Fine-scale population differentiation and gene flow in a terrestrial salamander (Plethodon cinereus) living in continuous habitat.

Several recent studies have shown that amphibian populations may exhibit high genetic subdivision in areas with recent fragmentation and urban development. Less is known about the potential for genetic differentiation in continuous habitats. We studied genetic differentiation of red-backed salamanders (Plethodon cinereus) across a 2-km transect through continuous forest in Virginia, USA. Mark-recapture studies suggest very little dispersal for this species, whereas homing experiments and post-Pleistocene range expansion both suggest greater dispersal abilities. We used six microsatellite loci to examine genetic population structure and differentiation between eight subpopulations of red-backed salamanders at distances from 200 m to 2 km. We also used several methods to extrapolate dispersal frequencies and test for sex-biased dispersal. We found small, but detectable differentiation among populations, even at distances as small as 200 m. Differentiation was closely correlated with distance and both Mantel tests and assignment tests were consistent with an isolation-by-distance model for the population. Extrapolations of intergenerational variance in spatial position (sigma(2)<15 m(2)) and pair-wise dispersal frequencies (4 Nm < 25 for plots separated by 300 m) both suggest limited gene flow. Additionally, tests for sex-biased dispersal imply that dispersal frequency is similarly low for both sexes. We suggest that these low levels of gene flow and the infrequent dispersal observed in mark-recapture studies may be reconciled with homing ability and range expansion if dispersing animals rarely succeed in breeding in saturated habitats, if dispersal is flexible depending on the availability of habitat, or if dispersal frequency varies across the geographic range of red-backed salamanders.

DDAVP use in patients undergoing transsphenoidal surgery for pituitary adenomas.

BACKGROUND: Disorders of fluid and sodium regulation, often termed "diabetes insipidus," are a frequent occurrence following surgery for pituitary adenomas. The present study was undertaken to identify the incidence of diabetes insipidus after pituitary surgery and its associated factors. METHODS: A retrospective review of the medical records 300 patients who underwent transsphenoidal surgery for pituitary adenoma was undertaken. Information regarding patient gender, perioperative serum sodium levels and urinary output volumes, tumor size, previous pituitary surgery, tumor subtype, and the use of DDAVP was gathered. A multivariate statistical analysis was performed. FINDINGS: Follow-up data were available on 288 patients. During the inpatient postoperative hospital stay, DDAVP was administered to 19% of all patients and 16% of patients not taking DDAVP preoperatively. Of patients with normal fluid/sodium regulation preoperatively, DDAVP was prescribed for 9% at discharge and 4% at 6 weeks postoperatively. Only 1.4% of patients were taking vasopressing replacement at the time of last follow-up. Significant correlations were found between gender, previous surgery, serum sodium levels, and urine volumes at various time points. Immunohistochemical type of tumor and tumor size were not related to DDAVP requirement. CONCLUSIONS: Transient hypotonic polyuria is frequently encountered after pituitary surgery. However, only a small number of patients will develop a long-term requiring for ongoing medical treatment. Previous surgery, female gender, and elevated serum sodium and urine volumes in perioperative period were associated with DDAVP requirement.

Ganglion cell-containing tumors of the pituitary gland.

The ganglion cell-containing tumors of the pituitary are rare lesions of undetermined histogenesis and nosology. A review of the literature revealed 42 such tumors, including the 3 cases described below. On the basis of this review, the tumors were divided into two histologic groups, one consisting of both adenomatous and gangliocytic elements (32 cases), and the other of the gangliocytic component only (10 cases). The first group of tumors were more common in females (23 of 32 cases) and were often active endocrinologically (28 of 32 cases), and acromegaly was the most common manifestation (19 cases). The second group was also more common in females (7 of 10 cases) but was less frequently active endocrinologically (3 of 19 cases). We review histologic and immunocytochemical findings in these tumors and discuss their histogenesis. We propose that the term mixed pituitary adenoma-gangliocytoma be used for the first group and gangliocytoma for the second. The two groups should be kept separate until their histogenesis is better understood.

The surgical workstation: surgical planning using generic software.

Computer software for rendering and display of three-dimensional data is becoming readily available for all types of computers. Such programs typically accept data from any source, compute a three-dimensional volume of data, and display it with a variety of rendering options. Although not specifically designed for medical image processing, these programs can provide very detailed and finely rendered images that are useful for surgical planning. We use one such program to display data from standard computed tomography scans, which gives us a photorealistic three-dimensional view of patient anatomy. This view can be modified to render tissues transparent, translucent, or opaque, and thus allows the surgeon to selectively enhance bony architecture, tumors, or other details. Images can be rotated, sliced, and displayed in the surgical position. Image animation can be added to facilitate the display of complex anatomic relationships. Our experience with this technology suggests that such programs can provide the basis for personal surgical workstations for medical image analysis and surgical planning. Further development of such generic imaging systems should allow this useful technology to become widely available for surgical planning and education. We discuss our experience with a typical generic imaging workstation.

Computed three-dimensional reconstruction of median-eminence capillary modules: image alignment and correlation.

Image alignment is an absolute requirement for three-dimensional (3-D) reconstruction from serial sections, and Fourier correlation is the most powerful way to compute alignments. The rotational and translational components of misalignment can be corrected by an iterative correlation procedure, but for images having significant differences, alignment can fail with a likelihood proportional to the extent of the differences. We found that translational correction was determined much more reliably when low-pass filters were applied to the product transforms from which the correlations were calculated. Rotational corrections based on polar analyses of the auto-correlations of the images instead of on the images directly contributed to more accurate alignments. These methods were used to generate 3-D reconstructions of brain capillary modules from serial-section mosaics of digitized transmission electron micrographs.

Computed alignment of dissimilar images for three-dimensional reconstructions.

Three-dimensional reconstructions from serial section images require the accurate registration of those images. Image correlation is the most powerful computed alignment method and its performance on identical images, or parts thereof, has been thoroughly studied. Correlation alignments of complex, dissimilar images can fail, however, with a likelihood proportional to the magnitude of the differences. We report that alignments can be computed more reliably and more accurately (higher-valued correlation coefficients) by the combined use of lowpass-filtered product transforms (from which the correlation functions are formed), autocorrelation correction of rotational misalignment, and covariance correction of translation misalignment. A simple rule is proposed for the lowpass filter cutoff radius depending on measures of the images' differences. These methods are demonstrated with a reconstruction of a capillary loop in the median eminence of the hypothalamus.

Vascular responses of choroid plexus during hypercapnia in rats.

The response of blood flow to choroid plexus (CPBF) during hypercapnia is controversial. The goal of this study was to determine the effect of hypercapnia on CPBF in unanesthetized rats. Rats breathed air or a mixture of 5-8% CO2 in air, and CPBF was measured with [14C]isopropyliodoamphetamine and quantitative autoradiography. In hypercapnic rats [arterial PCO2 61.6 +/- 1.6 (SE) mmHg; n = 7] CPBF was similar to that of normocapnic control rats (525 +/- 39 ml.min-1.100 g-1; arterial PCO2 42.7 +/- 0.6 mmHg; n = 5). In contrast, blood flow to cerebral cortex increased 67% during hypercapnia. CPBF in normocapnic rats that were treated with phentolamine was similar to untreated normocapnic and hypercapnic rat CPBF. However, during hypercapnia, CPBF in phentolamine-treated rats increased 29%. Responses were similar in blood flow to choroid plexus of lateral, third, and fourth ventricles. Our findings indicate that hypercapnia has no effect on CPBF when alpha-adrenergic receptors are intact. In contrast, after blockade of alpha-adrenergic receptors, hypercapnia increases CPBF. These findings suggest that, during hypercapnia, levels of sympathetic activity or blood-borne catecholamines are increased that prevent increases in CPBF.

Spinal cord ganglioglioma presenting as hydrocephalus.

We report a case of a 5 year old boy with a spinal cord ganglioglioma and hydrocephalus. The insidious onset with back stiffness and hamstring tightness, the diagnosis by magnetic resonance imaging, and the treatment by total excision is described. An adequate proven explanation for the hydrocephalus is lacking. Mechanisms which have been proposed include impaired cerebrospinal fluid absorption from increased cerebrospinal fluid protein, and arachnoiditis.

Role of catecholamines in regulating ovine median eminence blood flow.

Blood flow was measured in the ovine median eminence and neural lobe before and after the intravenous infusion of dopamine (n = 7), the D1 agonist SKF 38393 (n = 4), the D2 agonist bromocriptine (n = 4), and the dopamine antagonist haloperidol (n = 5). It was also measured before and after the intracarotid infusion of dopamine into eight naive sheep and seven sheep pretreated with phenoxybenzamine. Radiolabeled microspheres were used to determine regional cerebral and regional neurohypophysial blood flows (RNHBF) in these 35 adult female sheep anesthetized with pentobarbital sodium. Samples for serum prolactin measurement by radioimmunoassay were obtained before and after drug infusion. Intravenous dopamine infusion did not change median eminence or neural lobe blood flow (RNHBF) but increased renal and choroid plexus blood flow. Intravenous haloperidol caused a significant fall in RNHBF and blood flow in choroid plexus, caudate nucleus, and kidneys. Intracarotid dopamine infusion decreased RNHBF but increased choroid plexus blood flow. RNHBF was significantly greater in the seven sheep pretreated with phenoxybenzamine than in the eight naive sheep. These findings do not support a role for dopamine in the regulation of median eminence blood flow. The last observation does add support to the hypothesis that norepinephrine or epinephrine interaction with alpha-receptors plays a role in the control of ovine median eminence blood flow and hence in the regulation of delivery of humoral messages from the brain to the anterior pituitary gland.

Regional neurohypophysial and hypothalamic blood flow in rats during hypercapnia.

Regional cerebral blood flow (rCBF) was measured in the neurohypophysis and hypothalamus in normocapnic and hypercapnic rats using [14C]isopropyliodoamphetamine. Rats were surgically prepared using nitrous oxide and halothane and placed in plaster restraining casts. Hypercapnia was produced by increasing the fractional concentration of inspired CO2 (FICO2). rCBF in normocapnic rats was higher in the paraventricular nucleus, supraoptic nucleus, median eminence, and neural lobe than rates previously measured by use of diffusible tracers. During hypercapnia blood flow increased linearly with arterial PCO2 (PACO2) in all regions except the median eminence and neural lobe, which were not affected by hypercapnia. When rats were pretreated with phentolamine (1 mg/kg) to block the alpha-adrenergic receptors, blood flow in the median eminence and neural lobe increased significantly during hypercapnia. We conclude that blood flow in the cell bodies of the paraventricular nucleus and supraoptic nucleus is regulated differently during hypercapnia than blood flow in the nerve terminals in the median eminence and neural lobe. Furthermore, vasodilation produced by increased CO2 is offset by alpha-receptor stimulation in the median eminence and neural lobe.

Regional cerebral and neural lobe blood flow during insulin-induced hypoglycemia in unanesthetized rats.

The effects of hypoglycemia on regional cerebral blood flow (rCBF) were studied in awake restrained rats. The rats were divided into three groups consisting of a normoglycemic control group that received only saline, a hypoglycemic group A, which was given insulin 30 min before flow was measured, and a hypoglycemic group B, which was given insulin 90 and 30 min before flow was measured. Regional CBF was measured using 14C-iodoantipyrine. Mean plasma glucose was 8.76 mumol/ml in the control group, 2.63 mumol/ml in hypoglycemic group A, and 1.51 mumol/ml in hypoglycemic group B. Plasma epinephrine and norepinephrine concentrations increased to approximately 375% and 160%, respectively, of control values in hypoglycemic groups A and B. In the hypoglycemic group A, rCBF significantly increased in three brain regions. In the hypoglycemic group B, rCBF increased significantly in all brain regions measured, with the exception of the neural lobe, in which it decreased. The increase in rCBF ranged from 38% in the hypothalamus to 138% in the thalamus. Neural lobe blood flow significantly decreased by 31%. The neural lobe was the only brain region studied that is not protected by a blood-brain barrier. It may be sensitive to changes in the concentration of vasoactive agents in blood, such as epinephrine and norepinephrine.

Effect of differentiation inducers on growth characteristics of human glioma cell lines.

The effect of dimethylsulfoxide (DMSO) and iododeoxyuridine (IUdR) on the growth characteristics of two established human glioblastoma cell lines (FG and HMCN-1) was studied. The FG cell line has been characterized. The HMCN-1 cell line, established in our laboratory, consisted of fibroblastoid and polygonal cells that grew without contact inhibition. Subcutaneous injection of these cells into weanling athymic nude mice induced slowly growing, solid tumors that were histologically spindly with areas that were similar to the original tumor. Chromosomal analyses revealed a human heteroploid pattern with a modal number of 69. The cells of the original human glioma contained S-100 protein and glial fibrillary acidic protein (GFA protein), whereas the established cells failed to express markers. Prolonged treatment of glioma cells with DMSO generated a more adherent, normal human fibroblastoid phenotype that grew with contact inhibition. The new phenotype and proliferative restriction of these cells was evident as late as 50 days after discontinuation of treatment. The chemical induction of cell differentiation resulted in decreased tumorigenic potential in athymic nude mice.

Blood flow and functional responses correlate in the ovine neural lobe.

Regional neurohypophyseal and cerebral blood flow were measured in 5 awake unstressed female sheep with radiolabelled microspheres before and after the intracarotid infusion of a 3% NaCl solution. Plasma arginine vasopressin (AVP) levels were concurrently measured by radioimmunoassay. Following intracarotid sodium chloride infusion, neural lobe (but not median eminence) blood flow significantly increased, as did plasma AVP levels. Directed thirst and water-seeking behavior was observed, accompanied by a global increase in cortical blood flow. We conclude that the neuroendocrine response and the behavioral display induced by intracarotid sodium chloride infusion are accompanied by increases in blood flow in selected brain regions.

Three-dimensional reconstruction of median eminence microvascular modules.

To test the hypothesis that the median eminence microvasculature has a direct regulatory role in the hormonal communication between the brain and the pituitary gland, it is necessary to determine whether the physical means for such control (e.g. smooth muscle sphincters strategically located in the capillary plexus) actually exists. Our approach is to search for such structures in transmission electron micrographs of thin serial sections of the median eminence. The complexity of these images and the anticipated need to include large numbers of them in the study led us to consider computer reconstruction for this problem. We report here the successful three-dimensional reconstruction of capillary modules using digital image processing techniques for capillary feature detection/extraction, for construction of montages (mosaics) of overlapping images of the same section, and for automatic image registration by two independent methods without the use of fiducial marks. These tasks have been performed manually in nearly all the published neurobiological reconstructions; here they are performed by programs using only the mathematical properties of the images. Methods like those described here provide the only practical means for executing large scale reconstructions and gaining significant new information about the regulation of blood flow in this region of the brain.

Technical note: the use of nitroglycerin ointment after precarious neurosurgical wound closure.

It is suggested that the application of nitroglycerin ointment to neurosurgical wound closure exhibiting skin pallor or cyanosis can minimize necrosis and dehiscence. Examples of the use of this agent in patients undergoing myelomeningocele closure as well as in a premature infant undergoing ventriculoperitoneal shunting are described.

Resistance vessels supplying the median eminence of the rabbit, rat, and cat.

The ultrastructure of arterioles supplying the median eminence of eight rats, eight rabbits, and two cats was studied after vascular perfusion with phosphate buffered aldehyde fixatives. There were terminal arterioles with a lumen diameter of 50-70 micron within the pars tuberalis. Smaller arterioles (precapillary sphincters and metarterioles) with a lumen diameter of 15-20 micron were present on the surface of the median eminence. Arterioles were not observed to penetrate the neuropil but were seen to supply the external capillary plexus of the median eminence. Direct innervation of arterioles supplying the median eminence was not present and hence regulation of median eminence blood flow by peripheral sympathetic mechanisms appears unlikely. Resistance vessels were found to be closely related to axon terminals on the surface of the median eminence and to fenestrated capillaries of the external plexus. In addition, the endothelial cells of arterioles were characterized by the presence of pits and vesicles which may play a role in transendothelial transport. These findings suggest two mechanisms by which blood flow into the median eminence can be regulated: (a) by central catecholaminergic systems terminating in the median eminence and (b) by catecholamine secretions from the adrenal medulla.

Neurohemal contact in the internal zone of the rabbit median eminence.

The concept of neurosecretion as the mechanism by which neural control of adenohypophyseal function is accomplished was based on the observation that long capillary loops penetrate deeply into the supraopticohypophyseal tract as it passes through the median eminence internal zone. However, neural contact upon these capillary loops has not been demonstrated in the mammalian median eminence. The present transmission electron microscopic investigation of the rabbit median eminence demonstrates neurohemal contact in the median eminence internal zone. Axons containing small lucent vesicles 53.3 +/- 3.28 nm in diameter (mean +/- SEM) or small lucent and large granular vesicles with a mean diameter of 122.4 (+/- 3.28 nm) in their terminals make neurohemal contact with capillary loops in the internal zone and form a cuff about them. These terminals resemble terminals found in the external zone. Intravenous injection of the false neurotransmitter 5-hydroxydopamine (5-OH-DA) renders small lucent vesicles granular in both the external and internal zone. The effect of 5-OH-DA injection is abolished by concurrent reserpine administration. Whereas large granular vesicles in many terminals become lucent after reserpine administration, in others they remained electron dense. Viewed in the light of previous studies our findings suggest that the internal plexus arises from the external plexus and invaginates the neuropil carrying connective tissue and parvicellular axon terminals of aminergic and peptidergic systems from the external zone into the internal zone, that some elements making neurohemal contact with long capillary loops are terminals of the noradrenergic reticular infundibular tract arising outside the hypothalamus in the brainstem, and that long capillary loops form a system of repeating microvascular modules which markedly increase the surface available for neurohemal contact.

Aerobic glycolysis by the pituitary gland in vivo.

Arteriovenous differences of glucose, lactate, and pyruvate were measured across the pituitary glands of overnight-fasted female pigs to determine whether net uptake of glucose occurred, and if so, whether it was oxidized or converted to lactate. Arteriovenous differences were also measured across a portion of the cerebral cortex as a control. Cerebral cortex oxidized 84% of the glucose taken up, but this was not true in the pituitary gland, where glucose was almost completely converted to lactate. The arteriovenous difference across the pituitary gland was 0.61 mumol/ml for glucose while the venoarterial differences of lactate and pyruvate were 1.0 and 0.07 mumol/ml, respectively. The results indicated that little net oxidation of glucose either by the Krebs cycle or the pentose phosphate pathway occurs in the pituitary gland in vivo. Estimates of the amount of energy released from aerobic glycolysis indicate that, unless the requirements of the neurohypophysis are very different from those in the rest of brain, very little energy could be derived from the metabolism of glucose.