Biomedical subjects

M W Miller

Publications and source records attributed to M W Miller.

At least 145 records · Page 8Linked to original sources

PubMed1995

Gonadotropin-releasing hormone analog-induced patterns of luteinizing hormone secretion in female Wapiti (Cervus elaphus nelsoni) during the breeding season, anestrus, and pregnancy.

We conducted two studies to determine the pattern of GnRH analog-induced LH secretion in adult female wapiti during the breeding season, anestrus, and pregnancy. In the first study, we measured LH secretion during the breeding season and anestrus in five females challenged with each of five doses of GnRH analog (0.3, 1, 3, 10, and 30 micrograms/50 kg BW). In the second study, LH response was determined in six pregnant females treated with six doses of GnRH analog (0.5, 1, 2, 4, 8, and 16 micrograms/50 kg BW). Animals were fitted nonsurgically with indwelling jugular catheters, and blood samples were collected at 0, 30, 60, 90, 120, 180, 240, 300, 360, 420, and 480 min postinjection. Mean maximum serum concentrations of LH were not different (p = 0.45) between females treated during the breeding season (mean = 29.1 +/- 1.9 [SE] ng/ml) and anestrus (mean = 32.4 +/- 4.3 [SE] ng/ml); however, anestrous females required 3.3 times more GnRH analog (3 vs. 10 micrograms/50 kg BW) to produce the same response. Maximal inducible LH concentrations were lowest (mean = 7.7 +/- 2.5 [SE] ng/ml) for pregnant wapiti, and the magnitude of the response decreased exponentially (r2 = 0.98, p = 0.002, SEb = 0.65) during gestation. Although the magnitude of the response declined over time, maximal release consistently occurred at the same dose (2 micrograms/50 kg BW) (treatment x trial interaction, p = 0.53). We conclude from these studies that the amount of LH released in response to a given dose of GnRH analog depends on reproductive status.(ABSTRACT TRUNCATED AT 250 WORDS)

Anestrus↗

PubMed1995

Generation of neurons in the rat dentate gyrus and hippocampus: effects of prenatal and postnatal treatment with ethanol.

Neurons in the rat hippocampal formation (the dentate gyrus and the hippocampus) are born over a protracted period, from gestational day (G) 15 into adulthood. Dentate gyral neurons born prenatally are generated from the ventricular zone, whereas those born postnatally are derived from a secondary proliferative zone, the intrahilar zone. In contrast, hippocampal pyramidal neurons are generated only prenatally from the ventricular zone. In the neocortex, ethanol depresses the proliferation of cells in the ventricular zone and stimulates the proliferation of cells in the secondary proliferative zone. The present study tests the hypotheses that prenatal treatment with ethanol has a different effect on the generation of dentate gyral neurons than does postnatal ethanol treatment, and that these differences are determined by the timing of the ethanol exposure relative to the period and site of neuronal generation. Rats were treated with ethanol between G6 and G21 or between postnatal day (P) 4 and P12. They were given an injection of [3H]thymidine on G15, G18, G21, P6, P9, or P12. Rats were killed on P30-P35. The tissue was processed by standard autoradiographic methods and assessed using rigorous stereological procedures. The total number of neurons and the density of radiolabelled neurons in both the dentate gyrus and the CA1 region of the hippocampus were determined. Prenatal ethanol treatment decreased the total number of neurons in the CA1 segment of the hippocampus and had little impact on neuronal number in the dentate gyrus. Likewise, the number of hippocampal and dentate gyral neurons generated daily was significantly lower in ethanol-treated rats than in controls. Postnatal treatment to ethanol, however, significantly increased the total number of dentate gyral neurons and the density of neurons generated postnatally. These postnatal changes depended on the blood ethanol concentration (BEC). At moderate BECs, the total number of neurons in the dentate gyrus and the number of neurons generated was increased. At high BECs, however, neuronal number and neuronal generation were decreased. Postnatal ethanol treatment had no effect on the number of (total or radiolabeled) CA1 neurons. Thus, pre- and postnatal exposure to ethanol have opposite effects both on the number of neurons in the dentate gyrus and on the generation of neurons. These paradoxical effects likely result from three causes: the differential effects of ethanol on the two proliferative zones, the critical period of neuronal development, and the potentially opposite effects of moderate and high BEC.

Animals↗

PubMed1995

Cell cycle kinetics in fetal rat cerebral cortex: effects of prenatal treatment with ethanol assessed by a cumulative labeling technique with flow cytometry.

The effects of ethanol on the cell cycle kinetics of cortical precursor cells during the period of cortical neuronogenesis [between gestational day (G) 12 and G21] was systematically examined. Samples of dissociated cortical cells were harvested from the cerebral cortices of 13-, 15-, 17-, 19-, and 21-day-old fetuses. The fetuses were obtained from pregnant rats: (a) fed a liquid diet containing 6.7% (v/v) ethanol (Et) ad libitum, (b) pair-fed an isocaloric liquid control diet (Ct), or (c) fed chow and water (Ch) ad libitum. Before harvesting the cells, the fetuses were administered a series of 1-5 injections of bromodeoxyuridine (BrdU). The proportion of cells that incorporated the BrdU was assessed. Using these raw data, the S-phase length (Ts), total cell cycle length (Tc), and the growth fraction (GF; the fraction of the total population that was actively cycling) were determined with a cumulative labeling procedure. The Ts was approximately 8-9 hr, regardless of either the date of the injection or the dietary treatment of the dam. On the other hand, the Tc for the Ct- and Ch-treated rats increased over the gestational period. That is, the Tc was shortest on G13 and longest on G21. The Tc for Et-treated rats, however, did not change between G13 and G21. For the Ch- and Ct-treated groups, the GF decreased > 15-fold between G13 and G21. The decline (5-fold) for the Et-treated group over the same period, however, was not as great as it was for the Ct-treated fetuses.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Effect of pre- or postnatal exposure to ethanol on the total number of neurons in the principal sensory nucleus of the trigeminal nerve: cell proliferation and neuronal death.

Early exposure to ethanol reduces the number of neurons in many CNS structures in vivo. The present study determined whether such reductions are caused by the death of neurons. Three groups of ethanol-treated rats were prepared: those exposed to ethanol from gestational day (G) 11 to G19 (during the period of neuronal generation and migration), from postnatal day (P) 4 to P12 (during the period of synaptogenesis), or from P31 to P39 [after the mature structure and function of neurons in the principal sensory nucleus (PSN) of the trigeminal nerve was established]. During these times, pregnant dams or pups were fed a liquid ethanol-containing diet that produced peak blood ethanol concentrations of 137-157 mg/dl. The number of PSN neurons in mature rats exposed to ethanol pre- or postnatally was determined using stereological procedures. The number of PSN neurons was also calculated for rats pair-fed an isocaloric liquid control diet or fed chow and water and libitum. The volume of the PSN was not affected by pre- or postnatal ethanol exposure. The number of PSN neurons, however, was significantly affected by ethanol exposure in a time-dependent manner. Prenatal exposure lead to a 27.1% decrease in neuronal number. Early postnatal exposure led to a smaller decrease (-15.1%), and late postnatal exposure had no affect on the number of PSN neurons. These data show not only that ethanol directly depresses the proliferation of neuronal precursors, but also that ethanol causes the death of neurons during the period of synaptogenesis.

Animals↗

PubMed1995

A test of the hypothesis that cavitation at the focal area of an extracorporeal shock wave lithotripter produces far ultraviolet and soft x-ray emissions.

Church hypothesized that the violent collapse of microbubbles in water in the focal area of an extra-corporeal shock wave lithotripter (ESWL) can generate biologically damaging far uv and soft x-ray photons. Two techniques were used to test this hypothesis. Gassy water (10 ml) was exposed to ten piezoelectric lithotripter shocks (P+ = 43 MPa, P- = 9 MPa). The resultant sonoluminescence was filtered by optical band-pass filters and measured using a photomultiplier tube (PMT). Next, a commercially available scintillation cocktail (Ecoscint A), which is formulated to convert high energy photons to visible light, was exposed to varying numbers of lithotripter shocks and the relative luminescence intensity measured and compared to background and distilled water luminescence readings. Results showed support for the hypothesized presence of near uv emissions (approximately 250 nm) and marginal support for the production of higher energy photons, possibly including far uv and soft x-ray emissions.

Equipment Design↗

PubMed1995

Expression and transgenic studies of the mouse agouti gene provide insight into the mechanisms by which mammalian coat color patterns are generated.

Expression of the agouti gene from two different promoters, one active at the midpoint of the hair cycle and the other specific for the ventrum, is responsible for generating a range of mammalian pigmentation patterns. We demonstrate that in postnatal mice transcripts from both promoters are confined to the dermal papilla of hair follicles, as predicted by classical transplantation experiments. Transcripts from the hair cycle promoter are detected in the embryonic whisker plate but not in other regions of the body before birth, whereas ventral-specific transcripts are detected in the ventral trunk of the embryo as well as ventral whisker plate. To investigate further the embryonic origins of adult pigmentation patterns, we carried out a detailed analysis of agouti expression in the embryo. The ventral-specific agouti isoform is first expressed at E10.5 in neural crest-derived ventral cells of the second branchial arch, in anterior regions of the forelimb buds and in a narrow stripe of ventral mesenchyme. By E14.5 a continuous layer of expression is observed in the upper cells of the dermis, including cells of the developing dermal papillae, and covering the entire ventral surface of the head and trunk and dorsal surfaces of the distal forelimb and hindlimb. This expression pattern reflects the domain of yellow coloration evident in adult animals and suggests that the agouti gene is regulated in part by factors responsible for establishing differences between the dorsal and ventral surfaces of the body during embryogenesis. To test the hypothesis that agouti is a paracrine signaling molecule that can influence pigment production by hair follicle melanocytes when expressed by either dermis or epidermis, as suggested by recombination and transplantation experiments, we created transgenic animals in which agouti is expressed in basal cells of the epidermis. These animals display stripes of yellow hairs corresponding to regions of epidermal agouti expression, confirming that agouti signals melanocytes to synthesize yellow pigment and providing direct evidence that it functions in a paracrine manner with a restricted radius of action.

Agouti Signaling Protein↗

PubMed1995

Expression of nerve growth factor, p75, and trk in the somatosensory and motor cortices of mature rats: evidence for local trophic support circuits.

Neurotrophins such as nerve growth factor (NGF) are critical for the maintenance of CNS neurons. We determined the expression of NGF and the neurotrophin receptors p75 and trk in the somatosensory and motor cortices of mature rats with immunohistochemical techniques. Sections of mature rat cortex were processed immunohistochemically with primary antibodies directed against NGF, p75, or trk. The distribution of immunoreactive elements was examined, and stereological techniques were used to determine the density and size of immunoreactive cell bodies. Some sections processed for trk immunoreactivity were examined with an electron microscope. From the size and morphology of the labeled cells, it appeared that only neurons in the gray matter were NGF-positive. NGF was detected in one-third of the neurons in layers II-III, V, and VI of both somatosensory cortex and motor cortex; however, fewer than 1 in 12 of the layer IV neurons was NGF-positive. With the notable exception of layer V, few cell bodies (2-10% of the total population) were p75- or trk-immunoreactive. Layer Vb was replete with receptor-positive cell bodies; more than one-third of the layer Vb neurons were p75- or trk-positive. All labeled cells appeared to be pyramidal neurons. The distribution of p75 labeling with the two anti-p75 antibodies was indistinguishable. In addition, the neuropil in the supragranular laminae was p75- or trk-positive. Electron microscopy showed that trk immunoreactivity was also expressed by dendrites. Only rarely were immunoreactive axons detected. In summary, NGF is expressed by cortical neurons throughout cortex, and neurotrophin receptors are widely produced by postsynaptic targets. Thus, NGF appears to participate in an intracortical autoregulatory system. The strong expression of neurotrophin receptors by pyramidal neurons in layer Vb (the origin of brainstem and spinal cord projections) suggests that the neurotrophins are especially critical for the regulation of corticofugal projection systems.

Animals↗

PubMed1995

Measurement of organ blood flow with coloured microspheres in the rat.

OBJECTIVE: The aim was to establish a method for measuring organ blood flow in rats using commercially available, coloured, dye extraction microspheres. METHODS: A mixture of radiolabelled and dye extraction microspheres was infused into rats at rest (basal) and during intravenous administration of either angiotensin II (0.5 microgram.kg-1.min-1) or isoprenaline [12.5 ng.(g0.74)-1.min-1]. Tissues were removed and placed in test tubes, counted for radioactivity, then digested with 2N sodium hydroxide. Within the same tube, microspheres were isolated using centrifugation and the dye was extracted with dimethylformamide. The dye was quantified by spectrophotometry. RESULTS: Recovery of microspheres averaged greater than 95% for all tissues studied; larger reagent volumes were required to achieve this level of recovery from white adipose tissue. Statistical analyses showed excellent correlations between blood flow values obtained by the dye extraction and radiolabelled microsphere techniques. Blood flow values obtained with the radioactive technique tended to be slightly higher. There were no differences in the results obtained with the two techniques when they were simultaneously used to measure changes in organ blood flow induced by angiotensin II or isoprenaline. CONCLUSIONS: The coloured, dye extraction microsphere technique accurately measured organ blood flow in rats. This technique is potentially useful for estimating blood flow in any animal, even if tissue sample size is limited.

Adipose Tissue↗

PubMed1994

Developmental expression of a 56 kDa protein isolated from rat neocortex.

The expression of ALZ-50 immunoreactivity in the immature rat cortex was assessed using a variety of immunochemical techniques. The antigen recognized by ALZ-50 was isolated using immunoaffinity column chromatography. Unlike the ALZ-50-positive antigen found in the brains of people with Alzheimer's Disease (mol. wt. 68 kDa), the principal antigen expressed in the immature rat had a molecular weight of 56 kDa. The temporal expression of ALZ-50-positive antigens was determined with immunoblotting techniques. The expression of the 56 kDa protein appeared during the last prenatal week, increased to a peak during the second postnatal week and waned in the third postnatal week. Immunohistochemically, neonatal cortex contained many ALZ-50-positive neurons in the cortical subplate and the intermediate zone and a smattering of neurons in the cortical plate. The temporal expression of the ALZ-50-positive 56 kDa antigen was similar to that for fetal tau (tau-1); however, the principal protein identified by the anti-tau-1 antibody was considerably larger (being about 68-70 kDa). In contrast to ALZ-50, tau-1-immunoreactive elements were distributed in the subplate, the deep cortical plate, the intermediate zone and the subventricular zone. tau-1-positive axons passing through the superficial intermediate zone were conspicuous. Thus, the biochemical and anatomical evidence show that ALZ-50 and tau-1 recognize distinct proteins.

Animals↗

PubMed1994

The mouse lethal nonagouti (a(x)) mutation deletes the S-adenosylhomocysteine hydrolase (Ahcy) gene.

The lethal nonagouti (a(x)) mutation is a hypomorphic allele of the agouti coat color locus which, when homozygous, also leads to embryonic death around the time of implantation. To understand the molecular basis of these phenotypes, we identified and cloned a deletion breakpoint junction present in the ax chromosome. Long range restriction mapping demonstrated a simple deletion of approximately 100 kb, which does not affect agouti coding sequences, but begins only 4 kb 3' of the last exon, and thus may affect coat color by removing an agouti 3' enhancer. The Ahcy gene, which codes for the enzyme S-adenosylhomocysteine hydrolase (SAHase), is contained within a 20 kb region within the a(x) deletion. SAHase RNA and protein were detectable in early blastocysts and in embryonic stem cells, respectively, and analysis of embryos derived from an a(x)/a x a(x)/a embryo intercross indicated that a(x)/a embryos die between the late blastocyst and early implantation stages. Treatment of cultured embryos with an SAHase inhibitor, 3-deazaaristeromycin, or with metabolites that can result in elevated levels of cellular SAH, resulted in an inhibition of inner cell mass development, suggesting that loss of SAHase activity in a(x)/a(x) embryos is sufficient to explain their death around the time of implantation.

Adenosine Deaminase↗

PubMed1994

Functional nuclear pores reconstituted with beta 1-4 galactose-modified O-linked N-acetylglucosamine glycoproteins.

Nuclear pore proteins bearing O-linked N-acetylglucosamine (GlcNAc) are involved in nuclear transport, although a role for their glycosylation is not established. Xenopus egg extracts capable of reforming functional nuclei in vitro yielded nuclei with impaired transport and reduced nuclear pore density when depleted of wheat germ agglutinin-binding proteins. Many of the nuclear pores remaining in wheat germ agglutinin-depleted nuclei showed a striking loss of internal structure. Nuclear transport and normal nuclear pore structure were restored by the addition of nuclear pore glycoproteins from rat liver or Xenopus eggs. Glycoproteins modified by the addition of galactose to O-linked GlcNAc were also competent for assembling normal nuclear pores and restoring nuclear transport. Aphidicolin-sensitive DNA synthesis was unaffected by the removal or modification of O-linked GlcNAc glycoproteins. These data argue against a requirement for a lectin-like recognition of O-linked GlcNAc glycoproteins in nuclear pore assembly, nuclear transport, or DNA synthesis.

Acetylglucosamine↗

PubMed1994

Chylothorax associated with right-sided heart failure in five cats.

Chylothorax associated with right-sided congestive heart failure was diagnosed in 5 cats. One cat had restrictive pericardial disease, with mild pericardial effusion, and a heart-base chemodectoma. Two other cats had congestive cardiac disease (tetralogy of Fallot and tricuspid regurgitation in 1 cat, and endocardial cushion defect and tricuspid dysplasia in the other), and 2 cats had idiopathic cardiomyopathy. All cats had jugular venous distention, and echocardiographic evaluation helped define the nature of the cardiac disease in these cats. Subtotal pericardiectomy resulted in resolution of the chylothorax in the cat with the heart-base tumor, whereas medical management of the right-sided heart failure temporarily decreased pleural effusion in the cat with tetralogy of Fallot and in the 2 cats with cardiomyopathy.

Animals↗

PubMed1994

T helper cell dysfunction in systemic lupus erythematosus (SLE): relation to disease activity.

Patients with systemic lupus erythematosus (SLE) are known to have defects in both humoral and cellular immunity. The significance of defective T cell-mediated immunity and its relationship to disease activity have not been clearly established. We studied in vitro T helper cell (Th) function in 150 SLE outpatients and correlated Th function with validated measures of disease activity. Interleukin 2 (IL-2) production by peripheral blood mononuclear cells (PBMC) was measured after stimulation with the recall antigens influenza A virus (FLU) and tetanus toxoid (TET), irradiated allogeneic peripheral blood mononuclear cells (ALLO), and phytohemagglutinin (PHA). We observed three patterns of Th response: (1) 76 of 150 (50%) of patients responded to the recall antigens FLU and/or TET, ALLO, and PHA; (2) 62 of 150 (42%) of patients did not respond to recall antigens but responded to ALLO and PHA; and (3) 12 of 150 (8%) of patients did not respond to either recall antigens or ALLO antigens. This diminished T cell function was correlated with higher disease activity as measured by four scales of clinical activity, such that individuals who exhibited more in vitro immune dysfunction presented with significant increases in their clinical activity indices. The alterations in T cell function could not be accounted for by medication doses alone. Thus, SLE patients have multiple distinct defects at the level of the Th cell which are associated with clinical measures of disease activity.

Adult↗

PubMed1994

A test of the hypothesis that diagnostic ultrasound disrupts myelination in neonatal rats.

Neonatal rats were exposed or sham exposed for 30 min to pulsed ultrasound [2.25 MHz carrier frequency, 1 microsecond pulse length, 50 Hz pulse repetition frequency (PRF), 50 W/cm2 Imax, 2 mW/cm2 ITA], euthanised and prepared for electron microscopic analysis of the nodes of Ranvier of the dorsal and ventral roots of the spinal cord. There was also a cage control. All materials were processed and scored blindly, evaluating whether perinodal myelin was normal. Rats from all regimens had areas of disrupted myelination. There was no statistically significant difference among the regimens for absence of myelination. The results did not confirm an earlier report that diagnostic ultrasound disrupts myelination in neonatal rats.

Animals↗

PubMed1994

A test of the influence of cyclotron resonance exposures on diatom motility.

An attempt was made to test the hypothesis (McLeod et al. 1987; Smith et al. 1987) that a certain combination of direct current and alternating current magnetic field exposures at room temperature results in an increase in motility of a marine diatom (Amphora coffeaeformis) to a maximum value. Diatom motility increased as a function of calcium concentration in the medium, as reported by McLeod et al. (1987) and Smith et al. (1987). There was, however, no effect of the magnetic field exposures on diatom motility. The exposures employed 16-Hz magnetic fields with amplitudes of 21 or 29.7 microT (21 microT rms) as well as 21 microT (amplitude) fields at frequencies above and below the reported "resonance" frequency. All experiments were conducted double blindly, and each trial had its own positive control.

Calcium↗

PubMed1994

Effects of prenatal exposure to ethanol on the number of axons in the pyramidal tract of the rat.

We examined the effect of gestational ethanol exposure on the number of axons in the caudal pyramidal tract. Between gestational day (G) 6 and G21, inclusive, pregnant rats were fed a liquid ethanol-containing diet (Et), an isocaloric liquid control diet (Ct), or a diet of chow and water (Ch). On postnatal day 30, the offspring of these rats were killed and their caudal medullas were processed for electron microscopy. The overall size of the pyramidal tract and the space occupied by the axons was smaller in the Et-treated rats than in the Ct-treated rats. The myelinated axons were smaller and the myelin was thinner in the Et-treated rats than in the Ct-treated rats. These decreases produced an ethanol-induced increase in the density of axons in the pyramidal tract. In particular, the density of myelinated axons (but not nonmyelinated axons) was greater in Et-treated rats. The net result was that the estimated number of axons in the pyramidal tracts of the Et-treated rats was not significantly different than the number in the Ch- and Ct-treated rats. The present data demonstrate that ethanol does not affect the absolute number of axons in the pyramidal tract. As a result of the ethanol-induced microencephaly, however, the data translate into a relative increase in the number of pyramidal tract axons. This relative increase matches the ethanol-induced increase in the density of corticospinal projection neurons that may result from the retention of a developmentally exuberant projection.

Animals↗

PubMed1994

Ultrasonic cell lysis in vitro upon fractional, discontinuous exposure vessel rotation.

In polystyrene exposure vessels, a substantial fraction of suspended P388 cells was lysed by exposure to cw, 1-MHz ultrasound (5 W cm-2 spatial peak intensity, 5 min) in stationary vessels or those subjected to a small number of half rotations. Lysis was increased significantly by two half-rotations during exposure relative to stationary vessels. Lysis in stationary exposure vessels is generally considered to be minimal; it is shown that approximately 40% cell lysis occurs in 15%-20% of the stationary tubes. This result appears to relate to the distribution of random defects on the exposure vessel walls.

Animals↗

PubMed1994

Bubble recycling and ultrasonic cell lysis in a stationary exposure vessel.

An exposure system producing interleafed pulses of 1-MHz ultrasound from balanced, opposing transducers was used to test the bubble recycling hypothesis (as formulated with respect to rotating exposure vessels) in a stationary exposure vessel containing P388 cell suspensions. Cell lysis was measured in cell suspensions which had been exposed or sham-exposed to 1-MHz ultrasound (5 W/cm2 spatial peak pulse average intensity) delivered in continuously alternating, opposing pulses. The opposing pulse cycle frequency (i.e., gating frequency) varied from 0.1 Hz to 100 kHz, corresponding to single pulse durations ranging from 5 microseconds to 5 s. Unequivocal support for the bubble recycling hypothesis was obtained. Lytic yield increased as the gating frequency increased, passing through a maximum at gating frequencies of 100 Hz-1 kHz. As the gating frequency increased further, lytic yield declined rapidly. The results are discussed in relation to recent theoretical estimates of bubble translation speeds in an ultrasound field, and are found to be consistent with those estimates.

Animals↗