminals were found when injections were confined to the deepest layers of the colliculus. There was no evidence of anisotropy in the distribution of terminals from injections made at different rostrocaudal or mediolateral locations; neurons located in any one region in the colliculus could potentially influence any other region. This network of intrinsic connections in the cat superior colliculus could provide a means for deeper-layer efferent neurons to associate, and to modulate or coordinate their output. Interneurons could also provide a substrate for mutual inhibition between neurons at the rostral pole of the colliculus that are active during fixation, and more caudally located neurons whose activity is associated with saccadic eye movements.
Immunocytochemical techniques have been used to examine the distribution of substance-P (SP)-labeled neurons in the superior colliculus of rats from birth to adulthood. At birth, there are almost no SP-immunopositive neurons in the tectum. A small number of SP neurons appear over the next several days. However, the vast majority of SP neurons appear between P9 and P10, and by P12 have attained adult-like numbers and distribution. Neurons are confined to the superficial layers of the colliculus, specifically the upper two-thirds of the stratum griseum superficiale (SGS). There is no indication of a differential developmental sequence along rostrocaudal or mediolateral axes. Neuronal types can be distinguished as early as P6 and include horizontal, vertical, and multipolar cells. Substance-P-immunoreactive axons and boutons are also present in the superior colliculus at birth, and are for the most part confined to the deep layers. Boutons are generally of the en-passant type. The density of labeled axons and boutons increases progressively, and by P10 there is an almost adult-like lamination and patchiness. In the adult, labeled axons and boutons are most dense in the stratum opticum and stratum griseum intermedium. Bridges of dorsoventrally oriented labeled axons span the relatively label-poor stratum album intermedium. SP label in the stratum griseum profundum is dense and patchy, and there is also dense label in the stratum album profundum bordering the periaqueductal grey. The role of substance-P-labeled neurons in the superior colliculus is still a matter of speculation. The findings of this study indicate that SP neurons may play a role in intrinsic collicular circuitry.
G-protein-mediated inhibition of Ca2+ current is ubiquitous in neurons, and in synaptic terminals it can lead to a reduction in transmitter release (presynaptic inhibition). This type of Ca2+ current inhibition can often be relieved by prepulse depolarization, so the disinhibition of Ca2+ current can combine with Ca2+ -dependent mechanisms for activity-induced synaptic facilitation to amplify this form of short-term plasticity. We combine a mathematical model of a G-protein-regulated Ca2+ channel with a model of transmitter secretion to study the potential effects of G-protein-mediated Ca2+ channel inhibition and disinhibition on transmitter release and facilitation. We investigate several scenarios, with the goal of observing a range of behaviors that may occur in different synapses. We find that the effects of Ca2+ channel disinhibition depend greatly on the location and distribution of inhibited channels. Facilitation can be greatly enhanced if all channels are subject to inhibition or if the subpopulation of channels subject to inhibition are located closer to release sites than those insensitive to inhibition, an arrangement that has been suggested by recent experiments (Stanley and Mirotznik, 1997). We also find that the effect of disinhibition on facilitation is greater for longer action potentials. Finally, in the case of homosynaptic inhibition, where Ca2+ channel inhibition occurs through the binding of transmitter molecules to presynaptic autoreceptors, there will be little reduction in transmitter release during the first of two successive bursts of impulses. The reduction of release during the second burst will be significantly greater, and if the unbinding rate of autoreceptors is relatively low, then the effects of G-protein-mediated channel inhibition become more pronounced as the duration of the interburst interval is increased up to a critical point, beyond which the inhibitory effects become less pronounced. This is in contrast to presynaptic depression due to the depletion of the releasable vesicle pool, where longer interburst intervals allow for a more complete replenishment of the pool. Thus, G-protein-mediated Ca2+ current inhibition leads to a reduction in transmitter release, while having a highly variable amplifying effect on synaptic facilitation. The dynamic properties of this form of presynaptic inhibition are very different from those of vesicle depletion.