Biomedical subjects

W S Thomas

Publications and source records attributed to W S Thomas.

10 recordsLinked to original sources

PubMed1998

There is a limited critical period for dopamine's effects on D1 receptor expression in the developing rat neostriatum.

Neonatal lesions of the dopamine (DA) system have different behavioral and neurochemical effects than lesions made in adulthood. Previous data from this laboratory have indicated that in the early postnatal period, lesions to the DA system induced by instrastriatal 6-hydroxydopamine (6-OHDA) result in a rapid and permanent loss of striatal D1 binding sites, but D2 receptor binding is unaffected. The length of the postnatal period within which neonatal instrastriatal 6-OHDA administration is effective in modulating D1 receptor binding is not known. To determine when D1 and D2 receptors are vulnerable to lesions of the DA system, we administered 6-OHDA intrastriatally to damage the DA innervation at different ages in the early postnatal period, at day of birth/postnatal day 1 (P0/1), P7 or P15 and examined DA receptor binding at P90 with quantitative autoradiography. Using [3H]mazindol binding to DA transporters (DAT) to verify the extent of the lesion, we then quantified the number of D1 binding sites using [3H]SCH23390 and D2 sites with [3H]spiroperidol. There were significant reductions in DAT sites at P0/1 (78 to 88%) and P7 (67 to 81%) but less significant changes at P15 (34 to 50% losses). The lesions were most effective for the dorsal caudate-putamen than more ventrally or in the nucleus accumbens. Our results demonstrate a significant reduction in D1 sites in all regions of the neostriatum following lesions at P0/1. The dorsal caudate-putamen was affected the most (51% loss, and the nucleus accumbens (41%) and ventral caudate-putamen less so (31%). No significant changes in D1 receptors were found at P7 or P15 and D2 receptors were unaffected with lesions in any of the age groups. The results indicate that there is a critical period for affecting expression of D1 receptors and this effect may, in addition, be related to the pattern of DA loss. Additionally, regulation of D2 receptors by this degree of loss of DA innervation does not occur during the first two weeks postnatally.

Aging↗

PubMed1995

Agrin gene expression in ciliary ganglion neurons following preganglionic denervation and postganglionic axotomy.

Agrin is an extracellular matrix protein that has been implicated as a synaptogenic agent in the peripheral and central nervous systems. Both the level of expression and pattern of alternative splicing of agrin mRNA are developmentally regulated. As a step toward identifying signals important in regulating agrin gene expression in neurons, we examined the effects of postganglionic axotomy or preganglionic denervation on agrin mRNA levels and alternative splicing in ciliary ganglia of posthatch chicks. In comparison to unoperated age-matched controls, in situ hybridization with a pan-specific agrin cRNA probe demonstrated a significant decrease in neuronal agrin mRNA expression as a result of axotomy. Reverse transcription-polymerase chain reaction analysis demonstrated that axotomy also resulted in changes in the pattern of alternative splicing of agrin mRNA. Underlying these changes are decreases in the molar amounts of transcripts encoding the neuron-specific isoforms agrin8 and agrin19, homologous to rat agrin proteins that have high AChR aggregating activity. Similar, but less dramatic changes in agrin expression following axotomy were also observed in unoperated neurons on the contralateral side. In contrast, the only significant change in agrin gene expression following ganglionic denervation was a small decline in the relative abundance of agrin 8 mRNA in operated versus unoperated age-matched control ganglia. Major changes in agrin gene expression following axotomy but not denervation are consistant with the notion that agrin synthesized by ganglionic neurons exerts its effects in the periphery rather than at synapses formed between ciliary ganglion neurons and their preganglionic input. These data suggest that the pattern of alternative splicing and the absolute amount of agrin mRNA in ciliary ganglion neurons may be regulated by target tissue interactions.

Agrin↗

PubMed1994

Changing practice patterns in peripheral arterial disease.

The development of interventional radiologic techniques during the past decade has changed our approach to the treatment of lower extremity peripheral arterial disease (LE-PAD). Balloon and laser-assisted angioplasty, atherectomy (rotary and directional devices), stent implantation, and thrombolysis as well as combinations of all of these approaches, at times with concomitant or secondary surgery, have been used in our institution. A review of our practice patterns during the past 5 years was performed to analyze changing attitudes and results with these newer techniques. All new patients seen in consultation for LE-PAD during three alternate years were reviewed with regard to demographics, initial complaints, initial treatment modality, initial outcome, indications for and results of secondary treatment, and ultimate outcome (at 1 year). The 603 patients were seen during the following three 12-month periods: 1987 to 1988, 1989 to 1990, and 1991 to 1992. An intention-to-treat analysis revealed (1) the number of patients seen for peripheral arterial disease has increased steadily; (2) in the last year more were initially treated with intervention as the primary modality; (3) the results of such catheter-based procedures improved only slightly over this 5-year period, despite our learning curve and the fact that we discarded several ineffective interventional approaches; (4) the fraction of patients primarily operated on and the excellent results of surgery have not changed; and (5) the number of operations for proximal (aortoiliac) disease has decreased markedly, with a corresponding increase in distal reconstructions. The evolution of our current approach to the treatment of LE-PAD is based on this continuing experience.

Angioplasty, Balloon↗

PubMed1994

Computed tomography scanning findings associated with rapid expansion of abdominal aortic aneurysms.

PURPOSE: Early repair of abdominal aortic aneurysms (AAA) is particularly appropriate for those that are most likely to expand. Our aim was to define features on computed tomography (CT) scanning associated with subsequent rapid aneurysm expansion. METHODS: We reviewed CT scans of 80 patients with AAA (> 3.0 cm) who underwent CT scanning of the abdomen and pelvis two times, at least 6 months apart, between 1986 and 1992. The aneurysms initially measured 4.4 +/- 0.6 cm, and the mean interval between obtaining scans was 22 +/- 12 months. Clinical variables assessed included age, sex, medical risk factors, underlying cardiovascular and pulmonary diseases, and administration of beta blockers and lipid-lowering agents. Computer-aided measurements on each CT scan section included the maximal and minimal diameters and area of the aneurysm. Dimensions of the luminal thrombus and the arc of aneurysm wall covered by thrombus (TARC). Maximal aneurysm dimensions were related to juxtarenal aortic and second lumbar vertebral body dimensions. RESULTS: Mean aneurysm expansion was 0.26 +/- 0.25 cm/yr. CT scanning variables that correlated significantly with rate of expansion included the mean TARC (r = 0.43, p < 0.001), thrombus volume fraction (r = 0.37, p < 0.001), TARC on the largest aneurysm cross section (r = 0.34, p < 0.01), and thrombus area fraction (r = 0.30, p < 0.01). Rapid expansion (> 0.5 cm/yr) occurred in 15 (19%) aneurysms. The two predictors for rapid expansion on logistic regression analysis were mean TARC (p < 0.005) and the presence of carotid artery disease (p < 0.05). CONCLUSION: An increased AAA thrombus load is associated with a higher likelihood of rapid expansion and should weigh in favor of early surgical repair.

Aneurysm, Ruptured↗

PubMed1994

Polymorphonuclear leukocyte behavior in a nonhuman primate focal ischemia model.

There is increasing interest in the role of polymorphonuclear (PMN) leukocytes in the evolution of focal cerebral infarction. Surgical preparation of focal cerebral ischemia models may alter leukocyte reactivity and thereby make interpretation of leukocyte function following ischemia/reperfusion difficult. The effects of surgical preparation and of experimental ischemia/reperfusion on granulocyte function have been examined prospectively in a baboon model. Twenty-six adolescent male baboons underwent surgical preparation, of which 21 underwent middle cerebral artery occlusion/reperfusion. Four additional animals served as nonsurgical controls. Peripheral venous blood specimens were taken for performing assays of leukocyte function at defined intervals before and after both the surgical preparation (i.e., the overall procedure for implantation of the middle cerebral artery occlusion device) and occlusion/reperfusion. A stress-related elevation in total leukocyte number was attributed mainly to an increase in the number of circulating PMN leukocytes. Values rose from 13.9 +/- 4.9 x 10(3) to 27.8 +/- 5.8 x 10(3)/microliters, (+/- SD; n = 21) for total leukocyte number, with p < 0.001, and from 4.3 +/- 2.1 x 10(3) to 15.9 +/- 4.7 x 10(3)/microliters (n = 21) for PMN leukocytes, with p < 0.001. Surgical preparation had no effect (p > or = 0.4) on the ability of PMN leukocytes, isolated 24 h after the implantation procedure, to display polarization, O2.- production, or beta-glucuronidase release when stimulated with human C5a. A moderate decrease in the chemotactic response to C5a resolved within the 7-day postsurgery (preocclusion) period. Three-hour middle cerebral artery occlusion and 1-h reperfusion resulted in a significant reduction in C5a-induced polarization.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

P-selectin and intercellular adhesion molecule-1 expression after focal brain ischemia and reperfusion.

BACKGROUND AND PURPOSE: Polymorphonuclear leukocytes have been implicated in the development of the "no-reflow" phenomenon after focal cerebral ischemia and reperfusion. To further understand the role of granulocytes in microvascular occlusions, the responses of the granulocyte-endothelial cell adhesion molecules P-selectin and intercellular adhesion molecule-1 during middle cerebral artery ischemia and reperfusion were examined in a primate model. METHODS: Twelve adolescent male baboons were used for 2-hour middle cerebral artery occlusion (n = 3) or for 3-hour occlusion with 1-hour (n = 3), 4-hour (n = 3), and 24-hour (n = 3) reperfusion, and three separate unoperated primates served as controls. A quantitative immunohistochemical study of the microvascular distribution of P-selectin and intercellular adhesion molecule-1 was performed using 10-microns frozen sections from basal ganglia analyzed with computerized light microscopy video imaging. RESULTS: Significant (P < .05) persistent upregulation of P-selectin (beginning during ischemia) and transient upregulation of intercellular adhesion molecule-1 (at 1 and 4 hours of reperfusion) were observed on endothelium of selected post-capillary microvessels of the ischemic lenticulostriate artery territory. Platelet accumulation also occurred in this territory and was responsible for a significant proportion of the nonendothelial P-selectin signal at 24 hours after reperfusion. CONCLUSIONS: Focal cerebral ischemia/reperfusion stimulates endothelial P-selectin and intercellular adhesion molecule-1 expression in brain microvessels in the ischemic zone, which may contribute to enhanced leukocyte adherence and persistent activation.

Animals↗

PubMed1993

Developmental expression and alternative splicing of chick agrin RNA.

Agrin is a synaptic basal lamina protein that has been proposed to mediate motor neuron-induced clustering of acetylcholine receptors during development of the neuro-muscular junction. The chick ciliary ganglion is a parasympathetic ganglion that contains motor neurons that project to striated and smooth muscle targets in the eye. We have examined agrin gene expression in the chick ciliary ganglion during normal embryonic development using in situ hybridization and quantitative PCR techniques. Ganglia were specifically labeled by antisense agrin cRNA probes and the density of labeling changed during development. Hybridization was most intense in sections of ganglia obtained from embryos before embryonic Day 15 (E15), declining to relatively low levels by hatching at E20. Throughout embryonic development labeling was associated with glial cells, in addition to both ciliary and choroid neurons. Measurement of agrin mRNA levels by competitive PCR showed that agrin gene expression in the ganglion increased dramatically between E8 and E10, was sustained at high levels from E10 to E14, and declined thereafter. This time course is coincident with the period of synapse formation between ganglionic neurons and their peripheral targets. Previous studies in chick CNS have shown that alternative RNA splicing of a single exon encoding 11 amino acids gives rise to an active and an inactive agrin protein. Our analysis of RNA isolated from chick ciliary ganglia demonstrated that a second, previously uncharacterized exon encoding 8 amino acids can also be spliced into the same region. Alternative splicing of both the 8- and the 11-amino-acid exons results in expression of four distinct agrin transcripts in the ganglion. Changes in the level of total agrin mRNA in the ganglion reflect developmentally regulated changes in the levels of these alternatively spliced agrin isoforms. These results demonstrate that agrin is expressed in autonomic motor neurons of the peripheral nervous system and support a wider role for agrin as a synaptogenic protein, not limited to spinal motor neurons.

Agrin↗

PubMed1993

Tissue factor contributes to microvascular defects after focal cerebral ischemia.

BACKGROUND AND PURPOSE: Microvascular perfusion defects occur after occlusion and reperfusion of the middle cerebral artery in examples of focal cerebral ischemia. In addition to cellular (eg, polymorphonuclear leukocyte) contributors to the focal "no-reflow" phenomenon, activation of coagulation may also play a role. We have tested a potential role of tissue factor-mediated coagulation in the microvascular perfusion defects seen after focal cerebral ischemia-reperfusion in a baboon model of reversible middle cerebral artery occlusion with the murine anti-tissue factor monoclonal antibody TF9-6B4. Tissue factor is the principal resident procoagulant substance in cerebral tissues and has a distinct perivascular distribution. METHODS: Microvascular patency in the basal ganglia after 3-hour middle cerebral artery occlusion and 1-hour reperfusion was quantified by computerized video imaging of carbon-tracer perfused tissues. Animals were randomized to receive intravenous TF9-6B4 (10 mg/kg) 10 minutes before middle cerebral artery occlusion (n = 6) or no treatment (n = 6) in an open study. RESULTS: In the control animals, a significant decrease in patency was confirmed in microvessels less than 30 microns in diameter. Infusion of TF9-6B4 before middle cerebral artery occlusion produced a stable maximal level of circulating antibody within 10 minutes, which lasted the duration of ischemia and reperfusion. An increase in reflow in microvessels of all size classes occurred after TF9-6B4 infusion, which was significant in those 7.5 to 30 microns (P = .038) and 30 to 50 microns (P = .013) in diameter. CONCLUSIONS: These results indicate that tissue factor-mediated events may also contribute to no-reflow in noncapillary microvessels after focal cerebral ischemia.

Animals↗

PubMed1992

Tissue factor localization in non-human primate cerebral tissue.

Tissue factor (TF), the principal procoagulant of human brain, resides in specific regions of the non-human primate central nervous system. Immunohistochemical studies employing murine anti-human TF monoclonal antibodies (MoAbs) detected TF antigen in the cortex, basal ganglia, cerebellum, and cervical spinal cord in three normal baboon subjects. Although significantly less prominent than human cortical gray matter, a distinct partition of TF in gray matter > white matter was noted. The gray matter predilection of TF was confirmed in primate temporal and parietal lobe cortex by both sandwich ELISA and one-stage coagulation assay. Variation in the relative quantity of TF antigen was observed by ELISA among the three subjects studied. Procoagulant activity followed the pattern of TF antigen (cortical gray matter > basal ganglia > or = cerebellum > cortical white matter), and was 96.5-98.5% inhibitable by a function inhibiting anti-human TF MoAb combination. TF antigen was associated with the microvasculature of all cerebral tissues studied, and spared capillaries most selectively in the cerebral cortex, basal ganglia, and cerebellum. These findings suggest a highly specific ordering of TF antigen and related procoagulant activity in the central nervous system of the baboon, confined primarily to gray matter parenchyma, and to the non-capillary microvasculature.

Animals↗

PubMedDate not supplied

Uptake of C5a by polymorphonuclear leukocytes (PMNs) after focal cerebral ischemia. I. Effect of tirilazad mesylate intervention on C5a uptake by PMNs.

PMNs are believed to play an important role in ischemia and C5a uptake is an important functional indicator for G protein-coupled receptor trafficking. The ability of PMNs to internalize 125I-labeled C5a in vitro is an index of the functional state of these cells. We evaluated the effects of model preparation and focal cerebral ischemia by middle cerebral artery occlusion and reperfusion (MCA:O/R) on internalization of C5a by PMNs isolated from baboons (Papio anubis/cynocephalus). Similar assays were performed on PMNs isolated before and after exposing the animals undergoing MCA:O/R to an anti-inflammatory 21-aminosteroid, tirilazad mesylate (U74006F). Surgical implantation of the MCA occlusion device had no measureable effect on uptake of C5a to the cytosol by the PMN. In contrast, MCA:O/R appeared to decrease uptake of C5a. Both in vivo and in vitro administration of tirilazad, to otherwise untreated animals and to isolated cells, respectively, reduced baseline values of C5a uptake in the PMNs. Cytosolic uptake of C5a was also reduced in PMNs isolated from subjects that had undergone MCA:O/R and tirilazad treatment. These results suggest that focal cerebral ischemia, with or without exposure to tirilazad mesylate, may inhibit internalization of C5a by the PMN receptors. The effects of stroke on the ability of C5a to gain entry into the PMN may result from receptor down-regulation or "desensitization" of the cell, possibly due to activation of complement and generation of C5a which occupied the receptors. Alternatively, the effect of tirilazad presumably results from the ability of this drug to enter the membrane lipid layer and reduce fluidity.

Animals↗