Biomedical subjects

Mason R Mackey

Publications and source records attributed to Mason R Mackey.

6 recordsLinked to original sources

PubMed2004

Automated most-probable loss tomography of thick selectively stained biological specimens with quantitative measurement of resolution improvement.

We describe the technique and application of energy filtering, automated most-probable loss (MPL) tomography to intermediate voltage electron microscopy (IVEM). We show that for thick, selectively stained biological specimens, this method produces a dramatic increase in resolution of the projections and the computed volumes versus standard unfiltered transmission electron microscopy (TEM) methods. This improvement in resolution is attributed to the reduction of chromatic aberration, which results from the large percentage of inelastic electron-scattering events for thick specimens. These improvements are particularly evident at the large tilt angles required to improve tomographic resolution in the z-direction. This method effectively increases the usable thickness of selectively stained samples that can be imaged at a given accelerating voltage by dramatically improving resolution versus unfiltered TEM and increasing signal-to-noise versus zero-loss imaging, thereby expanding the utility of the IVEM to deliver information from within specimens up to 3 microm thick.

Animals↗

PubMed2004

Optic nerve damage in mice with a targeted type I collagen mutation.

PURPOSE: Transgenic (Col1a1(r/r)) mice gradually develop elevated intraocular pressure (IOP) with open angles. The present study was undertaken to evaluate optic nerve axonal loss with time in these mice. METHODS: The IOP of transgenic (Col1a1(r/r)) mice and control wild-type (Col1a1(+/+)) mice was measured at 7, 12, 16, 24, 36, and 54 weeks of age using a microneedle method. Transgenic Col1a1(r/r) and control Col1a1(+/+) mice at 24 and 54 weeks of age were randomly selected and their optic nerves were processed conventionally for electron microscopy. Optic nerve cross-sections were collected 300 micro m posterior to the globe. Low (200X) and high (10,000X) magnification images were collected systematically and were masked before analysis. For each nerve, cross-sectional area was measured in low magnification images, and axonal number was counted in high magnification images. RESULTS: Mean IOP of the transgenic Col1a1(r/r) mice was significantly higher than that of the control Col1a1(+/+) mice at 16, 24, 36, and 54 weeks by 21%, 42%, 41%, and 33% respectively (P < 0.05). The mean axonal density and total axonal number in the transgenic Col1a1(r/r) mice at 54 weeks of age (n = 10) was significantly less than those in the control Col1a1(+/+) mice at 24 weeks (n = 5) and 54 weeks (n = 5; P = 0.0081 and P = 0.020, respectively, analysis of variance, P < 0.05 for pair-wise comparisons). The mean axonal density and total axonal number in the transgenic Col1a1(r/r) mice at 54 weeks also were significantly less than in the transgenic Col1a1(r/r) mice at 24 weeks (n = 10). Mean axonal loss between 24 and 54 weeks of age in the transgenic Col1a1(r/r) mice was 28.7%. CONCLUSIONS: Transgenic Col1a1(r/r) mice develop sustained elevation of IOP and progressive optic nerve axon loss. This suggests that these mice may be useful as a mouse model of primary open angle glaucoma as well as for assessing the relationship between collagen type I metabolism and optic nerve axon loss.

Animals↗

PubMed2004

Regional optic nerve damage in experimental mouse glaucoma.

PURPOSE: To assess the relationship between regional variation of axon loss and optic nerve head anatomy in laser-induced experimental glaucoma in the mouse. METHODS: Experimental glaucoma was induced unilaterally in eight NIH Swiss black mice. Intraocular pressure (IOP) was measured for 12 weeks, and the mice were killed. The eyes were enucleated, and both optic nerves were dissected and processed conventionally for electron microscopy. Low- and high-magnification images of the optic nerve cross sections 300 microm posterior to the globe were collected systematically and masked before analysis. For each nerve, cross-sectional area was measured in low-magnification micrographs. Axon number and density were determined in the high-magnification micrographs. Loss of axonal density was compared between the superior and inferior and nasal and temporal areas of the optic nerve cross section. Additional cross-section micrographs were collected at 10- or 20-microm intervals throughout the optic nerve head. RESULTS: In the treated (glaucoma) eyes, mean IOP was 44% higher than that in the control eyes. The optic nerve cross-sectional area, mean axonal density, and total axonal number were significantly less than those in the control eyes (P < 0.01 for each). Axon loss in the superior optic nerve was greater than in the inferior optic nerve in each glaucomatous eye (P = 0.012). The ratio of axonal density in the superior and inferior optic nerve (superior-to-inferior [S/I] ratio) in all treated eyes was <1.0 and significantly lower than that in the control eyes (P = 0.012). The central retinal vessels occupied approximately 20% of the central optic nerve head cross-sectional area, gradually shifted position ventrally as they progressed toward the scleral foramen (the mouse does not have a lamina cribrosa), and exited the inferior retrobulbar optic nerve adjacent to the posterior of the globe. CONCLUSIONS: Ocular hypertension in the mouse eye sufficient to cause optic nerve damage induces preferential loss of superior optic nerve axons. Optic nerve axon loss appeared less among the axons that were near the major optic nerve blood vessels at the scleral foramen. Topographic differences in optic nerve axon loss should be considered when evaluating optic nerve damage in experimental laser-induced glaucoma in the mouse.

Animals↗

PubMed2003

Cometabolism of Cr(VI) by Shewanella oneidensis MR-1 produces cell-associated reduced chromium and inhibits growth.

Microbial reduction is a promising strategy for chromium remediation, but the effects of competing electron acceptors are still poorly understood. We investigated chromate (Cr(VI)) reduction in batch cultures of Shewanella oneidensis MR-1 under aerobic and denitrifying conditions and in the absence of an additional electron acceptor. Growth and Cr(VI) removal patterns suggested a cometabolic reduction; in the absence of nitrate or oxygen, MR-1 reduced Cr(VI), but without any increase in viable cell counts and rates gradually decreased when cells were respiked. Only a small fraction (1.6%) of the electrons from lactate were transferred to Cr(VI). The 48-h transformation capacity (Tc) was 0.78 mg (15 micromoles) Cr(VI) reduced. [mg protein](-1) for high levels of Cr(VI) added as a single spike. For low levels of Cr(VI) added sequentially, Tc increased to 3.33 mg (64 micromoles) Cr(VI) reduced. [mg protein](-1), indicating that it is limited by toxicity at higher concentrations. During denitrification and aerobic growth, MR-1 reduced Cr(VI), with much faster rates under denitrifying conditions. Cr(VI) had no effect on nitrate reduction at 6 microM, was strongly inhibitory at 45 microM, and stopped nitrate reduction above 200 microM. Cr(VI) had no effect on aerobic growth at 60 microM, but severely inhibited growth above 150 microM. A factor that likely plays a role in Cr(VI) toxicity is intracellular reduced chromium. Transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) of denitrifying cells exposed to Cr(VI) showed reduced chromium precipitates both extracellularly on the cell surface and, for the first time, as electron-dense round globules inside cells.

Biodegradation, Environmental↗

PubMed2003

Optic nerve damage in experimental mouse ocular hypertension.

PURPOSE: To evaluate optic nerve damage in mice after laser-induced ocular hypertension. METHODS: Ocular hypertension was induced unilaterally in 13 NIH Black Swiss mice by laser photocoagulation of the limbus. Over the following 12 weeks, intraocular pressure (IOP) was measured at regular intervals by the microneedle method. The optic nerves of these mice and of seven normal untreated mice were then processed conventionally for electron microscopy, and cross sections of the nerve 300 micro m posterior to the globe were collected. Low- and high-magnification images were collected systematically and masked before analysis. For each nerve, cross-sectional area was measured in low-magnification micrographs, and axon and glia numbers were counted in high-magnification micrographs. RESULTS: In normal untreated mice, the average number of axons was 59,597 +/- 3,112 (mean +/- SD). Variation among these measurements was 5.7% +/- 3.9%. After laser treatment, the duration of high IOP ranged from 2 to 12 weeks (6.2 +/- 3.6 weeks, mean +/- SD). The mean IOP in the treated eyes was 1.3 times greater than the mean IOP in the control eyes (P = 0.0012). The maximum IOP in the treated eyes was 1.6 times greater than that observed in the control eyes (P < 0.0001). The optic nerve cross-sectional area, mean axon density, and total number of axons in the treated eyes were significantly less than in the control eyes (28.5% +/- 23.4%, 57.8% +/- 37.8%, and 63.1% +/- 38.1%, respectively; P < 0.005 for each). The decrease in optic nerve cross-sectional area and the positive integral of elevated IOP and duration of IOP elevation correlated significantly with total axon loss (r(2) = 0.79, P < 0.0001 and r(2) = 0.36, P = 0.040, respectively). The number of astrocytes per cross section of optic nerve was significantly greater in the treated eyes than in the control eyes (P = 0.014). CONCLUSIONS: Laser-induced ocular hypertension in mouse eyes can induce optic nerve axon loss that correlates with the magnitude and duration of elevated IOP.

Animals↗

PubMed2002

Bid, Bax, and lipids cooperate to form supramolecular openings in the outer mitochondrial membrane.

Bcl-2 family proteins regulate the release of proteins like cytochrome c from mitochondria during apoptosis. We used cell-free systems and ultimately a vesicular reconstitution from defined molecules to show that outer membrane permeabilization by Bcl-2 family proteins requires neither the mitochondrial matrix, the inner membrane, nor other proteins. Bid, or its BH3-domain peptide, activated monomeric Bax to produce membrane openings that allowed the passage of very large (2 megadalton) dextran molecules, explaining the translocation of large mitochondrial proteins during apoptosis. This process required cardiolipin and was inhibited by antiapoptotic Bcl-x(L). We conclude that mitochondrial protein release in apoptosis can be mediated by supramolecular openings in the outer mitochondrial membrane, promoted by BH3/Bax/lipid interaction and directly inhibited by Bcl-x(L).

Animals↗