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Biomedical subjects

R A Meyer

Publications and source records attributed to R A Meyer.

At least 37 records · Page 2Linked to original sources
PubMed2001

Effect of acrosomal defects on fertility of bulls used in artificial insemination and natural breeding.

Four bulls that produced spermatozoa with a high percentage of abnormal acrosomes were individually placed in pens with females for 21 days. Frozen semen from 2 of the bulls was used for artificial insemination. One of the bulls was placed in a competitive mating situation with normal bulls at pasture. First service pregnancy rates were determined by transrectal ultrasonography 28 days after bull removal from breeding pens, or after the last artificial insemination. The results of competitive mating at pasture were determined from breeding observations, the phenotypic characteristics of calves sired, and blood typing for parentage. The results of these studies suggest that bulls that produce a high percentage of spermatozoa with indented acrosomes may have normal fertility when used in artificial insemination or in single sire mating; however, their fertility may be low when breeding competitively with bulls with normal spermiograms.

Acrosome↗
PubMed2001

Nerve harvesting procedures.

Autogenous nerve grafts currently set the standard for reconstruction of motor and sensory nerve injuries that cannot be repaired by mobilization, advancement, and approximation, and suturing without tension. Donor nerves such as the GAN and SN are easily accessible and frequently used in maxillofacial microneurosurgery. Other nerves (MACN, LCNF, LTN) may serve well in special nerve reconstruction situations. In the future, availability of biodegradable nerve conduits with neurotrophic factors may render obsolete the reconstruction of the short-span nerve gap (< 3 cm) by autogenous nerve grafts.

Absorbable Implants↗
PubMed2000

Effect of age on the expression of Pex (Phex) in the mouse.

Pex is a newly discovered gene (also called Phex) whose mutation is the cause of X-linked hypophosphatemia. Other members of this gene family encode endopeptidases that activate or inactivate endocrine and paracrine factors. Though embryonic bone expresses mRNA for the Pex gene at relatively high levels, we have found Pex expression to be widespread in adult organs and to be poorly expressed in adult bone. This led to the hypothesis that Pex mRNA expression changes with age. To test this, genetically normal mice of the B6C3H hybrid strain were studied at 0 (newborn), 2, 3, 10, and 72 weeks of age. Organs known to express Pex were collected, and RNA was extracted from them. Following reverse transcription, cDNA was amplified by the polymerase chain reaction with primers for Pex and G3PDH, a housekeeping gene. The amplimers were separated by electrophoresis, blotted onto nylon membranes, and hybridized with radioactively labeled internal oligonucleotide probes. The radioactivity was quantified, and the data were analyzed as the Pex/G3PDH ratio. The brain samples had high levels of Pex mRNA expression that rose slightly with age. Calvaria, kidney, and lung samples had the highest Pex mRNA expression at birth. In these organs Pex mRNA expression fell with age to undetectable or barely detectable levels. Thymus, heart, and skeletal muscle samples had low Pex mRNA expression at birth that did not change with age. Some organs showed a decline in G3PDH levels with age, but Pex expression decreased more, leading to a reduced Pex/G3PDH ratio. The widespread expression of mRNA for Pex suggests a role beyond that of phosphate homeostasis. The high level of expression in newborn animals suggests a role in growth and development. This seems to occur in addition to its role for the endocrine regulation of phosphate homeostasis by as yet unknown humoral agents that must occur throughout life. In summary, Pex mRNA expression is high in brain and bone at birth. Expression remains high in brain with age but falls with age in bone, kidney, and lung.

Aging↗
PubMed2000

Severe left ventricular hypertrophy in pediatric dialysis: prevalence and predictors.

Left ventricular hypertrophy (LVH) has been recognized as an independent risk factor for cardiovascular morbidity and mortality in adults with end-stage renal disease. However, the prevalence and severity of LVH in children on chronic dialysis therapy is not well established. Retrospectively, 64 chronic dialysis patients, aged 20 months to 22 years, on chronic dialysis had echocardiographic evaluation of LV mass (LVM) and geometry. Forty-eight (75%) children had LVH, including 22 of 26 (85%) on hemodialysis (HD) and 26 of 38 (68%) on peritoneal dialysis (PD). The prevalence of LVH in patients on HD was significantly higher than those on PD (P=0.02). Abnormal LV geometry was found in 51 of 64 (80%) patients: 25 patients (39%) had eccentric hypertrophy, 3 (5%) had concentric remodelling, and 23 (36%) had concentric LVH. Twenty-six children (41%) had severe LVH, defined as LVM index greater than 51 g/m2.7, which is associated with a fourfold greater risk for development of cardiovascular disease in adults. Patients with severe LVH had a significantly lower hemoglobin level (P=0.027) and longer duration of renal disease prior to the start of dialysis therapy (P=0.003) than patients without LVH. Multiple logistic regression analysis revealed HD as opposed to PD as a significant independent predictor for severe LVH (P=0.036). Higher systolic blood pressure remained in the final model as an independent predictor with a borderline level of significance (P=0.065). The results indicate that severe LVH and abnormal left ventricular geometry are common in young dialysis patients. Better control of blood pressure, anemia, and hypervolemia may be important in prevention or improving LVH.

Adolescent↗
PubMed2000

Secondary hyperalgesia persists in capsaicin desensitized skin.

Several lines of evidence suggest that secondary hyperalgesia to punctate mechanical stimuli arises from central sensitization to the input from primary afferent nociceptors. Conventional C-fiber nociceptors respond to heat stimuli and yet heat hyperalgesia is absent in the region of secondary hyperalgesia. This evidence suggests that the central sensitization to nociceptor input does not involve heat sensitive nociceptors. To test this hypothesis, we investigated whether desensitization of heat sensitive nociceptors by topical application of capsaicin led to an alteration in the secondary hyperalgesia. Two 2x2 cm areas on the volar forearm, separated by 1 cm, were treated in 10 healthy volunteers. One of the areas was desensitized by treatment with 10% topical capsaicin (6 h/day for 2 days). The other site served as vehicle control. Hyperalgesia was produced 2 days later by an intradermal injection of capsaicin (50 microg, 10 microl) at a point midway between the two treatment areas. Secondary hyperalgesia to noxious mechanical stimuli was investigated by using a blade probe (32 and 64 g) attached to a computer-controlled mechanical stimulator. In the area of topical capsaicin treatment, there was a marked increase in heat pain threshold and decrease in heat pain ratings indicating a pronounced desensitization of heat sensitive nociceptors. However, touch threshold and pain to pinching stimuli were not significantly altered. The intradermal capsaicin injection led to the development of a similar degree of secondary hyperalgesia at both the vehicle and capsaicin treatment areas. These results indicate that capsaicin insensitive nociceptive afferents play a dominant role not only in normal mechanical pain but also in secondary hyperalgesia to noxious mechanical stimuli.

Administration, Topical↗
PubMed2000

Spatial mapping of the zone of secondary hyperalgesia reveals a gradual decline of pain with distance but sharp borders.

The purpose of this study was to examine how pain to punctate mechanical stimuli varies with position within the zone of secondary hyperalgesia. Secondary hyperalgesia was produced by an intradermal injection of capsaicin (50 microg) into the volar forearm of human volunteers (n=9). Before and at 20, 60 and 100 min after the capsaicin injection, a computer-controlled electromechanical stimulator was used to deliver controlled-force stimuli to the skin via a 12-mm wide, 100-microm thick blade probe. Three forces (16, 32 and 64 g; 1 s) were each applied in a random order to 10 sites spaced in 1-cm increments along a line starting 1 cm from the injection site and ending near the wrist. At 40 and 80 min after capsaicin injection the 'zone of hyperalgesia' was determined with use of a hand-held 20-g von Frey probe. Whereas, before capsaicin, the blade probe produced little or no pain, after capsaicin the 32-g and 64-g stimuli evoked pain consistently within but not outside the border of secondary hyperalgesia determined with the von Frey probe. Within the zone of hyperalgesia the average pain ratings to the 64-g stimulus decreased exponentially with distance from the injection site. Surprisingly, the space constant for this exponential decay was large (about 18 cm), and thus the decrease in pain ratings from the center to the edge of the secondary zone was small (37%). However, pain ratings dropped precipitously just outside the zone of secondary hyperalgesia. This finding unlikely reflects a ceiling effect because pain ratings within the zone of secondary hyperalgesia increased linearly with force. The relatively uniform pain ratings to the blade stimuli within the zone of secondary hyperalgesia and the sharp border that delimits the zone of hyperalgesia indicate that this sensory disturbance approaches being an 'all-or-nothing' phenomenon. Thus, a two-state model for central plasticity is needed to explain secondary hyperalgesia.

Adult↗
PubMed2000

Effect of interposed periosteum in an animal physeal fracture model.

To study the effect of interposed periosteum on physeal fracture healing, 52 skeletally immature female Harlan Sprague-Dawley rats, 4 to 5 weeks of age, were randomized to one of three cohort groups. All animals underwent surgical dissection of the left proximal medial tibia; dissection consisted of superficial exposure and incision of a standard periosteal flap. Animals in Group I (fracture alone) underwent physeal fracture; those in Group II (fracture and periosteum) underwent physeal fracture with interposition of periosteum in the fracture site, and those in Group III (positive control) underwent physeal fracture, excision of 1/2 of the growth plate, and interposition of periosteum in the defect. After histologic examination of serial sections, fracture alone resulted in physeal injury frequently associated with small bar formation without a reduction in leg length. With the addition of interposition of periosteum into the fracture site, a small, but statistically significant, increase in leg length discrepancy frequently associated with small histologic bar formation occurred when compared with fracture alone.

Animals↗
PubMed2000

American College of Sports Medicine roundtable. The physiological and health effects of oral creatine supplementation.

Creatine (Cr) supplementation has become a common practice among professional, elite, collegiate, amateur, and recreational athletes with the expectation of enhancing exercise performance. Research indicates that Cr supplementation can increase muscle phosphocreatine (PCr) content, but not in all individuals. A high dose of 20 g x d(-1) that is common to many research studies is not necessary, as 3 g x d(-1) will achieve the same increase in PCr given time. Coincident ingestion of carbohydrate with Cr may increase muscle uptake; however, the procedure requires a large amount of carbohydrate. Exercise performance involving short periods of extremely powerful activity can be enhanced, especially during repeated bouts of activity. This is in keeping with the theoretical importance of an elevated PCr content in skeletal muscle. Cr supplementation does not increase maximal isometric strength, the rate of maximal force production, nor aerobic exercise performance. Most of the evidence has been obtained from healthy young adult male subjects with mixed athletic ability and training status. Less research information is available related to the alterations due to age and gender. Cr supplementation leads to weight gain within the first few days, likely due to water retention related to Cr uptake in the muscle. Cr supplementation is associated with an enhanced accrual of strength in strength-training programs, a response not independent from the initial weight gain, but may be related to a greater volume and intensity of training that can be achieved. There is no definitive evidence that Cr supplementation causes gastrointestinal, renal, and/or muscle cramping complications. The potential acute effects of high-dose Cr supplementation on body fluid balance has not been fully investigated, and ingestion of Cr before or during exercise is not recommended. There is evidence that medical use of Cr supplementation is warranted in certain patients (e.g.. neuromuscular disease); future research may establish its potential usefulness in other medical applications. Although Cr supplementation exhibits small but significant physiological and performance changes, the increases in performance are realized during very specific exercise conditions. This suggests that the apparent high expectations for performance enhancement, evident by the extensive use of Cr supplementation, are inordinate.

Adult↗
PubMed2000

Response of cutaneous A- and C-fiber nociceptors in the monkey to controlled-force stimuli.

The goal of this study was to determine the capacity of primary afferent nociceptive fibers (nociceptors) to encode information about noxious mechanical stimuli in primates. Teased-fiber techniques were used to record from 14 A-fiber nociceptors and 18 C-fiber nociceptors that innervated the hairy skin. Stimulus-response functions were examined with an ascending series of force-controlled stimuli. Stimulus-interaction effects were examined with use of a series of paired stimuli in which the interval between the stimulus pairs was varied systematically. Both A-fiber and C-fiber nociceptors exhibited a slowly adapting response to the stepped force stimuli. The response of the A fibers increased monotonically with increasing force, whereas the response of the C fibers reached a plateau at low force levels. The slope of the stimulus-response function for the A fibers was significantly steeper than that for the C fibers, and the total response was greater. The A fibers also provided more discriminative information regarding stimulus intensity. The C fibers demonstrated a significant fatigue in response when the interstimulus interval between the paired stimuli was </=150 s, whereas the A fibers did not demonstrate a significant fatigue until the interstimulus interval was </=30 s. This fatigue in response was not due to changes in tissue compliance. These results suggest that A- and C-fiber nociceptors have different mechanical transduction mechanisms. A-fiber nociceptors exhibit steeper stimulus-response functions and less fatigue than C-fiber nociceptors.

Adaptation, Physiological↗
PubMed2000

Cyclic AMP and LDL trigger a rapid enhancement in gap junction assembly through a stimulation of connexin trafficking.

Given the rapid turnover of connexin proteins, gap junction (GJ) assembly represents an important means of regulating the extent of GJ communication between cells. This report describes an increase in the level of GJ assembly within one hour following treatment with cAMP-elevating reagents or low density lipoprotein (LDL). Dye transfer methods and freeze-fracture with electron microscopy were used to assay junctional permeability and structure, respectively, subsequent to the dissociation, recovery and reaggregation of Novikoff hepatoma cells. Reaggregating cells in the presence of agents that increase cAMP levels (8-Br-cAMP, forskolin and IBMX) enhanced both dye transfer rates between cells and the extent of GJ formation 2- to 3-fold. These data and studies with the protein kinase A inhibitor, H-89, indicate that cAMP signaling plays a key role in enhanced assembly. The response to LDL parallels that to cAMP and relies on the activity of both adenylyl cyclase and protein kinase A. Immunoblot analysis revealed no change in the level of connexin43 (Cx43) or its phosphorylation states over a period of 2.5 hours. However, three agents (brefeldin A, monensin and nocodazole), that inhibit intracellular membrane trafficking by different mechanisms, all blocked the enhanced assembly of GJs when triggered by either elevated cAMP or exposure to LDL. Related studies, which employed trafficking inhibitors at different stages in GJ assembly, suggested that Cx43 trafficking during enhanced assembly is regulated, in part, by cell contact. Intracellular sources of Cx43 were characterized by colabeling for several markers of cytoplasmic membrane systems. We conclude that an increase in GJ assembly: (i) occurs rapidly in the presence of elevated cAMP or LDL, (ii) does not require an increase in Cx43 levels or major changes in Cx43 phosphorylation and (iii) is dependent upon the trafficking of Cx43 from intracellular storage sites.

1-Methyl-3-isobutylxanthine↗
PubMed2000

MRNA expression of Phex in mice and rats: the effect of low phosphate diet.

Phex is the gene whose mutation is the cause of X-linked hypophosphatemia in humans and mice. The organs expressing Phex in normal animals, and their possible sensitivity to stimulation by low phosphate diets, are unknown. In this study, Phex expression was measured in 6-wk-old normal B6C3H male and female mice and in 135 g Sprague-Dawley rats fed a normal phosphate diet or a low phosphate diet with deionized water ad libitum for 7 d. The animals were then anesthetized, and a variety of organs were collected and frozen in liquid nitrogen. Phex mRNA expression was measured in each organ by reverse transcription-polymerase chain reaction (RT-PCR) with primers specific for both Phex and glyceraldehyde-3-phosphate dehydrogenase (G3PDH). Southern blots were prepared, hybridized with 32P-labeled internal oligonucleotides, and quantified with a phosphor imager. The Phex/G3PDH ratio was computed, and the data were compiled as the mean +/- SEM. In these growing animals, the highest Phexexpression levels were found in the gonads, brain, and lung. In contrast, Phex expression in calvaria and femur was markedly less. Two significant changes were found in animals that were fed a low phosphate diet. Spleen showed a significant decrease in Phex mRNA levels on low phosphate diet (60+/-10% of normal P diet, n = 12/group, p = 0.002). The pituitary gland showed a significant increase in Phex expression with low phosphate diet (851+/-127% of G3PDH) over normal P diet (569+/-78%, n = 24 - 25/group, p = 0.03). No significant change was found in femur, calvaria, or a variety of soft tissues. In summary, Phex mRNA was found in most tissues examined. Expression levels varied by two orders of magnitude from highest to lowest with more in gonads, brain, and lung and with less in bone. Increased Phex mRNA was found in the pituitary gland of animals that were fed a low phosphate diet.

Animals↗
PubMed2000

Functional magnetic resonance imaging of muscle.

Muscle functional magnetic resonance imaging (MRI) is used to compare the relative involvement of different muscles recruited during exercise. The method relies on the activity-induced increase in the nuclear magnetic resonance transverse relaxation time (T2) of muscle water, which is caused by osmotically driven shifts of fluid into the myofibrillar space. In addition to imaging of whole muscle recruitment, muscle MRI may reveal changes in motor unit organization during disease.

Exercise↗
PubMed1999

Lumbar spinal fusion using recombinant human bone morphogenetic protein in the canine. A comparison of three dosages and two carriers.

STUDY DESIGN: A randomized, prospective and controlled animal study. OBJECTIVE: To evaluate lumbar spinal fusion using recombinant human bone morphogenetic protein 2 in a canine model. SUMMARY OF BACKGROUND DATA: Spinal fusion using autogenous bone grafting is associated with donor site morbidity and a nonunion rate of 5% to 35%. The use of recombinant human bone morphogenetic protein 2 as a bone graft substitute would eliminate donor site morbidity and perhaps augment the rate of successful fusion. METHODS: Mature beagles underwent bilateral paraspinal exposure at L4-L5, followed by transverse process decortication and randomization into one of six groups using differing doses of recombinant human bone morphogenetic protein 2 implanted using either a Type I collagen carrier or a polylactic acid carrier. Two control groups were used: one group without recombinant human bone morphogenetic protein 2 and another group using autogenous rib graft alone. RESULTS: Groups treated with recombinant human bone morphogenetic protein 2 demonstrated complete fusion in all animals. Animals treated with collagen carrier alone (no recombinant human bone morphogenetic protein 2) demonstrated complete absence of fusion. Successful fusion occurred in one of three canines in the autogenous bone graft group. Fusion masses in the recombinant human bone morphogenetic protein 2 treatment groups were significantly larger in size at 3 months than in the autogenous bone graft group. The collagen carrier was more biocompatible and biodegradable because residual polylactic acid carrier was seen with adjacent multinucleated giant cells. There was no evidence of spinal canal or nerve root encroachment in the recombinant human bone morphogenetic protein 2 treatment groups. CONCLUSIONS: The use of recombinant human bone morphogenetic protein 2 implanted using a Type I collagen carrier resulted in 100% fusion without adverse effects.

Animals↗
PubMed1999

Safety of recombinant human bone morphogenetic protein-2 after spinal laminectomy in the dog.

STUDY DESIGN: This was a randomized, blinded trial of the safety of the application of recombinant human bone morphogenetic protein (rhBMP)-2 or autologous bone graft onto a laminectomy defect of the dog in the presence or absence of a dural membrane puncture. OBJECTIVE: To test the safety of rhBMP-2 in an application in which direct contact of the material with neural tissue occurs. SUMMARY OF BACKGROUND DATA: Application of rhBMP-2 in laboratory animals stimulates local bone formation to effect spinal fusion and healing of segmental bone defects. The use of rhBMP-2 as a bone graft substitute in spinal fusion would eliminate donor site morbidity and may augment the rate of successful fusion. Because rhBMP-2 may unintentionally come in contact with neural tissue, the consequences of such a safety issue must be addressed in an animal model before human trials. METHODS: Twenty skeletally mature beagles underwent spinal exposure followed by bilateral laminectomy at L5. In half of the dogs, a puncture wound was made to the dura with the expression of cerebrospinal fluid at the site of the puncture. In randomly selected animals, the exposed dural elements received either autologous bone graft with the bone removed from the laminectomy site or an implant of the rhBMP-2 device. The animals was observed for 12 weeks with periodic clinical examinations and monthly computed tomographic scans. RESULTS: There was no clinical, radiographic, or histologic evidence of neurologic abnormalities in these animals. The rhBMP-2 stimulated bone growth in the laminectomy defect and came into direct contact with the dural membrane. There was no evidence of abnormal mineralization within the thecal sac or in the spinal cord itself. CONCLUSIONS: The rhBMP-2 implant stimulated bone formation in the laminectomy site. Neither autologous bone, rhBMP-2, nor the dural puncture had deleterious consequences for the animals.

Administration, Topical↗
PubMed1999

In vivo ultrasonographic exposimetry: human tissue-specific attenuation coefficients in the gynecologic examination.

OBJECTIVE: The purpose of the current study was to determine in vivo, tissue-specific ultrasonic attenuation coefficients for each of the tissue layers comprising the anterior abdominal wall, uterus, and vagina with use of a quantitative multilayer tissue model. We wanted to validate the "homogeneous" tissue model-based Food and Drug Administration derating factor of 0.3 dB/cm-MHz applied to obstetric-use ultrasonography systems. STUDY DESIGN: With use of a 3. 0-MHz mechanical sector scanner and our previously tested exposimetry equipment, we obtained a set of at least 5 separate acoustic pressure waveforms from each test subject by placing a calibrated 7-element linear-array hydrophone in the anterior vaginal fornix while she was undergoing transabdominal ultrasonography. Corresponding sets of reference in vitro acoustic pressure waveforms were also recorded for each test subject in a 37 degrees C water bath. All linear measurements of individual layer thicknesses and total distances were made on-line with use of electronic calipers. A set of multiple and independent insertion loss values, denoted ILn, was calculated for path n between the abdominal surface and the hydrophone from n sonograms for each test subject. Each tissue layer type was identified and its thickness along each path n was measured. The thickness of tissue type m along path n was denoted by dnm. The only unknown quantities left were the attenuation coefficients Am of each of the m tissue layers for that test subject. The overestimated set of equations dnm Am = ILn was solved for Am with use of a nonnegative least-squares solution technique. RESULTS: With use of data from 162 independent insertion loss estimate paths, the overall tissue-specific attenuation coefficients for each of the tissue layer types, expressed as mean value +/- SD, were 2.3 +/- 1.5 dB/cm-MHz for the skin and subcutaneous layer, 3.1 +/- 2.5 dB/cm-MHz for skeletal muscle, 0.6 +/- 0.5 dB/cm-MHz for myometrium, and 3.6 +/- 2.7 dB/cm-MHz for the vaginal wall. The overall insertion loss assuming the "homogeneous" tissue model was 0.7 +/- 0.3 dB/cm-MHz. CONCLUSIONS: We have determined the specific ultrasonic attenuation coefficients for each of the tissue layers comprising the anterior abdominal wall, uterus, and vagina and validated the Food and Drug Administration derating factor of 0.3 dB/cm-MHz applied to obstetric use ultrasonography systems. Of all the models proposed, the "homogeneous" tissue model appears to be the best model for determining ultrasonic exposure risk during reproductive ultrasonographic examinations.

Abdomen↗
PubMed1999

Mechanical hyperalgesia after spinal nerve ligation in rat is not reversed by intraplantar or systemic administration of adrenergic antagonists.

The development of alpha-adrenergic sensitivity in cutaneous nociceptors has been postulated as a mechanism for sympathetically maintained pain (SMP). In order to characterize the adrenergic receptors involved, we investigated the effects of intraplantar administration of alpha1-(prazosin) and alpha2-(yohimbine) adrenergic antagonists and systemic injection of phentolamine, a non-specific alpha-adrenergic blocker, on allodynic/hyperalgesic behavior in an animal model thought to mimic SMP in humans. Peripheral neuropathy in rats was induced by tight ligation of the L5/L6 spinal nerves. Mechanical hyperalgesia was quantified with von Frey hairs applied either for 3 s or repetitively to the plantar surface of the hindpaw. Responses to the 3 s duration stimulus were used to determine the paw withdrawal threshold with the up-down paradigm and repetitive stimuli were used to determine the response incidence of paw withdrawal to a given von Frey hair. Mechanical thresholds on the ipsilateral paw decreased significantly after ligation and were stable over the following 3 weeks. Intradermal administration of yohimbine or prazosin did not significantly alleviate mechanical hyperalgesia in L5/L6 ligated animals. Also systemic administration of phentolamine (1 and 5 mg/kg) did not alleviate the increased incidence of paw withdrawal in L5/L6 spinal nerve ligated animals. These results suggest that an alpha adrenergic interaction between sympathetic efferent and somatic afferent fibers does not play a critical role for the maintenance of mechanical hyperalgesia in this model for neuropathic pain.

Adrenergic alpha-1 Receptor Antagonists↗